JP4498142B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

In recent years, with the reduction in size and weight of electronic devices such as VTRs, mobile phones, and mobile computers, it has been desired to increase the energy density of secondary batteries that are power sources thereof. For this reason, research on non-aqueous electrolyte secondary batteries using lithium as a negative electrode has been actively conducted, and lithium ion secondary batteries using LiCoO ₂ as a positive electrode active material have already been put into practical use.
By the way, lithium, a lithium alloy, or a compound that absorbs and releases lithium is used for the negative electrode of the nonaqueous electrolyte secondary battery. As the non-aqueous electrolyte, a solution obtained by dissolving a lithium salt (electrolyte) in a non-aqueous solvent is often used. Such non-aqueous solvents include propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), γ- Butyllactone (γ-BL), tetrahydrofuran (THF), and 2-methyltetrahydrofuran (2-MeTHF) are known. On the other hand, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , and LiAlCl ₄ are known as lithium salts.
On the other hand, as the positive electrode active material, attention is paid to a material utilizing intercalation of a layered compound or a doping phenomenon.
Among those using intercalation of the layered compound, the chalcogenide compound exhibits relatively excellent charge / discharge cycle characteristics. However, the chalcogenide compound has a low electromotive force, and even when lithium metal is used as the negative electrode, the practical charging voltage is about 2 V at most, which satisfies the high electromotive force characteristic of the nonaqueous electrolyte secondary battery. is not.
In addition to chalcogenide compounds, active materials using layered compound intercalation exist. Among these active materials, V ₆ O ₁₃ , LiCoO ₂ , LiNiO ₂ and metal oxide compounds such as LiMn ₂ O ₄ utilizing a doping phenomenon are attracting attention because they have a characteristic of high electromotive force. In particular, the positive electrode containing LiNiO ₂ as an active material has an electromotive force of about 4 V, and the theoretical energy density has a large value of approximately 1 kWh / kg per positive electrode active material.
However, the nonaqueous electrolyte secondary battery including a positive electrode containing LiNiO ₂ as an active material has a problem that the charge / discharge cycle life is low.
On the other hand, the JP 63-121258 publication has a layered structure, the general formula _{A x B y C z D w} O 2 composite oxide represented by a non-aqueous secondary battery using the positive electrode is disclosed ing. In the general formula, A is at least one selected from alkali metals, B is a transition metal, C is at least one selected from the group of Al, In, and Sn, and D is (a) A (B) transition metals other than B, (c) IIa group elements, (d) Al, In, Sn, carbon, nitrogen, oxygen group IIIb, IVb group, Vb group, VIb group It represents at least one selected from the group of 2 to 6th element. x, y, z, and w are numbers of 0.05 ≦ x ≦ 1.10, 0.85 ≦ y ≦ 1.00, 0.001 ≦ z ≦ 0.10, and 0.001 ≦ w ≦ 0.10, respectively. Represents.
However, the non-aqueous secondary battery described in the above publication cannot obtain a sufficient cycle life.

An object of the present invention is to provide a nonaqueous electrolyte secondary battery having an improved charge / discharge cycle life.
According to the present invention, a nonaqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte,
The positive electrode active material includes oxide particles represented by the following formula (A) and oxide particles represented by the following formula (B), and the oxide particles represented by the formula (A) in the positive electrode active material A nonaqueous electrolyte secondary battery in which the ratio exceeds 50% by weight and the positive electrode active material satisfies the following formulas (1) to (5) is provided.
_{Li x Ni y Co z M w} O 2 (A)
_{Li a Co b M c O 2} (B)
However, said M is one or more elements selected from the group consisting of Mn, B, Al and Sn, and said molar ratios x, y, z, w, a, b, c are 0. 95 ≦ x ≦ 1.05, 0.7 ≦ y ≦ 0.95, 0.05 ≦ z ≦ 0.3, 0 ≦ w ≦ 0.1, 0.95 ≦ y + z + w ≦ 1.05, 0.95 ≦ a ≦ 1.05, 0.95 ≦ b ≦ 1.05, 0 ≦ c ≦ 0.05, 0.95 ≦ b + c ≦ 1.05,
1.4 ≦ (D _N90 / D _N50 ) ≦ 2 (1)
1.4 ≦ (D _N50 / D _N10 ) ≦ 2 (2)
1.4 ≦ (D _C90 / D _C50 ) ≦ 2 (3)
1.4 ≦ (D _C50 / D _C10 ) ≦ 2 (4)
1.5 ≦ (D _N50 / D _C50 ) ≦ 2.5 (5)
However, the _{D N10,} the _{D N50,} the _{D N90 is, Li x Ni y Co z M} w volume cumulative frequency of _{O 2} particles of 10%, 50%, showed a particle size of 90%, the _{D C10,} the D _C50 and D _C90 indicate particle diameters of Li _a Co _b M _c O ₂ particles with a volume cumulative frequency of 10%, 50%, and 90%.

FIG. 1 is a cross-sectional view showing a thin nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention.
FIG. 2 is an enlarged cross-sectional view showing a portion A of FIG.
FIG. 3 is a cross-sectional view showing a prismatic nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery according to the present invention.

