KR100841136B1 - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte including a positive electrode active material, a conductive agent and a binder.

The positive electrode active material includes an oxide particle represented by Chemical Formula 1 and an oxide particle represented by Chemical Formula 2, wherein a proportion of the oxide particles represented by Chemical Formula 1 in the positive electrode active material is greater than 50 wt%, and the positive electrode active material is Is characterized in that a nonaqueous electrolyte secondary battery satisfying Equations 1 to 5 is provided.

(Formula 1)

(Formula 2)

(Equation 1)

(Equation 2)

(Equation 3)

(Equation 4)

(Equation 5)

Description

Non-aqueous electrolyte secondary battery {NONAQUEOUS ELECTROLYTE SECONDARY CELL}

The present invention relates to a nonaqueous electrolyte secondary battery.

In recent years, with the miniaturization and weight reduction of electronic devices such as VTRs, cellular phones, and mobile computers, it is desired to increase the energy density of secondary batteries as its power sources. In this regard, studies on nonaqueous electrolyte secondary batteries using lithium as a negative electrode have been actively conducted, and lithium ion secondary batteries using LiCoO ₂ as a cathode active material have already been put into practical use.

By the way, the compound which occludes-releases lithium, a lithium alloy, or lithium is used for the negative electrode of a nonaqueous electrolyte secondary battery. As the nonaqueous electrolyte, one in which a lithium salt (electrolyte) is dissolved in a nonaqueous solvent is widely used. As such a non-aqueous solvent, propylene carbonate (PC), ethylene carbonate (EC), ethylmethyl 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 , LiAlCl ₄ are known as lithium salts.

On the other hand, attention has been paid to using intercalation or doping of layered compounds as the positive electrode active material.

Among the above-mentioned layered compound insertions, the chalcogenide compounds exhibit relatively good charge and discharge cycle characteristics. However, the chalcogenide compound has a low electromotive force, and even when lithium metal is used as a negative electrode, the practical charging voltage is only about 2 V, and does not satisfy that the electromotive force, which is a characteristic of the nonaqueous electrolyte secondary battery, must be high.

Active materials using intercalation of layered compounds are present in addition to chalcogenide compounds. Among these active materials, V ₆ O ₁₃ , LiCoO ₂ , LiNiO ₂ And LiMn ₂ O ₄ using doping Metal oxide compounds such as these have attracted attention in that they have a feature of high power. In particular, the positive electrode containing LiNiO ₂ as an active material has an electromotive force of about 4V and has a large value of theoretical energy density of approximately 1 mAh / kg per positive electrode active material.

However, a nonaqueous electrolyte secondary battery having a positive electrode containing LiNiO ₂ as an active material has a problem in that the charge and discharge cycle life is low.

On the other hand, Japanese Patent Application Laid-Open No. 63-121258 discloses a non-aqueous secondary battery having a layered structure and using a composite oxide represented by general formula A _x B _y C _z D _w O ₂ as a positive electrode. Is disclosed. In the above general formula, A is at least one member selected from alkali metals, B is a transition metal, C is at least one member selected from the group of Al, In, Sn, and D is an alkali metal other than (a) A, ( b) transition metals other than B, (c) Group IIa elements, (d) Groups IIb, Group IVb, Group Vb, and Group VIb except Al, In, Sn, carbon, nitrogen, and oxygen. One or more types selected from the group of elements are shown. x, y, z and w represent the numbers 0.05? x? 1.10, 0.85? y? 1.00, 0.001? z? 0.10, and 0.001? w? 0.10, respectively.

However, the non-aqueous secondary battery described in this publication was not able to obtain sufficient cycle life.

An object of the present invention is to provide a nonaqueous electrolyte secondary battery with improved charge and discharge cycle life.

According to the present invention, in a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte containing a positive electrode active material, a conductive agent and a binder,

The positive electrode active material includes an oxide particle represented by Chemical Formula 1 and an oxide particle represented by Chemical Formula 2, and a ratio of the oxide particles represented by Chemical Formula 1 in the positive electrode active material is more than 50% by weight, and further, the positive electrode active material The nonaqueous electrolyte secondary battery satisfying the following Equations 1 to 5 is provided.

(In Formula 1 and Formula 2,

M is at least one element selected from the group consisting of Mn, B, Al and Sn,

The 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, respectively. , 0.95 <a <1.05, 0.95 <b <1.05, 0 <c <0.05, 0.95 <b + c <1.05)

(In Equations 1, 2, 3, 4, and 5,

The D _N10 , the D _N50 and the D _N90 indicate that volume cumulative frequencies of Li _x Ni _y Co _z M _w O ₂ particles are 10%, 50%, and 90% particle diameters,

The D _C10 , the D _C50, and the D _C90 indicate that volume accumulation frequencies of Li _a Co _b M _c O ₂ particles are 10%, 50%, and 90% particle diameters.)

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;

2 is an enlarged cross-sectional view showing part A of FIG. 1, and

3 is a cross-sectional view showing a rectangular nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery according to the present invention.

An example of the nonaqueous electrolyte secondary battery according to the present invention will be described.

A nonaqueous electrolyte secondary battery according to the present invention includes a container, an electrode group housed in the container and including a positive electrode and a negative electrode, and a nonaqueous electrolyte stored in the electrode group.

In the secondary battery, a separator may be disposed between the positive electrode and the negative electrode, and a gel or solid nonaqueous electrolyte layer may be used instead of the separator.

The positive electrode, the negative electrode, the separator, the nonaqueous electrolyte and the container will be described below.

1) anode

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 an oxide particle represented by Formula 1 and an oxide particle represented by Formula 2 below. The proportion of the oxide particles represented by the following Chemical Formula 1 in the positive electrode active material is more than 50% by weight.

(Formula 1)

(Formula 2)

(In Formula 1 and Formula 2,

M is at least one element selected from the group consisting of Mn, B, Al and Sn,

The 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, respectively. , 0.95 ≤ a ≤ 1.05, 0.95 ≤ b ≤ 1.05, 0 ≤ c ≤ 0.05, 0.95 ≤ b + c ≤ 1.05)

In addition, the cathode active material satisfies Equations 1 to 5.

