JP2004296179A - Manufacturing method of lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a lithium secondary battery superior in high temperature cycle characteristics. <P>SOLUTION: An AC current having a frequency of 100 MHz or less is impressed at less than 25°C between a positive electrode and a negative electrode of a lithium secondary battery assembly which comprises the positive electrode having a positive electrode active material which lithium ion is inserted/separated in/from, the negative electrode having a negative electrode active material which lithium ion is inserted/separated in/from, and an electrolyte. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a lithium secondary battery. More specifically, the present invention relates to a method for manufacturing a lithium secondary battery having excellent high-temperature cycle characteristics.
[0002]
[Prior art]
Lithium secondary batteries are excellent in energy density and output density, and can be reduced in size and weight. Therefore, lithium secondary batteries have shown rapid growth as power supplies for portable devices such as notebook computers, mobile phones, and handy video cameras. In addition, it has attracted attention as a power source for electric vehicles and load leveling of electric power.
[0003]
A positive electrode used in a lithium secondary battery generally includes a current collector and a positive electrode active material layer formed on the surface thereof and containing a positive electrode active material, a conductive material, and a binder. As the positive electrode active material, a metal composite oxide of lithium and a transition metal, such as a lithium-manganese composite oxide, a lithium-cobalt composite oxide, or a lithium-nickel composite oxide, and a transition metal site of these metal composite oxides Polymetal composite oxides in which a part of the metal oxide is replaced with another metal have been attracting attention because high performance battery characteristics can be obtained. A lithium secondary battery using these lithium-based composite oxides has an advantage that a high voltage can be obtained and a high output can be obtained.
[0004]
At present, various processing techniques have been proposed to maximize the performance of lithium secondary batteries. For example, for the assembled secondary battery body, a low-temperature aging process of exposing the battery body to an atmosphere maintained at a temperature lower than room temperature for a predetermined time; a room-temperature aging process of exposing the battery body to an atmosphere maintained at room temperature for a predetermined time; A high-temperature aging process for exposing the battery body to an atmosphere maintained at a temperature higher than room temperature for a predetermined time; a rocking rotation process for rocking and / or rotating the battery body; a buffering process for returning the battery body to room temperature; A method of manufacturing a non-aqueous secondary battery having a high charge capacity and excellent cycle characteristics by performing one or more or any combination thereof among means such as a partial charge process for performing a partial charge. (See Patent Document 1): The temperature at the time of the first charge is set to 20 ° C. or less, and the charge current at that time is set to 1 C or less. Subjected to the electrodeposition, electrostatic capacitance 0.4mF / cm on the surface of the negative electrode²A method of forming the following negative electrode coating (SEI) to reduce irreversible capacity and improve cycle characteristics (see Patent Document 2): a positive electrode and a negative electrode using a layered rock salt structure lithium / nickel composite oxide as a positive electrode active material A method of improving the initial discharge capacity and cycle characteristics by performing an aging treatment of storing at a storage temperature of 40 ° C. or more and 90 ° C. or less on a lithium secondary battery formed by assembling (see Patent Document 3) has been proposed. I have.
[0005]
However, all of the lithium secondary batteries manufactured by these methods have insufficient repetitive charge / discharge characteristics (high-temperature cycle characteristics) under high-temperature conditions.
[0006]
[Patent Document 1]
JP-A-10-289729
[Patent Document 2]
JP-A-11-111267
[Patent Document 3]
JP 2000-340262 A
[0007]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a method for manufacturing a lithium secondary battery having excellent high-temperature cycle characteristics.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that high-temperature cycle characteristics can be improved by performing alternating current processing at a low temperature, and have completed the present invention.
That is, the present invention provides a lithium secondary battery assembly including a positive electrode including a positive electrode active material capable of inserting and removing lithium ions, a negative electrode including a negative electrode active material capable of inserting and removing lithium ions, and an electrolyte. A method for producing a lithium secondary battery, characterized in that an alternating current having a frequency of less than 25 ° C and a frequency of 100 MHz or less is applied between a three-dimensional positive electrode and a three-dimensional negative electrode.
