EP1290749A4

EP1290749A4 - Microporous solid electrolytes and methods for preparing them

Info

Publication number: EP1290749A4
Application number: EP00927894A
Authority: EP
Inventors: Dong Hun Jang; Sa Heum Kim; Han Jun Kim
Original assignee: Finecell Co Ltd
Current assignee: Finecell Co Ltd
Priority date: 2000-05-24
Filing date: 2000-05-24
Publication date: 2004-09-22
Also published as: JP2003536233A; EP1290749A1; CN1452794A; WO2001099220A1

Abstract

The present invention is directed to an electrolyte film and/or a solid electrolyte, having a microporous structure, for a rechargeable cell. According to the present invention, when preparing the electrolyte film and/or the solid electrolyte, an inorganic absorbent is added in the amount of more than 70 % by weight in a polymer matrix to prevent the porous structure from being destructed at the cell-assembling process such as lamination or pressing, whereby the absorbing power of a liquid electrolyte to the solid electrolyte film and the ionic conductivity can be maintained. The inorganic absorbent contained over the specific amount, together with the microporous structure, improves the capacity of absorbing the liquid electrolyte and, in particular, works as a structure element of increasing the mechanical strength of electrolyte film and/or solid electrolyte. Therefore, the good ionic conductivity can be maintained even after the assembly of cell.

Description

MICROPOROUS INORGANIC SOLID ELECTROLYTES AND METHODS FOR PREPARING THEM

TECHNICAL FIELD

The present invention relates to a solid electrolyte film usable in rechargeable cells. More particularly, it relates to a provision of pathways for ions mobile between a cathode and an anode during repeated charge and discharge of rechargeable cells by introducing liquid components and lithium salts (hereinafter, both are referred to as "liquid electrolytes") to a solid electrolyte film, having a microporous structure and containing an absorbent above the specific amount, according to the present invention.

The rechargeable cell of the present invention includes three essential components, i.e., a cathode, an anode and an electrolyte. The cell is made by laminating cathodes, anodes and electrolytes of sheet form. Materials for said anode are carbons or polymer materials in which lithium metal or lithium ions can be intercalated/deintercalated. Materials for said cathode are transition metal oxides or polymer materials in which lithium ions can be intercalated/deintercalated. Materials for said electrolyte can be used the one according to the present invention, and a liquid electrolyte is introduced thereto after assembling the cell.

BACKGROUND ART

An electrolyte in the cell such as a rechargeable cell or an electrochemical reaction system is disposed between the conductive surfaces of cathode and anode. The electrolyte is the insulator not having the electron conduction but has the ion conduction. General electrolytes so far are consisted of only liquid components; however, more recent attentions are concentrated on the solid electrolytes having many advantages. Among them, the researches of using polymer as electrolytes have been tried.

Since the pure polymer electrolyte containing polar hetero-atoms has very low ionic conductivity of 10^"8 S/cm, it is difficult to use it at room temperature. Therefore, the main research on the polymer electrolytes focuses on the improvement of conductivity and, as a representative example, it was proposed to introduce liquid electrolyte component into the structure of polymer.

Gel-type electrolytes disclosed in US Patent 5,219,679 which contain liquid electrolytes in a polymer backbone have the proper conductivity while exhibiting properties of polymers. However, they already contain a large amount of liquid electrolytes during the manu acture of the polymer electrolytes, and thus said patent has problems as a vaporization/loss of liquid component, resulting in the change of composition and the decrease of conductivity. Furthermore, since lithium salts in the liquid electrolyte are very sensitive to moisture, the strict dehumidifying condition is required for the manufacture of gel electrolyte.

A hybrid polymer electrolyte system proposed in US Patent Nos. 5,296,318 and 5,418,091 can minimize the moisture effect on the process of manufacturing cells by adding liquid electrolytes after the packaging of cells, while taking advantage of the merits of gel-type polymer electrolytes. Since the liquid electrolytes are added after an electrolyte film is prepared, it is necessary for the inside of the electrolyte film to have sites capable of absorbing liquid components therein. To this end, plasticizers/processing aids are added in the step of preparing the electrolyte film, and after the assembly of cell is complete, they are extracted by the use of an organic solvent. However, due to such a process, the above methods have fatal demerits that the reproducibility is low, manufacturing yield is reduced, and the automation for mass production is difficult.

In order to solve those problems, it was tried to form pores in a polymer film at the time of preparing it to make the absorption of liquid electrolyte ease. More specifically, it was proposed to cast a polymer solved in a solvent to the form of film and then bring the polymer film into contact with a non-solvent. In addition to that method, methods of introducing porosity into the polymer film by vulcanization, curing or elongation were proposed. When liquid electrolytes are absorbed in the polymer films prepared by the above methods, their ionic conductivity is over 10^"3 S/cm at room temperature, which is suitable for the commercial use. However, there is the problem that the process of introducing the porosity into the polymer is complicated, or the ionic conductivity drops rapidly because the porous structure made in the polymer film collapses easily during the lamination or pressing step for assembling a cell. In other words, the polymer electrolyte itself exhibits a good property but it is difficult to apply it to the real system of manufacturing a cell.

In order to solve the problem of the porosity collapse, the method was tried to apply a polymer film over cathode and/or anode directly and bring the resultant into contact with a non-solvent. However, the method that uses an electrode surface as the substrate for preparing the electrolyte film makes the manufacturing process complicated, and water used as the non-solvent has a bad influence on the cathode and/or anode. Therefore, it is difficult to apply it to the real system of manufacturing a cell. US Patent No. 5,631,103 discloses the electrolyte system to which an inorganic filler is added. However, the addition amount of the inorganic filler should increase for reaching the commercial level and thereby the mechanical strength of the polymer film becomes weak. Therefore, that method is not suitable for the real process. Further, said patent uses. the process of casting the polymer film by adding a processing aid therein and then removing it so as to introduce the porosity into the film, which raises the similar problem to that in US Patent Nos. 5,296,318 and 5,418,091.