(Equation 1)

(Equation 2)

(Equation 3)

(Equation 4)

(Equation 5)

(In Equations 1, 2, 3, 4, and 5,

The D _N10 indicates that the volume cumulative frequency of the Li _x Ni _y Co _z M _w O ₂ particles is 10% particle diameter,

The D _N50 indicates that the cumulative frequency of the Li _x Ni _y Co _z M _w O ₂ particles is 50% particle diameter,

The D _N90 indicates that the volume accumulation frequency of the Li _x Ni _y Co _z M _w O ₂ particles is 90% particle diameter,

On the other hand, the D _C10 indicates that the volume cumulative frequency of the Li _a Co _b M _c O ₂ particles is 10% particle diameter,

D _C50 indicates that the cumulative frequency of the Li _a Co _b M _c O ₂ particles is 50% particle diameter, and

D _C90 indicates that the volume cumulative frequency of the Li _a Co _b M _c O ₂ particles is 90% particle diameter.)

{Li _x Ni _y Co _z M _w O ₂ particles (hereinafter referred to as nickel-based particles)}

(Li)

The definition of the molar ratio x of lithium in the above range is based on the reason described below. When the molar ratio (x) is less than 0.95, Li ions that contribute to charge and discharge reactions are reduced and the discharge capacity is lowered. On the other hand, when the molar ratio x exceeds 1.05, mixing of Li ions into the Ni site occurs, so that the discharge capacity is lowered. In addition, since the reactivity decreases due to the change in crystal structure, the discharge voltage decreases. As for the range of molar ratio (x), 0.97 <x <= 1.03 is more preferable.

(Ni)

The definition of the molar ratio y of nickel in the above range is for the reasons described below. When the molar ratio (y) is less than 0.7 because the characteristics close to the discharge capacity of LiCoO ₂ to be difficult to achieve the improved energy density. On the other hand, when the molar ratio y exceeds 0.95, the discharge capacity becomes large, but decomposition of the crystal structure tends to occur with the charge and discharge cycle. As for the range of molar ratio y, 0.75 <= y <= 0.9 is more preferable.

(Co)

The molar ratio z of cobalt is defined in the above range due to the reasons described below. When the molar ratio z is less than 0.05, stacking of the Ni layer is likely to be disturbed, and decomposition of the crystal structure is likely to occur depending on the charge and discharge cycle. On the other hand, when the molar ratio z exceeds 0.3, it is necessary to set the synthesis temperature to 850 ° C or higher in order to arrange the stacking of the Co layer (to increase the crystallinity). Debonding occurs, deoxygenation reactions occur, and face removal to the R3m structure occurs, resulting in a decrease in discharge capacity. The more preferable range of molar ratio z is 0.1 ≦ z ≦ 0.25.

(Element M)

The element M has an effect of suppressing decomposition due to the charge and discharge cycle and can be a pillar supporting the structure of the crystal. In addition, it is also possible to suppress decomposition of the nonaqueous electrolyte at the reaction interface by addition of the element (M). However, when the molar ratio w exceeds 0.1, nickel easily enters the lithium ion site, so that the crystal structure may change and the discharge of a large current may be difficult. Therefore, the molar ratio w should be 0.1 or less. It is preferable. The more preferable range of molar ratio w is 0 ≦ w ≦ 0.07, still more preferably 0 ≦ w ≦ 0.05, and the most preferred range is 0 ≦ w ≦ 0.03. In order to fully acquire the effect of the addition of the element M, the lower limit 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 and discharge cycle life in a high temperature environment can be improved. This is presumably because the reaction in which a protective film derived from EC is formed on the surface of the positive electrode is accelerated, and the reaction between the positive electrode and γ-butyl lactone in a high temperature environment (around 45 ° C) is suppressed. In addition, Li _x Ni _y Co _z Sn _w O ₂ The mouth is Li _x Ni _y Co _z O ₂ And a mixture of Li ₂ SnO ₃ .

In addition, when Al or Mn is used as the element M, the stability of the crystal structure of the Li _x Ni _y Co _z M _w O ₂ particles increases, so that charging and discharging can be stably performed over a long period of time, and thus charging and discharging are performed. The cycle life can be further improved.

The reason for defining the sum (y + z + w) of the molar ratios y, z and w in the above range is explained. When (y + z + w) is less than 0.95, the Li ratio in the particles is increased, so that impurities which do not contribute to the charge / discharge reaction are generated and the discharge capacity is lowered. On the other hand, when (y + z + w) exceeds 1.05, the amount of Li contributing to the reaction is reduced, so that the discharge capacity is lowered.

The limitation of each of (D _N90 / D _N50 ) and (D _N50 / D _N10 ) within the range of 1.4 to 2 is due to the reasons described below. The fact that (D _N90 / D _N50 ) and (D _N50 / D _N10 ) is 1 means that the particle size distribution of the nickel-based particles is monodisperse. If (D _N90 / D _N50 ) and (D _N50 / D _N10 ) are less than 1.4, the particle size distribution of the nickel-based particles is narrow, and thus, the amount of active material charged in the positive electrode is insufficient and high capacity cannot be obtained.

On the other hand, nickel particle | grains whose (D _N90 / D _N50 ) exceeds 2 contain many particle | grains of a large particle diameter. Particles with large particle diameters have a large expansion and contraction due to occlusion and release of lithium, so that the progress of micronization is rapid. Therefore, when (D _N90 / D _N50 ) exceeds 2, _{micronization of the} nickel-based particles proceeds and the lifetime cannot be obtained long.

In addition, many nickel particles are contained in the nickel-type particle | grains with which (D _N50 / D _N10 ) exceeds 2. Since such nickel-based particles have high reactivity with the nonaqueous electrolyte, oxidative decomposition of the nonaqueous electrolyte proceeds and the charge and discharge cycle life is reduced.

More preferred ranges of (D _N90 / D _N50 ) and (D _N50 / D _N10 ), respectively, are from 1.5 to 1.9.

The content of nickel-based particles in the positive electrode active material is more than 50% by weight for the reasons described below. When content of the nickel type particle | grains in a positive electrode active material is 50 weight% or less, the discharge capacity (specific capacity) per unit weight falls. However, when the content of the nickel-based particles exceeds 90% by weight, there is a fear that a high discharge voltage and excellent large current charge / discharge characteristics may not be obtained. Therefore, the content of the nickel-based particles is more than 50% by weight, and 90% by weight or less. It is preferable to set it in the range of.

