CN100440589C - Functional polymer film-coated electrode and electrochemical device using the same - Google Patents

Functional polymer film-coated electrode and electrochemical device using the same Download PDF

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CN100440589C
CN100440589C CNB2004800325879A CN200480032587A CN100440589C CN 100440589 C CN100440589 C CN 100440589C CN B2004800325879 A CNB2004800325879 A CN B2004800325879A CN 200480032587 A CN200480032587 A CN 200480032587A CN 100440589 C CN100440589 C CN 100440589C
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China
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electrode
polymer
electrolyte
active material
electrode active
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CNB2004800325879A
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CN1875504A (en
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龙贤姮
李相英
金锡九
安谆昊
吴丙薰
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株式会社Lg化学
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation
    • Y02E60/122Lithium-ion batteries

Abstract

The present invention provides an electrode in which an electrode active material particles as being interconnected are applied on current collector, wherein the interconnected surface of electrode active material particles is coated with a polymer, the polymer being present as an independent phase, while maintaining a pore structure formed among the interconnected electrode active material particles as well as an electrochemical device including the electrode. Also, the present invention provides a method for manufacturing an electrode coated with a polymer present on an interconnected surface of electrode active material as an independent phase, while maintaining a pore structure formed among the electrode active material particles, which comprises the steps of: (a) coating slurry for an electrode including an electrode active material on a current collector and drying it to form an electrode; and (b) dipping the electrode obtained from a step (a) into a solution containing the polymer dissolved therein and a method for manufacturing an electrochemical device comprising the electrode obtained by the above method. The electrode coated with a polymer as an independent phase provides an electrochemical device with improved safety and prevents degradation of performance of an electrochemical device.

Description

The electrochemical device of functional polymer film-coated electrode and this electrode of use

Technical field

The electrode that the present invention relates to improve battery security and prevent cell performance degradation relates to the method for producing above-mentioned electrode, relates to electrochemical device that comprises described electrode and the method for producing this electrochemical device.More specifically, the present invention relates to electrode, this electrode is the surface that is coated on electrode active material by the electrolyte functional polymer that can be expanded by liquid phase electrolyte and/or dissolve as phase independently, and simultaneously between electrode active material particles, keep loose structure and obtain, with fail safe that improves electrochemical device and the degeneration that prevents the electrochemical device quality.The invention still further relates to the electrochemical device that comprises above-mentioned electrode.

Background technology

Recently, at the store energy technical elements more and more stronger concern is arranged.Battery extensively is used in mobile phone, camcorder, notebook computer, and the energy in PCs and the electric automobile produces further investigation and exploitation to this battery.From this point, electrochemical device receives very big concern.Concrete, developing chargeable secondary cell is the focus of paying close attention to.Recently, concentrated in the secondary cell field and carried out to improve the new electrode of capacity density and specific energy and the research and development of battery.

In the secondary cell that uses at present, come across the nineties in 20th century early stage lithium secondary battery have be higher than the conventional batteries of using aqueous electrolyte (as the Ni-MH battery, N-Cd battery, H 2SO 4-Pb battery etc.) driving voltage and energy density.For those reasons, lithium secondary battery is by favourable use.Yet the shortcoming of this lithium secondary battery is that use therein organic electrolyte may cause forming the problem of the secure context of battery burning and blast, and the method complexity of producing this battery.Up-to-date lithium ion polymer battery has corrected the above-mentioned shortcoming of lithium rechargeable battery, and expection is the best candidate who leads battery technology of future generation.Yet, comparing with lithium rechargeable battery, the common capacity of lithium ion polymer battery is lower.Particularly when it is in low temperature, the discharge capacity deficiency.Therefore, need to improve this problem.

Estimate and guarantee that battery security is important.Most important consideration is that this battery can not cause damage to the user when the faulty operation battery.For this purpose, the strict limit battery of safety standard of battery catches fire and explodes.Therefore, many methods of cell safety problem have been proposed to solve at present.

Concrete, as the more basic solution of battery security, advised using polyelectrolyte.Usually, battery security increases according to the order of liquid phase electrolyte, gel-type electrolyte and solid polymer electrolyte, and battery performance reduces by above-mentioned same sequence.Therefore well-known because this not good battery performance uses the battery of solid phase electrolyte also not become commercialized.Simultaneously, the commercial gel type polyelectrolyte that is suitable for is developed by the Sony and the Sanyo Electric Co., Ltd of Japan recently, and is disclosed in US patent No.6 respectively, and 509,123B1 and Japanese publication No.2000-299129.Also make the battery that uses this gel type polyelectrolyte.The characteristic of above-mentioned two types of batteries mentioning is briefly described hereinafter.

The battery of Sony uses polymer, such as PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) with contain the LiPF that is dissolved among EC (ethylene carbonate) and the PC (propylene carbonate) 6Electrolyte.Polymer and electrolyte mix with DMC (dimethyl carbonate) as solvent and form mixture, and this mixture is applied on the electrode surface then, DMC volatilization subsequently, thus the electrode that has the gel type polymer on it is provided.Then, electrode with based on polyolefinic barrier film (separator) tangle up preventing short circuit current, thereby battery is provided.

