JP4228163B2 - Cathode active material for non-aqueous electrolyte secondary battery and method for producing the same - Google Patents

Description

『確 認』
(1) 作製された実施例１並びに各比較例に係る二次電池を評価したところ、これ等電池のサイクル特性は、比較例２を除き実施例１の▲１▼▲２▼▲３▼と比較例１の▲１▼▲２▼が概ね良好であった。
(2) 次に、二次電池の初期容量（１回目の放電容量）についてはその値が高い程電池としての特性は良好なる評価を受けるが、サイト占有率が実施例１より高い比較例１の▲１▼▲２▼に係る二次電池は表１に示されたデータから確認されるように不合格（１５０ｍＡｈ／ｇ未満）のものであった。これに対し、実施例１の▲１▼▲２▼▲３▼に係る二次電池と比較例２に係る二次電池については１回目の放電容量が１５０（ｍＡｈ／ｇ）以上と高い放電容量を示している。
(3) また、１回目の放電容量が１５０（ｍＡｈ／ｇ）以上である実施例１と比較例２については上述したように示差走査熱量分析（ＤＳＣ）を行っている。
【００５０】
そして、ＤＳＣ曲線から、実施例１の(1)(2)(3)に係る二次電池については、発熱ピーク温度が比較例２に係る二次電池と較べて高温側へシフトしていると同時に、チタンの置換量の増大とともに発熱ピーク高さが減少しており、比較例２に係る二次電池と較べて実施例１の(1)(2)(3)に係る二次電池の熱安定性が改善されていることが確認される。
(4) 次に、チタンの置換量に対する第一回目の放電容量の変化を図４のグラフ図に示す。この図４から、チタン置換量の増大とともに放電容量は減少する傾向にあることが確認される。そして、このグラフ図から１５０ｍＡｈ／ｇ以上の高い放電容量を維持するためには、Ｌｉ（Ｎｉ0.83Ｃｏ0.17）1-yＴｉyＯ2で表されるリチウム含有複合酸化物のｙの値が、０＜ｙ≦０．０７の要件を満たす必要があることが確認される。
(5) 尚、実施例１の(1)(2)(3)に係るリチウム含有複合酸化物の合成条件はすべて７５０℃で２０時間としている。また、実施例１の(1)(2)(3)に係るリチウム含有複合酸化物の３ａサイトにおけるリチウム以外の金属イオンのサイト占有率はすべて２．０％以下となっているが、リチウム以外の金属イオンのサイト占有率が２．０％以上のリチウム含有複合酸化物についても同様の実験を行っており、これら二次電池も上記サイト占有率が５％以下であれば実施例１の(1)(2)(3)に係るリチウム含有複合酸化物と略同一の特性を示す傾向があることを確認している。
【００５１】
［参考例２］
正極活物質を合成するため、市販の水酸化リチウム一水和物と、球状の二次粒子から成りニッケルとコバルトのモル比が８３：１７で固溶してなる金属複合水酸化物と、市販の酸化チタンを、リチウムとリチウム以外の金属とのモル比が１：１となり、かつ、ニッケルとコバルトと亜鉛のモル比が、(1)８２：１７：１、(2)８１：１６：３、(3)７９：１６：５となるように秤量した後、球状の二次粒子の形骸が維持される程度の強さで十分に混合した。得られた混合粉末を、酸素気流中で３５０℃で仮焼した後、７５０℃で２０時間焼成し、室温まで炉冷した。得られた焼成物をＸ線回折で分析したところ、六方晶系の層状構造を有した所望のリチウム含有複合酸化物であることが確認できた。また、ＣｕのＫα線を用いた粉末Ｘ線回折法により得られた回折パターンのリートベルト解析から、３ａサイトの金属イオン混入率を求めた。この結果を以下の表２に示す。
【００５２】
次に、得られたリチウム含有複合酸化物を正極活物質として用い、実施例１と同様にして図１に示すような二次電池を作製した。
【００５３】
作製した二次電池は２４時間程度放置し、開回路電圧（ＯＣＶ）が安定した後、正極に対する電流密度を０．５ｍＡ／ｃｍ²とし、カットオフ電圧４．３−３．０Ｖで充放電試験を行った。得られた１回目の放電容量を表２に示す。
【００５４】
次に、参考例で合成された各リチウム含有複合酸化物の満充電状態での熱安定性を調べるためその熱的挙動について測定した。
【００５５】
尚、正極活物質からＬｉを引き抜く方法は、実施例１と同一の方法により行っている。すなわち、得られたリチウム含有複合酸化物（焼成物）６．０ｇを１Ｎの濃度に調整された塩酸水溶液１００ミリリットル（ｍｌ）中に投入し、５時間攪拌して、化学式Ｌｉ_1-x（Ｎｉ_0.83Ｃｏ_0.17）_1-yＺｎ_yＯ₂においてリチウム（Ｌｉ）をｘ＝０．７だけ引き抜いた。
【００５６】
次に、これをろ過し、残ったスラリーを、４０℃で２４時間、大気中で乾燥させた後、１５０℃で３日間、真空中にて加熱乾燥することで水分を蒸発させて、▲１▼Ｌｉ_0.3Ｎｉ_0.82Ｃｏ_0.17Ｚｎ_0.01Ｏ₂ 、▲２▼Ｌｉ_0.3Ｎｉ_0.81Ｃｏ_0.16Ｚｎ_0.03Ｏ₂ 、および、▲３▼Ｌｉ_0.3Ｎｉ_0.79Ｃｏ_0.16Ｚｎ_0.05Ｏ₂の各粉末を得た。
【００５７】
これ等粉末に、コイン電池を作製したときと同じ電解液を染み込ませ、密封式の試料ホルダーに入れて密閉し、熱重量測定（ＴＧ）を行うことで分解挙動を調べた。熱重量測定は昇温速度を１０℃／min とした。室温〜５００℃の温度に対する重量変化の微分曲線を図５のグラフ図に示し、また、−ｄＴＧ曲線の分解ピーク温度と分解ピーク高さを表２に示す。
【００５８】
［比較例２］
上述した比較例２に係るリチウム含有複合酸化物から、参考例２と同様、塩酸を用いてリチウムを式量ｘ＝０．７だけ引き抜いた試料を作製し、熱重量測定（ＴＧ）を行った。そして、室温〜５００℃の温度に対する重量変化の微分曲線を図５のグラフ図に示し、また、−ｄＴＧ曲線の分解ピーク温度と分解ピーク高さを表２に示す。
【００５９】
［比較例３］
正極活物質を合成するため、市販の水酸化リチウム一水和物と、球状の二次粒子から成りニッケルとコバルトのモル比が８３：１７で固溶してなる金属複合水酸化物と、市販の酸化チタンを、リチウムとリチウム以外の金属とのモル比が１：１となり、かつ、ニッケルとコバルトと亜鉛のモル比が、８２：１７：１となるように秤量した後、球状の二次粒子の形骸が維持される程度の強さで十分に混合した。得られた混合粉末を、酸素気流中において３５０℃で仮焼した後、その一方は(1)５５０℃で２０時間焼成し、他方は(2)８５０℃で２０時間焼成した以外は、参考例２と同様、リチウム含有複合酸化物から成る正極活物質を合成し、かつ、リチウムコイン二次電池を作製した。
【００６０】
そして、参考例２と同様、各リチウム含有複合酸化物における３ａサイトの金属イオンの混入率（％）と得られた各電池の１回目の放電容量を測定した。この結果を表２に示す。
【００６１】
【表２】

『確 認』
(1) 作製された参考例２並びに各比較例に係る二次電池を評価したところ、これ等電池のサイクル特性は、比較例２を除き参考例２の(1)(2)(3)と比較例３の(1)(2)が概ね良好であった。
(2) 次に、二次電池の初期容量（１回目の放電容量）についてはその値が高い程電池としての特性は良好なる評価を受けるが、サイト占有率が参考例２より高い比較例３の(1)(2)に係る二次電池は表２に示されたデータから確認されるように不合格のものであった。これに対し、参考例２の(1)(2)(3)に係る二次電池と比較例２に係る二次電池については１回目の放電容量が１５０（ｍＡｈ／ｇ）以上と高い放電容量を示している。
(3) また、１回目の放電容量が１５０（ｍＡｈ／ｇ）以上である参考例２と比較例２については上述したように熱重量測定（ＴＧ）を行っている。
【００６２】
そして、図５の−ｄＴＧ曲線から、参考例２の(1)(2)(3)に係る二次電池については、分解ピーク温度が比較例２に係る二次電池と較べて高温側へシフトしていると同時に、亜鉛の置換量の増大とともに分解ピーク高さが減少しており、比較例２に係る二次電池と較べて参考例２の(1)(2)(3)に係る二次電池の熱安定性が改善されていることが確認される。
(4) 次に、亜鉛の置換量に対する第一回目の放電容量の変化を図６のグラフ図に示す。この図６から、亜鉛置換量の増大とともに放電容量は減少する傾向にあることが確認される。そして、このグラフ図から、１５０ｍＡｈ／ｇ以上の高い放電容量を維持するためには、Ｌｉ（Ｎｉ0.83Ｃｏ0.17）1-yＺｎyＯ2で表されるリチウム含有複合酸化物のｙの値が、０＜ｙ≦０．１３の要件を満たす必要があることが確認される。
(5) 尚、参考例２の(1)(2)(3)に係るリチウム含有複合酸化物の合成条件はすべて７５０℃で２０時間としている。また、参考例２の(1)(2)(3)に係るリチウム含有複合酸化物の３ａサイトにおけるリチウム以外の金属イオンのサイト占有率はすべて１．５％未満となっているが、リチウム以外の金属イオンのサイト占有率が１．５％以上のリチウム含有複合酸化物についても同様の実験を行っており、これら二次電池も上記サイト占有率が３％以下であれば参考例２の(1)(2)(3)に係るリチウム含有複合酸化物と略同一の特性を示す傾向があることを確認している。
【００６３】
［参考例３］
正極活物質を合成するため、市販の水酸化リチウム一水和物と、球状の二次粒子から成りニッケルとコバルトのモル比が８３：１７で固溶してなる金属複合水酸化物と、市販の酸化チタンを、リチウムとリチウム以外の金属とのモル比が１：１となり、かつ、ニッケルとコバルトとチタンとマグネシウムのモル比が、７５：１５：５：５となるように秤量した後、球状の二次粒子の形骸が維持される程度の強さで十分に混合した。得られた混合粉末を、酸素気流中で３５０℃で仮焼した後、約８００℃で２０時間焼成し、室温まで炉冷した。得られた焼成物をＸ線回折で分析したところ、六方晶系の層状構造を有した所望のリチウム含有複合酸化物であることが確認できた。また、ＣｕのＫα線を用いた粉末Ｘ線回折法により得られた回折パターンのリートベルト解析から、３ａサイトの金属イオン混入率を求めた。この結果を以下の表３に示す。
【００６４】
次に、得られたリチウム含有複合酸化物を正極活物質として用い、実施例１と同様にして図１に示すような二次電池を作製した。
【００６５】