More preferred ranges are greater than 50% and 80% by weight.

{Li _a Co _b M _c O ₂ Particles (hereinafter referred to as Cobalt based particles)}

The definition of the molar ratio (a) of lithium in the above range is for the reason described below. When the molar ratio a is less than 0.95, Li ions that contribute to charge and discharge reactions are reduced, so that the discharge capacity is lowered. On the other hand, when the molar ratio (a) exceeds 1.05, impurities different from the LiCoO ₂ structure are generated, so that the discharge capacity is lowered. A more preferred range of molar ratio (a) is 0.97 ≦ a ≦ 1.03.

(Co)

The molar ratio (b) of cobalt is defined in the above range for the reasons described below. When the molar ratio (b) is less than 0.95, the (a / b) ratio becomes relatively large, so that Li ions that contribute to the charge / discharge reaction are reduced and the discharge capacity is lowered. On the other hand, when the molar ratio b exceeds 1.05, the ratio of (a / b) becomes relatively small, so that impurities which do not contribute to charging and discharging are generated and the discharge capacity is lowered. A more preferable range of molar ratio (b) is 0.97 ≦ b ≦ 1.03.

(Element M)

The element (M) plays a role of strengthening the structure to suppress or control the decomposition reaction of the nonaqueous electrolyte or to suppress the decomposition of the crystal structure by the charge / discharge cycle. In addition, since the crystal structure is strengthened when the valence of the element M does not change with respect to charging and discharging, the cycle characteristics are improved. However, when the molar ratio (c) exceeds 0.05, the amount of Co is relatively lowered and the amount of Li involved in the battery reaction is insufficient, so that the discharge capacity is lowered. Therefore, it is preferable to make molar ratio c into 0.05 or less. A more preferable range of 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 and discharge cycle life in a high temperature environment can be improved. This is presumably because the reaction in which a protective film derived from EC is formed on the surface of the positive electrode is accelerated, and the reaction between the positive electrode and γ-butyl lactone in a high temperature environment (around 45 ° C.) is suppressed. In addition, the Li _a Co _b Sn _c O ₂ particles are _a mixture of Li _a Co _b O ₂ and Li ₂ SnO ₃ .

The reason for defining the sum (b + c) of the molar ratios (b, c) in the above range is explained. When (b + c) is less than 0.95, the Li ratio in the particles increases, so that impurities which do not contribute to the charge / discharge reaction are generated and the discharge capacity is lowered. On the other hand, when (b + c) exceeds 1.05, the amount of Li contributing to the reaction decreases, so that the discharge capacity is lowered.

The limitation of each of (D _C90 / D _C50 ) and (D _C50 / D _C10 ) within the range of 1.4 to 2 is due to the reasons described below. The fact that (D _C90 / D _C50 ) and (D _C50 / D _C10 ) is 1 means that the particle size distribution of the cobalt-based particles is monodisperse. If (D _C90 / D _C50 ) and (D _C50 / D _C10 ) are less than 1.4, the particle size distribution of the cobalt-based particles is narrow, and thus the amount of active material charged in the positive electrode is insufficient, and thus high capacity cannot be obtained.

On the other hand, cobalt type particle | grains whose (D _C90 / D _C50 ) exceeds 2 contain many particle | grains of a big particle diameter. Since such cobalt-based particles have a low lithium diffusion rate, they cause a large decrease in current charge / discharge characteristics.

In addition, the cobalt type particle | grains whose (D _C50 / D _C10 ) exceeds 2 contains many microparticles. Since such cobalt-based particles have high reactivity with the nonaqueous electrolyte, oxidative decomposition of the nonaqueous electrolyte proceeds and the charge and discharge cycle life is reduced.

More preferred ranges of each of (D _C90 / D _C50 ) and (D _C50 / D _C10 ) are 1.5 to 1.9.

It is preferable that _DC50 of cobalt type particle _exists in the range of 0.2 micrometer or more and 30 micrometers or less. This is for the following reason. If the D _C50 is less than 0.2 µm, there is a possibility that the crystal growth of the cobalt-based particles becomes insufficient and a sufficient discharge capacity cannot be obtained. On the other hand, when D _C50 exceeds 30 µm, in addition to making it difficult to obtain a uniform anode surface at the time of production of the anode, the particle diameter becomes large, so that the surface area per volume decreases and the reactivity decreases. The more preferable range of D _C50 is 1 µm or more and 15 µm or less.

When the above-described nickel-based particles and cobalt-based particles satisfy the relationship of the above-described formulas (1) to (4) for the volume accumulation frequencies of 10%, 50%, and 90%, the particle diameter (D) (D _N50 / D _C50 ) Is described in the range of 1.5 to 2.5. If (D _N50 / D _C50 ) is greater than or equal to 1 and less than 1.5, the similarity between the particle size distribution of the nickel-based particles and the particle size distribution of the cobalt-based particles is high, thus expanding the expansion and contraction caused by lithium occlusion and release of the nickel-based particles. It becomes difficult to suppress by particle | grains, and a charge / discharge cycle life falls. In addition, the cobalt-based particles can make the average discharge voltage higher than that of the nickel-based particles, and can easily store and release lithium from the initial stage of discharge.

If (D _N50 / D _C50 ) is less than 1, the particle size distribution of the cobalt-based particles exists on the side of the particle diameter larger than that of the nickel-based particles, and thus the lithium diffusion rate of the cobalt-based particles is impaired, resulting in large current charge and discharge. Properties deteriorate.

When (D _N50 / D _C50 ) exceeds 2.5, the particle size distribution of the nickel-based particles is located on the side of the particle diameter which is significantly larger than the particle size distribution of the cobalt-based particles, so that the reactivity of the nickel-based particles and the reactivity of the cobalt-based particles are Difference is remarkable. As a result, the charge / discharge reaction easily occurs unevenly in the anode, and thus the charge / discharge cycle life decreases. Moreover, when a paste is prepared using such a positive electrode active material, since the dispersibility or coating property of a paste is impaired, it becomes difficult to obtain the positive electrode of stable quality. The more preferable range of (D _N50 / D _C50 ) is 1.6 to 2.4.

One type of nickel-based particles and one cobalt-based particle may be used for the positive electrode active material, but two or more types having different compositions may be used as the nickel-based particles, or two or more types having different compositions may be used as the cobalt-based particles.