[0009]
In this specification, a lithium secondary battery assembly refers to an assembly assembled to a state where charging and discharging, which is the basic performance of a battery, is possible, and is a product battery housed in a case? Whether or not.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
In the production method according to the present invention, a layer of a positive electrode active material-containing composition for a lithium secondary battery including a positive electrode active material capable of inserting and removing lithium ions, a conductive material and a binder is formed on the surface of the current collector. Is used.
[0011]
As the positive electrode active material into which lithium ions can be inserted and desorbed, any positive electrode active material commonly used for lithium secondary batteries can be used, but a lithium transition metal composite oxide is preferably used.
As the lithium transition metal composite oxide, lithium-manganese composite oxide, lithium-cobalt composite oxide, lithium-nickel composite oxide, or part of the transition metal site of these composite oxides is substituted with another metal. And a multimetal composite oxide composed of a plurality of transition metals. Among them, a lithium / nickel-based composite oxide is preferable because it gives a secondary battery having excellent high-temperature cycle characteristics.
[0012]
The basic composition of the lithium-nickel composite oxide is LiNiO₂, Li₂NiO₂, LiNi₂O₄Or Li₂Ni₂O₄And those obtained by partially replacing nickel with another element.
Of these, those represented by the following general formula (I) are preferred.
Li_aNi_bM_cO₂            (I)
(Where a is a number from 0.9 to 1.2, b is a number from 0.3 to 1.2, b + c is a number from 0.9 to 1.2, and M is Be, B, Mg, Al , Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, and Ga.)
[0013]
In the general formula (I), when a exceeds 1.2 and b + c is less than 0.9, a large amount of lithium replaces nickel sites in the crystal, so that the battery capacity decreases. On the other hand, if a is less than 0.9 and b + c exceeds 1.2, the amount of lithium that can participate in charge and discharge of the battery decreases, and the battery capacity decreases. Therefore, the lower limit of a is preferably 0.95, and the upper limit is 1.1, particularly preferably 1.05. The lower limit of b + c is preferably 0.95, and the upper limit is preferably 1.1, particularly preferably 1.05. The lower limit of b is preferably 0.3, and the upper limit is preferably 1.1, particularly preferably 1.05. Since M is not an essential component, c may be 0, and the upper limit is preferably 0.8, particularly preferably 0.7.
[0014]
M is an element selected from the group consisting of Be, B, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn and Ga, and in particular, B, Al, Cr, Those selected from the group consisting of Mn and Co are preferable because they give a secondary battery having a long cycle life. Of these, Al, Co, Al and Co, or Co and Mn are preferable, and Co is particularly preferable.
[0015]
As a lithium manganese-based composite oxide, the basic composition is LiMn.₂O₄And LiMnO₂And a part of these manganese from the group consisting of Be, B, Mg, Al, Ca, Sc, Ti, V, Cr, Ni, Fe, Co, Cu, Zn, Zr and Ga Examples include those substituted with the selected element. Among them, those having a spinel structure are preferable.
[0016]
As the lithium transition metal composite oxide, one having an average primary particle size of usually 0.01 μm or more and 30 μm or less as measured by SEM observation is used. The lower limit of the average primary particle size is preferably 0.02 μm, particularly 0.1 μm, and the upper limit is preferably 5 μm, particularly preferably 2 μm.
The average secondary particle diameter (average particle diameter) of the lithium transition metal composite oxide measured by a laser diffraction / scattering particle size distribution analyzer is usually 1 μm or more and 50 μm or less. If the average secondary particle size is less than 1 μm, the conductivity may be deteriorated due to reduced conductivity, and if it exceeds 50 μm, the coating properties may be poor. The lower limit of the average secondary particle diameter is preferably 4 μm, and the upper limit is preferably 40 μm, particularly preferably 30 μm.
[0017]
Further, the specific surface area of the lithium transition metal composite oxide measured by a BET method (nitrogen surface area method) based on ASTM D3037 using a BET type powder specific surface area measuring device is usually 0.1 m²/ G or more 10.0m²/ G or less. Specific surface area is 0.1m²If it is less than / g, the number of fine pores having a particle diameter of 1 μm or less is reduced, so that the high-temperature cycle characteristics of the secondary battery may be inferior. The specific surface area is 10.0 m²If it exceeds / g, the number of fine pores having a particle diameter of 1 μm or less increases, so that the high-temperature cycle characteristics of the secondary battery are improved, but the conductivity and the battery capacity may decrease. 0.3m as the lower limit of the specific surface area²/ G is preferred, and the upper limit is 5.0 m²/ G, especially 2.0 m²/ G is preferred.
