JP2003346805A - Non-aqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for suppressing degradation of a non-aqueous electrolyte when preserved at high temperatures. <P>SOLUTION: A non-aqueous electrolyte battery 1 comprises a positive electrode 2 having a positive electrode active material, a negative electrode 4 having a negative electrode active material, and a non-aqueous electrolyte. The positive electrode active material is a lithium-manganese composite compound indicated by a chemical formula of Li<SB>x</SB>Mn<SP>(m)</SP>O<SB>(x+m)/2</SB>. The specific surface area thereof is ≥0.1 m<SP>2</SP>/g to ≤7.0 m<SP>2</SP>/g. Symbol x in the chemical formula is ≥0.5 to ≤0.8, and symbol m in the chemical formula is ≥3.8 to ≤4.0. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte battery using a lithium-manganese composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art Among non-aqueous electrolyte batteries, a non-aqueous electrolyte secondary battery that can be charged and discharged is, for example, a camera-integrated VTR (vid
It is widely used as a power source for portable electronic devices such as eo tape recorders, mobile phones, and laptop computers. Non-aqueous electrolyte secondary batteries include lithium ion secondary batteries that can be used for a long time and are economical.

[0003] Lithium-ion secondary batteries are used as power sources for electronic equipment because they have higher voltage and higher energy density than lead batteries and nickel cadmium batteries as aqueous secondary batteries.

This lithium ion secondary battery is composed of a positive electrode and a negative electrode having an active material capable of reversibly inserting and removing lithium ions, and a non-aqueous electrolyte.
In this lithium ion secondary battery, a lithium-manganese composite oxide, a lithium-cobalt composite oxide, a lithium-nickel composite oxide, or the like having a spinel structure as a positive electrode active material is used. Among these, the lithium-manganese composite oxide is a cathode active material having a potential of 3 V or more with respect to lithium by being electrochemically oxidized and having a high energy density. Further, the lithium-manganese composite oxide is inexpensive because manganese is very rich in resources as compared with other composite oxides such as cobalt and nickel.

[0005] The lithium-manganese composite oxide is synthesized through a predetermined process such as mixing and firing a plurality of starting materials containing the constituent elements Li or Mn. However, lithium-manganese composite oxides
Insufficient mixing of the starting materials in the synthesis leads to non-uniform physical properties and particle sizes. For this reason, in a lithium ion secondary battery, when a lithium-manganese composite oxide having non-uniform physical properties and the like is used, battery characteristics are deteriorated.

In order to solve such a problem, a lithium-manganese composite oxide uses a pulverizer / mixer having a high pulverization / mixing capacity such as a vibration mill or a planetary ball mill to mix a plurality of starting materials when synthesizing. By mixing them sufficiently, it is possible to prevent the properties and the like from becoming non-uniform.

[0007]

However, in the above-mentioned lithium-manganese composite oxide, even when a plurality of starting materials are sufficiently mixed by using a pulverizer / mixer having a high pulverization / mixing ability during the synthesis, The specific surface area increases. When such a lithium-manganese composite oxide having a large specific surface area is used in a lithium-ion secondary battery, the active area reacting with the electrolytic solution becomes large, so that the electrolytic solution deteriorates, especially when stored at a high temperature. In addition, the capacity of the non-aqueous electrolyte significantly decreases after storage at a high temperature because the deterioration is remarkable.

Accordingly, the present invention has been proposed in view of such a conventional situation, and suppresses deterioration of a non-aqueous electrolyte, particularly deterioration of a non-aqueous electrolyte when stored at a high temperature. It is an object of the present invention to provide a non-aqueous electrolyte battery in which deterioration in characteristics is suppressed.

[0009]

A non-aqueous electrolyte battery according to the present invention, which achieves the above object, comprises a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having an electrolyte salt. The positive electrode active material has the chemical formula Li _x Mn
^(M) a lithium-manganese composite compound represented by O _{(x + m) / 2} , having a specific surface area of 0.1 m ² / g or more;
0 m ² / g or less, x in the chemical formula is 0.5 or more,
0.8 or less, m in the chemical formula is 3.8 or more,
A nonaqueous electrolyte battery having a range of 4.0 or less.

[0010] In the non-aqueous electrolyte battery configured as described above, the specific surface area of the positive electrode active material is 0.1 m ² / g or more and 7.0 or more.
By controlling the content to m ² / g or less, the contact area between the positive electrode active material and the nonaqueous electrolyte is appropriately controlled, so that the deterioration of the electrolytic solution is suppressed.

