JP2004006301A - Positive electrode for non-aqueous electrolyte secondary battery and its manufacturing method, and non-aqueous electrolyte secondary battery having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic solution secondary battery having a high charge and discharge capacity. <P>SOLUTION: This is a positive electrode for the non-aqueous electrolyte secondary battery characterized in that at least one kind of metal oxide chosen from a group of titanium oxide, alumina, zinc oxide, chromium oxide, lithium oxide, nickel oxide, copper oxide and iron oxide is dispersed among particles of at least one kind of lithium-contained compound oxide selected from a group composed of LiCoO<SB>2</SB>, LiNiO<SB>2</SB>and LiMn<SB>2</SB>O<SB>4</SB>. Furthermore, this is the non-aqueous electrolyte secondary battery provided with the positive electrode, a negative electrode, and an electrolyte composed of aprotic organic solvent and supporting salt. As the aprotic organic solvent, it is preferable that a phosphazene derivative and/or an isomer of the phosphazene derivative is added. <P>COPYRIGHT: (C)2004,JPO

Description

（式中、Ｒ^１、Ｒ^２、及びＲ^３は、一価の置換基又はハロゲン元素を表す。Ｘ^１は、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、イオウ、セレン、テルル、及びポロニウムからなる群より選ばれる元素の少なくとも１種を含む置換基を表す。Ｙ^１、Ｙ^２及びＹ^３は、２価の連結基、２価の元素、又は単結合を表す。）
（ＮＰＲ^４ _２）_ｎ　　・・・　（ＩＩ）
（式中、Ｒ^４は一価の置換基又はハロゲン元素を表す。ｎは３〜１５を表す。）
【００１２】
＜１０＞　上記式（ＩＩ）で表わされるホスファゼン誘導体が、下記式（ＩＩＩ）で表されることを特徴とする前記＜９＞に記載の非水電解液２次電池である。
（ＮＰＦ_２）_ｎ　　・・・　（ＩＩＩ）
（式中、ｎは３〜５を表す。）
【００１３】
＜１１＞　上記式（ＩＩ）で表わされるホスファゼン誘導体が、下記式（ＩＶ）で表されることを特徴とする前記＜９＞に記載の非水電解液２次電池である。
（ＮＰＲ^５ _２）_ｎ　　・・・　（ＩＶ）
（式中、Ｒ^５は一価の置換基又はフッ素を表し、全Ｒ^５のうち少なくとも１つはフッ素を含む一価の置換基又はフッ素であり、ｎは３〜５を表す。但し、全てのＲ^５がフッ素であることはない。）
【００１４】
＜１２＞　前記ホスファゼン誘導体が、２５℃において固体であって、下記式（Ｖ）で表されることを特徴とする前記＜８＞に記載の非水電解液２次電池である。
（ＮＰＲ^６ _２）_ｎ　　・・・　（Ｖ）
（式中、Ｒ^６は一価の置換基又はハロゲン元素を表す。ｎは３〜６を表す。）
【００１５】
＜１３＞　前記ホスファゼン誘導体の異性体が、下記式（ＶＩ）で表され、かつ下記式（ＶＩＩ）で表わされるホスファゼン誘導体の異性体であることを特徴とする前記＜８＞に記載の非水電解液２次電池である。
【化５】

【化６】

（式（ＶＩ）及び（ＶＩＩ）において、Ｒ^７、Ｒ^８及びＲ^９は、一価の置換基又はハロゲン元素を表す。Ｘ^２は、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、イオウ、セレン、テルル、及びポロニウムからなる群より選ばれる元素の少なくとも１種を含む置換基を表す。Ｙ^７及びＹ^８は、２価の連結基、２価の元素、又は単結合を表す。）
【００１６】
【発明の実施の形態】
以下に、本発明を詳細に説明する。
本発明の非水電解液２次電池用の正極は、リチウム含有複合酸化物と、該リチウム含有複合酸化物の粒子間に分散させた金属酸化物とからなり、必要に応じて、導電剤及び結着剤等の非水電解液２次電池の技術分野で通常使用されている添加剤を含む。
【００１７】
本発明で使用するリチウム含有複合酸化物は、リチウムと遷移金属との複合酸化物であり、非水電解液２次電池の正極活物質として起電反応に直接あずかる物質である。該リチウム含有複合酸化物としては、ＬｉＣｏＯ_２、ＬｉＮｉＯ_２、ＬｉＭｎ_２Ｏ_４、ＬｉＦｅＯ_２及びＬｉＦｅＰＯ_４等が挙げられ、これらの中でも、ＬｉＣｏＯ_２、ＬｉＮｉＯ_２、ＬｉＭｎ_２Ｏ_４が好ましい。これらのリチウム含有複合酸化物は、１種単独で使用してもよく、２種以上を併用してもよい。また、上記リチウム含有複合酸化物は、Ｆｅ、Ｍｎ、Ｃｏ及びＮｉからなる群から選択される２種又は３種の遷移金属を含む複合酸化物であってもよく、この場合、該複合酸化物は、ＬｉＦｅ_ｘＣｏ_ｙＮｉ_{（１ − ｘ − ｙ）}Ｏ_２（式中、０≦ｘ＜１、０≦ｙ＜１、０＜ｘ＋ｙ≦１）、あるいは、ＬｉＭｎ_ｘＦｅ_ｙＯ_{２ − ｘ − ｙ}等で表される。上記リチウム含有複合酸化物の粒径は１〜６０μｍであり、好ましくは２０〜４０μｍである。粒径が１μｍ未満又は６０μｍを超えると、正極合材（正極活物質、導電剤及び結着剤からなる）成形時にパッキングが悪くなるか、又は単位体積中に含まれる正極活物質量が少なくなるため、充放電容量が減少することがあるので好ましくない。
【００１８】
本発明に用いる金属酸化物としては、酸化チタン、アルミナ、酸化亜鉛、酸化クロム、酸化リチウム、酸化ニッケル、酸化銅、酸化鉄が挙げられ、これらは１種単独でも、２種以上の併用であってもよい。該金属酸化物は非常に微細な粒子であるのが好ましく、その粒径は１０ｎｍ〜１μｍであり、好ましくは２０ｎｍ〜６０ｎｍである。粒径が１０ｎｍ未満の粒子は工業的には合成が困難であり、１μｍを超えると単位体積当りに含まれる正極活物質の量が減少して、単位体積当りのエネルギー量が減少するため好ましくない。
【００１９】
本発明では、リチウム含有複合酸化物の粒子間に、金属酸化物を分散させているので、リチウム含有複合酸化物粒子間に隙間が生じる。該隙間には電解液が効率よく浸入できるため、電解液とリチウム含有複合酸化物との接触面積が増大し、その結果としてリチウム含有複合酸化物の利用率が上がり、充放電容量が向上する。
【００２０】
リチウム含有複合酸化物粒子間に隙間を形成する金属酸化物の中でも酸化チタンが特に好ましく、その理由として、酸化チタンは、非水電解液２次電池の電池電極反応を阻害しないこと、効果的に水分を吸収して電池の安定性に寄与するだけでなく、添加により著しく導電性を低下させることが無い（内部抵抗が上昇しない）こと等が挙げられる。
【００２１】
本発明の正極における金属酸化物の質量は、リチウム含有複合酸化物の質量に対し、０．５％から４％が好ましい。金属酸化物の質量が、リチウム含有複合酸化物の質量に対し、０．５％未満であると、金属酸化物をリチウム含有複合酸化物の粒子間に分散させて隙間を形成する効果が十分でなく、４％を超えると、単位体積当りの正極活物質量が減少すると同時に、リチウム含有複合酸化物の粒子表面が金属酸化物で覆われ、電解液とリチウム含有複合酸化物との接触面積が減少してしまうため好ましくない。
【００２２】
本発明の非水電解液２次電池用の正極に、必要に応じて添加する添加剤のうち、導電剤としてはアセチレンブラック等が挙げられ、結着剤としてはポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等が挙げられる。これらの添加剤を使用するときは、従来と同様の配合割合、例えば、正極用粉末：導電剤：結着剤＝８：１：１〜８：１：０．２（質量比）で配合できる。
【００２３】
正極の形状としては、特に制限はなく、電極として公知の形状の中から適宜選択することができる。例えば、シート状、円柱形状、板状形状、スパイラル形状等が挙げられる。
【００２４】
本発明の非水電解液２次電池用の正極は、前記リチウム含有複合酸化物の粒子間に、非常に微細な金属酸化物の粒子が分散されているのが好ましいため、金属酸化物は、好ましくはゾルゲル法により調製する。なお、非常に微細な粒子が調製できさえすれば、調製法は特に制限されない。
【００２５】
本発明の非水電解液２次電池に用いる正極は、下記の第１乃至第４の工程に従って製造することができる。
第１の工程では、有機溶媒中に、前記リチウム含有複合酸化物と、チタン、アルミニウム、亜鉛、クロム、リチウム、ニッケル、銅及び鉄からなる群から選択される少なくとも１種の金属のアルコキシドとを加え混合して、混合液を調製する。有機溶媒としては、メタノール、エタノール等の低沸点アルコール或いはアセトン等の低沸点ケトン類等が好ましく、特にエタノールが好ましい。一方、金属アルコキシドにおけるアルコキシ基としては、有機溶媒に対する金属アルコキシドの溶解性の観点から、イソプロポキシ基、ｎ−プロポキシ基等が好ましい。
【００２６】
第２の工程では、第１工程で調製した混合液に水を加え、前記金属アルコキシドの加水分解反応により、該金属アルコキシドに対応する金属水酸化物を生成する。なお、第２の工程は、氷冷しながら行うのが好ましい。
【００２７】
次に、第３の工程で、金属水酸化物を含有した液を加熱・乾燥することにより、溶媒を除去しながら金属水酸化物を金属酸化物にし、該金属酸化物をリチウム含有複合酸化物粒子間に分散させた正極用粉末を製造する。なお、溶媒の除去と脱水を完全に行うため、加熱・乾燥は１２０〜３００℃の温度で充分な時間行うのが好ましい。
【００２８】
次に、第４の工程で、第３の工程で得た正極用粉末を所定の形状に成形して非水電解液２次電池用の正極を得る。成形方法は、非水電解液２次電池の製造過程で破損しない程度の強度の正極が成形できれば特に限定されず、従来公知の方法が使用できる。例えば、上記正極用粉末と、前述の導電材及び結着剤等の添加剤と、酢酸エチルやエタノール等の有機溶媒とを混合・混錬した後、ロール圧延により所望の厚さ・幅のシートを作製することによっても実施できる。
【００２９】
上記の方法で得られた正極は、リチウム含有複合酸化物の粒子間に非常に微細な金属酸化物粒子が分散されており、単位体積当りの正極活物質量（リチウム含有複合酸化物量）を大きく減ずることなく、リチウム含有複合酸化物のみからなる正極に比べ、充放電容量が著しく高い非水電解液２次電池の正極である。
【００３０】
本発明の非水電解液２次電池は、上述した正極と、負極と、非プロトン性有機溶媒及び支持塩からなる電解液とを備え、必要に応じて、セパレーター等の非水電解液２次電池の技術分野で通常使用されている部材を備える。
【００３１】
本発明の非水電解液２次電池の負極は、例えば、リチウム又はリチウムイオン等を吸蔵・放出可能である。従って、その材料としては、例えば、リチウム又はリチウムイオン等を吸蔵・放出可能であれば特に制限はなく、公知の負極材料から適宜選択して使用できる。例えば、リチウムを含む材料、具体的には、リチウム金属自体、リチウムと、アルミニウム、インジウム、鉛又は亜鉛等との合金、リチウムをドープした黒鉛等の炭素材料等が好適に挙げられ、これらの中でも安全性がより高い点で黒鉛等の炭素材料が好ましい。これらの材料は、１種単独で使用してもよく、２種以上を併用してもよい。負極の形状としては、特に制限はなく、前記正極の形状と同様の公知の形状から適宜選択することができる。
【００３２】
本発明の非水電解液２次電池の電解液は、非プロトン性有機溶媒と、支持塩とからなる。非水電解液２次電池の負極は、前述のようにリチウム等のアルカリ金属を含むため、水との反応性が非常に高く、従って、溶媒には水と反応しない非プロトン性有機溶媒を用いる。該非プロトン性有機溶媒は、電解液の低粘度化が可能であり、容易に電池としての最適なイオン導電性を達成することができる。
【００３３】
非プロトン性有機溶媒としては、特に制限はないが、電解液の粘度を低く抑える観点から、エーテル化合物やエステル化合物等が挙げられる。具体的には、１，２−ジメトキシエタン、テトラヒドロフラン、ジメチルカーボネート、ジエチルカーボネート、ジフェニルカーボネート、エチレンカーボネート、プロピレンカーボネート、γ−ブチロラクトン、γ−バレロラクトン、エチルメチルカーボネート等が好適に挙げられる。これらの中でも、エチレンカーボネート、プロピレンカーボネート、γ−ブチロラクトン等の環状エステル化合物、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート等の鎖状エステル化合物、１、２−ジメトキシエタン等の鎖状エーテル化合物等が好適である。特に、環状のエステル化合物は、比誘電率が高くリチウム塩等の溶解性に優れる点で、鎖状のエステル化合物及びエーテル化合物は、低粘度であるため電解液の低粘度化の点で好適である。これらは１種単独で使用してもよく、２種以上を併用してもよいが、２種以上を併用するのが好適である。非プロトン性有機溶媒の２５℃における粘度としては、特に制限はないが、３．０ｍＰａ・ｓ（３．０ｃＰ）以下が好ましく、２．０ｍＰａ・ｓ（２．０ｃＰ）以下がより好ましい。
【００３４】
支持塩としては、リチウムイオンのイオン源となる支持塩等が好ましい。該リチウムイオンのイオン源としては、特に制限はないが、例えば、ＬｉＣｌＯ_４、ＬｉＢＦ_４、ＬｉＰＦ_６、ＬｉＣＦ_３ＳＯ_３、及び、ＬｉＡｓＦ_６、ＬｉＣ_４Ｆ_９ＳＯ_３、Ｌｉ（ＣＦ_３ＳＯ_２）_２Ｎ、Ｌｉ（Ｃ_２Ｆ_５ＳＯ_２）_２Ｎ等のリチウム塩が好適に挙げられる。これらは、１種単独で使用してもよく、２種以上を併用してもよい。
【００３５】
支持塩の電解液に対する配合量としては、電解液（溶媒成分）１ｋｇに対し０．２〜１モルが好ましく、０．５〜１モルがより好ましい。配合量が０．２モルに満たないと、電解液の充分な導電性を確保することができず、電池の充放電特性に支障をきたすことがある一方、１モルを超えると、電解液の粘度が上昇し、前記リチウムイオン等の充分な移動度が確保できないため、前述と同様に電解液の充分な導電性を確保できず、電池の充放電特性に支障をきたすことがある。
【００３６】
前記非プロトン性有機溶媒には、ホスファゼン誘導体及び／又はホスファゼン誘導体の異性体が添加されているのが好ましい。前述のようにリチウム含有複合酸化物の粒子間に特定の金属酸化物を分散させることにより、非水電解液２次電池の充放電容量を向上させることができるが、更に非プロトン性有機溶媒にホスファゼン誘導体及び／又はホスファゼン誘導体の異性体を添加することによって、充放電容量を更に向上させることができる。
【００３７】
また、従来の非水電解液２次電池の電解液に用いられている非プロトン性有機溶媒をベースとした電解液においては、短絡時等に大電流が急激に流れ、電池が異常に発熱した際に、気化・分解してガスが発生したり、発生したガス及び熱により電池の破裂・発火が起こることがあるため危険性が高いが、これら従来の電解液に、ホスファゼン誘導体が含有されていれば、２００℃以下程度の比較的低温における電解液の気化・分解等が抑制され、発火・引火の危険性が低減される。また、仮に負極材料の溶融等により電池内部での発火があっても、類焼の危険性が低い。さらに、リンには、電池を構成する高分子材料の連鎖分解を抑制する作用があるため、発火・引火の危険性は効果的に低減され、高電圧・高放電容量、大電流放電性等の優れた電池性能をも併せ持つ非水電解液２次電池を提供することが可能となる。
【００３８】
また更に、ハロゲン（例えばフッ素）を含むホスファゼンは、万が一の燃焼時には活性ラジカルの捕捉剤として機能するし、有機置換基を有するホスファゼンは、燃焼時に極材及びセパレーター上に炭化物（チャー）を生成するため酸素の遮断効果もある。加えて充電の際にも、ホスファゼンはデンドライト生成の抑制効果を有するために無添加系に比してより安全性は高くなる。
【００３９】
尚、本発明において、発火・引火の危険性は、ＪＩＳ　Ｋ　７２０１に従った酸素指数測定により評価した。なお、酸素指数とは、ＪＩＳ　Ｋ　７２０１に規定の所定の試験条件下において、材料が燃焼を持続するのに必要な体積パーセントで表される最低酸素濃度の値をいい、酸素指数が低いことは発火・引火の危険性が高いことを意味し、反対に酸素指数が高いことは発火・引火の危険性が低いことを意味する。本願では、上記酸素指数に準じた限界酸素指数で発火・引火の危険性を評価した。
【００４０】
ホスファゼン誘導体及び／又はホスファゼン誘導体の異性体が添加された電解液は、限界酸素指数が２１体積％以上であることが好ましい。限界酸素指数が２１体積％未満であると、発火・引火の抑制効果が十分でないことがある。大気条件下では酸素指数は２０．２体積％に相当するため、限界酸素指数２０．２体積％では大気中で燃焼することを意味する。発明者らの鋭意検討により、限界酸素指数２１体積％以上であれば自己消火性を、２３体積％以上であれば難燃性を、２５体積％以上であれば不燃性を有することを見出した。
【００４１】
なお、ここで表記している自己消火性・難燃性・不燃性は、ＵＬ９４ＨＢ法に準拠する方法で定義されるものであり、不燃性石英ファイバーに１．０ｍｌの電解液を染み込ませ１２７ｍｍ×１２．７ｍｍの試験片を作製し、該試験片を大気環境下で着火した際、着火した炎が２５〜１００ｍｍラインの間で消化し、かつ網からの落下物にも着火が認められなかった場合を自己消火性有りとし、着火した炎が装置の２５ｍｍラインまで到達せず、かつ網からの落下物にも着火が認められなかった場合を難燃性ありとし、着火が認められなかった場合（燃焼長０ｍｍ）を不燃性ありとしたものである。
【００４２】
非プロトン性有機溶媒に添加するホスファゼン誘導体としては、特に制限はないが、粘度が比較的低く、支持塩を良好に溶解する観点からは、２５℃における粘度が３００ｍＰａ・ｓ（３００ｃＰ）以下であって、次式（Ｉ）又は次式（ＩＩ）で表されるホスファゼン誘導体が好ましい。
【００４３】
【化７】

