JP2001023617A - Manufacture of lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having a high energy density capable of being used at a high temperature in which an electric capacity is large and a charge/discharge cycle durability is excellent. SOLUTION: The lithium secondary battery provided with a positive electrode active substance represented by a formula: LixMnyM1-yO2 (M is one kind or more of Al, Fe, Co, Ni, Mg or Cr, 0<x<=1.1, 0.5<=y<=1); a negative electrode active substance and an organic electrolyte containing a lithium ion is charged at 4.0-4.8 V at 60-100 deg.C in a manufacture step. A time for applying a voltage of 4.0-4.8 V is 0.5 hours to 7 days.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, as devices have become more portable and cordless, expectations are growing for lithium secondary batteries that are small, lightweight, and have a high energy density. As an active material for a non-aqueous electrolyte secondary battery, LiCoO ₂ ,
Composite oxides of lithium and a transition metal, such as LiNiO ₂ , LiMn ₂ O ₄ , and LiMnO ₂ , are known. In particular, recently, research on lithium and manganese composite oxides has been actively conducted as a highly safe and inexpensive material. Further, development of a high voltage, high energy density lithium secondary battery in which the above active material is used as a positive electrode active material and combined with a negative electrode active material such as a carbon material capable of inserting and extracting lithium has been promoted.

In general, the above-mentioned positive electrode active materials have different electrode characteristics such as electric capacity, reversibility of occlusion and desorption of lithium ions, operating voltage and safety, depending on the type of transition metal constituting the composite oxide. .

For example, LiCoO ₂ and LiNi _0.8 Co
Non-aqueous electrolyte secondary batteries using a composite oxide having a layered rock salt structure containing cobalt or nickel, such as _0.2 O ₂ , as a positive electrode active material are 140 to 160 mAh / g and 19, respectively.
A relatively high capacity density of 0 to 210 mAh / g can be achieved, and good charge / discharge characteristics are exhibited in a high voltage range of 2.5 to 4.3 V. However, when the battery is heated and charged,
The problem that the charged positive electrode active material reacts with the solvent of the electrolytic solution to cause the battery to easily generate heat, the problem that the cost of the active material is high because cobalt or nickel as the raw material is expensive, and the problem in the 2.5 to 3.5 V region. There is a problem such as low capacity.

On the other hand, relatively inexpensive manganese is used as a raw material.
LiMn_TwoO_Four-Based spinel-type composite oxide as active material
The lithium secondary battery used was a cathode active material and an electrolytic
Heat generation of battery due to reaction with liquid solvent is relatively unlikely
Has a capacity of 100 to 120 mAh / g and
Or lower than when a positive electrode active material containing nickel is used
No. At room temperature, it has charge / discharge cycle durability.
Degrades rapidly in the low voltage region below V,
When used at 0-60 ° C, the charge / discharge cycle durability is
poor. Therefore, LiCoO_Two, LiNi_0.8Co_0.2
O_TwoAnd LiMn _TwoO_FourLithium secondary battery using carbon as active material
Ponds are subject to safety, charge / discharge cycle durability, etc.
The upper limit of the operating temperature is 60 ° C, and it is usually charged below 50 ° C
Have been.

However, for applications such as power storage, a secondary battery that operates safely and durably at 60 ° C. or higher is desired from the viewpoint of heat balance, but such a battery has not yet been developed. In WO97 / 30487, LiCo
When manufacturing a lithium secondary battery using O ₂ as a positive electrode active material, aging at a low circuit temperature of 2 to 30 ° C. and a high temperature of 40 to 70 ° C. with an open circuit voltage of 2.5 to 3.8 V results in capacity or charge / discharge. Although it has been reported that deterioration due to cycling can be improved, the absolute value of the capacity was low even with this method, and was not sufficient.

[0007] On the other hand, LiMnO ₂ is expected to have a high capacity in principle, and is therefore promising. LiMnO _{2 has} an orthorhombic structure composed of β-NaMnO ₂ type structure and α-N
A monoclinic having a layered rock salt structure having an aMnO ₂ type structure is known. Since orthorhombic LiMnO ₂ can operate up to a low voltage range of about 2 V, it can be expected to have a higher capacity than LiMn ₂ O ₄ , but the charge / discharge cycle durability is poor because it gradually transitions to a spinel phase by repeated charge / discharge. There's a problem.

