JP3316111B2 - Manufacturing method of lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, there has been remarkable progress in reducing the size, weight, and thickness of electronic devices. Particularly in the OA field, the size and weight of electronic devices have been reduced from desktop types to laptop types and notebook types. In addition, the field of new small electronic devices such as electronic notebooks and electronic still cameras has emerged.In addition to the miniaturization of conventional hard disks and floppy disks, the development of memory cards, which are new small memory media, has been promoted. ing. In the wave of downsizing, lightening, and thinning of such electronic devices, secondary batteries supporting these electric powers are also required to have high performance such as high energy density, high voltage, and high output. Amid such demands, the development of lithium secondary batteries as high energy density batteries has been rapidly advanced, and secondary batteries using carbon materials for the negative electrode have been attracting attention as highly safe and reliable secondary batteries. I have. Since the carbon electrode is in a discharged state unlike a conventional lithium electrode, the positive electrode is generally made of LiCoO ₂ , Li
Those in a discharged state such as NiO ₂ and LiMnO ₂ are used (for example, Japanese Unexamined Patent Application Publication No. 3-252665). However, the first discharge of the lithium secondary battery using the carbon electrode is performed by charging and discharging the positive electrode in the second and subsequent cycles because the first discharge of the lithium electrode using the carbon electrode is smaller than the first cycle. Energy is charged. Therefore, since the capacity balance between the positive electrode and the negative electrode is different, it is necessary to mount either the positive electrode or the negative electrode excessively, so that the energy density of the battery cannot be increased so much. To solve this problem, for example, in Japanese Patent Application Laid-Open Nos. 5-251111 and 5-242911, a positive electrode in a discharged state and a carbon electrode are spirally wound through a separator, and lithium is short-circuited to the carbon electrode. Discloses a method of charging a carbon electrode with a capacity that is insufficient due to charging and discharging of the carbon electrode. However, since it is difficult to uniformly charge the spirally wound carbon electrode, an overdischarged portion or an unreacted portion is generated in the positive electrode, the capacity is reduced, and the cycle characteristics are shortened. JP-A-5-2587
43 shows a method of treating a carbon material with a LiI solution to charge the carbon electrode with insufficient capacity in the first charge and discharge of the carbon electrode. However, there is a problem in safety because highly corrosive iodine is brought into the battery system.

[0003]

The present invention solves the above-mentioned problems of the prior art,
It is an object of the present invention to provide a method for manufacturing a highly reliable high energy density lithium secondary battery.

[0004]

[Constitution] The present inventors have made intensive studies and found that when a lithium secondary battery is manufactured using a charged carbon electrode as a negative electrode and a charged positive electrode, the energy originally possessed by the positive electrode and the negative electrode can be extracted. Thus, the present inventors have found that a lithium secondary battery having high energy density and high reliability can be provided, and have reached the present invention. That is,
The present invention relates to a method for manufacturing a lithium secondary battery combining a charged carbon anode and a charged cathode, wherein lithium corresponding to the amount required for full charge of the battery is deposited on the discharged carbon anode. And a method of manufacturing a lithium secondary battery, which is formed in the form of a lithium thin film by a vacuum process selected from the group consisting of sputtering and sputtering. The method for charging the carbon negative electrode used in the lithium secondary battery of the present invention includes a method of charging by electrolysis in an electrolytic solution, a method of charging by short-circuiting the carbon negative electrode and lithium in the electrolytic solution, and a method of laminating lithium on the carbon negative electrode. A method of charging by immersing in an electrolytic solution, a method of laminating lithium on a carbon anode and then heating to produce an intercalation compound of carbon and lithium, and the like can be exemplified. A method in which lithium is laminated on a carbon negative electrode and then charged by immersion in an electrolytic solution for charging can be easily performed, and in consideration of battery mounting, a method in which lithium is laminated on a carbon negative electrode and then immersed in the electrolytic solution and charged. The positive and negative electrodes can be mounted on the battery container by a dry process without causing a short circuit at the time of mounting. And intercalated electrode is preferable because the negative electrode becomes the charge and discharge state. The amount of lithium deposited on the carbon negative electrode is an amount necessary for charging the carbon electrode. Unnecessary lithium for charging remains on the carbon electrode as excess lithium, which leads to generation of dendrite, which is not preferable. The method of laminating lithium on the carbon negative electrode is based on a vacuum process such as vapor deposition or sputtering of lithium or a lithium alloy. The vacuum process is a preferred method because the control of the amount of lamination is easy.

