JPH09106834A - Lithium-ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase capacity and cycle stability of capacity and to use A1 for a collector of a positive electrode, by using a negative electrode containing mainly a carbon material capable of storing Li-ions, a positive electrode containing mainly a Li-containing transition metal chalcogenide compound, and a predetermined compound contained as an electrolyte. SOLUTION: A Li-ion secondary battery is composed of a negative electrode 2 containing mainly a carbon material capable of storing Li-ions, a positive electrode 1 containing mainly a Li-containing transition metal chalcogenide compound, and an electrolyte solution containing, as an electrolyte, a Li bis-(fluoroalkylsulfonyl) imide having alkyl group of which the carbon number is two or more. The carbon material constituting the negative electrode is not limited in particular so far as it is capable of storing Li-ions. For example, graphite, activated carbon, or the like is used. For a collector, foil of metal such as Cu, Ni and the like is mentioned, and Cu is preferable from an aspect of electroconductivity. As a binder, a homopolymer or a copolymer, or the like of tetrafluoroethylene or trifluoroethylene is used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to bis (fluoroalkylsulfonyl) having an alkyl group having 2 or more carbon atoms.
The present invention relates to a lithium ion secondary battery containing an electrolytic solution containing imide lithium as an electrolyte.

[0002]

2. Description of the Related Art Conventionally, inorganic electrolytes such as lithium tetrafluoroborate and lithium hexafluorophosphate have been used as electrolytes of non-aqueous electrolytes for lithium ion secondary batteries.
These inorganic electrolytes have the drawbacks of causing self-discharging when the battery is stored in a charged state for a long period of time, and reacting with a part of solvent molecules during a charge / discharge cycle to reduce the battery capacity. Lithium fluoroalkyl sulfonate has been considered as an electrolyte for solving these drawbacks, but the electric conductivity of the organic solvent solution of lithium fluoroalkyl sulfonate is lower than that of the solution of the inorganic electrolyte, so the battery performance is low.

On the other hand, as an electrolyte having the advantages of both an inorganic electrolyte and lithium fluoroalkyl sulfonate, JP-A-5-326018 and JP-A-6-176769 are known.
Although bis (trifluoromethanesulfonyl) imide lithium described in Japanese Patent Publication No. 1994-242242 is mentioned, pitting corrosion of aluminum occurs in an electrolytic solution using this salt as an electrolyte, so that it is light as a battery material, easy to process and inexpensive. There is a drawback that aluminum cannot be used.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a lithium ion electrolyte containing a non-aqueous electrolyte solution, which has a high capacity and a high capacity cycle stability, and which can use aluminum for the current collector of the positive electrode. It is to provide the next battery.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies, and as a result, the use of bis (fluoroalkylsulfonyl) imide lithium having an alkyl group having 2 or more carbon atoms as an electrolyte solves the above problems. It was found that it is possible to achieve the present invention. That is, the present invention is as follows. 1. Negative electrode mainly composed of carbon material capable of occluding lithium ions, positive electrode mainly composed of lithium-containing transition metal chalcogen compound, and electrolysis using bis (fluoroalkylsulfonyl) imide lithium having an alkyl group having 2 or more carbon atoms as an electrolyte Lithium ion secondary battery consisting of liquid. 2. The lithium ion secondary battery as described in 1 above, wherein the copper foil serves as a negative electrode current collector, the aluminum foil serves as a positive electrode current collector, and bis (fluoroalkylsulfonyl) imide lithium having an alkyl group having 2 or more carbon atoms is used as an electrolyte. battery.

The present invention will be described in detail below. The lithium ion secondary battery of the present invention includes a negative electrode mainly composed of a carbon material capable of storing lithium ions, a positive electrode mainly composed of a lithium-containing transition metal chalcogen compound, and a bis (fluoroalkyl) having an alkyl group having 2 or more carbon atoms. (Sulfonyl) imide Lithium is used as an electrolyte.

The negative electrode constituting the lithium ion secondary battery of the present invention is composed mainly of a carbon material capable of storing lithium ions, and a current collector, a binder and the like. The carbon material is not particularly limited as long as it can absorb lithium ions, and examples thereof include graphitizable carbon such as graphite and needle coke, and non-graphitizable carbon such as activated carbon and glassy carbon. Specific examples of the current collector include metal foils of copper, nickel and the like, and copper is preferable in terms of conductivity and the like.
Specific examples of the binder include a homopolymer or copolymer of tetrafluoroethylene, a homopolymer or copolymer of trifluoroethylene, a homopolymer or copolymer of vinylidene fluoride, or a homopolymer of vinyl fluoride. Or synthetic rubber such as copolymer, polybutadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), isoprene rubber (IR), butyl rubber (IIR),
Polyethylene (LDPE or HDPE) and ethylene copolymers, polystyrene (PS), polyacrylonitrile (PAN) and the like can be mentioned.