[0018]
As the conductive material, any material known to be used for a lithium secondary battery can be used. Examples include carbon black and graphite.
As the binder, any of those known to be used in lithium secondary batteries can be used. For example, resins such as polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate, and polyethylene; rubbers such as styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, and fluorine rubber; and high molecular substances such as polyvinyl acetate and cellulose. Is mentioned.
[0019]
The composition for a positive electrode active material for a lithium secondary battery contains 65% to 98.9% by weight of a positive electrode active material, 1% to 20% by weight of a conductive material, and 0.1% to 20% by weight of a binder. It is preferable that the content is less than or equal to% by weight.
When the amount of the positive electrode active material is less than 65% by weight, it is difficult to sufficiently secure battery characteristics such as battery capacity. On the other hand, if it exceeds 98.9% by weight, it is difficult to secure mechanical strength as an electrode and to obtain a good cycle life. The lower limit of the positive electrode active material contained in the composition is preferably 70% by weight, particularly preferably 80% by weight, and the upper limit is preferably 97% by weight, particularly preferably 95% by weight.
[0020]
If the conductive material is less than 1% by weight, it is difficult to obtain a good cycle life. On the other hand, if it exceeds 20% by weight, the volume battery capacity decreases. The lower limit of the conductive material is preferably 2% by weight, particularly 3% by weight, and the upper limit is preferably 10% by weight, particularly preferably 5% by weight.
When the amount of the binder is less than 0.1% by weight, it is difficult to secure mechanical strength as an electrode. On the other hand, if it exceeds 20% by weight, battery characteristics such as battery capacity and conductivity cannot be sufficiently ensured. The lower limit of the binder is preferably 3% by weight, particularly 5% by weight, and the upper limit is preferably 15% by weight, particularly preferably 10% by weight.
The composition containing a positive electrode active material for a lithium secondary battery further includes LiFePO4.₄And other positive electrode active materials capable of inserting and extracting lithium ions.
[0021]
Examples of a method for manufacturing the positive electrode include a dry method and a wet method. In the case of the dry method, the positive electrode is manufactured by forming the positive electrode active material-containing composition for a lithium secondary battery into a film. In the case of the wet method, a coating solution prepared by dispersing the lithium secondary battery positive electrode active material-containing composition in a solvent is applied to the surface of the current collector and dried, and then subjected to a consolidation treatment by a uniaxial press or a roll press. Thereby, a positive electrode is manufactured.
[0022]
Solvents used for preparing the coating solution include ether solvents such as ethylene oxide and tetrahydrofuran; ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as methyl acetate and methyl acrylate; diethyltriamine and N, N-dimethylaminopropyl Amine solvents such as amines; aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; and water.
[0023]
Examples of the material of the current collector of the positive electrode include aluminum, stainless steel, nickel-plated steel, and the like. Of these, aluminum, particularly aluminum foil, is preferable. The thickness of the current collector is usually 1 to 1000 μm. A thickness of 5 to 500 μm, especially 5 to 100 μm is preferred.
The lithium secondary battery positive electrode active material-containing composition layer is preferably formed to have a thickness of 1 to 1000 μm, particularly 10 to 200 μm.
[0024]
As the negative electrode, a layer of a negative electrode active material containing a negative electrode active material capable of inserting and removing lithium ions and a binder, and if necessary, a conductive material, and a layer of a negative electrode active material-containing composition for a lithium secondary battery are formed on the current collector surface by a conventional method. The one formed is used.
As the negative electrode active material, any material capable of inserting and removing lithium ions can be used. For example, lithium, lithium aluminum alloy; graphite, coal-based or petroleum-based coke carbide, coal-based or petroleum-based pitch carbide, needle coke, pitch coke, carbide such as phenolic resin or crystalline cellulose, furnace black or acetylene black, etc. Carbon black; SnO, SnO₂, Sn_1-xM¹ _xO (where M¹Represents Hg, P, B, Si, Ge or Sb, and x represents a number satisfying 0 <x <1. ), Sn₃O₂(OH)₂, Sn_3-xM² _xO₂(OH)₂(Where M²Represents Mg, P, B, Si, Ge, Sb or Mn, and x represents a number satisfying 0 <x <3. ), LiSiO₂, SiO₂Or LiSnO₂And a metal oxide such as Li metal composite oxide.
