JP2012185913A - Positive electrode active material for lithium ion secondary battery use, positive electrode for lithium ion secondary battery use, and lithium ion secondary battery - Google Patents

Abstract

A positive electrode active material for a lithium ion secondary battery capable of exhibiting excellent initial charge / discharge efficiency, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.
A positive electrode active material for a lithium ion secondary battery has a general formula: Li _{(2-0.5x) y} □ _{(2-0.5x) (1-y)} Mn _1-x M _1.5x O ₃ (Where Li is lithium, □ is a vacancy in the crystal structure, Mn is manganese, M is Ni _α Co _β Mn _γ (Ni is nickel, Co is cobalt, Mn is manganese, α, β and γ are And 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5.) And x and y are 0 <x <1.00 and 0 <y <1 , And a crystal structure belonging to the space group C2 / m.
[Selection] Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery. More specifically, the present invention relates to a positive electrode active material for a lithium ion secondary battery that can exhibit excellent initial charge / discharge efficiency, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the same.

  In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide emissions has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that will be the key to the practical application of these technologies is thriving. Has been done.

  As a secondary battery for driving a motor, a lithium ion secondary battery having a high theoretical energy is attracting attention, and is currently being developed rapidly. Lithium ion secondary batteries generally have a positive electrode formed by applying a positive electrode slurry containing a positive electrode active material and a binder to both sides of a positive electrode current collector, and a negative electrode slurry containing a negative electrode active material and a binder on both sides of the negative electrode current collector. And a negative electrode formed by applying to the battery and an electrolyte positioned between the negative electrode and the battery case.

  In order to improve the capacity characteristics and output characteristics of the lithium ion secondary battery, selection of each active material is extremely important.

Conventionally, as a positive electrode active material for a lithium ion secondary battery having a high discharge capacity, the following general formula xLi [Mn _1/2 Ni _1/2 ] O ₂ .yLiCoO ₂ .zLi [Li _1/3 Mn _2/3 ] O ₂ (x + y + z = 1, 0 <x <1, 0 ≦ y <0.5, 0 <z <1) and a layered positive electrode active material (solid solution) having Li ₂ MnO ₃ as a parent structure is used. (See Patent Document 1).

JP 2007-287445 A

  However, the positive electrode active material for a lithium ion secondary battery described in Patent Document 1 has a problem that the capacity loss (initial irreversible capacity) at the time of initial charge / discharge is large and the initial charge / discharge efficiency is low.

  The present invention has been made in view of such problems of the prior art. And the place made into the objective is providing the positive electrode active material for lithium ion secondary batteries which can exhibit the outstanding initial stage charge / discharge efficiency, the positive electrode for lithium ion secondary batteries, and a lithium ion secondary battery using the same It is in.

  The inventors of the present invention have made extensive studies in order to achieve the above object. As a result, the inventors have found that the above object can be achieved by immersing a predetermined layered transition metal oxide in an acidic solution, and have completed the present invention.

That is, the positive electrode active material for a lithium ion secondary battery of the present invention is a layered transition metal oxide represented by the general formula (1) and having a crystal structure belonging to the space group C2 / m.
Li _{(2-0.5x) y} □ _{(2-0.5x) (1-y)} Mn _1-x M _1.5x O ₃ (1)
(In the formula (1), Li is lithium, □ is a vacancy in the crystal structure, Mn is manganese, M is Ni _α Co _β Mn _γ (Ni is nickel, Co is cobalt, Mn is manganese, α, β And γ satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5.), X and y are 0 <x <1.00, 0 < satisfying the relationship of y <1.00.)

Moreover, the positive electrode for lithium ion secondary batteries of this invention is a positive electrode for lithium ion secondary batteries which has the positive electrode active material layer formed in the surface of an electrical power collector.
And the said positive electrode active material layer contains the positive electrode active material for lithium ion secondary batteries of the said this invention.

Furthermore, the lithium ion secondary battery of the present invention includes a positive electrode for a lithium ion secondary battery having a positive electrode active material layer formed on the surface of a current collector, an electrolyte layer, and a negative electrode for a lithium ion secondary battery. It is a lithium ion secondary battery provided with the battery element containing the at least 1 unit cell laminated | stacked in order.
And the said positive electrode active material layer contains the positive electrode active material for lithium ion secondary batteries of the said this invention.

  According to the present invention, since a predetermined layered transition metal oxide is immersed in an acidic solution, a positive electrode active material for a lithium ion secondary battery capable of exhibiting excellent initial charge / discharge efficiency, and a lithium ion secondary battery A positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the positive electrode active material can be provided.