According to the nonaqueous electrolyte battery, the molar ratio x between Li and Mn in the positive electrode active material is set to a range of 0.5 or more and 0.8 or less, and the valence analysis value m of Mn is set to 3. 8 or more;
By setting the range to 0 or less, the crystal structure of the positive electrode active material becomes stable, so that the charge / discharge cycle characteristics can be maintained and the capacity after high-temperature storage can be secured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-aqueous electrolyte battery to which the present invention is applied will be described in detail with reference to the drawings.

The non-aqueous electrolyte battery 1 is a lithium secondary battery, as shown in FIG. 1, a positive electrode 2, a positive electrode can 3 containing the positive electrode 2, a negative electrode 4, and a negative electrode cover 5 containing the negative electrode 4. When,
It has a separator 6 interposed between the positive electrode 2 and the negative electrode 4, a non-aqueous electrolyte, and a gasket 7. The nonaqueous electrolyte battery 1 includes the positive electrode 2, the negative electrode 4, the separator 6, and the nonaqueous electrolyte, which are formed by caulking the positive electrode can 3 and the negative electrode lid 5 through the gasket 7. Lid 5
And the structure is enclosed.

The positive electrode 2 has a positive electrode mixture layer 2b containing a positive electrode active material formed on a positive electrode current collector 2a. For the positive electrode current collector 2a, for example, a thin metal such as aluminum or a mesh metal is used. The positive electrode mixture layer 2b contains, for example, a positive electrode active material, a conductive agent such as graphite or carbon black, and a binder such as polyvinylidene fluoride.

As the positive electrode active material, a lithium / manganese composite oxide containing light metal lithium and having a spinel structure represented by the chemical formula Li _x Mn ^(m) O _{(x + m) / 2} is used. Note that x in the chemical formula indicates a molar ratio of Li to Mn in the lithium-manganese composite oxide, and m is a valence analysis value of Mn.

The valence analysis value m of Mn is a value indicating the valence of Mn in the lithium-manganese composite oxide. This Mn
Is determined as follows. When obtaining the valence analysis value m of Mn, first, the total manganese content in the lithium-manganese composite oxide is determined. The total manganese content is
It was determined as follows. The lithium-manganese composite oxide was dissolved in a mixed solution of concentrated hydrochloric acid and sulfuric acid, and this solution was diluted with pure water. After dilution, sodium pyrophosphate decahydrate was added to the mixed solution, and ph =
Adjusted to 7. The total manganese amount is determined by potentiometric titration of the resulting mixed solution with a potassium permanganate standard solution.

Next, the amount of tetravalent manganese in the lithium-manganese composite oxide is determined. The amount of tetravalent manganese is 55
It is determined by dissolving a lithium-manganese composite oxide in an oxalic acid solution under an environment of from 60 to 60 degrees, and titrating this solution with a potassium permanganate solution. By applying the total manganese amount thus obtained as A and the tetravalent manganese amount as B as Equation 1 shown below, the valence analysis value of Mn is obtained.

[0018]

(Equation 1)

This positive electrode active material is synthesized by the following synthesis method. When synthesizing this positive electrode active material, first, lithium carbonate, nitrate, oxide or hydroxide as a starting material and manganese carbonate, nitrate, oxide, sulfide or hydroxide are used. The mixture is sufficiently pulverized and mixed by using a high-performance pulverizer / mixer such as a vibrating mill so as to have a predetermined composition, thereby producing a mixture. Next, the mixture is compression-molded by applying a predetermined pressure by a tablet-type compression molding machine to form a molded body. The obtained molded body is fired at about 420 ° C. in an atmosphere containing oxygen. Thus, a lithium-manganese composite oxide having a spinel structure is synthesized as the positive electrode active material.

The lithium-manganese composite oxide synthesized as described above has a specific surface area controlled in the range of 0.1 m ² / g or more and 7.0 m ² / g or less, and has the chemical formula Li _x
Mn ^{( m)} O _{(x + m) / 2,} where x in the chemical formula is in the range of 0.5 or more and 0.8 or less, and m in the chemical formula is 3.8 or more and 4.0 or less. Controlled to a range.

When the specific surface area of the lithium-manganese composite oxide is smaller than 0.1 m ² / g, in the non-aqueous electrolyte battery 1, the contact area between the non-aqueous electrolyte and the positive electrode active material becomes small. The load characteristics on the second side are reduced, and the battery capacity is reduced. On the other hand, the specific surface area is 7.0 m
If it is larger than ² / g, in the non-aqueous electrolyte battery 1, the contact area between the non-aqueous electrolyte and the positive electrode active material increases, so that the positive electrode active material and the non-aqueous electrolyte react excessively in a high temperature environment. As a result, the non-aqueous electrolyte is deteriorated and the battery capacity is reduced.

