JP3944899B2 - Non-aqueous secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery having improved cycle performance, charge / discharge capacity, and thermal stability.
[0002]
[Prior art]
In recent years, with the reduction in size and weight of portable electronic devices, non-aqueous secondary batteries having high output and high energy density have been actively developed as power sources. Currently, LiCoO ₂ is mainly used as the positive electrode active material of the non-aqueous secondary battery, but a composite oxide containing lithium and manganese as main components (hereinafter referred to as “lithium manganese composite oxide”) is used. Mn is attracting attention because it has a large reserve and is cheaper than Co and Ni.
[0003]
[Problems to be solved by the invention]
Lithium manganese composite oxides have a problem that when used as a positive electrode active material, there is a large capacity drop associated with battery charge / discharge cycles under high temperature conditions. As one of the causes of the performance deterioration at this high temperature, elution of manganese from the lithium manganese composite oxide is considered.
[0004]
An object of the present invention is to provide a nonaqueous secondary battery that suppresses elution of manganese, which is a particular problem when using a lithium manganese composite oxide, and has excellent charge / discharge cycle characteristics at high temperatures. .
[0005]
[Means for Solving the Problems]
The invention of claim 1 is a non-aqueous secondary battery using lithium manganese composite oxide particles as a positive electrode active material, and the appearance of the lithium manganese composite oxide particles is a large number of polygonal primary particles gathered on the surface. It is a spherical secondary particle having irregularities, and the density of the spherical secondary particle is larger on the inside than the surface, and the surface of the spherical secondary particle is coated with a metal oxide or metal sulfide. It is a feature.
[0006]
According to the first aspect of the present invention, it is possible to provide a non-aqueous secondary battery having a large capacity density and excellent charge / discharge cycle characteristics.
[0007]
According to a second aspect of the present invention, in the non-aqueous secondary battery, Li _x Mn _y M _z O ₄ (where 1.05 <x <1.2, 1.8 <y <1) is used as the lithium manganese composite oxide. .95, 0 <z <0.1, and M is one or more elements selected from Al and Mg). A spinel structure lithium manganese composite oxide is used.
[0008]
According to invention of Claim 2, the non-aqueous secondary battery excellent in the charge / discharge cycle characteristic under high temperature can be provided.
[0009]
The invention according to claim 3 is the non-aqueous secondary battery, wherein the metal oxide or metal sulfide covering the surface of the lithium manganese composite oxide particles is at least one selected from the group consisting of Mg, Al, Ti and Sn. It is characterized by containing these metals.
[0010]
According to invention of Claim 3, the non-aqueous secondary battery which was excellent in the charge / discharge cycle characteristic under higher temperature can be provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0012]
The present invention is a non-aqueous secondary battery using lithium manganese composite oxide particles as a positive electrode active material, and the appearance of the lithium manganese composite oxide particles is a collection of polygonal primary particles and a large number of irregularities on the surface. The spherical secondary particles are characterized in that the density of the spherical secondary particles is larger in the inside than the surface, and the surface of the spherical secondary particles is coated with a metal oxide or metal sulfide.
[0013]
In the present invention, the appearance of the lithium manganese composite oxide particles used for the positive electrode active material is spherical secondary particles in which polygonal primary particles are aggregated and have a large number of irregularities on the surface. Therefore, the lithium manganese composite oxide particles have a large specific surface area per particle.
[0014]
The term “spherical secondary particles” as used herein means that the appearance of secondary particles formed by agglomeration of primary particles is “substantially spherical” and is limited to complete “spherical”. It is not intended to include particles that are nearly spherical.
[0015]
Further, in the spherical secondary particles of the lithium manganese composite oxide, the internal density is larger than the surface density. As described above, the inside of the lithium manganese composite oxide particles may be tightly packed with primary particles without generating cavities, but more preferably, the primary particles are only packed closely without forming cavities. Rather, it is better that the gaps between the primary particles are smaller than when the primary particles are simply collected. For example, in an extreme case, it looks like the primary particles are aggregated when you look at the outer surface, but when you look at the inside it looks like it is made up of one particle. . As another example, the growth of primary particles is progressing to such an extent that the grain boundaries are difficult to understand inside.
