JP2003229128A - Non-aqueous secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery that has superior load characteristics and high capacity and is superior in durability against charge and discharge cycle. <P>SOLUTION: This is a non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, in which the active material of the positive electrode contains a plurality of lithium complex oxide particles containing Ni and Mn, cobalt complex oxide particles are adhered to the surface of the lithium complex oxide particles, and the plural lithium complex oxide particles are connected integrally by the cobalt complex oxide particles and form composite particles. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous secondary battery using a lithium composite oxide as an active material for a positive electrode.

[0002]

2. Description of the Related Art In recent years, with the development of portable electronic devices such as mobile phones and notebook computers and the practical use of electric vehicles, small-sized, lightweight and high-capacity secondary batteries have been required. It was At present, as a high-capacity secondary battery that meets this demand, a non-aqueous secondary battery represented by a lithium secondary battery using LiCoO ₂ as a positive electrode active material and a carbon-based material as a negative electrode active material has been commercialized. There is. The lithium secondary battery has a high energy density and can be reduced in size and weight, and thus has attracted attention as a power source for portable electronic devices.

LiCoO ₂ used as the positive electrode active material of this lithium secondary battery is widely used as a suitable positive electrode active material because it is easy to manufacture and easy to handle. Further, LiCoO ₂ itself has high electron conductivity, and delithiated lithium LiC0 ₂ has further improved electron conductivity, so that it can be charged and discharged with a large current density. For this reason, LiCoO ₂ is mainly used as a positive electrode active material for a lithium secondary battery used in a mobile phone or the like that requires load characteristics especially at low temperatures. However, since LiCoO ₂ is produced using Co, which is a rare metal, as a raw material, it is expected that resource shortage will become serious in the future. Further, since the price of cobalt itself is high and the price fluctuation is large, it is desirable to develop a positive electrode active material that is inexpensive and has a stable supply. In addition, when LiCoO ₂ is used as the positive electrode active material, the thermal stability of cobalt dioxide formed after charging is low, which poses a problem in battery safety in a charged state.

As a positive electrode active material to replace LiCoO ₂ for a lithium secondary battery, it is necessary to be inexpensive, have a battery capacity equal to or more than conventional, and have a load characteristic equal to or more than conventional. . Among them, Li ₂ Mn ₄ O ₉ and L, which are lithium manganese oxides having a spinel structure,
i ₄ Mn ₅ O ₁₂ , LiMn ₂ O _{4 and the} like have been attracting attention, and in particular, LiMn ₂ O ₄ can be charged and discharged in a voltage range near 4 V with respect to Li, and has excellent thermal stability. Therefore, research is actively conducted (Japanese Patent Laid-Open No. 6-768).
24, JP-A-7-73883, JP-A-7-
230802, JP-A-7-245106, etc.). Further, the composition formula _{LiNi 1-xy Co x M y} O 2 ( where a 0 ≦ x <1,0 ≦ y ≦ 0.25, M is an element comprising at least one of Al or Mn) represented by The layered structure of lithium nickel oxide, which exhibits a high capacity, has been actively studied.

[0005]

By the way, LiCoO 2
The theoretical discharge capacity of ₂ is 274 mAh / g, but when deep charge / discharge is performed, LiCoO ₂ undergoes a phase change and affects the cycle life. Therefore, the practical discharge capacity of an actual lithium secondary battery is 125-125. It is in the range of 140 mAh / g.

On the other hand, the theoretical discharge capacity of LiMn ₂ O ₄ is 148 mAh / g, but this LiMn ₂ O ₄ also has L
Like iCoO _2, it undergoes a phase change during charge and discharge, and
When a carbon-based material is used as the negative electrode active material, the irreversible capacity of the carbon-based material is large, so that the discharge capacity that can be actually used in a battery is reduced to about 90 to 105 mAh / g. As is clear from this, LiM
When n ₂ O ₄ is used as the positive electrode active material, LiCo
There is a problem that the battery capacity cannot be increased as compared with the case where O ₂ is used as the positive electrode active material.

In a lithium secondary battery using LiMn ₂ O ₄ as a positive electrode active material, LiMn ₂ during charging and discharging
_Since the structure of ₂ O ₄ itself is unstable, the cycle characteristics are L
There is also a problem that it is worse than the iCoO ₂ system battery.

On the other hand, the theoretical discharge capacity of lithium nickel oxide having a layered structure is 278 mAh / g, which is almost the same as the theoretical discharge capacity of LiCoO ₂ , but since the operating potential is low, it is about 160 to 200 mAh / g in the same potential region. Although the positive electrode active material has a high discharge capacity of g, the amount of gas generated increases as the content of nickel increases, and the safety of the battery decreases. Furthermore, as the charge and discharge reaction increases the tetravalent value of nickel and decreases the electron conductivity, the load characteristic is LiCoO ₂
There is a problem that it is inferior to.

Based on these facts, as a result of continuing earnest studies, we have obtained the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn.
_{(1-xy-δ) /} 2 M y O 2 ( however, 0 ≦ x ≦ 0.05, -0 .
05 ≦ α ≦ 0.05, 0 ≦ y <0.45, −0.24 ≦ δ
≦ 0.24, M is Ti, Cr, Fe, Co, C
A lithium manganate having a layered structure represented by one or more elements selected from the group consisting of u, Zn, Al, Ge and Sn), which has almost the same discharge capacity as LiCoO ₂ (15
0 mAh / g or more), excellent thermal stability, and inexpensive cathode active material was invented. However, this positive electrode active material was inferior in loading characteristics to LiCoO ₂ because of its high nickel content.