作製した二次電池は２４時間程度放置し、開回路電圧（ＯＣＶ）が安定した後、正極に対する電流密度を０．５ｍＡ／ｃｍ²とし、カットオフ電圧４．３−３．０Ｖで充放電試験を行った。得られた１回目の放電容量を表３に示す。
【００６６】
次に、参考例で合成された各リチウム含有複合酸化物の満充電状態での熱安定性を調べるためその熱的挙動について測定した。
【００６７】
尚、正極活物質からＬｉを引き抜く方法は、実施例１と同一の方法により行っている。すなわち、得られたリチウム含有複合酸化物（焼成物）６．０ｇを１Ｎの濃度に調整された塩酸水溶液１００ミリリットル（ｍｌ）中に投入し、５時間攪拌して、化学式Ｌｉ_1-x（Ｎｉ_0.83Ｃｏ_0.17）_1-2yＴｉ_yＭｇ_yＯ₂においてリチウム（Ｌｉ）をｘ＝０．７だけ引き抜いた。
【００６８】
次に、これをろ過し、残ったスラリーを、４０℃で２４時間、大気中で乾燥させた後、１５０℃で３日間、真空中にて加熱乾燥することで水分を蒸発させて、Ｌｉ_0.3Ｎｉ_0.75Ｃｏ_0.15Ｔｉ_0.05Ｍｇ_0.05Ｏ₂の粉末を得た。
【００６９】
この粉末に、コイン電池を作製したときと同じ電解液を染み込ませ、密封式の試料ホルダーに入れて密閉し、熱重量測定（ＴＧ）を行うことで分解挙動を調べた。熱重量測定は昇温速度を１０℃／min とした。室温〜５００℃の温度に対する重量変化の微分曲線を図７のグラフ図に示し、また、−ｄＴＧ曲線の分解ピーク温度と分解ピーク高さを表３に示す。
【００７０】
［比較例４］
正極活物質を合成するため、市販の水酸化リチウム一水和物と、球状の二次粒子から成りニッケルとコバルトのモル比が８３：１７で固溶してなる金属複合水酸化物と、市販の酸化チタンを、リチウムとリチウム以外の金属とのモル比が１：１となり、かつ、ニッケルとコバルトとチタンとマグネシウムのモル比が、(1)６６：１４：１０：１０、(2)６２：１３：１２．５：１２．５、(3)７５：１５：５：５、(4)７５：１５：５：５となるように秤量した後、球状の二次粒子の形骸が維持される程度の強さで十分に混合した。得られた混合粉末を、酸素気流中において３５０℃で仮焼した後、(1)と(2)については約８００℃で２０時間焼成し、また、上記(3)については５５０℃で２０時間焼成する一方、(4)については８５０℃で２０時間焼成した以外は、参考例３と同様、リチウム含有複合酸化物から成る正極活物質を合成し、かつ、リチウムコイン二次電池を作製した。
【００７１】
そして、参考例３と同様、各リチウム含有複合酸化物における３ａサイトの金属イオンの混入率（％）と得られた各電池の１回目の放電容量を測定した。この結果を表３に示す。
【００７２】
【表３】

『確 認』
(1) 作製された参考例３並びに各比較例に係る二次電池を評価したところ、これ等電池のサイクル特性は、比較例２を除き参考例３と比較例４の(1)(2)(3)(4)概ね良好であった。
(2) 次に、二次電池の初期容量（１回目の放電容量）についてはその値が高い程電池としての特性は良好なる評価を受けるが、サイト占有率が参考例３より高い比較例４の(1)(2)(3)(4)に係る二次電池は表３に示されたデータから確認されるように不合格のものであった。これに対し、参考例３に係る二次電池と比較例２に係る二次電池については１回目の放電容量が１５０（ｍＡｈ／ｇ）以上と高い放電容量を示している。
(3) また、１回目の放電容量が１５０（ｍＡｈ／ｇ）以上である参考例３と比較例２については上述したように熱重量測定（ＴＧ）を行っている。
【００７３】
そして、図７の−ｄＴＧ曲線から、参考例３に係る二次電池については、分解ピーク温度が比較例２に係る二次電池と較べて高温側へシフトしていると同時に、チタンとマグネシウムの置換量の増大とともに分解ピーク高さが減少しており、比較例２に係る二次電池と較べて参考例３に係る二次電池の熱安定性が改善されていることが確認される。
(4) 次に、チタンとマグネシウムの置換量に対する第一回目の放電容量の変化を図８のグラフ図に示す。この図８から、チタン・マグネシウム置換量の増大とともに放電容量は減少する傾向にあることが確認される。そして、このグラフ図から、１５０ｍＡｈ／ｇ以上の高い放電容量を維持するためには、Ｌｉ（Ｎｉ0.83Ｃｏ0.17）1-2yＴｉyＭｇyＯ2で表されるリチウム含有複合酸化物のｙの値が、０＜ｙ≦０．０６の要件を満たす必要があることが確認される。
(5) 尚、参考例３に係るリチウム含有複合酸化物はＬｉＮｉ1-x-2yＣｏxＴｉyＭｇyＯ2で表されるリチウム含有複合酸化物であるが、ＬｉＮｉ1-x-2yＣｏxＺｎyＭｇyＯ2で表されるリチウム含有複合酸化物についても同様の実験を行っており、これら二次電池も上記サイト占有率が３％以下であれば参考例３に係るリチウム含有複合酸化物と略同一の特性を示す傾向があることを確認している。
【００７４】
【発明の効果】
請求項１に係る非水系電解質二次電池用正極活物質によれば、
ＬｉＮｉ1-x-yＣｏxＴｉyＯ2（但し、０＜ｘ≦０．２０、０＜ｙ≦０．０７）で表され、かつ、層状構造を有する六方晶系のリチウム含有複合酸化物により構成されると共に、上記リチウム含有複合酸化物における3a、3b、6cの各サイトを［Ｌｉ］3a［Ｎｉ1-x-yＣｏxＴｉy］3b［Ｏ2］6cで表示した場合、上記リチウム含有複合酸化物のＸ線回折によるリートベルト解析から得られた3aサイトにおけるリチウム以外の金属イオンのサイト占有率が５％以下に設定されているため、高い初期容量とサイクル特性を維持したまま、高温安定性に優れた非水系電解質二次電池を提供できる効果を有する。
【００７６】
次に、請求項３〜５に係る非水系電解質二次電池用正極活物質の製造方法によれば、請求項１〜２に係る非水系電解質二次電池用正極活物質を製造できる効果を有する。
【図面の簡単な説明】
【図１】 実施例並びに参考例に係る二次電池の構成説明図。
【図２】実施例１の▲１▼▲２▼▲３▼に係る各リチウム含有複合酸化物粉末の示差走査熱量(ＤＳＣ)測定で求められた温度に対するＤＳＣ曲線のグラフ図。
【図３】比較例２に係るリチウム含有複合酸化物粉末の示差走査熱量(ＤＳＣ)測定で求められた温度に対するＤＳＣ曲線のグラフ図。
【図４】実施例１に係るリチウム含有複合酸化物粉末のチタン置換量ｙに対する第一回目の放電容量の変化を示すグラフ図。
【図５】 比較例２と参考例２の(1)(2)(3)に係る各リチウム含有複合酸化物粉末の熱重量（ＴＧ）測定で求められた温度に対する重量変化の微分曲線のグラフ図。
【図６】 参考例２に係るリチウム含有複合酸化物粉末の亜鉛置換量ｙに対する第一回目の放電容量の変化を示すグラフ図。
【図７】 比較例２と参考例３に係る各リチウム含有複合酸化物粉末の熱重量（ＴＧ）測定で求められた温度に対する重量変化の微分曲線のグラフ図。
【図８】 参考例３と比較例４の(1)(2)に係るリチウム含有複合酸化物粉末のチタン・マグネシウム合計の置換量ｙに対する第一回目の放電容量の変化を示すグラフ図。
【符号の説明】
１ 正極（評価用電極）
２ セパレーター
３ リチウム金属負極
４ ガスケット
５ 正極缶
６ 負極缶[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material composed of a lithium-containing composite oxide and applied to a non-aqueous electrolyte secondary battery. In particular, the thermal stability of the battery is improved without impairing the initial capacity of the battery with excellent cycle characteristics. The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same.
[0002]
[Prior art]
In recent years, with rapid advancement of electronic technology, electronic devices have been reduced in size and weight one after another. In particular, with the recent spread of portable devices such as mobile phones and notebook computers, the development of small and lightweight batteries with high energy density is also strongly desired for portable power sources used in these devices.
[0003]
Conventionally, aqueous secondary batteries such as lead livestock batteries and nickel-cadmium batteries have been used as secondary batteries for general purposes. However, these aqueous secondary batteries are relatively excellent in cycle characteristics, but are not satisfactory from the viewpoint of battery capacity per weight and environmental protection.
[0004]
Under such circumstances, research and development of non-aqueous electrolyte lithium ion secondary batteries using lithium-doped lithium-doped materials such as lithium, lithium alloys, metal oxides, or carbon as a negative electrode has been actively conducted. .