（式中、Ｒ^１、Ｒ^２、及びＲ^３は、一価の置換基又はハロゲン元素を表す。Ｘ^１は、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、イオウ、セレン、テルル、及び、ポロニウムからなる群から選ばれる元素の少なくとも１種を含む有機基を表す。Ｙ^１、Ｙ^２及びＹ^３は、２価の連結基、２価の元素、又は単結合を表す。）
（ＮＰＲ^４ _２）_ｎ　　・・・　（ＩＩ）
（式中、Ｒ^４は、一価の置換基又はハロゲン元素を表す。ｎは３〜１５を表す。）
【００４４】
式（Ｉ）又は式（ＩＩ）で表されるホスファゼン誘導体の２５℃における粘度としては、３００ｍＰａ・ｓ（３００ｃＰ）以下であることが必要であり、１００ｍＰａ・ｓ（１００ｃＰ）以下が好ましい。粘度が、３００ｍＰａ・ｓ（３００ｃＰ）を超えると、支持塩が溶解し難くなり、正極材料、セパレーター等への濡れ性が低下し、電解液の粘性抵抗の増大によりイオン導電性が著しく低下し、特に、氷点以下等の低温条件下での使用において性能不足となる。また、これらのホスファゼン誘導体は液状であるため、通常の液状電解質と同等の導電性、優れたサイクル特性を有している。
【００４５】
式（Ｉ）において、Ｒ^１、Ｒ^２及びＲ^３としては、一価の置換基又はハロゲン元素であれば特に制限はない。一価の置換基としては、アルコキシ基、アルキル基、カルボキシル基、アシル基、アリール基等が挙げられ、これらの中でも、電解液を低粘度化し得る点で、アルコキシ基が好ましい。一方、ハロゲン元素としては、フッ素、塩素、臭素等が好適に挙げられる。Ｒ^１〜Ｒ^３は、総て同一の種類の置換基でもよく、それらのうちのいくつかが異なる種類の置換基でもよい。
【００４６】
前記アルコキシ基としては、例えばメトキシ基、エトキシ基、プロポキシ基、ブトキシ基等や、メトキシエトキシ基、メトキシエトキシエトキシ基等のアルコキシ置換アルコキシ基等が挙げられる。これらの中でも、Ｒ^１〜Ｒ^３としては、総てがメトキシ基、エトキシ基、メトキシエトキシ基、又は、メトキシエトキシエトキシ基が好適であり、低粘度・高誘電率の観点から、総てがメトキシ基又はエトキシ基であるのが特に好適である。
【００４７】
前記アルキル基としては、メチル基、エチル基、プロピル基、ブチル基、ペンチル基等が挙げられる。前記アシル基としては、ホルミル基、アセチル基、プロピオニル基、ブチリル基、イソブチリル基、バレリル基等が挙げられる。前記アリール基としては、フェニル基、トリル基、ナフチル基等が挙げられる。
【００４８】
これらの一価の置換基中の水素元素は、ハロゲン元素で置換されているのが好ましく、ハロゲン元素としては、フッ素、塩素、臭素が好適であるが、この中でもフッ素が特に好ましく、次いで塩素が好ましい。フッ素を使用した場合には塩素と比較してサイクル特性が良好である傾向がある。
【００４９】
式（Ｉ）において、Ｙ^１、Ｙ^２及びＹ^３で表される２価の連結基としては、例えば、ＣＨ_２基のほか、酸素、硫黄、セレン、窒素、ホウ素、アルミニウム、スカンジウム、ガリウム、イットリウム、インジウム、ランタン、タリウム、炭素、ケイ素、チタン、スズ、ゲルマニウム、ジルコニウム、鉛、リン、バナジウム、ヒ素、ニオブ、アンチモン、タンタル、ビスマス、クロム、モリブデン、テルル、ポロニウム、タングステン、鉄、コバルト、ニッケルからなる群から選ばれる元素の少なくとも１種を含む２価の連結基が挙げられ、これらの中でも、ＣＨ_２基、及び、酸素、硫黄、セレン、窒素からなる群から選ばれる元素の少なくとも１種を含む２価の連結基が好ましく、硫黄及び／又はセレンの元素を含む２価の連結基が特に好ましい。また、Ｙ^１、Ｙ^２及びＹ^３は、酸素、硫黄、セレン等の２価の元素、又は単結合であってもよい。Ｙ^１〜Ｙ^３は総て同一種類でもよく、いくつかが互いに異なる種類でもよい。
【００５０】
式（Ｉ）において、Ｘ^１としては、有害性、環境等への配慮の観点からは、炭素、ケイ素、窒素、リン、酸素、及び、イオウからなる群から選ばれる元素の少なくとも１種を含む有機基が好ましい。これらの有機基の内、次式（ＶＩＩＩ）、（ＩＸ）又は（Ｘ）で表される構造を有する有機基がより好ましい。
【００５１】
【化８】

【化９】

【化１０】

但し、式（ＶＩＩＩ）、（ＩＸ）、（Ｘ）において、Ｒ^１０〜Ｒ^１４は、一価の置換基又はハロゲン元素を表す。Ｙ^１０〜Ｙ^１４は、２価の連結基、２価の元素、又は単結合を表し、Ｚ^１は２価の基又は２価の元素を表す。
【００５２】
式（ＶＩＩＩ）、（ＩＸ）、（Ｘ）において、Ｒ^１０〜Ｒ^１４としては、式（Ｉ）におけるＲ^１〜Ｒ^３で述べたのと同様の一価の置換基又はハロゲン元素がいずれも好適に挙げられる。又、これらは、同一有機基内において、それぞれ同一の種類でもよく、いくつかが互いに異なる種類でもよい。式（ＶＩＩＩ）のＲ^１０とＲ^１１とは、及び式（Ｘ）のＲ^１３とＲ^１４とは、互いに結合して環を形成していてもよい。
【００５３】
式（ＶＩＩＩ）、（ＩＸ）、（Ｘ）において、Ｙ^１０〜Ｙ^１４で表される基としては、式（Ｉ）におけるＹ^１〜Ｙ^３で述べたのと同様の２価の連結基又は２価の元素等が挙げられ、同様に、硫黄及び／又はセレンの元素を含む基である場合には、電解液の発火・引火の危険性が低減するため特に好ましい。これらは、同一有機基内において、それぞれ同一の種類でもよく、いくつかが互いに異なる種類でもよい。
【００５４】
式（ＶＩＩＩ）において、Ｚ^１としては、例えば、ＣＨ_２基、ＣＨＲ（Ｒは、アルキル基、アルコキシル基、フェニル基等を表す。以下同様。）基、ＮＲ基のほか、酸素、硫黄、セレン、ホウ素、アルミニウム、スカンジウム、ガリウム、イットリウム、インジウム、ランタン、タリウム、炭素、ケイ素、チタン、スズ、ゲルマニウム、ジルコニウム、鉛、リン、バナジウム、ヒ素、ニオブ、アンチモン、タンタル、ビスマス、クロム、モリブデン、テルル、ポロニウム、タングステン、鉄、コバルト、ニッケルからなる群から選ばれる元素の少なくとも１種を含む２価の基等が挙げられ、これらの中でも、ＣＨ_２基、ＣＨＲ基、ＮＲ基のほか、酸素、硫黄、セレンからなる群から選ばれる元素の少なくとも１種を含む２価の基が好ましい。特に、硫黄及び／又はセレンの元素を含む２価の基の場合には、電解液の発火・引火の危険性が低減するため好ましい。また、Ｚ^１は、酸素、硫黄、セレン等の２価の元素であってもよい。
【００５５】
これら有機基としては、特に効果的に発火・引火の危険性を低減し得る点で、式（ＶＩＩＩ）で表されるようなリンを含む有機基が特に好ましい。また、有機基が、式（ＩＸ）で表されるようなイオウを含む有機基である場合には、電解液の小界面抵抗化の点で特に好ましい。
【００５６】
式（ＩＩ）において、Ｒ^４としては、一価の置換基又はハロゲン元素であれば特に制限はない。一価の置換基としては、アルコキシ基、アルキル基、カルボキシル基、アシル基、アリール基等が挙げられ、これらの中でも、電解液を低粘度化し得る点で、アルコキシ基が好ましい。一方、ハロゲン元素としては、例えば、フッ素、塩素、臭素等が好適に挙げられる。アルコキシ基としては、例えば、メトキシ基、エトキシ基、メトキシエトキシ基、プロポキシ基、フェノキシ基等が挙げられ、これらの中でも、メトキシ基、エトキシ基、メトキシエトキシ基が特に好ましい。これらの置換基中の水素元素は、ハロゲン元素で置換されているのが好ましく、ハロゲン元素としては、フッ素、塩素、臭素等が好適に挙げられる。
【００５７】
式（Ｉ）、（ＩＩ）、（ＶＩＩＩ）〜（Ｘ）におけるＲ^１〜Ｒ^４、Ｒ^１０〜Ｒ^１４、Ｙ^１〜Ｙ^３、Ｙ^１０〜Ｙ^１４、Ｚ^１を適宜選択することにより、より好適な粘度、添加・混合に適する溶解性等を有するホスファゼン誘導体の合成が可能となる。これらホスファゼン誘導体は、１種単独で使用してもよく、２種以上を併用してもよい。
【００５８】
前記式（ＩＩ）のホスファゼン誘導体の中でも、電解液を低粘度化して電池の低温特性を向上させ、更に電解液の耐劣化性を向上させる観点からは、次式（ＩＩＩ）で表されるホスファゼン誘導体が特に好ましい。
（ＮＰＦ_２）_ｎ　　・・・　（ＩＩＩ）
（式中、ｎは３〜５を表す。）
【００５９】
式（ＩＩＩ）で表されるホスファゼン誘導体は常温（２５℃）で低粘度の液体であり、かつ、凝固点降下作用を有する。このため、該ホスファゼン誘導体を電解液に添加することにより、電解液に優れた低温特性を付与することが可能となり、また、電解液の低粘度化が達成され、低内部抵抗及び高い導電率を有する非水電解液２次電池を提供することが可能となる。このため、特に気温の低い地方や時期において、低温条件下で使用しても、長時間に渡って優れた放電特性を示す非水電解液２次電池を提供することが可能となる。
【００６０】
式（ＩＩＩ）において、ｎとしては、電解液に優れた低温特性を付与し得、電解液の低粘度化が可能な点で、３〜４が好ましく、３がより好ましい。ｎの値が小さい場合には沸点が低く、接炎時の着火防止特性を向上させることができる。一方、ｎの値が大きくなるにつれて、沸点が高くなるため、高温でも安定に使用することができる。上記性質を利用して目的とする性能を得るために、複数のホスファゼンを適時選択し、使用することも可能である。
【００６１】
式（ＩＩＩ）におけるｎ値を適宜選択することにより、より好適な粘度、混合に適する溶解性、低温特性等を有する電解液の調製が可能となる。これらのホスファゼン誘導体は、１種単独で使用してもよく、２種以上を併用してもよい。
【００６２】
式（ＩＩＩ）で表されるホスファゼン誘導体の粘度としては、２０ｍＰａ・ｓ（２０ｃＰ）以下であれば特に制限はないが、導電性の向上及び低温特性の向上の観点からは、１０ｍＰａ・ｓ（１０ｃＰ）以下が好ましく、５ｍＰａ・ｓ（５ｃＰ）以下がより好ましい。なお、本発明において粘度は、粘度測定計（Ｒ型粘度計Ｍｏｄｅｌ　ＲＥ５００−ＳＬ、東機産業（株）製）を用い、１ｒｐｍ、２ｒｐｍ、３ｒｐｍ、５ｒｐｍ、７ｒｐｍ、１０ｒｐｍ、２０ｒｐｍ、及び５０ｒｐｍの各回転速度で１２０秒間づつ測定し、指示値が５０〜６０％となった時の回転速度を分析条件とし、その際の粘度を測定することによって求めた。
【００６３】
前記式（ＩＩ）のホスファゼン誘導体の中でも、電解液の耐劣化性を向上させ、電解液に優れた不燃性を付与する観点からは、次式（ＩＶ）で表されるホスファゼン誘導体が特に好ましい。
（ＮＰＲ^５ _２）_ｎ　　・・・　（ＩＶ）
（式中、Ｒ^５は一価の置換基又はフッ素を表し、全Ｒ^５のうち少なくとも１つはフッ素を含む一価の置換基又はフッ素であり、ｎは３〜５を表す。但し、全てのＲ^５がフッ素であることはない。）
【００６４】
前記式（ＩＩ）のホスファゼン誘導体を含有すれば、電解液に優れた自己消火性ないし難燃性を付与して電解液の安全性を向上させることができるが、式（ＩＶ）で表され、全Ｒ^５のうち少なくとも１つがフッ素を含む一価の置換基であるホスファゼン誘導体を含有すれば、電解液により優れた不燃性を付与することが可能となる。更に、式（ＩＶ）で表され、全Ｒ^５のうち少なくとも１つがフッ素であるホスファゼン誘導体を含有すれば、更に優れた不燃性を付与することが可能となる。
【００６５】
なお、式（ＩＶ）において、全Ｒ^５がフッ素であり、かつｎが３である環状のホスファゼン誘導体自体は不燃性であり、炎が近づいた際の着火を防止する効果は大きいが、沸点が非常に低いことから、それらが全て揮発してしまうと残された非プロトン性有機溶媒等が燃焼してしまう。
【００６６】
式（ＩＶ）における一価の置換基としては、アルコキシ基のほか、アルキル基、アシル基、アリール基、カルボキシル基等が挙げられ、電解液の不燃性の向上に特に優れる点で、アルコキシ基が好適である。該アルコキシ基としては、メトキシ基、エトキシ基、プロポキシ基等のほか、メトキシエトキシ基等のアルコキシ基置換アルコキシ基等が挙げられ、不燃性に優れる点及び電解液の低粘度化に優れる点で、メトキシ基、エトキシ基、プロポキシ基が特に好ましい。
【００６７】
式（ＩＶ）において、ｎとしては、電解液に優れた不燃性を付与し得る点で、３〜４が好ましい。
【００６８】
前記一価の置換基は、フッ素で置換されているのが好ましく、式（ＩＶ）のＲ^５が一つもフッ素でない場合は、少なくとも一つの一価の置換基はフッ素含む。
【００６９】
前記フッ素のホスファゼン誘導体における含有量としては、３〜７０重量％が好ましく、７〜４５重量％がより好ましい。含有量が前記数値範囲内であれば、本発明の特有の効果である「不燃性」を特に好適に奏することができる。
【００７０】
式（ＩＶ）で表されるホスファゼン誘導体の分子構造としては、前述のフッ素以外にも塩素、臭素等のハロゲン元素を含んでいてもよい。但し、フッ素が最も好ましく、次いで塩素が好ましい。フッ素を使用した場合には塩素と比較してサイクル特性が良好である傾向がある。
【００７１】
式（ＩＶ）におけるＲ^５及びｎ値を適宜選択することにより、より好適な不燃性、粘度、混合に適する溶解性等を有する電解液の調製が可能となる。これらのホスファゼン誘導体は、１種単独で使用してもよく、２種以上を併用してもよい。
【００７２】
非プロトン性有機溶媒に添加するホスファゼン誘導体としては、電解液の粘度上昇を抑制しつつ、電解液の耐劣化性を向上させ、電解液に自己消化性乃至難燃性を付与する観点からは、２５℃（常温）において固体であって、次式（Ｖ）で表されるホスファゼン誘導体も好ましい。
（ＮＰＲ^６ _２）_ｎ　　・・・　（Ｖ）
（式中、Ｒ^６は一価の置換基又はハロゲン元素を表す。ｎは３〜６を表す。）
【００７３】
式（Ｖ）で表されるホスファゼン誘導体は常温（２５℃）で固体であるため、電解液に添加すると電解液中で溶解して電解液の粘度が上昇する。しかし、後述するように所定の添加量であれば電解液の粘度上昇率が低く、低内部抵抗及び高い導電率を有する非水電解液２次電池となる。加えて、式（Ｖ）で表されるホスファゼン誘導体は電解液中で溶解するため、電解液の長期安定性に優れる。
【００７４】
式（Ｖ）において、Ｒ^６としては、一価の置換基又はハロゲン元素であれば特に制限はなく、一価の置換基としては、アルコキシ基、アルキル基、カルボキシル基、アシル基、アリール基等が挙げられる。また、ハロゲン元素としては、例えば、フッ素、塩素、臭素、ヨウ素等のハロゲン元素が好適に挙げられる。これらの中でも、特に電解液の粘度上昇を抑制し得る点で、アルコキシ基が好ましい。該アルコキシ基としては、メトキシ基、エトキシ基、メトキシエトキシ基、プロポキシ基（イソプロポキシ基、ｎ−プロポキシ基）、フェノキシ基、トリフルオロエトキシ基等が好ましく、電解液の粘度上昇を抑制し得る点で、メトキシ基、エトキシ基、プロポキシ基（イソプロポキシ基、ｎ−プロポキシ基）、フェノキシ基、トリフルオロエトキシ基等がより好ましい。前記一価の置換基は、前述のハロゲン元素を含むのが好ましい。
【００７５】
式（Ｖ）において、ｎとしては、電解液の粘度上昇を抑制し得る点で、３又は４が特に好ましい。
【００７６】
式（Ｖ）で表されるホスファゼン誘導体としては、例えば、前記式（Ｖ）においてＲ^６がメトキシ基であってｎが３である構造、式（Ｖ）においてＲ^６がメトキシ基及びフェノキシ基の少なくとも何れかであってｎが４である構造、式（Ｖ）においてＲ^６がエトキシ基であってｎが４である構造、式（Ｖ）においてＲ^６がイソプロポキシ基であってｎが３又は４である構造、式（Ｖ）においてＲ^６がｎ−プロポキシ基であってｎが４である構造、式（Ｖ）においてＲ^６がトリフルオロエトキシ基であってｎが３又は４である構造、式（Ｖ）においてＲ^６がフェノキシ基であってｎが３又は４である構造が、電解液の粘度上昇を抑制し得る点で、特に好ましい。
【００７７】
式（Ｖ）における各置換基及びｎ値を適宜選択することにより、より好適な粘度、混合に適する溶解性等を有する電解液の調製が可能となる。これらのホスファゼン誘導体は、１種単独で使用してもよく、２種以上を併用してもよい。
【００７８】
非プロトン性有機溶媒に添加するホスファゼン誘導体の異性体としては、特に制限されないが、非水電解液２次電池の低温特性を向上させ、電解液に自己消化性乃至難燃性を付与し、更に、電解液の耐劣化性を向上させる観点から、次式（ＶＩ）で表され、かつ次式（ＶＩＩ）で表されるホスファゼン誘導体の異性体が好ましい。
【化１１】