As described above, by substituting the constituent elements of the lithium manganese oxide having a layered structure such as LiMnO ₂ with nickel and cobalt, the crystal structure is stabilized,
As a result, it is possible to increase the capacity by improving the reversibility during charge and discharge and to impart durability during charge and discharge cycles. However, since this positive electrode active material mainly utilizes the oxidation-reduction reaction of nickel during charge and discharge, it has a poor load characteristic as compared with LiCoO ₂ like lithium nickel oxide, and therefore, it has a poor load characteristic. In order to apply it to the positive electrode active material for batteries for terminals, it is essential to improve the load characteristics.

The present invention has been made to solve the above-mentioned conventional problems, and has excellent load characteristics and high capacity,
It is an object of the present invention to provide a non-aqueous secondary battery having excellent durability against charge / discharge cycles.

[0012]

In order to achieve the above object, a non-aqueous secondary battery of the present invention is a non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode is active. As a substance, a plurality of lithium composite oxide particles containing Ni and Mn are included, the cobalt composite oxide particles are fixed to the surface of the lithium composite oxide particles, and the plurality of lithium composite oxide particles are formed by the cobalt composite oxide particles. It is characterized by using composite particles in which particles are connected and integrated.

In the above composite particles, since the lithium composite oxide particles are connected by the cobalt composite oxide particles having high electron conductivity, the electron conductivity of the whole positive electrode active material is improved. The load characteristics of the water secondary battery can be improved.

Further, the non-aqueous secondary battery of the present invention comprises the lithium battery
The um complex oxide particles have the general formula Li _{1 + x + α}Ni
_{(1-x-y + δ) / 2}Mn_{(1-xy-δ) / 2}M_yO₂(However, 0 ≦ x
≤0.05, -0.05≤α≤0.05, 0≤y <0.4
5, −0.24 ≦ δ ≦ 0.24, M is Ti, Cr,
Consists of Fe, Co, Cu, Zn, Al, Ge and Sn
A composition represented by one or more elements selected from the group)
Preferably.

By using the lithium composite oxide particles having the above composition, the crystal structure of the particles is stabilized, and the high capacity,
It is possible to provide a non-aqueous secondary battery having excellent durability against charge / discharge cycles.

Further, in the non-aqueous secondary battery of the present invention, the cobalt composite oxide particles are preferably composed of lithium cobalt oxide or a composite oxide in which a part of cobalt of lithium cobalt oxide is replaced with another metal element. . This is because lithium cobalt oxide and a composite oxide obtained by substituting a part of cobalt of lithium cobalt oxide with another metal element have excellent electron conductivity.

In the non-aqueous secondary battery of the present invention, the composite particles are Ni, Mn, M (where M is Ti, Cr, F).
e, Co, Cu, Zn, Al, one or more elements selected from the group consisting of Ge and Sn) and Co,
The atomic ratio of Ni, Mn, M, and Co is (1-
x−y + δ) / 2: (1-x−y−δ) / 2: y: z
(However, 0 ≦ x ≦ 0.05, 0 ≦ y <0.45, 0.
It is preferable that 4 <y + z <0.85, and −0.24 ≦ δ ≦ 0.24). With this composition, the composite particles of the present invention can be easily formed. In particular,
By setting M to Co, the cobalt composite oxide particles can be reliably fixed to the surface of the lithium composite oxide particles. Further, as the value of z increases, the proportion of the cobalt composite oxide particles increases, the electron conductivity is improved and the load characteristics are improved, but the stability of the composite particles is reduced accordingly. The value of y + z, which indicates the upper limit of the total amount, is preferably less than 0.85.

The method for producing a non-aqueous secondary battery of the present invention is a method for producing a non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, which is a compound containing Ni and Mn as constituent elements. And a compound containing Co as a constituent element, L
By mixing with the compound of i and firing the mixture, N
i, Mn, M (where M is Ti, Cr, Fe, Co,
It contains at least one element selected from the group consisting of Cu, Zn, Al, Ge and Sn) and Co, and its atomic ratio is (1-x-y + δ) / 2: (1-x) on average. -Y-
δ) / 2: y: z (where 0 ≦ x ≦ 0.05, 0 ≦ y
<0.45, 0.4 <y + z <0.85, -0.24 ≦
The positive electrode active material represented by δ ≦ 0.24) is formed.

Thus, as the active material of the positive electrode, N
A plurality of lithium composite oxide particles containing i and Mn are included, cobalt composite oxide particles are fixed to the surface of the lithium composite oxide particles, and the plurality of lithium composite oxide particles are connected by the cobalt composite oxide particles. The integrated composite particles can be reliably formed.

Further, in the method for producing a non-aqueous secondary battery of the present invention, the compound containing Ni and Mn as constituent elements is:
Further, it is preferable to contain M as a constituent element.

Further, the method for producing a non-aqueous secondary battery of the present invention comprises a compound containing Ni and Mn as constituent elements,
When the compound containing Co as a constituent element and the compound containing Li are mixed, a compound containing M as a constituent element may be further mixed.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, according to the embodiments of the present invention,
The present invention will be described more specifically. The non-aqueous secondary battery of the present invention comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte, and contains a plurality of lithium composite oxide particles containing Ni and Mn as an active material of the positive electrode. Cobalt composite oxide particles are fixed to the surface of, and composite particles obtained by connecting and integrating the plurality of lithium composite oxide particles by the cobalt composite oxide particles are used.

The positive electrode active material of the present invention comprises cobalt composite oxide particles having good electron conductivity and lithium composite oxide particles containing Ni and Mn which are excellent in structural stability and thermal stability. The composite particles are firmly fixed and connected together. When the positive electrode active material of the present invention is analyzed by the X-ray diffraction method, it is recognized as a mixed phase containing two hexagonal crystals having different lattice constants. As a result, the cobalt composite oxide particles secure an electron conduction path between the lithium composite oxide particles, and the electrons are smoothly supplied to the lithium composite oxide particles containing Ni and Mn. Can be improved.