表１から明らかなように、ニッケル系粒子の配合量が５０重量％よりも多い試料１〜４は、放電容量（ｍＡｈ／ｇ）を試料５〜７に比較して高くすることができ、また、ＬｉＣｏＯ_２（試料７）に比較して少ない量で高い放電容量が得られることがわかる。
以下の実施例では、コバルト系粒子とニッケル系粒子との混合比の違いによる比容量差に起因する影響を少なくするために、負極の塗布量を一定として、正極活物質の混合比に合わせて正極塗布量（正極活物質含有量）を変化させて電池作製をおこなった。An example of the nonaqueous electrolyte secondary battery according to the present invention will be described.
The nonaqueous electrolyte secondary battery according to the present invention includes a container, an electrode group that is housed in the container and includes a positive electrode and a negative electrode, and a nonaqueous electrolyte that is held by the electrode group.
In this secondary battery, a separator may be disposed between the positive electrode and the negative electrode, or a gel or solid nonaqueous electrolyte layer may be used instead of the separator.
Hereinafter, the positive electrode, the negative electrode, the separator, the nonaqueous electrolyte, and the container will be described.
1) Positive electrode
The positive electrode includes a current collector and a positive electrode layer supported on one or both surfaces of the current collector and containing a positive electrode active material.
The positive electrode active material includes oxide particles represented by the following formula (A) and oxide particles represented by the following formula (B). The ratio of the oxide particles represented by the formula (A) in the positive electrode active material exceeds 50% by weight.
Li _x Ni _y Co _z M _w O ₂ (A)
Li _a Co _b M _c O ₂ (B)
However, said M is one or more elements selected from the group consisting of Mn, B, Al and Sn, and said molar ratios x, y, z, w, a, b, c are 0. 95 ≦ x ≦ 1.05, 0.7 ≦ y ≦ 0.95, 0.05 ≦ z ≦ 0.3, 0 ≦ w ≦ 0.1, 0.95 ≦ y + z + w ≦ 1.05, 0.95 ≦ a ≦ 1.05, 0.95 ≦ b ≦ 1.05, 0 ≦ c ≦ 0.05, 0.95 ≦ b + c ≦ 1.05 are shown.
Moreover, this positive electrode active material satisfies the following formulas (1) to (5).
1.4 ≦ (D _N90 / D _N50 ) ≦ 2 (1)
1.4 ≦ (D _N50 / D _N10 ) ≦ 2 (2)
1.4 ≦ (D _C90 / D _C50 ) ≦ 2 (3)
1.4 ≦ (D _C50 / D _C10 ) ≦ 2 (4)
1.5 ≦ (D _N50 / D _C50 ) ≦ 2.5 (5)
However, D _N10 Is the Li _x Ni _y Co _z M _w O ₂ The volume cumulative frequency of particles is 10%, and the particle size D _N50 Is the Li _x Ni _y Co _z M _w O ₂ The volume cumulative frequency of the particles is 50%, and the particle size D _N90 Is the Li _x Ni _y Co ₂ M _w O ₂ The volume cumulative frequency of particles is 90%. Meanwhile, D _C10 Is the Li _a Co _b M _c O ₂ The volume cumulative frequency of particles is 10%, and the particle size D _C50 Is the Li _a Co _b M _c O ₂ The volume cumulative frequency of the particles is 50%, and the particle size D _C90 Is the Li _a Co _b M _c O ₂ The volume cumulative frequency of particles is 90%.
{Li _x Ni _y Co _z M _w O ₂ Particle (hereinafter referred to as nickel-based particle)}
(Li)
The reason why the molar ratio x of lithium is defined in the above range is for the reason described below. When the molar ratio x is less than 0.95, the Li ions contributing to the charge / discharge reaction are reduced and the discharge capacity is reduced. On the other hand, when the molar ratio x exceeds 1.05, Li ions are mixed into the Ni site, so that the discharge capacity is reduced. In addition, since the reactivity decreases due to the change in crystal structure, the discharge voltage decreases. A more preferable range of the molar ratio x is 0.97 ≦ x ≦ 1.03.
(Ni)
The reason why the molar ratio y of nickel is defined within the above range is for the reason described below. When the molar ratio y is less than 0.7, LiCoO ₂ Therefore, it becomes difficult to achieve an improvement in energy density. On the other hand, when the molar ratio y exceeds 0.95, the discharge capacity increases, but the crystal structure is likely to be decomposed along with the charge / discharge cycle. A more preferable range of the molar ratio y is 0.75 ≦ y ≦ 0.9.
(Co)
The reason why the molar ratio z of cobalt is defined in the above range is for the reason described below. When the molar ratio z is less than 0.05, the stacking of the Ni layer tends to be disturbed, and the crystal structure is likely to be decomposed along with the charge / discharge cycle. On the other hand, when the molar ratio z exceeds 0.3, the synthesis temperature needs to be 850 ° C. or higher in order to adjust the stacking of the Co layer (increase the crystallinity). As a result, a deoxygenation reaction occurs, a deviation from the R3m structure occurs, and the discharge capacity decreases. A more preferable range of the molar ratio z is 0.1 ≦ z ≦ 0.25.
(Element M)
The element M has an effect of suppressing decomposition due to the charge / discharge cycle, and can serve as a pillar supporting the crystal structure. Further, by adding the element M, it is possible to suppress the decomposition of the nonaqueous electrolyte at the reaction interface. However, if the molar ratio w exceeds 0.1, nickel is likely to be mixed into the lithium ion site, so that the crystal structure may change and it may be difficult to discharge a large current. It is desirable to make it 1 or less. A more preferable range of the molar ratio w is 0 ≦ w ≦ 0.07, a more preferable range is 0 ≦ w ≦ 0.05, and a most preferable range is 0 ≦ w ≦ 0.03. In order to sufficiently obtain the effect of adding the element M, the lower limit value of the molar ratio w is preferably set to 0.001.
Among the elements M, Sn is preferable. When Sn is used as the element M, the charge / discharge cycle life in a high temperature environment can be improved. This is presumed to be because the reaction of forming a protective coating derived from EC on the surface of the positive electrode is promoted, and the reaction between the positive electrode and γ-butyllactone in a high temperature environment (around 45 ° C.) is suppressed. The Li _x Ni _y Co _z Sn _w O ₂ The particles are Li _x Ni _y Co _z O ₂ And Li ₂ SnO ₃ And a mixture.
When Al or Mn is used as the element M, Li _x Ni _y Co _z M _w O ₂ Since the stability of the crystal structure of the particles is increased, charging / discharging can be performed stably over a long-term cycle, and the charge / discharge cycle life can be further improved.
The reason why the total (y + z + w) of the molar ratios y, z, and w is defined in the above range will be described. When (y + z + w) is less than 0.95, the Li ratio in the particles increases, so that impurities that do not contribute to the charge / discharge reaction are generated, and the discharge capacity decreases. On the other hand, when (y + z + w) exceeds 1.05, the amount of Li contributing to the reaction decreases, and the discharge capacity decreases.
(D _N90 / D _N50 ) And (D _N50 / D _N10 ) Is limited to the range of 1.4 to 2 for the reason described below. (D _N90 / D _N50 ) And (D _N50 / D _N10 1) means that the particle size distribution of the nickel-based particles is monodispersed. (D _N90 / D _N50 ) And (D _N50 / D _N10 ) Less than 1.4, the particle size distribution of the nickel-based particles is narrow, so the active material filling amount of the positive electrode is insufficient and a high capacity cannot be obtained.
On the other hand, (D _N90 / D _N50 The nickel-based particles in which) exceeds 2 contain many large particles. Large particles have a large expansion and contraction associated with insertion and extraction of lithium, so that the progress of pulverization is fast. Therefore, (D _N90 / D _N50 ) Exceeds 2, the pulverization of nickel-based particles proceeds and a long life cannot be obtained.
Also, (D _N50 / D _N10 The nickel-based particles having more than 2) contain many fine particles. Since such nickel-based particles have high reactivity with respect to the non-aqueous electrolyte, the oxidative decomposition of the non-aqueous electrolyte proceeds and the charge / discharge cycle life is reduced.
(D _N90 / D _N50 ) And (D _N50 / D _N10 ) A more preferable range of each is 1.5 to 1.9.
The reason why the content of nickel-based particles in the positive electrode active material is more than 50% by weight is as follows. When the content of nickel-based particles in the positive electrode active material is 50% by weight or less, the discharge capacity (specific capacity) per unit weight decreases. However, if the content of nickel-based particles exceeds 90% by weight, a high discharge voltage and excellent large current charge / discharge characteristics may not be obtained. Therefore, the content of nickel-based particles is more than 50% by weight, It is desirable to be within the range of 90% by weight or less.
A more preferable range is 50 to 80% by weight.
{Li _a Co _b M _c O ₂ Particles (hereinafter referred to as cobalt-based particles)}
The reason why the molar ratio a of lithium is defined in the above range is for the reason described below. When the molar ratio a is less than 0.95, Li ions contributing to the charge / discharge reaction are reduced, so that the discharge capacity is lowered. On the other hand, when the molar ratio a exceeds 1.05, LiCoO ₂ Since impurities different from the structure are generated, the discharge capacity is reduced. A more preferable range of the molar ratio a is 0.97 ≦ a ≦ 1.03.
(Co)
The reason why the molar ratio b of cobalt is defined within the above range is for the reason described below. When the molar ratio b is less than 0.95, since the (a / b) ratio is relatively large, Li ions contributing to the charge / discharge reaction are reduced, and the discharge capacity is reduced. On the other hand, when the molar ratio b exceeds 1.05, since the (a / b) ratio is relatively small, impurities not involved in charge / discharge are generated and the discharge capacity is reduced. A more preferable range of the molar ratio b is 0.97 ≦ b ≦ 1.03.
(Element M)