It is sectional drawing which shows the outline of an example of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a graph which shows the result of the powder X-ray-diffraction measurement of each example.

  Hereinafter, the positive electrode active material for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery of the present invention will be described in detail.

First, a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention will be described in detail.
The positive electrode active material for a lithium ion secondary battery of the present embodiment is a layered transition metal oxide represented by the general formula (1) and having a crystal structure belonging to the space group C2 / m.
Li _{(2-0.5x) y} □ _{(2-0.5x) (1-y)} Mn _1-x M _1.5x O ₃ (1)
(In the formula (1), Li is lithium, □ is a vacancy in the crystal structure, Mn is manganese, M is Ni _α Co _β Mn _γ (Ni is nickel, Co is cobalt, Mn is manganese, α, β And γ satisfy the relationship 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, α + β + γ = 1), and x and y are 0 <x < (The relationship of 1.00 and 0 <y <1.00 is satisfied.)

  Since such a positive electrode active material can exhibit excellent initial charge / discharge efficiency when used in a lithium ion secondary battery, it is preferably used for a positive electrode for a lithium ion secondary battery or a lithium ion secondary battery.

Here, when x is not 0 <x <1.00, the layered transition metal oxide whose crystal structure belongs to the space group C2 / m is not obtained. Moreover, it is preferable that x is 0.1 or more because the composition is unlikely to be close to Li ₂ MnO ₃ and charging / discharging becomes easy. Furthermore, it is preferable that x is 0.5 or less because the charge / discharge capacity per weight of the positive electrode active material can be 200 mAh / g or higher, which is higher than that of the existing layered positive electrode active material.
When y is not 0 <y <1.00, the layered transition metal oxide whose crystal structure belongs to the space group C2 / m is not obtained. Moreover, it is preferable that y is 0.94 or more because a decrease in discharge capacity can be suppressed.

Further, when α is not α ≦ 0.5, the positive electrode active material contains nickel (Ni) within the range of x shown above on the condition that nickel (Ni) is divalent, and the crystal structure is It is not a layered transition metal oxide belonging to the space group C2 / m.
Further, when β is not β ≦ 0.33, on the condition that nickel (Ni) is divalent, nickel (Ni) is included in the positive electrode active material within the range of x shown above, and the positive electrode active It does not become a layered transition metal oxide containing cobalt (Co) in the material and having a crystal structure belonging to the space group C2 / m.
When γ is not γ ≦ 0.5, nickel (Ni) and cobalt (Co) are added to the positive electrode active material within the range of x shown above on condition that nickel (Ni) is divalent. Furthermore, on the condition that manganese (Mn) is tetravalent, the layered transition metal oxide whose crystal structure belongs to the space group C2 / m is not obtained.

The positive electrode active material can be obtained, for example, by immersing a layered transition metal oxide represented by the general formula (2) and having a crystal structure belonging to the space group C2 / m in an acidic solution.
Li _2-0.5x Mn _1-x M _1.5x O ₃ (2)
(In the formula (2), Li is lithium, Mn is manganese, M is Ni _α Co _β Mn _γ (Ni is nickel, Co is cobalt, Mn is manganese, α, β, and γ are 0 <α ≦ 0. .5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, α + β + γ = 1 is satisfied), and x is 0 <x <1.00, preferably 0.1 ≦ x Satisfies the relation of ≦ 0.5.)

  At this time, examples of the acidic compound contained in the acidic solution to be used include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, and weak acids such as acetic acid. And although it does not specifically limit, It is preferable to use the weak acid whose acid dissociation constant is larger than 0 from a viewpoint that it is easy to obtain the positive electrode active material which has desired performance.

  The ratio of the acidic compound (AC) in the acidic solution to lithium (Li) in the layered transition metal oxide represented by the general formula (2) and having a crystal structure belonging to the space group C2 / m (AC / From the viewpoint of easily obtaining a positive electrode active material having desired performance, Li) is preferably 0.01 to 1.00, more preferably 0.05 to 0.20 in terms of molar ratio.

Next, a positive electrode active material for a lithium ion secondary battery according to another embodiment of the present invention will be described in detail.
The positive electrode active material for a lithium ion secondary battery of the present embodiment is a layered transition metal oxide represented by the general formula (3) and having a crystal structure belonging to the space group C2 / m.
Li _{(2-0.5x) y} □ _{(2-0.5x) (1-y)} Mn _1-x M _1.5x O ₃ (3)
(In Formula (3), Li is lithium, □ is a vacancy in the crystal structure, Mn is manganese, M is Ni _α Co _β Mn _γ M ¹ _δ (Ni is nickel, Co is cobalt, Mn is manganese, M ¹ Represents at least one selected from the group consisting of aluminum (Al), iron (Fe), copper (Cu), magnesium (Mg), and titanium (Ti), and α, β, γ, and δ are 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, 0 <δ ≦ 0.1, α + β + γ + δ = 1.), And x and y are 0 <x < (The relationship of 1.00 and 0 <y <1.00 is satisfied.)