This will be described with reference to a conceptual diagram. Figure 1
It is a conceptual diagram of the composite particle which comprises the positive electrode active material of this invention. In FIG. 1, the composite particles constituting the positive electrode active material of the present invention include a plurality of lithium composite oxide particles 1 containing Ni and Mn, and the cobalt composite oxide particles 2 adhere to the surface of the lithium composite oxide particles 1. The plurality of lithium composite oxide particles 1 are connected and integrated by the cobalt composite oxide particles 2. As a result, a conductive network of cobalt composite oxide particles is formed between a plurality of lithium composite oxide particles, and even if the lithium composite oxide particles having low load characteristics are used, the load characteristics of the positive electrode active material as a whole are improved. Can be achieved.

It is most desirable that all of the positive electrode active materials are the above composite particles, but the positive electrode active material contains lithium composite oxide particles other than the above composite particles, or cobalt composite oxide particles, or these two types. It may contain oxide particles, or may be a mixture with an active material other than these.

In the present invention, the lithium composite oxide particles and the cobalt composite oxide particles may be primary particles or secondary particles, respectively. In order to further improve the electron conductivity, both the lithium composite oxide particles and the cobalt composite oxide particles are preferably primary particles.

Further, the positive electrode active material of the present invention having the above structure has two diffraction peaks in the diffraction angle range of 17 ° to 20 ° in the X-ray diffraction measurement using CuKα ray, and the diffraction angle is There are at least two diffraction peaks in the range of 43 ° to 46 °, and in the two diffraction peaks in the diffraction angle range of 43 ° to 46 °, the full width at half maximum of the diffraction peak on the low angle side and the diffraction peak on the high angle side The half widths of the peaks are different, and the half width of the diffraction peak on the low angle side is larger than that of the diffraction peak on the high angle side.

The composite particles constituting the positive electrode active material of the present invention include Ni, Mn and M (where M is T
i, Cr, Fe, Co, Cu, Zn, Al, Ge and S
one or more elements selected from the group consisting of n) and C
O, and the atomic ratio of Ni, Mn, M, and Co is (1-x-y + [delta]) / 2: (1-x-y- [delta]) / on average.
2: y: z (where 0 ≦ x ≦ 0.05, 0 ≦ y <0.
45, 0.4 <y + z <0.85, -0.24≤δ≤0.
Those having a composition represented by 24) can be used. Particularly, it is preferable that M is Co.

The lithium composite oxide particles constituting the above composite particles have the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} M
_{n (1-xy-δ)} / 2 M y O 2 ( however, 0 ≦ x ≦ 0.05, -
0.05 ≦ α ≦ 0.05, 0 ≦ y <0.45, −0.24
≦ δ ≦ 0.24, M is Ti, Cr, Fe, Co,
Those having a composition represented by one or more elements selected from the group consisting of Cu, Zn, Al, Ge and Sn) are preferable. The lithium composite oxide particles have a layered structure.

Lithium composite having the above composition having a layered structure
The oxide particles are selected for the following reasons. That is,
In the lithium manganese oxide, the ratio of trivalent Mn is high.
Then, the crystal structure is unstable due to the Yarn-Teller effect.
Is known to become. Therefore, the present inventors
In order to realize the stabilization of the crystal structure, LiMnO₂Against
And increase the average valence of Mn as a composition containing excess Li.
Combining or LiMnO ₂Mn of layered lithium composite
Elements that can stably form oxides, such as Co and Ni
It is thought that it is effective to replace with
The kind and amount ratio of elements were examined in detail.

As a result, the general formula Li _{1 + x} Ni _{(1-x) / 2} Mn
Ni and M represented by _{(1-x) / 2} O ₂ (0 ≦ x ≦ 0.05)
The amount ratio of n is (1-x) / 2: (1-x) / 2, that is, 1:
1, based on the composition in which Li is excessive by the sum (x) of the decrease amounts of Ni and Mn (each x / 2), the amount ratio of Ni and Mn is δ / 2 (−0.24 ≦ δ ≦ 0 .24), the amount ratio of Li has a width of α (−0.05 ≦ α ≦ 0.05), and Ni and Mn are each y / 2 (0
≦ y <0.45) M (M is Ti, Cr, Fe, C)
o, Cu, Zn, Al, Ge and Sn), a composition substituted with one or more elements selected from the group consisting of the following formulas: ie, Li _{1 + x + α} Ni _{(1-x-y + δ) / 2 Mn (1-xy -δ} ) / 2 M y
O ₂ (however, 0 ≦ x ≦ 0.05, −0.05 ≦ α ≦ 0.0
5, 0 ≦ y <0.45, −0.1 ≦ δ ≦ 0.1, and M
Is a composition range represented by one or more elements selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn), and the layered crystal structure is stabilized, resulting in charge / discharge. It was found that a lithium composite oxide having excellent reversibility and durability against charge / discharge cycles can be obtained.

As a result of a more detailed study, it was found that a lithium composite oxide having particularly excellent characteristics can be obtained in the vicinity of a composition in which the amount ratio of Ni, Mn and M is 1: 1: 1. That is, the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn
In _{(1-xy-δ) /} 2 M y O 2, in the composition range of 0.2 <y <0.45 centered at y = 1/3, the stability of the crystal structure becomes higher, 0 ≦ It was found that a single phase was more easily obtained than y ≦ 0.2. Therefore, in the above general formula, 0 ≦ x ≦ 0.05, −0.05 ≦ α ≦ 0.0
5, 0.2 <y <0.45, -0.24 ≦ δ ≦ 0.24 lithium composite oxide (where M is Ti, Cr, F
One or more elements selected from the group consisting of e, Co, Cu, Zn, Al, Ge and Sn) can be preferably used in the present invention.