Meanwhile, Japanese laid-open patent gazette No. 99-16561 discloses the polymer electrolyte system adding an inorganic filler to the porous structure made of a polyvinylidene fluoride-based resin. This system provides a good ionic conductivity at room temperature and a mechanical strength possible to cast the form of film; however, the content of inorganic material is only 1.9 to 66% by weight (corresponding to 2 to

200 parts by weight based on the 100 parts by weight of polyvinylidene fluoride-based resin), preferably 4.8 to 33.3% by weight (corresponding to 5 to 50 parts by weight) based upon the total amount of electrolyte film, which is not sufficient to support the porous structure, resulting in the collapse of the porous structure of polymer electrolyte and the short of the cell at the cell-assembling process. Moreover, since the ionic conductivity of electrolyte cannot be maintained to the constant level at practice, a cell having good properties cannot be manufactured.

The problems of the prior arts mentioned above can be summarized as the following:

(1) The electrolyte made of pure polymer has the poor ionic conductivity and thus it is difficult to apply that to the real process of manufacturing a cell.

(2) The gel-type polymer electrolyte made under the condition containing a liquid electrolyte has a good ionic conductivity at room temperature because the ion conduction is carried out by the liquid electrolyte, but the process condition is limited and it is difficult to maintain the constant capacity. (3) The hybrid polymer electrolyte which is made by adding plasticizers/processing aids to make a film form and then removing them and resultantly rendering a liquid electrolyte absorbed, is advantageous in that its process is less affected by the manufacturing condition and it has a sufficient ion conductivity; however, the complicated multi-steps and the additional materials are required, and thus the process cost rises and the automation of process is difficult. (4) The polymer electrolyte into which the porosity is introduced by various methods such as solvent/non-solvent exchange, vulcanization, curing, extension, etc., has the problem that the microporous structure is collapsed at a lamination or pressing process and thus the absoφtion of liquid electrolyte is not sufficient.

(5) The method of forming the film of porous structure on an electrode surface is advantageous in increasing the adhesive strength of the electrode surface, but its processing condition is not simple and thus it is not preferable.

(6) There was a trial of improving the mechanical strength by adding an inorganic material but it could not completely solve the problem that the porous structure is collapsed at the process of assembling a cell and the ionic conductivity cannot be maintained.

Meanwhile, the present inventors provided, in PCT 99/KR99/00798, the system wherein the conductivity of lithium ion can be increased by introducing the microporosity into the electrolyte film matrix containing an absorbent to make the absoφtion of liquid electrolyte easier. In said system the liquid electrolyte susceptible to moisture is added after the assembly of cell, whereby it is not necessary to remove said absorbent after the cell assembly. Furthermore, the plasticizers or processing aids as in US patent Nos. 5,296,318, 5,418,091 and 5,631,103 are not required and the process is simple and the cost of process is low. However, as mentioned above, the present inventors found the fact that the problem may occur that the microporous structure of solid electrolyte film collapses and the absoφtive power drops at the step of binding a cathode and/or anode with the film. Therefore, the present inventors found that the absorbent of more than the specific amount is necessary so as to solve the above problem and thus accomplished the present invention.

DISCLOSURE OF INVENTION

Accordingly, the present invention provides adding inorganic materials, performing the functions of a structure filler as well as an absorbent, in more than the specific amount, to prevent the collapse of a porous structure and maintain the absoφtive power of solid electrolyte film and the conductivity of lithium ion at the cell- assembling process such as lamination or the pressing. The absorbent particles contained in more than the specific amount, together with the porous structure, improves the ability of absorbing the liquid electrolyte and, particularly, works as the structure element of improving the mechanical strength of electrolyte film and/or solid electrolyte. Therefore, the good conductivity of lithium ion can also be maintained even after the assembly of cell. Moreover, a separate operation is not necessary for the absoφtion of liquid electrolyte, and the essential feature can be exhibited that the liquid electrolyte is introduced after the assembly of cell.

The solid electrolyte according to the present invention contains an inorganic absorbent and also contains the electrolyte film of a microporous structure and an ion conductive liquid electrolyte. In other words, the solid electrolyte for a rechargeable cell can be made by the activation process of rendering the ionic conductive liquid electrolyte absorbed into the microporous electrolyte film made of only the inorganic absorbent and a polymer binder. The term "electrolyte film" used in the present specification refers to an electrolyte film which is in the dried condition and does not contain any liquid electrolytes. The term "solid electrolytes" used in the present specification means said electrolyte film having an ionic conductivity by incoφorating liquid electrolytes thereto. Although the solid electrolytes are not in a complete solid state since they contain liquid electrolytes, they are called "solid electrolytes" in order to be distinguished from the liquid electrolytes because the basic backbone of solid electrolytes starts from the electrolyte film at a solid state.

Said electrolyte film can be preferably prepared by means of a phase inversion method. Examples of such method include wet process and dry process. The wet process refers to a process for the preparation of an electrolyte film, which comprises the steps of: dissolving a mixture of an absorbent and a polymer binder in a solvent for the polymer binder, making the resulting solution to a film form, exchanging the solvent with a non-solvent for the polymer binder, and then drying the resulting material to. form an electrolyte film. On the other hand, the dry process refers to a process for the preparation of an electrolyte film, which comprises the steps of: mixing a mixture of an absorbent and a polymer binder with a solvent for dissolving the polymer binder, a non- solvent which does not dissolve the polymer binder, a pore former and a wetting agent, making the resulting mixture into a film form, and drying the resulting film completely.

The inorganic absorbent used in the present invention should absorb a liquid electrolyte due to the high affinity to the liquid electrolyte or increase the absoφtive power of the liquid electrolyte, and should not have the electron conductivity. Also, they should have the good mechanical, thermal, chemical and electrochemical properties. As such inorganic absorbents, it is possible to use one or two or more particles selected from the group consisting of mineral particles, synthetic oxide compound particles and mesoporous molecular sieves. Examples of said mineral particles include mineral particles having phyllosilicate structures such as clay, paragonite, montmorillonite and mica. Examples of said synthetic oxide compounds particles include zeolite, porous silica, porous alumina and magnesium oxide. Examples of mesoporous molecular sieves include mesoporous molecular sieves made of oxide compounds such as silica and having a pore diameter in 2 to 30 nm. Said mineral particles, synthetic oxide compounds particles and mesoporous molecular sieves may be used in the form of a mixture wherein two or more absorbents selected from the above mentioned absorbents are combined.