Therefore, when the lithium-manganese composite oxide is used for the non-aqueous electrolyte battery 1 while controlling the specific surface area to be in the range of 0.1 m ² / g or more and 7.0 m ² / g or less, Since the contact area between the liquid and the positive electrode active material becomes appropriate, the load characteristics of the positive electrode 2 are reduced and the deterioration of the non-aqueous electrolyte in a high temperature environment is suppressed, and the decrease in the battery capacity of the non-aqueous electrolyte battery 1 is suppressed. Let it.

When the molar ratio x of Li to Mn in the lithium-manganese composite oxide is smaller than 0.5, the crystal structure of the positive electrode active material is deteriorated each time charge and discharge are repeated, and the charge and discharge cycle characteristics are deteriorated. descend. When the molar ratio x of Li to Mn is larger than 0.8, the doping / dedoping amount of lithium ions is greatly reduced.
The initial capacity decreases.

Therefore, in the lithium-manganese composite oxide, the molar ratio x of Li to Mn is 0.5 or more and 0.1 or more.
By controlling to a range of 8 or less, the crystal structure is stabilized and the discharge capacity is increased. Therefore, when such a lithium-manganese composite oxide is used for the non-aqueous electrolyte battery 1, the amount of doping / de-doping of lithium ions increases, so that a decrease in the initial capacity is suppressed and the non-aqueous electrolyte battery 1, the capacity and the charge / discharge cycle characteristics after storage at a high temperature are prevented from deteriorating.

Further, in the lithium-manganese composite oxide, when the valence analysis value m of Mn is smaller than 3.8,
As the initial capacity decreases, the capacity after high-temperature storage decreases. When the valence analysis value m of Mn is greater than 4.0, the initial capacity increases, but the Mn valence increases.
As the capacity retention rate during high-temperature storage decreases, the capacity after high-temperature storage decreases. Therefore, the lithium-manganese composite oxide has a valence analysis value m of Mn of 3.8 or more,
By controlling the content to be not more than 4.0, the doping / dedoping ability of lithium ions is maintained, the reactivity with the electrolytic solution is reduced, and the reduction of the initial capacity and the deterioration of the nonaqueous electrolytic solution are suppressed. Therefore, a decrease in the capacity of the nonaqueous electrolyte battery 1 after storage at a high temperature is suppressed.

The positive electrode can 3 is formed in a dish shape with a shallow bottom for storing the positive electrode 2. For example, aluminum, stainless steel, nickel and the like are sequentially laminated in the thickness direction from the inside where the positive electrode 2 is stored. And serves as an external positive electrode 2 of the nonaqueous electrolyte battery 1.

In the negative electrode 4, a negative electrode layer 4b containing a negative electrode active material is formed on a negative electrode current collector 4a. Negative electrode current collector 4
a is used as needed, and as the current collector, for example, a thin metal such as copper, a reticulated metal, or the like is used. The negative electrode layer 4b is made of, for example, a light metal such as lithium, an alloy with a light metal, or a negative electrode mixture containing a substance doped with a light metal such as lithium in advance and a binder. Examples of the binder include polyvinylidene fluoride and polytetrafluoroethylene.

Metals capable of forming alloys with light metals such as lithium include semiconductors such as B, Si and As, for example.
Mg, B, Al, Ga, In, Si, Ge, Sn, P
b, Sb, Bi, Cd, Ag, Zn, Hf, Zr, Y and the like. In addition, in the alloy compound of a metal capable of forming an alloy with lithium, when the above-described metal element capable of forming an alloy with lithium is M, the chemical formula is MsM'tLiu.
(M ′ is Li or one or more metal elements other than M, s is a numerical value greater than 0, and t and u are numerical values of 0 or more). Alloy compounds include, for example, Li-Al,
Li-Al-M1 (M1 is a 2A group, 3B group, 4B group,
M1 includes AlSb, CuMgSb, and the like.

[0029] Among the metals capable of forming an alloy with lithium, a group 3B typical element is preferable because the density of the negative electrode layer 4b can be increased and the battery capacity can be increased. In particular, among the group 3B typical elements, Si and Sn
Is more preferable because the theoretical discharge capacity per unit volume is large.

For example, alloy compounds containing Si and Sn
M2xSi, M2xSn (M2 is Si or
Is one or more metal elements excluding Sn. )
Compound. Specifically, SiB₄, SiB₆, Mg
₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoS
i₂, CoSi₂, NiSi₂, CaSi₂, CrSi
₂, Cu₅Si, FeSi₂, MnSi₂, NbS
i₂, TaSi₂, VSi ₂, WSi₂, ZnSi₂etc
Is mentioned.