[0005]
By the way, lithium-containing composite oxides, particularly lithium cobalt composite oxides (LiCoO) that are relatively easy to synthesize.₂) Is used as a positive electrode active material, and a high voltage of 4V class can be obtained. As for this type of lithium ion secondary battery, development for obtaining excellent initial capacity characteristics and cycle characteristics has been actively conducted, and various results have already been obtained.
[0006]
However, since lithium cobalt complex oxide uses a rare and expensive cobalt compound as a raw material, the cost of the active material and the battery is increased, and improvement of the active material is desired. That is, the unit price per capacity of a battery using this lithium cobalt composite oxide is as high as about four times that of a nickel metal hydride battery. Therefore, reducing the cost of the active material and making it possible to manufacture a cheaper lithium ion secondary battery has great industrial significance in terms of reducing the weight and size of currently popular portable devices.
[0007]
Here, as a new material for a positive electrode active material for a lithium ion secondary battery, a lithium nickel composite oxide (LiNiO) using nickel which is cheaper than cobalt.₂). This lithium nickel composite oxide exhibits a lower electrochemical potential than lithium cobalt composite oxide, so that decomposition due to oxidation of the electrolytic solution is less likely to be a problem, higher capacity can be expected, and the battery is as high as cobalt Development is actively done because it shows voltage. However, this lithium nickel composite oxide has the following drawbacks even if a lithium nickel composite oxide synthesized purely with nickel alone and having an excellent stoichiometric composition is obtained. In other words, the lithium ion secondary battery using the lithium nickel composite oxide as a positive electrode active material has inferior cycle characteristics as compared with a lithium ion secondary battery using the lithium cobalt composite oxide as a positive electrode active material, and in a high temperature environment. When the battery is used or stored, the battery performance is relatively easily lost.
[0008]
Therefore, various proposals as described below have been made for the lithium nickel composite oxide for the purpose of solving these drawbacks. For example, in Japanese Patent Application Laid-Open No. 8-213015, for the purpose of improving the self-discharge characteristics and cycle characteristics of a lithium ion secondary battery, Li_xNi_aCo_bM_cO₂(However, 0.8 ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1 .2, M is a lithium-containing composite oxide represented by at least one element selected from Al, V, Mn, Fe, Cu, and Zn. In Japanese Patent Laid-Open No. 8-45509, As a positive electrode active material that can maintain good battery performance during storage and use, Li_wNi_xCo_yB_zO₂(However, 0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, x + y + z = 1) has been proposed. JP-A-8-32299 proposes a lithium-containing composite oxide in which 5 at% or less of nickel is substituted with gallium for the purpose of improving cycle characteristics and overcharge resistance.
[0009]
Further, the lithium nickel composite oxide proposed in these publications has a higher charge capacity and discharge capacity than the above-described lithium cobalt composite oxide, and LiNiO.₂Compared with the conventional lithium nickel composite oxide shown in (5), the cycle characteristics are certainly improved. However, when left in a fully charged state in a high temperature environment, decomposition starts with the release of oxygen from a lower temperature than the lithium cobalt composite oxide. As a result, the internal pressure of the battery rises, causing the worst In this case, there was a risk that the battery would explode.
[0010]
On the other hand, in Japanese Patent Laid-Open No. 5-242891, the purpose of improving the thermal stability of a positive electrode active material for a lithium ion secondary battery is Li_aM_bNi_cCo_dO_e(However, M is at least one metal selected from the group consisting of Al, Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, and 0 <a <1.3, In the range of 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1).