Simultaneously, with regard to the battery of Sanyo, negative electrode at first, anode and be entangled in based on polyolefinic barrier film and form battery together.Then, PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), the mixture fusion of PEGDMA (polyethylene glycol dimethacrylate) and initator and organic carbonate.Then, the mixture of described generation is injected in the battery of into previous formation, and is crosslinked under optimum conditions then, thereby forms gel-type polymer electrolyte.In this case, form electrolyte in battery assembling back original position in battery.

Yet, prepare above-mentioned two kinds of gel-type polymer method of electrolyte show very complicated, thereby productivity is not high.In addition, above-mentioned two types electrolyte causes only producing the limited improvement of battery performance and fail safe.

Improve the method for battery security as another, the open No.0366344 of Korean Patent discloses and a kind of conducting polymer has been coated on the lip-deep method of electrode active material.Yet in this case, problem is that the electrode active material particles that scribbles conducting polymer trends towards assembling, and since the used solvent and the shearing force of step of following manufacturing electrode the surface of conducting polymer and electrode active material may be kept apart.In addition, although conducting polymer allows electronics to move, it is very limited that lithium ion moves, thereby causes the degeneration of battery performance.

The accompanying drawing summary

The above-mentioned and other purpose of the present invention, feature and advantage in conjunction with the accompanying drawings, will become according to following detailed description more obvious, wherein:

Fig. 1 is that manufacturing of the present invention is coated with the schematic diagram as the structure of the method for the electrode of the polymer of independent phase and the electrode active material that forms thus;

Fig. 2 a and 2b are the views that the present invention is used for relatively being coated with the electrode of polymer, and wherein Fig. 2 a is the schematic diagram that part scribbles prior art polymers, and Fig. 2 b is the schematic diagram that scribbles as the electrode of the polymer of independent phase;

Fig. 3 is the schematic diagram of expression state, wherein after injecting liquid phase electrolyte by dissolving as the high viscosity electrolyte that the polymer that is coated on the electrode active material surface of independent phase forms, be evenly distributed in electrolyte and the barrier film;

Fig. 4 shows the figure that concerns between the viscosity of the change in concentration of electrolyte polymer soluble and electrolyte and the ionic conductivity;

Fig. 5 is SEM (scanning electron microscopy) photo that shows the electrode structure of embodiment 3, wherein the surface coated of electrode active material have polymer as independent phase (polymethyl methacrylate, PMMA);

Fig. 6 is the figure that shows negative electrode and the calorific value of the reaction generation of electrolyte in each lithium secondary battery of embodiment 1-4, described battery is compared with the lithium secondary battery that Comparative Examples 1 comprises conventional electrodes, contains the electrode of electrode active material surface coated as the polymer of independent phase;

Fig. 7 is the figure that shows negative electrode and the calorific value of the reaction generation of electrolyte in each lithium secondary battery of embodiment 4-6, described battery is compared with the lithium secondary battery that comprises conventional electrodes and barrier film of Comparative Examples 1, comprises the electrode active material surface coated as the electrode of the polymer of independent phase and/or be coated with the barrier film of this polymer;

Fig. 8 is the figure of charging that shows each lithium secondary battery of embodiment 1-4, and this battery and Comparative Examples 1 comprise the lithium secondary battery comparison of conventional electrodes, comprise the electrode of electrode active material surface coated as the polymer of independent phase; With

Fig. 9 is the figure of charging that shows each lithium secondary battery of embodiment 4-6, the lithium secondary battery that this battery and Comparative Examples 1 comprise conventional electrodes and barrier film relatively comprises that the electrode active material surface coated has as the electrode of the polymer of independent phase and/or is coated with the barrier film of polymer.

Disclosure of the Invention

We have found that working as the electrode that obtains by conventional method is impregnated in the polymer solution to form the polymer coating as independent phase on the electrode active material surface, and when keeping the cavernous structure that forms by the space between the electrode active material particles simultaneously, might solve the problem that occurs in the prior art, described problem comprises the gathering of electrode active material particles and separating of polymer coating, and obtains to prevent cell performance degradation and the effect of improving battery security.

Therefore, an object of the present invention is to provide the electrode that can improve battery security and prevent cell performance degradation, a kind of method for preparing this electrode, the method that comprises the electrochemical device of this electrode and produce this electrochemical device.

One aspect of the present invention, provide the electrode active material particles of interconnection to be applied to electrode on the current-collector, wherein the interconnect surface of electrode active material particles is coated with polymer, this polymer exists mutually as independent, keeps the cavernous structure that forms between the electrode active material particles of interconnection simultaneously.Electrochemical device also is provided, preferably comprises the lithium secondary battery of described electrode.

Another aspect of the present invention provides the method for producing electrode, and may further comprise the steps: the electrode slurry that (a) will contain electrode active material is coated on current-collector, and dry this slurry forms electrode; (b) electrode that step (a) is obtained is impregnated into and contains in the solution that is dissolved in polymer wherein, make to form polymer coating, keep the cavernous structure that forms between the electrode active material particles simultaneously in electrode active material interconnect surface as independent phase.The method of producing the electrochemical device that contains the electrode that is obtained by above-mentioned same procedure also is provided.