The particle size of inorganic absorbents is preferably not more than 40μm, more preferably, not more than 20μm so as not to decrease the mechanical strength and the uniformity of the electrolyte film. However, when the particle size is excessively small, the absoφtive power drops or the electrolyte film tends to be made to the dense structure, and thus it is not preferable. The prior art such as Japanese laid-open patent gazette 1999-16561 uses the inorganic material of very small particle size (e.g., less than 20nm); however, in this case, the inorganic material cannot work as an absorbent and instead may prevent the crystallinity of filler or polymer film. Namely, for the puφose of exhibiting the properties of absorbent and structure element together as in the present invention, the inorganic absorbent should have the particle size of more than 50nm or the aggregated form in the several μm unit. The form of inorganic absorbent is not particularly restricted and can be fiber, needle, plate or sphere form, but an asymmetric form is preferable so as to increase the mechanical strength of electrolyte film. The first puφose of the present invention is to make the solid electrolyte maintaining the absoφtive power of liquid electrolyte and the ionic conductivity, which results from the fact that the microporous structure is not destroyed and have a mechanical strength even after the assembly of cell. The present inventors found that the amount of inorganic absorbent is a key condition for the accomplishment of the above puφose. The amount of inorganic absorbent is preferably at least more than 70% by weight based upon the amount of electrolyte film consisting of the inorganic absorbent and the polymer binder, more preferably 70% to 95% by weight. When it is more than 95% by weight, the ionic conductivity does not increase according to the increase of the amount, and instead the mechanical strength of the formed electrolyte film and the surface adhesive power between electrodes deteriorates. To the contrary, 70% by weight is the starting point where the below problems occur.

Firstly, when the inorganic amount is not more than 70% by weight, the absorptive power of liquid electrolyte and the ionic conductivity decrease largely because the porous structure of solid electrolyte film tends to collapse at the laminating or pressing step for the assembly of cell. The present inventors made solid electrolyte films having the different amount of inorganic absorbents and then observed the change of the thickness and the change of ionic conductivity depending on the external pressure applied at the cell manufacturing process. From such an experiment, it was found the fact that the thickness of solid electrolyte film and the ionic conductivity change suddenly from 70% by weight. This fact was not suggested or taught at the prior arts and was discovered by the present inventors for the first time. When based upon the experimental fact, only more than 70% by weight guarantees the cell having a good performance where the porous structure of solid electrolyte is not destructed against the external pressure applied at the manufacturing process and dose not lose the ability of absorbing the liquid electrolyte, thereby maintaining the ionic conductivity. Secondly, when the inorganic amount is not more than 70% by weight, the deformation of shape becomes large because the volume portion of polymer is large to the total weight of a solid electrolyte. Namely, since the shrinkage/swelling occurs at the step of drying electrolyte or the step of impregnating liquid electrolyte after the assembly of cell, the dimensional stability of electrolyte film/solid electrolyte drops.

Thirdly, when the inorganic amount is not more than 70% by weight, even though many absorbents are contained, it is difficult to solve completely the problems indicated at the electrolyte mainly comprising polymers. For example, like in the prior polymer electrolytes, the deterioration at low or high temperature occurs. Generally, since the motion of polymer chains directly affects the ionic conductivity in polymer electrolytes, the effect of temperature on the ionic conductivity becomes significant. Particularly, at the low temperature, the motion of polymer chains is restricted, which significantly reduces the ionic conductivity, thereby resulting in severe deterioration in the performance of a cell. On the other hand, using the inorganic absorbent as in the present invention increases the ionic conductivity. Furthermore, using the inorganic absorbent, not being susceptible to the temperature, in more than the specific amount, minimizes the effect of temperature contrary to the property of the existing polymer electrolytes. Also, as the inorganic absorbent of a large amount is contained in an electrolyte, the electrolyte according to the present invention has a merit in that the resistance against ignition or explosion is improved compared to the electrolytes containing the organic material such as polymers at a large amount.

In consideration of the fact that the addition amount of inorganic materials is generally around 50% by weight or less than it at the prior art or other relevant art, the discovery that the above problems can be solved only when the organic absorbent is contained in more than the specific amount is extremely exceptional to the existing general concept, and it was accomplished by many experimental and analysis based upon the large addition of inorganic material.

As a polymer binder, it is possible to use most common polymers. Among them, it is preferred to use a mixture of one or two or more polymers selected from the group consisting of polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and maleic anhydride, polyvinylchloride, polyvinylacohol, polyvinyl formal, polymethylmethacrylate, polymethacrylate, cellulose triacetate, polyurethane, polyimide, polycarbonate, polysulfone, polyether, polyethylene oxide, polyolefine such as polyethylene or polypropylene, polyisobutylene, polybutyldiene, polyacrylonitrile, acrylonitrilebutyldiene rubber, ethylene-propylene-diene-monomer, tetra(ethylene glycol)diacrylate, polydimethylsiloxane and polysilicon, or copolymers or polymer blends thereof.

The polymer binders of which the property changes largely or in which a crosslinking reaction, a curing reaction and the like occur by a heat and a pressure are not preferred. Also, it is not preferred to induce polymerization, copolymerization, crosslinking, curing reaction by adding at least one kind of material at the state of monomer. That is because unreacted monomers may be impregnated in the inorganic absorbent and later it reacts with electrolyte compounds to decrease the performance of cell, and thus the separate process of removing themi is necessary. Therefore, it is preferred to avoid the condition that the above problems may occur at the manufacturing process of electrolyte film or the assembly process of cell.

As a solvent for the polymer binder which has the solubility for the polymer binder, a mixture of one or two or more solvents selected from the group consisting of N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile, cyclohexanone, chloroform, dichloromethane, hexamethylphosphoramide, dimethylsulfoxide, acetone and dioxane.

As a non-solvent for the polymer binder which does not have the solubility for the polymer binder or has little solubility and which has the compatibility for the solvents, it is possible to use a mixture of one or two or more selected from the group consisting of water, ethanol, ethylene glycol, glycerol, acetone, dichloroemethane, ethylacetate, butanol, pentanol, hexanol and ether.

In the following, the process for the preparation of said solid electrolyte having a porous structure is explained in greater detail.

Wet process The solid electrolyte having the porous structure according to the present invention can be prepared by wet process consisting of five steps, i.e., dissolving a polymer binder, mixing an inorganic absorbent, film casting, making porous polymer matrix and drying, and activation.