[0011]
In the lithium ion secondary battery using the lithium-containing composite oxide as the positive electrode active material, the cycle characteristics and the thermal stability are certainly improved. However, depending on the element selected as the metal M, LiNiCoO₂The initial capacity, which is the most important for battery performance, is that these different atoms enter into the atomic layer surface that should originally be composed of lithium and inhibit diffusion of lithium, even if it is difficult to make a solid solution. Had the problem of a large drop.
[0012]
[Problems to be solved by the invention]
As described above, the conventional non-aqueous electrolyte secondary battery using the lithium nickel composite oxide as the positive electrode active material has a problem that it is difficult to provide high temperature stability while maintaining high initial capacity and cycle characteristics. Was.
[0013]
The present invention has been made paying attention to such problems, and the object of the present invention is to provide a non-aqueous electrolyte that has excellent cycle characteristics and can improve the thermal stability of the battery without impairing the initial capacity of the battery. It is providing the positive electrode active material for secondary batteries, and its manufacturing method.
[0014]
[Means for Solving the Problems]
Therefore, as a result of various studies conducted by the present inventors in order to solve the above problems, a lithium-containing composite oxide in which a part of nickel is substituted with cobalt and titanium or cobalt and zinc is applied to the positive electrode active material. When the site occupancy of metal ions other than lithium at the lithium site is adjusted to a predetermined value or less, the above-mentioned problems do not occur and high temperature capacity and cycle characteristics are maintained, and high temperature stability is excellent. It has been found that a non-aqueous electrolyte secondary battery can be obtained. The present invention has been completed based on such technical findings.
[0015]
  That is, the invention according to claim 1
  Based on the positive electrode active material applied to non-aqueous electrolyte secondary batteries,
  LiNi1-x-yCoxTiyO2 (where 0 <x≤0.20, 0 <y≤0.07) and a hexagonal lithium-containing composite oxide having a layered structure, Rietveld analysis of the above lithium-containing composite oxide by X-ray diffraction when the sites 3a, 3b and 6c in the lithium-containing composite oxide are represented by [Li] 3a [Ni1-x-yCoxTiy] 3b [O2] 6c The site occupancy of metal ions other than lithium at the 3a site obtained from is less than 5%.To do.
[0016]
  Claims2Relates to an invention of a positive electrode active material that realizes a high packing density when a positive electrode plate of a secondary battery is formed using a positive electrode active material powder.
[0017]
  That is, the claim2The invention according to
  Claim1Based on the positive electrode active material for a non-aqueous electrolyte secondary battery according to the invention described in
  The shape of the secondary particles in the positive electrode active material is spherical or elliptical.
[0018]
  Next, the claim3-5Claims1The present invention relates to an invention that specifies a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.
[0019]
  That is, the claim3The invention according to
  On the premise of the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1,
  Lithium compound, nickel compound, cobalt compound and titanium compound are mixed and this mixture is650 ° C or higher and 750 ° C or lowerAnd obtained by heat treatment under conditions of 4 hours or more,
  Claim4The invention according to
  A metal composite hydroxide (provided that 0 <x ≦ 0.20), a lithium compound, and a titanium compound are mixed at a molar ratio of nickel to cobalt of (1-x): x.650 ° C or higher and 750 ° C or lowerIn addition, it is obtained by heat treatment under conditions of 4 hours or more.
[0023]
  Claims5The invention according to
  Claim4Based on the manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary battery described,
  The secondary particle shape in the metal composite hydroxide is spherical or elliptical.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0025]
  As described above, the present invention provides a lithium-containing composite oxide in which a part of nickel is substituted with cobalt and titanium (LiNi1-x-yCoxTiyO2).Is applied to the positive electrode material to provide a non-aqueous electrolyte secondary battery excellent in high-temperature stability while maintaining high initial capacity and cycle characteristics. In addition, since the lithium-containing composite oxide in which a part of nickel is substituted with cobalt and zinc has the same characteristics as the lithium-containing composite oxide according to the present invention,Lithium-containing composite oxide in which part of nickel is substituted with cobalt and zinc (LiNi1-x-yCoxZnyO2), lithium-containing composite oxide in which part of nickel is substituted with cobalt, titanium and magnesium (LiNi1-x-2yCoxTiyMgyO2) ), Lithium-containing composite oxide in which a part of nickel is substituted with cobalt, zinc and magnesium (LiNi1-x-2yCoxZnyMgyO2)Are also described as reference examples.
[0026]
That is, the present invention relates to an active material in which a part of nickel is substituted with cobalt for improving cycle characteristics. Lithium nickel composite oxide (LiNiO₂) Is considered to be a battery active material, it is charged and discharged by lithium desorption / insertion. The fully charged state of about 200 mAh / g is LiNiO₂About 70% of lithium is desorbed. That is, Li_0.3NiO₂However, at this time, a part of nickel is trivalent and tetravalent. Tetravalent nickel is very unstable and easily releases oxygen at high temperatures to become divalent (NiO). Such decomposition behavior accompanied with oxygen release at a high temperature can be evaluated by performing thermogravimetric measurement of the positive electrode material in which lithium is extracted by 70 at% and charged. This is because the positive electrode active material in a charged state is sealed together with the electrolyte, and the decomposition start temperature associated with oxygen release can be specified by observing the change in weight with respect to temperature.
[0027]
As a result of research on the thermal stability of the positive electrode material by such a method, it has been found that titanium, zinc, and magnesium are effective in improving the thermal stability. That is, the lithium nickel composite oxide (LiNiO) in which a part of nickel is replaced with cobalt.₂3b site) is further replaced with the above titanium to increase the amount of titanium replaced and reduce the amount of heat generated by the reaction with the electrolyte, and lithium in which a part of nickel is replaced with cobalt. By substituting the zinc in the 3b site of the nickel composite oxide with the above zinc, a remarkable effect of making the decomposition reaction very gentle as the amount of zinc substitution increased was recognized. Further, the 3b site of the lithium nickel composite oxide in which a part of nickel is substituted with cobalt is further substituted with equimolar titanium and magnesium or equimolar zinc and magnesium, thereby decomposing the active material under high temperature conditions. Has been found to be significantly suppressed. However, since the initial capacity tends to decrease as the amount of substitution of titanium, zinc and magnesium increases, the amount of substitution in the case of titanium alone or zinc alone is from the balance between thermal stability improvement and initial capacity decline. The total substitution amount in the case of 7 at% or less, 13 at% or less, and equimolar titanium and magnesium or equimolar zinc and magnesium is required to be 12 at% or less.
[0028]
  Next, the stoichiometry of the lithium-containing composite oxide was examined using a Rietveld analysis by X-ray diffraction [eg, Rayoung, ed., “The Rietveld Method”, Oxford University Press (1992)]. The index is the site occupancy of each ion. In the case of a hexagonal compound, there are 3a, 3b, and 6c sites. When LiNiO2 has a complete stoichiometric composition, the 3a site is lithium, the 3b site is nickel, and the 6c site is 100% oxygen. Shows the site occupancy rate. It can be said that the lithium nickel composite oxide in which the site occupancy of the lithium ions at the 3a site is 97% or more is excellent in stoichiometry. When considered as a battery active material, since lithium can be desorbed and inserted, the integrity of the crystal can be maintained even if lithium deficiency occurs. Therefore, in practice, it is considered a good method to show the stoichiometry or the completeness of the crystal with the mixing rate of the metal ions at the 3a site. Here, the charge / discharge reaction of the battery proceeds by reversibly entering and leaving the lithium ions at the 3a site. Therefore, if metal ions other than lithium are mixed into the 3a site, which is a lithium diffusion path in the solid phase, the diffusion path is inhibited, which may cause deterioration of the charge / discharge characteristics of the battery. Therefore, as a result of repeated studies on positive electrode active materials synthesized by various methods, metal ions other than lithium at the 3a site obtained by Rietveld analysis of the diffraction pattern obtained by the powder diffraction method using X-rays. While finding that there is a deep relationship between the contamination rate and the initial characteristics of the battery,According to the present inventionIn the case of a lithium-containing composite oxide (LiNi1-x-yCoxTiyO2), it has been found that when the above value is 5% or less, the initial capacity and cycle characteristics of the battery can be improved.. As a reference exampleIn the case of a lithium-containing composite oxide (LiNi1-x-yCoxZnyO2), it was found that the initial capacity and cycle characteristics of the battery can be improved when the above value is 3% or less, and the lithium-containing composite oxide (LiNi1-x-2yCoxTiyMgyO2) And lithium-containing composite oxide (LiNi1-x-2yCoxZnyMgyO2), it was found that the initial capacity and cycle characteristics of the battery can be improved when the above values are 3% or less.