The cobalt composite oxide particles having the function of imparting electron conductivity in the positive electrode active material of the present invention include lithium cobalt oxide or a composite oxide in which a part of cobalt of lithium cobalt oxide is replaced with another metal element. Can be used. All of these have excellent electron conductivity and also function as a positive electrode active material. As the metal element substituting for cobalt of lithium cobalt oxide, Ti,
Mn, Ni, Fe, Al, Ge, Sn or the like can be used. The amount of substitution is preferably 25 mol% or less.

Next, a method for producing the composite particles which are the positive electrode active material of the present invention will be described. As a method for producing the composite particles, if the Li compound, the Mn compound, the Ni compound and the like are simply mixed and fired, the Ni of the present invention can be obtained.
And a plurality of lithium composite oxide particles containing Mn, wherein the cobalt composite oxide particles are fixed to the surface of the lithium composite oxide particles, and the plurality of lithium composite oxide particles are integrally connected by the cobalt composite oxide particles. It is difficult to synthesize composite particles that have been converted into composite particles. This is Ni and M
Since the diffusion rate of n and the like is slow in the solid, it is difficult to uniformly diffuse them in the synthetic reaction, and it is considered that the above elements are not uniformly distributed in the produced lithium composite oxide. Therefore, the present inventors have made detailed studies on the method of synthesizing the composite particles of the present invention, and as a result, by utilizing a reaction system in which phase separation spontaneously occurs in a lithium composite oxide having a layered structure, It has become possible to produce composite particles having the structure of the invention. That is, the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ) / 2} Co
_y O ₂ (where 0 ≦ x ≦ 0.05, −0.05 ≦ α ≦ 0.0.
05, 0 ≤ y <0.45, -0.24 ≤ δ ≤ 0.24) by utilizing the solid solubility limit of the lithium composite oxide having a layered structure and containing an excess amount of Co therein. The particles of the lithium composite oxide having a layered structure and the particles of the cobalt composite oxide can be separately aggregated into particles, and the particles of the cobalt composite oxide are unevenly distributed on the surface of the lithium composite oxide particles. The inventors have invented that it is possible to produce composite particles in which the cobalt composite oxide is firmly bonded between the oxide particles.

As described above, the composite particles of the present invention are prepared by preliminarily preparing a compound containing Ni and Mn as constituent elements and Co.
It is necessary to separately prepare a compound containing a as a constituent element and a compound of Li, mix these, and then calcine them. The composition and blending amount of each compound are such that the positive electrode active material after firing is Ni, Mn, M (where M is Ti, Cr, Fe, Co, Cu, Zn, Al,
Containing one or more elements selected from the group consisting of Ge and Sn) and Co, the atomic ratio of which is (1
−x−y + δ) / 2: (1−x−y−δ) / 2: y: z
(However, 0 ≦ x ≦ 0.05, 0 ≦ y <0.45, 0.
4 <y + z <0.85, −0.24 ≦ δ ≦ 0.24). This makes it possible to reliably produce the composite particles having the structure of the present invention.

In the above manufacturing method, M must be contained in a compound containing Ni and Mn as constituent elements, or a compound containing Co as constituent elements, and / or a compound of Li. You may prepare and mix the compound containing as an element.

The compound containing Ni and Mn as constituent elements is, for example, a coprecipitated compound containing Ni and Mn, a hydrothermally synthesized compound, a mechanically synthesized compound and a compound obtained by heat-treating them. For example, Ni _0.5 Mn _0.5 (OH) ₂ , NiMn ₂ O ₄ ,
An oxide or hydroxide of Ni and Mn such as Ni _0.5 Mn _0.5 OOH can be preferably used.

As described above, a compound containing Ni and Mn as constituent elements, a compound containing Co as constituent elements, a compound of Li, and a compound containing M as constituent elements are mixed and fired. The composite particles of the present invention can also be obtained by using, but if possible, Ni and M
It is preferable to use a complex compound containing n and M. In addition, Ni, Mn and M in this composite compound
The composition ratio may be appropriately selected according to the composition of the intended composite particles.

As the compound containing Co as a constituent element, cobalt carbonate, cobalt hydroxide, cobalt oxide or the like can be used.

As the Li compound, various lithium salts can be used. For example, lithium hydroxide.
Monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate,
Lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate,
Lithium sulfate, lithium oxide, etc. can be used,
Among them, lithium hydroxide monohydrate is preferably used because it does not generate harmful substances such as carbon dioxide, nitrogen oxides, and sulfur oxides, which adversely affect the environment.

The compound containing Ni and Mn as constituent elements, the compound containing Co as constituent elements, the compound of Li and the like are mixed in a composition ratio according to the composition of the intended composite particles of the present invention. The composite particles of the present invention can be synthesized by firing the mixture in an atmosphere containing oxygen at about 700 to 1100 ° C. for 1 to 24 hours.

The heat treatment for firing is as follows.
Rather than raising the temperature to a predetermined temperature at once, the temperature is once heated to a temperature lower than the firing temperature (about 250 to 850 ° C.) and held at that temperature for preheating, and further raised to a predetermined firing temperature. It is preferable to allow the reaction to proceed. This is because in the process of producing the composite oxide of the present invention, the reaction between the compound of Li and the compound containing Ni and Mn as constituent elements occurs stepwise, and finally the lithium composite oxide is obtained via the intermediate product. This is because it is considered that a product is generated. Here, when the temperature is raised to the firing temperature all at once, the Li compound and the compound containing Ni and Mn as constituent elements partially react until the final stage, and the lithium composite oxide produced thereby is not formed. This may interfere with the reaction of the reactants or impair the homogeneity of the composition. Further, in order to shorten the time required for the reaction step and obtain a homogeneous composite oxide, it is effective to perform heating stepwise. The preheating time is not particularly limited, but it is usually about 0.5 to 30 hours.