[0025]
As the binder, any of those known to be used in lithium secondary batteries can be used. For example, resins such as polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate, and polyethylene; rubbers such as styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, and fluorine rubber; and high molecular substances such as polyvinyl acetate and cellulose. Is mentioned.
As the conductive material, any material known to be used for a lithium secondary battery can be used. Examples include carbon black and graphite.
[0026]
The lithium secondary battery negative electrode active material-containing composition preferably contains the negative electrode active material in an amount of 65% by weight or more and 99.9% by weight or less and the binder in an amount of 0.1% by weight or more and 20% by weight or less. When a conductive material is used, it is preferably used in an amount of 0.1% by weight or more and 20% by weight or less.
If the negative electrode active material in the composition for a negative electrode active material for a lithium secondary battery is less than 65% by weight, it is difficult to sufficiently secure battery characteristics such as battery capacity. On the other hand, if it exceeds 99.9% by weight, it is difficult to secure mechanical strength as an electrode and to obtain a good cycle life. The lower limit of the negative electrode active material contained in the composition is preferably 70% by weight, particularly preferably 80% by weight, and the upper limit is preferably 97% by weight, particularly preferably 95% by weight.
[0027]
When the amount of the binder is less than 0.1% by weight, it is difficult to secure mechanical strength as an electrode. On the other hand, if it exceeds 20% by weight, battery characteristics such as battery capacity and conductivity cannot be sufficiently ensured. The lower limit of the binder is preferably 3% by weight, particularly 5% by weight, and the upper limit is preferably 15% by weight, particularly preferably 10% by weight.
If the conductive material is less than 0.1% by weight, it may be difficult to obtain a good cycle life. On the other hand, if it exceeds 20% by weight, the volume battery capacity decreases. The lower limit of the conductive material is preferably 2% by weight, particularly 3% by weight, and the upper limit is preferably 10% by weight, particularly preferably 5% by weight.
[0028]
Examples of the method for producing the negative electrode include a method in which a coating solution prepared by dispersing a negative electrode active material in a solvent together with a binder is applied to the surface of the current collector, dried, and subjected to a consolidation treatment using a uniaxial press or a roll press. Is mentioned.
Examples of the solvent used for producing the negative electrode include ether solvents such as ethylene oxide and tetrahydrofuran; ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as methyl acetate and methyl acrylate; diethyltriamine and N, N-dimethylaminopropylamine And aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; and water.
[0029]
Examples of the material of the current collector of the negative electrode include foils of copper, nickel, stainless steel, nickel-plated steel, and the like, and among these, copper foil is preferable.
[0030]
As the electrolyte used for the electrolytic solution, any of those known to be used for lithium secondary batteries can be used. For example, an electrolyte used for an organic electrolyte, a solid polymer electrolyte, a gel electrolyte, an inorganic solid electrolyte, and the like can be mentioned. Of these, the electrolyte used for the organic electrolyte is preferable. Examples of the electrolyte used for the organic electrolyte include LiCl, LiBr, and LiClO.₄, LiAsF₆, LiPF₆, LiBF₄, LiB (C₆H₅)₄, LiCH₃SO₃, LiCF₃SO₃, LiN (SO₂CF₃)₂, LiN (SO₂C₂F₅)₂, LiN (SO₃CF₃)₂And LiC (SO₂CF₃)₃And the like.
[0031]
Examples of the organic solvent used for the electrolyte include diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolan, and 4-methyl- Ethers such as 1,3-dioxolane; ketones such as 4-methyl-2-pentanone; fatty acid esters such as methyl formate, methyl acetate and methyl propionate; dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene Carbonates such as carbonate, propylene carbonate, butylene carbonate and vinylene carbonate; lactones such as γ-butyrolactone and γ-valerolactone; halogenated hydrocarbons such as 1,2-dichloroethane; sulfolane, methylsulfolane Sulfolane compounds such as acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile and the like; amines such as diethylamine, ethylenediamine and triethanolamine; phosphates such as trimethyl phosphate and triethyl phosphate , N, N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, and other aprotic polar solvents.