【化１２】

（式（ＶＩ）及び（ＶＩＩ）において、Ｒ^７、Ｒ^８、及びＲ^９は、一価の置換基又はハロゲン元素を表す。Ｘ^２は、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、イオウ、セレン、テルル、及びポロニウムからなる群より選ばれる元素の少なくとも１種を含む置換基を表す。Ｙ^７及びＹ^８は、２価の連結基、２価の元素、又は単結合を表す。）
【００７９】
式（ＶＩ）で表され、式（ＶＩＩ）で表されるホスファゼン誘導体の異性体は、電解液に添加されると、電解液に極めて優れた低温特性を発現させ得る。
【００８０】
式（ＶＩ）におけるＲ^７、Ｒ^８及びＲ^９としては、一価の置換基又はハロゲン元素であれば特に制限はなく、一価の置換基としては、アルコキシ基、アルキル基、カルボキシル基、アシル基、アリール基等が挙げられる。又、ハロゲン元素としては、例えば、フッ素、塩素、臭素等のハロゲン元素が好適に挙げられる。これらの中でも、特に電解液の低温特性及び電気化学的安定性の点で、フッ素及びアルコキシ基等が好ましい。また、電解液の低粘度化の点で、フッ素、アルコキシ基、及びフッ素等を含むアルコキシ基等が好ましい。Ｒ^７〜Ｒ^９は、総て同一の種類の置換基でもよく、それらのうちのいくつかが異なる種類の置換基でもよい。
【００８１】
アルコキシ基としては、例えばメトキシ基、エトキシ基、プロポキシ基、ブトキシ基等や、メトキシエトキシ基、メトキシエトキシエトキシ基等のアルコキシ置換アルコキシ基等が挙げられる。これらの中でも、Ｒ^７〜Ｒ^９としては、総てがメトキシ基、エトキシ基、メトキシエトキシ基、又はメトキシエトキシエトキシ基が好適であり、低粘度・高誘電率の観点から、総てがメトキシ基又はエトキシ基であるのが特に好適である。アルキル基としては、メチル基、エチル基、プロピル基、ブチル基、ペンチル基等が挙げられる。アシル基としては、ホルミル基、アセチル基、プロピオニル基、ブチリル基、イソブチリル基、バレリル基等が挙げられる。アリール基としては、フェニル基、トリル基、ナフチル基等が挙げられる。これらの置換基中の水素元素は、ハロゲン元素で置換されているのが好ましく、ハロゲン元素としては、フッ素、塩素、臭素が好適であるが、この中でもフッ素が特に好ましく、次いで塩素が好ましい。フッ素を使用した場合には塩素と比較してサイクル特性が良好である傾向がある。
【００８２】
式（ＶＩ）において、Ｙ^７及びＹ^８で表される２価の連結基としては、例えば、ＣＨ_２基のほか、酸素、硫黄、セレン、窒素、ホウ素、アルミニウム、スカンジウム、ガリウム、イットリウム、インジウム、ランタン、タリウム、炭素、ケイ素、チタン、スズ、ゲルマニウム、ジルコニウム、鉛、リン、バナジウム、ヒ素、ニオブ、アンチモン、タンタル、ビスマス、クロム、モリブデン、テルル、ポロニウム、タングステン、鉄、コバルト、ニッケルからなる群から選ばれる元素の少なくとも１種を含む２価の連結基が挙げられ、これらの中でも、ＣＨ_２基、及び、酸素、硫黄、セレン、窒素からなる群から選ばれる元素の少なくとも１種を含む２価の連結基が好ましい。また、Ｙ^７及びＹ^８は、酸素、硫黄、セレン等の２価の元素、又は単結合であってもよい。電解液の難燃性が向上する点では、硫黄及び／又は酸素の元素を含む２価の連結基、酸素元素、並びに硫黄元素が特に好ましく、電解液の低温特性に優れる点では、酸素元素を含む２価の連結基、及び酸素元素が特に好ましい。Ｙ^７及びＹ^８は、同一種類でもよく、互いに異なる種類でもよい。
【００８３】
式（ＶＩ）において、Ｘ^２としては、有害性、環境等への配慮の観点からは、炭素、ケイ素、窒素、リン、酸素、及び、硫黄からなる群から選ばれる元素の少なくとも１種を含む置換基が好ましく、次式（ＸＩ）、（ＸＩＩ）又は（ＸＩＩＩ）で表される構造を有する置換基がより好ましい。
【００８４】
【化１３】