In the step of firing the mixture, the dry-mixed mixture may be used as it is, but the mixture is dispersed in a solvent such as ethanol to form a slurry, and the mixture is slurried in a planetary ball mill for about 30 to 60 minutes. It is preferable to mix and dry the mixture, and to calcine it, because the homogeneity of the compound to be synthesized can be further enhanced.

The atmosphere for the heat treatment is an atmosphere containing oxygen, such as air, argon, helium,
It may be performed in a mixed atmosphere of an inert gas such as nitrogen and oxygen gas, or in oxygen gas. The proportion of oxygen in the atmosphere is preferably 10 to 100% by volume.

The flow rate of the gas is the mixture 10
It is preferably 1 dm ³ / min or more per 0 g, and
More preferably 5 dm ³ / min. If the gas flow rate is low,
That is, when the gas flow rate is slow, the reaction proceeds nonuniformly,
Impurities such as Mn ₂ O ₃ and Li ₂ MnO ₃ are easily generated.

Other than the positive electrode active material described above, the non-aqueous secondary battery of the present invention can be manufactured, for example, as follows.

The positive electrode is obtained by mixing the positive electrode active material with a conductive additive such as flaky graphite or acetylene black, if necessary, and a binder such as polytetrafluoroethylene or polyvinylidene fluoride. It is produced by molding the obtained positive electrode mixture by an appropriate means.

Lithium or a lithium-containing compound is usually used as the active material of the negative electrode facing the positive electrode. As the lithium-containing compound, a lithium alloy such as a Li-Al alloy, a Li-Pb alloy, a Li-In alloy, and a Li-Ga alloy, or an element capable of forming an alloy with lithium such as Si, Sn, and Mg-Si alloy, or The alloy is mentioned. Furthermore, in addition to oxide-based materials such as Sn oxides and Si oxides, carbonaceous materials such as graphite and fibrous carbon, lithium-containing composite nitrides and the like can be used.

In the negative electrode, the negative electrode active material is mixed with the negative electrode active material, if necessary, in the same manner as in the case of the positive electrode, by adding a binder, a conductive auxiliary agent and the like, and the obtained negative electrode mixture is molded by an appropriate means. Made by.

The positive electrode and the negative electrode can be molded by pressure-molding the positive electrode mixture or the negative electrode mixture, or the positive electrode mixture or the negative electrode mixture is made into a paste or slurry by water or other appropriate solvent. Various means can be adopted, such as coating or impregnating each coating material on a substrate that also functions as a current collector and then drying the coating material to form a coating film integrated with the substrate.

Here, as the substrate that also functions as a current collector, for example, a metal net such as aluminum, stainless steel, titanium, or copper, punching metal, expanded metal, foam metal, or metal foil is used. However, a method of forming a coating film of the mixture on a metal foil as a substrate and pressurizing the coating film to obtain a sheet-shaped positive electrode or negative electrode is preferably used.

As the non-aqueous electrolyte in the non-aqueous secondary battery of the present invention, an organic solvent-based liquid electrolyte (electrolyte) in which an electrolyte is dissolved in an organic solvent, or a polymer electrolyte in which the electrolyte is retained in a polymer Etc. can be used.

The organic solvent contained in the electrolytic solution or the polymer electrolyte is not particularly limited, but it is preferable that the chain ester is contained from the viewpoint of load characteristics. Examples of such chain esters include dimethyl carbonate (DMC) and diethyl carbonate (D
EC), ethyl methyl carbonate (EMC), ethyl acetate (EA), methyl propionate (MP), and other organic solvents having a chained COO-bond. These chain esters can be used alone or in combination of two or more, and in order to improve the low temperature characteristics, these chain esters must account for 50% by volume or more of the total organic solvent. Is preferred, and the chain ester is 65 in all organic solvents.
It is more preferable to occupy volume% or more, and most preferable to occupy 75 volume% or more.

However, as the organic solvent, an ester having a high dielectric constant (an ester having a dielectric constant of 30 or more) is mixed with the chain ester in order to improve the battery capacity, as compared with the case where only the chain ester is used. It is preferable to use. Specific examples of the ester having a high dielectric constant include, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone (γ-).
BL), ethylene glycol sulfite (EGS) and the like, and those having a cyclic structure such as ethylene carbonate and propylene carbonate are particularly preferable. From the viewpoint of discharge capacity, it is preferable that such an ester having a high dielectric constant is contained in the total organic solvent in an amount of 10% by volume or more, and particularly 20% by volume or more. From the viewpoint of compatibility with load characteristics, 40% by volume or less is preferable, and 25% by volume or less is more preferable.

Examples of the solvent that can be used in combination with the ester having a high dielectric constant include 1,2-dimethoxyethane (1,2-DME) and 1,3-dioxolane (1,2).
3-DO), tetrahydrofuran (THF), 2-methyl-tetrahydrofuran (2-Me-THF), diethyl ether (DEE) and the like. In addition, an amine imide-based organic solvent, a sulfur-containing or fluorine-containing organic solvent, or the like can be used.

As the electrolyte to be dissolved in the organic solvent, for example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAs can be used.
F ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ S
O ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN
_{(CF 3 SO 2) 2,} LiC (CF 3 SO 2) 3, LiC n F
_{2n + 1} SO ₃ (n ≧ 2) and the like are used alone or in combination of two or more. Among them, L, which gives good charge / discharge characteristics
iPF ₆ , LiC ₄ F ₉ SO _{3 and the} like are preferably used.
The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is 0.3 to 1.7 mol / dm ³ , and particularly 0.1.
It is preferably about 4-1.5 mol / dm ³ .

Further, in order to improve the safety and storage characteristics of the battery, the non-aqueous electrolyte may contain an aromatic additive. As the aromatic additive, benzene having an alkyl group such as cyclohexylbenzene or t-butylbenzene, or fluorobenzene is preferably used.

