CN1758475A

CN1758475A - Safety lithium-ion electric core

Info

Publication number: CN1758475A
Application number: CNA2004100811296A
Authority: CN
Inventors: 李鑫; 肖久梅; 曹东亮; 李雪坎
Original assignee: Xi'an Dinasi Science & Technology Co Ltd
Current assignee: Xi'an Dinasi Science & Technology Co Ltd
Priority date: 2004-10-10
Filing date: 2004-10-10
Publication date: 2006-04-12

Abstract

This invention relates to a safety Li ionic battery chip, the positive or negative pole plate of said chip is coated with a PVDF microporous layer with low thermal shrinkage rate having good solution absorption ability and an anti-thermal shrinkage function, which can increase the electrochemical and safety property of the chip.

Description

A kind of safety lithium-ion electric core

Technical field

The present invention relates to lithium rechargeable battery.

Technical background

Lithium rechargeable battery has operating voltage height, the big advantage of energy density and is widely used in electronic products such as mobile phone, notebook computer.

Owing to adopted the high organic electrolyte of decomposition voltage; be at battery and overcharge; fortuitous event such as inside or external short circuit may catch fire; the danger of blast; for guaranteeing the chemical property and the fail safe of battery; usually battery design is the pattern that electric core adds the protection electronic circuit; however; the situation that inefficacy is arranged when protecting electronic circuit still; electricity core itself has then been made certain Safety Design; the high-strength polyolefin micro-porous film that has hot turn-off function such as use; the unexpected adstante febre fusion cut-off current in inside; weaken or stop the generation of thermal runaway reaction; but high-intensity microporous polyolefin film is owing to exist vertical thermal contraction of 10-30% in the shutoff of being heated in 135-170 ℃ of temperature range; just might cause; negative plate physics short circuit and catching fire; therefore blast remedies the fail safe that this defective can improve electric core.

The liquid lithium ion of common extensive application electricity core in addition, the little porous septum of employed high-strength polyolefin is general to the electrolyte absorbency, in winding-structure, particularly at the fillet position at the two ends of electric core, exist electrolyte not have the slit of complete filling between positive and negative plate and the barrier film easily, the inconsistency that causes electric core capacity to descend and produce in batches is especially more obvious when high power capacity electricity core is produced in enormous quantities.

The electrostrictive polymer core adopts porous Kynoar PVDF-HFP as membrane layer usually, after the imbibition swelling, use as electrolyte, because the little porous layer intensity of Kynoar is low, can not satisfy the requirement of winding process, usually film thickness is about 50 microns, the gel electrolyte conductivity is lower than common liquid lithium ion electricity core, and low-temperature conductive is also not enough.

The composite characteristic of lithium ion secondary electricity core requires the productivity ratio of battery electrochemical stability, battery security, battery constantly to improve.In order to improve battery behavior, require barrier film to have suitable nanoscale aperture and porosity and permeability and high intensity and hot turn-off capacity, low thermal contraction, prevent the generation of thermal runaway in the battery.Be limited to existing barrier film and be difficult to all satisfy above-mentioned all harsh performance requirements, therefore wish to develop to take into account above-mentioned every performance, between the high-temperature region, have little porous septum layer that low percent thermal shrinkage (MD, TD direction are all less than 5%) can prevent the short circuit of positive and negative plate physics.

The object of the present invention is to provide have good effectively turn-off performance and low percent thermal shrinkage and have high porosity and gas permeability, fine hole shape to be fit to the particular design that lithium rechargeable battery is used, it can improve electric core electrochemical properties and fail safe.

For overcoming above-mentioned shortcoming and defect, improve the fail safe of liquid lithium ion electricity core, special proposition the present invention.

Summary of the invention

The present inventor has carried out deep research for solving above-mentioned problem, finds to adopt following method to make the little porous layer of Kynoar separately, can be before being warming up to fusing point thermal contraction almost nil.At first polyvinylidene fluoride resin 5-25 part is dissolved in the intensive polar solvent, the plasticizer that adds 10-50 part then, coat after mixing on the smooth substrate, the control thickness about 60 microns, treat to immerse after the solvent evaporates drying second solvent bathe in extracting fall plasticizer and promptly get the little porous layer barrier film of Kynoar.The percent thermal shrinkage of test individual layer little porous septum after 100-150 ℃/30min heat exposes in MD, TD direction all less than 5%.

Porous Kynoar PVDF-HFP uses as single membrane layer, and the intensity of barrier film can not satisfy continuous production requirement, and the barrier film deflection is relatively poor.And the pole piece after the employing process roller process then can be avoided this difficult problem as carrier, and can trying one's best of little porous septum work is thin, such as 5 microns thickness, and if the independent manufacturing single-layer septum that approaches like this is impossible.The thickness of control porous Kynoar micro-porous film is at the 5-20 micron, porosity 40-80%, aperture 0.01-5 micron, to the chemical property that guarantees electric core and effectively barriers function be good.