The element M plays a role of strengthening the structure for suppressing or controlling the decomposition reaction of the nonaqueous electrolyte and suppressing the decomposition of the crystal structure due to the charge / discharge cycle. Moreover, when the valence of the element M does not change with respect to charging / discharging, since the crystal structure is strengthened, cycle characteristics are improved. However, when the molar ratio c exceeds 0.05, the amount of Co is relatively decreased, and the amount of Li involved in the battery reaction is insufficient, so that the discharge capacity is decreased. Therefore, the molar ratio c is desirably 0.05 or less. A more preferable range of the molar ratio c is 0.001 ≦ c ≦ 0.03.
Among the elements M, Sn is preferable. When Sn is used as the element M, the charge / discharge cycle life in a high temperature environment can be improved. This is presumed to be because the reaction of forming a protective coating derived from EC on the surface of the positive electrode is promoted, and the reaction between the positive electrode and γ-butyllactone in a high temperature environment (around 45 ° C.) is suppressed. The Li _a Co _b Sn _c O ₂ The particles are Li _a Co _b O ₂ And Li ₂ SnO ₃ And a mixture.
The reason why the total (b + c) of the molar ratios b and c is defined within the above range will be described. When (b + c) is less than 0.95, the Li ratio in the particles increases, so that impurities that do not contribute to the charge / discharge reaction are generated, and the discharge capacity decreases. On the other hand, when (b + c) exceeds 1.05, the amount of Li contributing to the reaction decreases, and the discharge capacity decreases.
(D _C90 / D _C50 ) And (D _C50 / D _C10 ) Is limited to the range of 1.4 to 2 for the reason described below. (D _C90 / D _C50 ) And (D _C50 / D _C10 ) Of 1 means that the particle size distribution of the cobalt-based particles is monodispersed. (D _C90 / D _C50 ) And (D _C50 / D _C10 ) Less than 1.4, the particle size distribution of the cobalt-based particles is narrow, so that the active material filling amount of the positive electrode is insufficient and a high capacity cannot be obtained.
On the other hand, (D _C90 / D _C50 The cobalt-based particles in which) exceeds 2 contain many large particles. Since such cobalt-based particles have a low lithium diffusion rate, the large current charge / discharge characteristics are deteriorated.
Also, (D _C50 / D _C10 The cobalt-based particles in which) exceeds 2 contain many fine particles. Since such cobalt-based particles have high reactivity with the non-aqueous electrolyte, the oxidative decomposition of the non-aqueous electrolyte proceeds and the charge / discharge cycle life is reduced.
(D _C90 / D _C50 ) And (D _C50 / D _C10 ) A more preferable range of each is 1.5 to 1.9.
D of cobalt-based particles _C50 Is preferably in the range of 0.2 μm or more and 30 μm or less. This is due to the following reason. D _C50 If the thickness is less than 0.2 μm, the crystal growth of the cobalt-based particles is insufficient and there is a possibility that a sufficient discharge capacity cannot be obtained. On the other hand, D _C50 When the thickness exceeds 30 μm, it is difficult to obtain a uniform positive electrode surface during the production of the positive electrode, and since the particle size is large, the surface area per volume is reduced and the reactivity is lowered. D _C50 The more preferable range is 1 μm or more and 15 μm or less.
When the nickel-based particles and cobalt-based particles described above satisfy the relationships (1) to (4) described above for the volume accumulation frequencies of 10%, 50%, and 90%, the particle diameter D (D _N50 / D _C50 ) Will be described in the range of 1.5 to 2.5. (D _N50 / D _C50 ) Is 1 or more and less than 1.5, the similarity between the nickel particle size distribution and the cobalt particle size distribution is high. It becomes difficult to suppress, and the charge / discharge cycle life is reduced. Further, the cobalt-based particles can make the average discharge voltage higher than that of the nickel-based particles, and can easily occlude / release lithium from the initial stage of discharge. (D _N50 / D _C50 ) Is smaller than 1, since the particle size distribution of the cobalt-based particles is larger than the particle size distribution of the nickel-based particles, the lithium diffusion rate of the cobalt-based particles is impaired, and the large current charge / discharge characteristics are to degrade.
(D _N50 / D _C50 ) Exceeds 2.5, the particle size distribution of the nickel-based particles is significantly larger than the particle size distribution of the cobalt-based particles, so the difference between the reactivity of the nickel-based particles and the reactivity of the cobalt-based particles is Become prominent. As a result, the charge / discharge reaction tends to occur non-uniformly in the positive electrode, so that the charge / discharge cycle life is reduced. In addition, when a paste is prepared using such a positive electrode active material, the dispersibility or coating property of the paste is impaired, so that it is difficult to obtain a positive electrode with stable quality. (D _N50 / D _C50 ) Is more preferably 1.6 to 2.4.
The positive electrode active material may be one type of nickel-based particles and one type of cobalt-based particles. However, two or more types of nickel-based particles having different compositions may be used, or two or more types of cobalt-based particles having different compositions. May be used.
The said positive electrode is produced by the method demonstrated to the following (i)-(iii), for example.
(I) The positive electrode active material, the conductive agent and the binder are suspended in an appropriate solvent, and the resulting mixture slurry is applied to a current collector, dried, pressed, and cut into a desired size By doing so, a positive electrode is obtained. At this time, the application amount of the slurry per one side of the current collector is 100 to 400 g / m. ² It is preferable to be within the range.
(Ii) A positive electrode is obtained by kneading a positive electrode active material, a conductive agent and a binder, molding the resulting mixture into a pellet, and then crimping the resulting pellet to a current collector.
(Iii) A positive electrode is obtained by kneading a positive electrode active material, a conductive agent, and a binder, molding the resulting mixture into a sheet, and then pressure bonding the obtained sheet to a current collector.
Examples of the conductive agent include carbon black such as acetylene black and ketjen black, graphite, and the like.
Examples of the binder include polyvinylidene fluoride (PVdF), and monomer components such as vinylidene fluoride (VdF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), perfluoro An alkyl vinyl ether (PFA), a copolymer containing ethylene, a terpolymer or the like can be used.
The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 10% by weight of the conductive agent, and 2 to 10% by weight of the binder.
As the current collector, for example, an aluminum foil, a stainless steel foil, or a titanium foil can be used, but an aluminum foil is most preferable in view of tensile strength, electrochemical stability, flexibility during winding, and the like. The thickness of the foil at this time is preferably 10 μm or more and 30 μm or less. In addition to the foil-like current collector, a perforated current collector such as a punched metal or an expanded metal may be used.
2) Negative electrode
The negative electrode includes a current collector and a negative electrode layer carried on one side or both sides of the current collector.
The negative electrode layer contains lithium ions or compounds that occlude and release lithium atoms. Examples of such compounds include conductive polymers (eg, polyacetal, polyacetylene, polypyrrole, etc.), carbon materials such as organic sintered bodies, and the like.
The characteristics of the carbon material can be adjusted by the type of raw material and the sintering method. Specific examples of the carbon material include a graphite-based carbon material, a carbon material in which a graphite crystal part and an amorphous part are mixed, and a carbon material having a turbulent structure with no regularity in the lamination of crystal layers. .
The said negative electrode is produced by the method demonstrated to the following (I)-(III), for example.
(I) Lithium ions or a compound that occludes / releases lithium atoms and a binder are suspended in a suitable solvent, and the resulting mixture slurry is applied to a current collector, dried, and then pressed. A negative electrode is obtained by cutting into a desired size. At this time, the amount of slurry applied to one side of the current collector is 50 to 200 g / m. ² It is preferable to be within the range.
(II) After kneading lithium ion or a compound that occludes / releases lithium atoms and a binder, and molding the resulting mixture into a pellet, the resulting pellet is pressure-bonded to a current collector. obtain.
(III) A compound that occludes / releases lithium ions or a lithium atom and a binder are kneaded, and the resulting mixture is molded into a sheet shape. obtain.
Examples of the binder include the same ones as described for the positive electrode.
As the current collector of the negative electrode, for example, a copper foil, a nickel foil or the like can be used. In view of electrochemical stability and flexibility, copper foil is most preferred. The thickness of the foil at this time is preferably 8 μm or more and 20 μm or less. In addition to the foil-like current collector, a perforated current collector such as a punched metal or an expanded metal may be used.
3) Non-aqueous electrolyte
As the non-aqueous electrolyte, those having a substantially liquid or gel-like form can be used. The liquid nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent. On the other hand, the gel-like non-aqueous electrolyte contains a liquid non-aqueous electrolyte and a gelling agent that gels the liquid non-aqueous electrolyte. Examples of the gelling agent include polyethylene oxide and polyacrylonitrile.
Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), diethoxyethane (DEE), and γ-butyl. Examples include lactone (γ-BL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane, 1,3-dimethoxypropane, and the like. The kind of non-aqueous solvent to be used can be one kind or two or more kinds.
Examples of the electrolyte include lithium perchlorate (LiClO). ₄ ), Lithium tetrafluoroborate (LiBF) ₄ ), Lithium hexafluoroarsenide (LiAsF) ₆ ), Lithium trifluoromethanesulfonate (LiCF) ₃ SO ₃ ), Bistrifluoromethylsulfonylimide lithium [(LiN (CF ₃ SO ₂ ) ₂ ], LiN (C ₂ F ₅ SO ₂ ) ₂ And lithium salts such as lithium aluminum tetrachloride. The type of electrolyte used can be one type or two or more types.
The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 1.5 mol / L.
4) Separator
This separator is formed from a porous sheet.
For example, a porous film or a non-woven fabric can be used as the porous sheet. The porous sheet is preferably made of at least one material selected from, for example, polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.
5) Container
The shape of the container can be, for example, a bottomed cylindrical shape, a bottomed rectangular tube shape, a bag shape, a cup shape, or the like.
The container can be formed of, for example, a resin, a sheet including a resin layer, a metal plate, a metal film, or the like.
Examples of the resin include polyolefin such as polyethylene and polypropylene, nylon, and the like.
The resin layer included in the sheet can be formed from, for example, polyethylene, polypropylene, nylon, or the like. As the sheet, it is preferable to use a sheet in which a metal layer and protective layers disposed on both sides of the metal layer are integrated. The metal layer is made of, for example, aluminum, stainless steel, iron, copper, nickel or the like. Among these, aluminum that is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, but may be formed from a combination of two or more types of metals. Of the two protective layers, the protective layer in contact with the outside serves to prevent damage to the metal layer. This external protective layer is formed of one type of resin layer or two or more types of resin layers. On the other hand, the internal protective layer plays a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective phase is formed of one type of resin layer or two or more types of resin layers. In addition, a thermoplastic resin can be disposed on the surface of the internal protective layer.
The metal plate and the metal film can be formed of, for example, iron, stainless steel, or aluminum.
A thin nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view showing a thin non-aqueous electrolyte secondary battery which is an example of a non-aqueous electrolyte secondary battery according to the present invention, and FIG. 2 is an enlarged cross-sectional view showing part A of FIG. As shown in FIG. 1, an electrode group 2 is accommodated in the container 1. The electrode group 2 has a structure in which a laminate composed of a positive electrode, a separator, and a negative electrode is wound into a flat shape. As shown in FIG. 2, the laminate includes a separator 3, a positive electrode layer 4 having a positive electrode layer 4, a positive electrode current collector 5, and a positive electrode layer 4, a separator 3, a negative electrode layer 7, and a negative electrode. Negative electrode 9 including current collector 8 and negative electrode layer 7, separator 3, positive electrode layer 4, positive electrode 6 including positive electrode current collector 5 and positive electrode layer 4, separator 3, negative electrode layer 7 and negative electrode current collector 8 And the negative electrode 9 having the above structure is laminated in this order. One end of the strip-like positive electrode lead 10 is connected to the positive electrode current collector 5 of the positive electrode group 2, and the other end is extended from the container 1. On the other hand, one end of the strip-like negative electrode lead 11 is connected to the negative electrode current collector 8 of the negative electrode group 2 and the other end is extended from the container 1.
In addition, in FIG. 1 and FIG. 2 described above, the electrode group in which the positive electrode and the negative electrode are wound in a flat shape with a separator interposed therebetween is used, but the electrode group by folding the positive electrode and the negative electrode with a separator interposed therebetween, An electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween may be used.
Moreover, the example which applied this invention to the square nonaqueous electrolyte secondary battery is shown in FIG.
As shown in FIG. 3, an electrode group 13 is accommodated in a bottomed rectangular cylindrical container 12 made of metal such as aluminum. In the electrode group 13, a positive electrode 14, a separator 15 and a negative electrode 16 are laminated in this order and wound in a flat shape. A spacer 17 having an opening near the center is disposed above the electrode group 13.
The nonaqueous electrolyte is held in the electrode group 13. A sealing plate 18 b having an explosion-proof mechanism 18 a and having a circular hole opened near the center is laser welded to the opening of the container 12. The negative electrode terminal 19 is disposed in a circular hole of the sealing plate 18b via a hermetic seal. The negative electrode tab 20 drawn out from the negative electrode 16 is welded to the lower end of the negative electrode terminal 19. On the other hand, a positive electrode tab (not shown) is connected to a container 12 that also serves as a positive electrode terminal.
The positive electrode active material of the non-aqueous electrolyte secondary battery according to the present invention described above is Li _a Co _b M _c O ₂ Particles (cobalt-based particles) and Li over 50% by weight _x Ni _y Co _z M _w O ₂ Particles (nickel-based particles) and satisfy the above-mentioned formulas (1) to (5).
According to such a secondary battery, it is possible to improve the positive electrode active material filling density and the charge / discharge cycle life while securing a high discharge voltage and excellent large current charge / discharge characteristics.
That is, the discharge capacity (specific capacity) per unit weight can be improved by increasing the content of nickel-based particles in the positive electrode active material to more than 50% by weight.
In addition, (D _N90 / D _N50 ) Within the range of 1.4 to 2, among the nickel-based particles, particles that are extremely large in expansion and contraction associated with insertion and extraction of lithium can be reduced. On the other hand, (D _C90 / D _C50 ) Within the range of 1.4 to 2 can ensure a high lithium diffusion rate in the positive electrode active material.
(D of nickel-based particles _N50 / D _N10 ) And cobalt-based particles (D _C50 / D _C10 ) Within the range of 1.4 to 2, the reactivity of the positive electrode active material with respect to the non-aqueous electrolyte can be lowered, so that the oxidative decomposition of the non-aqueous electrolyte can be suppressed.
In addition, (D _N50 / D _C50 ) Within the range of 1.5 to 2.5, the particle size distribution of the positive electrode active material can have an appropriate width, so that the packing density of the positive electrode active material can be improved. At the same time, the expansion and contraction associated with the lithium occlusion / release of the nickel-based particles can be suppressed by the cobalt-based particles having a smaller degree of expansion and contraction, so that the pulverization of the nickel-based particles can be suppressed.
Therefore, according to the present invention, it is possible to realize a nonaqueous electrolyte secondary battery that simultaneously satisfies the discharge voltage, specific capacity, large current charge / discharge characteristics, active material packing density, and charge / discharge cycle life.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<Measurement of specific capacity of positive electrode (mAh / g)>
First, LiCoO, which is a cobalt-based particle ₂ Particles and nickel-based particles LiNi _0.81 Co _0.19 O ₂ Particles were mixed at a weight ratio shown in Table 1 below to prepare Samples 1 to 7.
Working electrodes were prepared using Samples 1 to 7 as active materials. That is, 0.03 part by weight of polytetrafluoroethylene (PTFE), 0.06 part by weight of acetylene black (AB), and 1 part by weight of an active material were kneaded in an agate mortar, formed into a sheet with a roller press, and then a nickel mesh. A 1 cm × 1 cm working electrode containing about 0.05 g of an active material was produced.
The Li foil was pressed onto a nickel net to produce a 2 cm × 2 cm counter electrode and a 0.5 cm × 0.5 cm reference electrode. A cell was produced by arranging the working electrode and the counter electrode so as to face each other with a glass filter interposed therebetween, and arranging the reference electrode so as not to contact the counter electrode and the working electrode.
The cell is connected to a glass container that can be energized through a metallic wire, and a non-aqueous electrolyte (ethylene carbonate (EC) and γ-butyllactone are mixed at a volume ratio of 1: 2 until the cell is immersed) LiBF in water solvent ₄ And 1.5 mol / L was dissolved) and sealed. The work was performed inside a glove box with a dew point of −80 ° C.
Charging was performed at a constant current of 1 mA up to 4.25 V, and charging was performed at a constant voltage of 4.25 V after reaching 4.25 V. The total time for constant current charging and constant voltage charging was 20 hours. The discharge was performed at 1.0 mA, and the discharge amount until reaching 3.0 V was defined as the discharge capacity. A value obtained by dividing the discharge capacity by the weight of the active material in the working electrode is shown in Table 1 as specific capacity (mAh / g). Table 1 also shows 1 g of LiCoO. ₂ The weights of the samples 1 to 7 that can obtain the same discharge capacity as the discharge capacity are also shown.