The said positive electrode is produced by the method demonstrated to the following (i)-(iv), for example.

(i) A positive electrode is obtained by apply | coating the mixture slurry obtained by suspending a positive electrode active material, a electrically conductive agent, and a binder to a suitable solvent, drying, pressing, and cutting to a desired magnitude | size. At this time, it is preferable to make the application amount of the slurry per side of an electrical power collector into the range of 100 g / m <2> -400 g / m <2>.

(Ii) A positive electrode is obtained by molding a mixture obtained by kneading a positive electrode active material, a conductive agent and a binder into pellets, and then compressing the obtained pellets into a current collector.

(Iii) The mixture obtained by kneading the positive electrode active material, the conductive agent and the binder is molded into a sheet shape, and then the obtained sheet is pressed against the current collector to obtain a positive electrode.

Examples of the conductive agent include carbon black such as acetylene black and Ketjen black, and graphite.

Examples of the binder include polyvinylidene fluoride (PVdF), vinylidene fluoride (VdF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), as monomer components, Perfluoroalkyl vinyl ether (PFA), copolymer containing ethylene, terpolymer, etc. can be used.

The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 wt% to 95 wt% of the positive electrode active material, 3 wt% to 10 wt% of the conductive agent, and 2 wt% to 10 wt% of the binder.

As the current collector, for example, aluminum foil, stainless foil, titanium foil can be used, but aluminum foil is most preferred in consideration of tensile strength, electrochemical stability, and flexibility in winding. It is preferable that the thickness of the foil at this time is 10 micrometers or more and 30 micrometers or less. In addition to the foil shape, the current collector may use a porous current collector such as a punched metal and an expanded metal.

2) cathode

The negative electrode includes a current collector, and a negative electrode layer supported on one side or both sides of the current collector.

The negative electrode layer contains a compound that occludes and releases lithium ions or lithium atoms. As such a compound, carbonaceous materials, such as a conductive polymer (for example, polyacetal, polyacetylene, polypyrrole, etc.), an organic substance sintered compact, etc. are mentioned, for example.

The said carbon material can adjust a characteristic by the kind of raw material, or a sintering method. Specific examples of the carbon material include graphite-based carbon materials, carbon materials in which graphite crystal portions and non-crystallized parts are mixed, carbon materials having a hard layer structure without regularity in lamination of crystal layers, and the like. Can be.

The said negative electrode is produced by the method demonstrated to the following (I)-(III), for example.

(I) A mixture slurry obtained by suspending and releasing lithium ions or lithium atoms and a binder in a suitable solvent is applied to a current collector, dried, and pressed to cut to a desired size to obtain a negative electrode. At this time, it is preferable to make the application | coating amount of the slurry per side of an electrical power collector into the range of 50 g / m <2> -200 g / m <2>.

(II) The mixture obtained by kneading a compound which occludes and releases lithium ions or lithium atoms and a binder is molded into pellets, and then the obtained pellets are pressed into a current collector to obtain a negative electrode.

(III) The mixture obtained by kneading a compound which occludes and releases lithium ions or lithium atoms and a binder is molded into a sheet shape, and then the obtained sheet is pressed onto a current collector to obtain a negative electrode.

As said binder, the thing similar to what was demonstrated by the positive electrode mentioned above is mentioned.

Copper foil, nickel foil, etc. can be used as an electrical power collector of the said negative electrode, for example. Copper foil is most preferable in consideration of electrochemical stability and flexibility. As thickness of foil at this time, it is preferable that they are 8 micrometers or more and 20 micrometers or less. In addition to the thin shape, the current collector may be a current collector having holes such as punched metal and expanded metal.

3) non-aqueous electrolyte

As the nonaqueous electrolyte, those having a substantially liquid or gel 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 nonaqueous electrolyte includes a liquid nonaqueous electrolyte and a gelling agent for gelling the liquid nonaqueous electrolyte. As a gelling agent, polyethylene oxide, polyacrylonitrile, etc. are mentioned, for example.

Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and die Methoxyethane (DEE), γ-butyllactone (γ-BL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane, 1,3-dimethoxypropane Etc. can be mentioned. The kind of nonaqueous solvent used can be one type or two or more types.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and bistrifluoro Lithium salts such as methylsulfonylimide lithium [(LiN (CF ₃ SO ₂ ) ₂ ], LiN (C ₂ F ₅ SO ₂ ) ₂ , aluminum tetrachloride, etc.). I can do it in two or more kinds.

The amount of the electrolyte dissolved in the nonaqueous solvent is preferably in the range of 0.5 mol / L to 1.5 mol / L.

4) separator

The separator is formed of a porous sheet.

As the porous sheet, for example, a porous film or a nonwoven fabric may be used. It is preferable that the said porous sheet consists of one or more types of materials chosen from polyolefin and cellulose, for example. As said polyolefin, polyethylene and polypropylene are mentioned, for example. Among these, a porous film made of polyethylene, polypropylene or both is preferable because it can improve the safety of the secondary battery.

5) containers

The shape of the container may be, for example, a cylinder with a bottom, a cylinder with a bottom, a bag, a cup, or the like.

The container may be formed of, for example, a resin, a sheet including a resin layer, a metal plate, a metal film, or the like.

As said resin, polyolefin like nylon and a polypropylene, nylon etc. are mentioned, for example.

The resin layer included in the sheet may be formed of, for example, polyethylene, polypropylene, nylon, or the like. It is preferable to use the sheet | seat in which the metal layer and the protective layer arrange | positioned at both surfaces of the said metal layer were integrated as said sheet | seat. The metal layer is formed of, for example, aluminum, stainless steel, iron, copper, nickel, or the like. Among the above, aluminum which is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed of one kind of metal, or may be formed by integrating two or more kinds of metals. A protective layer in contact with the outside of the two protective layers serves to prevent damage to the metal layer. The outer protective layer is formed from one type of resin layer or two or more types of resin layers. On the other hand, the inner protective layer serves to prevent the metal layer from being corroded by the nonaqueous electrolyte. The inner protective phase is formed of one type of resin layer or two or more types of resin layers. Moreover, a thermoplastic resin can be arrange | positioned at the surface of such an inner protective layer.

The metal plate and the metal film may be formed of, for example, iron, stainless steel, or aluminum.