In general, nickel (Ni), cobalt (Co), and manganese (Mn) are used in terms of improving material purity and electronic conductivity, aluminum (Al), iron (Fe), copper (Cu), magnesium (Mg) and Titanium (Ti) is known to contribute to capacity and output characteristics from the viewpoint of improving the stability of the crystal structure.
Therefore, it is estimated that the positive electrode active material represented by the general formula (3) also exhibits excellent initial charge / discharge efficiency when used in a lithium ion secondary battery. It is suitably used for a positive electrode for an ion secondary battery or a lithium ion secondary battery.

Here, when x is not 0 <x <1.00, the layered transition metal oxide whose crystal structure belongs to the space group C2 / m is not obtained. Moreover, it is preferable that x is 0.1 or more because the composition is unlikely to be close to Li ₂ MnO ₃ and charging / discharging becomes easy. Furthermore, it is preferable that x is 0.5 or less because the charge / discharge capacity per weight of the positive electrode active material can be 200 mAh / g or higher, which is higher than that of the existing layered positive electrode active material.
When y is not 0 <y <1.00, the layered transition metal oxide whose crystal structure belongs to the space group C2 / m is not obtained. Moreover, it is preferable that y is 0.94 or more because a decrease in discharge capacity can be suppressed.

Further, when α is not α ≦ 0.5, the positive electrode active material contains nickel (Ni) within the range of x shown above on the condition that nickel (Ni) is divalent, and the crystal structure is It is not a layered transition metal oxide belonging to the space group C2 / m.
Further, when β is not β ≦ 0.33, on the condition that nickel (Ni) is divalent, nickel (Ni) is included in the positive electrode active material within the range of x shown above, and the positive electrode active It does not become a layered transition metal oxide containing cobalt (Co) in the material and having a crystal structure belonging to the space group C2 / m.
When γ is not γ ≦ 0.5, nickel (Ni) and cobalt (Co) are added to the positive electrode active material within the range of x shown above on condition that nickel (Ni) is divalent. Furthermore, on the condition that manganese (Mn) is tetravalent, the layered transition metal oxide whose crystal structure belongs to the space group C2 / m is not obtained.
Further, when δ is not δ ≦ 0.1, in the positive electrode active material within the range of x shown above, provided that nickel (Ni) is divalent and manganese (Mn) is tetravalent. In addition, nickel (Ni), cobalt (Co) and manganese (Mn) are included, and the crystal structure is not a layered transition metal oxide belonging to the space group C2 / m.

The positive electrode active material can be obtained, for example, by immersing a layered transition metal oxide represented by the general formula (4) and having a crystal structure belonging to the space group C2 / m in an acidic solution.
Li _2-0.5x Mn _1-x M _1.5x O ₃ (4)
(In formula (4), Li is lithium, Mn is manganese, M is Ni _α Co _β Mn _γ M ¹ _δ (Ni is nickel, Co is cobalt, Mn is manganese, M ¹ is aluminum (Al), iron (Fe ), Copper (Cu), magnesium (Mg) and titanium (Ti), at least one selected from the group consisting of α, β, γ and δ is 0 <α ≦ 0.5, 0 ≦ β ≦ 0 .33, 0 <γ ≦ 0.5, 0 <δ ≦ 0.1, α + β + γ + δ = 1)), and x is 0 <x <1.00, preferably 0.1 ≦ x Satisfies the relation of ≦ 0.5.)

  At this time, examples of the acidic compound contained in the acidic solution to be used include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, and weak acids such as acetic acid. And although it does not specifically limit, It is preferable to use the weak acid whose acid dissociation constant is larger than 0 from a viewpoint that it is easy to obtain the positive electrode active material which has desired performance.

  Further, the ratio of the acidic compound (AC) in the acidic solution to the lithium (Li) in the layered transition metal oxide represented by the general formula (4) and having a crystal structure belonging to the space group C2 / m (AC / From the viewpoint of easily obtaining a positive electrode active material having desired performance, Li) is preferably 0.01 to 1.00, more preferably 0.05 to 0.20 in terms of molar ratio.

  Next, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the dimension ratio of drawing quoted by the following embodiment is exaggerated on account of description, and may differ from an actual ratio.