[0005] As the negative electrode material used in the battery of the present invention, graphite and other carbonaceous materials are mixed and used. Graphite is preferably natural graphite, and examples of the carbonaceous negative electrode active material include pitch coke, synthetic polymers, and fired bodies of natural polymers. In the present invention, synthetic polymers such as phenol and polyimide, and natural polymers are used. From 400 to 80
Conductive carbon obtained by firing an insulating or semiconductive carbon material, coal, pitch, synthetic polymer, or natural polymer obtained by firing in a reducing atmosphere at 0 ° C. in a reducing atmosphere at 800 to 1300 ° C. Carbon, coke, pitch, synthetic polymer, and natural polymer obtained by calcining at a temperature of 2000 ° C. or more in a reducing atmosphere are used. A carbon body and natural graphite fired in a reducing atmosphere at a temperature of not less than ° C. have excellent potential flatness and have preferable electrode characteristics. Natural graphite has favorable properties in terms of potential flatness and current properties,
It has a problem of decomposing propylene carbonate which is a solvent of a general-purpose electrolytic solution conventionally used for non-aqueous secondary batteries. By using a composite of natural graphite and another carbon body as the negative electrode, it is possible to produce a negative electrode that does not decompose the electrolytic solution while maintaining the potential flatness and current characteristics of natural graphite. The carbon body is formed into a sheet by a wet papermaking method using the carbon body and the binder, or by a coating method using a coating material in which an appropriate binder is mixed with a carbon material. Teflon, polyethylene, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene / butadiene rubber,
Nitrocellulose, cyanoethylcellulose, polyacrylonitrile, polyvinyl fluoride, polyvinylidene fluoride, polychloroprene, polyvinylpyridine, and the like, which may be used alone or as a mixture, and furthermore, may have an electrolytic solution resistance by copolymerization or the like. Used to enhance. The electrode can be manufactured by supporting the electrode on a current collector as required by a method such as application, adhesion, and pressure bonding.

[0006] The positive electrode used in the lithium secondary battery of the present invention also needs to be charged. Although the positive electrode used in the lithium secondary battery of the present invention can be charged by electrolysis, it is preferable that the active material itself be in a charged state. For example, MnO ₂ , Mn ₂ O ₃ , Co
O ₂ , NiO ₂ , TiO ₂ , V ₂ O ₅ , V ₃ O ₈ , Cr ₂ O ₃ ,
Fe ₂ (SO ₄ ) ₃ , Fe ₂ (MoO ₂ ) ₃ , Fe ₂ (WO ₂ )
₃ , metal oxides such as FeO ₂ , TiS ₂ , MoS ₂ , FeS
And transition metal chalcogen compounds containing no lithium, such as metal sulfides. By controlling the charge state of the negative electrode, LiCoO ₂ and LiN in a discharged state are controlled.
It is also possible to composite a lithium composite oxide such as iO ₂ or LiMnO ₂ or a conductive polymer such as polyaniline or polypyrrole.