First of all, a polymer binder is dissolved in a solvent and then an inorganic absorbent is added in the solution and sufficiently mixed to be dispersed uniformly. The solid content of said mixed solution is preferably 5 to 60% by weight based on the total weight of the solution. If the content is not more than 5% by weight, the mechanical strength of an electrolyte film decreases and if the content is more than 60% by weight, the inorganic absorbent cannot be dispersed sufficiently or the viscosity of the mixed solution becomes high, which is problematic. In order to facilitate the dispersion of the inorganic absorbent, a magnetic stirrer, a mechanical stirrer, a planetary mixer or a high-speed disperser can be used to stir the mixed solution. While stirring, an ultrasonic stirrer may be adopted to prevent the absorbent from agglomerating or bubbling during the mixing. In addition, if desired, the mixed solution may be subjected to defoaming and filtration steps.

After the polymer binder and the inorganic absorbent are uniformly mixed, the resulting mixture is made to the form of film. For example, the mixed solution may be poured on a flat plate and then be subjected to casting. Alternatively, the mixed solution may be extracted from a die with a fixed gap and then coated onto a substrate. As the substrate can be used materials which have a chemical, thermal and mechanical stability and can be separated from the electrolyte film during a lamination process. For example, polymer film such as polyester, polytetrafluoroethylene, paper, etc., can be used. Various other application methods can be selected.

After casting, the film is contacted with a non-solvent to exchange the solvent for polymer binder. For example, it is possible to extract the solvent by immersing the film in a non-solvent pool. Accordingly, it is preferable to select the combination of a miscible solvent and a non-solvent. The immersion time in the non-solvent pool varies from one minute to one hour depending on the kinds of the solvents and non-solvents. When the time is shorter, it is difficult to obtain sufficient porosity. On the contrary, when the time exceeds the defined time, the productivity becomes decreased, which is not preferable. The temperature in the pool is preferably from 10°C to 90°C, more preferably from 20°C to 80°C. If the temperature is lower than that, it is difficult to obtain sufficient porosity. If the temperature is excessively high, the mechanical strength of the electrolyte film decreases, which is not preferable. After the extraction of the solvent and completely drying the resulting film, an electrolyte film is made. Dry process

The solid electrolyte having a porous structure according to the present invention can be prepared by dry process consisting of five steps, i.e., dissolving a polymer binder, mixing an inorganic absorbent, adding additives (non-solvent, pore former, wetting agent), film casting and drying, and activation.

A polymer binder is dissolved in a solvent and then an inorganic absorbent is added in the solution and sufficiently mixed to be dispersed uniformly. The dispersing or mixing step is identical with that in the wet process. After the polymer binder and the absorbent are uniformly mixed, a non-solvent is added in an amount range of not causing the precipitation of the polymer binder. In order to facilitate the formation of microporous structure, it is preferable to add a pore former or a wetting agent. The step of film casting is identical with that in the wet process. After the completion of making a film, the resulting electrolyte film is completely dried at 20°C to 200°C to make an electrolyte film.

When compared to the wet process, as the dry process has the below demerits, it is more preferable to use the wet process than the dry process.

(1) In the case of dry process, it is comparatively difficult to completely disperse or mix an absorbent, a polymer binder and additives. When a complete dispersion or mixing is not conducted, (i) it become difficult to accomplish an even dispersion of the pore former or the absorbent, (ii) it is not easy to cast into the form of an electrolyte film and (iii) the mechanical strength and reproducibility become decrease. Namely, in the event that the pore former or the absorbent is dispersed unevenly, it was confirmed that (a) the reaction in a cell proceeds non-uniformly localized state when the electrolyte film is used as an electrolyte for an electrochemical cell; (b) the casting in the form of film becomes difficult; and (c) the mechanical strength decreases, which limited the dry process severely.

(2) The dry process necessitates the addition of non-solvents in order to form pores and in view of the principle of the dry process, the solvent should be evaporated prior to the non-solvents so that pores can be formed. If the non-solvents are evaporated prior to the solvents, pores cannot be formed. In this regard, it is essential that the non- solvents should have non-volatile property or higher boiling points than solvents. For this reason, the dry process is likely to have a problem of residual non-solvents. In other words, non-solvents, which have higher boiling point than solvents or are nonvolatile, are difficult to remove completely from the electrolyte film during a dry step. Therefore, another step (for example, extraction with alcohol or ether or increasing the drying temperature sufficiently) should be taken in order to remove completely the non- solvents. In addition, since said non-solvent is chemically and electrochemically unstable, if said non-solvent remains in the electrolyte film, it may cause side reactions or oxidation or reduction with repeated charge and discharge of a cell. As a result, the deterioration of cell performance such as capacity decrease of cells or gas evolution may happen. The same problems apply to the other additives besides non-solvents. It is considered that the process for the preparation of electrolyte film solely consisting of an absorbent and a polymer binder by way of complete removal of additives or the like may be complicated, which render the reproducibility of this process difficult.

It is preferred that the thickness of the film in the present invention is controlled in the range of 20 to 200μm. If the thickness of the film is not more than 20μm, the mechanical strength decreases and thus it is not preferable. On the contrary, if the thickness of the film exceeds 200μm, the ionic conductivity decreases and thus it is not preferable. It is preferable for the electrolyte film of the present invention to have the pore diameter of less than 20μm, more preferable less than lOμm, and further more preferable 0.01 to 5μm. It is preferred for the electrolyte film of the present invention to have the porosity of 5 to 95%, more preferable 20 to 90%, and further more preferable 40 to 85%.

The liquid electrolyte to be absorbed in the microporous electrolyte film prepared as above can be prepared by dissolving lithium salt in an organic solvent.

It is preferred that said organic solvent has high polarity and no reactivity to lithium metal so as to improve the degree of dissociation of ions by raising the polarity of electrolyte and to facilitate ion conduction by lowering local viscosity around ions. Examples of such an organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC), dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), γ-butyrolactone (GBL), dimethylsulfoxide (DMSO), 1,3-dioxane (DO), tetrahydrofuran (THF), 2-methyltetrahydrofuran, sulfolane, N,N-dimethylformamide (DMF), diglyme (DME), triglyme and tetraglyme. In particular, it is preferred that the organic solvent is used in the form of mixed solutions of two or more solvents consisting of high viscosity solvents and low viscosity solvents.

Said lithium salt is preferred to have low lattice energy and a high degree of dissociation. Examples of such a lithium salt include LiClO , LiBF₄, LiPF₆, LiAsF₆, LiSCN, LiCF₃SO₃, LiN(CF₃SO₂)₂ and LiC(CF₃SO₂)₃. The selective mixtures thereof can also be used. The concentration of the lithium salt is preferably 0.5M to 2M.