【化１４】

【化１５】

【００８５】
但し、式（ＸＩ）、（ＸＩＩ）、（ＸＩＩＩ）において、Ｒ^１５〜Ｒ^１９は、一価の置換基又はハロゲン元素を表す。Ｙ^１５〜Ｙ^１９は、２価の連結基、２価の元素、又は単結合を表し、Ｚ^２は２価の基又は２価の元素を表す。
【００８６】
式（ＸＩ）、（ＸＩＩ）、（ＸＩＩＩ）において、Ｒ^１５〜Ｒ^１９としては、式（ＶＩ）におけるＲ^７〜Ｒ^９で述べたのと同様の一価の置換基又はハロゲン元素がいずれも好適に挙げられる。又、これらは、同一置換基内において、それぞれ同一の種類でもよく、いくつかが互いに異なる種類でもよい。式（ＸＩ）のＲ^１５とＲ^１６とは、及び式（ＸＩＩＩ）のＲ^１８とＲ^１９とは、互いに結合して環を形成していてもよい。
【００８７】
式（ＸＩ）、（ＸＩＩ）、（ＸＩＩＩ）において、Ｙ^１５〜Ｙ^１９で表される基としては、式（ＶＩ）におけるＹ^７〜Ｙ^８で述べたのと同様の２価の連結基又は２価の元素等が挙げられ、同様に、硫黄及び／又は酸素の元素を含む２価の連結基、酸素元素、或いは硫黄元素である場合には、電解液の難燃性が向上するため特に好ましい。また、電解液の低温特性に優れる点では、酸素元素を含む２価の連結基、及び酸素元素が特に好ましい。これらは、同一置換基内において、それぞれ同一の種類でもよく、いくつかが互いに異なる種類でもよい。
【００８８】
式（ＸＩ）において、Ｚ^２としては、例えば、ＣＨ_２基、ＣＨＲ（Ｒは、アルキル基、アルコキシル基、フェニル基等を表す。以下同様。）基、ＮＲ基のほか、酸素、硫黄、セレン、ホウ素、アルミニウム、スカンジウム、ガリウム、イットリウム、インジウム、ランタン、タリウム、炭素、ケイ素、チタン、スズ、ゲルマニウム、ジルコニウム、鉛、リン、バナジウム、ヒ素、ニオブ、アンチモン、タンタル、ビスマス、クロム、モリブデン、テルル、ポロニウム、タングステン、鉄、コバルト、ニッケルからなる群から選ばれる元素の少なくとも１種を含む２価の基等が挙げられ、これらの中でも、ＣＨ_２基、ＣＨＲ基、ＮＲ基のほか、酸素、硫黄、セレンからなる群から選ばれる元素の少なくとも１種を含む２価の基が好ましい。また、Ｚ^２は、酸素、硫黄、セレン等の２価の元素であってもよい。特に、硫黄及び／又はセレン元素を含む２価の基、硫黄元素、或いはセレン元素である場合には、電解液の難燃性が向上するため好ましい。また、電解液の低温特性に優れる点では、酸素元素を含む２価の基、及び酸素元素が特に好ましい。
【００８９】
これら置換基としては、特に効果的に自己消火性ないし難燃性を発現し得る点で、式（ＸＩ）で表されるようなリンを含む置換基が特に好ましい。更に、式（ＸＩ）において、Ｚ^２、Ｙ^１５及びＹ^１６が酸素元素である場合には、特に、電解液に極めて優れた低温特性を発現させることが可能となる。また、置換基が、式（ＸＩＩ）で表されるような硫黄を含む置換基である場合には、電解液の小界面抵抗化の点で特に好ましい。
【００９０】
式（ＶＩ）、及び（ＸＩ）〜（ＸＩＩＩ）におけるＲ^７〜Ｒ^９、Ｒ^１５〜Ｒ^１９、Ｙ^７〜Ｙ^８、Ｙ^１５〜Ｙ^１９、Ｚ^２を適宜選択することにより、より好適な粘度、添加・混合に適する溶解性、低温特性等を有する電解液の調製が可能となる。これらの化合物は、１種単独で使用してもよく、２種以上を併用してもよい。
【００９１】
式（ＶＩ）で表される異性体は、式（ＶＩＩ）で表されるホスファゼン誘導体の異性体であり、例えば、式（ＶＩＩ）で表されるホスファゼン誘導体を生成する際の真空度及び／又は温度を調節することで製造でき、該異性体の電解液における含有量（体積％）は、下記測定方法により測定することができる。
＜＜測定方法＞＞
ゲルパーミエーションクロマトグラフィー（ＧＰＣ）又は高速液体クロマトグラフィーによって試料のピーク面積を求め、該ピーク面積を、予め求めておいた前記異性体のモルあたりの面積と比較することでモル比を得、更に比重を考慮して体積換算することで測定できる。
【００９２】
式（ＶＩＩ）で表されるホスファゼン誘導体としては、粘度が比較的低く、支持塩を良好に溶解し得るものが好ましい。式（ＶＩＩ）のＲ^７〜Ｒ^９、Ｙ^７〜Ｙ^８及びＸ^２としては、式（ＶＩ）のＲ^７〜Ｒ^９、Ｙ^７〜Ｙ^８及びＸ^２の説明で述べたのと同様のものが総て好適に挙げられる。
【００９３】
式（Ｉ）、式（ＩＩ）、式（Ｖ）若しくは式（ＶＩＩ）で表されるホスファゼン誘導体又は式（ＶＩ）で表される異性体としては、分子構造中にハロゲン元素を含む置換基を有するものが好ましい。分子構造中に、ハロゲン元素を含む置換基を有すると、誘導されるハロゲンガスによって、ホスファゼン誘導体又は異性体の含有量が少なくても、効果的に電解液の発火・引火の危険性を低減させることが可能となる。なお、置換基にハロゲン元素を含む化合物においては、ハロゲンラジカルの発生が問題となることがあるが、本発明で用いるホスファゼン誘導体及びホスファゼン誘導体の異性体は、分子構造中のリン元素がハロゲンラジカルを捕捉し、安定なハロゲン化リンを形成するため、このような問題は発生しない。
【００９４】
ホスファゼン誘導体又はホスファゼン誘導体の異性体におけるハロゲン元素の含有量としては、２〜８０重量％が好ましく、２〜６０重量％がより好ましく、２〜５０重量％が更に好ましい。含有量が２重量％未満では、ハロゲン元素を含ませる効果が十分に現れないことがある一方、８０重量％を超えると粘度が高くなるため、電解液に添加した際にその導電率が低下することがある。
【００９５】
式（Ｉ）、式（ＩＩ）、式（ＩＶ）、式（Ｖ）、式（ＶＩＩ）で表されるホスファゼン誘導体の引火点としては、特に制限は無いが、発火の抑制等の点から、１００℃以上が好ましく、１５０℃以上がより好ましい。一方、式（ＩＩＩ）で表されるホスファゼン誘導体は引火点を有さない。ここで、引火点とは、具体的には、物質表面に炎が広がり、少なくとも該物質表面の７５％を覆う温度をいい、該引火点は、空気と燃焼性混合物を形成する傾向度を見る尺度となるものである。ホスファゼン誘導体が、１００℃以上に引火点を有するか、又は引火点を有さないと、発火等が抑制され、また、仮に電池内部で発火等が生じても、引火して電解液表面に燃え広がる危険性を低下させることが可能となる。
【００９６】
式（ＩＩＩ）若しくは式（Ｖ）で表されるホスファゼン誘導体を、又は式（ＶＩ）で表される異性体及び式（ＶＩＩ）で表されるホスファゼン誘導体を添加すると、支持塩の分解が抑制され電解液が著しく安定化する。従来の非水電解液２次電池において、電解液として用いられているエステル系等の電解液においては、例えば、支持塩であるＬｉＰＦ_６塩等のリチウムイオン源等が、経時と共にＬｉＦ及びＰＦ_５に分解し、発生するＰＦ_５ガスや、該発生したＰＦ_５ガスが更に水等と反応して発生する弗化水素ガス等により、腐蝕が進行して劣化すると考えられる。つまり、電解液の導電性が低下する上に、発生する弗化水素ガスで極材が劣化する現象が起こる。一方、ホスファゼン誘導体及びホスファゼン誘導体の異性体は、例えば、前記ＬｉＰＦ_６等のリチウムイオン源の分解を抑制し安定化に寄与する。したがって、従来の電解液にホスファゼン誘導体及び／又はホスファゼン誘導体の異性体を添加することにより、電解液の分解反応が抑制され、腐蝕、劣化を好適に抑制することが可能となる。
【００９７】
以下に、ホスファゼン誘導体及びホスファゼン誘導体の異性体の電解液における含有量を示す。
「限界酸素指数」の観点から、電解液に対する式（Ｉ）又は式（ＩＩ）で表されるホスファゼン誘導体の含有量は５体積％以上が好ましく、１０から５０体積％がより好ましい。含有量を前記数値範囲内の値に調整することにより、電解液の発火・引火の危険性は効果的に低減される。なお、引火の危険性は効果的に低減されるが、その範囲は用いる支持塩の種類や電解液の種類によって異なり、具体的には用いる系が最も低粘度に抑えられ、かつ限界酸素指数が２１体積％以上になる含有量を適時きめることで最適化される。
【００９８】
「自己消火性」の観点から、電解液における式（Ｖ）で表されるホスファゼン誘導体の含有量は２０重量％以上が好ましく、式（ＶＩ）で表される異性体と式（ＶＩＩ）で表されるホスファゼン誘導体との総含有量は２０体積％以上が好ましい。含有量が該数値範囲内であれば、電解液に十分な自己消火性を発現させることができる。
【００９９】
「難燃性」の観点から、電解液における式（Ｖ）で表されるホスファゼン誘導体の含有量は３０重量％以上が好ましく、式（ＶＩ）で表される異性体と式（ＶＩＩ）で表されるホスファゼン誘導体との総含有量は３０体積％以上が好ましい。含有量が該数値範囲内であれば、電解液に十分な難燃性を発現させることができる。
【０１００】
「不燃性」をより好適に付与し得る観点から、電解液における式（ＩＶ）で表されるホスファゼン誘導体の含有量は、１０体積％以上が好ましく、１５体積％以上がより好ましい。含有量が１０体積％未満では、電解液に特に優れた「不燃性」を発現させ得ないことがある。
【０１０１】
「低温特性」の観点から、電解液における式（ＩＩＩ）で表されるホスファゼン誘導体の含有量は１体積％以上が好ましく、３体積％以上がより好ましく、５体積％以上が更に好ましく、式（ＶＩ）で表される異性体と式（ＶＩＩ）で表されるホスファゼン誘導体との総含有量は１体積％以上が好ましく、２体積％以上がより好ましく、５体積％以上が更に好ましい。含有量が、１体積％に満たないと、電解液の低温特性が十分でない。
【０１０２】
「耐劣化性」の観点から、電解液における式（ＩＩＩ）で表されるホスファゼン誘導体の含有量は２体積％以上が好ましく、３〜７５体積％がより好ましく、式（ＩＶ）で表されるホスファゼン誘導体の含有量は２体積％以上が好ましく、２〜７５体積％がより好ましく、（Ｖ）で表されるホスファゼン誘導体の含有量は２重量％以上が好ましく、２〜２０重量％がより好ましく、式（ＶＩ）で表される異性体と式（ＶＩＩ）で表されるホスファゼン誘導体との総含有量は２体積％以上が好ましく、３〜７５体積％がより好ましい。含有量が、該数値範囲内であれば、電解液の劣化を好適に抑制することができる。
【０１０３】
「低粘度化」の観点から、電解液における式（ＩＩＩ）で表されるホスファゼン誘導体の含有量は３〜８０体積％が好ましい。含有量が３体積％未満では、電解液を十分に低粘度化できない。
【０１０４】
「粘度上昇抑制」の観点から、電解液における式（Ｖ）で表されるホスファゼン誘導体の含有量は４０重量％以下が好ましく、３５重量％以下がより好ましく、３０重量％以下が更に好ましい。含有量が４０重量％を超えると、電解液の粘度上昇が著しく大きくなり、内部抵抗が高く導電率が低くなり好ましくない。
【０１０５】
「不燃性」、「自己消火性」ないし「難燃性」の観点から、電解液としては、式（ＩＶ）若しくは式（Ｖ）で表される環状ホスファゼン誘導体、又は式（ＶＩ）で表される異性体及び式（ＶＩＩ）で表されるホスファゼン誘導体と、ＬｉＰＦ_６並びにエチレンカーボネート及び／又はプロピレンカーボネートとを含む場合、或いは式（ＩＶ）若しくは式（Ｖ）で表される環状ホスファゼン誘導体、又は式（ＶＩ）で表される異性体及び式（ＶＩＩ）で表されるホスファゼン誘導体と、ＬｉＣＦ_３ＳＯ_３及びプロピレンカーボネートとを含む場合が特に好ましい。これらの場合には、前述の記載に関わらず、含有量が少量であっても、不燃性、自己消火性ないし難燃性が非常に高い。
【０１０６】
即ち、この場合には、式（ＩＶ）で表される環状ホスファゼン誘導体の電解液における含有量としては、特に優れた不燃性を発現させるためには、５体積％以上が好ましい。また、式（Ｖ）で表される環状ホスファゼン誘導体の電解液における含有量としては、自己消火性を発現させるためには２〜５重量％が好ましく、難燃性を発現させるためには５重量％を超える量が好ましい。また、式（ＶＩ）で表される異性体及び式（ＶＩＩ）で表されるホスファゼン誘導体との電解液における総含有量としては、自己消火性を発現させるためには１．５〜２．５体積％が好ましく、難燃性を発現させるためには２．５体積％を超える量が好ましい。
【０１０７】
本発明の非水電解液２次電池に使用する他の部材としては、非水電解液２次電池の正負極間に、両極の接触による電流の短絡を防止する役割で介在させるセパレーターが挙げられる。セパレーターの材質としては、両極の接触を確実に防止し得、かつ、電解液を通したり含んだりできる材料、例えば、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン等の合成樹脂製の不織布、薄層フィルム等が好適に挙げられる。これらの中でも、厚さ２０〜５０μｍ程度のポリプロピレン又はポリエチレン製の微孔性フィルムが特に好適である。
【０１０８】
本発明では、上述のセパレーターの他にも、通常電池に使用されている公知の各部材が好適に使用できる。
【０１０９】
以上に説明した本発明の非水電解液２次電池の形態としては、特に制限はなく、コインタイプ、ボタンタイプ、ペーパータイプ、角型又はスパイラル構造の円筒型電池等、種々の公知の形態が好適に挙げられる。スパイラル構造の場合は、例えば、シート状の正極を作製して集電体を挟み、これに、負極（シート状）を重ね合わせて巻き上げる等により、非水電解液２次電池を作製することができる。
【０１１０】
【実施例】
以下に、実施例を挙げて本発明を更に詳しく説明するが、本発明はこれらの実施例によりその範囲を限定されるものではない。
【０１１１】
（実施例１）
非水電解液２次電池用正極を、下記の方法で作製した。
エタノール　１０ｍＬ中に、チタンイソプロポキシド（Ｔｉ［ＯＣＨ（ＣＨ_３）_２］_４）（アルドリッチ製）０．０７ｇ（０．２５ｍｍｏｌ）を加え、大気下、３０分間撹拌して溶解させた。次に、生成したエタノール溶液に、撹拌しながら、ＬｉＣｏＯ_２（日本化学工業社製）１ｇを添加し分散させた。
次に、該分散液を氷冷しながら、これに水　０．５ｍＬ（２７ｍｍｏｌ）を添加し、これによりチタンイソプロポキシドを水酸化チタン（Ｔｉ（ＯＨ）_４）にした。
次に、生成した水酸化チタンを含有する混合液を、８０℃で加熱乾燥し、更に、３００℃で１時間乾燥することにより水酸化チタンを酸化チタンにし、該酸化チタンがＬｉＣｏＯ_２粒子間に分散された粉末を得た。このようにして得られた粉末をガラスチューブのオーブンに仕込み、１００℃で１時間脱水して、正極用粉末にした。正極用粉末中の酸化チタンの質量は、ＬｉＣｏＯ_２の質量に対し２％であった。
【０１１２】
上記正極用粉末１００質量部に対して、アセチレンブラックを１０質量部、ポリテトラフルオロエチレン（ＰＴＦＥ）を１０質量部添加し、有機溶媒（酢酸エチルとエタノールとの５０／５０体積％混合溶媒）で混練した後、ロール圧延により厚さ１００μｍ、幅４０ｍｍの薄層状の正極シートを作製した。その後、得られた正極シート２枚を用いて、表面に導電性接着剤を塗布した、厚さ２５μｍのアルミニウム箔（集電体）を挟み込み、これに厚さ２５μｍのセパレーター（微孔性フィルム：ポリプロピレン製）を介在させ、厚さ１５０μｍのリチウム金属箔を重ね合わせて巻き上げ、円筒型電極を作製した。該円筒型電極の正極長さは約２６０ｍｍであった。
【０１１３】
電解液は、ジエチルカーボネート　５０体積％とエチレンカーボネート　５０体積％との混合溶液に、ＬｉＢＦ_４（支持塩）を０．７５ｍｏｌ／ｋｇの濃度で溶解させることにより調製した。該電解液を前記円筒型電極に注入して封口し、単三型リチウム電池を作製した。
【０１１４】
該電池を、２５℃の大気下、上限電圧４．５Ｖ、下限電圧３．０Ｖ、放電電流１００ｍＡ、充電電流５０ｍＡの条件で、５０サイクルまで充放電を繰り返した。その結果、初期における充放電容量は１４５ｍＡｈ／ｇであり、５０サイクル後の充放電容量は１４２ｍＡｈ／ｇであった。
【０１１５】
また、上記電解液の限界酸素指数をＪＩＳ　Ｋ　７２０１に従って測定したところ、１７．１体積％であった。
【０１１６】
（従来例１）
ＬｉＣｏＯ_２１００質量部に対して、アセチレンブラックを１０質量部、ポリテトラフルオロエチレン（ＰＴＦＥ）を１０質量部添加し、有機溶媒（酢酸エチルとエタノールとの５０／５０体積％混合溶媒）で混練した後、ロール圧延により厚さ１００μｍ、幅４０ｍｍの薄層状の正極シートを作製する以外は実施例１と同様にして単三型リチウム電池を作製し、同様に充放電容量を測定した。その結果、初期における充放電容量は１４１ｍＡｈ／ｇであり、５０サイクル後の充放電容量は１３０ｍＡｈ／ｇであった。
【０１１７】
（実施例２〜３及び比較例１〜２）
ＬｉＣｏＯ_２粒子間に分散させる酸化チタンの量を表１記載のように変更する以外は実施例１と同様にして正極用粉末を調製し、リチウム２次電池を作製した。得られた電池に対して、実施例１と同様にして充放電容量を測定した。結果を表１に示す。
【０１１８】
【表１】

【０１１９】
（実施例４〜５）
酸化チタンの代わりに表２に示す金属酸化物をＬｉＣｏＯ_２の粒子間に分散（ＬｉＣｏＯ_２の質量に対する各金属酸化物の質量は２％）させた以外は実施例１と同様にして正極用粉末を調製し、リチウム２次電池を作製した。得られた電池に対して、実施例１と同様にして充放電容量を測定した。結果を表２に示す。
【０１２０】
【表２】

【０１２１】
（実施例６）
ホスファゼン誘導体Ａ（前記式（ＩＶ）において、ｎが３であり、６つのＲ^５のうち２つがエトキシ基、４つがフッ素である環状ホスファゼン誘導体化合物、２５℃における粘度：１．２ｍＰａ・ｓ（１．２ｃＰ））　１０体積％と、ジエチルカーボネート　４５体積％とエチレンカーボネート　４５体積％との混合溶液に、ＬｉＢＦ_４（リチウム塩）を０．７５ｍｏｌ／ｋｇの濃度で溶解させることにより電解液を調製する以外は実施例１と同様にして単三型リチウム電池を作製し、同様に充放電容量を測定した。その結果、初期における充放電容量は１４５ｍＡｈ／ｇであり、５０サイクル後の充放電容量は１４４ｍＡｈ／ｇであった。また、実施例１と同様に電解液の限界酸素指数を測定したところ、限界酸素指数は２２．７体積％であった。
【０１２２】
（実施例７）
ホスファゼン誘導体Ａの代わりにホスファゼン誘導体Ｂ（前記式（ＩＶ）において、ｎが３であり、６つのＲ^５のうち１つがエトキシ基、５つがフッ素である環状ホスファゼン誘導体化合物、２５℃における粘度：１．２ｍＰａ・ｓ（１．２ｃＰ））を用いた以外は、実施例６と同様に電解液を調製して非水電解液２次電池を作製し、同様に充放電容量及び限界酸素指数を測定した。結果を表３に示す。
【０１２３】
（実施例８）
ホスファゼン誘導体Ａの代わりにホスファゼン誘導体Ｃ（前記式（ＩＶ）において、ｎが４であり、８つのＲ^５のうち１つがエトキシ基、７つがフッ素である環状ホスファゼン誘導体化合物、２５℃における粘度：１．３ｍＰａ・ｓ（１．３ｃＰ））を用いた以外は、実施例６と同様に電解液を調製して非水電解液２次電池を作製し、同様に充放電容量及び限界酸素指数を測定した。結果を表３に示す。
【０１２４】
（実施例９）
ホスファゼン誘導体Ａの代わりにホスファゼン誘導体Ｄ（前記式（ＩＶ）において、ｎが３であり、６つのＲ^５のうち１つがＯＣＨ_２ＣＦ_３、５つがフッ素である環状ホスファゼン誘導体化合物、２５℃における粘度：１．８ｍＰａ・ｓ（１．８ｃＰ））を用いた以外は、実施例６と同様に電解液を調製して非水電解液２次電池を作製し、同様に充放電容量及び限界酸素指数を測定した。結果を表３に示す。
【０１２５】
【表３】