LiMnO_TwoFe, Ni, Co, Cr or
The positive electrode active material to which Al is added is disclosed in JP-A-10-13481.
2, the synthesized LiMnM¹O_Two(M
¹= Fe, Co, Ni, Cr, Al)
According to the results of the analysis, _TwoStructure and charge and discharge
Electric cycle stability is inadequate.

Further, monoclinic LiMnO ₂ also has a problem that the charge / discharge speed is slow, and the capacity does not start to develop unless the charge / discharge cycle is performed for about 10 to 30 cycles. Specifically, LiAl _0.25 Mn _0.75 O having a monoclinic layered rock salt structure
₂ shows that the capacity at the first and second cycles at a discharge rate of C / 5 at room temperature is 110 mAh / g.
It has been reported that the capacity increases to 180 mAh / g at a discharge rate of 50 mAh / g at a discharge rate of C / 15 (Young-I. Jang et al., Electroc).
hem. Solid-State Lett. , 1,1
3 (1998)).

Further, the monoclinic layered rock salt structure and the orthorhombic LiAl _0.05 Mn _0.95 O ₂ , and the LiMnO ₂ having the monoclinic layered rock salt structure all have a capacity of the first or second cycle at 55 ° C. If the charge / discharge cycle is not 7 to 30 cycles, the capacity is not stable in a state of increased capacity, the ultimate capacity is low, and the capacity is rapidly reduced when charged / discharged rapidly. (Yet-Ming Chiang et al., E
electrochem. Solid-State Le
tt. , 2, 107 (1999)).

As a method for producing monoclinic and orthorhombic LiMnO _2, a production method by a solid phase reaction method is described in the above two documents. Further, a method has been reported in which monoclinic LiMnO ₂ is directly produced by hydrothermally treating a manganese oxide in a lithium salt aqueous solution containing a hydroxide of an alkali metal other than lithium (JP-A-11-2112).
8). However, a lithium secondary battery that can operate stably at high temperatures even when the one obtained by this method is used as a positive electrode active material has not been obtained.

[0012]

Therefore, the present invention can be used in a wide voltage range, has a large capacity at a high current density, has a high energy density, has excellent charge / discharge cycle durability, can operate at high temperatures, and is safe. It is an object of the present invention to provide a method for manufacturing a highly reliable lithium secondary battery.

[0013]

Means for Solving the Problems The present invention, Li _x Mn _y M
_1-y O ₂ (where M is Al, Fe, Co,
At least one element selected from the group consisting of Ni, Mg and Cr, where 0 <x ≦ 1.1 and 0.5 ≦ y ≦ 1. ) A positive electrode active material layer containing a composite oxide as a main component and a negative electrode active material layer capable of inserting and extracting lithium ions were opposed to each other via a separator, and were impregnated with an organic electrolyte solution containing lithium ions. Thereafter, there is provided a method for manufacturing a lithium secondary battery, wherein a voltage of 4.0 to 4.8 V is applied between a positive electrode active material layer and a negative electrode active material layer at 60 to 100 ° C.

Further, the present invention is represented by _{Li x Mn y M 1-y} O 2 ( however, M is Al, Fe, Co, Ni, Mg
And Cr are at least one element selected from the group consisting of 0 <x ≦ 1.1 and 0.5 ≦ y ≦ 1. After the positive electrode active material layer mainly composed of a composite oxide and the negative electrode active material layer capable of inserting and extracting lithium ions are opposed to each other via a polymer electrolyte containing lithium ions and an organic solvent, 60 to 100 ° C. between the active material layer and the negative electrode active material layer
Wherein a voltage of 4.0 to 4.8 V is applied to the lithium secondary battery.

[0015]

Li _x Mn _y M _1-y in DETAILED DESCRIPTION OF THE INVENTION The present invention
Y in the composite oxide represented by O ₂ is 0.5 or more and 1 or less. If y is less than 0.5, the capacity decreases. In order to obtain a secondary battery having a large capacity and excellent cycle durability, y is particularly preferably 0.75 to 0.99, more preferably 0.90 to 0.90.
０．９0.97 is preferred.