[0029]
  AndAccording to the present inventionThe lithium-containing composite oxide (LiNi1-x-yCoxTiyO2) can be obtained by mixing a lithium compound, a nickel compound, a cobalt compound, and a titanium compound, and heat-treating the mixture (claims).3),Furthermore,A metal composite hydroxide (where 0 <x ≦ 0.20), a lithium compound, and a titanium compound are mixed at a molar ratio of nickel to cobalt of (1-x): x, and the mixture is heat treated. To getAlso(Claim 4).As a reference exampleThe lithium-containing composite oxide (LiNi1-x-yCoxZnyO2) can be obtained by mixing a lithium compound, a nickel compound, a cobalt compound, and a zinc compound and heat-treating this mixture, and the molar ratio of nickel to cobalt is (1-x): It is obtained by mixing a metal composite hydroxide (where 0 <x ≦ 0.20), a lithium compound, and a zinc compound that are solid-dissolved in x, and heat-treating the mixture. it can. Similarly, for the lithium-containing composite oxide (LiNi1-x-2yCoxTiyMgyO2) and the lithium-containing composite oxide (LiNi1-x-2yCoxZnyMgyO2), lithium compounds, nickel compounds, cobalt compounds, titanium compounds or zinc compounds, and magnesium The compound can be obtained by mixing the compound and heat-treating the mixture, and a metal complex hydroxide in which the molar ratio of nickel to cobalt is (1-x): x, where 0 <x ≦ 0.20), a lithium compound, a titanium compound or a zinc compound, and a magnesium compound, and this mixture can be obtained by heat treatment.
[0030]
  Examples of the lithium compound include lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium nitrate, and lithium peroxide. Examples of the nickel compound include nickel oxide, nickel hydroxide, nickel carbonate, nickel nitrate, Examples of the nickel compound include cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt nitrate, cobalt sulfate, and cobalt chloride. Examples of the titanium compound include titanium oxide, titanium chloride, and the like in addition to metal titanium. Examples of the zinc compound include zinc metal, zinc oxide, zinc carbonate, zinc sulfate, zinc nitrate, and zinc chloride. Examples of the magnesium compound include magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium nitrate, Such as basic magnesium carbonate It can Shimesuru. Further, by setting the heat treatment conditions of the above-mentioned mixture to 600 ° C. or more and less than 850 ° C. and 4 hours or more, titanium, zinc, titanium and magnesium, or zinc and magnesium can be completely produced without generating different phases such as LiTiO 2, Li 2 ZnO 2 and MgO. It can be dissolved and can achieve high completeness of crystal structure. AlsoThe lithium-containing composite oxide (LiNi1-x-yCoxTiyO2) [where 0 <y ≦ 0.07] or the lithium-containing composite oxide (LiNi1-x-yCoxZnyO2) is obtained by setting the heat treatment conditions to 650 ° C. or higher and 750 ° C. or lower. [However, with respect to 0 <y ≦ 0.13], the site occupancy of metal ions other than lithium at the 3a site can be reliably reduced to 5% or 3% or less. The lithium-containing composite oxide (LiNi1-x-2yCoxTiyMgyO2) and the lithium-containing composite oxide (LiNi1-x-2yCoxZnyMgyO2) [provided that 0 <y ≦ 0.06] other than lithium at the 3a site It is possible to reliably reduce the site occupancy of the metal ions to 3% or less.
[0031]
  Further, when a positive electrode plate of a battery is formed using such a positive electrode active material powder, a high tap density is required for the powder itself in order to achieve a high packing density. For this purpose, it is desirable that the particle shape of the powder is spherical or elliptical.2). In addition, a spherical or elliptical positive electrode active material powder can be obtained by using, as a raw material, a secondary particle in the metal composite hydroxide having a spherical or elliptical shape.5).
[0032]
  In this way, a hexagonal lithium-containing composite oxide (LiNi1-x-yCoxTiyO2) having a layered structure in which a part of nickel is substituted with cobalt and titanium, and the site occupation of metal ions other than lithium at the 3a site The rate is 5% or lessBy applying as a positive electrode active material, it is possible to provide a non-aqueous electrolyte secondary battery excellent in high-temperature stability while maintaining a high initial capacity and cycle characteristics. As a reference exampleA hexagonal lithium-containing composite oxide (LiNi1-x-yCoxZnyO2) having a layered structure in which a part of nickel is substituted with cobalt and zinc, and the site occupancy of metal ions other than lithium at the 3a site is 3 %, A hexagonal lithium-containing composite oxide (LiNi1-x-2yCoxTiyMgyO2) having a layered structure in which a part of nickel is substituted with cobalt, titanium, and magnesium, and other than lithium at the 3a site This is a hexagonal lithium-containing composite oxide (LiNi1-x-2yCoxZnyMgyO2) having a layered structure in which the site occupancy of metal ions is 3% or less, and a part of nickel is substituted with cobalt, zinc and magnesium. Once the site occupancy rate of metal ions other than lithium at the 3a site is 3% or less Applied as positive electrode active materialIn this case, it is possible to provide the same non-aqueous electrolyte secondary battery.
[0033]
【Example】
Examples of the present invention will be specifically described below.
[0034]
[Example 1]
In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a nickel / cobalt molar ratio of 83:17, and a commercially available product The molar ratio of lithium to a metal other than lithium is 1: 1, and the molar ratio of nickel, cobalt, and titanium is {circle around (1)} 82: 17: 1, {circle around (2)} 81: 16: 3. (3) After weighing to 79: 16: 5, the mixture was sufficiently mixed with such a strength that the shape of spherical secondary particles was maintained. The obtained mixed powder was calcined at 350 ° C. in an oxygen stream, calcined at 750 ° C. for 20 hours, and cooled to room temperature. When the obtained fired product was analyzed by X-ray diffraction, it was confirmed that it was a desired lithium-containing composite oxide having a hexagonal layered structure. Also, from the Rietveld analysis of the diffraction pattern obtained by the powder X-ray diffraction method using Cu Kα rays (ie, the Rietveld analysis of the powder X-ray diffraction pattern using Cu Kα rays), the metal ions at the 3a site The mixing rate was determined. The results are shown in Table 1 below.
[0035]
Next, using the obtained lithium-containing composite oxide as a positive electrode active material, a secondary battery as shown in FIG. 1 was produced. In FIG. 1, 1 is a positive electrode (evaluation electrode), 2 is a separator, 3 is a lithium metal negative electrode, 4 is a gasket, 5 is a positive electrode can, and 6 is a negative electrode can.
[0036]
First, 90% by weight of active material powder was mixed with 5% by weight of acetylene black and 5% by weight of polyvinylidene fluoride (PVDF), and n-methylpyrrolidone (NMP) was added to form a paste. The active material weight after drying the aluminum foil of 20 μm thickness is 0.05 g / cm²Then, after vacuum drying at 120 ° C., it was punched into a disk shape having a diameter of 1 cm to obtain a positive electrode.
[0037]
Also, lithium metal is applied as the negative electrode, and 1 mol / liter LiClO is used as the electrolyte._FourAn equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) was used as a supporting salt.