[Configuration of lithium ion secondary battery]
FIG. 1 is a cross-sectional view schematically showing an example of a lithium ion secondary battery according to an embodiment of the present invention.
As shown in FIG. 1, the lithium ion secondary battery 1 of this embodiment has a configuration in which a battery element 10 to which a positive electrode tab 21 and a negative electrode tab 22 are attached is enclosed in an exterior body 30. In the present embodiment, the positive electrode tab 21 and the negative electrode tab 22 are led out in the opposite direction from the inside of the exterior body 30 to the outside. Although not shown, the positive electrode tab and the negative electrode tab may be led out in the same direction from the inside of the exterior body to the outside. Moreover, such a positive electrode tab and a negative electrode tab can be attached to the positive electrode collector and negative electrode collector which are mentioned later by ultrasonic welding, resistance welding, etc., for example.

[Positive electrode tab and negative electrode tab]
The positive electrode tab 21 and the negative electrode tab 22 are made of materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. However, the material is not limited to these, and a conventionally known material used as a tab for a lithium ion secondary battery can be used.
The positive electrode tab and the negative electrode tab may be made of the same material or different materials. Further, as in the present embodiment, a separately prepared tab may be connected to a positive electrode current collector and a negative electrode current collector described later, and each positive electrode current collector and each negative electrode current collector described later are extended. A tab may be formed.

[Exterior body]
For example, the exterior body 30 is preferably formed of a film-shaped exterior material from the viewpoints of miniaturization and weight reduction, but is not limited thereto, and the exterior body for a lithium ion secondary battery is not limited thereto. Conventionally known materials used for the body can be used.
When applied to an automobile, for example, a polymer-metal composite laminate sheet having excellent thermal conductivity is used from the viewpoint of efficiently transferring heat from the automobile heat source and heating the inside of the battery to the battery operating temperature quickly. Is preferred.

[Battery element]
As shown in FIG. 1, the battery element 10 in the lithium ion secondary battery 1 of the present embodiment includes a positive electrode 11 in which a positive electrode active material layer 11B is formed on both surfaces of a positive electrode current collector 11A, an electrolyte layer 13, The negative electrode current collector 12A has a structure in which a plurality of negative electrodes 12 each having a negative electrode active material layer 12B formed thereon are stacked. At this time, the positive electrode active material layer 11B formed on one surface of the positive electrode current collector 11A of one positive electrode 11 and the negative electrode current collector 12A of the negative electrode 12 adjacent to the one positive electrode 11 are formed. A plurality of layers of a positive electrode, an electrolyte layer, and a negative electrode are stacked in this order so that the negative electrode active material layer 12 </ b> B faces the electrolyte layer 13.

  As a result, the adjacent positive electrode active material layer 11B, electrolyte layer 13 and negative electrode active material layer 12B constitute one unit cell layer. Therefore, the lithium ion secondary battery 1 of the present embodiment has a configuration in which a plurality of single battery layers 14 are stacked and electrically connected in parallel. Note that the negative electrode current collector 12a located in the outermost layer of the battery element 10 has a negative electrode active material layer 12B formed on only one side. In addition, an insulating layer (not shown) may be provided on the outer periphery of the unit cell layer to insulate between the adjacent positive electrode current collector and negative electrode current collector. Such an insulating layer is preferably formed of a material that retains the electrolyte contained in the electrolyte layer and the like and prevents electrolyte leakage from the outer periphery of the single cell layer. Specifically, general-purpose plastics such as polypropylene (PP), polyethylene (PE), polyurethane (PUR), polyamide resin (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polystyrene (PS), etc. Or thermoplastic olefin rubber can be used. Silicone rubber can also be used.

[Positive electrode current collector and negative electrode current collector]
The positive electrode current collector 11A and the negative electrode current collector 12A are made of a conductive material such as an aluminum foil, a copper foil, or a stainless steel (SUS) foil. However, the material is not limited to these, and a conventionally known material used as a current collector for a lithium ion secondary battery can be used.