The lithium ion secondary battery of the present invention is constructed.
The positive electrode mainly contains a lithium-containing transition metal chalcogen compound.
The body is composed of a current collector, a binder, a conductive agent and the like. Re
The transition metal chalcogen compound containing titanium is Li_(1-x)C
oO_Two, Li_(1-x)NiO_Two, Li_(1-x)Co_(1-y)N
i_yO_Two, LiMn_TwoO_Four, Li_(1-x)Co_(1-y)M _y
O_Two, Li_(1-x)A_zCo_(1-y)M_yO_Two(M is Co,
Represents a transition metal other than Ni, Al, In, Sn, where A is L
Represents an alkali metal other than i. ) And the like. Current collection
As the body, specifically, aluminum, aluminum alloy
Metal foil of gold, stainless steel, etc. can be mentioned, processability, price
Aluminum is preferable from the viewpoint of the above. As a binder
Is specifically a homopolymer of tetrafluoroethylene or
Copolymer, homopolymer or copolymer of trifluoroethylene
Polymer, vinylidene fluoride homopolymer or copolymer, polymer
A homopolymer or a copolymer of vinyl fluoride can be used.
Conductive agents include acetylene black and carbon black.
Ku and the like.

The electrolytic solution constituting the lithium ion secondary battery of the present invention comprises an electrolyte, bis (fluoroalkylsulfonyl) imide lithium having an alkyl group having 2 or more carbon atoms, and a solvent. Bis (fluoroalkylsulfonyl) imide lithium having an alkyl group having 2 or more carbon atoms is a compound represented by the following general formula. General formula; (C _n F _{(2n-m + 1)} H _m SO ₂ ) ₂ NLi (where n is an integer of 2 or more, usually 2 or more and 8 or less, preferably 2 or more and 6 or less, and further, Preferably 3
Or 4, and m represents an integer of 0 or more and 2n or less. ) When n is 2 or more, aluminum can be used for the collector of the positive electrode. Further, when n exceeds 8, the imidolithium becomes substantially insoluble in the non-aqueous solvent solution, which is not preferable. Specific examples of the lithium imide include bis (heptafluoropropanesulfonyl) imide lithium, bis (1,1,2,2,3,3-hexafluoropropanesulfonyl) imide lithium, and bis (1,1-difluoropropanesulfonyl). Examples thereof include imide lithium and bis (nonafluorobutanesulfonyl) imide lithium.

A method for synthesizing these lithium salts is described in Inorganic Chemistry, 23.
(23) P. 3727 (1984), a reaction product of a fluoroalkylsulfonyl fluoride and ammonia, a fluoroalkylsulfonylamide is reacted with sodium methylate to synthesize sodium sulfonylalkylsulfonylamide, and then reacted with hexamethyldisilazane and trimethylsilylfluoroalkylsulfonyl. Method of further reacting fluoroalkylsulfonyl fluoride as sodium imide, then neutralizing with sulfuric acid to obtain bis (fluoroalkylsulfonyl) imide, and further reacting with lithium carbonate to obtain the bis (fluoroalkylsulfonyl) imide lithium , Tokuhei Hira 3-501
Examples thereof include a method of obtaining the bis (fluoroalkylsulfonyl) imide lithium by reacting a fluoroalkylsulfonyl halide described in JP-A 860 with lithium bis (trimethylsilyl) amide.

The solvent which is another component of the electrolytic solution is not particularly limited as long as it dissolves the bis (fluoroalkylsulfonyl) imide lithium which is the electrolyte. Specifically, propylene carbonate (P
C), cyclic carbonates represented by ethylene carbonate (EC), dimethyl carbonate (DMC),
Acyclic carbonates represented by methyl ethyl carbonate (MEC), diethyl carbonate (DEC), γ-butyrolactone (γBL), ε-caprolactone (εCL), methyl propionate (MP), ethyl butyrate (EA), etc. Representative cyclic and acyclic esters,
Tetrahydrofuran (THF), dimethoxyethane (D
ME), ethers typified by diethylene glycol dimethyl ether, nitriles typified by acetonitrile (AN), propionitrile, and the like, and they are used alone or in a mixture of two or more. In the case of a mixed solvent system of two or more, a combination of a solvent having a high dielectric constant and a solvent having a lower viscosity and a higher coordinating power for lithium ions than the high dielectric constant solvent is preferable. γBL, DMC, MEC, DEC, TH
F, DME, EC and γBL, DMC, MEC, DEC,
THF, DME and the like can be mentioned. The volume ratio of the high dielectric constant solvent to the low viscosity solvent is preferably 2: 1 to 1: 2, more preferably 1.5: 1 to 1: 1.5.