[0038]
Then, a 2032 type coin battery as shown in FIG. 1 was produced in a glove box in an Ar atmosphere in which the electrolytic solution was soaked into a polyethylene separator and the dew point was controlled at −80 ° C.
[0039]
The produced secondary battery is left for about 24 hours, and after the open circuit voltage (OCV) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm.²And a charge / discharge test was performed at a cut-off voltage of 4.3-3.0V. Table 1 shows the obtained first discharge capacity.
[0040]
Next, the thermal behavior of each lithium-containing composite oxide synthesized in the example was measured in order to investigate the thermal stability in a fully charged state.
[0041]
In addition, as a method of extracting Li from the positive electrode active material (as described above, a fully charged state of about 200 mAh / g is a state in which about 70% of lithium is desorbed from the lithium-containing composite oxide) In addition to the method, there is known a method in which an active material is dispersed in an acid aqueous solution and stirred (see Arai et al., 38th Battery Symposium Abstracts p83, 1997). Unlike the electrochemical method, this method can extract Li under the condition that there is no influence of a conductive agent or a binder. By applying this to thermal analysis, the thermal behavior of the active material alone can be obtained. Can be evaluated.
[0042]
Therefore, according to this method, 6.0 g of the obtained lithium-containing composite oxide (calcined product) was put into 100 ml (ml) of hydrochloric acid aqueous solution adjusted to a concentration of 1 N, and stirred for 5 hours._1-x(Ni_0.83Co_0.17)_1-yTi_yO₂In this case, lithium (Li) was extracted by x = 0.7.
[0043]
Next, this was filtered, and the remaining slurry was dried in the atmosphere at 40 ° C. for 24 hours, and then dried by heating at 150 ° C. for 3 days in a vacuum to evaporate the moisture, and ▲ 1 ▼ Li_0.3Ni_0.82Co_0.17Ti_0.01O₂, ▲ 2 ▼ Li_0.3Ni_0.81Co_0.16Ti_0.03O₂And (3) Li_0.3Ni_0.79Co_0.16Ti_0.05O₂Each powder was obtained.
[0044]
These powders were impregnated with the same electrolyte as that used to produce coin batteries, sealed in a sealed sample holder, and subjected to differential scanning calorimetry (DSC) to investigate thermal behavior. In differential scanning calorimetry, the heating rate was set to 10 ° C./min. The DSC curve with respect to the temperature of 100 ° C. to 300 ° C. is shown in the graph of FIG. 2, and the exothermic peak temperature and exothermic peak height of the DSC curve are shown in Table 1.
[0045]
[Comparative Example 1]
In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a nickel / cobalt molar ratio of 83:17, and a commercially available product After the titanium oxide was weighed so that the molar ratio of lithium to a metal other than lithium was 1: 1 and the molar ratio of nickel, cobalt, and titanium was 82: 17: 1, a spherical secondary Thoroughly mixed with sufficient strength to maintain particle morphology. The obtained mixed powder was calcined at 350 ° C. in an oxygen stream, one of which was fired at 1) 550 ° C. for 20 hours and the other was fired at 2) 850 ° C. for 20 hours. As in Example 1, a positive electrode active material composed of a lithium-containing composite oxide was synthesized, and a lithium coin secondary battery was produced.
[0046]
Then, as in Example 1, the metal ion mixing rate (%) at the 3a site in each lithium-containing composite oxide and the first discharge capacity of each battery obtained were measured. The results are shown in Table 1.
[0047]
[Comparative Example 2]
In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate and nickel hydroxide composed of spherical secondary particles were weighed so that the molar ratio of lithium to nickel was 1: 1, A positive electrode active material composed of a lithium-containing composite oxide was synthesized and a lithium coin secondary battery was prepared in the same manner as in Example 1, except that the mixture was sufficiently mixed with a strength sufficient to maintain the shape of spherical secondary particles. Produced.
[0048]
Then, as in Example 1, the metal ion mixing rate (%) at the 3a site in the lithium-containing composite oxide and the first discharge capacity of the obtained battery were measured. The results are shown in Table 1. Further, in the same manner as in Example 1, a sample obtained by extracting lithium by a formula amount x = 0.7 was prepared using hydrochloric acid, and differential scanning calorimetry (DSC) was performed. FIG. 3 shows a DSC curve with respect to a temperature of 100 ° C. to 300 ° C. Table 1 shows the exothermic peak temperature and exothermic peak height of the DSC curve.
[0049]
[Table 1]

"Confirmation"
(1) When the fabricated secondary batteries according to Example 1 and each comparative example were evaluated, the cycle characteristics of these batteries were as follows: (1) (2) (3) in Example 1 except for Comparative Example 2. In Comparative Example 1, (1) and (2) were generally good.
(2) Next, with regard to the initial capacity (first discharge capacity) of the secondary battery, the higher the value, the better the characteristics as the battery are evaluated, but the comparative example 1 in which the site occupancy is higher than in Example 1 The secondary batteries according to (1) and (2) were rejected (less than 150 mAh / g) as confirmed from the data shown in Table 1. In contrast, the secondary battery according to (1), (2), and (3) of Example 1 and the secondary battery according to Comparative Example 2 have a high discharge capacity of 150 (mAh / g) or more at the first time. Is shown.
(3) As described above, differential scanning calorimetry (DSC) is performed on Example 1 and Comparative Example 2 in which the first discharge capacity is 150 (mAh / g) or more.
[0050]
  And, from the DSC curve, regarding the secondary battery according to (1), (2) and (3) of Example 1, the exothermic peak temperature is shifted to the high temperature side as compared with the secondary battery according to Comparative Example 2. At the same time, the exothermic peak height decreases with an increase in the amount of titanium substitution. Compared with the secondary battery according to Comparative Example 2, the heat of the secondary battery according to (1) (2) (3) of Example 1 It is confirmed that the stability is improved.
(4) Next, the change in the discharge capacity for the first time with respect to the substitution amount of titanium is shown in the graph of FIG. FIG. 4 confirms that the discharge capacity tends to decrease as the titanium substitution amount increases. In order to maintain a high discharge capacity of 150 mAh / g or more from this graph, the value of y of the lithium-containing composite oxide represented by Li (Ni0.83Co0.17) 1-yTiyO2 is 0 <y It is confirmed that it is necessary to satisfy the requirement of ≦ 0.07.
(5) The synthesis conditions of the lithium-containing composite oxide according to (1), (2), and (3) of Example 1 are all set at 750 ° C. for 20 hours. Further, the site occupancy rates of metal ions other than lithium at the 3a site of the lithium-containing composite oxide according to (1), (2) and (3) of Example 1 are all 2.0% or less. A similar experiment was also conducted for a lithium-containing composite oxide having a metal ion site occupancy ratio of 2.0% or more. In these secondary batteries, if the site occupancy ratio is 5% or less, ( 1) It has been confirmed that the lithium-containing composite oxides according to (2) and (3) tend to exhibit substantially the same characteristics.
[0051]
  [Reference example 2]
  In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a nickel / cobalt molar ratio of 83:17, and a commercially available product The molar ratio of lithium to a metal other than lithium is 1: 1, and the molar ratio of nickel, cobalt, and zinc is (1) 82: 17: 1 and (2) 81: 16: 3. (3) After weighing to 79: 16: 5, the mixture was sufficiently mixed with such a strength that the shape of spherical secondary particles was maintained. The obtained mixed powder was calcined at 350 ° C. in an oxygen stream, calcined at 750 ° C. for 20 hours, and cooled to room temperature. When the obtained fired product was analyzed by X-ray diffraction, it was confirmed that it was a desired lithium-containing composite oxide having a hexagonal layered structure. Moreover, the metal ion mixing rate of 3a site was calculated | required from the Rietveld analysis of the diffraction pattern obtained by the powder X-ray-diffraction method using the K alpha ray of Cu. The results are shown in Table 2 below.
[0052]
Next, using the obtained lithium-containing composite oxide as a positive electrode active material, a secondary battery as shown in FIG.