Hereinafter, will describe the present invention in detail.

Usually, the electrode that forms of conventional method comprises bonding and be attached to the electrode active material of current-collector by adhesive.According to the present invention, above-mentioned electrode is impregnated in the solution that contains polymer, the electrolyte functional polymer that can be expanded by liquid phase electrolyte and/or dissolve preferably, thereby with polymer-coated this electrode.

Polymer solution permeates the cavernous structure that forms between the electrode active material particles in the electrode easily and enters electrode interior.Therefore, can keep the cavernous structure (see figure 1) that forms between the electrode active material particles simultaneously with the interconnect surface of thin conforming layer coating electrode active material.Be coated with according to prior art in the electrode of electrolyte polymer soluble, electrolyte polymer soluble coating as the surface that is present in electrode active material mutually of mixing with adhesive (referring to Fig. 2 a).On the contrary, in being coated with the electrode of polymer of the present invention, polymer coating is as independently single exist mutually (referring to Fig. 2 b).

Because above-mentioned architectural feature, electrode of the present invention can be improved battery security simultaneously and prevent the degeneration of battery performance.

At first, electrode of the present invention can improve the fail safe of battery, and wherein the interconnect surface of electrode active material is coated with the polymer as independent phase, keeps the cavernous structure that forms between the electrode active material particles simultaneously.In other words, when the electrode of routine for example overcharges owing to extreme condition or high-temperature storage when becoming instability, they trend towards the electrolyte effect with high response.Yet electrode of the present invention is owing to the surface coated of electrode active material in the electrode has the polymer that exists mutually with independent, even electrode active material does not contact with electrolyte inject liquid phase electrolyte in the battery assembling after, but still contacts with polymer.Therefore, can significantly prevent extreme condition for example overcharge or high-temperature storage under the electrode active material that takes place and the side reaction between the electrolyte.In addition, can also reduce the side reaction between electrode and the liquid phase electrolyte calorific value that produces and the formation that suppresses dendritic crystal on the electrode surface, thereby significantly improve battery security.

In addition, electrode of the present invention forms electrode by conventional method, then it is impregnated in the solution that contains polymer with polymer-coated and obtain.On the contrary, the electrode of conventional coated polymeric forms electrode by the active material that uses coating then by with conducting polymer or inorganic substances coating electrode active material.Therefore, can prevent the gathering of electrode active material or be coated on the separation of the adhesive on the electrode active material, and basic simultaneously distribution and the structure that keeps forming the material of electrode.In addition, can keep the basic physics character (comprising battery capacity and battery performance) of battery and the structural stability of battery for a long time.

In addition, when being coated on the polymer of electrode active material interconnect surface when being the electrolyte functional polymer that to be expanded by liquid phase electrolyte or to dissolve, can improve battery security as independent phase.More specifically, can be expanded and/or the electrolyte dissolved polymers electrolyte dissolving that preferred electrolyte polymer soluble is injected into, thereby the electrolyte (referring to Fig. 3) of formation liquid-like gel or high viscosity liquid form after the battery assembling by electrolyte.Such electrolyte has the advantage of liquid phase electrolyte and gel-type electrolyte.In other words, cause oxygen and the electrolyte reaction with relative high viscosity described herein that disintegrating of cathode construction produces owing to for example overcharging with condition such as high-temperature storage, thereby suppress the side reaction between electrode and the electrolyte.Finally, can reduce calorific value and the improvement battery security that produces by side reaction.

Secondly, electrode of the present invention can make the degeneration of battery performance minimize, and wherein the interconnect surface of electrode active material is coated with the polymer as independent phase, keeps the loose structure that forms between the electrode active material particles simultaneously.In other words, because electrode of the present invention has polymer coating, this coating forms by prefabricated electrode is impregnated in the solution that contains polymer, and the cavernous structure between the electrode active material particles is kept makes electrolyte can penetrate into the inside that electrode enters electrode rapidly.In addition, a kind of like this thickness is that 1 μ m or thin polymer coating still less minimize the reduction of lithium ion rate travel.

In addition, when the interconnect surface that is coated on active material is the electrolyte functional polymer that can be expanded by liquid phase electrolyte or dissolve as the polymer of independent phase, can prevent the degeneration of battery performance.More specifically, when being used for polymer of the present invention and being the electrolyte functional polymer that to be expanded by electrolyte and/or to dissolve, the electrolyte that injects in battery assembling back can penetrate into polymer, and the polymer that comprises infiltration electrolyte wherein that obtains has the ability of conduction electrolyte ion.So, opposite with conducting polymer that does not have the conductive routine of electrolyte ion or inorganic matter, polymer of the present invention, the inflatable and/or electrolyte polymer soluble of preferred electrolyte can prevent the degeneration of battery performance.In addition, the expandable and/or electrolyte polymer soluble of electrolyte has excellent electrolyte affinity, and the electrode that is coated with same polymer also has the electrolyte affinity of increase, thereby estimates to improve battery performance.In addition, when polymer was used to the carbon anode active material, the irreversible capacity of anode may be lowered, thereby the raising of battery total capacity is provided.