[0007] The secondary battery of the present invention basically comprises the above-described positive electrode.
And a negative electrode and electrolyte, and a separator
Used. As an electrolyte used in the secondary battery of the present invention
Examples thereof include those in which an electrolyte salt is dissolved in a non-aqueous solvent.
Non-aqueous solvents include carbonate solvents (propylene carbonate
Bonate, ethylene carbonate, butylene carbonate
G, dimethyl carbonate, diethyl carbonate),
Amide solvent (N-methylformamide, N-ethylform
Muamide, N, N-dimethylformamide, N-methyl
Acetamide, N-ethylacetamide, N-methylpi
Rosilinone), lactone solvent (γ-butyl lactone, γ
Valerolactone, δ-valerolactone, 3-methyl-
1,3-oxazolidin-2-one etc.), alcohol-soluble
Medium (ethylene glycol, propylene glycol,
Serine, methyl cellosolve, 1,2-butanediol,
1,3-butanediol, 1,4-butanediol, di
Glycerin, polyoxyalkylene glycol, cyclo
Hexanediol, xylene glycol, etc.), ether
Solvents (methylal, 1,2-dimethoxyethane, 1,2
-Diethoxyethane, 1-ethoxy-2-methoxyethane
, Alkoxy polyalkylene ether, etc.), nitrile
Solvents (benzonitrile, acetonitrile, 3-methoxy
Propionitrile, etc.), phosphoric acids and phosphate esters
(Normal phosphoric acid, metaphosphoric acid, pyrophosphoric acid, polyphosphoric acid, phosphorous acid,
Limethyl phosphate, etc.), 2-imidazolidinones
(1,3-dimethyl-2-imidazolidinone, etc.), pyro
Lidones, sulfolane solvents (sulfolane, tetramethyle
Sulfolane), a furan solvent (tetrahydrofuran, 2
-Methyltetrahydrofuran, 2,5-dimethoxytet
Lahydrofuran), dioxolan, dioxane, diclo
Loethane can be used alone or in combination of two or more.
You. Of these, preferred are carbonates and ethers.
And furan solvents. As the electrolyte salt in the present invention
Is particularly restricted as long as it is used as a normal electrolyte.
Although not limited, for example, LiBR_Four(R is a phenyl group,
Alkyl group), LiPF₆, LiSbF₆, LiAsF₆,
LiBF_Four, LiClO_Four, CF_ThreeSO_ThreeLi, (CF_ThreeS
O_Two)_TwoNLi, (CF_ThreeSO_Two)_ThreeCLi, C₆F₉SO_ThreeL
i, C₈F ₁₇SO_ThreeLi, LiTFB, LiAlCl_Four
And the like. Preferably CF_ThreeSO_ThreeL
i, (CF_ThreeSO_Two)_TwoNLi, (CF_ThreeSO_Two)_ThreeCLi,
C₆F₉SO_ThreeLi, C₈F₁₇SO_ThreeSulfonic acid type such as Li
It is an anionic electrolyte. Electrolyte as separator
It has low resistance to ion migration of the solution and
Good durability is used, for example, glass,
One type of stell, Teflon, polypropylene, PTFE, etc.
Non-woven fabrics or woven fabrics selected from the above materials are exemplified.
Also, these electrolytes and separators can be used instead of or in combination
Then, a solid electrolyte can be used. For example, inorganic
In the system, metals such as AgCl, AgBr, AgI and LiI
Halide, RbAg_FourI_Five, RbAg_FourI_FourCN etc.
I can do it. Also, in the organic system, polyethylene oxide,
Polypropylene oxide, polyvinylidene fluoride,
Using acrylamide or the like as a polymer matrix,
A complex in which an electrolyte salt is dissolved in a polymer matrix,
Alternatively, these gel cross-linked products, low molecular weight polyethylene ox
Polymerization of ion dissociation groups such as side and crown ether
Polymer solid electrolyte grafted to the main chain, or
Gel-like polymer solid containing the electrolyte solution in a molecular weight polymer
Electrolytes. Embodiment of the lithium secondary battery of the present invention
Is not particularly limited, but coins, sheets, circles
It can be mounted on various types of batteries such as cylinders and gums.

[0008]

EXAMPLES Reference Example 1 d ₀₀₂ is the average particle diameter were weighed polyvinylidene fluoride 15 parts by weight to 100 parts by weight of carbon material of 10μm in 3.336A, and mixed by adding N- methylpyrrolidone paste did. This was applied to a 20 μm copper foil and dried to form a carbon electrode. Lithium is added to this carbon electrode
A 150 μm lithium foil is stuck through a 50-mesh stainless steel mesh to bond 1M LiN (CF ₃ SO ₂ ) ₂ /
The carbon negative electrode was immersed in an ethylene carbonate solution for one day to make it charged. 80 parts by weight of crystalline V ₂ O _5, 12 parts by weight of graphite and 8 parts by weight of polytetrafluoroethylene were kneaded, and a positive electrode was produced by pressure molding. The negative electrode,
The positive electrode was punched into a circular shape having a diameter of 16 mm, bonded together via a polypropylene nonwoven fabric, and assembled into a bolt / nut type cell. The electrolyte is 1 M LiN (CF ₃ SO ₂ ) ₂
/ Ethylene carbonate solution was used. The capacity of each of the positive electrode and the negative electrode with respect to the lithium electrode was 5 mAh. Charge / discharge was performed at a charge / discharge current of 2 mA in the range of 2.5 V to 3.7 V. Table 1 shows the results.