[0053]
The produced secondary battery is left for about 24 hours, and after the open circuit voltage (OCV) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm.²And a charge / discharge test was performed at a cut-off voltage of 4.3-3.0V. The obtained first discharge capacity is shown in Table 2.
[0054]
  next,Reference exampleIn order to investigate the thermal stability of each lithium-containing composite oxide synthesized at the full charge state, its thermal behavior was measured.
[0055]
The method for extracting Li from the positive electrode active material is the same as in Example 1. That is, 6.0 g of the obtained lithium-containing composite oxide (calcined product) was put into 100 ml (ml) of an aqueous hydrochloric acid solution adjusted to a concentration of 1 N and stirred for 5 hours._1-x(Ni_0.83Co_0.17)_1-yZn_yO₂In this case, lithium (Li) was extracted by x = 0.7.
[0056]
Next, this was filtered, and the remaining slurry was dried in the atmosphere at 40 ° C. for 24 hours, and then dried by heating at 150 ° C. for 3 days in a vacuum to evaporate the moisture, and ▲ 1 ▼ Li_0.3Ni_0.82Co_0.17Zn_0.01O₂, ▲ 2 ▼ Li_0.3Ni_0.81Co_0.16Zn_0.03O₂And (3) Li_0.3Ni_0.79Co_0.16Zn_0.05O₂Each powder was obtained.
[0057]
These powders were impregnated with the same electrolyte as that used to produce coin batteries, sealed in a sealed sample holder, and subjected to thermogravimetry (TG) to examine decomposition behavior. Thermogravimetry was performed at a heating rate of 10 ° C./min. A differential curve of weight change with respect to a temperature of room temperature to 500 ° C. is shown in the graph of FIG. 5, and the decomposition peak temperature and decomposition peak height of the −dTG curve are shown in Table 2.
[0058]
  [Comparative Example 2]
  From the lithium-containing composite oxide according to Comparative Example 2 described above,Reference example 2In the same manner as described above, a sample in which lithium was drawn by a formula amount x = 0.7 was prepared using hydrochloric acid, and thermogravimetry (TG) was performed. And the differential curve of the weight change with respect to the temperature of room temperature-500 degreeC is shown in the graph of FIG. 5, and the decomposition peak temperature and decomposition peak height of a -dTG curve are shown in Table 2. FIG.
[0059]
  [Comparative Example 3]
  In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a nickel / cobalt molar ratio of 83:17, and a commercially available product After the titanium oxide was weighed so that the molar ratio of lithium to a metal other than lithium was 1: 1 and the molar ratio of nickel, cobalt and zinc was 82: 17: 1, a spherical secondary Thoroughly mixed with sufficient strength to maintain particle morphology. After the obtained mixed powder was calcined at 350 ° C. in an oxygen stream, one was (1) calcined at 550 ° C. for 20 hours, and the other was (2) calcined at 850 ° C. for 20 hours.Reference example 2Similarly, a positive electrode active material composed of a lithium-containing composite oxide was synthesized, and a lithium coin secondary battery was produced.
[0060]
  AndReference example 2In the same manner as above, the mixing rate (%) of metal ions at the 3a site in each lithium-containing composite oxide and the first discharge capacity of each battery obtained were measured. The results are shown in Table 2.
[0061]
[Table 2]

  "Confirmation"
(1) MadeReference example 2In addition, when the secondary batteries according to the respective comparative examples were evaluated, the cycle characteristics of these batteries except for the comparative example 2Reference example 2(1) (2) (3) and (1) (2) of Comparative Example 3 were generally good.
(2) Next, as the initial capacity (first discharge capacity) of the secondary battery is higher, the characteristics as a battery are better evaluated.Reference example 2The secondary batteries according to (1) and (2) of higher comparative example 3 were rejected as confirmed from the data shown in Table 2. In contrast,Reference example 2The secondary battery according to (1), (2) and (3) and the secondary battery according to Comparative Example 2 show a high discharge capacity of 150 (mAh / g) or more at the first discharge.
(3) The first discharge capacity is 150 (mAh / g) or more.Reference example 2In Comparative Example 2, thermogravimetry (TG) is performed as described above.
[0062]
  From the -dTG curve of FIG.Reference example 2As for the secondary batteries according to (1), (2) and (3), the decomposition peak temperature is shifted to a higher temperature than that of the secondary battery according to Comparative Example 2, and at the same time, the amount of zinc replacement increases. The decomposition peak height has decreased, compared with the secondary battery according to Comparative Example 2.Reference example 2It is confirmed that the thermal stability of the secondary battery according to (1), (2) and (3) is improved.
(4) Next, the graph of FIG. 6 shows the first change in discharge capacity with respect to the zinc substitution amount. FIG. 6 confirms that the discharge capacity tends to decrease as the zinc replacement amount increases. From this graph, in order to maintain a high discharge capacity of 150 mAh / g or more, the y value of the lithium-containing composite oxide represented by Li (Ni0.83Co0.17) 1-yZnyO2 is 0 < It is confirmed that it is necessary to satisfy the requirement of y ≦ 0.13.
(5) In addition,Reference example 2The synthesis conditions for the lithium-containing composite oxide according to (1), (2) and (3) are all 750 ° C. and 20 hours. Also,Reference example 2The site occupancy of metal ions other than lithium at the 3a site of the lithium-containing composite oxide according to (1), (2) and (3) is less than 1.5%. A similar experiment was conducted for a lithium-containing composite oxide having an occupancy ratio of 1.5% or more. These secondary batteries also have a site occupancy ratio of 3% or less.Reference example 2It has been confirmed that the lithium-containing composite oxides according to (1), (2) and (3) tend to exhibit substantially the same characteristics.
[0063]
  [Reference example 3]
  In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a nickel / cobalt molar ratio of 83:17, and a commercially available product The titanium oxide was weighed so that the molar ratio of lithium to a metal other than lithium was 1: 1, and the molar ratio of nickel, cobalt, titanium, and magnesium was 75: 15: 5: 5. Thorough mixing was carried out at such a strength that spherical secondary particles were maintained. The obtained mixed powder was calcined at 350 ° C. in an oxygen stream, calcined at about 800 ° C. for 20 hours, and cooled to room temperature. When the obtained fired product was analyzed by X-ray diffraction, it was confirmed that it was a desired lithium-containing composite oxide having a hexagonal layered structure. Moreover, the metal ion mixing rate of 3a site was calculated | required from the Rietveld analysis of the diffraction pattern obtained by the powder X-ray-diffraction method using the K alpha ray of Cu. The results are shown in Table 3 below.
[0064]
Next, using the obtained lithium-containing composite oxide as a positive electrode active material, a secondary battery as shown in FIG.
[0065]
The produced secondary battery is left for about 24 hours, and after the open circuit voltage (OCV) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm.²And a charge / discharge test was performed at a cut-off voltage of 4.3-3.0V. Table 3 shows the obtained first discharge capacity.
[0066]
  next,Reference exampleIn order to investigate the thermal stability of each lithium-containing composite oxide synthesized at the full charge state, its thermal behavior was measured.
[0067]
The method for extracting Li from the positive electrode active material is the same as in Example 1. That is, 6.0 g of the obtained lithium-containing composite oxide (calcined product) was put into 100 ml (ml) of an aqueous hydrochloric acid solution adjusted to a concentration of 1 N and stirred for 5 hours._1-x(Ni_0.83Co_0.17)_1-2yTi_yMg_yO₂In this case, lithium (Li) was extracted by x = 0.7.
[0068]
Next, this was filtered, and the remaining slurry was dried in the atmosphere at 40 ° C. for 24 hours, and then dried by heating at 150 ° C. for 3 days in a vacuum to evaporate the water._0.3Ni_0.75Co_0.15Ti_0.05Mg_0.05O₂Of powder was obtained.