In the present invention, the positive electrode active material layer and the negative electrode active material layer are opposed to each other with a separator interposed therebetween, and are impregnated with a specific organic electrolyte and then charged. Alternatively, charging is performed after the positive electrode active material layer and the negative electrode active material layer are opposed to each other via a specific polymer electrolyte. In the production method of the present invention, between the positive electrode active material layer and the negative electrode active material layer at 4.0 to 100 ° C., 4.0 to 4.0.
A voltage of 8 V is applied and maintained in this voltage range (hereinafter, referred to as “V”).
This operation is referred to as voltage holding).
It may be carried out by applying a voltage of 4.0 to 4.8 V at １００100 ° C., or by applying an open circuit voltage of 4.0 to 4.8 V at 60 to 100 ° C. after the above charging. May be implemented.

When the voltage holding temperature is lower than 60 ° C., the effect of increasing the capacity by the voltage holding and the effect of improving the rapid charge / discharge performance are small. On the other hand, when the voltage holding temperature exceeds 100 ° C., the electrochemical deterioration of the electrodes and the electrolyte becomes remarkable. The voltage holding temperature is particularly preferably from 70 to 90C. On the other hand, when the voltage for holding the voltage is less than 4.0 V, the capacity increasing effect and the rapid charge / discharge performance improving effect by the voltage holding are small. If the voltage for holding the voltage exceeds 4.8 V, the electrochemical deterioration of the electrodes and the electrolyte will increase. The voltage for holding the voltage is particularly preferably 4.2 to 4.5 V.

The voltage holding time is not particularly limited, but is preferably 0.5 hours to 7 days. When the time is less than 0.5 hour, the effect of increasing the capacity is small. Particularly preferably 2 hours or more
5 days. In addition, the relationship between the temperature and the voltage for holding the voltage may be set within the above-described range, in which case the voltage is set lower when the temperature is set higher, and the voltage is set higher when the temperature is set lower.

The composite oxide represented by _{Li x Mn y M 1-y} O 2 in the present invention is a layered rock salt structure or orthorhombic monoclinic in a state before voltage holding monoclinic It is preferred that the system has a layered rock salt structure. When the monoclinic layered rock salt structure is used, the charge / discharge cycle durability of the lithium secondary battery obtained by the present invention is increased.

The reason why the capacitance by the voltage held in the present invention is rapid charge and discharge performance is improved or increased is not clear, 60 ° C. in a state in which the _{Li x Mn y M 1-y} O 2 lithium by charging is dedoped It is presumed that when the temperature is maintained at the above high temperature, some change in the crystal structure occurs at an accelerated rate.

The previous voltage holding in the present invention Li _x Mn _y M _1-y
O ₂ has a monoclinic layered rock salt structure or orthorhombic structure, but after a voltage holding in a manufacturing process or a charge / discharge cycle after a secondary battery is manufactured, the original layered rock salt structure or an oblique crystal is not always required. It is not necessary to keep the tetragon. _{Li x Mn y M 1-y} O 2
After the charge / discharge cycle, the layer structure has changed from the layered structure to an amorphous state to a considerable extent, and an X-ray diffraction spectrum of the spinel phase may be obtained in some cases, but a high effect such as improvement in capacity is obtained.

The positive electrode active material layer in the present invention is formed, for example, as follows. That is, a slurry or a kneaded material is formed by mixing a carbon-based conductive material such as acetylene black, graphite, and Ketjen black with a binder or a solvent or a dispersion medium of the binder in the lithium-manganese composite oxide powder, In the case of (1), the positive electrode current collector is applied or supported, and in the case of a kneaded material, a positive electrode active material layer is formed on the positive electrode current collector by press rolling or pressing. At this time, polyvinylidene fluoride, polytetrafluoroethylene,
Polyamide, carboxymethyl cellulose, acrylic resin and the like are used. Aluminum foil, stainless steel foil, or the like is used as the positive electrode current collector.

In the present invention, the porosity of the positive electrode active material layer is preferably 27 to 37%. When the porosity is less than 27%, the electrolyte is less likely to be impregnated into the electrodes, and the internal resistance of the battery tends to increase. If it exceeds 37%, the volume of the positive electrode active material layer increases, and the charge / discharge capacity per unit volume tends to decrease. The porosity is particularly preferably 30 to 35%. The porosity of the positive electrode active material layer is determined by pressing conditions for press-rolling the positive electrode body formed by forming the positive electrode active material layer on the positive electrode current collector,
It can be controlled by the content of the solvent or the dispersion medium when forming the slurry or the kneaded material.