[Positive electrode active material layer]
The positive electrode active material layer 11B includes the above-described positive electrode active material for a lithium ion secondary battery of the present invention as a positive electrode active material, and may include a binder and a conductive auxiliary agent as necessary.
The positive electrode active material layer may contain other positive electrode active materials in addition to the positive electrode active material of the present invention described above. As another positive electrode active material, for example, a lithium-containing compound is preferable from the viewpoint of capacity and output characteristics. Examples of such lithium-containing compounds include composite oxides containing lithium and transition metal elements, phosphate compounds containing lithium and transition metal elements, sulfate compounds containing lithium and transition metal elements, and lithium and transition metals. A solid solution containing an element can be mentioned, and a lithium-transition metal composite oxide is particularly preferable from the viewpoint of obtaining higher capacity and output characteristics.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium nickel cobalt composite oxide (LiNiCoO ₂ ), and lithium nickel. Manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ), lithium nickel manganese cobalt composite oxide (Li (NiMnCo) O ₂ , Li (LiNiMnCo) O ₂ ), lithium manganese composite oxide having a spinel structure (LiMn ₂ O ₄ ) and the like. Specific examples of the phosphate compound containing lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFeMnPO ₄ ). In these composite oxides, for example, for the purpose of stabilizing the structure, a part of the transition metal may be substituted with another element.

As a specific example of a solid solution containing lithium and a transition metal element, xLiM ^I O _2. (1-x) Li ₂ M ^II O ₃ (0 <x <1, M ^I is an average oxidation state 3+, M ^II is an average And one or more transition metal elements having an oxidation state of 4+), LiM ^III O ₂ —LiMn ₂ O ₄ (M ^III is a transition metal element such as Ni, Mn, Co, or Fe).

  As the binder, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN) and other thermoplastic resins, epoxy resins, polyurethane resins, urea resins and other thermosetting resins, styrene butadiene rubber Examples thereof include rubber materials such as (SBR). However, the material is not limited to these, and a known material conventionally used as a binder for a lithium ion secondary battery can be used. These binders may be used alone or in combination of two or more.

  Examples of the conductive aid include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. However, the material is not limited to these, and a conventionally known material that is used as a conductive additive for a lithium ion secondary battery can be used. These conductive assistants may be used alone or in combination of two or more.

[Negative electrode active material layer]
The negative electrode active material layer 12B includes one or more negative electrode materials capable of inserting and extracting lithium as a negative electrode active material, and includes a binder and a conductive auxiliary agent as necessary. You may go out. In addition, the binder and the conductive auxiliary agent described above can be used.
Examples of the negative electrode material capable of inserting and extracting lithium include graphite (natural graphite, artificial graphite, etc.), which is highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen) Carbon materials such as black, acetylene black, channel black, lamp black, oil furnace black, thermal black, fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril; Si, Ge, Sn, Pb, Al, In Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl Elemental elements that alloy with lithium, such as Oxide containing an element (silicon monoxide _{(SiO), SiO x (0} <x <2), tin dioxide _{(SnO 2), SnO x (} 0 <x <2), etc. SnSiO ₃₎ and carbide (silicon carbide ( SiC) and the like; metal materials such as lithium metal; and lithium-transition metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ). However, it is not limited to these, The conventionally well-known material used as a negative electrode active material for lithium ion secondary batteries can be used. These negative electrode active materials may be used alone or in combination of two or more.

  A negative electrode active material other than the above may be used. In addition, when the optimum particle diameter is different in expressing the unique effect of each active material, the optimum particle diameters may be mixed and used for expressing each unique effect. There is no need to make the particle size of the material uniform.

[Electrolyte layer]
As the electrolyte layer 13, for example, an electrolyte solution, a polymer gel electrolyte, a solid polymer electrolyte formed in a separator described later, and a layer structure formed using a solid polymer electrolyte, or a polymer gel electrolyte or a solid polymer electrolyte are used. Examples thereof include those having a laminated structure formed thereon.
For example, the electrolyte solution is preferably one that is usually used in a lithium ion secondary battery, and specifically has a form in which a lithium salt is dissolved in an organic solvent. Examples of the lithium _{salt, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anion salts such _{as, LiCF 3 SO 3, Li (} CF 3 SO 2 ) ₂ N, at least one lithium salt selected from organic acid anion salts such as Li (C ₂ F ₅ SO ₂ ) ₂ N, and the like. Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC); chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC). Ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; methyl propionate; Esters such as amides; Amides such as dimethylformamide; One using at least one selected from methyl acetate and methyl formate, or a mixture using an organic solvent such as an aprotic solvent can be used. . In addition, as a separator, the microporous film which consists of polyolefins, such as polyethylene and a polypropylene, can be mentioned, for example.
Examples of the polymer gel electrolyte include those containing a polymer constituting the polymer gel electrolyte and an electrolytic solution in a conventionally known ratio.
The polymer gel electrolyte is a solid polymer electrolyte having ion conductivity containing the above-mentioned electrolytic solution usually used in a lithium ion secondary battery, but is not limited to this. A structure in which a similar electrolyte solution is held in a polymer skeleton having no conductivity is also included.
For example, polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), etc. are used as the polymer having no lithium ion conductivity used in the polymer gel electrolyte. it can. However, it is not necessarily limited to these. Note that PAN, PMMA, etc. are in a class that has almost no ionic conductivity, and therefore can be a polymer having the above ionic conductivity, but here, they are used for a polymer gel electrolyte. This is exemplified as a polymer having no lithium ion conductivity.
Examples of the solid polymer electrolyte include those obtained by dissolving the lithium salt in polyethylene oxide (PEO), polypropylene oxide (PPO), and the like.
The thickness of the electrolyte layer is preferably thinner from the viewpoint of reducing internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