The liquid electrolyte can be added in the amount of 20 to 90 % by weight, preferably 40 to 85 % by weight, based on the total amount of electrolytes including the liquid electrolyte. In this case, the lithium ion conductivity in the solid electrolyte is from 1 to 3mS/cm at room temperature.

The present invention is directed to a rechargeable cell, particularly to a rechargeable lithium cell wherein said porous solid electrolyte is used as an electrolyte.

The method of preparing the rechargeable cell with the solid electrolyte according the present invention is described below.

The assembly of a cell is accomplished to bind a cathode and an anode with the inteφosed electrolyte film, which is made by the above steps, in the manner of lamination, pressing or the like. The cathode and the anode are prepared separately, and the cathode is electrically connected to a cathode current collector, and the anode is electrically connected to an anode current collector. Thus, the constructed assembly is activated to be able to absorb the liquid electrolyte, thereby obtaining an electrochemical cell which is ready to operate.

Preparing an electrolyte film and electrodes (cathode and anode) separately is preferable because the quality control, the process design and the equipment are simple. If necessary, in order to increase the binding ability between the electrode and the electrolyte film and render the thickness of the electrolyte film thinner, a solid electrolyte slurry consisting of an absorbent, a polymer binder, a solvent, etc. may be directly applied on the electrode to form an electrolyte film. However, the above method is not preferable because it will be hard to adopt the method when the electrode and the electrolyte film do not correspond with each other, or when the electrode or the electrolyte film is easy to pollute or lose their performance in the course of manufacturing process. The process that an electrolyte film is placed between electrodes and then assembled or laminated to a cell by lamination or pressing may be modified in consideration of the performance of cell or the process condition, (i) An electrolyte film is first laminated on one electrode of a cathode and an anode, and then the other electrode is laminated on the other side of the electrolyte film, (ii) Electrolyte films are laminated on the surfaces of a cathode and an anode, respectively, and then the cathode and the anode are laminated at the state that the electrolytes face each other, (iii) A cathode, an electrolyte and an anode are simultaneously laminated in order.

In the lamination process, it is preferable to set the laminating condition so as to minimize the decrease of the electrolyte film within the range of not more than 50% by volume. The volume decrease of the electrolyte film means the destruction of a porous structure, but a little decrease of volume is inevitable for the lamination by heating and or pressing. Therefore, it is advantageous to find the laminating condition capable of minimizing the decrease of volume. As mentioned above, it was confirmed that the addition of inorganic absorbent over at least 70% by weight, which is one of the most important features of the present invention, can minimize such volume decrease.

If desired, in order to restrict the volume decrease of the electrolyte, the method may be used to set a temperature and a pressure low as possible and to render the binding between electrodes and an electrolyte film conducted by an adhesive layer. For example, PE solution/dispersion, efhylene/ethylacrylate-based or ethylene/vinyl acetate- based adhesive, etc can be used. However, these adhesive components should have the thermal, chemical and electrochemical stability, and the adhesive layer made of them should not destroy the porous structure of surface and not increase the resistance of surface. Therefore, it is not preferable to use the adhesive layer in view of the fabrication of a cell and the control of performance. The procedures for the preparation of the cathode or anode are as follows. The cathode or anode consists of a current collector and an active material layer. The active material layer comprises of active materials, conducting materials and binders, etc. Besides, various additives may be introduced in order to improve the performance of cells. The current collectors, conducting materials, binders and additives, which are contained in the cathode or anode, may be identical or different, depending on desired objectives. Each mixture of the cathode or anode materials is kneaded to give slurry. The resulting slurry is made to a thin film by means of casting, coating and screen printing and then the resulting thin film is combined with a current collector by means of pressing or lamination to form a cathode and/or an anode. Alternatively, the slurry may be directly coated on a current collector to form a cathode and/or an anode.

The. current collector provides mobile pathways for electrons, which are generated in the oxidation/reduction reaction, taking place in the cathode or the anode. As a current collector, grids, foils, punching foils and etching foils, etc., may be generally used, depending on the performance or manufacturing processes of the cell. The use of grids can increase the loading of the active material, but it may complicate the manufacturing process. The use of foils can improve the performance of the cell and simplify the manufacturing process, but it may deteriorate the compactness of the active materials. Copper, aluminum, nickel, titanium, stainless steel, carbon, etc., can be used as the current collector. Generally, aluminum is used for the cathode and copper is used for the anode. The current collector may be conducted, if desired, with the pretreatment such as washing, surface treatment or adhesive layer coating.

The active material is the most crucial component of an electrochemical cell since it determines the performance of cell in view of the fact that the charge and discharge reaction (or oxidation/reduction reaction) of cells take place on this material. Furthermore, the active material possesses the largest content in the active material layer. As a cathode active material, it is possible to use transition metal oxides/sulfides, organic compounds, polymer compounds, etc. Preferably, it is possible to use metal oxides or polymer materials such as lithium cobalt oxide (Li_xCoO₂), lithium nickel oxide (Li_xNiO₂), lithium nickel cobalt oxide (Li_xNiyCOi.yO^, spinel type lithium manganese oxide (Li_xMn₂O₄), manganese dioxide (MnO₂), etc. As an anode active material, alkali metals, alkali earth metals, carbon, oxide compounds or sulfide compounds of transition metals, organic compounds and polymer compounds may be used, preferably carbon or polymer materials can be used. It is essential that the active materials should be chosen in accordance with the desired performance or use of a cell.

The conducting material refers to a material that is added to the cathode or anode in order to improve the electronic conductivity, and is generally carbon. Among them, the conducting material is preferably graphite, cokes, activated carbon and carbon black, more preferably graphite and carbon black. One or two or more of conducting materials selected from the above group can be used and there is no difference whether they are synthetic or natural materials. The conducting materials are added in an amount of 3 to 15% by weight based on the total weight of the electrode materials. If the amount of the conducting materials added is not more than 3% by weight, the electrical conductivity falls, causing the problem of over voltage. If the amount exceeds 15% by weight, the energy density per unit volume decreases and the side reaction due to the conducting materials become severe.