[0032]
Among these, a high dielectric constant solvent having a relative dielectric constant of 20 or more at 25 ° C. is preferable. Examples of such a solvent include ethylene carbonate or propylene carbonate, or a compound in which a hydrogen atom thereof is substituted with a halogen atom, an alkyl group, or the like. The proportion of the high dielectric constant solvent in the whole organic solvent is usually 20% by weight or more. It is preferable that the high dielectric constant solvent accounts for 30% by weight or more, especially 40% by weight or more of the whole organic solvent.
A separator may be interposed between the positive electrode and the negative electrode of the lithium secondary battery. As the separator, a polyolefin such as polyethylene and polypropylene; a microporous film of a polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyester, polyamide, polysulfone, polyacrylonitrile, cellulose and cellulose acetate; Non-woven fabric filters such as glass fiber are exemplified. Of these, polyethylene microporous films are preferred.
[0033]
In the present invention, an alternating current having a frequency of 100 MHz or less at a temperature of less than 25 ° C. is applied between a positive electrode and a negative electrode of a lithium secondary battery assembly, usually in the form of a product, assembled using the above-described materials.
By performing this process, the cycle characteristics of the battery, particularly the high-temperature cycle characteristics, are greatly improved. Although the reason is unknown, it is considered that the electrolytic solution permeates into the inside of the pores of the electrode active material-containing composition layer, and the wettability of the pore walls is greatly improved. That is, since the application of the alternating current is performed at a low temperature, the volume of the gas existing in the pores of the electrode active material-containing composition layer including the pores of the active material itself is contracted. In this state, when the electrolytic solution vibrates due to the application of an alternating current, the electrolytic solution penetrates deep into the pores, displacing the gas existing there, and wets the pore walls. It is thought that the electrolyte solution can be more easily permeated during use.
[0034]
The application of the alternating current to the lithium secondary battery assembly according to the present invention can be performed at any time after the assembly of the lithium secondary battery.
Lithium rechargeable batteries are usually subjected to conditioning such as charging / discharging before shipment, aging to keep the battery at a specific temperature for a certain period of time, and pulse application tests for applying a constant current intermittently. May be performed.
[0035]
The conditioning process is usually performed by charging and discharging at 2.5 V or more and 4.5 V or less. The lower limit of the charge / discharge voltage in the conditioning treatment is preferably 2.8 V, particularly 3 V, and the upper limit is preferably 4.3 V, particularly 4.2 V. At this time, it is preferable to repeat the charge and discharge two to ten times with a constant current of 0.01 to 3 C. The lower limit of the current value is preferably 0.1 C, particularly 0.2 C, and the upper limit is preferably 2 C, particularly 1 C. Further, the lower limit of the number of repetitions is preferably 3 times, and the upper limit is preferably 5 times, particularly preferably 3 times. When charging and discharging are repeated, the voltage and the current may be different from each other.
[0036]
The charge and discharge are preferably performed at 0 ° C. or more and 60 ° C. or less. The lower limit of the charging / discharging temperature is preferably 10 ° C., particularly 15 ° C., and the upper limit is preferably 40 ° C., particularly preferably 35 ° C.
As the conditioning, the CCCV (constant current / constant voltage) method or the CC (low current) method is used for the initial charge / discharge, and the 1C-CCCV method, 3C-CCCV method, 0.2C-CC method or 1C is used for the second and subsequent charge / discharge. -CC method and the like are preferable.
[0037]
In a preferred aspect of the present invention, the alternating current processing is performed after the SOC (State of Charge) reaches 10% in the conditioning processing. After one charge / discharge, it is preferable to perform an alternating current process at a voltage of OCV (Open Circuit Voltage) of SOC 10% or more. When the SOC is less than 10%, the battery resistance is often high, and when an alternating current is applied, the load on the battery may increase. Therefore, in order to check the initial charge / discharge capacity, after charging / discharging between a voltage between the upper limit and the lower limit at a low current of 1 C or less, the battery is charged so that the SOC becomes 10 to 100%, and then subjected to the AC current processing. Is preferably performed.
[0038]
In the aging process, the battery that has been subjected to the conditioning process may be allowed to stand without being charged or discharged, or the battery may be continuously charged so as to maintain the voltage after the conditioning process.