Example 1
<Preparation of positive electrode active material>
First, the raw material of the positive electrode active material (solid solution) was synthesized by the composite carbonate method. Specifically, nickel sulfate, cobalt sulfate, and manganese sulfate were weighed so that nickel (Ni), cobalt (Co), and manganese (Mn) had a predetermined molar ratio. Subsequently, these were dissolved in ion-exchanged water to prepare a mixed aqueous solution. Further, aqueous ammonia was added dropwise to the mixed aqueous solution until pH 7 was reached, and an aqueous sodium carbonate (Na ₂ CO ₃ ) solution was further added dropwise to precipitate Ni—Co—Mn composite carbonate. During the dropwise addition of the aqueous sodium carbonate solution, the pH was maintained at 7 with aqueous ammonia. Furthermore, the obtained composite carbonate was suction filtered, washed with water, dried at 120 ° C. for 5 hours, and calcined at 500 ° C. for 5 hours to obtain a Ni—Co—Mn composite oxide. Further, a small excess of lithium hydroxide (LiOH.H ₂ O) was added to the obtained composite oxide so as to have a predetermined molar ratio, and the mixture was mixed in an automatic mortar for 30 minutes, and then at 900 ° C. for 12 hours. After baking and rapid cooling using liquid nitrogen, the raw material of the positive electrode active material (solid solution) (Li _1.85 Ni _0.18 Co _0.10 Mn _0.87 O ₃ (in formula (2), α = 0) 4, β = 0.22, γ = 0.38, and x = 0.3, and hereinafter referred to as “positive electrode active material raw material A”).
Next, a part of lithium (Li) was removed by solution treatment. Specifically, the positive electrode active material A is an aqueous hydrogen chloride (HC1) solution that is 20 times the amount of the active material. The amount of HCl in the acidic aqueous solution is the mol of lithium in the positive electrode active material A. And the mixture was stirred for 2 hours, filtered and washed with water, and the solid was vacuum dried at 80 ° C. to obtain a positive electrode active material of this example.

<Method for analyzing elemental composition of positive electrode active material>
A part of the obtained positive electrode active material is used as a sample, which is dissolved in an acid, and lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) contained in the solution are inductively coupled plasma light emission. Quantitative analysis was performed by inductively coupled plasma emission spectroscopy (ICP-AES) using a spectroscopic analyzer (ICP-AES SPS-3520UV type, manufactured by SII Nanotechnology).
The production conditions and the results obtained are shown in Table 1. In addition, the amount of Li in Table 1 is a relative amount when the amount of Li in Comparative Example 1 described later is 100 mol%. Further, nickel (Ni), manganese (Mn), and cobalt (Co) did not change regardless of the treatment solution type.

<Structural analysis method of positive electrode active material>
A sample (powder) of a part of the obtained positive electrode active material was powdered using an X-ray diffractometer (manufactured by Mac Science Co., MXP18VAHF) according to the measurement conditions of voltage 40 kV, current 200 mA, X-ray wavelength: Cu-Kα. X-ray diffraction measurement was performed.
The obtained results are shown in FIG. 2 together with the data of the standard sample.

(Examples 2 to 4, Comparative Example 1 and Comparative Example 2)
In the solution treatment, sulfuric acid (H ₂ SO ₄ ) aqueous solution was used as an acidic aqueous solution (Example 2), nitric acid (HNO ₃ ) aqueous solution was used (Example 3), and acetic acid (CH ₃ COOH) aqueous solution was used. The same operation as in Example 1 was repeated except that the solution treatment was not performed (Comparative Example 1) and that ion-exchanged water (H ₂ O) was used (Comparative Example 2). Thus, the positive electrode active material of each example was obtained.
In the same manner as in Example 1, element composition analysis and structural analysis of the positive electrode active material were performed. The production conditions and the obtained results are shown in Table 1 or FIG. 2 (although not shown in FIG. 2, similar results were obtained for Example 4).