As is apparent from Table 1, Samples 1 to 4 in which the amount of nickel-based particles is more than 50% by weight can have a higher discharge capacity (mAh / g) than Samples 5 to 7, and LiCoO ₂ It can be seen that a high discharge capacity can be obtained with a small amount as compared with (Sample 7).
In the following examples, in order to reduce the influence caused by the difference in specific capacity due to the difference in the mixing ratio between cobalt-based particles and nickel-based particles, the coating amount of the negative electrode is made constant and the mixing ratio of the positive electrode active material is adjusted. Batteries were produced by changing the positive electrode coating amount (positive electrode active material content).

<Preparation of positive electrode>
As the cobalt-based particles, LiCoO having a volume cumulative frequency 10% particle diameter D _C10 of 1.9 μm, a volume cumulative frequency 50% particle diameter D _C50 of 3.3 μm, and a volume cumulative frequency 90% particle diameter D _C90 of 5.7 μm. _Two particles were prepared. Further, as the nickel-based particles, the volume cumulative frequency 10% particle diameter _{D N10} is 4 [mu] m, a volume cumulative frequency 50% particle diameter _{D N50} is 7 [mu] m, LiNi volume cumulative frequency 90% particle diameter _{D N90} is 11.6 _{0. 81} Co _0.19 O ₂ particles were prepared.
Table 2 shows (D _N50 / D _N10 ), (D _N90 / D _N50 ), (D _C50 / D _C10 ), (D _C90 / D _C50 ), and (D _N50 / D _C50 ).
The volume cumulative frequencies of 10%, 50%, and 90% were measured by the method described below. That is, the particle size for each of the nickel-based particles and the cobalt-based particles and the occupied volume of the particles in each particle size interval are measured by a laser diffraction / scattering method. When the volume of the particle size interval is 10% of the total, the particle size is 10% of the volume cumulative frequency, the particle size of 50% is the volume cumulative frequency of 50%, and 90%. The particle diameter is set to a volume cumulative frequency of 90%.
First, 3 parts by weight of polyvinylidene fluoride (trade name: # 1100, manufactured by Kureha Chemical Industry) was dissolved in 25 parts by weight of N-methylpyrrolidone. A mixture of 8.9 parts by weight of the LiCoO ₂ particles and 80.1 parts by weight of the LiNi _0.81 Co _0.19 O ₂ particles is used as a positive electrode active material, and this positive electrode active material and a conductive material are used. 8 parts by weight of graphite (trade name: KS6 manufactured by Lonza) was added to the polyvinylidene fluoride solution, and the mixture was stirred and mixed using a dissolver and a bead mill to prepare a positive electrode slurry. This slurry was applied to both sides of a 15 μm thick aluminum foil using a die coater at regular intervals, dried, pressed at a constant linear pressure (kgf / cm), and slitted to obtain a reel-like positive electrode. . The density per unit volume of the active material (active material density: g / cm ³ ) was calculated from the thickness of the positive electrode layer, and the results are shown in Table 3 below.
In Table 2, the weight ratio W _N (% by weight) of LiNi _0.81 Co _0.19 O ₂ particles and the weight ratio Wc (% by weight) of LiCoO ₂ particles are also shown.
<Production of negative electrode>
10 parts by weight of graphite powder (trade name: KS15, manufactured by Lonza) is added to 100 parts by weight of mesophase pitch-based carbon fiber powder (manufactured by Petka) and mixed. Further, styrene / butadiene latex (product of Asahi Kasei Kogyo Co., Ltd.) Name L1571, solid content is 48 wt%) 4.2 parts by weight, carboxymethylcellulose (Daiichi Kogyo Seiyaku brand name BSH12) aqueous solution (solid content 1 wt%) 130 parts by weight as a thickener, distilled water 20 Part by weight was added and mixed to prepare a slurry.
This slurry was applied to both sides of a copper foil having a thickness of 10 μm with a die coater at regular intervals, dried, pressed and slitted to obtain a reel-shaped negative electrode.
<Preparation of non-aqueous electrolyte>
A nonaqueous electrolytic solution was obtained by dissolving LiBF _{4 in} a nonaqueous solvent in which ethylene carbonate (EC) and γ-butyllactone (GBL) were mixed at a volume ratio of 1: 2 to 1.5 mol / L.
<Battery assembly>
The positive electrode made of polypropylene, in which an aluminum ribbon having a thickness of 100 μm and a length of 70 mm is ultrasonically welded to a predetermined position in advance as a current collector tab of the positive electrode, and a polyimide protective tape for preventing a short circuit is attached to the welding site A separator and a negative electrode current collecting tab were previously ultrasonically welded at predetermined positions with a nickel ribbon having a thickness of 100 μm and a length of 70 mm, and a protective tape made of polyimide was applied to the welded portion to prevent a short circuit. After laminating in this order, it was wound into a flat shape and pressed at 90 ° C. for 30 seconds to produce an electrode group.
On the other hand, a container formed by cup-forming a 0.1 mm thick laminate film in which the electrode group side of the aluminum foil was coated with polyethylene and the outside was coated with nylon was prepared.
The electrode group and the electrolyte solution were housed in the container, and a thin non-aqueous electrolyte secondary battery (width 35 mm, length 62 mm) was assembled by heat sealing. The liquid injection process to the sealing process were performed in a glove box controlled at a dew point of −80 ° C. in an Ar atmosphere.