【０１２６】
これらの結果から、金属酸化物をリチウム含有複合酸化物の粒子間に分散させることにより充放電容量及びサイクル特性が向上することがわかる。また、リチウム含有複合酸化物の粒子間に金属酸化物を分散させることに加え、ホスファゼン誘導体を添加して電解液を調製することにより、充放電容量及びサイクル特性が更に向上し、かつ、電解液の限界酸素指数が上昇し電池の安全性が向上することが分かる。
【０１２７】
【発明の効果】
本発明によれば、リチウム含有複合酸化物の粒子間に特定の金属酸化物を分散させた粉末からなる正極を用いて非水電解液２次電池を構成することにより、充放電容量が高い非水電解液２次電池を提供することができる。
また、リチウム含有複合酸化物の粒子間に特定の金属酸化物を分散させた粉末からなる正極と、ホスファゼン誘導体及び／又はホスファゼン誘導体の異性体を添加した電解液とを用いて非水電解液２次電池を構成することにより、充放電容量が著しく高く、かつ安全性が高い非水電解液２次電池を提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery provided with the positive electrode.
[0002]
[Prior art]
Conventionally, NiCd batteries have been mainly used as secondary batteries for memory backup of AV / information devices such as personal computers and VTRs, and power sources for driving them. In recent years, it has the advantages of high voltage and high energy density and exhibits excellent self-discharge properties. Therefore, nonaqueous electrolyte secondary batteries (metal lithium secondary batteries, lithium ion Battery, etc.) has received a great deal of attention, and various developments have been attempted, some of which have been commercialized. For example, more than half of notebook computers and mobile phones are driven by non-aqueous electrolyte secondary batteries.
[0003]
In these nonaqueous electrolyte secondary batteries, a lithium-containing composite oxide is used as a material for forming a positive electrode, and carbon is frequently used as a material for forming a negative electrode. Various organic solvents have been used as electrolytes for the purpose of reducing the risk and increasing the driving voltage. In addition, since a nonaqueous electrolyte secondary battery for a camera uses an alkali metal (particularly, lithium metal or lithium alloy) or the like as a negative electrode material, the electrolyte is usually an ester organic solvent or the like. Aprotic organic solvents have been used.
[0004]
[Problems to be solved by the invention]
As described above, the current nonaqueous electrolyte secondary battery has a higher energy density than the NiCd battery, and thus has the advantage of having a high charge / discharge capacity, but in order to further reduce the burden of charging by the user. It is necessary to further improve the charge / discharge capacity.
[0005]
Further, when an alkali metal (particularly lithium metal or lithium alloy) is used as a negative electrode material of a non-aqueous electrolyte secondary battery, the alkali metal has a very high activity against moisture. When water is incomplete due to invasion of water or the like, there is a problem that the anode material and water react with each other to generate hydrogen, ignite, or the like, which is dangerous. In addition, since lithium metal has a low melting point (about 170 ° C.), if a large current suddenly flows during a short circuit or the like, the battery may abnormally generate heat and cause a very dangerous situation such as melting of the battery. There is also. Further, there is a problem that the electrolyte solution based on the organic solvent is vaporized and decomposed to generate gas due to the heat generation of the battery, and the generated gas causes the battery to burst or ignite.
[0006]
Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high charge / discharge capacity.
Another object of the present invention is to provide a highly safe nonaqueous electrolyte secondary battery in addition to high charge / discharge capacity.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-described problems, and as a result, by improving the positive electrode in a non-aqueous electrolyte secondary battery using a lithium-containing composite oxide as a positive electrode active material, a high charge-discharge capacity was obtained. A non-aqueous electrolyte secondary battery is obtained, and a phosphazene derivative and / or an isomer of a phosphazene derivative is added to the electrolyte to further increase the charge / discharge capacity and the safety. Was obtained, and the present invention was completed.
[0008]
That is, the present invention
<1> @LiCoO₂, LiNiO₂And LiMn₂O₄Between particles of at least one lithium-containing composite oxide selected from the group consisting of: titanium oxide, alumina, zinc oxide, chromium oxide, lithium oxide, nickel oxide, copper oxide, and iron oxide A positive electrode for a non-aqueous electrolyte secondary battery, wherein at least one kind of metal oxide is dispersed.
<2> The positive electrode for a non-aqueous electrolyte secondary battery according to <1>, wherein the metal oxide is titanium oxide.
<3> The nonaqueous electrolysis according to <1> or <2>, wherein the mass of the metal oxide is 0.5% to 4% with respect to the mass of the lithium-containing composite oxide. It is a positive electrode for a liquid secondary battery.
[0009]
<4> {(I)} LiCoO in an organic solvent₂, LiNiO₂And LiMn₂O₄And at least one lithium-containing composite oxide selected from the group consisting of: and an alkoxide of at least one metal selected from the group consisting of titanium, aluminum, zinc, chromium, lithium, nickel, copper, and iron. Mixing to produce a mixture,
(II) a step of adding water to the mixed solution to form a metal hydroxide;
(III) A positive electrode in which a metal hydroxide is converted into a metal oxide by heating and drying a liquid containing the generated metal hydroxide, and the metal oxide is dispersed between particles of the lithium-containing composite oxide. A step of producing a powder;
(IV) a step of forming the positive electrode powder to produce a positive electrode;
A method for producing a positive electrode for a non-aqueous electrolyte secondary battery, comprising:
<5> The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to <4>, wherein the metal is titanium.
<6> The alkoxide of the metal is titanium isopropoxide (Ti [OCH (CH₃)₂]₄<4> The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to <4>, wherein
[0010]
<7> A non-aqueous electrolyte secondary battery including the positive electrode according to any one of <1> to <3>, a negative electrode, and an electrolyte including an aprotic organic solvent and a supporting salt.
<8> The nonaqueous electrolyte secondary battery according to <7>, wherein a phosphazene derivative and / or an isomer of the phosphazene derivative are added to the aprotic organic solvent.
[0011]
<9> The above-mentioned <8>, wherein the phosphazene derivative has a viscosity of 300 mPa · s (300 cP) or less at 25 ° C. and is represented by the following formula (I) or the following formula (II). It is a non-aqueous electrolyte secondary battery.
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(Where R¹, R², And R³Represents a monovalent substituent or a halogen element. X¹Represents a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium, and polonium. Y¹, Y²And Y³Represents a divalent linking group, a divalent element, or a single bond. )
(NPR⁴ ₂)_n・ ・ ・ (II)
(Where R⁴Represents a monovalent substituent or a halogen element. n represents 3 to 15. )
[0012]
<10> The non-aqueous electrolyte secondary battery according to <9>, wherein the phosphazene derivative represented by the formula (II) is represented by the following formula (III).
(NPF₂)_n・ ・ ・ (III)
(In the formula, n represents 3 to 5.)
[0013]
<11> The non-aqueous electrolyte secondary battery according to <9>, wherein the phosphazene derivative represented by the formula (II) is represented by the following formula (IV).
(NPR⁵ ₂)_n・ ・ ・ (IV)
(Where R⁵Represents a monovalent substituent or fluorine, and all R⁵At least one is a monovalent substituent containing fluorine or fluorine, and n represents 3 to 5. However, all R⁵Cannot be fluorine. )
[0014]
<12> The nonaqueous electrolyte secondary battery according to <8>, wherein the phosphazene derivative is solid at 25 ° C. and represented by the following formula (V).
(NPR⁶ ₂)_n・ ・ ・ (V)
(Where R⁶Represents a monovalent substituent or a halogen element. n represents 3 to 6. )
[0015]
<13> The non-aqueous solution according to <8>, wherein the isomer of the phosphazene derivative is an isomer of a phosphazene derivative represented by the following formula (VI) and represented by the following formula (VII): It is an electrolyte secondary battery.
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(In formulas (VI) and (VII), R⁷, R⁸And R⁹Represents a monovalent substituent or a halogen element. X²Represents a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium, and polonium. Y⁷And Y⁸Represents a divalent linking group, a divalent element, or a single bond. )
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is composed of a lithium-containing composite oxide and a metal oxide dispersed between particles of the lithium-containing composite oxide. Contains additives commonly used in the technical field of non-aqueous electrolyte secondary batteries such as binders.
[0017]
The lithium-containing composite oxide used in the present invention is a composite oxide of lithium and a transition metal, and is a substance that directly participates in an electromotive reaction as a positive electrode active material of a nonaqueous electrolyte secondary battery. As the lithium-containing composite oxide, LiCoO₂, LiNiO₂, LiMn₂O₄, LiFeO₂And LiFePO₄And among them, among them, LiCoO₂, LiNiO₂, LiMn₂O₄Is preferred. These lithium-containing composite oxides may be used alone or in combination of two or more. Further, the lithium-containing composite oxide may be a composite oxide containing two or three types of transition metals selected from the group consisting of Fe, Mn, Co, and Ni. Is LiFe_xCo_yNi_{(1 − x − y)}O₂(Where 0 ≦ x <1, 0 ≦ y <1, 0 <x + y ≦ 1) or LiMn_xFe_yO_{2 − x − y}And so on. The particle diameter of the lithium-containing composite oxide is 1 to 60 μm, preferably 20 to 40 μm. When the particle size is less than 1 μm or more than 60 μm, the packing becomes poor during molding of the positive electrode mixture (comprising the positive electrode active material, the conductive agent and the binder), or the amount of the positive electrode active material contained in a unit volume is reduced. Therefore, the charge / discharge capacity may decrease, which is not preferable.
[0018]
Examples of the metal oxide used in the present invention include titanium oxide, alumina, zinc oxide, chromium oxide, lithium oxide, nickel oxide, copper oxide, and iron oxide. These may be used alone or in combination of two or more. You may. The metal oxide is preferably very fine particles, the particle size of which is between 10 nm and 1 μm, preferably between 20 nm and 60 nm. Particles having a particle size of less than 10 nm are industrially difficult to synthesize, and if the particle size exceeds 1 μm, the amount of the positive electrode active material contained per unit volume decreases, and the amount of energy per unit volume decreases, which is not preferable. .
[0019]
In the present invention, since the metal oxide is dispersed between the particles of the lithium-containing composite oxide, gaps are generated between the lithium-containing composite oxide particles. Since the electrolytic solution can efficiently enter the gap, the contact area between the electrolytic solution and the lithium-containing composite oxide increases, and as a result, the utilization rate of the lithium-containing composite oxide increases, and the charge / discharge capacity improves.
[0020]
Among the metal oxides that form gaps between the lithium-containing composite oxide particles, titanium oxide is particularly preferable, because titanium oxide does not inhibit the battery electrode reaction of the nonaqueous electrolyte secondary battery. It not only contributes to the stability of the battery by absorbing moisture, but also does not significantly lower the conductivity by the addition (the internal resistance does not increase).
[0021]
The mass of the metal oxide in the positive electrode of the present invention is preferably 0.5% to 4% with respect to the mass of the lithium-containing composite oxide. When the mass of the metal oxide is less than 0.5% with respect to the mass of the lithium-containing composite oxide, the effect of dispersing the metal oxide between the particles of the lithium-containing composite oxide to form a gap is sufficient. When the content exceeds 4%, the amount of the positive electrode active material per unit volume decreases, and at the same time, the particle surface of the lithium-containing composite oxide is covered with the metal oxide, and the contact area between the electrolyte and the lithium-containing composite oxide is reduced. It is not preferable because it decreases.
[0022]
Among the additives to be added to the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, acetylene black or the like may be used as a conductive agent, and polyvinylidene fluoride (PVDF) or polybutadiene may be used as a binder. Examples include tetrafluoroethylene (PTFE). When these additives are used, they can be blended at the same blending ratio as in the past, for example, powder for positive electrode: conductive agent: binder = 8: 1: 1 to 8: 1: 0.2 (mass ratio). .
[0023]
The shape of the positive electrode is not particularly limited, and can be appropriately selected from known shapes of electrodes. For example, a sheet shape, a column shape, a plate shape, a spiral shape, and the like can be given.
[0024]
The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is preferably such that very fine metal oxide particles are dispersed between the lithium-containing composite oxide particles. It is preferably prepared by a sol-gel method. The preparation method is not particularly limited as long as very fine particles can be prepared.
[0025]
The positive electrode used in the nonaqueous electrolyte secondary battery of the present invention can be manufactured according to the following first to fourth steps.
In the first step, the lithium-containing composite oxide and an alkoxide of at least one metal selected from the group consisting of titanium, aluminum, zinc, chromium, lithium, nickel, copper, and iron are mixed in an organic solvent. Add and mix to prepare a mixture. As the organic solvent, low-boiling alcohols such as methanol and ethanol or low-boiling ketones such as acetone are preferable, and ethanol is particularly preferable. On the other hand, the alkoxy group in the metal alkoxide is preferably an isopropoxy group, an n-propoxy group, or the like, from the viewpoint of the solubility of the metal alkoxide in an organic solvent.
[0026]
In the second step, water is added to the mixed solution prepared in the first step, and a metal hydroxide corresponding to the metal alkoxide is generated by a hydrolysis reaction of the metal alkoxide. Note that the second step is preferably performed while cooling with ice.
[0027]
Next, in a third step, by heating and drying the liquid containing the metal hydroxide, the metal hydroxide is converted to a metal oxide while removing the solvent, and the metal oxide is converted to a lithium-containing composite oxide. A powder for a positive electrode dispersed between particles is produced. In order to completely remove and dehydrate the solvent, the heating and drying are preferably performed at a temperature of 120 to 300 ° C. for a sufficient time.
[0028]
Next, in a fourth step, the positive electrode powder obtained in the third step is formed into a predetermined shape to obtain a positive electrode for a non-aqueous electrolyte secondary battery. The forming method is not particularly limited as long as a positive electrode having such a strength as not to be damaged during the manufacturing process of the nonaqueous electrolyte secondary battery can be used, and a conventionally known method can be used. For example, after mixing and kneading the powder for the positive electrode, additives such as the conductive material and the binder described above, and an organic solvent such as ethyl acetate or ethanol, a sheet having a desired thickness and width is obtained by roll rolling. Can also be implemented.
[0029]
In the positive electrode obtained by the above method, very fine metal oxide particles are dispersed between particles of the lithium-containing composite oxide, and the amount of the positive electrode active material per unit volume (the amount of the lithium-containing composite oxide) is increased. It is a positive electrode of a non-aqueous electrolyte secondary battery having a remarkably high charge / discharge capacity as compared with a positive electrode composed of only a lithium-containing composite oxide without reduction.
[0030]
The non-aqueous electrolyte secondary battery of the present invention includes the above-described positive electrode, a negative electrode, and an electrolyte comprising an aprotic organic solvent and a supporting salt, and if necessary, a non-aqueous electrolyte secondary such as a separator. It has members commonly used in the battery technical field.
[0031]
The negative electrode of the nonaqueous electrolyte secondary battery of the present invention is capable of inserting and extracting lithium or lithium ions, for example. Therefore, the material is not particularly limited as long as it can occlude and release lithium or lithium ions, for example, and can be appropriately selected from known negative electrode materials. For example, a material containing lithium, specifically, lithium metal itself, an alloy of lithium and aluminum, indium, lead or zinc, a carbon material such as graphite doped with lithium, and the like are preferable. A carbon material such as graphite is preferable in terms of higher safety. These materials may be used alone or in combination of two or more. The shape of the negative electrode is not particularly limited, and can be appropriately selected from known shapes similar to the shape of the positive electrode.
[0032]
The electrolyte of the nonaqueous electrolyte secondary battery of the present invention comprises an aprotic organic solvent and a supporting salt. Since the negative electrode of the nonaqueous electrolyte secondary battery contains an alkali metal such as lithium as described above, the reactivity with water is very high, and therefore, an aprotic organic solvent that does not react with water is used as a solvent. . The aprotic organic solvent can reduce the viscosity of the electrolytic solution, and can easily achieve optimal ionic conductivity as a battery.
[0033]
The aprotic organic solvent is not particularly limited, but includes an ether compound and an ester compound from the viewpoint of suppressing the viscosity of the electrolytic solution to be low. Specifically, 1,2-dimethoxyethane, tetrahydrofuran, dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, ethyl methyl carbonate and the like are preferably exemplified. Among these, ethylene carbonate, propylene carbonate, cyclic ester compounds such as γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, chain ester compounds such as diethyl carbonate, and chain ether compounds such as 1,2-dimethoxyethane are preferable. It is. In particular, a cyclic ester compound has a high relative dielectric constant and is excellent in solubility of a lithium salt and the like, and a chain ester compound and an ether compound have a low viscosity, and thus are suitable in terms of reducing the viscosity of an electrolytic solution. is there. These may be used alone or in combination of two or more, but it is preferable to use two or more in combination. The viscosity of the aprotic organic solvent at 25 ° C. is not particularly limited, but is preferably 3.0 mPa · s (3.0 cP) or less, and more preferably 2.0 mPa · s (2.0 cP) or less.
[0034]
As the supporting salt, a supporting salt serving as an ion source of lithium ions and the like are preferable. The ion source of the lithium ions is not particularly limited.₄, LiBF₄, LiPF₆, LiCF₃SO₃And LiAsF₆, LiC₄F₉SO₃, Li (CF₃SO₂)₂N, Li (C₂F₅SO₂)₂A lithium salt such as N is preferably used. These may be used alone or in combination of two or more.
[0035]
The compounding amount of the supporting salt with respect to the electrolytic solution is preferably 0.2 to 1 mol, more preferably 0.5 to 1 mol, per 1 kg of the electrolytic solution (solvent component). If the amount is less than 0.2 mol, sufficient conductivity of the electrolyte cannot be secured, which may hinder the charge / discharge characteristics of the battery. Since the viscosity increases and sufficient mobility of the lithium ions or the like cannot be secured, sufficient conductivity of the electrolyte cannot be secured as described above, which may hinder the charge / discharge characteristics of the battery.
[0036]
It is preferable that a phosphazene derivative and / or an isomer of the phosphazene derivative are added to the aprotic organic solvent. By dispersing a specific metal oxide between the particles of the lithium-containing composite oxide as described above, the charge / discharge capacity of the nonaqueous electrolyte secondary battery can be improved. By adding the phosphazene derivative and / or the isomer of the phosphazene derivative, the charge / discharge capacity can be further improved.
[0037]
Further, in the electrolyte based on the aprotic organic solvent used for the electrolyte of the conventional non-aqueous electrolyte secondary battery, a large current suddenly flows when a short circuit occurs, and the battery abnormally generates heat. At this time, gas is generated by vaporization / decomposition, and the generated gas and heat may rupture or ignite the battery, which poses a high risk.However, these conventional electrolytes contain a phosphazene derivative. This suppresses vaporization and decomposition of the electrolyte at a relatively low temperature of about 200 ° C. or less, and reduces the risk of ignition and ignition. Also, even if ignition occurs inside the battery due to melting of the negative electrode material or the like, the risk of burning is low. In addition, phosphorus has the effect of suppressing chain decomposition of the polymer material that constitutes the battery, effectively reducing the risk of ignition and ignition, and high voltage, high discharge capacity, high current discharge, etc. It is possible to provide a non-aqueous electrolyte secondary battery that also has excellent battery performance.
[0038]
Still further, phosphazene containing halogen (for example, fluorine) functions as a scavenger for active radicals in the event of burning, and phosphazene having an organic substituent generates carbide (char) on the electrode material and the separator during burning. Therefore, it also has the effect of blocking oxygen. In addition, even during charging, phosphazene has an effect of suppressing dendrite generation, so that the safety is higher than that of a non-added system.
[0039]
In the present invention, the risk of ignition or ignition was evaluated by measuring the oxygen index according to JIS K 7201. The oxygen index refers to a value of a minimum oxygen concentration expressed as a volume percentage required for the material to sustain combustion under predetermined test conditions specified in JIS K 7201. A higher risk of ignition / flammability means a higher oxygen index means a lower risk of fire / ignition. In the present application, the risk of ignition / flammability was evaluated based on the limiting oxygen index according to the oxygen index.
[0040]
The electrolyte to which the phosphazene derivative and / or the isomer of the phosphazene derivative is added preferably has a limiting oxygen index of 21% by volume or more. If the limiting oxygen index is less than 21% by volume, the effect of suppressing ignition and ignition may not be sufficient. Since the oxygen index is equivalent to 20.2% by volume under atmospheric conditions, a limit oxygen index of 20.2% by volume means burning in the atmosphere. The inventors of the present invention have conducted intensive studies and found that if the limiting oxygen index is at least 21% by volume, self-extinguishing properties will be exhibited, if at least 23% by volume, flame retardancy will be obtained, and if at least 25% by volume, nonflammability will be exhibited. .
[0041]
The self-extinguishing, flame-retardant, and non-flammable properties described herein are defined by a method based on the UL94HB method, and the non-combustible quartz fiber is impregnated with 1.0 ml of an electrolyte solution and 127 mm × When a 12.7 mm test piece was prepared and the test piece was ignited in an air environment, the ignited flame was extinguished between the 25 and 100 mm lines, and no ignition was found on the falling object from the net. The case is self-extinguishing, the case where the ignited flame did not reach the 25 mm line of the device, and the case where the falling object from the net did not ignite was regarded as flame-retardant, and the case where ignition was not found (Combustion length of 0 mm) is considered nonflammable.
[0042]
The phosphazene derivative to be added to the aprotic organic solvent is not particularly limited. However, from the viewpoint of relatively low viscosity and good dissolution of the supporting salt, the viscosity at 25 ° C. is 300 mPa · s (300 cP) or less. Thus, a phosphazene derivative represented by the following formula (I) or (II) is preferable.
[0043]
Embedded image