A thin nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery according to the present invention will be described with reference to FIGS. 1 and 2.

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, and FIG. 2 is an enlarged cross-sectional view showing part A of FIG. As shown in FIG. 1, the electrode group 2 is housed in the container 1. The electrode group 2 has a structure in which a laminate composed of an anode, a separator, and a cathode is wound in a flat shape. The laminate is composed of a separator 3, a positive electrode layer 4, a positive electrode current collector 5, and a positive electrode layer 4, as shown in FIG. 2 (from the lower side of the figure). 3) a negative electrode 9 having a negative electrode layer 7 and a negative electrode current collector 8 and a negative electrode layer 7, a separator 3, a positive electrode layer 4 and a positive electrode current collector 5 and a positive electrode layer ( A positive electrode 6 having a 4), a separator 3, a negative electrode layer 7 and a negative electrode 9 having a negative electrode current collector 8 are laminated in this order. One end of the strip-shaped positive electrode lead 10 is connected to the positive electrode current collector 5 of the positive electrode group 2, and the other end thereof extends from the container 1. On the other hand, one end of the strip-shaped negative electrode lead 11 is connected to the negative electrode current collector 8 of the negative electrode group 2, and the other end thereof extends from the container 1.

1 and 2 described above, although the electrode group in which the positive electrode and the negative electrode are wound in a flat shape through a separator is used, the electrode group folded between the positive electrode and the negative electrode through the separator or the positive electrode and the negative electrode are laminated through the separator. One electrode group or the like may be used.

3 illustrates an example in which the present invention is applied to a rectangular nonaqueous electrolyte secondary battery.

As shown in FIG. 3, the electrode group 13 is accommodated in the rectangular cylindrical container 12 with a metal bottom, such as aluminum, for example. In the electrode group 13, the positive electrode 14, the separator 15, and the negative electrode 16 are stacked in this order and wound in a flat shape. The spacer 17 having an opening in the vicinity of the center is disposed above the electrode group 13.

The nonaqueous electrolyte is held in the electrode group 13. The sealing plate 18b which has an explosion-proof mechanism 18a and which has a circular hole opened in the center vicinity is laser-welded to the opening part of the container 12. As shown in FIG. The negative electrode terminal 19 is arranged in the circular hole of the sealing plate 18b through welding sealing. 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 the container 12 which also serves as a positive electrode terminal.

The cathode active material of the nonaqueous electrolyte secondary battery according to the present invention described above includes Li _a Co _b M _c O ₂ particles (cobalt-based particles) and 50 wt% or more of Li _x Ni _y Co _z M _w O ₂ particles (nickel-based) Particle | grains), and also satisfy | fills Formula (1)-(5) mentioned above.

According to such a secondary battery, it is possible to improve the charge density and charge / discharge cycle life of the positive electrode active material while ensuring high discharge voltage and excellent large current charge / discharge characteristics.

That is, the discharge capacity (specific capacity) per unit weight can be improved by making content of the nickel type particle | grains in a positive electrode active material more than 50 weight%.

Further, by setting the (D _N90 / D _N50 ) of the nickel-based particles within the range of 1.4 to 2, the particles having extremely large expansion and contraction due to the occlusion release of lithium in the nickel-based particles can be made small. On the other hand, by setting (D _C90 / D _C50 ) of the cobalt-based particles within the range of 1.4 to 2, it is possible to ensure a high lithium diffusion rate in the positive electrode active material.

By setting (D _N50 / D _N10 ) of the nickel-based particles and (D _C50 / D _C10 ) of the cobalt-based particles within the range of 1.4 to 2, the reactivity of the positive electrode active material with the nonaqueous electrolyte can be lowered, thereby oxidatively decomposing the nonaqueous electrolyte. Can be suppressed.

Further, by setting (D _N50 / D _C50 ) within the range of 1.5 to 2.5, the particle size of the positive electrode active material can also have a width suitable for distribution, and thus the packing density of the positive electrode active material can be improved. At the same time, expansion shrinkage due to lithium occlusion and release of nickel particles can be further suppressed by cobalt particles having a small degree of expansion and shrinkage, and therefore micronization of nickel 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 amount, large current charge / discharge characteristics, active material charge 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 amount of anode (mAh / g)>

First, cobalt particles of LiCoO ₂ to the particles, and nickel-based particles having a particle O ₂ LiNi _{0 .81 .19 0} Co were mixed at a weight ratio shown in Table 1 was prepared as a sample 1-7.

The working electrode was produced using the samples 1-7 as an active material. That is, 0.03 parts by weight of polytetrafluoroethylene (PTFE), 0.06 parts by weight of acetylene black (AB), and 1 part by weight of the active material are kneaded in an agate mortar and sheeted by a roller press, and then pressed into a nickel network. Then, a working electrode of 1 cm × 1 cm containing about 0.05 g of the active material was produced.

Li foil was crimped | bonded to the mesh made from nickel, and the counter electrode of 2 cm x 2 cm and the reference electrode of 0.5 cm x 0.5 cm were produced. The cell was produced by arranging the working electrode and the counter electrode to face each other via a glass filter, and placing the reference electrode so as not to contact the counter electrode and the working electrode.

The cell was connected to a glass container capable of conducting electricity through a metallic wire, and a nonaqueous electrolyte (ethylene carbonate (EC) and γ-butyllactone were mixed in a volume ratio of 1: 2 until the cell was immersed). LiBF ₄ dissolved 1.5 mol / L)) was filled and then sealed. The operation was carried out inside a glove box at a dew point of -80 ° C.

The charge was charged up to 4.25 V at a constant current of 1 mA and then at a constant voltage of 4.25 V from the time when it reached 4.25 V. The sum total of the time of constant current charge and constant voltage charge was made into 20 hours. Discharge was performed at 1.0 mA, and the discharge amount until reaching 3.0V was made into discharge capacity. The value obtained by dividing the discharge capacity by the weight of the active material in the working electrode was shown in Table 1 below as a specific amount (mAh / g). Table 1 also shows the weights of Samples 1 to 7 in which the same discharge capacity as that of 1 g of LiCoO ₂ was obtained.

As can be seen from Table 1, Samples 1 to 4 in which the compounding amount of nickel-based particles were more than 50% by weight can increase the discharge capacity (mAh / g) compared to Samples 5 to 7, and also LiCoO ₂ (Sample 7 It can be seen that a high discharge capacity is obtained in a small amount as compared with).