[0016]
As described above, the lithium manganese composite oxide particles of the present invention have a large specific surface area per particle, and the inner density of the particles is larger than that of the surface. Compared to those assembled in a spherical shape, ion diffusion and electronic conduction in the particles are good, and a large charge / discharge rate can be maintained, and unstable phases that are likely to occur inside the particles are reduced. .
[0017]
Furthermore, when producing a positive electrode in which a positive electrode mixture prepared by mixing a conductive additive such as acetylene black and a binder such as polyvinylidene fluoride (PVdF) is applied on an aluminum foil. Compared with those in which polygonal primary particles constitute lithium manganese composite oxide particles as they are, the binding property of each particle is good without obstructing the passage of lithium ions with less conductive aid and binder. It is possible to maintain a large capacity density and good charge / discharge cycle performance.
[0018]
And since the surface of the base material particles having such good performance is coated with metal oxides or metal sulfides, the effects of these coatings appear remarkably, and non-chargeable cycle performance is excellent. An aqueous secondary battery can be realized.
[0019]
As the metal oxide or metal sulfide, for example, oxides or sulfides such as Mg, Al, Ti, Sn, Mo and W can be used, and in particular, those using Mg, Al, Ti and Sn. Well, it is possible to use a plurality of these materials. And the elution of manganese is suppressed by coat | covering these materials.
[0020]
Although there is no restriction | limiting in particular about the magnitude | size of lithium manganese complex oxide particle, When producing a positive electrode using a conductive support agent and a binder as mentioned above, an average particle diameter shall be 10 micrometers-20 micrometers. Preferably, the primary particle size is 0.5 μm or more and 5 μm or less. If the particle size is too large, it will take too much time for lithium to pass, and if the particle size is too small, the specific surface area will increase and manganese will be easily eluted. The specific surface area of the lithium manganese composite oxide particles is not particularly limited, but is preferably 0.1 m ² / g or more and 1.0 m ² / g or less because the charge / discharge cycle life can be increased.
[0021]
The lithium manganese composite oxide serving as a base material is not particularly limited, for example, can be a lithium-manganese composite oxide having a spinel structure represented by LiMn ₂ O ₄ having a composition, a part of the manganese sites Al , Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Mg, Li, etc. substituted with other metals, oxygen sites partially substituted with sulfur or halogen elements, oxygen Those having a certain amount of non-stoichiometry can be used.
[0022]
Among them, Li _x Mn _y M _z O ₄ (where 1.05 <x <1.2, 1.8 <y <1.95, 0 <z <0.1, M is selected from Al and Mg 1 The spinel-structure lithium manganese composite oxide represented by an element of more than species is excellent in charge / discharge cycle characteristics at high temperatures and is excellent as a base material.
[0023]
The lithium manganese composite oxide particles used in the present invention can be produced, for example, by mixing starting materials containing lithium, manganese and other materials as required, followed by firing and cooling in the presence of oxygen. Examples of the lithium compound used as a starting material include Li ₂ CO ₃ , LiNO ₃ , LiOH, LiOH · H ₂ O, LiCl, CH ₃ COOLi, Li ₂ O, dicarboxylic acid Li, and fatty acid Li. Examples of manganese compounds used as starting materials include manganese oxides such as Mn ₂ O ₃ and MnO ₂ , manganese salts such as MnCO ₃ , Mn (NO ₃ ) ₂ , manganese dicarboxylate, and fatty acid manganese.
[0024]
In the case of producing lithium manganese oxide substituted with other metal elements, the compounds of other metal elements used as starting materials include oxides, hydroxides, nitrates, carbonates, dicarboxylates, fatty acid salts. And ammonium salts.
[0025]
These starting materials are mixed by a method such as wet mixing, dry mixing, ball milling, coprecipitation and the like, and then fired and cooled. For example, after the calcination, the starting material is fired in an oxygen atmosphere at a temperature of about 600 to 850 ° C. And then gradually cooling to about 500 ° C. or less at a rate of 10 ° C./min or after calcination and firing at a temperature of about 600 to 850 ° C. in an air or oxygen atmosphere and then a temperature of about 400 ° C. A method of annealing in an oxygen atmosphere is used. A boron compound can be used as a flux as a method of firing so that the inside is dense.