(Where R¹, R², And R³Represents a monovalent substituent or a halogen element. X¹Represents an organic group containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium, and polonium. Y¹, Y²And Y³Represents a divalent linking group, a divalent element, or a single bond. )
(NPR⁴ ₂)_n・ ・ ・ (II)
(Where R⁴Represents a monovalent substituent or a halogen element. n represents 3 to 15. )
[0044]
The viscosity at 25 ° C. of the phosphazene derivative represented by the formula (I) or (II) needs to be 300 mPa · s (300 cP) or less, and preferably 100 mPa · s (100 cP) or less. When the viscosity exceeds 300 mPa · s (300 cP), the supporting salt becomes difficult to dissolve, the wettability to the positive electrode material, the separator, and the like is reduced, and the ionic conductivity is significantly reduced due to an increase in the viscous resistance of the electrolytic solution. In particular, the performance is insufficient when used under low temperature conditions such as below the freezing point. Further, since these phosphazene derivatives are liquid, they have the same conductivity and excellent cycle characteristics as ordinary liquid electrolytes.
[0045]
In the formula (I), R¹, R²And R³Is not particularly limited as long as it is a monovalent substituent or a halogen element. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, an aryl group, and the like. Among them, an alkoxy group is preferable because the viscosity of the electrolytic solution can be reduced. On the other hand, preferred examples of the halogen element include fluorine, chlorine, and bromine. R¹~ R³May be all the same type of substituents, and some of them may be different types of substituents.
[0046]
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like, and an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group. Among these, R¹~ R³As all, methoxy group, ethoxy group, methoxyethoxy group, or methoxyethoxyethoxy group is preferable, and from the viewpoint of low viscosity and high dielectric constant, it is particularly preferable that all are methoxy group or ethoxy group. It is suitable.
[0047]
Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group.
[0048]
The hydrogen element in these monovalent substituents is preferably substituted with a halogen element, and as the halogen element, fluorine, chlorine, and bromine are preferable. Among them, fluorine is particularly preferable, and then chlorine is used. preferable. When fluorine is used, the cycle characteristics tend to be better than chlorine.
[0049]
In the formula (I), Y¹, Y²And Y³Examples of the divalent linking group represented by₂In addition to the groups, oxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, Examples include divalent linking groups containing at least one element selected from the group consisting of antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, and nickel.₂A divalent linking group containing a group and at least one element selected from the group consisting of oxygen, sulfur, selenium, and nitrogen is preferable, and a divalent linking group containing an element of sulfur and / or selenium is particularly preferable. Also, Y¹, Y²And Y³May be a divalent element such as oxygen, sulfur, selenium, or a single bond. Y¹~ Y³May be of the same type, or some may be of different types.
[0050]
In the formula (I), X¹From the viewpoint of consideration of harmfulness, environment, and the like, an organic group containing at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur is preferable. Among these organic groups, an organic group having a structure represented by the following formula (VIII), (IX) or (X) is more preferable.
[0051]
Embedded image