In addition, when being coated on the polymer of electrode active material interconnect surface as independent phase when being the electrolyte soluble polymer, polymer is dissolved in the electrolyte that is injected in the battery to form high viscosity electrolyte as mentioned above.Not only increase provides the small reduction of ionic conductance to such high viscosity electrolyte according to viscosity, but also in the surface of two electrodes and their hole, the surface and the infiltration of their hole of the surface of the electrode active material of electrode, barrier film and distribute, cause in the whole volume of battery, moving the generation of caused cell reaction, succeeded by improving battery performance by lithium ion.

Preferably be coated on the polymer on the electrode surface, the polymer that preferably is coated on the electrode active material interconnect surface has high as far as possible dielectric constant.Because the extent of dissociation of salt in electrolyte depends on the dielectric constant of solvent for use in the electrolyte, the polymer with high-k can improve the extent of dissociation of salt in the high viscosity electrolyte that forms by dissolve polymer.The dielectric constant of polymer can change at (under frequency 1kHz measure) between 1.0 to 100, and preferred 10 or more than.

According to the present invention, the kind that depends on the liquid phase electrolyte of use, be coated on the polymer on the electrode surface, the polymer that preferably is coated on the electrode active material interconnect surface can be soluble, expandable or insoluble polymer, or has the polymer of mixed nature.Concrete, the soluble and/or electrolyte swellable polymer of electrolyte is particularly preferred.Be coated on lip-deep soluble, the expandable or insoluble polymer of electrode active material, or the polymer with mixed nature the side reaction between electrode active material and the electrolyte can be suppressed, thereby battery security can be improved.

When polymer is that the electrode that is coated with same polymer also has the electrolyte affinity of raising, thereby improves battery performance when having the expandable and electrolyte polymer soluble of the electrolyte of excellent electrolyte affinity.Concrete, the electrolyte swellable polymer absorbs the liquid phase electrolyte that battery assembling back is injected, thereby has the electrolyte ion conductibility, thereby improves battery performance.In addition, the high viscosity electrolyte that the electrolyte dissolving that the electrolyte polymer soluble is injected by battery assembling back has liquid phase electrolyte and gel-type electrolyte advantage with formation, thereby the degeneration that improves the fail safe of battery and prevent battery performance.

When electrolyte swellable polymer and electrolyte polymer soluble were used as mixture, above-mentioned effect was by the degeneration of synergistic combination to improve battery security and to prevent battery performance.

Among above-mentioned polymer, the solubility parameter that can be used for the insoluble polymer of electrolyte of the present invention is 18.0 (J 1/2/ cm 3/2) or still less.When the solubility parameter of polymer is 18 or still less the time, polymer can not be dissolved in the conventional battery liquid phase electrolyte.

Can be used for the expandable and electrolyte soluble polymer solubility parameter of electrolyte of the present invention is 18.0 (J 1/2/ cm 3/2) or more, preferably at 18.0 (J 1/2/ cm 3/2) and 30 (J 1/2/ cm 3/2) between.

The example that the electrolyte swellable polymer is concrete comprises poly(ethylene oxide), polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyacrylonitrile-styrol copolymer, polyvinyl chloride (PVC), PVP, polyvinyl acetate, the polyethylene vinyl acetate ester copolymer, gelatin or its mixture, but be not limited thereto.

The concrete example of electrolyte soluble polymer comprises cyano-containing (polymer CN), pulullan polysaccharide, cellulose acetate, acetylbutyrylcellulose, cellulose acetate propionate, polyethylene glycol, glyme, Polyethylene glycol dimethyl ether, polypyrrole alkane ketone or its mixture, but be not limited thereto.The polymer of cyano-containing is particularly preferred, and its concrete example comprises the cyanoethyl pulullan polysaccharide, cyanoethyl polyvinyl alcohol, cyanethyl cellulose, cyanoethyl sucrose or the like.All materials with above-mentioned feature can be used alone or in combination.

Be coated on the polymer coating on the electrode surface, the preferred coating on the interconnect surface of electrode active material, as independent phase, its thickness is preferably between 1nm and 1 μ m, more preferably between 10nm and 100nm.When thickness less than 1nm, its can not prevent effectively mainly overcharge or the high-temperature storage condition under the electrode active material and side reaction between the electrolyte and the exothermic reaction that take place.So it can not improve the fail safe of battery.When thickness greater than 1 μ m, the infiltration that needs the cost long time to make polymer pass through electrolyte is expanded or dissolve, and lithium-ion-conducting reduces, thus the performance of reduction battery.

Consider the relation between battery performance and the fail safe, the amount that is present in the lip-deep polymer of electrode active material can change.The amount of preferred polymers based on the weight of electrode active material from 0.01wt% to 50wt%.In addition, the amount of polymer can be controlled individually in negative electrode or the anode.

Comprise as the independent electrode of the lip-deep polymer of electrode active material that is coated on mutually and compare the porosity reduction with the electrode that does not comprise polymer.After coated polymeric, the porosity that the space between the electrode active material particles forms preferably is controlled in 1% to 50% scope.The hole of electrode is the part of filling electrolyte wherein.When the porosity of electrode less than 1% the time, the ratio of electrolyte (E) and electrode active material (M), promptly E/M is too low, because the lithium ion transfer deficiency diminishes battery performance.When the porosity of electrode greater than 50% the time, overcharge or the high-temperature storage condition under side reaction between electrolyte and the electrode active material too develop, thereby diminish battery security.