[0026]
The coating layer can be formed, for example, by a method in which a raw material of a material to be the coating layer is supplied to lithium manganese composite oxide particles prepared in advance in a gas phase or a liquid phase, and the coating layer is deposited. When it is desired to form it at a lower cost, for example, there is a method of preparing a slurry containing lithium manganese composite oxide particles and a coating layer raw material, drying it, and firing it in an oxygen atmosphere. In this case, as a coating layer raw material to be used, Is preferably dissolved or suspended in the slurry solvent used, and water-soluble salts of metal elements, oxide sols and the like constituting the coating layer can be used. As the slurry solvent, water or an organic solvent can be used, and the drying can be performed by, for example, a spray drying method that makes it easy to form a uniform coating layer.
[0027]
The positive electrode material for a non-aqueous secondary battery of the present invention is used as an active material for a positive electrode of a non-aqueous secondary battery. Such a positive electrode is usually a positive electrode compound containing the active material, a binder and a conductive agent. Used as an agent. Examples of the binder (binder) include polyvinylidene fluoride, polytetrafluoroethylene, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine. Rubber etc. are mentioned.
[0028]
Examples of the conductive agent include graphite fine particles, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke. The contents of the active material, the binder and the conductive agent in the positive electrode are usually about 20 to 90% by weight, 10 to 50% by weight and 1 to 20% by weight, respectively. The positive electrode can be obtained by applying and drying a slurry containing the above materials.
[0029]
The secondary battery of the present invention can be produced by combining the positive electrode, the negative electrode, the electrolyte, and the like by a conventional method using the lithium manganese composite oxide particles as the positive electrode active material.
[0030]
As the active material used for the negative electrode, for example, lithium, a lithium alloy, or a carbon material capable of inserting and releasing lithium can be used. Examples of the carbon material include graphite, coal-based coke, petroleum-based coke, and coal-based pitch. Carbide, petroleum pitch carbide, needle coke, pitch coke, phenol resin, crystalline cellulose, etc., and partially carbonized carbon materials, furnace black, acetylene black, pitch carbon fiber, etc. it can. The negative electrode can be prepared by applying a mixture containing the active material and the binder on the copper foil. As the binder, a binder such as PVdF or SBR can be used.
[0031]
When a separator is used, a microporous polymer film such as polysulfone, polyacrylonitrile, polypropylene, or polyethylene can be used.
[0032]
As the electrolyte serving as the ion conductor, an organic electrolyte, a polymer solid electrolyte, a gel electrolyte, an inorganic solid electrolyte, or the like can be used. For example, when using an organic electrolyte, examples of the organic solvent include carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides. And phosphoric acid ester compounds can be used. Specifically, propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2-pentanone, 1 , 2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile , Butyronitrile, Ronitoriru, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, alone or two or more kinds of mixed solvents such as triethyl phosphate may be used. The solutes dissolved in these solvents include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₂ , LiB (C ₆ H ₅ ) ₂ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, etc. Etc. can be used alone or in combination.
[0033]
When using a polymer solid electrolyte, for example, polyethylene oxide, polypropylene oxide, polyethyleneimine, etc. can be used, and the polymer is used as a gel electrolyte by adding the above solvent together with the above solute. Is also possible. Further, when an inorganic solid electrolyte is used, for example, LiI, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (where M = Al, Sc, Y, and La are selected. Li _0.5-3x RE _{0.5 + x} TiO ₃ (however, at least one selected from the group consisting of RE = La, Pr, Nd and Sm), 4.9LiI-34.1Li ₂ O-61B ₂ O ₅ , 33.3Li ₂ O-66.7SiO _{2 and} other oxide glasses, 0.45LiI-0.37Li ₂ S-0.26B ₂ S ₃ , 0.30LiI-0.42Li ₂ S-0.28SiS _{2 and the} like The sulfide glass or the like can be used.
[0034]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0035]
[Example 1]
Lithium hydroxide (LiOH), dimanganese trioxide (Mn ₂ O ₃ ) and boehmite (AlOOH) are mixed in an amount of 1.1: 1.85: 0.05 and heated at 850 ° C. for 24 hours. Thus, a lithium manganese composite oxide (specific surface area 0.9 m ² / g, average particle size 15 μm, average particle size 2 μm of primary particles visible from the surface measured by SEM observation of particles having the largest distribution of 15 μm) was obtained. This lithium manganese composite oxide powder is dispersed in an aqueous solution of ammonium ammonium oxalate to form a slurry, which is spray-dried, crushed, and heated at 500 ° C. for 1 hour, so that the surface of the lithium manganese composite oxide particles is titanium oxide. A positive electrode active material coated with was obtained.