Embedded image

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However, in formulas (VIII), (IX) and (X), R¹⁰~ R¹⁴Represents a monovalent substituent or a halogen element. Y¹⁰~ Y¹⁴Represents a divalent linking group, a divalent element, or a single bond;¹Represents a divalent group or a divalent element.
[0052]
In the formulas (VIII), (IX) and (X), R¹⁰~ R¹⁴Is represented by R in the formula (I)¹~ R³Any of the same monovalent substituents and halogen elements as described in (1) are preferably used. Further, these may be of the same type or different from each other within the same organic group. R of formula (VIII)¹⁰And R¹¹And R of formula (X)¹³And R¹⁴And may combine with each other to form a ring.
[0053]
In the formulas (VIII), (IX) and (X), Y¹⁰~ Y¹⁴The group represented by the formula:¹~ Y³The same divalent linking group or divalent element as mentioned in the above may be mentioned. Similarly, when the group contains a sulfur and / or selenium element, there is a danger of ignition and ignition of the electrolytic solution. Is particularly preferred because it reduces the These may be of the same type within the same organic group, or some may be of different types.
[0054]
In the formula (VIII), Z¹As, for example, CH₂Group, CHR (R represents an alkyl group, an alkoxyl group, a phenyl group, etc .; the same applies hereinafter), an NR group, oxygen, sulfur, selenium, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, Selected from the group consisting of thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel And other divalent groups containing at least one of the following elements.₂In addition to the group, CHR group and NR group, a divalent group containing at least one element selected from the group consisting of oxygen, sulfur and selenium is preferable. In particular, a divalent group containing an element of sulfur and / or selenium is preferable because the risk of ignition and ignition of the electrolytic solution is reduced. Also, Z¹May be a divalent element such as oxygen, sulfur, and selenium.
[0055]
As these organic groups, an organic group containing phosphorus as represented by the formula (VIII) is particularly preferable in that the risk of ignition and ignition can be reduced particularly effectively. Further, when the organic group is an organic group containing sulfur as represented by the formula (IX), it is particularly preferable from the viewpoint of reducing the interface resistance of the electrolytic solution.
[0056]
In the formula (II), R⁴Is not particularly limited as long as it is a monovalent substituent or a halogen element. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, an aryl group, and the like. Among them, an alkoxy group is preferable because the viscosity of the electrolytic solution can be reduced. On the other hand, preferred examples of the halogen element include fluorine, chlorine, and bromine. Examples of the alkoxy group include a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group, a phenoxy group and the like. Among these, a methoxy group, an ethoxy group and a methoxyethoxy group are particularly preferable. The hydrogen element in these substituents is preferably substituted with a halogen element, and as the halogen element, fluorine, chlorine, bromine and the like are preferred.
[0057]
R in formulas (I), (II), (VIII) to (X)¹~ R⁴, R¹⁰~ R¹⁴, Y¹~ Y³, Y¹⁰~ Y¹⁴, Z¹By appropriately selecting, it becomes possible to synthesize a phosphazene derivative having more suitable viscosity, solubility suitable for addition and mixing, and the like. These phosphazene derivatives may be used alone or in combination of two or more.
[0058]
Among the phosphazene derivatives of the formula (II), from the viewpoint of improving the low-temperature characteristics of the battery by lowering the viscosity of the electrolyte and further improving the deterioration resistance of the electrolyte, the phosphazene represented by the following formula (III) Derivatives are particularly preferred.
(NPF₂)_n・ ・ ・ (III)
(In the formula, n represents 3 to 5.)
[0059]
The phosphazene derivative represented by the formula (III) is a low-viscosity liquid at ordinary temperature (25 ° C.) and has a freezing point depressing action. For this reason, by adding the phosphazene derivative to the electrolytic solution, it is possible to impart excellent low-temperature characteristics to the electrolytic solution, and a low viscosity of the electrolytic solution is achieved, and a low internal resistance and high conductivity are obtained. It is possible to provide a non-aqueous electrolyte secondary battery having the same. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that exhibits excellent discharge characteristics over a long period of time even when used under low-temperature conditions, particularly in a region or at a time when the temperature is low.
[0060]
In the formula (III), n is preferably from 3 to 4, and more preferably 3, from the viewpoint that excellent low-temperature characteristics can be imparted to the electrolytic solution and the viscosity of the electrolytic solution can be reduced. When the value of n is small, the boiling point is low, and the ignition prevention characteristics at the time of flame contact can be improved. On the other hand, as the value of n increases, the boiling point increases, so that it can be used stably even at high temperatures. It is also possible to select and use a plurality of phosphazenes as appropriate in order to obtain the desired performance by utilizing the above properties.
[0061]
By appropriately selecting the value of n in the formula (III), it becomes possible to prepare an electrolyte having more suitable viscosity, solubility suitable for mixing, low-temperature characteristics, and the like. These phosphazene derivatives may be used alone or in combination of two or more.
[0062]
The viscosity of the phosphazene derivative represented by the formula (III) is not particularly limited as long as it is 20 mPa · s (20 cP) or less, but from the viewpoint of improving conductivity and improving low-temperature characteristics, it is 10 mPa · s (10 cP). ) Or less, and more preferably 5 mPa · s (5 cP) or less. In the present invention, the viscosity was measured using a viscometer (R-type viscometer Model @ RE500-SL, manufactured by Toki Sangyo Co., Ltd.) at 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 rpm, and 50 rpm. The rotation speed was measured at intervals of 120 seconds, and the rotation speed when the indicated value became 50 to 60% was used as an analysis condition, and the viscosity was measured at that time.
[0063]
Among the phosphazene derivatives of the formula (II), a phosphazene derivative represented by the following formula (IV) is particularly preferable from the viewpoint of improving the deterioration resistance of the electrolytic solution and imparting excellent nonflammability to the electrolytic solution.
(NPR⁵ ₂)_n・ ・ ・ (IV)
(Where R⁵Represents a monovalent substituent or fluorine, and all R⁵At least one is a monovalent substituent containing fluorine or fluorine, and n represents 3 to 5. However, all R⁵Cannot be fluorine. )
[0064]
When the phosphazene derivative of the formula (II) is contained, the electrolyte can be provided with excellent self-extinguishing properties or flame retardancy to improve the safety of the electrolyte. All R⁵If at least one of them contains a phosphazene derivative which is a monovalent substituent containing fluorine, it is possible to impart more excellent nonflammability to the electrolytic solution. Further, as represented by the formula (IV), all R⁵If at least one of them contains a phosphazene derivative in which at least one is fluorine, it is possible to impart more excellent nonflammability.
[0065]
In the formula (IV), all R⁵Is fluorine, and the cyclic phosphazene derivative in which n is 3 is itself nonflammable, and has a great effect of preventing ignition when a flame approaches. However, since the boiling point is extremely low, all of them are volatilized. If this occurs, the remaining aprotic organic solvent and the like will burn.
[0066]
Examples of the monovalent substituent in the formula (IV) include an alkoxy group, an alkyl group, an acyl group, an aryl group, a carboxyl group, and the like. The alkoxy group is particularly excellent in improving the nonflammability of the electrolytic solution. It is suitable. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, and the like, and an alkoxy group-substituted alkoxy group such as a methoxyethoxy group, and the like.In terms of excellent nonflammability and low viscosity of the electrolytic solution, A methoxy group, an ethoxy group and a propoxy group are particularly preferred.
[0067]
In the formula (IV), n is preferably 3 or 4 from the viewpoint that excellent nonflammability can be imparted to the electrolytic solution.
[0068]
The monovalent substituent is preferably substituted by fluorine, and R 1 of the formula (IV)⁵When at least one is not fluorine, at least one monovalent substituent contains fluorine.
[0069]
The content of the fluorine in the phosphazene derivative is preferably from 3 to 70% by weight, and more preferably from 7 to 45% by weight. When the content is within the above numerical range, “nonflammability” which is a special effect of the present invention can be particularly suitably exerted.
[0070]
The molecular structure of the phosphazene derivative represented by the formula (IV) may include a halogen element such as chlorine and bromine in addition to the above-mentioned fluorine. However, fluorine is most preferred, followed by chlorine. When fluorine is used, the cycle characteristics tend to be better than chlorine.
[0071]
R in formula (IV)⁵By appropriately selecting the n value and the n value, it becomes possible to prepare an electrolyte having more suitable nonflammability, viscosity, solubility suitable for mixing, and the like. These phosphazene derivatives may be used alone or in combination of two or more.
[0072]
As the phosphazene derivative to be added to the aprotic organic solvent, while suppressing the increase in the viscosity of the electrolytic solution, improving the deterioration resistance of the electrolytic solution, from the viewpoint of imparting self-digestibility or flame retardancy to the electrolytic solution, A phosphazene derivative which is solid at 25 ° C. (normal temperature) and represented by the following formula (V) is also preferable.
(NPR⁶ ₂)_n・ ・ ・ (V)
(Where R⁶Represents a monovalent substituent or a halogen element. n represents 3 to 6. )
[0073]
Since the phosphazene derivative represented by the formula (V) is solid at normal temperature (25 ° C.), when added to the electrolytic solution, it is dissolved in the electrolytic solution and the viscosity of the electrolytic solution increases. However, as will be described later, if the addition amount is a predetermined amount, the non-aqueous electrolyte secondary battery has a low rate of increase in the viscosity of the electrolyte, and has a low internal resistance and a high conductivity. In addition, since the phosphazene derivative represented by the formula (V) dissolves in the electrolytic solution, the electrolytic solution has excellent long-term stability.
[0074]
In the formula (V), R⁶Is not particularly limited as long as it is a monovalent substituent or a halogen element. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Further, as the halogen element, for example, a halogen element such as fluorine, chlorine, bromine, and iodine is preferably exemplified. Among these, an alkoxy group is particularly preferable in that the increase in the viscosity of the electrolytic solution can be suppressed. The alkoxy group is preferably a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group (isopropoxy group, n-propoxy group), a phenoxy group, a trifluoroethoxy group, or the like, which can suppress an increase in the viscosity of the electrolytic solution. And a methoxy group, an ethoxy group, a propoxy group (isopropoxy group, n-propoxy group), a phenoxy group, a trifluoroethoxy group and the like are more preferable. The monovalent substituent preferably contains the halogen element described above.
[0075]
In the formula (V), n is particularly preferably 3 or 4 from the viewpoint that the increase in the viscosity of the electrolytic solution can be suppressed.
[0076]
The phosphazene derivative represented by the formula (V) includes, for example, R⁶Is a methoxy group and n is 3, in the formula (V),⁶Is a methoxy group and / or a phenoxy group, and n is 4.⁶Is an ethoxy group and n is 4, R in the formula (V)⁶Is an isopropoxy group and n is 3 or 4, R in the formula (V)⁶Is an n-propoxy group and n is 4, R in the formula (V)⁶Is a trifluoroethoxy group and n is 3 or 4, R in the formula (V)⁶Is a phenoxy group, and a structure in which n is 3 or 4 is particularly preferable since the increase in the viscosity of the electrolytic solution can be suppressed.
[0077]
By appropriately selecting the substituents and the n value in the formula (V), it becomes possible to prepare an electrolyte having more suitable viscosity, solubility suitable for mixing, and the like. These phosphazene derivatives may be used alone or in combination of two or more.
[0078]
The isomer of the phosphazene derivative to be added to the aprotic organic solvent is not particularly limited, but improves the low-temperature characteristics of the nonaqueous electrolyte secondary battery, imparts self-digestibility or flame retardancy to the electrolyte, and From the viewpoint of improving the deterioration resistance of the electrolytic solution, isomers of a phosphazene derivative represented by the following formula (VI) and represented by the following formula (VII) are preferable.
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(In formulas (VI) and (VII), R⁷, R⁸, And R⁹Represents a monovalent substituent or a halogen element. X²Represents a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium, and polonium. Y⁷And Y⁸Represents a divalent linking group, a divalent element, or a single bond. )
[0079]
When the isomer of the phosphazene derivative represented by the formula (VI) and the formula (VII) is added to the electrolytic solution, the electrolytic solution can exhibit extremely excellent low-temperature characteristics.
[0080]
R in formula (VI)⁷, R⁸And R⁹Is not particularly limited as long as it is a monovalent substituent or a halogen element. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Further, as the halogen element, for example, a halogen element such as fluorine, chlorine, and bromine is preferably exemplified. Among these, fluorine and an alkoxy group are particularly preferable in view of the low-temperature characteristics and electrochemical stability of the electrolytic solution. Further, from the viewpoint of reducing the viscosity of the electrolytic solution, fluorine, an alkoxy group, and an alkoxy group containing fluorine and the like are preferable. R⁷~ R⁹May be all the same type of substituents, and some of them may be different types of substituents.
[0081]
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like, and an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group. Among these, R⁷~ R⁹Are preferably all methoxy groups, ethoxy groups, methoxyethoxy groups, or methoxyethoxyethoxy groups, and from the viewpoints of low viscosity and high dielectric constant, it is particularly preferable that all are methoxy groups or ethoxy groups. It is. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. The hydrogen element in these substituents is preferably substituted with a halogen element, and as the halogen element, fluorine, chlorine, and bromine are preferred. Of these, fluorine is particularly preferred, and then chlorine is preferred. When fluorine is used, the cycle characteristics tend to be better than chlorine.
[0082]
In the formula (VI), Y⁷And Y⁸Examples of the divalent linking group represented by₂In addition to the groups, oxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, Examples include divalent linking groups containing at least one element selected from the group consisting of antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, and nickel.₂A group and a divalent linking group containing at least one element selected from the group consisting of oxygen, sulfur, selenium and nitrogen are preferred. Also, Y⁷And Y⁸May be a divalent element such as oxygen, sulfur, selenium, or a single bond. In terms of improving the flame retardancy of the electrolytic solution, divalent linking groups containing sulfur and / or oxygen elements, oxygen elements, and sulfur elements are particularly preferable. In terms of excellent low-temperature characteristics of the electrolytic solution, oxygen A divalent linking group containing and an oxygen element are particularly preferred. Y⁷And Y⁸May be the same type or different types.
[0083]
In the formula (VI), X²As a substituent, a substituent containing at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur is preferable from the viewpoint of consideration of harmfulness, environment, and the like. A substituent having a structure represented by (XI), (XII) or (XIII) is more preferable.
[0084]
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[0085]
However, in formulas (XI), (XII) and (XIII), R^Fifteen~ R¹⁹Represents a monovalent substituent or a halogen element. Y^Fifteen~ Y¹⁹Represents a divalent linking group, a divalent element, or a single bond;²Represents a divalent group or a divalent element.
[0086]
In the formulas (XI), (XII) and (XIII), R^Fifteen~ R¹⁹As R in the formula (VI)⁷~ R⁹Any of the same monovalent substituents and halogen elements as described in (1) are preferably used. These may be of the same type within the same substituent, or may be of different types. R of the formula (XI)^FifteenAnd R¹⁶And R of formula (XIII)¹⁸And R¹⁹And may combine with each other to form a ring.
[0087]
In the formulas (XI), (XII) and (XIII), Y^Fifteen~ Y¹⁹A group represented by the formula (VI)⁷~ Y⁸The same divalent linking group or divalent element as mentioned in the above may be mentioned, and similarly, when the divalent linking group contains a sulfur and / or oxygen element, an oxygen element, or a sulfur element, Is particularly preferable because the flame retardancy of the electrolytic solution is improved. In addition, a divalent linking group containing an oxygen element and an oxygen element are particularly preferable in that the low temperature characteristics of the electrolytic solution are excellent. These may be of the same type within the same substituent, or some may be of different types.
[0088]
In the formula (XI), Z²As, for example, CH₂Group, CHR (R represents an alkyl group, an alkoxyl group, a phenyl group, etc .; the same applies hereinafter), an NR group, oxygen, sulfur, selenium, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, Selected from the group consisting of thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel And other divalent groups containing at least one of the following elements.₂In addition to the group, CHR group and NR group, a divalent group containing at least one element selected from the group consisting of oxygen, sulfur and selenium is preferable. Also, Z²May be a divalent element such as oxygen, sulfur, and selenium. In particular, a divalent group containing sulfur and / or selenium, a sulfur element, or a selenium element is preferable because the flame retardancy of the electrolytic solution is improved. In addition, a divalent group containing an oxygen element and an oxygen element are particularly preferable in that the low temperature characteristics of the electrolytic solution are excellent.
[0089]
As these substituents, a phosphorus-containing substituent represented by the formula (XI) is particularly preferable in that the self-extinguishing property or the flame retardancy can be particularly effectively exhibited. Further, in the formula (XI), Z², Y^FifteenAnd Y¹⁶In the case where is an oxygen element, particularly, the electrolyte solution can exhibit extremely excellent low-temperature characteristics. In addition, when the substituent is a substituent containing sulfur as represented by the formula (XII), it is particularly preferable from the viewpoint of reducing the interface resistance of the electrolytic solution.
[0090]
R in formulas (VI) and (XI) to (XIII)⁷~ R⁹, R^Fifteen~ R¹⁹, Y⁷~ Y⁸, Y^Fifteen~ Y¹⁹, Z²By appropriately selecting, it becomes possible to prepare an electrolytic solution having more suitable viscosity, solubility suitable for addition and mixing, low-temperature characteristics, and the like. These compounds may be used alone or in combination of two or more.
[0091]
The isomer represented by the formula (VI) is an isomer of the phosphazene derivative represented by the formula (VII), for example, the degree of vacuum and / or the degree of production of the phosphazene derivative represented by the formula (VII) It can be produced by adjusting the temperature, and the content (vol%) of the isomer in the electrolytic solution can be measured by the following measuring method.
<< Measuring method >>
The peak area of the sample is determined by gel permeation chromatography (GPC) or high performance liquid chromatography, and the peak area is compared with the previously determined area per mole of the isomer to obtain a molar ratio. It can be measured by converting the volume in consideration of the specific gravity.
[0092]
As the phosphazene derivative represented by the formula (VII), those having a relatively low viscosity and capable of satisfactorily dissolving the supporting salt are preferable. R of the formula (VII)⁷~ R⁹, Y⁷~ Y⁸And X²Is represented by R in the formula (VI)⁷~ R⁹, Y⁷~ Y⁸And X²The same ones as described in the above description are all suitably mentioned.
[0093]
As the phosphazene derivative represented by the formula (I), the formula (II), the formula (V) or the formula (VII) or the isomer represented by the formula (VI), a substituent containing a halogen element in a molecular structure is used. Are preferred. When the molecular structure has a substituent containing a halogen element, the danger of ignition and ignition of the electrolytic solution is effectively reduced by the derived halogen gas even if the content of the phosphazene derivative or the isomer is small. It becomes possible. In a compound containing a halogen element as a substituent, generation of a halogen radical may be a problem.However, in the phosphazene derivative and the isomer of the phosphazene derivative used in the present invention, the phosphorus element in the molecular structure is a halogen radical. Such problems do not occur because trapping and formation of a stable phosphorus halide.
[0094]
The content of the halogen element in the phosphazene derivative or the isomer of the phosphazene derivative is preferably from 2 to 80% by weight, more preferably from 2 to 60% by weight, and still more preferably from 2 to 50% by weight. When the content is less than 2% by weight, the effect of including a halogen element may not be sufficiently exhibited, while when the content exceeds 80% by weight, the viscosity increases, so that when added to the electrolytic solution, the conductivity decreases. Sometimes.
[0095]
The flash point of the phosphazene derivative represented by the formula (I), the formula (II), the formula (IV), the formula (V), or the formula (VII) is not particularly limited, but from the viewpoint of suppressing ignition and the like, 100 ° C. or higher is preferable, and 150 ° C. or higher is more preferable. On the other hand, the phosphazene derivative represented by the formula (III) has no flash point. Here, specifically, the flash point refers to a temperature at which a flame spreads on the surface of a substance and covers at least 75% of the surface of the substance, and the flash point refers to a tendency of forming a combustible mixture with air. It is a measure. If the phosphazene derivative has a flash point at 100 ° C. or higher or does not have a flash point, ignition and the like are suppressed, and even if ignition or the like occurs inside the battery, it ignites and burns on the surface of the electrolyte. It is possible to reduce the risk of spreading.
[0096]
When the phosphazene derivative represented by the formula (III) or (V), or the isomer represented by the formula (VI) and the phosphazene derivative represented by the formula (VII) are added, decomposition of the supporting salt is suppressed. The electrolyte is significantly stabilized. In a conventional non-aqueous electrolyte secondary battery, an ester-based electrolytic solution or the like used as an electrolytic solution includes, for example, LiPF as a supporting salt.₆A lithium ion source such as a salt becomes LiF and PF over time.₅Decomposed into PF₅Gas or the generated PF₅It is considered that corrosion progresses and deteriorates due to hydrogen fluoride gas or the like generated by the gas further reacting with water or the like. In other words, the conductivity of the electrolytic solution is reduced, and the electrode material is deteriorated by the generated hydrogen fluoride gas. On the other hand, the phosphazene derivative and the isomer of the phosphazene derivative are, for example, LiPF₆And the like to suppress decomposition of the lithium ion source and contribute to stabilization. Therefore, by adding a phosphazene derivative and / or an isomer of a phosphazene derivative to a conventional electrolytic solution, a decomposition reaction of the electrolytic solution is suppressed, and corrosion and deterioration can be suitably suppressed.
[0097]
The content of the phosphazene derivative and the isomer of the phosphazene derivative in the electrolytic solution is shown below.
From the viewpoint of the “limit oxygen index”, the content of the phosphazene derivative represented by the formula (I) or the formula (II) with respect to the electrolytic solution is preferably 5% by volume or more, more preferably 10 to 50% by volume. By adjusting the content to a value within the above numerical range, the risk of ignition and ignition of the electrolytic solution is effectively reduced. Although the danger of ignition is effectively reduced, the range varies depending on the type of the supporting salt and the type of the electrolytic solution to be used. Specifically, the system to be used is suppressed to the lowest viscosity, and the limiting oxygen index is low. It is optimized by appropriately determining the content of 21% by volume or more.
[0098]
From the viewpoint of “self-extinguishing properties”, the content of the phosphazene derivative represented by the formula (V) in the electrolytic solution is preferably 20% by weight or more, and the isomer represented by the formula (VI) and the content represented by the formula (VII) The total content of the phosphazene derivative and the phosphazene derivative is preferably 20% by volume or more. When the content is within the above numerical range, the electrolyte solution can exhibit sufficient self-extinguishing properties.
[0099]
From the viewpoint of “flame retardancy”, the content of the phosphazene derivative represented by the formula (V) in the electrolytic solution is preferably 30% by weight or more, and the isomer represented by the formula (VI) and the content represented by the formula (VII) The total content of the resulting phosphazene derivative is preferably 30% by volume or more. When the content is within the above numerical range, the electrolyte solution can exhibit sufficient flame retardancy.
[0100]
From the viewpoint of more suitably imparting “nonflammability”, the content of the phosphazene derivative represented by the formula (IV) in the electrolytic solution is preferably 10% by volume or more, and more preferably 15% by volume or more. If the content is less than 10% by volume, particularly excellent “nonflammability” may not be exhibited in the electrolytic solution.
[0101]
From the viewpoint of “low-temperature characteristics”, the content of the phosphazene derivative represented by the formula (III) in the electrolytic solution is preferably 1% by volume or more, more preferably 3% by volume or more, still more preferably 5% by volume or more. The total content of the isomer represented by VI) and the phosphazene derivative represented by the formula (VII) is preferably at least 1 vol%, more preferably at least 2 vol%, even more preferably at least 5 vol%. If the content is less than 1% by volume, the low temperature characteristics of the electrolytic solution are not sufficient.
[0102]
From the viewpoint of “deterioration resistance”, the content of the phosphazene derivative represented by the formula (III) in the electrolytic solution is preferably 2% by volume or more, more preferably 3% to 75% by volume, and represented by the formula (IV). The content of the phosphazene derivative is preferably 2% by volume or more, more preferably 2 to 75% by volume, and the content of the phosphazene derivative represented by (V) is preferably 2% by weight or more, more preferably 2 to 20% by weight. The total content of the isomer represented by the formula (VI) and the phosphazene derivative represented by the formula (VII) is preferably at least 2% by volume, more preferably from 3 to 75% by volume. When the content is within the above numerical range, deterioration of the electrolytic solution can be suitably suppressed.
[0103]
From the viewpoint of “reducing the viscosity”, the content of the phosphazene derivative represented by the formula (III) in the electrolytic solution is preferably from 3 to 80% by volume. When the content is less than 3% by volume, the viscosity of the electrolyte cannot be sufficiently reduced.
[0104]
From the viewpoint of “suppression of viscosity increase”, the content of the phosphazene derivative represented by the formula (V) in the electrolytic solution is preferably equal to or less than 40% by weight, more preferably equal to or less than 35% by weight, and still more preferably equal to or less than 30% by weight. If the content is more than 40% by weight, the viscosity of the electrolytic solution will increase significantly, and the internal resistance will be high and the electrical conductivity will be low.
[0105]
From the viewpoint of “nonflammability”, “self-extinguishing” or “flame retardancy”, the electrolyte is a cyclic phosphazene derivative represented by the formula (IV) or (V) or a formula (VI). And a phosphazene derivative represented by the formula (VII)₆And ethylene carbonate and / or propylene carbonate, or a cyclic phosphazene derivative represented by the formula (IV) or (V), or an isomer represented by the formula (VI) and a compound represented by the formula (VII) Phosphazene derivative and LiCF₃SO₃And propylene carbonate. In these cases, regardless of the above description, even if the content is small, the nonflammability, self-extinguishing property, or flame retardancy is very high.
[0106]
That is, in this case, the content of the cyclic phosphazene derivative represented by the formula (IV) in the electrolytic solution is preferably 5% by volume or more in order to exhibit particularly excellent nonflammability. Further, the content of the cyclic phosphazene derivative represented by the formula (V) in the electrolyte is preferably 2 to 5% by weight for exhibiting self-extinguishing properties, and 5% by weight for exhibiting flame retardancy. % Is preferred. The total content of the isomer represented by the formula (VI) and the phosphazene derivative represented by the formula (VII) in the electrolytic solution is preferably 1.5 to 2.5 in order to exhibit self-extinguishing properties. Volume% is preferable, and an amount exceeding 2.5% by volume is preferable to exhibit flame retardancy.
[0107]
As another member used in the nonaqueous electrolyte secondary battery of the present invention, a separator interposed between the positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery in a role of preventing a short circuit of current due to contact between both electrodes can be cited. . As the material of the separator, a material that can surely prevent contact between the two electrodes and can pass or contain an electrolytic solution, for example, a nonwoven fabric made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, a thin film film, or the like Are preferred. Among these, a polypropylene or polyethylene microporous film having a thickness of about 20 to 50 μm is particularly preferable.
[0108]
In the present invention, in addition to the above-described separator, known members generally used for batteries can be suitably used.
[0109]
The form of the non-aqueous electrolyte secondary battery of the present invention described above is not particularly limited, and various known forms such as a coin type, a button type, a paper type, a square type or a spiral type cylindrical battery, etc. Preferred examples are given. In the case of a spiral structure, for example, a nonaqueous electrolyte secondary battery can be produced by, for example, producing a sheet-like positive electrode, sandwiching a current collector, and laminating and winding a negative electrode (sheet-like) over the current collector. it can.
[0110]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0111]
(Example 1)
A positive electrode for a nonaqueous electrolyte secondary battery was produced by the following method.
Titanium isopropoxide (Ti [OCH (CH₃)₂]₄) (Manufactured by Aldrich) (0.07 g, 0.25 mmol) was added, and the mixture was stirred and dissolved in the atmosphere for 30 minutes. Next, LiCoO 2 is added to the produced ethanol solution while stirring.₂1 g (manufactured by Nippon Chemical Industry Co., Ltd.) was added and dispersed.
Next, while the dispersion was ice-cooled, 0.5 mL (27 mmol) of water was added thereto, whereby titanium isopropoxide was converted to titanium hydroxide (Ti (OH)₄).
Next, the mixed solution containing the generated titanium hydroxide is heated and dried at 80 ° C., and further dried at 300 ° C. for 1 hour to convert titanium hydroxide to titanium oxide.₂A powder dispersed between the particles was obtained. The powder thus obtained was charged into a glass tube oven and dehydrated at 100 ° C. for 1 hour to obtain a positive electrode powder. The mass of titanium oxide in the powder for the positive electrode is LiCoO₂Was 2% based on the mass of
[0112]
10 parts by mass of acetylene black and 10 parts by mass of polytetrafluoroethylene (PTFE) are added to 100 parts by mass of the positive electrode powder, and the mixture is mixed with an organic solvent (50/50 volume% mixed solvent of ethyl acetate and ethanol). After kneading, a thin layered positive electrode sheet having a thickness of 100 μm and a width of 40 mm was prepared by roll rolling. Thereafter, using the two obtained positive electrode sheets, a 25 μm-thick aluminum foil (current collector) coated with a conductive adhesive on its surface was sandwiched, and a 25 μm-thick separator (microporous film: A 150 μm-thick lithium metal foil was overlapped and wound up with a polypropylene electrode interposed therebetween to produce a cylindrical electrode. The length of the positive electrode of the cylindrical electrode was about 260 mm.
[0113]
The electrolytic solution was prepared by mixing LiBF in a mixed solution of 50% by volume of diethyl carbonate and 50% by volume of ethylene carbonate in LiBF.₄It was prepared by dissolving (supporting salt) at a concentration of 0.75 mol / kg. The electrolytic solution was injected into the cylindrical electrode and sealed to prepare an AA lithium battery.
[0114]
The battery was repeatedly charged and discharged up to 50 cycles in an atmosphere of 25 ° C. under the conditions of an upper limit voltage of 4.5 V, a lower limit voltage of 3.0 V, a discharge current of 100 mA, and a charge current of 50 mA. As a result, the charge / discharge capacity at the initial stage was 145 mAh / g, and the charge / discharge capacity after 50 cycles was 142 mAh / g.
[0115]
The critical oxygen index of the electrolyte was measured according to JIS K 7201 and found to be 17.1% by volume.
[0116]
(Conventional example 1)
LiCoO₂10 parts by mass of acetylene black and 10 parts by mass of polytetrafluoroethylene (PTFE) were added to 100 parts by mass, and kneaded with an organic solvent (50/50 volume% mixed solvent of ethyl acetate and ethanol). AA lithium batteries were prepared in the same manner as in Example 1 except that a thin layered positive electrode sheet having a thickness of 100 μm and a width of 40 mm was prepared by roll rolling, and the charge / discharge capacity was measured in the same manner. As a result, the charge / discharge capacity at the initial stage was 141 mAh / g, and the charge / discharge capacity after 50 cycles was 130 mAh / g.
[0117]
(Examples 2-3 and Comparative Examples 1-2)
LiCoO₂A positive electrode powder was prepared in the same manner as in Example 1 except that the amount of titanium oxide dispersed between the particles was changed as shown in Table 1, and a lithium secondary battery was produced. The charge / discharge capacity of the obtained battery was measured in the same manner as in Example 1. Table 1 shows the results.
[0118]
[Table 1]