Comparative Example 1 A bolt / nut type cell was prepared and charged and discharged in the same manner as in Reference Example 1, except that a carbon electrode which was not charged was used as the negative electrode. Table 1 shows the results.

Comparative Example 2 Comparative Example 1 was the same as Comparative Example 1 except that 80 parts by weight of LiCoO _2, 12 parts by weight of graphite, and 8 parts by weight of polytetrafluoroethylene were kneaded for the positive electrode and an electrode produced by pressure molding was used. To produce a bolt / nut type cell. The capacity of the positive electrode was 5 mAh. 2m
Charging / discharging was performed at a charging / discharging current of A in the range of 2.5 V to 4.2 V. Table 1 shows the results.

[Table 1]

Example 1 A carbon material 1 having d ₀₀₂ of 3.35 ° and an average particle size of 8 μm
15 parts by weight of polyvinylidene fluoride was weighed to 00 parts by weight, N-methylpyrrolidone was added and mixed to form a paste. This was applied to a copper foil of 20 μm and dried to form a carbon electrode, which was punched to a diameter of 16 mm. The charge amount required for the first charge of the carbon electrode is 6.7 mAh, and the discharge amount is 5 mAh. Lithium was laminated on the carbon electrode by vacuum deposition. The deposition amount of lithium is controlled by weight, and the weight of lithium corresponding to 6.7 mAh is 1.73 mg. The same positive electrode as in Reference Example 1 was used as the positive electrode, and the positive electrode and the negative electrode were bonded together via a polypropylene nonwoven fabric, and incorporated into a bolt / nut type cell. For the electrolyte, ethylene carbonate and propylene carbonate were used in a ratio of 2: 1.
A solution obtained by dissolving 1.5 M of LiBF ₄ in a solvent mixed at a volume ratio was used. After a bolt / nut type cell was prepared and left for one day, charging / discharging was performed at a charging / discharging current of 2 mA in the range of 2.5 V to 3.7 V. As shown in Table 2, the best performance was obtained by laminating the amount of charge necessary for the first charge of the carbon electrode.

[Table 2]

Example 2 Polyaniline, crystalline V ₂ O ₅ and N-methylpyrrolidone were mixed and dispersed at a ratio of 2: 8: 50 (weight ratio), applied to aluminum having a thickness of 20 μm, and heated at 80 ° C. To produce a positive electrode. The capacity of this positive electrode is 5 mAh,
Since polyaniline is in a discharged state, the charged state of the entire positive electrode is about 85%. A bolt / nut type cell was prepared in the same manner as in Example 1 using a carbon negative electrode having a lithium stacking amount of 1.5 mg in Example 1 and left for 1 day, and then 2 m
A charge / discharge was performed at a charge / discharge current of A in the range of 2.5 V to 3.7 V. The discharge capacity after 100 cycles is 4.7 mAh
Met.

[0013]

[Effect] A highly reliable lithium secondary battery having a high energy density can be provided.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-235372 (JP, A) JP-A-4-332484 (JP, A) JP-A-4-206276 (JP, A) JP-A-4- 109553 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02 H01M 4/04

Claims (3)

(57) [Claims] 1. A method for producing a lithium secondary battery in which a charged carbon negative electrode and a charged positive electrode are combined, comprising the steps of: depositing lithium on a discharged carbon negative electrode in an amount required for full charge of the battery. Forming a lithium secondary battery by a vacuum process selected from the group consisting of vapor deposition and sputtering. 2. The method for manufacturing a lithium secondary battery according to claim 1, wherein lithium corresponding to an amount necessary for fully charging the battery is formed by a vacuum process selected from the group consisting of vapor deposition and sputtering. A method for producing a lithium secondary battery, comprising: injecting an electrolytic solution after a carbon negative electrode having a positive electrode and a positive electrode in a charged state are opposed to each other. 3. The method for producing a lithium secondary battery according to claim 1, wherein a lithium-free transition metal chalcogen compound is used as a positive electrode active material in the positive electrode.