The composite oxide represented by _{Li x Mn y M 1-y} O 2 used in the present invention include a mixture of the compound and a manganese compound and a lithium compound containing a metal element M by the solid phase method 500-1000 It is manufactured by calcining at 100C or hydrothermal synthesis at 100-300C. When obtaining a composite oxide having a monoclinic layered rock salt structure, a manganese compound and a compound containing a metal element M are added to an aqueous solution containing a lithium element and a hydroxide of an alkali metal other than lithium. It is preferable to produce by hydrothermal synthesis at ~ 300 ° C.

When produced by hydrothermal synthesis, it is preferable that the hydroxide of an alkali metal other than lithium contains a high concentration of potassium hydroxide or sodium hydroxide. In addition, the manganese compound and the compound containing the metal element M are the same as the coprecipitated hydroxide, coprecipitated oxide or coprecipitated oxyhydroxide of manganese and metal element M. It is particularly preferable to add the compound to an aqueous solution containing the substance.

The manganese compound used as a raw material includes oxides (Mn ₂ O ₃ , MnO, MnO _2, etc.) or hydrates thereof,
Oxyhydroxide and the like. The valence of manganese in the manganese compound is preferably trivalent. The manganese compounds may be used alone or as a mixture of two or more.

When the lithium-manganese composite oxide is produced by a solid phase method, for example, an alkali such as ammonia is added to an aqueous solution containing manganese nitrate and a nitrate of the metal element M to form a coprecipitated hydroxide. This coprecipitated hydroxide powder is dispersed in an aqueous lithium hydroxide solution, and the solid obtained by evaporating the slurry to dryness is controlled by controlling the oxygen partial pressure in a range from 10 ^-2 to 10 ^-7 atm. It is obtained by firing at 800 to 960 ° C. At this time, by adjusting the oxygen partial pressure and the firing temperature, monoclinic crystals and orthorhombic crystals can be separately formed.

As the compound containing the metal element M as a raw material, hydroxide, oxide, oxyhydroxide, chloride, nitrate and the like are used. A simple metal M may be used instead of the compound containing the metal element M. These may be used alone or as a mixture of two or more.

In the lithium secondary battery of the present invention, carbonate is preferable as the solvent of the organic electrolyte or the organic solvent contained in the polymer electrolyte. Carbonate is cyclic,
Any chain type can be used. As the cyclic carbonate, propylene carbonate, ethylene carbonate (hereinafter, referred to as “carbonate”)
EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (hereinafter referred to as DEC), ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate and the like. In the present invention, the above carbonates can be used alone or in combination of two or more. Moreover, you may mix and use it with another solvent. Further, depending on the material of the negative electrode active material, the combined use of a chain carbonate and a cyclic carbonate may improve the discharge characteristics, cycle durability, and charge / discharge efficiency.

The solute contained in the organic electrolyte and the polymer electrolyte includes ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , B
F ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ CO ₂ ⁻ ,
A lithium salt having (CF ₃ SO ₂ ) ₂ N ⁻ or the like as an anion is preferable, and it is preferable to use at least one of them.

When a polymer electrolyte is used, a vinylidene fluoride / hexafluoropropylene copolymer (for example, trade name: Kayner, manufactured by Atochem Co.) may be used as the organic solvent, or vinylidene fluoride disclosed in JP-A-10-294131. It is preferable to add a perfluoro (propyl vinyl ether) copolymer or the like and add the above solute to use it as a gel polymer electrolyte.

In the above-mentioned organic electrolytic solution or polymer electrolyte, it is preferable that the electrolyte composed of a lithium salt is contained in an amount of 0.2 to 2.0 mol / l. Outside of this range, the ionic conductivity decreases and the electrical conductivity of the electrolyte decreases. More preferably, it is 0.5 to 1.5 mol / liter.

The negative electrode active material in the present invention is a material capable of inserting and extracting lithium ions. The material forming the negative electrode active material is not particularly limited, for example, lithium metal,
Examples thereof include a lithium alloy, a carbon material, an oxide mainly containing a metal belonging to Groups 14 and 15 of the periodic table, a carbide such as silicon carbide and boron carbide, a silicon oxide compound, and titanium sulfide. As the carbon material, those obtained by thermally decomposing an organic substance under various thermal decomposition conditions, artificial graphite, natural graphite, earth graphite, expanded graphite, flaky graphite and the like can be used. As the oxide, a compound mainly composed of tin oxide can be used.