Example 1 described above except that the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight and the amount of LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight. A thin nonaqueous electrolyte secondary battery was produced in the same manner as described.

Example 1 described above except that the amount of LiCoO ₂ particles in the positive electrode is 35.6 parts by weight and the amount of LiNi _0.81 Co _0.19 O ₂ particles is 53.4 parts by weight. A thin nonaqueous electrolyte secondary battery was produced in the same manner as described.

As nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having DN ₁₀ of 5.3 μm, DN ₅₀ of 7.7 μm, and DN ₉₀ of 11.1 μm were used, and the LiCoO ₂ particles in the positive electrode Except that the blending amount is 26.7 parts by weight and the blending amount of the LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight, it is the same as described in Example 1 above. A thin non-aqueous electrolyte secondary battery was manufactured.

As the nickel-based _particles, in _{D N10} is 3.3 [mu] _{m, D N50} is at 6.5 [mu] _m, with _{D N90} is used _LiNi 0.81 _{Co 0.19} O ₂ particles 12.5 .mu.m, the LiCoO ₂ particles Seikyokuchu Except that the blending amount is 26.7 parts by weight and the blending amount of the LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight, it is the same as described in Example 1 above. A thin non-aqueous electrolyte secondary battery was manufactured.

As the cobalt-based particles, LiCoO ₂ particles having DC ₁₀ of 2.7 μm, DC ₅₀ of 3.9 μm, and DC ₉₀ of 5.8 μm are used, and the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight. And a thin non-aqueous electrolyte secondary battery in the same manner as described in Example 1 except that the blending amount of LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight. Manufactured.

As the cobalt-based particles, LiCoO ₂ particles having DC ₁₀ of 1.6 μm, DC ₅₀ of 3 μm, and DC ₉₀ of 5.7 μm are used, and the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight, A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of LiNi _0.81 Co _0.19 O ₂ particles was 62.3 parts by weight. .

As nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having DN ₁₀ of 4.7 μm, DN ₅₀ of 8 μm, and DN ₉₀ of 13.6 μm were used, and the amount of LiCoO ₂ particles contained in the positive electrode Is 26.7 parts by weight, and the amount of LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight. A water electrolyte secondary battery was manufactured.

As nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having DN ₁₀ of 2.9 μm, DN ₅₀ of 5.2 μm, and DN ₉₀ of 8.9 μm were used, and LiCoO ₂ particles in the positive electrode were used. Except that the blending amount is 26.7 parts by weight and the blending amount of the LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight, it is the same as described in Example 1 above. A thin non-aqueous electrolyte secondary battery was manufactured.

As the cobalt-based _particles, in _{D C10} is 1.9 _.mu.m, with _{D C50} is 3.3 [mu] _m, when _{D C90} is obtained by the _LiCo 0.97 _{Sn 0.03} O ₂ particles (LiCoO ₂ 100 parts by weight of 5.7 .mu.m 3 1 part by weight of Li ₂ SnO ₃ ), the amount of LiCo _0.97 Sn _0.03 O ₂ particles in the positive electrode is 26.7 parts by weight, and LiNi _0.81 Co _0.19 A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the amount of O ₂ particles was 62.3 parts by weight.

The nickel-based particles are LiNi _0.78 Co _0.18 Sn _0.03 O ₂ particles (LiNi _0.81 Co _0.19 O _{2) having} DN ₁₀ of 4 μm, DN ₅₀ of 7 μm, and DN ₉₀ of 11.6 μm. (Mixture containing 3.1 parts by weight of Li ₂ SnO ₃ when using 100 parts by weight), the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight, and LiNi _0.78 Co _{0. A} thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of ₁₈ Sn _0.03 O ₂ particles was 62.3 parts by weight.

Example 1 described above, except that LiNi _0.76 Co _0.18 Al _0.06 O ₂ particles having DN ₁₀ of 4 μm, DN ₅₀ of 7 μm, and DN ₉₀ of 11.6 μm are used as nickel-based particles. A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described above.

表２、表３から明らかなように、実施例１〜１３の二次電池は、活物質密度、エネルギー密度および充放電サイクル寿命が比較例１〜７と比較して高いことがわかる。
これに対し、リチウムニッケルコバルト複合酸化物のみを正極活物質として用いる比較例１の二次電池は、充放電サイクル寿命が著しく低かった。正極活物質中のリチウムニッケルコバルト複合酸化物の含有量が５０重量％以下である比較例２の二次電池と、リチウムコバルト複合酸化物のみを活物質として用いる比較例７の二次電池は、放電時の平均作動電圧が高くなるものの、充放電サイクル寿命が短くなった。
（Ｄ_Ｃ５０／Ｄ_Ｃ１０）と（Ｄ_Ｃ９０／Ｄ_Ｃ５０）が１．４〜２の範囲を外れる比較例３、４の二次電池と、（Ｄ_Ｎ５０／Ｄ_Ｃ５０）が１．５〜２．５の範囲を外れる比較例５，６の二次電池は、活物質密度、１Ｃ容量、エネルギー密度及び充放電サイクル寿命のいずれもが実施例１〜１３に比較して低かった。
なお、前述した実施例においては、ＬｉＣｏＯ_２粒子とＬｉＮｉ_０．８１Ｃｏ_０．１９Ｏ_２粒子の２種類からなる正極活物質に適用した例を説明したが、正極活物質としては、充放電サイクル寿命を改善できる限り、ＬｉＣｏＯ_２粒子とＬｉＮｉ_０．８１Ｃｏ_０．１９Ｏ_２粒子にＬｉＭｎ_２Ｏ_４のような他の種類の粒子を混合させた３種類以上の粒子からなるものを用いることができる。
また、前述した実施例においては、薄型非水電解質二次電池および角形非水電解質二次電池に適用した例を説明したが、円筒形非水電解質二次電池、コイン型非水電解質二次電池にも同様に適用することができる。Example 1 described above, except that LiNi _0.76 Co _0.18 Mn _0.06 O ₂ particles having DN ₁₀ of 4 μm, DN ₅₀ of 7 μm, and DN ₉₀ of 11.6 μm are used as nickel-based particles. A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described above.
<Comparative example 1>
Explained in Example 1 above, except that only the LiNi _0.81 Co _0.19 O ₂ particles having DN ₁₀ of 4 μm, DN ₅₀ of 7 μm and DN ₉₀ of 11.6 μm were used as the positive electrode active material. A thin non-aqueous electrolyte secondary battery was produced in the same manner as described above.
<Comparative example 2>
Example 1 described above except that the amount of LiCoO ₂ particles in the positive electrode is 53.4 parts by weight and the amount of LiNi _0.81 Co _0.19 O ₂ particles is 35.6 parts by weight. A thin nonaqueous electrolyte secondary battery was produced in the same manner as described.
<Comparative Example 3>
As the cobalt-based particles, LiCoO ₂ particles having DC ₁₀ of 2.7 μm, DC ₅₀ of 3.4 μm, and DC ₉₀ of 4.3 μm are used, and the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight. And a thin non-aqueous electrolyte secondary battery in the same manner as described in Example 1 except that the blending amount of LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight. Manufactured.
<Comparative example 4>
As the cobalt-based particles, LiCoO ₂ particles having DC ₁₀ of 1.5 μm, DC ₅₀ of 3.5 μm, and DC ₉₀ of 8.4 μm are used, and the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight. And a thin non-aqueous electrolyte secondary battery in the same manner as described in Example 1 except that the blending amount of LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight. Manufactured.
<Comparative Example 5>
As the cobalt-based particles, LiCoO ₂ particles having DC ₁₀ of 3.8 μm, DC ₅₀ of 6.1 μm, and DC ₉₀ of 10 μm are used, and the amount of LiCoO ₂ particles in the positive electrode is 26.7 parts by weight, A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of LiNi _0.81 Co _0.19 O ₂ particles was 62.3 parts by weight. .
<Comparative Example 6>
As the cobalt-based particles, LiCoO ₂ particles having a DC ₁₀ of 1.5 μm, a DC ₅₀ of 2.6 μm, and a DC ₉₀ of 4.5 μm are used, and the amount of the LiCoO ₂ particles in the positive electrode is 26.7 parts by weight. And a thin non-aqueous electrolyte secondary battery in the same manner as described in Example 1 except that the blending amount of LiNi _0.81 Co _0.19 O ₂ particles is 62.3 parts by weight. Manufactured.
<Comparative Example 7>
As the positive electrode active _material, in _{D C10} is 1.9 _.mu.m, with _{D C50} is 3.3 [mu] _m, but using _{D C90} only LiCoO ₂ particles 5.7 .mu.m, in a similar manner as described in Example 1 above A thin non-aqueous electrolyte secondary battery was manufactured.
For the obtained secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 7, 0.2 C capacity, 1 C capacity, battery thickness, average discharge voltage, energy density, and cycle life were measured by the method described below. The results are shown in Table 3 below.
<Rated capacity>
The assembled secondary battery was initially charged at a constant current of 140 mA (equivalent to 0.2 CmA) up to 4.2 V at 20 ° C., and after reaching 4.2 V, the battery was initially charged at a constant voltage for a total of 12 hours. The discharge capacity when discharged at a constant current of 140 mA up to 3.0 V was measured to obtain the rated capacity at 0.2 C discharge. The results are shown in Table 3 below.
<1.0C discharge capacity>
After charging at a constant current of 140 mA up to 4.2 V, charge for a total of 12 hours at a constant voltage of 4.2 V, and then discharge at a constant current of 1 CmA (700 mA) up to 3.0 V. The capacity was measured at 1.0 C discharge, and the results are shown in Table 3 below.
<Battery thickness measurement / energy density>
After charging to 4.2 V at a constant current of 140 mA, charging was further performed at a constant voltage of 4.2 V for a total of 12 hours, and the thickness of the battery at the time of 4.2 V was measured. The average voltage was obtained from the integrated value of the discharge curve up to 3.0 V at 0.2 CmA (140 mA). The volume energy density was determined from the width (35 mm) and length (62 mm) of the battery excluding the positive and negative current collecting tabs, the measured battery thickness, and the average voltage. The results are shown in Table 3.
<Cycle life>
Charging was performed at a constant current of 1 C (700 mA) up to 4.2 V, and after reaching 4.2 V, charging was performed at a constant voltage for a total of 3 hours, and discharging was performed at 1 C up to 3.0 V. The number of cycles at which the discharge capacity reached 80% of the discharge capacity at the first cycle was measured, and the results are shown in Table 3 below as the cycle life.