As the negative electrode active material, a group 4B compound excluding carbon and containing one or more nonmetallic elements can also be used. For example, SiC, Si ₃ N ₄ , Si ₂ N ₂
O, Ge ₂ N ₂ O, SiOx (0 <x ≦ 2), SnOx
(0 <x ≦ 2), LiSiO, LiSnO and the like. Further, as the negative electrode active material, a material containing one or more Group 4B elements can be used. Still further, a material containing a metal other than the group 4B element including lithium can be used.

Examples of the method for synthesizing the negative electrode active material include a method of adding lithium to the above-mentioned metal capable of forming an alloy with lithium and mixing and synthesizing a lithium-containing compound, a method of bonding lithium metal, and a method of electrochemically bonding lithium metal. In addition, there are a method of inserting lithium into a metal capable of forming an alloy with lithium, a method of performing a chemical reaction with n-butyllithium, and the like.

As the negative electrode active material, a carbonaceous material or a compound containing lithium in a carbonaceous material is also used. The carbonaceous material can appropriately perform doping / dedoping of lithium and prevent deposition of lithium on the negative electrode, thereby suppressing deterioration of battery characteristics. Carbonaceous materials include
Examples include non-graphitizable carbon, easily graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compounds, fired bodies, carbon fibers, and activated carbon. Among them, the cokes include pitch coke, needle coke, petroleum coke and the like. The organic polymer compound fired body is obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature and carbonizing the material, and is partially classified as non-graphitizable carbon or easily graphitizable carbon. Some are done.

The negative electrode lid 5 is formed in a dish shape with a shallow bottom for accommodating the negative electrode 4 and is made of, for example, a plate of stainless steel whose surface is nickel-plated.
Of the external negative electrode 4.

The separator 6 separates the positive electrode 2 and the negative electrode 4 from each other, prevents a short circuit of current due to contact between the two electrodes, and allows lithium ions in the non-aqueous electrolyte solution 7 to pass through. The separator 6 is a microporous film made of a resin having a large number of fine pores having an average particle diameter of about 5 μm or less.
As the resin, for example, olefin-based polymer, propylene-based polymer, cellulose-based polymer, polyimide,
There are nylon, glass fiber, alumina fiber and the like. Among them, polypropylene and polyolefin are preferable resins for the separator 6 because they have an excellent short-circuit prevention effect and can improve the safety of the battery by a shutdown effect.

The separator 6 has a thickness of 5 μm or more,
The range is 50 μm or less. The thickness of the separator 6 is 5 μm
If the thickness is thinner, for example, the active material and the deposited lithium will break through the separator 6 and short-circuit the positive electrode 2 and the negative electrode 4. On the other hand, if the thickness of the separator 6 is greater than 50 μm, the ratio of the separator 6 in the battery increases, and the battery capacity decreases.

The separator 6 has a porosity representing a ratio of a void volume in the entire volume of the separator 6 of not less than 20% and not more than 60%.
The range is as follows. The porosity of the separator 6 is 20%
If it is smaller, the pores are too small, for example, preventing the movement of lithium ions between the positive and negative electrodes. On the other hand, if the porosity of the separator 6 is larger than 60%, the separator has too many porosity, for example, lithium or the like deposited on the electrode passes through the vacancy of the separator and short-circuits the positive and negative electrodes. Sometimes. Therefore, the thickness should be 5 μm or more,
By using the separator 6 having a range of 0 μm or less and a porosity of 20% or more and 60% or less, the nonaqueous electrolyte battery 1 having excellent safety and cycle characteristics can be obtained.

The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte salt. Any organic solvent can be used as long as it is used for a non-aqueous electrolyte battery.For example, propylene carbonate, ethylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane , 1,2-diethoxyethane, γ-butyrolactone, tetrabidrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole ,
There are acetate, butyrate, propionate and the like.

As the electrolyte salt, any one can be used as long as it is used for a non-aqueous electrolyte battery. For example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiB
F ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF
Any one or a mixture of plural kinds of ₃ SO ₃ Li, LiCl, LiBr and the like is used. Among them, L
Since iPF ₆ can obtain high ionic conductivity, charge-discharge cycle characteristics are improved.

The gasket 7 is made of, for example, an insulating resin such as polypropylene. The gasket 7 insulates the positive electrode can 3 from the negative electrode lid 5 and is sealed by applying asphalt or the like to the surface. Maintain airtightness inside and prevent leakage of non-aqueous electrolyte.