[0036]
A surface SEM photograph of the lithium manganese composite oxide particles obtained here is shown in FIG. 1, and an SEM photograph of the inside of the particles taken by pulverizing the particles is shown in FIG. As can be seen from FIG. 1, the external appearance of the lithium manganese composite oxide particles is spherical secondary particles in which polygonal primary particles are aggregated to have a large number of irregularities on the surface. Moreover, as shown in FIG. 2, the inside of the spherical secondary particles is densely packed, and the density of the inside is larger than that of the surface.
[0037]
The positive electrode mixture was prepared by mixing a positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) in a weight ratio of 90: 4: 6, and applying this onto an aluminum foil to prepare a positive electrode. .
[0038]
The negative electrode was produced by applying a mixture obtained by mixing graphite and PVdF in a weight ratio of 90:10 on a copper foil.
[0039]
Using these positive and negative electrodes, they were wound through a porous polyethylene film and inserted into a metal case, and a mixed solution of ethylene carbonate and diethyl carbonate (50 vol%: 50 vol%) in which 1 mol / l LiPF ₆ was dissolved was used. The nonaqueous secondary battery was manufactured by injecting and sealing the case.
[0040]
[Comparative Example 1]
A non-aqueous battery was produced in the same manner as in Example 1 except that the lithium manganese composite oxide powder used in Example 1 was used as it was without being coated with a metal oxide.
[0041]
[Comparative Example 2]
Instead of the lithium manganese composite oxide powder base material used in Example 1, lithium manganese composite oxide powder having no polygonal primary particles shown in the SEM photograph of FIG. 3 was used. A non-aqueous secondary battery was produced in the same manner as in Example 1 except that a similar titanium oxide film was formed and used as the positive electrode active material.
[0042]
[Comparative Example 3]
Instead of the lithium manganese composite oxide powder base material used in Example 1, lithium manganese composite oxide particles having pores inside as shown in the SEM photograph of FIG. 4 were used, and this was the same as in Example 1. A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the titanium oxide film was formed and used as the positive electrode active material.
[0043]
These batteries were subjected to a charge / discharge cycle test at an environmental temperature of 60 ° C. Charging / discharging was charging / discharging with a constant current at a current value corresponding to 1 C (voltage range: 4.1 V to 3.0 V).
[0044]
The capacity retention ratio after 200 cycles (percentage of capacity after 200 cycles with respect to the initial capacity) is 85% for the battery of Example 1, 80% for the battery of Comparative Example 1, 75% for the battery of Comparative Example 2, and Comparative Example 74% for 3 batteries.
[0045]
【The invention's effect】
According to the present invention, it is possible to commercialize a non-aqueous secondary battery having excellent charge / discharge cycle characteristics at high temperatures.
[Brief description of the drawings]
1 is a surface SEM photograph of powder used in Example 1. FIG.
2 is a SEM photograph showing the inside of the powder particles used in Example 1. FIG.
3 is a surface SEM photograph of the powder used in Comparative Example 2. FIG.
4 is an SEM photograph showing the inside of powder particles used in Comparative Example 3. FIG.

Claims (3)

A nonaqueous secondary battery using lithium manganese composite oxide particles as a positive electrode active material, and the appearance of the lithium manganese composite oxide particles is a spherical shape in which polygonal primary particles are aggregated and have a large number of irregularities on the surface. A non-aqueous secondary particle, wherein the spherical secondary particle has a higher density inside than a surface thereof, and the spherical secondary particle surface is coated with a metal oxide or metal sulfide. battery. Lithium manganese composite oxide is Li _x Mn _y M _z O ₄ (where 1.05 <x <1.2, 1.8 <y <1.95, 0 <z <0.1, M is Al, The nonaqueous secondary battery according to claim 1, wherein the lithium manganese composite oxide has a spinel structure represented by one or more elements selected from Mg). The non-aqueous secondary battery according to claim 1 or 2, wherein the metal oxide or metal sulfide contains at least one metal selected from the group consisting of Mg, Al, Ti, and Sn.

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