Making Kynoar is little porous layer of matrix, can adopt homopolymerization type Kynoar PVDF or copoly type Kynoar PVDF-HFP, the weight average molecular weight of Kynoar is 200,000-500,000 for good, cross low molecular weight, Kynoar easily is dissolved in electrolyte, too high molecular weight, the Kynoar swelling is not enough.Homopolymerization type Kynoar can adopt the Kynar 740,761 or the Kynar 301F of Elf atochem company, and three's fusing point is at 155-172 ℃.Copoly type Kynoar PVDF-HFP can adopt the Kynar 2800/2801/2850/2851 of Elf atochem company, and fusing point is at 155-172 ℃.

Little porous layer is to make like this; at first polyvinylidene fluoride resin 5-25 part is dissolved in the intensive polar solvent under vacuum or inert gas shielding; the plasticizer that adds 10-50 part then; after mixing the glue of deaeration coated on the pole piece after the roll compacting, treat to immerse after the solvent evaporates drying second solvent bathe in extracting fall the battery pole piece that plasticizer promptly obtains having little porous layer.Treat after the solvent evaporates drying also not extracting elasticizer and directly use.Plasticizer can adopt a kind of or mixture among neck dibatyl phithalate DBP, diethyl carbonate DEC, the propylene carbonate PC.Polar solvent is N, dinethylformamide, N, N-dimethylacetylamide, a kind of or its mixture in the N-methyl pyrrolidone etc.

Little porous layer is coating method on electric core pole piece, both can be on anode pole piece, and also can be on cathode pole piece; Both can be coated with by single face, also can two-sidedly be coated with; Even back positive and negative of the polyalkene diaphragm that do not adopt can short circuit yet as long as can guarantee in principle to reel.

The lithium ion secondary electricity core of making according to the method described above exposes still safety of back battery in 100-150 ℃/30min heat, does not take place on fire and blast.

Adopt that above-mentioned principle makes liquid lithium ion secondary electricity core, the capacity consistency is better, corresponding battery material is with the desirable lower limit of volume, mass production can be saved cost.

Embodiment:

Material prescription: Kynar 2801:15 part; 30 parts of dibutyl phthalates (DBP); N, N-dimethylacetylamide: 55 parts.

Processing method:

At first in the vacuum stirring still with Kynar 2801 and N, the N-dimethylacetylamide carries out dispersing and mixing to be handled 1-2 hour, was mixed with even glue; Add the dibutyl phthalate dispersing and mixing then and handled 1-2 hour, be mixed with even glue; The glue of deaeration is coated a side of the not welding electrode ear of anode pole piece after the roll compacting and cathode pole piece respectively, treat to immerse after the solvent evaporates drying the electric core positive and negative plate that extracting in the methanol bath is fallen plasticizer, treated promptly to obtain having after the solvent evaporates drying little porous layer; With positive plate, polyalkene diaphragm, negative plate coiling, fill in Stainless Steel Shell, the explosion-proof covering board of burn-oning successively, changes into, seals at fluid injection after the vacuumize, manufactures safer electric core.

Claims

1, a kind of safety lithium-ion electric core is characterized in that the negative or positive electrode pole piece of this electricity core is coated with little porous layer that Kynoar is a matrix after through the roller process operation, little porous layer thickness 5-20 micron, and porosity 40-80%, aperture 0.01-5 micron,

2, be little porous layer of matrix according to the described Kynoar of claim 1, it is characterized in that adopting homopolymerization type Kynoar PVDF or copoly type Kynoar PVDF-HFP is the matrix manufacturing.

3, be little porous layer of matrix according to the described Kynoar of claim 1, the weight average molecular weight that it is characterized in that Kynoar is 200,000-500,000.

4, according to the little porous layer of the described Kynoar of claim 2, it is characterized in that homopolymerization type Kynoar can adopt the Kynar 740,761 or the Kynar 301F of Elf atochem company, little porous layer at 100-150 ℃ of percent thermal shrinkage less than 5%.

5, according to the little porous layer of the described Kynoar of claim 2, it is characterized in that copoly type Kynoar PVDF-HFP can adopt the Kynar 2800/2801/2850/2851 of Elf atochem company, little porous layer at 100-150 ℃ of percent thermal shrinkage less than 5%.

6, according to the little porous layer of the described Kynoar of claim 1, it is characterized in that little porous layer is to make like this, at first polyvinylidene fluoride resin 5-25 part is dissolved in the intensive polar solvent, the plasticizer that adds 10-50 part then, coat after mixing on the pole piece after the roll compacting, treat to immerse after the solvent evaporates drying second solvent bathe in extracting fall the battery pole piece that plasticizer promptly obtains having little porous layer.

7, according to the little porous layer of the described Kynoar of claim 6, it is characterized in that little porous layer is to make like this, at first polyvinylidene fluoride resin 5-25 part is dissolved in the intensive polar solvent, the plasticizer that adds 10-50 part then, coat after mixing on the pole piece after the roll compacting, treat directly to use without extracting after the solvent evaporates drying.

8,, it is characterized in that plasticizer can adopt a kind of or mixture among neck dibatyl phithalate DBP, diethyl carbonate DEC, the propylene carbonate PC according to claim 6 and 7 described plasticizer.

9,, it is characterized in that polar solvent is N, dinethylformamide, N, N-dimethylacetylamide, a kind of or mixture in the N-methyl pyrrolidone according to claim 6 and 7 described intensive polar solvents.