The non-aqueous electrolyte battery 1 having the above structure is
It is manufactured as follows. First, the positive electrode 2 is manufactured. The positive electrode 2 has a specific surface area and a molar ratio of Li to Mn by the above-described synthesis method, a positive electrode active material including a lithium-manganese composite oxide in which the valence analysis value of Mn is controlled, a conductive material, and a binder. The positive electrode mixture coating solution containing
a on a metal foil such as an aluminum foil,
After drying to form the positive electrode mixture layer 2b, the positive electrode current collector 2a
And the positive electrode mixture layer 2b are collectively cut out into a predetermined shape.

Next, the negative electrode 4 is manufactured. The negative electrode 4 was formed by uniformly applying a negative electrode mixture coating solution containing a negative electrode active material and a binder on a metal foil such as a copper foil to be a negative electrode current collector 4a, and forming a dried negative electrode layer 4b. A negative electrode current collector 4a, a negative electrode layer 4b,
And Li metal foil are collectively cut out into a predetermined shape.

Next, the cathode 2 was accommodated in the cathode can 3, the anode 4 was accommodated in the anode cover 5, and a separator 6 made of a porous film was arranged between the cathode 2 and the anode 4. Inject the non-aqueous electrolyte. Next, the positive electrode can 3, the negative electrode cover 5 and the positive electrode can 3 are caulked and sealed via a gasket 7 coated with asphalt or the like on the surface thereof, thereby forming a coin type having a structure in which the positive electrode 2, the separator 6, and the negative electrode 4 are sequentially laminated. Then, the non-aqueous electrolyte battery 1 is manufactured.

In the non-aqueous electrolyte battery 1 manufactured as described above, the specific surface area of Li _x Mn ^(m) O _{(x + m) / 2} is from 0.1 m ² / g to 7.0 m ² / g. By controlling to within the range, the contact area between the positive electrode active material and the non-aqueous electrolyte becomes appropriate, and excessive reaction between the positive electrode active material and the non-aqueous electrolyte in a high-temperature environment is suppressed. Since the deterioration of the water electrolyte is prevented, the capacity deterioration after high-temperature storage is suppressed.

In the non-aqueous electrolyte battery 1, Li _x Mn
^{(M) In the} positive electrode active material represented by O _{(x + m) / 2} , the molar ratio x of Li to Mn is 0.5 or more and 0.8 or more.
In the following range, the valence analysis value m of Mn is 3.8 or more;
Li _x Mn by controlling the range to 0 or less.
^{(M) The} charge / discharge cycle characteristics can be maintained by stabilizing the crystal structure of O _{(x + m) / 2} , and the capacity after high-temperature storage can be secured.

Therefore, in the non-aqueous electrolyte battery 1, a sufficient initial capacity and good charge / discharge cycle characteristics are obtained, and the capacity is small even when exposed to a high-temperature environment. In this case, the electronic device can be used for a long time even after being exposed to a high temperature environment.

The nonaqueous electrolyte battery 1 to which the present invention is applied
Is not particularly limited with respect to the battery shape, and may be used in various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape. Further, the non-aqueous electrolyte battery 1 has a gel state obtained by impregnating an organic polymer with a solid electrolyte containing an electrolyte salt instead of a non-aqueous electrolyte or a matrix composed of a non-aqueous solvent and an electrolyte salt. An electrolyte can be used.

[0048]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a sample in which a lithium secondary battery was actually manufactured as a nonaqueous electrolyte battery to which the present invention is applied will be described.

Sample 1 In sample 1, first, a lithium-manganese composite oxide as a positive electrode active material was synthesized. When synthesizing this lithium-manganese composite oxide, manganese dioxide and lithium carbonate are mixed at a molar ratio x of Li to Mn in the positive electrode active material of 0.1.
Each sample was weighed so as to be 58, and pulverization and mixing were sufficiently performed by a vibration mill for 5 hours. Next, the mixture was compression-molded at a predetermined pressure by a tablet-type compression molding machine to form a molded body. Next, the obtained molded body was placed in an atmosphere containing oxygen for 420 minutes.
It was baked at about ℃ and classified. Thus, a lithium / manganese composite oxide having a spinel structure having a specific surface area of 0.11 m ² / g and a valence analysis value m of Mn of 3.82 was synthesized.

Next, a positive electrode was manufactured. When preparing a positive electrode, 80 parts by weight of the positive electrode active material obtained as described above, 15 parts by weight of graphite as a conductive agent, and 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder are used. By mixing, a positive electrode mixture was synthesized. Next, the obtained positive electrode mixture is uniformly coated on a 30 μm-thick aluminum foil serving as a positive electrode current collector and dried to form a positive electrode mixture layer, and the positive electrode current collector and the positive electrode mixture are formed. The layers were punched at once into a disk having a diameter of 15 mm and a thickness of 0.3 mm. The punched positive electrode current collector and positive electrode mixture layer were accommodated in a positive electrode can laminated in the order of aluminum, stainless steel, and nickel from the inside of the container.