In the following examples, the coating amount of the negative electrode is made constant so as to reduce the effect caused by the difference in specific capacity caused by the difference in the mixing ratio of the cobalt-based particles and the nickel-based particles, and the amount of the positive electrode applied in accordance with the mixing ratio of the positive electrode active material. The battery was produced by changing (positive electrode active material content).

<Example 1>

<Production of Anode>

As the cobalt-based particles, the volume accumulation frequency 10% particle diameter (D _C10 ) is 1.9 μm, the volume accumulation frequency 50% particle diameter (D _C50 ) is 3.3 μm, and the volume accumulation frequency 90% particle diameter (D _C90 ) is 5.7 μm. LiCoO ₂ particles were prepared. In addition, the nickel-based particles had a volume accumulation frequency of 10% particle diameter (D _N10 ) of 4 μm, a volume accumulation frequency of 50% particle diameter (D _N50 ) of 7 μm, and a volume accumulation frequency of 90% particle diameter (D _N90 ) of It prepared the O ₂ particles _.19 LiNi _{0 .81} Co ₀ of 11.6 ㎛.

(D _N50 / D _N10 ), (D _N90 / D _N50 ), (D _C50 / D _C10 ), (D _C90 / D _C50 ) and (D _N50 / D _C50 ) are shown in Table 2 below.

Volume accumulation frequency 10%, 50%, 90% particle diameter was measured by the method described below. In other words, the particle diameters of the nickel-based particles and the cobalt-based particles and the occupying volume of the particles in the respective particle diagram sections are measured by laser diffraction and scattering methods. The particle diameter is 10% of the cumulative frequency when the volume is 10% of the total volume, and the particle diameter at 50% is the 50% particle diameter. The particle diameter is 90% of the volume accumulation frequency.

First, 3 parts by weight of polyvinylidene fluoride (Kureha Chemical Co., Ltd. product name: # 1100) 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 was used as a positive electrode active material, and 8 parts by weight of graphite (trade name: KS6 manufactured by Ronze) was used as the positive electrode active material and the conductive material. It added to the solution, stirred and mixed using the dissolva and the bead mill, and prepared the positive electrode slurry. The slurry was applied to both sides of an aluminum foil having a thickness of 15 μm using a die coater at regular intervals, dried, pressed at a constant linear pressure (kgf / cm), and slit to obtain a reel-shaped 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.

Further, Table 2 shows the stage was LiNi _{0 .81} Co _{0 .19} O weight ratio of the _second particle (W _N) (% by weight) and the weight ratio of LiCoO ₂ particles (Wc) (% by weight).

<Production of Cathode>

To 100 parts by weight of mesophase pitch-based carbon fiber powder (manufactured by Petokasha), 10 parts by weight of graphite powder (Lonzersha brand name: KS15) is added and mixed, and further, styrene / butadiene latex (Asahi Kasei Kogyo Co., Ltd. brand name L1571 , 48 parts by weight of solids) 4.2 parts by weight, 130 parts by weight of an aqueous solution (1% by weight of solids) of carboxymethylcellulose (BSH12 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener, and 20 parts by weight of distilled water were added and mixed to prepare a slurry. did.

The said slurry was apply | coated with the die coater at regular intervals on both surfaces of the copper foil of thickness 10 micrometers, and after drying, it pressed and slit and obtained the reel-shaped negative electrode.

<Preparation of nonaqueous electrolyte amount>

Ethylene carbonate (EC) and γ- butyrolactone (GBL) with a volume ratio of 1: 1.5 by mol / L of LiBF ₄ dissolved in a non-aqueous solvent mixture to obtain a second non-aqueous electrolyte.

<Assembly of battery>

The positive electrode, the separator made of polypropylene, and the like, in which an aluminum ribbon having a thickness of 100 μm and a length of 70 mm is previously ultrasonically welded to a predetermined position as a positive electrode current collector tab, and a protective tape made of polyimide for preventing short circuit is adhered to the welding site. As the current collector tab of the negative electrode, a nickel ribbon having a thickness of 100 μm and a length of 70 mm was ultrasonically welded to a predetermined position, and the negative electrode in which a polyimide protective tape was attached to the welding site was laminated in this order in order to prevent short circuit, respectively. It wound in shape and pressed at 90 degreeC for 30 second, and produced the electrode group.

On the other hand, the container formed by carrying out cup molding to the laminate film of thickness 0.1mm which coat | covered polyethylene and the outside on the electrode group side of aluminum foil, respectively was prepared.

The electrode group and the electrolyte solution were housed in the container, and heat-sealed to assemble a thin nonaqueous electrolyte secondary battery (35 mm in width and 62 mm in length). The process from the pouring process to the sealing process was carried out in a glove box controlled at a dew point of -80 ° C under Ar atmosphere.

<Example 2>

The amount of the LiCoO ₂ particles in the positive electrode 26.7 parts by weight, and also in the same manner as that described in the above Example 1 except that the compounding amount of LiNi _{0 .81} Co _{0 .19} O ₂ particles 62.3 parts by weight of the thin non-aqueous electrolyte secondary battery Prepared.

<Example 3>

The amount of the LiCoO ₂ particles in the positive electrode 35.6 parts by weight, and also in the same manner as that described in the above Example 1 except that the compounding amount of LiNi _{0 .81} Co _{0 .19} O ₂ particles 53.4 parts by weight of the thin non-aqueous electrolyte secondary battery Prepared.

<Example 4>

As the nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having D _N10 of 5.3 μm, D _N50 of 7.7 μm, and D _N90 of 11.1 μm were used, and the compounding amount of LiCoO ₂ particles in the positive electrode was 26.7 parts by weight. to the amount of LiNi _{0 .81} Co _{0 .19} O ₂ 62.3 parts by weight of the particles other than flat by the same method as that described in the above-described example 1 was prepared the non-aqueous electrolyte secondary battery.

<Example 5>

As the nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having D _N10 of 3.3 μm, D _N50 of 6.5 μm, and D _N90 of 12.5 μm were used, and the blending amount of LiCoO ₂ particles in the positive electrode was 26.7 parts by weight, and LiNi except that the compounding amount of _{0 .81} Co _{0 .19} O ₂ particles 62.3 parts by weight was prepared in the same manner as a thin nonaqueous electrolyte secondary battery as set forth in the above-described first embodiment.