[0069]
The powder was impregnated with the same electrolyte as that used to produce the coin battery, sealed in a sealed sample holder, and subjected to thermogravimetry (TG) to examine the decomposition behavior. Thermogravimetry was performed at a heating rate of 10 ° C./min. The differential curve of the weight change with respect to the temperature of room temperature to 500 ° C. is shown in the graph of FIG. 7, and the decomposition peak temperature and the decomposition peak height of the −dTG curve are shown in Table 3.
[0070]
  [Comparative Example 4]
  In order to synthesize the positive electrode active material, a commercially available lithium hydroxide monohydrate, a metal composite hydroxide composed of spherical secondary particles and having a nickel / cobalt molar ratio of 83:17, and a commercially available product The molar ratio of lithium to a metal other than lithium is 1: 1, and the molar ratio of nickel, cobalt, titanium, and magnesium is (1) 66: 14: 10: 10, (2) 62 : 13: 12.5: 12.5, (3) 75: 15: 5: 5, (4) After weighing to 75: 15: 5: 5, the shape of spherical secondary particles is maintained. Mix thoroughly at a certain strength. The obtained mixed powder was calcined at 350 ° C. in an oxygen stream, and then fired at about 800 ° C. for 20 hours for (1) and (2), and for 20 hours at 550 ° C. for (3) above. While (4) was fired at 850 ° C. for 20 hours,Reference example 3Similarly, a positive electrode active material composed of a lithium-containing composite oxide was synthesized, and a lithium coin secondary battery was produced.
[0071]
  AndReference example 3In the same manner as above, the mixing rate (%) of metal ions at the 3a site in each lithium-containing composite oxide and the first discharge capacity of each battery obtained were measured. The results are shown in Table 3.
[0072]
[Table 3]

  "Confirmation"
(1) MadeReference example 3In addition, when the secondary batteries according to the respective comparative examples were evaluated, the cycle characteristics of these batteries except for the comparative example 2Reference example 3In Comparative Example 4, (1), (2), (3), and (4) were generally good.
(2) Next, as the initial capacity (first discharge capacity) of the secondary battery is higher, the characteristics as a battery are better evaluated.Reference example 3The secondary batteries according to (1), (2), (3), and (4) of Comparative Example 4 were unacceptable as confirmed from the data shown in Table 3. In contrast,Reference example 3As for the secondary battery according to the above and the secondary battery according to Comparative Example 2, the first discharge capacity is as high as 150 (mAh / g) or higher.
(3) The first discharge capacity is 150 (mAh / g) or more.Reference example 3In Comparative Example 2, thermogravimetry (TG) is performed as described above.
[0073]
  From the -dTG curve of FIG.Reference example 3As for the secondary battery according to the present invention, the decomposition peak temperature is shifted to a higher temperature than the secondary battery according to Comparative Example 2, and at the same time, the decomposition peak height decreases as the substitution amount of titanium and magnesium increases. Compared to the secondary battery according to Comparative Example 2Reference example 3It is confirmed that the thermal stability of the secondary battery according to is improved.
(4) Next, the graph of FIG. 8 shows the first change in discharge capacity with respect to the substitution amount of titanium and magnesium. FIG. 8 confirms that the discharge capacity tends to decrease as the titanium / magnesium substitution amount increases. From this graph, in order to maintain a high discharge capacity of 150 mAh / g or more, the y value of the lithium-containing composite oxide represented by Li (Ni0.83Co0.17) 1-2yTiyMgyO2 is 0 < It is confirmed that the requirement of y ≦ 0.06 needs to be satisfied.
(5) In addition,Reference example 3The lithium-containing composite oxide is a lithium-containing composite oxide represented by LiNi1-x-2yCoxTiyMgyO2, but the same experiment was also conducted for the lithium-containing composite oxide represented by LiNi1-x-2yCoxZnyMgyO2. These secondary batteries also have a site occupancy of 3% or less.Reference example 3It has been confirmed that there is a tendency to exhibit substantially the same characteristics as the lithium-containing composite oxide.
[0074]
【The invention's effect】
  According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1,
  LiNi1-x-yCoxTiyO2 (where 0 <x≤0.20, 0 <y≤0.07) and a hexagonal lithium-containing composite oxide having a layered structure, Rietveld analysis of the above lithium-containing composite oxide by X-ray diffraction when the sites 3a, 3b and 6c in the lithium-containing composite oxide are represented by [Li] 3a [Ni1-x-yCoxTiy] 3b [O2] 6c The site occupancy of metal ions other than lithium at the 3a site obtained from the above is set to 5% or less, so that the non-aqueous electrolyte secondary battery has excellent high-temperature stability while maintaining high initial capacity and cycle characteristics The effect that can be provided.
[0076]
  next,Claims 3-5According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention,Claims 1-2It has the effect which can manufacture the positive electrode active material for nonaqueous electrolyte secondary batteries which concerns on this.
[Brief description of the drawings]
FIG. 1 ExampleAnd reference examplesThe structure explanatory drawing of the secondary battery which concerns on.
2 is a graph of a DSC curve with respect to temperature obtained by differential scanning calorimetry (DSC) measurement of each lithium-containing composite oxide powder according to (1), (2) and (3) of Example 1. FIG.
3 is a graph of a DSC curve versus temperature obtained by differential scanning calorimetry (DSC) measurement of a lithium-containing composite oxide powder according to Comparative Example 2. FIG.
4 is a graph showing a change in discharge capacity for the first time with respect to a titanium substitution amount y of the lithium-containing composite oxide powder according to Example 1. FIG.
FIG. 5 and Comparative Example 2Reference example 2The graph figure of the differential curve of the weight change with respect to the temperature calculated | required by the thermogravimetric (TG) measurement of each lithium containing complex oxide powder which concerns on (1) (2) (3).
[Fig. 6]Reference example 2The graph which shows the change of the discharge capacity of the 1st time with respect to the zinc substitution amount y of the lithium containing complex oxide powder which concerns.
FIG. 7 and Comparative Example 2Reference example 3The graph of the differential curve of the weight change with respect to the temperature calculated | required by the thermogravimetric (TG) measurement of each lithium containing complex oxide powder which concerns on.
[Fig. 8]Reference example 3The graph which shows the change of the discharge capacity of the 1st time with respect to the substitution amount y of the total titanium and magnesium of the lithium containing complex oxide powder concerning (1) and (2) of Comparative Example 4.
[Explanation of symbols]
1 Positive electrode (Evaluation electrode)
2 Separator
3 Lithium metal negative electrode
4 Gasket
5 Positive electrode can
6 Negative electrode can

Claims (5)

In the positive electrode active material applied to the non-aqueous electrolyte secondary battery,
LiNi1-x-yCoxTiyO2 (where 0 <x≤0.20, 0 <y≤0.07) and a hexagonal lithium-containing composite oxide having a layered structure, Rietveld analysis of the above lithium-containing composite oxide by X-ray diffraction when the sites 3a, 3b and 6c in the lithium-containing composite oxide are represented by [Li] 3a [Ni1-x-yCoxTiy] 3b [O2] 6c A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the site occupancy of metal ions other than lithium at 3a sites obtained from 3 is 5% or less. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the shape of the secondary particles in the positive electrode active material is spherical or elliptical. In the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 1,
A positive electrode for a non-aqueous electrolyte secondary battery obtained by mixing a lithium compound, a nickel compound, a cobalt compound, and a titanium compound, and heat-treating the mixture under conditions of 650 ° C. or higher and 750 ° C. or lower and 4 hours or longer. A method for producing an active material. In the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 1,
A metal composite hydroxide (where 0 <x ≦ 0.20), a lithium compound, and a titanium compound, in which the molar ratio of nickel and cobalt is (1-x): x, is mixed, and this mixture Is obtained by heat treatment under conditions of 650 ° C. or higher and 750 ° C. or lower and 4 hours or longer. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4 , wherein the shape of the secondary particles in the metal composite hydroxide is spherical or elliptical.

Images