The binder refers to a component to be added to enhance the binding ability of the active material and is generally a polymer compound. The polymer compounds that are used in the preparation of the solid electrolyte film may serve as binders. It is preferable to use binders, which are the same as polymers of the electrolyte film or have miscibility. The binder may be added in an amount of 15% by weight or less based on the total weight of the electrode materials. If the amount of binder is less than required, the binding ability of the electrodes may decrease. If the amount of binder exceeds 15% by weight, the processability and porosity of the electrodes decrease.

The additives refer to materials, which are added to improve the performance of cells or electrodes and can be chosen within a wide range in accordance with desired performances or use. The additives are added to improve the binding ability with composite electrodes inside or current collectors, to induce the porosity or non- crystallinity of the composite electrodes, to improve the dispersibility of the composite electrode constituting materials or the efficiency of the process for the manufacturing of the electrodes, to prohibit the overcharge/overdischarge of the active materials, to recombine or remove the side reaction products, or to improve the absorption ability of the liquid electrolytes. Generally, salts, organic/inorganic compounds, minerals and polymer compounds can be used as additives, and absorbents added to the electrolyte film can be chosen.

In summary, the solid electrolyte according to the present invention and the rechargeable cell using it have the below merits compared to the prior art.

(1) The manufacturing process and the requirement of materials are simple. The formation of film is simple and the good porosity can be obtained by a simple method such as the wet process; therefore, it is very simple in comparison with the prior art, i.e., the method of vulcanization, curing or elongation, particularly, the method using plasticizers/processing aids. In addition, the electrolyte film according to the present invention has a simple constitution containing the large amount of the inorganic absorbents and the small amount of the polymer binder, and plasticizers/processing aids, curing polymers, crosslinking polymers or fibrous structure materials are not required separately.

(2) The performance and stability of the electrolyte is excellent. The ionic conductivity is high because the conduction of ions proceeds via liquid phase impregnated in the porous structure. The content of a polymer is low and the content of an inorganic absorbent is high, thereby (i) the ionic conductivity is not affected by a temperature, (ii) the mechanical, thermal and electrochemical stability is excellent, and (iii) the dimensional stability is good because the volume change is little. Furthermore, the electrolyte according to the present invention has a broad electrochemical potential window and the resistance to ignition and explosion. Particularly, the inorganic absorbent contained in over the specific amount also works as a structure element, which improves the resistance to lamination or pressing process and thus the performance of electrolyte decreases little even after the assembly of cell.

(3) The assembly of cell is simple. A particular dehumidifying atmosphere is not required during the preparation of electrolyte film and the assembly of cell; therefore, the manufacturing process is simple and the automation of mass production is easy.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows graphs demonstrating the experimental results of linear sweep voltammetry to determine the electrochemical stability of the solid electrolyte according to the present invention.

Figures 2, 4 and 5 show a variation of discharge capacity of cell in which an inorganic absorbent according to the present invention is used. Figure 3 shows a variation at the thickness and ionic conductivity of the films which were prepared with the different contents of inorganic absorbents, wherein the variation is expressed relatively compared to initial values.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the solid electrolyte according to the present invention and the process for the preparation of cells by using said solid electrolyte are explained in detail. The production of the solid electrolyte and the examination of performances were carried out. In addition, the solid electrolyte was assembled together with the anode and cathode to form a cell and then the procedure to examine the performance of the cell is described. However, the present invention is not limited to those examples and various modifications are possible within the scope of the invention.

Example 1 (Wet process: Experiment according to the kind and amount of inorganic absorbent and the kind of liquid electrolyte)

14g of PVdF was dissolved in 86g of NMP to make a polymer binder solution. An inorganic absorbent was added to the solution and then continuously stirred until the inorganic absorbent was completely dispersed. In order to prohibit the absorbent particles from agglomerating with each other, the solution was subjected to ultrasonic stirring for 30 minutes while stirring. The mixed solution thus prepared was coated onto a glass plate in thickness of lOOμm. The coated film was soaked in a non-solvent bath for approximately 10 minutes, which was removed from the bath and then dried at 70°C for 1 hour. The porous electrolyte film thus prepared was soaked in a liquid electrolyte solution for approximately 10 minutes. After the liquid electrolyte was completely absorbed, the weight change was determined. The ionic conductivity was also determined by the use of an alternate current impedance method.

Table 1 summarizes the kinds of inorganic absorbents and binders, the properties of the porous solid electrolyte in accordance with its content and conductivity. In order to compare the ability of the porous electrolyte film absorbing the liquid electrolyte, absorption capacity (Δ_ab) was defined as follows:

Δ_ab = [amount of the liquid electrolyte absorbed (mg)]/[weight of the electrolyte film (mg)]

In addition, the case that the volumes of solvents comprising liquid electrolytes are not specified means that the solvents are mixed in the same volume.

At the above Table 1 and the below Table 2, the item "mechanical strength" was determined at the form of electrolyte film or at the state that a liquid electrolyte is impregnated, and thus it is different from the meaning that an electrolyte film exhibits the resistance to lamination or pressing at the assembly of cells. That is, ones which have a good mechanical strength at the tables may exhibit the different property depending on the content of inorganic absorbent at the assembly of cells.

Example 2 (Wet process: Experiments according to the kind of binders) Experiments were conducted by varying the kind of binders in the same manner to Example 1 and the results are summarized in Table 2.

Example 3 (Dry process)

0.5g of P(VdF-HFP) was dissolved to 8g of acetone in 20ml vial to prepare a polymer binder solution. To the resulting mixture 1.17g of paragonite was added and then continuously stirred until its particles were completely dispersed. In order to prohibit the absorbent particles from agglomerating with each other, the resulting solution was further subjected to ultrasonic stirring for 30 minutes while stirring. To the resulting mixed solution 0.9g of ethylene glycol, O.lg of Triton X-100 (wetting agent) and 1.8 g of isopropanol (pore former) were added and then the resulting mixture was subjected to ultrasonic stirring for approximately 10 minutes until the added mixture was uniformly mixed. The mixed solution thus prepared was coated onto a glass plate in thickness of lOOμm. The coated film was dried at 40°C for approximately 2 hours, which was further dried for approximately 6 hours in a vacuum drier set to 50°C. The electrolyte film thus prepared was soaked in an EC/DEC IM LiPF₆ solution for approximately 10 minutes. After the liquid electrolyte was completely absorbed, the weight change was determined. Δ_ab value measured by the use of the weight change was 7.5. The conductivity determined at room temperature by an alternate current impedance method was 2.0 mS/cm.