The shape of the lithium ion secondary battery composed of the negative electrode, the positive electrode and the electrolytic solution is not particularly limited and may be various shapes such as a cylindrical shape, a square shape and an elliptic shape.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to Examples. <Reference example> Synthesis of lithium bis (perfluoro-1-butanesulfonyl) imide In a 300 ml four-necked flask equipped with a Teflon rotor, a condenser, and a dropping funnel, a 1M tetrahydrofuran solution of lithium bis (trimethylsilyl) amide 150
After adding ml and cooling to 0 ° C., perfluoro-1-butanesulfonyl fluoride 9 was added from a dropping funnel with stirring.
0.6 g (= 0.300 mol) was added dropwise over about 1 hour. After completion of the dropping, the temperature was gradually returned to room temperature while continuing stirring, and the reaction was continued for about 7 days. After completion of the reaction, the crude bis (perfluoro-1-butanesulfonyl) imide lithium obtained by distilling off the solvent was dissolved in diethyl carbonate, the insoluble matter was filtered off, the solvent was distilled off, and then dissolved in water. Then, the insoluble matter is filtered off and dried under vacuum to obtain 75.0 g (0.1
28 mol) of purified bis (perfluoro-1-butanesulfonyl) imide lithium was obtained. Yield 85.2%.

[0014]

Example 1 A cylindrical non-aqueous electrolyte battery shown in FIG. 1 was produced as follows. First, LiCoO ₂ was crushed with a ball mill to an average particle size of 3 μm, and then 0.025 part by weight of graphite, 0.025 part by weight of acetylene black, and 0.02 part by weight of polyvinylidene fluoride as a binder per 1 part by weight of this powder. In addition, a paste prepared by using dimethylformamide was applied to one surface of an aluminum foil having a thickness of 15 μm so that the dry film thickness was 100 μm, and the positive electrode 1
Was prepared. On the other hand, a commercially available petroleum-based needle coke (KOA-SJ Coke manufactured by Koa Oil Co., Ltd.) was pulverized with a ball mill to an average particle size of 10 μm. BET surface area of this needle coke, true density, surface spacing d obtained from X-ray diffraction
₀₀₂ and Lc ₍₀₀₂₎ are 11 m ² · g ⁻¹ and 2.1, respectively.
It was 3 g · cm ⁻³ , 3.44 Å, 52 Å. To 1 part by weight of this powder, 0.05 part by weight of polyvinylidene fluoride was added as a binder, and made into a paste using dimethylformamide, and applied to one side of a copper foil having a thickness of 10 μm so that the dry film thickness was 130 μm. Then, the negative electrode 2 was produced.
The positive electrode 1 and the negative electrode 2 have a positive electrode lead terminal 3 made of aluminum and a negative electrode lead terminal 4 made of copper for collecting current.
Welded respectively. Then, between the positive electrode 1 and the negative electrode 2,
By laminating each other with the separator 5 made of a microporous film made of polyethylene interposed, and winding many times, a spirally wound electrode body was produced. Then, the spirally wound electrode body was housed in the SUS battery container 6. The negative electrode lead terminal 4 into the battery container 6
Was connected to the inner bottom of the battery by spot welding, and the positive electrode lead terminal 3 was similarly connected to the battery sealing plate 7.

Next, in the battery can container 6 accommodating the electrode body, bis (perfluoro-) synthesized as an electrolyte in a mixed solvent prepared by mixing propylene carbonate and dimethoxyethane at a volume ratio of 1: 1. An electrolytic solution prepared by dissolving 1-butanesulfonyl) imidolithium so as to have a concentration of 0.7 mol · dm ⁻³ was poured, and the battery container 6 and the battery sealing plate 7 were packed through a polypropylene packing 8. Sealed by fitting and caulking, outer diameter 20 mm,
A cylindrical non-aqueous electrolyte battery having a height of 50 mm was produced. This battery was subjected to a charge / discharge test at room temperature (about 20 ° C.) with a charge / discharge current of 1 A, a charge end voltage of 4.2 V, and a discharge end voltage of 2.7 V. The discharge capacity of the first cycle was 0.88 A.
h, discharge capacity retention rate for the 200th cycle (percentage of the discharge capacity for the 200th cycle divided by the capacity for the 1st cycle)
The result was 91%.