(Example 5 to Example 9)
In the solution treatment, the CH ₃ COOH amount in the acetic acid (CH ₃ COOH) aqueous solution was set to 0.05 (Example 5), 0.10 (Example 6), 0 in molar ratio to lithium in the positive electrode active material raw material A. .30 (Example 7), 0.50 (Example 8), and 1.00 (Example 9), except that the same operation as in Example 4 was repeated to obtain the positive electrode active material of each example. It was.
Similarly to the above, elemental composition analysis and structural analysis of the positive electrode active material were performed. Table 2 shows the production conditions and the results obtained. The amount of Li in Table 2 is a relative amount when the amount of Li in Comparative Example 1 is 100 mol%. Further, nickel (Ni), manganese (Mn), and cobalt (Co) did not change regardless of the treatment solution type.

(Examples 10 to 14, Comparative Example 3)
When synthesizing the raw material of the positive electrode active material, nickel sulfate, cobalt sulfate and manganese sulfate are weighed so that nickel (Ni), cobalt (Co) and manganese (Mn) have other predetermined molar ratios, and Li _{1 .77} Ni _0.32 Co _0.05 Mn _0.86 O ₃ (In the formula (2), α = 0.464, β = 0.072, γ = 0.464, x = 0.46. Hereinafter referred to as “positive electrode active material raw material B”), and the same operations as in Example 5, Example 6, Example 4, Example 8, Example 9, and Comparative Example 1 were repeated, and the positive electrode of each example was obtained. An active material was obtained.
Similarly to the above, elemental composition analysis and structural analysis of the positive electrode active material were performed. Table 3 shows the production conditions and the results obtained. The amount of Li in Table 3 is a relative amount when the amount of Li in Comparative Example 3 is 100 mol%. Further, nickel (Ni), manganese (Mn), and cobalt (Co) did not change regardless of the treatment solution type.

<Preparation of positive electrode>
First, 80 parts by mass of the obtained positive electrode active material, 10 parts by mass of acetylene black as a conductive auxiliary agent, and 10 parts by mass of polyvinylidene fluoride as a binder were kneaded, and this was mixed with N-methyl-2-pyrrolidone (NMP). Were added and mixed to prepare a positive electrode slurry.
Next, the obtained positive electrode slurry was applied to an aluminum foil as a current collector so that the thickness of the positive electrode active material layer became 70 μm, and vacuum dried at 80 ° C. to obtain positive electrodes of respective examples.

<Production of battery>
First, the obtained positive electrode and a negative electrode obtained by attaching metallic lithium to a stainless steel disk were opposed to each other, and a separator (material: polyolefin, thickness: 20 μm) was disposed therebetween. Next, the laminate of the negative electrode, separator, and positive electrode is placed in a coin cell (CR2032, material: stainless steel (SUS316)), the following electrolytic solution is injected, and the lithium ion secondary battery (half cell) of each example is sealed. Got.
As an electrolytic solution, lithium hexafluorophosphate as an electrolyte salt is mixed with an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 1: 2 (volume ratio). (LiPF ₆₎ the concentration was used dissolved at a 1 mol / L.

<Charge / discharge characteristics evaluation of lithium ion secondary battery>
The obtained lithium ion secondary battery was subjected to a charge / discharge cycle test, an initial charge / discharge capacity was measured, and a charge / discharge efficiency was calculated. Specifically, in an atmosphere of 30 ° C., the battery is charged to 4.8 V by a constant voltage method (CC, current: 0.1 C), paused for 10 minutes, and then constant current method (CC, current: 0.1 C). Then, the battery was discharged to 2 V and charged and discharged for 10 minutes after discharging.
The obtained results are also shown in Tables 1-3.

  As shown in Table 1, the acid molar ratio was constant (0.20) with respect to the amount of Li in the positive electrode active material, and the influence of the acid type on the performance was evaluated. From Table 1, it can be seen that when Comparative Example 2 using ion-exchanged water is compared with Comparative Example 1 in which solution treatment is not performed, there is no significant change in charge / discharge identification. Moreover, it can be seen from Table 1 that the charge / discharge capacity is significantly reduced in Example 1 using a hydrogen chloride solution and Example 2 using a sulfuric acid aqueous solution. From Table 1, it can be seen that although the charge / discharge efficiency is high, the discharge capacity is greatly reduced. Moreover, in Example 3 using nitric acid aqueous solution from Table 1, although charging / discharging efficiency improves a little, it turns out that discharge capacity falls. It can be seen from Table 1 that in Example 4 using an acetic acid aqueous solution, the charge / discharge efficiency can be improved without significantly reducing the discharge capacity.