As the separator, one having sufficient strength and capable of holding a large amount of electrolytic solution is preferable, and from such a viewpoint, it is made of polypropylene or polyethylene having a thickness of 10 to 50 μm and a porosity of 30 to 70%. A microporous film or a nonwoven fabric made of a copolymer of propylene and ethylene is preferably used.

[0059]

EXAMPLES Examples of the present invention will be described below. However, the present invention is not limited to only those examples.

Example 1 2% by mass of ammonia water, the pH of which was adjusted to about 12 by adding sodium hydroxide, was prepared in a reaction vessel, and while vigorously stirring this, nickel sulfate and manganese nitrate were added. 1 mol / dm
The mixed aqueous solution containing each ³ at a rate of 46cm ³ / minute, and then added dropwise using a metering pump, respectively 25 wt% aqueous ammonia at a rate of 3.3 cm ³ / min, generating a coprecipitated compound of Ni and Mn Let At this time, the temperature of the reaction solution is 50
The temperature was maintained at 0 ° C., and an aqueous sodium hydroxide solution having a concentration of 3.2 mol / dm ³ was also added dropwise at the same time so that the pH of the reaction solution was maintained around 12. Furthermore, in the reaction,
Nitrogen gas was purged at a rate of 1 dm ³ / min so that the atmosphere of the reaction liquid became an inert atmosphere.

The obtained product was washed with water, filtered and dried to obtain a hydroxide containing Ni and Mn in a ratio of 1: 1. 0.03 mol of this hydroxide and 0.07 mol of cobalt hydroxide were added. , 0.1 mol of LiOH.H ₂ O were weighed, the mixture was dispersed in ethanol to form a slurry, which was mixed for 40 minutes with a planetary ball mill and dried at room temperature to prepare a mixture. Then, the mixture is placed in an alumina crucible and heated to 800 ° C. in an air stream of 1 dm ³ / min, held at that temperature for 2 hours for preheating, and further heated to 1000 ° C. for 12 hours. A composite oxide was synthesized by firing. The synthesized oxide was ground in a mortar and stored as a powder in a desiccator.

When the composition of the above oxide powder was measured by an atomic absorption spectrometer, the atomic ratio of Ni, Mn and Co was 0.33: 0.33: 1.54 on average. all right.

(Example 2) A hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 in a ratio of 1: 1 0.0
35 mol, 0.065 mol of cobalt hydroxide,
0.1 mol of LiOH.H ₂ O was weighed out, and the composite oxide in which the atomic ratio of Ni, Mn and Co was 0.33: 0.33: 1.23 on average in the same manner as in Example 1 below. The thing was synthesized.

Example 3 A hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 at a ratio of 1: 1 0.0
4 mol, 0.06 mol of cobalt hydroxide, 0.
1 mol of LiOH.H ₂ O was weighed, and
In the same manner as above, a composite oxide having an average atomic ratio of Ni, Mn and Co of 0.33: 0.33: 0.99 was synthesized.

(Example 4) A hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 at a ratio of 1: 1 0.0
45 mol, 0.055 mol of cobalt hydroxide,
0.1 mol of LiOH.H ₂ O was weighed out, and the compound oxide in which the atomic ratio of Ni, Mn and Co was 0.33: 0.33: 0.81 on average in the same manner as in Example 1 below. The thing was synthesized.

(Example 5) 0.05 hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 at a ratio of 1: 1
5 mol, 0.05 mol of cobalt hydroxide, 0.
1 mol of LiOH.H ₂ O was weighed, and
In the same manner as above, a composite oxide having an average atomic ratio of Ni, Mn and Co of 0.33: 0.33: 0.66 was synthesized.

Comparative Example 1 Synthesis was carried out in the same manner as in Example 1.
Hydroxide containing Ni and Mn in a ratio of 1: 1 0.0
6 mol, 0.04 mol of cobalt hydroxide, 0.
1 mol of LiOH ・ H₂O was weighed, and the following Example 1
Li as_1.0Ni_0.30Mn_0.30Co _0.40O₂Table
Was prepared.

Comparative Example 2 Hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 at a ratio of 1: 1 0.0
67 mol, 0.033 mol of cobalt hydroxide,
0.1 mol of LiOH.H ₂ O was weighed, and Li _1.0 Ni _0.33 Mn _0.33 Co _0.33 O ₂ was weighed in the same manner as in Example 1.
A composite oxide represented by

Comparative Example 3 Hydroxide 0.1 containing Ni and Mn in the ratio of 5: 3 synthesized in the same manner as in Example 1
6 mol, 0.04 mol of cobalt hydroxide, 0.
20 mol of LiOH.H ₂ O was weighed, and a composite oxide represented by Li _1.0 Ni _0.50 Mn _0.31 Co _0.19 O ₂ was synthesized in the same manner as in Example 1 below.

(Comparative Example 4) The composite oxide synthesized in Comparative Example 2 and the LiCoO ₂ powder were mixed at a molar ratio of 0.6: 0.4 so that the composition was the same as in Example 3 as a whole. To prepare a mixture.

Reference Example 1 0.16 mol of nickel hydroxide, 0.04 mol of cobalt hydroxide, 0.2 m
Lithium hydroxide was mixed in the same manner as in Example 1 and calcined in oxygen at 650 ° C. for 12 hours, pulverized and mixed, and calcined again in oxygen at 850 ° C. for 12 hours to obtain Li.
A composite oxide represented by Ni _0.80 Co _0.20 O ₂ was synthesized.

Reference Example 2 0.20 mol of cobalt hydroxide and 0.20 mol of LiOH.H ₂ O were weighed, and lithium cobalt oxide represented by LiCoO ₂ was synthesized in the same manner as in Example 1 below. did.