The aging treatment is usually performed at -10 ° C or more and 70 ° C or less. The lower limit of the aging treatment temperature is preferably 0 ° C., particularly 15 ° C., and the upper limit is preferably 50 ° C., particularly 30 ° C.
The period for performing the aging process is usually from one hour to one month. The lower limit is preferably 2 hours, particularly 6 hours, and more preferably 12 hours, and the upper limit is preferably 1 week, particularly 3 days.
[0039]
The pulse application test is usually performed at a voltage of 2.5 V or more and 4.5 V or less. The lower limit of the voltage in the pulse application test is preferably 3 V, particularly 3.5 V, and the upper limit is preferably 4.3 V, particularly 4.1 V. The current value at this time is 0.01 to 20C. The lower limit of the current value is preferably 0.1 C, particularly 0.2 C, and the upper limit is preferably 10 C, particularly 5 C. The pulse application test is usually performed at -40 to 60C. The lower limit of the temperature is preferably -30 ° C, particularly -20 ° C, and the upper limit is preferably 50 ° C, particularly preferably 40 ° C.
[0040]
The alternating current process can be performed at any point in these processes. Further, the alternating current processing may be performed plural times.
Preferable time points for performing the AC current processing include, for example, after completion of conditioning, after aging, and before and after the pulse application test. Of course, it may be performed during these processes.
[0041]
The application of the alternating current is performed at less than 25 ° C. The temperature is preferably lower as long as the electrolyte does not freeze, and it is preferably performed at 0 ° C. or lower, particularly -10 ° C. or lower. However, it is generally considered unfavorable to lower the temperature below -40 ° C, as lower temperatures are more costly. In general, it is preferably carried out at -40 ° C to -10 ° C, particularly preferably at -35 ° C to -15 ° C.
[0042]
The frequency of the alternating current is preferably higher in view of the action on the electrolytic solution, but it is sufficient that the frequency is 100 MHz or less, which is a range that can be obtained with a normal alternating current generator. If the lower limit is less than 1 Hz, it is not advantageous. If the lower limit is less than 1 mHz, the treatment requires a long time, and is not practical.
The application of the alternating current may be performed at a constant frequency, or may be performed by sweeping the frequency. The amplitude of the alternating current is usually ± 500 mV or less. It is preferably performed at ± 150 mV or less, particularly ± 20 mV or less.
[0043]
A known AC generation control device can be used for the AC current processing. For example, a commercially available AC impedance device can be used.
[0044]
【Example】
The present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.
(Example 1)
Average secondary particle diameter 9 μm, specific surface area 0.7 m by BET method²/ G layered lithium-nickel-cobalt-aluminum composite oxide (Li_1.05Ni_0.80Co_0.15Al_0.05O₂) As a positive electrode active material, acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and polytetrafluoroethylene powder as a binder, and the positive electrode active material, the conductive material, and the binder are 75/20/5, respectively. The sheet prepared by mixing so as to obtain a weight% was punched out into a circular shape having a diameter of 12 mm, and this was press-bonded to an aluminum expanded metal to obtain a positive electrode.
[0045]
Further, 92.5 parts by weight of graphite powder having an average particle diameter of 8 to 12 μm and 7.5 parts by weight of polyvinylidene fluoride (PVDF # 1300, manufactured by Kureha Chemical Industry Co., Ltd.) were dispersed in N-methylpyrrolidone. The slurry was applied to one side of a copper foil having a thickness of 20 μm, dried, punched out into a circular shape having a diameter of 12 mm, and pressed to obtain a negative electrode.
[0046]
The amount of active material was adjusted so that the A / C balance between the positive electrode and the negative electrode was 1.2.
A positive electrode is placed in a positive electrode can, a porous polyethylene film having a thickness of 25 μm is placed thereon as a separator, pressed with a polypropylene gasket, a negative electrode is placed thereon, and a spacer for thickness adjustment is further placed. Was placed. LiPF was added to a mixed solvent of 3 parts by weight of ethylene carbonate and 7 parts by weight of diethyl carbonate.₆Was added and dissolved sufficiently so as to be 1 mol / liter, and the mixture was sufficiently permeated. Then, a negative electrode can was placed and sealed, thereby producing a coin cell.