Next, a negative electrode was manufactured. The negative electrode was formed by punching Li metal into a disk having a diameter of 15.5 mm and a thickness of 0.8 mm.
From the inside of the container, a punched Li metal was pressed against a negative electrode lid laminated in the order of stainless steel and nickel to produce a negative electrode.

When preparing the negative electrode, the negative electrode current collector 4a and the negative electrode layer 4b were punched into a disk having a diameter of 15.5 mm and a thickness of 0.8 mm, and a negative electrode lid laminated in the order of stainless steel and nickel from the inside of the container. A negative electrode may be manufactured by pressing Li metal and the punched negative electrode current collector 4a and the negative electrode layer 4b.

Next, a non-aqueous electrolyte was prepared. The non-aqueous electrolytic solution was prepared by mixing LiClO ₄ at 1 mol / L in a solvent prepared by mixing propylene carbonate and dimethoxyethane in equal volumes.
, A non-aqueous electrolyte was prepared.

Next, a thickness of 50 μm is provided between the positive electrode and the negative electrode.
And a nonaqueous electrolyte was injected into the positive electrode can and the negative electrode lid, and the positive electrode can and the negative electrode lid were crimped and sealed via a gasket made of polypropylene. As described above, a coin-type lithium secondary battery having a diameter of 20 mm and a thickness of 1.6 mm was produced.

Sample 2 In sample 2, a lithium-manganese composite oxide was synthesized with a specific surface area of 0.52 m ² / g when synthesizing the positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 3 In sample 3, a lithium-manganese composite oxide was synthesized with a specific surface area of 1.06 m ² / g when synthesizing the positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 4 In sample 4, a lithium-manganese composite oxide was synthesized with a specific surface area of 7.00 m ² / g when synthesizing the positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 5 In sample 5, when synthesizing the positive electrode active material, the lithium / manganese composite oxide was synthesized with the molar ratio of Li to Mn being 0.50. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 6 In sample 6, when synthesizing the positive electrode active material, the lithium-manganese composite oxide was synthesized with the molar ratio of Li to Mn being 0.80. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 7 In Sample 7, a lithium-manganese composite oxide was synthesized with the valence analysis value of Mn being 4.00 when synthesizing the positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 8 In sample 8, a lithium-manganese composite oxide was synthesized with a specific surface area of 0.08 m ² / g when synthesizing a positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 9 In sample 9, a lithium / manganese composite oxide was synthesized with a specific surface area of 8.20 m ² / g when synthesizing the positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 10 In sample 10, a lithium-manganese composite oxide having a molar ratio of Li to Mn of 0.45 was synthesized when a positive electrode active material was synthesized. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 11 In Sample 11, a lithium-manganese composite oxide was synthesized at a molar ratio of Li to Mn of 0.90 when synthesizing the positive electrode active material. Next, a coin-type lithium secondary battery was manufactured in the same manner as in Sample 1, except that this lithium-manganese composite oxide was used as a positive electrode active material.

Sample 12 In Sample 12, when the positive electrode active material was synthesized, the manganese valence analysis value was set to 3.73 to synthesize a lithium-manganese composite oxide. Next, except that this lithium-manganese composite oxide was used as a positive electrode active material, Sample 1 was used.
In the same manner as in the above, a coin-type lithium secondary battery was produced.

Sample 13 In Sample 13, when the positive electrode active material was synthesized, the valence analysis value of Mn was 4.06 to synthesize a lithium-manganese composite oxide. Next, except that this lithium-manganese composite oxide was used as a positive electrode active material, Sample 1 was used.
In the same manner as in the above, a coin-type lithium secondary battery was produced.

Next, Samples 1 to 5 prepared as described above were used.
For the lithium secondary battery of Sample 13, the initial capacity ratio, the discharge capacity retention rate after high-temperature storage, the discharge capacity ratio after high-temperature storage, and the discharge capacity retention rate at the 100th cycle were measured. Table 1 below shows the measurement results of Samples 1 to 13. The Li / Mn molar ratio in Table 1 is the ratio of the number of moles of Li to the number of moles of Mn.

[0068]

[Table 1]

In Table 1, samples 1 to 13
Was evaluated as follows. When evaluating the initial capacity ratio, each sample was charged and discharged under the conditions of a charging current of 1 mA, a constant current constant voltage charging up to an upper limit voltage of 3.3 V, and a constant current discharging up to a discharge current of 4 mA and a discharge end voltage of 2.0 V. Was charged and discharged for the first time. Next, each sample was charged and discharged in the second cycle under the same charge and discharge conditions as the initial charge and discharge, and the discharge capacity in the second cycle was measured. The initial capacity ratio is a value indicating the ratio of the discharge capacity in the second cycle of each sample to the discharge capacity in the second cycle of sample 4.