Regarding the composite oxides of Examples 1 to 5, Comparative Examples 1 to 4 and Reference Examples 1 and 2, X by CuKα ray was used.
A line diffraction measurement was performed. The results are shown in Table 1. In addition, among these, X in Example 3, Example 5, Comparative Example 1 and Comparative Example 2
The line diffraction patterns are shown in FIGS.

[0074]

[Table 1]

As a result of X-ray diffraction measurement, the X-rays of Examples 1 to 5 were obtained.
The diffraction patterns all had the same characteristics. That is, diffraction
Within the angle range of 17 ° to 20 °, the difference in diffraction angle is 0.1 °
Has two diffraction peaks from 0 to 0.3 °, and
The angle of diffraction is 0.3 ° within the range of 43 ° to 46 °
There were two diffraction peaks at 0.6 °. Well
Further, from the X-ray diffraction patterns of the above Examples 1 to 5, the present invention was obtained.
The composite oxide used for is a lithium composite oxide (LiNi
_{(1-y) / 2}Mn_{(1-y) / 2}Co_yO₂, Where y is approximately 0.
3 to 0.4) and lithium cobalt oxide (LiCoO₂)of
It was confirmed to be composed of two phases. this is,
The peaks of the X-ray diffraction patterns of Examples 1 to 5 above are single
Phase lithium composite oxide (LiNi_{(1-y) / 2}Mn_{(1-y) / 2}
Co_yO₂, Where y is approximately 0.3 to 0.4) and
Lithium cobalt oxide (LiCoO ₂) Is almost the same as the peak
By hitting.

However, the half-value widths of the two diffraction peaks in which the diffraction angles of the X-ray diffraction patterns of Examples 1 to 5 are in the range of 43 ° to 46 ° are larger than those when they are present alone. The value is 0.2 ° or more, and the half width of the diffraction peak on the low angle side is larger than that of the diffraction peak on the high angle side, and the diffraction peak on the low angle side is broader. It was confirmed. From this, it was found that in the composite oxide used in the present invention, two phases having different compositions and lattice constants are mutually related.

Further, in Examples 1 to 5, the positions of these diffraction peaks hardly changed and only the peak intensities changed, although the composition as the whole composite oxide changed. , The lithium composite oxide and lithium cobalt oxide that compose these composite oxides are
The compositions of Examples 1 to 5 were almost the same, and it was estimated that the composition of the composite oxide as a whole changed due to the change in the amount ratio.

Further, the composite oxide of Example 3 was subjected to morphological observation with a scanning electron microscope (SEM) and elemental analysis with an electron probe microanalyzer (EPMA), and two types of particles having different compositions were found. It was confirmed that the composite particles were bonded to each other and integrated with each other. By taking such a particle morphology, lithium cobalt oxide having high electron conductivity binds a plurality of lithium composite oxide particles containing Ni, Mn, and Co and having poor electron conductivity, and an electron conduction path is formed between the particles. It is skillfully formed.

On the other hand, the X-ray diffraction patterns of Comparative Examples 1 to 3 show a single-phase layered structure, and the diffraction angle is from 17 ° to 2 °.
Only one diffraction peak was present in each of the range of 0 ° and the diffraction angle of 43 ° to 46 °. Further, in Comparative Example 4, which is a mixture of a lithium composite oxide and lithium cobalt oxide, two diffraction peaks were present in each of the above ranges, but the half width was smaller than that of the above Examples, The diffraction peak on the low angle side was also sharp.

Next, using the composite oxides of Examples 1 to 5, Comparative Examples 1 to 4 and Reference Example 1, non-aqueous secondary batteries were prepared by the following method.

First, 2 parts of N-methyl-2-pyrrolidone was added to 20 parts by mass of polyvinylidene fluoride as a binder.
50 parts by mass was added and heated to 60 ° C. to dissolve polyvinylidene fluoride in N-methyl-2-pyrrolidone to prepare a binder solution. 450 parts by mass of the above composite oxide as a positive electrode active material was added to this binder solution, 5 parts by mass of carbon black and 25 parts by mass of graphite were further added as a conduction aid, and the mixture was stirred to prepare a slurry paint. This coating is evenly applied to both sides of an aluminum foil having a thickness of 20 μm and dried, then pressure-molded by a roller press machine, and then cut to an average thickness of 190 μm and a length of 54 m.
A strip-shaped positive electrode having a size of m and a width of 483 mm was produced.

The positive electrode produced as described above and the negative electrode made of lithium foil were used, and the thickness between each electrode was 25 μm.
A separator made of the microporous polyethylene film of was placed. Then, LiPF ₆ was added to a mixed solvent of ethylene carbonate and ethylmethyl carbonate at a volume ratio of 1: 3.
Was dissolved in a concentration of 1.0 mol / dm ³ as an electrolytic solution, and a lithium reference electrode was placed for evaluation of the positive electrode active material to obtain a non-aqueous secondary battery.

Next, using the above non-aqueous secondary battery, load characteristics
In order to evaluate the
mA / cm²After charging to 4.3V at room temperature,
Was discharged at a current density of 3.0 V. The result is
Flow density 0.5 mA / cm²Discharge capacity when discharged by 1
Current density of 1, 2, 4, 6 mA / cm ²
Table 2 shows the capacity retention rate (%) when the temperature was raised.