[0047]
As an initial conditioning process, two cycles of charging and discharging at an upper limit voltage of 4.1 V and a lower limit voltage of 3.0 V were performed by a CC method with a 0.2 C current value. After the battery was relaxed for one hour, it was charged to a DOD (depth of discharge) of 40% at a current value of 1 / (3C) and allowed to stand for one hour.
After the obtained coin cell was allowed to stand in a low-temperature atmosphere of -30 ° C for about 1 hour, a constant voltage and an amplitude of 10 mV were applied using an AC impedance device (SI1287 Electrochemical Interface, 1255B Frequency Response Analyzer; manufactured by Solartron). The alternating current processing was performed by sweeping once at 50 selected frequencies by dividing the frequency between 1 mHz and 100 MHz into 49 equally spaced parts on a logarithmic axis. The OCV immediately before performing the alternating current processing was 3786 mV. This AC current treatment required about one hour. After the AC current treatment, the coin cell was returned to normal temperature.
[0048]
The coin cell subjected to the alternating current treatment was repeatedly charged and discharged at 60 ° C. at a constant current of 2 C, a charge upper limit voltage of 4.1 V, and a discharge lower limit voltage of 3.0 V for 100 cycles. The discharge capacity after 100 cycles is Q₁₀₀And the maximum discharge capacity Q_MAXThe high-temperature cycle capacity retention rate when the cycle indicating was the X-th time was calculated by equation (2), and was 80%.
Q₁₀₀/ Q_MAX× (100−X) / 100 (2)
[0049]
(Example 2)
In Example 1, after the initial conditioning treatment, charging and discharging were performed once each at ℃ C, 1C, and 3C at 25 ° C. for 10 seconds, and further, at -30 ° C., １ ／ C, ＣC, 1C, The procedure was performed in the same manner as in Example 1 except that a pulse application test in which discharge was performed once at 2 C for 10 seconds was performed, and then an alternating current process was performed. The high-temperature cycle capacity retention was 80%. The OCV immediately before the AC current processing was 3729 mV.
[0050]
(Example 3)
In Example 2, LiPF was used in a mixed solvent of 3 parts by weight of ethylene carbonate, 3 parts by weight of dimethyl carbonate, and 4 parts by weight of ethyl methyl carbonate.₆Was prepared in the same manner as in Example 2 except that a coin cell was prepared using an electrolytic solution in which 1 mol / liter was dissolved, and the constant current in the high-temperature cycle test was 1 C. The high-temperature cycle capacity retention was 85%. The OCV immediately before the alternating current processing was 3761 mV. The time required for the AC treatment was about 1 hour.
[0051]
(Example 4)
In Example 3, after performing an initial conditioning process and a pulse application test on a coin cell, the frequency between 10 mHz and 100 MHz with an amplitude of 10 mV is equally divided on a logarithmic axis at equal intervals, and is selected once at a frequency of 71 points. The same operation as in Example 3 was performed except that the alternating current processing was performed by sweeping. The high-temperature cycle capacity retention was 85%. The time required for the AC current processing was about 10 minutes.
[0052]
(Example 5)
Example 4 was performed in the same manner as in Example 4 except that the pulse application test was not performed. The high-temperature cycle capacity retention rate was 85% or more. The time required for the AC current processing was about 10 minutes.
[0053]
(Example 6)
In Example 1, the positive electrode active material had an average secondary particle diameter of 13 μm and a specific surface area of 0.5 m.²/ G of spinel compound lithium manganese aluminum composite oxide (Li_1.04Mn_1.80Al_0.20O₄) And using a mixed solvent of 3 parts by weight of ethylene carbonate, 3 parts by weight of dimethyl carbonate and 4 parts by weight of ethyl methyl carbonate in a mixed solvent of LiPF₆Was prepared in the same manner as in Example 1 except that an electrolytic solution in which was dissolved so as to be 1 mol / liter was used. An initial conditioning process, a pulse application test, and an AC current process were performed on this in the same manner as in Example 2. However, the high temperature cycle test was performed at a constant current of 1C. The high-temperature cycle capacity retention was 79%. The OCV immediately before the AC current processing was 4154 mV, and the time required for the AC processing was about 1 hour.