In addition, when polymer is the expandable and/or electrolyte soluble polymer of electrolyte, the electrode that is coated with same polymer has the liquid phase electrolyte affinity of raising, thereby the contact angle between electrode and the stand-by liquid phase electrolyte reduces.Compare with the electrode that does not comprise polymer, contact angle preferably reduces by 1 ° or more.

Have on the electrode active material surface polymer coating that exists mutually as independent, keep the electrode of loose structure between the interconnection particle of electrode active material simultaneously, can be by following method manufacturing.

In one embodiment, use well known to a person skilled in the art that conventional method forms electrode.Concrete, electrode slurry comprises electrode active material, optional being coated on the current-collector with adhesive and/or conduction reagent is dried then.Then, as shown in Figure 1, electrode is impregnated into and has has wherein dispersed or dissolved polymer, the solution of the expandable and/or electrolyte soluble polymer of preferred electrolyte, thus use polymer-coated electrode, solvent is volatilized and dry then.

Although above-mentioned solvent has no particular limits, preferred dissolution degree parameter is similar to the solubility parameter of stand-by polymer and has lower boiling solvent.Such solvent can mix equably with polymer, and can easily be removed after coated polymeric.Operable solvent comprises acetone, oxolane, and carrene, chloroform, dimethyl formamide, N-N-methyl-2-2-pyrrolidone N-(NMP), cyclohexane, water or its mixture, but be not limited thereto.

For polymer solution coating electrode, can use any method known to those skilled in the art with preparation as mentioned above.Can use several different methods, comprise dip coated, mold pressing coating, print roll coating, scraper coating (comma coating) or its combination.

Shown in Fig. 2 b and 5, in the electrode of making as mentioned above, be coated on the electrode active material polymer not with the adhesive physical mixed, but be present in mutually on the surface of electrode active material as independent, keep the porosity that the space between the electrode active material particles forms simultaneously.So can improve battery security and performance.

In addition, the invention provides and comprise negative electrode, anode, be inserted in the electrochemical device of the barrier film between negative electrode and the anode, negative electrode wherein, anode or two electrodes all are coated with polymer, and this polymer is present on the electrode active material interconnect surface mutually as independent, keeps the loose structure that forms between the electrode active material particles simultaneously.

This electrochemical device comprises all devices that carry out electrochemical reaction.The concrete example of this electrochemical device comprises various primary cells, secondary cell, fuel cell, solar cell and capacitor.

In order to use above-mentioned electrode to make electrochemical device, can use any conventional method known to those skilled in the art.In one embodiment, the production method of this electrochemical device comprises the steps: to insert barrier film with the formation assembly between two electrodes, and injects electrolyte in assembly.

Electrode adhesion of the present invention depends primarily on the physical characteristic that is coated on the polymer on the electrode surface to barrier film.In fact, electrode adhesion is a high polarity at this polymer to barrier film, suitably makes under low glass state conversion temperature (Tg) or low melting point temperature (Tm) condition.So, can take to twine (winding), lamination and folding technology are to arrive barrier film with electrode adhesion.As a result, electrochemical device can be by the several different methods manufacturing.

On the interconnect surface of electrode active material, be coated with polymer, be preferably the electrode and the assembled formation assembly of barrier film of the expandable and/or electrolyte soluble polymer of electrolyte, then liquid phase electrolyte is injected into this assembly, the physical characteristic that depends on polymer, the polymer that is coated with on the electrode active material surface is inflated and/or dissolves.

Concrete, be the expandable and electrolyte soluble polymer of electrolyte when being coated on the lip-deep polymer of electrode active material, this polymer can comprise liquid phase electrolyte after injecting this liquid phase electrolyte.Preferably, the amount of liquid phase electrolyte, still is not limited thereto from 0.1wt% to 20wt% based on the weight of injecting electrolyte polymer before in the polymer.This content can depend on the porosity of the viscosity of polymer, solvent types, liquid phase electrolyte of use and electrode and change that condition is that content is not higher than for fully filling the concentration in the hole between the electrode active material particles.

When using the electrolyte soluble polymer, polymer dissolution forms high viscosity electrolyte after injecting liquid phase electrolyte.Concrete, to form based on the liquid phase electrolyte before being introduced in electrochemical device at liquid phase electrolyte, preferred high viscosity electrolyte comprises the polymer of 0.01wt% to 20wt%.When polymer content greater than 20wt%, the problem of existence be need the cost long time with polymer dissolution in electrolyte, and the electrolyte soluble polymer can not be dissolved in the electrolyte in the given time fully, thereby reduces battery performance.

Preferably, the viscosity of 25 ℃ of following high viscosity electrolyte is greater than the viscosity 0.01cP of the liquid phase electrolyte of dissolve polymer or more not wherein.