[0084]

[Table 2]

As is clear from Table 2, Examples 1-5
Is the capacity retention rate (discharge efficiency) when the current density is increased.
However, it is understood that it is higher than Comparative Examples 1 to 4. Looking at the capacity retention rate at a current density of 6 mA / cm ² , Comparative Examples 1 to 3
Is 65 to 66%. This is higher discharge efficiency than the composite oxide of Reference Example 1, but not a practical value. Further, Examples 1 to 5 exhibited a capacity retention rate of 86% or more as expected even when discharged at a current density of 6 mA / cm ² . this is,
It is considered that the coexistence of two phases, a lithium composite oxide composed of nickel, manganese, and cobalt and a cobalt composite oxide mainly containing cobalt, dramatically improved the discharge efficiency at high current density. To be Furthermore, from the capacity retention ratios of Examples 1 to 5, it can be seen that the discharge efficiency improves as the cobalt content in the positive electrode active material increases. However, as can be seen from the comparison between Example 5 and Comparative Example 1, this dramatic improvement in discharge efficiency is not simply due to an increase in the cobalt content, but the above lithium composite oxide and cobalt composite oxide. It is considered that this has been achieved by the present invention of coexisting.

In addition, LiNi _0.33 Mn _0.33 Co _0.33 O ₂
In the material of Comparative Example 4 in which the lithium composite oxide represented by (Comparative Example 2) and lithium cobalt oxide (Reference Example 2) are mixed, lithium cobalt oxide having high electron conductivity is mixed to some extent. It can be seen that the discharge efficiency is improved. However, the ratio of Ni, Mn, and Co is in Comparative Example 4
As is clear from the comparison with Example 3 which is the same as the above, the discharge efficiency can be more effectively increased by using the positive electrode active material having the structure of the present invention.

[0087]

As described above, the positive electrode active material includes a plurality of lithium composite oxide particles containing Ni and Mn, and the cobalt composite oxide particles are fixed to the surface of the lithium composite oxide particles. By using the composite particles in which the plurality of lithium composite oxide particles are connected and integrated by the cobalt composite oxide particles, a non-aqueous electrolyte having excellent load characteristics, high capacity, and excellent durability against charge / discharge cycles is used. A secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of composite particles constituting a positive electrode active material of the present invention.

FIG. 2 is a view showing an X-ray diffraction pattern of a composite oxide of Example 3.

FIG. 3 is a view showing an X-ray diffraction pattern of a composite oxide of Example 5.

FIG. 4 is a view showing an X-ray diffraction pattern of a composite oxide of Comparative Example 1.

FIG. 5 is a view showing an X-ray diffraction pattern of a composite oxide of Comparative Example 2.

FIG. 6 is a diagram showing X-ray diffraction patterns in the range of diffraction angles of 17 ° to 20 ° for the composite oxides of Example 3, Example 5, Comparative Example 1 and Comparative Example 2.

FIG. 7 is a diagram showing X-ray diffraction patterns in the diffraction angles of the composite oxides of Example 3, Example 5, Comparative Example 1 and Comparative Example 2 in the range of 43 ° to 46 °.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazutaka Uchitomi             Hitachi Ma, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F term (reference) 5H029 AJ03 AJ04 AJ05 AJ12 AK03                       AL02 AL06 AL12 AM03 AM04                       AM05 AM07 CJ02 CJ08 CJ22                       CJ23 DJ17 HJ02                 5H050 AA07 AA08 AA09 AA15 BA17                       CA08 CA09 CB02 CB07 CB12                       FA18 FA19 GA02 GA10 GA22                       GA23 HA02

Claims (8)

[Claims] 1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein Ni is used as an active material of the positive electrode.
And a plurality of lithium composite oxide particles containing Mn, wherein the cobalt composite oxide particles are fixed to the surface of the lithium composite oxide particles, and the plurality of lithium composite oxide particles are integrally connected by the cobalt composite oxide particles. A non-aqueous secondary battery, characterized by using composite particles formed into a material. 2. The lithium composite oxide particles have a general formula of Li _{1 + x + α} Ni _{(1-xy + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O.
₂ (However, 0≤x≤0.05, -0.05≤α≤0.0
5, 0 ≦ y <0.45, −0.24 ≦ δ ≦ 0.24, and M is Ti, Cr, Fe, Co, Cu, Zn, Al,
The non-aqueous secondary battery according to claim 1, having a composition represented by one or more elements selected from the group consisting of Ge and Sn. 3. The cobalt composite oxide particles are composed of lithium cobalt oxide or a composite oxide in which a part of cobalt of lithium cobalt oxide is replaced with another metal element.
Or the non-aqueous secondary battery according to 2. 4. The composite particle comprises Ni, Mn, M (where M is Ti, Cr, Fe, Co, Cu, Zn, Al,
One or more elements selected from the group consisting of Ge and Sn) and Co, and the atomic ratio of Ni, Mn, M, and Co is (1-x−y + δ) / 2: (1 -X
−y−δ) / 2: y: z (where 0 ≦ x ≦ 0.05,
0 ≦ y <0.45, 0.4 <y + z <0.85, −0.
24 ≦ δ ≦ 0.24), The non-aqueous secondary battery according to claim 1. 5. The non-aqueous secondary battery according to claim 2, wherein the M is Co. 6. A method for producing a non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, comprising a compound containing Ni and Mn as constituent elements, a compound containing Co as constituent elements, and Li. Ni, Mn, M (where M is Ti, Cr, F
e, Co, Cu, Zn, Al, one or more elements selected from the group consisting of Ge and Sn) and Co,
The atomic ratio is (1-x−y + δ) / 2: (1
−x−y−δ) / 2: y: z (where 0 ≦ x ≦ 0.0
5, 0 ≦ y <0.45, 0.4 <y + z <0.85, −
A method for producing a non-aqueous secondary battery, comprising forming the positive electrode active material represented by the formula: 0.24 ≦ δ ≦ 0.24). 7. The method for producing a non-aqueous secondary battery according to claim 6, wherein the compound containing Ni and Mn as constituent elements further contains M as a constituent element. 8. A compound containing M as a constituent element is mixed when the compound containing Ni and Mn as a constituent element, the compound containing Co as a constituent element, and the compound of Li is mixed. Item 7. A method for manufacturing a non-aqueous secondary battery according to item 6.