  It can be seen from FIG. 2 that there is no difference in the crystal structure even if the type of acid to be immersed is different.

  As shown in Table 2, the effect of acetic acid concentration on performance was evaluated. From Table 2, it can be seen that when at least the molar ratio of acetic acid is 0.05 to 0.20 with respect to the amount of Li in the positive electrode active material, the charge / discharge efficiency can be improved without greatly reducing the discharge capacity.

  As shown in Table 3, the effect of the concentration of acetic acid on the performance was evaluated in active materials having other compositions (positive electrode active material raw material B). From Table 3, it can be seen that the same tendency as in the case of using the positive electrode active material A is shown. It can also be seen that the charge / discharge efficiency can be improved without reducing the discharge capacity until the molar ratio of acetic acid is 0.50 with respect to the amount of Li in the positive electrode active material.

  From the Li amounts shown in Tables 1 to 3, it can be seen that the discharge capacity tends to decrease when the Li amount is less than 94 mol%. The amount of Li is a relative amount when the amount of Li in Comparative Example 1 or Comparative Example 3 in Comparative Example 1 is 100 mol%.

  As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention. That is, the positive electrode for a lithium ion secondary battery or the lithium ion secondary battery of the present invention may be any material as long as the positive electrode active material layer contains a predetermined layered transition metal oxide as the positive electrode active material. There is no particular limitation.

For example, the present invention can be applied not only to the laminate type battery described above but also to conventionally known forms and structures such as a button type battery and a can type battery.
Further, for example, the present invention can be applied not only to the above-described stacked type (flat type) battery but also to conventionally known forms and structures such as a wound type (cylindrical type) battery.
Furthermore, for example, the present invention is not only the above-described normal (internal parallel connection type) battery but also a bipolar type (internal series connection type) when viewed in terms of an electrical connection form (electrode structure) in a lithium ion secondary battery. ) Conventionally known forms and structures such as batteries can also be applied.
Note that a battery element in a bipolar battery generally includes a bipolar electrode having a positive electrode active material layer formed on one surface of a current collector and a negative electrode active material layer formed on the other surface, and an electrolyte layer. It has a configuration in which a plurality of layers are stacked.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Battery element 11 Positive electrode 11A Positive electrode collector 11B Positive electrode active material layer 12 Negative electrode 12A Negative electrode collector 12B Negative electrode active material layer 13 Electrolyte layer 14 Single battery layer 21 Positive electrode tab 22 Negative electrode tab 30 Exterior body

Claims (6)

General formula (1)
Li _{(2-0.5x) y} □ _{(2-0.5x) (1-y)} Mn _1-x M _1.5x O ₃ (1)
(In the formula (1), Li is lithium, □ is a vacancy in the crystal structure, Mn is manganese, M is Ni _α Co _β Mn _γ (Ni is nickel, Co is cobalt, Mn is manganese, α, β And γ satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5.), X and y are 0 <x <1.00, 0 < y <1.00 is satisfied.), and is a layered transition metal oxide having a crystal structure belonging to the space group C2 / m, and a positive electrode active material for a lithium ion secondary battery.   2. The lithium ion secondary battery according to claim 1, wherein in the formula (1), x and y satisfy a relationship of 0.1 ≦ x ≦ 0.5 and 0.94 ≦ y <1.00. Positive electrode active material for secondary battery. General formula (2)
Li _2-0.5x Mn _1-x M _1.5x O ₃ (2)
(In the formula (2), Li is lithium, Mn is manganese, M is Ni _α Co _β Mn _γ (Ni is nickel, Co is cobalt, Mn is manganese, α, β, and γ are 0 <α ≦ 0. .5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5 is satisfied), and x satisfies the relationship 0 <x <1.00. 3. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the positive electrode active material is obtained by immersing a layered transition metal oxide belonging to the space group C2 / m in an acidic solution.   The ratio of the acidic compound (AC) in the acidic solution to the lithium (Li) in the layered transition metal oxide represented by the general formula (2) whose crystal structure belongs to the space group C2 / m (AC / Li) The molar ratio of 0.01 to 1.00 is a positive electrode active material for a lithium ion secondary battery according to claim 3.   A positive electrode for a lithium ion secondary battery comprising a positive electrode active material layer containing the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4 on a surface of a current collector.   A positive electrode for a lithium ion secondary battery having a positive electrode active material layer containing the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4 on the surface of the current collector, an electrolyte layer, A lithium ion secondary battery comprising a battery element including at least one single battery in which a negative electrode for a lithium ion secondary battery is laminated in this order.

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