Example 4 (Comparative Example: Experiment of preparing solid electrolyte having non-porous structure)

14g of PVdF was dissolved to 86g of NMP to prepare a polymer binder solution. 2g of Paragonite powder was 1.85g of the polymer binder solution and then continuously stirred until its particles were completely mixed. In order to prohibit the absorbent particles from agglomerating with each other, the resulting solution was further subjected to ultrasonic stirring for 30 minutes while stirring. The mixed solution thus prepared was coated onto a glass plate in thickness of lOOμm. The coated film was dried at room temperature for approximately 2 hours and then was further dried for 6 hours in a vacuum drier of which the temperature was controlled to approximately 50°C. The electrolyte film thus prepared was soaked in EC/DMC IM LiPF₆ solution for approximately 10 minutes. After the liquid electrolyte was completely absorbed, the weight change was determined and the conductivity was determined by the use of an alternate current impedance method. Lithium ionic conductivity measured at room temperature was 0.72 mS/cm. The present example differs from Examples 1 to 3 in the fact that a process for forming porous structures was not conducted. From the result of the present example, it is confirmed that the process of introducing the porosity as the wet process or the dry process is necessary for the improvement of the cell performance. Example 5 (Experiment of electrochemical stability)

In order to determine the electrochemical stability of the porous solid electrolyte, the linear sweep voltammetry method was carried out by the use of a stainless steel (#304) as a working electrode and a lithium metal as a counter electrode and a reference electrode. The electrochemical voltage applied in the linear sweep voltammetry was from an open circuit voltage to 5.5V, and the scan rate of the linear sweep voltammetry was lOmV/sec. The results of the linear sweep voltammetry measured on the porous solid electrolyte prepared by the methods of Example l-(h), 1-(1), l-(n) and 2-(s) are shown as A, B, C and D, respectively, in Fig. 1. As seen from Fig.l, the solid electrolyte according to the present invention is stable until 4.8V in the electrochemical aspect. Also, it can be seen that synthetic oxide absorbents are more stable than natural mineral absorbents.

Example 6 (Experiment of cell performance)

In order to determine the performances of a cell using a solid electrolyte, cells were prepared as the below. A cathode was prepared by mixing an oxide active material, a conducting carbon powder, a polymer binder and additives at the weight ratio of 82:7:8:3 as in a slurry phase, and coating the slurry on an aluminum grid, and then drying it. An anode was prepared by mixing an artificial graphite, a conducting carbon powder, a polymer binder and additives at the weight ratio of 85:3:10:2 as in a slurry phase, and coating the slurry on copper grid, and then drying it. Three (3) layers of the cathode, the electrolyte film and the anode were laminated simultaneously to make a cell, and then to the cell a liquid electrolyte was absorbed. The cell was sealed with a packing film except electrode terminals. The charge and discharge test on thus fabricated cells was carried out. The constant current was applied with a rate charging the reversible capacity within 2 hours (C/2 rate) until the cell voltage became 4.2 V, and then the constant voltage of 4.2 V was applied again until the current decreased down to C/10 mA. Subsequently, the discharging current was applied with a rate discharging the voltage down to 2.5 V or 2.75 V within 2 hours (C/2 rate). The charge and discharge experiment was repeated and the change of discharge capacity with the charge and discharge was measured. The cell constitution and the test results are summarized in the following Table 3 and shown in Fig. 2. As listed in Table 3, the solid electrolyte refers to the conditions where a liquid electrolyte is absorbed into an electrolyte film. In addition, the solid electrolyte obtained in Example 4 was not applied for cell tests.

Table 3

Fig.2 illustrates the discharge capacity with repeated charge and discharge of the cell obtained by the respective examples in comparison with the first discharge capacity. From the test results, it was confirmed that the use of the solid electrolytes (Examples 6- u, v, x) obtained by the wet process (Examples 1 and 2) shows much better cell performances than that of the solid electrolyte (Example 6-w) obtained by the dry process (Example 3). Namely, the solid electrolyte containing inorganic absorbent and prepared by the wet process has a much better effect on the total cell performances (charge and discharge performance, etc.), although the electrolyte film or solid electrolyte itself does not show any significant differences in properties (ionic conductivity, mechanical strength, etc.).

Example 7 (Experiment of the property according to the amount variation of Paragonite used as an inorganic absorbent)

10cm² of porous solid electrolyte films was prepared by varying the amount of

Paragonite powders being the inorganic absorbent as in Example 1 and then pressed by an experimental pressing machine at 130°C during 15 sees with the pressure of 1 metric ton. The change of thickness between before and after pressing was measured and the change of ionic conductivity between before and after pressing was also measured by the use of an alternate current impedance method, the results of which are summarized in Table 4. Fig. 3 shows the results wherein the film thickness and the ionic conductivity after the pressing are expressed as the percentage based upon those before the pressing. The liquid electrolyte used when measuring the ionic conductivity is EC/DMC/DEC IM LiPF₆. Table 4

From the above results, it is confirmed that, when the content of inorganic absorbent is more than 70% by weight (Example 7-cc and the next thereof), there is little difference between the film thickness and the ionic conductivity after pressing and those before pressing. Namely, it can be seen that, although the difference of the ionic conductivity between the electrolyte films or the solid electrolytes themselves does not depend on the content of the inorganic absorbent largely, the affect of its content becomes large when the electrolyte films .or the solid electrolytes go through the pressing process.

Example 8 (Experiment of the property according to the amount variation of Zeolite used as an inorganic absorbent) The experiment using Zeolite as an inorganic absorbent was conducted in the same manner as Example 7. The change in the electrolyte film and the ionic conductivity between before and after pressing are summarized in Table 5.

Table 5

As the results of Example 7, it is confirmed that, when the content of inorganic absorbent is more than 70% by weight (Example 8-11 and the next thereof), there is little difference between the film thickness and the ionic conductivity after pressing and those before pressing. When summarizing the results of Example 7 and the present Example, it can be seen that the characteristic phenomenon mentioned above is not largely related to the kind of inorganic materials. It can also be anticipated that, when fabricating cells with those electrolytes by a lamination or a pressing and then measuring the performance of the cells, the distinctive difference depending on the content of inorganic absorbents will be exhibited. Example 9 (Experiment of cell performance according to the variation of the kind and content of inorganic absorbent)

Cells were constituted in the same manner as Example 6 and the effect by the variation of the kind and content of inorganic absorbents was examined. The constitution of cells and the test results are summarized in Table 6 and drawn up in Figs.