As is apparent from Tables 2 and 3, the secondary batteries of Examples 1 to 13 have higher active material density, energy density, and charge / discharge cycle life than those of Comparative Examples 1 to 7.
In contrast, the secondary battery of Comparative Example 1 using only the lithium nickel cobalt composite oxide as the positive electrode active material had a remarkably low charge / discharge cycle life. The secondary battery of Comparative Example 2 in which the content of the lithium nickel cobalt composite oxide in the positive electrode active material is 50% by weight or less, and the secondary battery of Comparative Example 7 using only the lithium cobalt composite oxide as an active material, Although the average operating voltage during discharge increased, the charge / discharge cycle life decreased.
The secondary battery of Comparative Examples 3 and 4 in which (D _C50 / D _C10 ) and (D _C90 / D _C50 ) are out of the range of 1.4 to 2, and (D _N50 / D _C50 ) is 1.5 to 2. In the secondary batteries of Comparative Examples 5 and 6 outside the range of 5, all of the active material density, 1C capacity, energy density, and charge / discharge cycle life were lower than those of Examples 1-13.
In the embodiment described above, a description has been given of an example of applying the positive electrode active material made of two kinds of LiCoO ₂ particles and _LiNi 0.81 _{Co 0.19} O ₂ particles, as the positive electrode active material, the charge-discharge cycle As long as the lifespan can be improved, it is necessary to use a material composed of three or more kinds of particles obtained by mixing LiCoO ₂ particles and LiNi _0.81 Co _0.19 O ₂ particles with other kinds of particles such as LiMn ₂ O _4. it can.
In the above-described embodiments, examples of applying to a thin nonaqueous electrolyte secondary battery and a rectangular nonaqueous electrolyte secondary battery have been described. However, a cylindrical nonaqueous electrolyte secondary battery and a coin-type nonaqueous electrolyte secondary battery are described. It can be similarly applied to.

  As described above in detail, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having an improved charge / discharge cycle life.

Claims (7)

A non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte,
The positive electrode active material includes oxide particles represented by the following formula (A) and oxide particles represented by the following formula (B), and the oxide particles represented by the formula (A) in the positive electrode active material The ratio exceeds 50% by weight, and the positive electrode active material satisfies the following formulas (1) to (5).
_{Li x Ni y Co z M w} O 2 (A)
_{Li a Co b M c O 2} (B)
However, said M is one or more elements selected from the group consisting of Mn, B, Al and Sn, and said molar ratios x, y, z, w, a, b, c are 0. 95 ≦ x ≦ 1.05, 0.7 ≦ y ≦ 0.95, 0.05 ≦ z ≦ 0.3, 0 ≦ w ≦ 0.1, 0.95 ≦ y + z + w ≦ 1.05, 0.95 ≦ a ≦ 1.05, 0.95 ≦ b ≦ 1.05, 0 ≦ c ≦ 0.05, 0.95 ≦ b + c ≦ 1.05,
1.4 ≦ (D _N90 / D _N50 ) ≦ 2 (1)
1.4 ≦ (D _N50 / D _N10 ) ≦ 2 (2)
1.4 ≦ (D _C90 / D _C50 ) ≦ 2 (3)
1.4 ≦ (D _C50 / D _C10 ) ≦ 2 (4)
1.5 ≦ (D _N50 / D _C50 ) ≦ 2.5 (5)
However, the _{D N10,} the _{D N50,} the _{D N90 is, Li x Ni y Co z M} w volume cumulative frequency of _{O 2} particles of 10%, 50%, showed a particle size of 90%, the _{D C10,} the D _C50 and D _C90 indicate particle diameters of Li _a Co _b M _c O ₂ particles with a volume cumulative frequency of 10%, 50%, and 90%. The _Li a _Co b _M c _{O 2} wherein _{D C50} of the particles, the non-aqueous electrolyte secondary battery according to claim 1, wherein in the range of 0.2Myuemu～30myuemu. The nonaqueous electrolyte secondary battery according to claim 1, wherein a particle size ratio (D _N90 / D _N50 ) is 1.5 or more and 1.9 or less. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a particle size ratio (D _N50 / D _N10 ) is 1.5 or more and 1.9 or less. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a particle size ratio (D _C90 / D _C50 ) is 1.5 or more and 1.9 or less. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a particle size ratio (D _C50 / D _C10 ) is 1.5 or more and 1.9 or less. The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the oxide particles represented by the formula (A) in the positive electrode active material is more than 50 wt% and 90 wt% or less.

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