[0054]
(Example 7)
In Example 1, the positive electrode active material had an average secondary particle diameter of 15 μm and a specific surface area of 0.5 m.²/ G of spinel compound lithium manganese aluminum composite oxide (Li_1.04Mn_1.80Al_0.20O₄) And using a mixed solvent of 3 parts by weight of ethylene carbonate, 3 parts by weight of dimethyl carbonate and 4 parts by weight of ethyl methyl carbonate in a mixed solvent of LiPF₆Was prepared in the same manner as in Example 1 except that an electrolytic solution in which was dissolved at 1 mol / liter was used. An initial conditioning process, a pulse application test, and an AC current process were performed on this in the same manner as in Example 6. The high-temperature cycle capacity retention was 82%. The OCV immediately before the AC current processing was 4150 mV, and the time required for the AC processing was about 1 hour.
[0055]
(Comparative Example 1)
In Example 1, after the initial conditioning process, a high-temperature cycle test was performed in the same manner as in Example 1 without performing the alternating current process. The high-temperature cycle capacity retention was 71%.
[0056]
(Comparative Example 2)
In Example 2, after the pulse application test, the high-temperature cycle test was performed without performing the alternating current processing. The high-temperature cycle capacity retention was 69%.
[0057]
(Comparative Example 3)
In the second embodiment, after the pulse application test, an alternating current at 25 ° C. and an amplitude of 10 mV, and a frequency between 10 mHz and 100 MHz, which is equally divided on a logarithmic axis at equal intervals of 70, and the frequency is swept once at 71 points selected each time Except having performed the process, it carried out similarly to Example 2. The high temperature cycle capacity retention was 75%. This AC current processing required about 10 minutes.
[0058]
(Comparative Example 4)
In Example 2, after performing the pulse application test, the sample was allowed to stand at 25 ° C. for one day, and the high-temperature cycle test was performed without performing the AC current treatment. The high-temperature cycle capacity retention was 54%.
[0059]
(Comparative Example 5)
In Example 2, after performing the pulse application test, the sample was allowed to stand at −30 ° C. for one day, and the high-temperature cycle test was performed without performing the alternating current treatment. The high-temperature cycle capacity retention was 70%.
[0060]
(Comparative Example 6)
In Example 1, 0.2C-CCCV charging, 0.2C discharging, and 0.2C charging / discharging were performed once each as an initial conditioning process, and a pulse application test was performed in the same manner as in Example 2; A high temperature cycle test was performed without performing current treatment. The high temperature cycle capacity retention was 75%.
[0061]
(Comparative Example 7)
In Example 3, after performing the initial conditioning process, the high-temperature cycle test was performed without performing the pulse application test and the AC current process. The high-temperature cycle capacity retention was 79%.
[0062]
(Comparative Example 8)
In Example 6, a high-temperature cycle test was performed without performing the alternating current processing. The high-temperature cycle capacity retention was 66%.
[0063]
(Comparative Example 9)
In Example 7, a high-temperature cycle test was performed without performing the alternating current processing. The high-temperature cycle capacity retention was 78%.
[0064]
【The invention's effect】
By using the method for manufacturing a lithium secondary battery according to the present invention, a lithium secondary battery having excellent high-temperature cycle characteristics can be manufactured.

Claims (6)

A positive electrode having a positive electrode active material capable of inserting and removing lithium ions, a negative electrode having a negative electrode active material capable of inserting and removing lithium ions, and a positive electrode and a negative electrode of a lithium secondary battery assembly having an electrolyte solution And applying an alternating current having a frequency of 100 MHz or less at a temperature lower than 25 ° C. to the lithium secondary battery. The method for producing a lithium secondary battery according to claim 1, wherein the application of the alternating current is performed at 0 ° C or less. The method for producing a lithium secondary battery according to claim 1, wherein the application of the alternating current is performed at -10C or lower. 4. The method for manufacturing a lithium secondary battery according to claim 1, wherein the lithium secondary battery assembly has been subjected to at least one charge / discharge treatment. The method for manufacturing a lithium secondary battery according to any one of claims 1 to 4, wherein a charging / discharging process is performed on the lithium secondary battery assembly to which an alternating current has been applied. The method for manufacturing a lithium secondary battery according to claim 1, wherein an alternating current having an amplitude of ± 500 mV or less is applied.