The negative electrode active material layer is preferably formed on a negative electrode current collector. As the negative electrode current collector, a copper foil, a nickel foil or the like is used. When an organic electrolyte is used, a porous polyethylene film, a porous polypropylene film, or the like is preferably used as a separator interposed between the positive electrode active material layer and the negative electrode active material layer.

Since the lithium secondary battery obtained by the present invention has a high energy density and a high output density as compared with conventional products, particularly at a high temperature of 60 ° C. or higher, it is preferable to operate the battery at 60 to 85 ° C. . Therefore, it is particularly useful as an electric power storage application in which the ambient temperature tends to be relatively high, a load leveling, a main power supply or an auxiliary power supply for electric vehicles and hybrid vehicles. The shape of the lithium secondary battery obtained by the present invention is not particularly limited. A sheet shape (a so-called film shape), a folded shape, a wound-type bottomed cylindrical shape, a coin shape, and the like are selected according to the application.

[0036]

The following examples (Examples 1 to 7) and comparative examples (Example 8)
To 13), the present invention will be specifically described, but the present invention is not limited thereto.

Example 1 An aqueous solution containing manganese nitrate and chromium nitrate was co-precipitated by adding an aqueous solution of ammonium hydroxide.
Heating and drying at 150 ° C. yielded a manganese-chromium coprecipitated hydroxide. The manganese-chromium coprecipitated hydroxide was added to the aqueous lithium hydroxide solution, and after stirring, the solvent was evaporated to dryness to obtain a solid. This solid was calcined at 950 ° C. for 3 hours under normal pressure at an oxygen partial pressure of 10 ⁻⁶ atm to obtain a powder.

As a result of X-ray diffraction analysis of the powder by CuKα ray, 2θ = 18 °, 37 °, 39 °, 45 °, 61 °
, 65 ° and 67 ° diffraction peaks, and a layered rock salt type LiM belonging to the space group C2 / m having a monoclinic phase
nO it was found to be ₂ structure. The elemental analysis of the powder revealed that the powder was LiMn _0.95 Cr _0.05 O ₂ .

The above powder was used as a positive electrode active material, and the positive electrode active material, acetylene black and polytetrafluoroethylene were mixed (80/15/5 by weight), kneaded while adding toluene, and formed into a sheet. This sheet has a diameter of 13
mm and vacuum dried at 180 ° C. for 2 hours. The above sheet was used as a positive electrode active material layer in an argon glove box and placed on an aluminum foil positive electrode current collector having a diameter of 18 mm and a thickness of 20 μm.

As the separator, a porous polypropylene having a thickness of 25 μm was used. Further, a metal lithium foil having a thickness of 500 μm was used as the negative electrode active material layer, and the negative electrode current collector was made of SUS31.
A 6 L foil was used. 1 LiPF ₆ for electrolyte
A solution dissolved in a 1: 1 mixed solvent of EC and DEC so as to have a mole / liter was used. In the argon glove box, the case made of SUS316L is
So that the cap made of US316L is on the negative electrode side,
The positive electrode active material layer and the negative electrode active material layer face each other with a separator interposed therebetween and are housed in a case together with a current collector, and have a diameter of 20 m.
m, a coin cell having a thickness of 3.2 mm was assembled.

Using this coin cell, the battery was charged at a constant current of 4.3 mA at a current density of 150 mA per gram of the positive electrode active material in a constant temperature bath at 75 ° C. in the air, and then charged at a constant voltage of 4.3 V. Ten hours after the start of charging, the application of the voltage of 4.3 V was completed, and a lithium secondary battery was obtained. In this charging, the holding time at 4.0 V or more was 9.0 hours, and the voltage holding time at 4.2 V or more was 8.5 hours.

The above lithium secondary battery was charged at 50 ° C. with a current density of 30 mA per gram of the positive electrode active material and an upper limit voltage of 4.3 V.
And constant current discharge at 50 ° C. at a current density of 30 mA per 1 g of the positive electrode active material and a lower limit voltage of 2.0 V. The discharge capacity and discharge energy in the second cycle were determined to be 202 mAh / g, respectively. 615mWh / g
Met. After repeating the charge and discharge cycle further,
The discharge capacity and discharge energy at the 10th cycle were 2
00 mAh / g and 608 mWh / g were maintained.