In addition, preferably when external temperature raises, the calorific value that comprises electrode pair electrolyte in the electrochemical device of high viscosity electrolyte is lower than the calorific value 0.01J/g of conventional batteries or more.In addition, preferably compare with the electrochemical device of routine, calorific value reaches peaked temperature and raises 0.01 ℃ or more.

Preferably, the electrochemical device that obtains from said method is a lithium secondary battery, and wherein lithium secondary battery comprises lithium metal secondary battery, lithium rechargeable battery, lighium polymer secondary battery, lithium ion polymer secondary cell or the like.

Electrode of the present invention, it is coated with as the polymer of independent phase and keeps loose structure between electrode active material particles simultaneously, can apply electrode active material on current-collector according to the method known to those skilled in the art and form.Concrete, active material of cathode can comprise the active material of cathode of any routine that is used for conventional electrochemical device negative electrode at present.The concrete nonrestrictive example of active material of cathode comprises the lithium insert material, for example lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or its composite oxides.In addition, active material of positive electrode can comprise the active material of positive electrode of any routine that is used for conventional electrochemical device anode at present.The concrete nonrestrictive example of active material of positive electrode comprises for example lithium metal of lithium insert material, lithium alloy, carbon, petroleum coke, activated carbon, graphite or other carbonaceous material.The nonrestrictive example of cathode collector comprises aluminium foil, nickel foil or its combination.The nonrestrictive example of anode collector comprises Copper Foil, goldleaf, nickel foil, copper alloy foil or its combination.

Can be used for liquid phase electrolyte of the present invention and comprise formula A +B -The salt of expression, wherein A +Expression is selected from Li +, Na +, K +Alkali metal cation and its combination, B-represents to be selected from PF6 -, BF4 -, Cl -, Br -, I -, ClO 4, ASF 6 -, CH 3CO 2 -, CF 3SO 3 -, N (CF 3SO 2) 2 -, C (CF 2SO 2) 3 -Anion and combination thereof, salt is dissolved or dissociate in the organic solvent that is selected from propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl-sulfoxide, acetonitrile, dimethoxy-ethane, diethoxyethane, oxolane, N-N-methyl-2-2-pyrrolidone N-(NMP), methyl ethyl carbonate (EMC), gamma-butyrolacton and composition thereof.Yet, can be used for electrolyte of the present invention and be not limited to above-mentioned example.

Have no particular limits although can be used for barrier film of the present invention, preferably use porous septum, comprise based on polypropylene, polyethylene or polyolefinic porous septum.In addition, according to the present invention, barrier film can by be coated with polymer about the same method of the method for making electrode as mentioned above, be preferably the electrolyte soluble polymer.

The electrochemical device that obtains from said method can be cylindrical, prismatic, bag shape or coin sample shape, but the shape of electrochemical device is had no particular limits.

Implement best mode of the present invention

Below will describe the preferred embodiment of the invention in detail.Be to be understood that the following example purpose, and the invention is not restricted to this as example.

Reference example 1. is measured viscosity and the ionic conductivity that comprises the electrolyte that is dissolved in polymer wherein

Change the concentration of electrolyte soluble polymer, measure the viscosity and the ionic conductivity of electrolyte.

In this embodiment, the electrolyte soluble polymer is the cyanoethyl pulullan polysaccharide, and electrolyte is to comprise the 1M LiPF that is dissolved in wherein 6The mixed organic solvents of EC/PC/DEC (weight ratio=3/2/5).The concentration of cyanoethyl pulullan polysaccharide is controlled to be 0wt% in the electrolyte, 5wt% and 10wt%.

The concentration of cyanoethyl pulullan polysaccharide is depended in the variation of viscosity and ionic conductivity, and monitors by naked eyes.The result is presented at following table 1 and Fig. 4.As table 1 and shown in Figure 4, when a spot of electrolyte soluble polymer is that the cyanoethyl pulullan polysaccharide is dissolved, the viscosity of electrolyte improves significantly, but ionic conductivity reduces a little.

[table 1]

Be dissolved in the concentration of electrolyte functional polymer in the electrolyte ????η(cP) ????σ(mS/cm) ????0wt% ????5.2 ????6.524 ????5wt% ????16.5 ????4.991 ????10wt% ????74.1 ????3.729

[embodiment 1~6. make the electrode and the barrier film of coated polymeric, and the lithium secondary battery that comprises above-mentioned electrode and shim]

Embodiment 1

Manufacturing is coated with the electrode of cyanoethyl pulullan polysaccharide

94wt% is as the lithium cobalt composite oxide of active material of cathode, and 3wt% is added in N-N-methyl-2-2-pyrrolidone N-(NMP) solvent as the PVDF of adhesive as the carbon black of electric conducting material and 3wt%, so that produce the mixed slurry that is used for negative electrode.Described mixed slurry is applied on aluminium (Al) film as the thickness 20 μ m of cathode collector, and the dry negative electrode that produces.

Simultaneously, in acetone, dissolve about 1 hour to form the solution of concentration 1wt% at about 30 ℃ of cyanoethyl pulullan polysaccharides (degree of polymerization about 600).Prefabricated negative electrode was impregnated into polymer solution about 1 to 3 minute by dip-coating method, and bubbles all in the hole are discharged from, and the negative electrode that was coated with then is dry under the room temperature vacuum.