[0016]

Example 2 In the same manner as in Example 1, only the electrolytic solution contained 0.7 mol · dm ⁻³ propylene carbonate / dimethoxyethane of bis (perfluoro-1-butanesulfonyl) imide lithium in a volume ratio of 1 / 1.25. A cylindrical nonaqueous electrolytic battery having an outer diameter of 20 mm and a height of 50 mm was prepared as a mixed solvent solution, and charged at a charge / discharge current of 1 A, a charge end voltage of 4.2 V, and a discharge end voltage of 2.7 V at room temperature (about 20 ° C.). When a discharge test was conducted, the discharge capacity in the first cycle was 0.86.
Ah, the discharge capacity retention rate at the 200th cycle (the discharge capacity at the 200th cycle divided by the capacity at the 1st cycle) was 90%.

[0017]

Example 3 In the same manner as in Example 1, a 0.25 mol · dm ⁻³ propylene carbonate solution of lithium bis (perfluoro-1-butanesulfonyl) imide was used as the electrolytic solution only, with an outer diameter of 20 mm and a height of 50 mm. A cylindrical non-aqueous electrolyte battery was produced, and the charge / discharge current was 1 A and the end-of-charge voltage was 4.2.
When a charge / discharge test was performed at room temperature (about 20 ° C.) with V and discharge end voltage of 2.7 V, the discharge capacity at the first cycle was 0.67 Ah, and the discharge capacity retention ratio at the 200th cycle (2
As a result, the discharge capacity at the 00th cycle was divided by the capacity at the first cycle to obtain 94%.

[0018]

[Comparative Example 1] In the same manner as in Example 1, the outer diameter of the electrolytic solution was a mixed solvent solution of 1.0 mol · dm ⁻³ propylene carbonate / dimethoxyethane volume ratio 1/1 of bis (trifluoromethanesulfonyl) imide lithium. 20
mm, height 50 mm, a cylindrical non-aqueous electrolyte battery was prepared,
When a charge / discharge test was conducted at a room temperature (about 20 ° C.) with a charge / discharge current of 1 A, a charge end voltage of 4.2 V, and a discharge end voltage of 2.7 V, the discharge capacity at the first cycle was 0.90 Ah, but 2 cycles. In the end, charging and discharging became impossible. When the battery was disassembled and examined, the aluminum foil of the positive electrode was cut due to corrosion.

[0019]

[Comparative Example 2] In the same manner as in Example 1, except that only the electrolytic solution was a 1.0 mol · dm-3 propylene carbonate / dimethoxyethane volume ratio 1/1 mixed solvent solution, the outer diameter was 20 mm and the height was high. A cylindrical non-aqueous electrolyte battery having a length of 50 mm was prepared, and the charge / discharge current was 1 A and the charge end voltage was 4.
When a charge / discharge test was performed at room temperature (about 20 ° C.) with a discharge end voltage of 2 V and a discharge end voltage of 2.7 V, the discharge capacity at the first cycle was 0.89 Ah and the discharge capacity retention ratio at the 200th cycle (discharge capacity at the 200th cycle). Was divided by the capacity of the first cycle) and the result was 72%.

[0020]

Comparative Example 3 In the same manner as in Example 1, except for the electrolytic solution, 1.0 mol of lithium perfluoro-1-butanesulfonate was used.
・ Dm ^-3 propylene carbonate / dimethoxyethane volume ratio 1/1 mixed solvent solution, outer diameter 20 mm, height 5
A 0 mm cylindrical non-aqueous electrolyte battery was prepared, and the charging / discharging current was 1
A, a charge-discharge test was performed at room temperature (about 20 ° C.) with a charge end voltage of 4.2 V and a discharge end voltage of 2.7 V.
The discharge capacity in the first cycle was 0.49 Ah.

[0021]

According to the present invention, it is possible to provide a lithium ion secondary battery having a high capacity and a high capacity cycle stability, and capable of using aluminum for the current collector of the positive electrode. is there.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view of a non-aqueous electrolyte battery used in Example 1 of the present invention.

[Explanation of symbols]

 1 band positive electrode 2 band negative electrode 3 positive electrode lead terminal 4 negative electrode lead terminal 5 separator 6 battery container 7 battery sealing plate 8 packing 9 insulating plate

Claims (2)

[Claims] 1. A negative electrode mainly composed of a carbon material capable of absorbing lithium ions, a positive electrode mainly composed of a lithium-containing transition metal chalcogen compound, and a bis (fluoroalkylsulfonyl) imide lithium having an alkyl group having 2 or more carbon atoms. A lithium-ion secondary battery comprising an electrolyte solution containing the electrolyte. 2. A copper foil as a negative electrode current collector, an aluminum foil as a positive electrode current collector, and an bis (fluoroalkylsulfonyl) imide lithium whose alkyl group has 2 or more carbon atoms as an electrolyte. 1. The lithium ion secondary battery according to 1.