[0119]
(Examples 4 and 5)
In place of titanium oxide, metal oxides shown in Table 2 were replaced with LiCoO₂Dispersed between particles (LiCoO₂The powder for the positive electrode was prepared in the same manner as in Example 1 except that the mass of each metal oxide was 2% based on the mass of the lithium secondary battery. The charge / discharge capacity of the obtained battery was measured in the same manner as in Example 1. Table 2 shows the results.
[0120]
[Table 2]

[0121]
(Example 6)
A phosphazene derivative A (in the above formula (IV), n is 3, 6 R⁵Cyclic phosphazene derivative compound in which two are ethoxy groups and four are fluorine, viscosity at 25 ° C .: 1.2 mPa · s (1.2 cP)) 10 vol%, diethyl carbonate 45 vol% and ethylene carbonate 45 vol% LiBF in a mixed solution of₄An AA lithium battery was prepared in the same manner as in Example 1 except that the (lithium salt) was dissolved at a concentration of 0.75 mol / kg to prepare an electrolytic solution, and the charge / discharge capacity was measured in the same manner. As a result, the charge / discharge capacity at the initial stage was 145 mAh / g, and the charge / discharge capacity after 50 cycles was 144 mAh / g. The limiting oxygen index of the electrolytic solution was measured in the same manner as in Example 1. As a result, the limiting oxygen index was 22.7% by volume.
[0122]
(Example 7)
Instead of the phosphazene derivative A, a phosphazene derivative B (in the above formula (IV), n is 3 and 6 R⁵An electrolytic solution was prepared in the same manner as in Example 6, except that one of them was an ethoxy group, and five were fluorine, a cyclic phosphazene derivative compound, and the viscosity at 25 ° C .: 1.2 mPa · s (1.2 cP)). Thus, a non-aqueous electrolyte secondary battery was prepared, and the charge / discharge capacity and the limiting oxygen index were measured in the same manner. Table 3 shows the results.
[0123]
(Example 8)
Instead of the phosphazene derivative A, a phosphazene derivative C (in the above formula (IV), n is 4 and 8 R⁵An electrolytic solution was prepared in the same manner as in Example 6, except that one of them was an ethoxy group, and seven were fluorine, a cyclic phosphazene derivative compound, and a viscosity at 25 ° C .: 1.3 mPa · s (1.3 cP)). Thus, a non-aqueous electrolyte secondary battery was prepared, and the charge / discharge capacity and the limiting oxygen index were measured in the same manner. Table 3 shows the results.
[0124]
(Example 9)
In place of the phosphazene derivative A, a phosphazene derivative D (in the above formula (IV), n is 3,⁵One of them is OCH₂CF₃And a non-aqueous electrolyte solution 2 was prepared in the same manner as in Example 6 except that a cyclic phosphazene derivative compound in which five were fluorine, and a viscosity at 25 ° C. of 1.8 mPa · s (1.8 cP)) was used. A secondary battery was prepared, and the charge / discharge capacity and the limiting oxygen index were measured in the same manner. Table 3 shows the results.
[0125]
[Table 3]

[0126]
From these results, it is found that the charge / discharge capacity and the cycle characteristics are improved by dispersing the metal oxide between the particles of the lithium-containing composite oxide. Further, in addition to dispersing the metal oxide between the particles of the lithium-containing composite oxide, by adding a phosphazene derivative to prepare an electrolytic solution, the charge / discharge capacity and cycle characteristics are further improved, and the electrolytic solution It can be seen that the critical oxygen index increases and the safety of the battery improves.
[0127]
【The invention's effect】
According to the present invention, a non-aqueous electrolyte secondary battery is configured using a positive electrode made of a powder in which a specific metal oxide is dispersed between particles of a lithium-containing composite oxide, so that a non-aqueous electrolyte has a high charge / discharge capacity. A water electrolyte secondary battery can be provided.
Further, a nonaqueous electrolytic solution 2 is prepared by using a positive electrode comprising a powder in which a specific metal oxide is dispersed between particles of a lithium-containing composite oxide and an electrolytic solution to which a phosphazene derivative and / or an isomer of a phosphazene derivative is added. By configuring the secondary battery, a non-aqueous electrolyte secondary battery having extremely high charge / discharge capacity and high safety can be provided.

Claims (13)

Between particles of at least one lithium-containing composite oxide selected from the group consisting of LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ , titanium oxide, alumina, zinc oxide, chromium oxide, lithium oxide, nickel oxide, copper oxide And at least one metal oxide selected from the group consisting of iron oxide and iron oxide is dispersed in the positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the metal oxide is titanium oxide. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a mass of the metal oxide is 0.5% to 4% with respect to a mass of the lithium-containing composite oxide. 4. Positive electrode. (I) at least one lithium-containing composite oxide selected from the group consisting of LiCoO ₂ , LiNiO ₂ and LiMn ₂ O _{4 in} an organic solvent, titanium, aluminum, zinc, chromium, lithium, nickel, copper and Adding and mixing an alkoxide of at least one metal selected from the group consisting of iron to produce a mixed solution;
(II) adding water to the mixture to form a metal hydroxide;
(III) For a positive electrode, a metal hydroxide is converted into a metal oxide by heating and drying a liquid containing the generated metal hydroxide, and the metal oxide is dispersed between particles of the lithium-containing composite oxide. A step of producing a powder;
(IV) a step of molding the powder for the positive electrode to produce a positive electrode, the method for producing a positive electrode for a non-aqueous electrolyte secondary battery. The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein the metal is titanium. Alkoxides of said metal, a positive electrode manufacturing method for a nonaqueous electrolyte secondary battery according to claim 4, characterized in that the titanium isopropoxide _{(Ti [OCH (CH 3)} 2] 4). A non-aqueous electrolyte secondary battery comprising the positive electrode according to claim 1, a negative electrode, and an electrolyte comprising an aprotic organic solvent and a supporting salt. The nonaqueous electrolyte secondary battery according to claim 7, wherein a phosphazene derivative and / or an isomer of the phosphazene derivative are added to the aprotic organic solvent. The non-aqueous electrolyte according to claim 8, wherein the phosphazene derivative has a viscosity of 300 mPa · s (300 cP) or less at 25 ° C and is represented by the following formula (I) or (II). Secondary battery.

(Wherein, R ¹ , R ² , and R ³ represent a monovalent substituent or a halogen element. X ¹ represents carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, Represents a substituent containing at least one element selected from the group consisting of sulfur, selenium, tellurium, and polonium, wherein Y ¹ , Y ² and Y ³ are a divalent linking group, a divalent element, or a single bond Represents.)
_{^{(NPR 4 2) n ··· (}} II)
(In the formula, R ⁴ represents a monovalent substituent or a halogen element. N represents 3 to 15.) The non-aqueous electrolyte secondary battery according to claim 9, wherein the phosphazene derivative represented by the formula (II) is represented by the following formula (III).
(NPF ₂ ) _n ... (III)
(In the formula, n represents 3 to 5.) The non-aqueous electrolyte secondary battery according to claim 9, wherein the phosphazene derivative represented by the formula (II) is represented by the following formula (IV).
_{^{(NPR 5 2) n ··· (}} IV)
(In the formula, R ⁵ represents a monovalent substituent or fluorine, at least one of all R ⁵ is a monovalent substituent containing fluorine or fluorine, and n represents 3 to 5, provided that all of them are represented by 3 to 5. of R ⁵ is that there is no fluorine.) The non-aqueous electrolyte secondary battery according to claim 8, wherein the phosphazene derivative is solid at 25 ° C and is represented by the following formula (V).
_{^{(NPR 6 2) n ··· (}} V)
(In the formula, R ⁶ represents a monovalent substituent or a halogen element. N represents 3 to ^6. ) The non-aqueous electrolyte secondary battery according to claim 8, wherein the isomer of the phosphazene derivative is represented by the following formula (VI) and a phosphazene derivative represented by the following formula (VII). battery.

(In the formulas (VI) and (VII), R ⁷ , R ⁸ and R ⁹ represent a monovalent substituent or a halogen element. X ² represents carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, A substituent containing at least one element selected from the group consisting of antimony, bismuth, oxygen, sulfur, selenium, tellurium, and polonium, wherein Y ⁷ and Y ⁸ are a divalent linking group, a divalent element, Or represents a single bond.)