4 and 5. As seen from Table 6, each of solid electrolytes is in the state that liquid electrolytes are absorbed in electrolyte films.

Table 6

As can be seen from the above test results, the case that the content of inorganic absorbents is more than 70% by weight in solid electrolytes (Examples 9-tt, uu or Examples 9-xx, yy) exhibits the better performance than the case that the content is otherwise. When summarizing the results of Examples 7, 8 and the present Example, it is seen that, although there is little difference in properties such as an ionic conductivity, a mechanical strength, etc., according to the content of inorganic absorbent, solely with electrolyte films or solid electrolytes themselves, they undergo the laminating or pressing process when fabricated to cells and thus the effect of the absorbent content exhibits largely. In other words, it can be said that, when the content of inorganic absorbent is over 70% by weight, the ability of absorbing the liquid electrolyte is not lost even after the assembly of cell and has an excellent influence on the cell performance. It is also confirmed that such phenomenon is exhibited regardless of the kind of inorganic absorbents.

INDUSTRIAL APPLICABILITY

The present invention provides solid electrolytes having a good ionic conductivity by rendering a liquid electrolyte absorbed easily in the electrolyte film wherein an inorganic absorbent is added and the porosity is introduced; methods of preparing those solid electrolytes; and lithium rechargeable cells using the solid electrolytes as an electrolyte. The solid electrolytes according to the present invention have merits in that the manufacturing process and the requirement of materials are simple, the capacity and stability of the electrolyte is good, and the assembly of cell using it is easy. In particular, the porosity of the electrolyte film and the ability of absorbing the liquid electrolyte can be maintained at the lamination or pressing process due to the inorganic absorbent added in over the specific amount, whereby the good properties even after the assembly of cell as well as of the solid electrolyte by itself can be maintained.

Claims

WHAT IS CLAIMED IS:

1. A solid electrolyte for rechargeable cells, comprising: an electrolyte film having a thickness of 20 to 200μm and microporous structures, wherein the electrolyte film contains an inorganic absorbent having a particle size not more than 40μm in an amount of at least more than 70% by weight based on the total weight of the electrolyte film under the dried condition that no liquid electrolyte is contained therein; and an ion conductive liquid electrolyte in an amount of 20 to 90% by weight based on the total weight of the electrolyte including liquid electrolyte.

2. The solid electrolyte for rechargeable cells according to Claim 1, wherein the content of the inorganic absorbent is 70 to 95% by weight.

3. The solid electrolyte for rechargeable cells according to Claim 1, wherein said inorganic absorbent is a mixture of one or two or more selected from the group consisting of mineral particles having phyllosilicate structures such as clay, paragonite, montmorillonite and mica; synthetic oxide compounds particles such as zeolite, porous silica and porous alumina, magnesium oxide; mesoporous molecular sieves having 2 to

30μm of pore diameter made of oxide compounds or polymers; and other commercially available absorbents; said polymer binder is a mixture of one or two or more selected from the group consisting of polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and maleic anhydride, polyvinylchloride, polymethylmethacrylate, poiymethacrylate, cellulose triacetate, polyurethane, polysulfone, polyether, polyethylene, polypropylene, polyethylene oxide, polyisobutylene, polybutylidene, polyvinylalcohol, polyacrylonitrile, polyimide, polyvinyl formal, acrylonitrilebutyldiene rubber, ethylene-propylene-diene-monomer, tetraethyleneglycol diacrylate, polydimethylsiloxane, polycarbonate and silicon polymer, or their copolymers or their blends;

4. The solid electrolyte of rechargeable cells according to Claim 1, wherein said electrolyte film is prepared by the wet process comprising the steps of dispersing the inorganic absorbent in a solution consisting of the polymer binder and its solvent, making the resulting mixture into a film, exchanging the solvent with a non-solvent for the polymer binder, and then drying the resulting material.

5. The solid electrolyte of rechargeable cells according to Claim 4, wherein said solvent for the polymer binders is a mixture of one or two or more solvents selected from the group consisting of N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile, cyclohexanone, chloroform, dichloromethane, hexamethylphosphoramide, dimethylsulfoxide, acetone and dioxane; and said non-solvent for the polymer binders is a mixture of one or two or more selected from the group consisting of water, ethanol, ethylene glycol, glycerol, acetone, dichloroemethane, ethylacetate, butanol, pentanol, hexanol and ether.

6. The solid electrolyte for rechargeable cells according to one of Claims 1 to 4, wherein said solid electrolyte is prepared by an activation procedure in which an ion conductive liquid electrolyte is absorbed into said electrolyte film, and said ion conductive liquid electrolyte is obtained by dissolving one or two or more lithium salts selected from the group consisting of LiClO₄, LiBF , LiPF₆, LiAsF₆, LiSCN, LiCF₃SO₃, LiN(CF₃SO₂)₂ and LiC(CF₃SO₂)₃ in a mixture of one or two or more organic solvents selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, γ-butyrolactone, 1,3-dioxane, tetrahydrofuran, 2- methyltetrahydrofuran, dimethylsulfoxide, sulfolane, N,N-dimethylformamide, diglyme, triglyme and tetraglyme in the concentration of 0.5M to 2M.

7. A lithium rechargeable cell, which is obtained by the following steps of: dispersing an inorganic absorbent having the particle size of not more than 40 μm in a solution consisting of a polymer binder and its solution in the weight ratio of 70/30 to 95/5 based upon the polymer binder, making the resulting mixture into a film, exchanging said solvent with a non-solvent for the polymer binder and drying it to form a microporous electrolyte film having the thickness of 20 to 200 μm in which the diameter of micro pores is not more than 20μm and the porosity rate is 5 to 95%, arranging the resulting electrolyte film between a cathode and an anode, laminating and binding the resulting structure by the manner such as lamination or pressing to assembly them in the form of a cell, and then subjecting the resulting cell to absorb an ion conductive liquid electrolyte.

8. The lithium rechargeable cell according to Claim 7, wherein said cathode and said anode are prepared in a separate way to the electrolyte film, the polymer binder used in the cathode and/or the anode is the same or is compatible with the polymer binder of the electrolyte film, the additive used in the cathode and/or the anode is one or two or more mixtures selected from the absorbents used in the electrolyte film.