<Example 6>

And a cobalt-based particles is 2.7 D _C10 ㎛, D and _C50 are 3.9 ㎛, the _C90 D, and the amount of the 5.8 ㎛ LiCoO ₂ particles in the positive electrode at the same time and using the LiCoO ₂ particles 26.7 parts by weight, and LiNi _{0 .81} Co to the amount of _{0 .19} O ₂ particles 62.3 parts by weight was prepared in the same manner except that the thin non-aqueous electrolyte secondary battery as set forth in the above-described first embodiment.

<Example 7>

And a cobalt-based particles is 1.6 D _C10 ㎛, D 3 ㎛ _C50 is a, D is _C90 and the amount of the 5.7 ㎛ LiCoO ₂ particles in the positive electrode at the same time and using the LiCoO ₂ particles 26.7 parts by weight, and LiNi _{0 .81} Co to the amount of _{0 .19} O ₂ particles 62.3 parts by weight was prepared in the same manner except that the thin non-aqueous electrolyte secondary battery as set forth in the above-described first embodiment.

<Example 8>

As the nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having D _N10 of 4.7 μm, D _N50 of 8 μm, and D _N90 of 13.6 μm were used, and the compounding quantity of LiCoO ₂ particles in the positive electrode was 26.7 parts by weight, in addition, except that the amount of LiNi _{0 .81} Co _{0 .19} O ₂ particles 62.3 parts by weight of thin in the same manner as that described in the above-described example 1 was prepared the non-aqueous electrolyte secondary battery.

Example 9

As the nickel-based particles, LiNi _0.81 Co _0.19 O ₂ particles having a D _N10 of 2.9 μm, a D _N50 of 5.2 μm, and a D _N90 of 8.9 μm were used, and the compounding quantity of the LiCoO ₂ particles in the positive electrode was 26.7 parts by weight. to the amount of LiNi _{0 .81} Co _{0 .19} O ₂ 62.3 parts by weight of the particles other than flat by the same method as that described in the above-described example 1 was prepared the non-aqueous electrolyte secondary battery.

 <Example 10>

As cobalt-based particles, LiCo _0.97 Sn _0.03 O ₂ particles having a D _C10 of 1.9 μm, a D _C50 of 3.3 μm, and a D _C90 of 5.7 μm (a mixture containing 3.1 parts by weight of Li ₂ SnO ₃ with 100 parts by weight of LiCoO ₂ ) use, and the amount of the LiCo _{0 .97} Sn _{0 .03} O ₂ particles in the positive electrode, and 26.7 parts by weight, and the above-described embodiment except that the blending amount of LiNi _{0 .81} Co _{0 .19} O ₂ particles 62.3 parts by weight example In the same manner as described in 1, a thin nonaqueous electrolyte secondary battery was manufactured.

<Example 11>

And a nickel-based particles is D _N10 4 ㎛, D _N50, and the 7 ㎛, D _N90 is 11.6 ㎛ of LiNi _0.78 Co _0.18 Sn _0.03 O ₂ particles _{(LiNi 0 .81 Co 0 .19 O} 2 100 When 3.1 parts by weight using a mixture containing by weight of Li ₂ SnO ₃₎ and at the same time, the amount of the LiCoO ₂ particles in the positive electrode, and 26.7 parts by weight, and _{LiNi 0 .78 Co 0 .18 Sn 0} .03 O 2 62.3 the amount of the particles by weight A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except for the negative portion.

<Example 12>

As the nickel-based particles, except that LiNi _0.76 Co _0.18 Al _0.06 O ₂ particles having D _N10 of 4 μm, D _N50 of 7 μm, and D _N90 of 11.6 μm were used, and were thin in the same manner as described in Example 1 above. A nonaqueous electrolyte secondary battery was produced.

Example 13

As the nickel-based particles, they were thin in the same manner as described in Example 1 except that LiNi _0.76 Co _0.18 Mn _0.06 O ₂ particles having a D _N10 of 4 μm, a D _N50 of 7 μm, and a D _N90 of 11.6 μm were used. A nonaqueous electrolyte secondary battery was produced.

Comparative Example 1

Thin nonaqueous electrolyte secondary in the same manner as described in Example 1 except that only LiNi _0.81 Co _0.19 O ₂ particles having D _N10 of 4 μm, D _N50 of 7 μm, and D _N90 of 11.6 μm were used as the positive electrode active material. The battery was prepared.

 Comparative Example 2

The amount of the LiCoO ₂ particles in the positive electrode 53.4 parts by weight, and also in the same manner as that described in the above Example 1 except that the compounding amount of LiNi _{0 .81} Co _{0 .19} O ₂ particles 35.6 parts by weight of the thin non-aqueous electrolyte secondary battery Prepared.

Comparative Example 3

And a cobalt-based particles is 2.7 D _C10 ㎛, D and _C50 are 3.4 ㎛, D _C90 of the 4.3 ㎛ By using the LiCoO ₂ particles, and the amount of the LiCoO ₂ particles in the positive electrode 26.7 parts by weight, and LiNi _{0 .81} A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of the Co _{0 19} O ₂ particles was 62.3 parts by weight.

 <Comparative Example 4>

And a cobalt-based particles is 1.5 D _C10 ㎛, _C50 D is 3.5 ㎛ and, D is _C90 By using the LiCoO ₂ particles is 8.4 ㎛, and the amount of the LiCoO ₂ particles in the positive electrode 26.7 parts by weight, and LiNi _{0 .81} A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of the Co _{0 19} O ₂ particles was 62.3 parts by weight.

 Comparative Example 5

And a cobalt-based particles is 3.8 D _C10 ㎛, _C50 D is 6.1 ㎛ and, D is _C90 By using the LiCoO ₂ particles of 10 ㎛, and the amount of the LiCoO ₂ particles in the positive electrode 26.7 parts by weight, and LiNi _{0 .81} A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of the Co _{0 19} O ₂ particles was 62.3 parts by weight.

Comparative Example 6

And a cobalt-based particles is 1.5 D _C10 ㎛, D and _C50 are 2.6 ㎛, D _C90 of the 4.5 ㎛ By using the LiCoO ₂ particles, and the amount of the LiCoO ₂ particles in the positive electrode 26.7 parts by weight, and LiNi _{0 .81} A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the amount of the Co _{0 19} O ₂ particles was 62.3 parts by weight.