1-2. manufacturing lithium secondary battery

(manufacturing anode)

In N-N-methyl-2-2-pyrrolidone N-(NMP), add the carbon dust of 93wt% respectively as active material of positive electrode as solvent, 6wt% is as the polyvinylidene fluoride (PVDF) of adhesive, with the carbon black of 1wt%, be used for the mixed slurry of anode with generation as electric conducting material.Mixture paste is applied on copper (Cu) film as 10 μ m thickness of anode collector, and the dry anode that produces, and this anode is then by roll-in.

(assembling of battery)

The negative electrode of Huo Deing and anode and three layers of barrier film being formed by polypropylene, polyethylene/polypropylene (PP/PE/PP) are become assembly by heap-shaped as mentioned above, contain 1M lithium hexafluoro phosphate (LiPF then 6) electrolyte (ethylene carbonate (EC)/propylene carbonate (PC)=50/50 (v/v)) be injected into wherein so that battery to be provided.

Embodiment 2. cyanoethyl polyvinyl alcohol

Repeat embodiment 1 to make negative electrode and battery, be used as polymer except the cyanoethyl polyvinyl alcohol replaces the cyanoethyl pulullan polysaccharide.

Embodiment 3. polymethyl methacrylates (PMMA)

Repeat embodiment 1 to make negative electrode and battery, be used as polymer except polymethyl methacrylate (PMMA) replaces the cyanoethyl pulullan polysaccharide.

Embodiment 4. scribbles the negative electrode and the anode of cyanoethyl pulullan polysaccharide

Repeat embodiment 1 making negative electrode and anode, except negative electrode and anode all use the cyanoethyl pulullan polysaccharide to be coated with.

Embodiment 5. comprises the negative electrode that scribbles the cyanoethyl pulullan polysaccharide, the battery of anode and barrier film

Cyanoethyl fluran (degree of polymerization about 600) is dissolved in the acetone, is coated on formation on the surface of three layers of barrier film of PP/PE/PP by dip-coating method then.After coating, barrier film room temperature and 100 ℃ with the hot-air drying to obtain the barrier film finished product of the about 1 μ m of polymer coating thickness.

Then, repeat embodiment 1 making negative electrode, anode, barrier film and battery, except electrode and barrier film all use the cyanoethyl pulullan polysaccharide to be coated with.

Embodiment 6. Polyethylene glycol dimethyl ether

Repeat embodiment 5 to make battery, be used as polymer except Polyethylene glycol dimethyl ether (molecular weight=1,000) replaces the cyanoethyl pulullan polysaccharide.

Comparative example 1. is made electrode and the lithium secondary battery that does not have polymer coating

Repeat embodiment 1 to make electrode and battery, except electrode does not scribble polymer.

Experimental example 1. surface analyses

As described below electrode active material surface in the electrode that scribbles polymer of the present invention is analyzed.

Observe use polymethyl methacrylate (PMMA) as the surface of polymer by scanning electron microscopy (SEM) from the negative electrode of embodiment 3 acquisitions.

Shown that polymethyl methacrylate (PMMA) is coated on the surface of electrode active material equably to the about 10nm of thickness, keeps the cavernous structure (referring to Fig. 5) between the electrode active material particles that scribbles this polymer simultaneously.

The thermal stability of experimental example 2. evaluation of lithium secondary battery

For the thermal stability of each lithium secondary battery of estimating embodiment 1-6 and comparative example 1, carry out following test.

Each battery is charged to 4.2V, and is disassembled to isolate negative electrode and accepts differential scanning calorimetric (DSC) then to measure the thermal stability to 350 ℃.

Each lithium secondary battery that has shown embodiment of the invention 1-6 is compared with the battery of comparative example 1 has improved thermal stability (referring to Fig. 6 and 7).Because electrode of the present invention is included on the electrode active material surface polymer coating that exists mutually as independent, for example overcharging in extreme condition does not contact with highly reactive electrolyte with the high temperature storage bottom electrode but contacts with polymer.Therefore, the calorific value that the side reaction between electrode and the electrolyte produces reduces, and causes the improvement of battery security.In addition, be coated on the lip-deep polymer of electrode active material, preferred electrolyte soluble polymer is dissolved in the liquid phase electrolyte forming high viscosity electrolyte, thereby prevents the side reaction between electrode and the electrolyte and improve battery security.

Therefore, as can be seen: comprise and be coated with on the electrode active material surface polymer that exists mutually as independent, the lithium secondary battery of keeping the electrode of pore structure between the electrode active material particles simultaneously has good thermal stability.

The performance of experimental example 3. evaluation of lithium secondary battery

Be the performance of each lithium secondary battery of assessment embodiment 1-6 and comparative example 1, measure the capacity and the C-speed of each battery.

Each battery that has shown embodiment 1-6 uses the battery of conventional electrodes to compare with comparative example 1 performance that equates basically is provided, and only compares with latter's battery except the performance of the former battery and reduces (referring to Fig. 8 and 9) when the 2C discharge test a little.Concrete, wherein two electrodes each battery of all being coated with the embodiment 4-6 of polymer shows that initial capacity increases about 3%.The raising of considering this capacity may be that described polymer is for being coated on the expandable or electrolyte soluble polymer of the lip-deep electrolyte of active material of positive electrode because polymer causes the reduction of anode irreversible capacity.