The charge / discharge capacity retention ratio of the 100th cycle of Samples 1 to 13 was evaluated as follows. 10
When measuring the discharge capacity retention ratio at the 0th cycle, charge / discharge was repeated 100 times for each sample under the same charge / discharge conditions as the initial charge / discharge, and the discharge capacity at the 100th cycle was measured. The discharge capacity maintenance rate at the 100th cycle is:
This is a value indicating the discharge capacity at the 100th cycle with respect to the discharge capacity at the second cycle as a ratio.

The capacity retention ratio of Samples 1 to 13 after storage at high temperature and the discharge capacity ratio after storage at high temperature were evaluated as follows. When measuring the capacity retention rate after high-temperature storage, each sample was charged and discharged for 5 cycles under the same charge and discharge conditions as the initial charge and discharge, and then charged under the same charge conditions as the initial charge. It was stored in a 60 ° C. atmosphere for 60 days. After storage, each sample was discharged at room temperature under the same charge / discharge conditions as the first charge / discharge, then 10 cycles of charge / discharge were performed under the same charge / discharge conditions as the first charge / discharge, and the discharge capacity was measured for each cycle.

The capacity retention rate after storage at high temperature is a value indicating the highest discharge capacity in 10 cycles of charge and discharge after storage at high temperature with respect to the initial capacity. The discharge capacity ratio after high-temperature storage is calculated by multiplying the initial capacity ratio by the discharge capacity retention rate after high-temperature storage.

From the evaluation results shown in Table 1, the ratio of the positive electrode active material
0.1m surface area²/ g or more, 7.0m ²/ g or less
Samples 1 to 4 have a specific surface area of 0.08 m²/
g retention rate after high temperature storage compared to sample 8
And that the discharge capacity ratio after storage at high temperatures has increased.
I understand.

In Sample 8, since the specific surface area of the positive electrode active material was 0.08 m ² / g, the contact area between the positive electrode active material and the non-aqueous electrolyte was reduced, and the load characteristics of the positive electrode were reduced. The initial capacity and the capacity retention rate after high-temperature storage are reduced. For this reason, in Sample 8, the discharge capacity ratio after high-temperature storage also decreases.

Also, from the results shown in Table 1, Samples 1 to 4 in which the specific surface area of the positive electrode active material is 0.1 m ² / g or more and 7.0 m ² / g or less have a specific surface area of 7.0 m ² / g or less. 00m
It can be seen that the discharge capacity retention ratio after high-temperature storage and the discharge capacity ratio after high-temperature storage are larger than those of Sample 9 larger than ² / g.

In sample 9, since the specific surface area of the positive electrode active material was too large at 8.20 m ² / g, the contact area between the positive electrode active material and the nonaqueous electrolyte was large, and the lithium-manganese composite oxide was Since the aqueous electrolyte reacts excessively in a high temperature environment, the non-aqueous electrolyte deteriorates.
Therefore, in Sample 9, the discharge capacity retention rate after high-temperature storage is reduced. Therefore, in Sample 9, the discharge capacity ratio after high-temperature storage also decreases.

For these samples, samples 1 to
Sample 4 has a specific surface area of 0.1 m ² / g or more and 7.0 m
By controlling to ² / g or less, the contact area between the positive electrode active material and the specific surface area becomes appropriate, so that the load characteristics of the positive electrode and the deterioration of the non-aqueous electrolyte in a high temperature environment are suppressed. Therefore, a decrease in battery capacity is suppressed. Therefore, in Samples 1 to 4, the discharge capacity ratio after high-temperature storage is good.

Further, from the results shown in Table 1, Samples 2, 5 and 6 in which the molar ratio of Li to Mn is in the range of 0.5 to 0.8 are 0%. 1 compared to sample 10 which is .45
It can be seen that the discharge capacity maintenance ratio at the 00th cycle is large.

In Sample 10, since the molar ratio of Li to Mn is 0.45, the crystal structure of the positive electrode active material is unstable. For this reason, in the sample 10, since the crystal structure of the positive electrode active material is deteriorated by repeating charge and discharge, the discharge capacity retention ratio at the 100th cycle is reduced.

Further, from the results shown in Table 1, Samples 2, 5, and 6 in which the molar ratio of Li to Mn is in the range of 0.5 or more and 0.8 or less have the molar ratio of Li to Mn of 0. It can be seen that the initial capacity ratio and the discharge capacity ratio after high-temperature storage are higher than those of Sample 11 which is 0.90.