Comparative Example 7

A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that only LiCoO ₂ particles having a D _C10 of 1.9 μm, a D _C50 of 3.3 μm, and a D _C90 of 5.7 μm were used as the positive electrode active material. .

The secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 7 obtained were measured by 0.2 C capacity, 1 C capacity, battery thickness, average discharge voltage, energy density and cycle life by the method described below. The results are shown in Table 3 below.

<Rated capacity>

The assembled secondary battery was charged at a constant current of 140 mA (equivalent to 0.2 C mA) to 4.2 V at 20 ° C. and after 4.2 V was charged for a total of 12 hours in a constant voltage. The discharge capacity at the time of discharge at a constant current of 140 mA to 3.0V was measured, and it was set as the rated capacity in 0.2C discharge, and the result is shown in following Table 3.

<1.0 C discharge capacity>

After charging at a constant current of 140 mA at 4.2 V, charging was carried out for a total of 12 hours at a constant voltage of 4.2 V, followed by measuring the discharge capacity when discharging at a constant current of 1 C㎃ (700 mA) to 3.0 V. It was set as the capacity | capacitance in C discharge, and the result is shown in Table 3 below.

<Cell thickness measurement, energy density>

After charging was carried out to 140 V at constant current of 140 kV, charging was carried out for a total of 12 hours at a constant voltage of 4.2 V, and the thickness of the battery at 4.2 V was measured. The average voltage was calculated | required from the integral value of a discharge curve from 0.2 CPa (140 mA) to 3.0V. The volume energy density was calculated from the width (35 mm), length (62 mm), measured cell thickness, and average voltage of the battery excluding the current collector tabs of the positive and negative electrodes. 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 for 3 hours at a constant voltage in total, and discharge 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 a cycle life.

As shown in Table 2 and Table 3, it can be seen that the secondary batteries of Examples 1 to 13 have a higher active material density, energy density, and charge / discharge cycle life compared with Comparative Examples 1 to 7.

On the other hand, the secondary battery of the comparative example 1 which uses only lithium nickel cobalt complex oxide as a positive electrode active material had the remarkably low charge / discharge cycle life. The secondary battery of Comparative Example 2 having a lithium nickel cobalt composite oxide content of 50% by weight or less in the positive electrode active material and the secondary battery of Comparative Example 7 using only lithium cobalt composite oxide as an active material have a high average operating voltage during discharge. The discharge cycle life is shortened.

(D _C50 / D _C10 ) and (D _C90 / D _C50 ) of the secondary batteries of Comparative Examples 3 and 4 outside the range of 1.4 to 2, and (D _N50 / D _C50 ) of the Comparative Example of outside the range of 1.5 to 2.5 The secondary batteries of 5 and 6 had lower active material density, 1 C capacity, energy density and charge / discharge cycle life as compared with Examples 1 to 13.

Also, as in the above embodiment it has been described an example of application of the positive electrode active material made of two kinds of LiCoO ₂ particles and LiNi _{0 .81} Co _{0 .19} O ₂ particles, a cathode active material capable of improving the charge-and-discharge cycle life, LiCoO ₂ can be used consisting of particles with LiNi _{0 .81} three or more types of a mixture of different types of particles, such as LiMn ₂ O ₄ in Co _{0 .19} O ₂ particle.

In addition, in the above-described embodiment, the example applied to the thin nonaqueous electrolyte secondary battery and the square nonaqueous electrolyte secondary battery has been described, but the same applies to the cylindrical nonaqueous electrolyte secondary battery and the coin type nonaqueous electrolyte secondary battery.

As described above, the present invention can provide a nonaqueous electrolyte secondary battery having an improved charge / discharge cycle life.

Claims (7)

In a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte comprising a positive electrode active material, a conductive agent and a binder, The positive electrode active material includes an oxide particle represented by the following Chemical Formula 1 and an oxide particle represented by the following Chemical Formula 2, and a ratio of the oxide particles represented by the following Chemical Formula 1 in the positive electrode active material is greater than 50 wt%, and the positive electrode Non-aqueous electrolyte secondary battery, characterized in that the active material satisfies the following formula (1) to (5). (Formula 1)

(Formula 2)

(In Formula 1 and Formula 2, M is at least one element selected from the group consisting of Mn, B, Al and Sn, The molar ratios x, y, z, w, a, b and 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, respectively. , 0.95 ≦ a ≦ 1.05, 0.95 ≦ b ≦ 1.05, 0 ≦ c ≦ 0.05, and 0.95 ≦ b + c ≦ 1.05). (Equation 1)

(Equation 2)

(Equation 3)

(Equation 4)

(Equation 5)

(In Equations 1, 2, 3, 4, and 5, The D _N10 , the D _N50, and the D _N90 represent volume cumulative frequencies of Li _x Ni _y Co _z M _w O ₂ particles having a particle diameter of 10%, 50%, and 90%, D _C10 , D _C50 and D _C90 indicate that volume accumulation frequencies of Li _a Co _b M _c O ₂ particles are 10%, 50%, and 90% particle diameters). The method of claim 1, The non-aqueous electrolyte secondary battery, wherein the D _C50 of the Li _a Co _b M _c O ₂ particles is in the range of 0.2 μm to 30 μm. The method of claim 1, Particle diameter _ratio (D _N90 / D _N50 ) is a non-aqueous electrolyte secondary battery, characterized in that 1.5 to 1.9 or less. The method of claim 1, Particle diameter _ratio (D _N50 / D _N10 ) is a non-aqueous electrolyte secondary battery, characterized in that 1.5 to 1.9 or less. The method of claim 1, Particle diameter _ratio (D _C90 / D _C50 ) is a non-aqueous electrolyte secondary battery, characterized in that 1.5 to 1.9 or less. The method of claim 1, Particle diameter _ratio (D _C50 / D _C10 ) is a non-aqueous electrolyte secondary battery, characterized in that 1.5 to 1.9 or less. The method of claim 1, Non-aqueous electrolyte secondary battery, characterized in that the ratio of the oxide particles represented by the formula (1) in the positive electrode active material is more than 50% by weight and 90% by weight or less.

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