Therefore, can find out and be coated with polymer, specifically be the independent expandable and/or electrolyte soluble polymer of electrolyte that exists mutually of conduct on the electrode active material surface, keep the electrode of the pore structure between the electrode active material particles simultaneously, prevent the lithium secondary battery performance degradation.

Industrial applicibility

It can be seen from the above, as the electrolyte functional polymer of independent phase and keep the degeneration that electrode that the pore structure between the electrode active material particles obtains improves the fail safe of battery and prevents battery performance, described functional polymer can be expanded by liquid phase electrolyte and/or dissolve by coating on the electrode active material surface.

Although invention has been described with embodiment preferred with the most practical, be to be understood that the present invention is not limited to disclosed embodiment and accompanying drawing, and just the opposite, the application is intended to cover different modifications and variations and the spirit and scope that do not deviate from claim.

Claims (14)

1. electrode, wherein Hu Lian electrode active material particles is applied on the current-collector, wherein the interconnect surface of electrode active material particles is coated with the electrolyte polymer soluble, this polymer exists mutually with independent, keep the pore structure that forms between the electrode active material particles of interconnection simultaneously, and this polymer is selected from following at least a: the cyanoethyl pulullan polysaccharide, the cyanoethyl polyvinyl alcohol, cyanethyl cellulose, cyanoethyl sucrose, pulullan polysaccharide, acetylbutyrylcellulose, cellulose acetate propionate and glyme.
2. the electrode of claim 1, wherein the dielectric constant range of the polymer of measuring at frequency 1kHz is from 1.0 to 100.
3. the electrode of claim 1 wherein depends on the type of the liquid phase electrolyte of use, and the solubility parameter scope of electrolyte polymer soluble is from 18.0J 1/2/ cm 3/2To 30J 1/2/ cm 3/2
4. the electrode of claim 1, wherein the thickness of polymer coating from 1nm to 1 μ m.
5. the electrode of claim 1, wherein the porosity of electrode from 1% to 50%.
6. an electrochemical device comprises negative electrode, anode, places the barrier film between electrode and the liquid phase electrolyte, and wherein negative electrode, anode or two electrodes are the described electrodes of claim 1.
7. the electrochemical device of claim 6, wherein electrochemical device is a lithium secondary battery.
8. the electrochemical device of claim 6, wherein liquid phase electrolyte comprises the salt of following general formula (I) representative, described salt dissolves in being selected from following at least a organic solvent or dissociates: propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl-sulfoxide, acetonitrile, dimethoxy-ethane, diethoxyethane, oxolane, N-N-methyl-2-2-pyrrolidone N-(NMP), methyl ethyl carbonate (EMC) and gamma-butyrolacton;
A +B -(I)
A wherein +Expression alkali metal cation or its combination, and B -Represent anion or its combination.
9. the electrochemical device of claim 6 is wherein dissolved by mix liquid phase electrolyte after injecting liquid phase electrolyte as the independent lip-deep polymer of electrode active material that is coated on mutually, to form the part of electrolyte.
10. the electrochemical device of claim 9, wherein after injecting liquid phase electrolyte, be introduced in electrochemical device composition before based on liquid phase electrolyte, the amount of the polymer that the electrolyte that forms as the independent polymer that is coated on the electrode active material surface mutually by dissolving comprises is 0.01-20wt%.
11. the electrochemical device of claim 9, by dissolving as independent be coated on mutually electrolyte that the lip-deep polymer of electrode active material forms be penetrated into equably two electrodes of electrochemical device the surface, be present in the hole in electrode active material or the electrode, the surface of barrier film and the hole of barrier film.
12. a method of producing the described electrode of claim 1, described method comprises the steps:
(a) coating is used to contain the slurry of the electrode of electrode active material and the dry electrode that forms on current-collector; With
(b) electrode that forms with the solution coat step (a) that contains the electrolyte polymer soluble that is dissolved in wherein.
13. the method for claim 12, wherein step (b) is selected from following method by use and finishes: dip coated, mold pressing coating, print roll coating, scraper coating and combination thereof.
14. a method of producing electrochemical device may further comprise the steps:
(a) coating is used to contain the slurry of the electrode of electrode active material on current-collector, and the dry electrode that forms, the electrode that obtains is impregnated into the solution that contains the electrolyte polymer soluble that is dissolved in wherein, to provide claim 1 the described electrode that is coated with the electrolyte polymer soluble, and this polymer is selected from following at least a: the cyanoethyl pulullan polysaccharide, the cyanoethyl polyvinyl alcohol, cyanethyl cellulose, cyanoethyl sucrose, pulullan polysaccharide, acetylbutyrylcellulose, cellulose acetate propionate and glyme are then by using electrode and barrier film to form assembly; With
(b) liquid phase electrolyte is injected in the assembly of step (a) acquisition.
CNB2004800325879A 2003-11-05 2004-11-04 Functional polymer film-coated electrode and electrochemical device using the same CN100440589C (en)

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