In sample 11, since the molar ratio of Li to Mn is 0.90, lithium ions that can contribute to charging and discharging are greatly reduced, and the initial capacity ratio is reduced. For this reason, in Sample 11, although the initial capacity is small, the capacity retention rate during high-temperature storage is high,
The discharge capacity ratio after high-temperature storage is reduced.

In contrast to these samples, in sample 2, sample 5 and sample 6, by controlling the molar ratio of Li to Mn to a range of 0.5 or more and 0.8 or less, repetition of charge / discharge and high-temperature storage were performed. As a result, the deterioration of the crystal structure of the positive electrode active material due to the above is suppressed, and lithium ions that can participate in charge and discharge are secured, so that the discharge capacity ratio after storage at high temperatures and the discharge capacity retention rate at the 100th cycle are improved.

Further, from the results shown in Table 1, Sample 2 having a valence analysis value of Mn in the range of 3.8 or more and 4.0 or less was obtained.
Also, it can be seen that Sample 7 has a higher discharge capacity ratio after high-temperature storage than Sample 12, in which the valence analysis value of Mn is 3.73.

In sample 12, since the valence analysis value of Mn is 3.73, the initial capacity decreases with a decrease in the Mn valence, so that the discharge capacity ratio after high-temperature storage also decreases.

Further, from the results shown in Table 1, Sample 2 having a valence analysis value of Mn in the range of 3.8 or more and 4.0 or less was obtained.
Also, it can be seen that Sample 7 has a larger discharge capacity ratio after high-temperature storage than Sample 13 in which the valence analysis value of Mn is 4.06.

In sample 13, since the valence analysis value of Mn is 4.06, although the initial capacity is increased, M
Due to the increase of the n valence, the lithium-manganese composite oxide and the non-aqueous electrolyte react excessively in a high-temperature environment and the non-aqueous electrolyte deteriorates, so that the discharge capacity ratio after high-temperature storage decreases. .

In contrast to these samples, Samples 2 and 7 had Mn valence analysis values of 3.8 or more,
By controlling to a range of 4.0 or less, it is possible to secure the initial capacity and to suppress a decrease in the capacity retention rate during high-temperature storage. Therefore, in Samples 2 and 7, the discharge capacity ratio after high-temperature storage is good.

As described above, in the positive electrode active material used in the lithium secondary battery, the specific surface area is in the range of 0.1 m ² / g to 7.0 m ² / g, and the molar ratio of Li to Mn is 0.1. The range of 5 or more and 0.8 or less and the valence analysis value of Mn in the range of 3.8 or more and 4.0 or less are required to reduce the discharge capacity ratio after high-temperature storage and the discharge capacity retention rate at the 100th cycle. It is clear that this is effective in producing a lithium secondary battery in which the reduction is suppressed.

[0089]

As described in detail above, in the nonaqueous electrolyte battery according to the present invention, the contact area between the positive electrode active material and the nonaqueous electrolyte is controlled by controlling the specific surface area of the positive electrode active material. Therefore, deterioration of the non-aqueous electrolyte in a high-temperature environment is suppressed. In addition, the nonaqueous electrolyte battery controls the molar ratio of Li to Mn of the positive electrode active material and the valence analysis value of Mn, thereby maintaining the charge-discharge cycle characteristics by stabilizing the crystal structure of the positive electrode active material, It is possible to secure the capacity after high-temperature storage. Therefore, according to the present invention, a non-aqueous electrolyte battery in which deterioration of battery characteristics is suppressed by suppressing deterioration of the non-aqueous electrolyte and stabilizing the crystal structure of the positive electrode active material is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an internal structure of a coin-type nonaqueous electrolyte to which the present invention is applied.

[Explanation of symbols]

1 Non-aqueous electrolyte battery, 2 positive electrode, 3 positive electrode can, 4 negative electrode, 5 negative electrode lid, 6 separator, 7 gasket

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 5H029 AJ07 AK03 AL02 AL06 AL12                       AM03 AM04 AM07 BJ03 BJ12                       HJ02 HJ07                 5H050 AA10 BA16 BA17 CA09 CB02                       CB07 CB12 FA02 HA02 HA07

Claims (1)

[Claims] 1. A positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having an electrolyte salt, wherein the positive electrode active material has a chemical formula of Li _x Mn ^(m) O
_It is a lithium-manganese composite compound represented by _{(x + m) / 2} , having a specific surface area of 0.1 m ² / g or more and 7.0 m ² / g or less, and x in the chemical formula of 0.5 or more. A non-aqueous electrolyte battery, wherein m in the chemical formula is 3.8 or more and 4.0 or less.