Example 2 A lithium secondary battery obtained in the same manner as in Example 1 was heated at 75 ° C. for 150 g per 1 g of the positive electrode active material.
Discharge was performed at a constant current of 2.0 V at a current density of mA, and the discharge was terminated 10 hours after the start of discharge. The discharge capacity and discharge energy were 285 mAh / g and 720 mWh / g, respectively. Of the discharge capacity of 285 mAh / g, the discharge capacity at a current density of 150 mA per 1 g of the positive electrode active material was 230.
mAh / g, and the rapid discharge performance was also good.

Example 3 A lithium secondary battery obtained in the same manner as in Example 1 was heated at 65 ° C. for 30 g per 1 g of the positive electrode active material.
A constant current discharge at a current density of A with a lower limit voltage of 2.0 V,
When the discharge capacity and discharge energy in the second cycle were determined, they were 225 mAh / g and 645 mWh / g, respectively.

Example 4 A lithium secondary battery obtained in the same manner as in Example 1 was treated at 30 ° C. for 30 m / g of the positive electrode active material.
A constant current discharge at a current density of A with a lower limit voltage of 2.0 V,
When the discharge capacity and discharge energy in the second cycle were determined, they were 130 mAh / g and 420 mWh / g, respectively.

Example 5 A lithium secondary battery was obtained in the same manner as in Example 1 except that charging was performed at 70 ° C. and 4.4 V. This lithium secondary battery is heated at 50 ° C. for 3 g per 1 g of the positive electrode active material.
Constant current charging at a current density of 0 mA and an upper limit voltage of 4.3 V, constant current discharge at 50 ° C. at a current density of 30 mA per 1 g of the positive electrode active material and a lower limit voltage of 2.0 V, and discharge capacity and discharge energy in the second cycle Were 195 mAh / g and 592 mWh / g, respectively.

Example 6 A powder of a lithium-manganese-iron composite oxide was obtained in the same manner as in Example 1 except that iron nitrate was used instead of chromium nitrate. The powder produced by X-ray diffraction analysis was a monoclinic layered rock salt type LiMnO as in Example 1.
It turns out that it has _two structures. Further, elemental analysis of the powder revealed that the composition was LiMn _0.95 Fe _0.05 O ₂ .

A coin cell was prepared in the same manner as in Example 1, and the same amount as in Example 1 was obtained in a constant temperature bath at 80 ° C. for 1 g of the positive electrode active material.
The battery was charged at a constant current of 4.3 V at a current density of 50 mA, and then charged at a constant voltage of 4.3 V. The application of a voltage of 4.3 V was terminated 10 hours after the start of charging to obtain a lithium secondary battery.
In this charging, the voltage holding time at 4.0 V or more was 8.8 hours, and the voltage holding time at 4.2 V or more was 8.3 hours.

Using the above lithium secondary battery, constant current charging was performed at 80 ° C. at a current density of 30 mA per gram of the positive electrode active material and an upper limit voltage of 4.3 V, and at a current density of 30 mA per gram of the positive electrode active material and a lower limit voltage of 2 V. The discharge capacity and the discharge energy in the second cycle were determined by discharging at a constant current of 0.0 V, and were 233 mAh / g and 638 mWh / g, respectively.
Met.

[Example 7] A manganese-aluminum coprecipitated hydroxide was synthesized in the same manner as in Example 1 except that aluminum nitrate was used instead of chromium nitrate. Obtained. The powder produced by X-ray diffraction analysis is a monoclinic layered rock salt type L
It was found that the structure was iMnO ₂ . Further, elemental analysis of the powder revealed that the powder was LiMn _0.93 Al _0.07 O ₂ .

A coin cell was prepared in the same manner as in Example 1 and the positive electrode active material 1 was placed in a thermostat at 75 ° C. in the same manner as in Example 1.
The battery was charged at a constant current of 4.3 mA at 150 mA per g, and then charged at a constant voltage of 4.3 V. The application of a voltage of 4.3 V was terminated 10 hours after the start of charging to obtain a lithium secondary battery.
In this charging, the holding time at 4.0 V or more was 8.8 hours, and the holding time at 4.2 V or more was 8.3.
It was time.

Using the above-mentioned lithium secondary battery, constant current charging was performed at 75 ° C. at a current density of 30 mA per 1 g of the positive electrode active material and an upper limit voltage of 4.3 V, and at a current density of 30 mA per 1 g of the positive electrode active material and the lower limit voltage. The discharge capacity and discharge energy in the second cycle after constant current discharge at 2.0 V were determined to be 213 mAh / g and 615 mWh / g, respectively.

Example 8 A lithium secondary battery was manufactured in the same manner as in Example 1 except that the voltage was not held at 75 ° C. Using this lithium secondary battery, charging and discharging were performed in the same manner as in Example 1, and the discharge capacity and discharge energy at the second cycle were determined. The results were 135 mAh / g and 435 mWh /, respectively.
g.

[Example 9] A lithium secondary battery was fabricated in the same manner as in Example 3, except that the voltage was not held at 75 ° C. Using this lithium secondary battery, charging and discharging were performed in the same manner as in Example 3, and the discharge capacity and discharge energy at the second cycle were determined. The results were 160 mAh / g and 505 mWh /, respectively.
g.

Example 10 A lithium secondary battery was manufactured in the same manner as in Example 4 except that the voltage was not held at 75 ° C. Using this lithium secondary battery, charging and discharging were performed in the same manner as in Example 4, and the discharge capacity and discharge energy at the second cycle were determined. The results were 92 mAh / g and 301 mWh / g, respectively.
Met.

[Example 11] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the voltage for holding the voltage was changed to 3.9V. Using this lithium secondary battery, charging and discharging were performed in the same manner as in Example 1, and the discharge capacity and discharge energy in the second cycle were determined.
/ G.

Example 12 A lithium secondary battery was manufactured in the same manner as in Example 1 except that the voltage holding temperature was changed to 30 ° C. Using this lithium secondary battery, charging and discharging were performed in the same manner as in Example 1, and the discharge capacity and discharge energy at the second cycle were determined. The results were 150 mAh / g and 482 mWh /, respectively.
g.

Example 13 A lithium secondary battery was fabricated in the same manner as in Example 6, except that the voltage was not held. Using this lithium secondary battery, charging and discharging were performed in the same manner as in Example 6, and the discharge capacity and discharge energy in the second cycle were found to be 180 mAh / g and 572 mWh / g, respectively.

[0059]

According to the present invention, it can be used in a wide voltage range, has a large capacity at a high current density, has a high energy density, has high safety, and has good charge / discharge cycle durability which can be used even at 60 ° C. or higher. A lithium secondary battery can be obtained.

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Claims (5)

[Claims] Represented by 1. A _{Li x Mn y M 1-y} O 2 ( where
M is one or more elements selected from the group consisting of Al, Fe, Co, Ni, Mg and Cr, and 0 <x ≦ 1.
1, 0.5 ≦ y ≦ 1. ) A positive electrode active material layer containing a composite oxide as a main component and a negative electrode active material layer capable of inserting and extracting lithium ions were opposed to each other via a separator, and were impregnated with an organic electrolyte solution containing lithium ions. Then, between 60 to 100 ° C. between the positive electrode active material layer and the negative electrode active material layer.
A method for producing a lithium secondary battery, comprising applying a voltage of 0 to 4.8 V. Represented by wherein _{Li x Mn y M 1-y} O 2 ( where
M is one or more elements selected from the group consisting of Al, Fe, Co, Ni, Mg and Cr, and 0 <x ≦ 1.
1, 0.5 ≦ y ≦ 1. After the positive electrode active material layer mainly composed of a composite oxide and the negative electrode active material layer capable of inserting and extracting lithium ions are opposed to each other via a polymer electrolyte containing lithium ions and an organic solvent, 4.0 to 4.0 at 60 to 100 ° C. between the active material layer and the negative electrode active material layer.
A method for manufacturing a lithium secondary battery, comprising applying a voltage of 8V. 3. The method for producing a lithium secondary battery according to claim 1, wherein the time for applying a voltage of 4.0 to 4.8 V is 0.5 hours to 7 days. 4. The composite oxide according to claim 1, wherein the composite oxide has a monoclinic layered rock salt structure before applying a voltage of 4.0 to 4.8 V. Of manufacturing a lithium secondary battery. 5. A method of using a lithium secondary battery obtained by operating the lithium secondary battery obtained by the production method according to claim 1, at a temperature of 60 to 85 ° C.