KR20010055896A - Solid Electrolytes for Secondary Cell and Methods for Preparing Them - Google Patents

Abstract

PURPOSE: A solid electrolyte for secondary cell, that is, lithium battery is provided to accomplish a desired lithium ionic conductivity and improved mechanical, thermal, electro-chemical stabilities sufficient to reduce discharging amount at charging/discharging cycle by comprising specific inorganic absorbent to provide a space to absorb liquid component and lithium salt. CONSTITUTION: The solid electrolyte for lithium battery having 10-200 micrometers of thickness in dry state and about more than 10exp(-4)S/cm of ionic conductivity at ordinary temperature comprises 30-95 wt.% of powdered inorganic absorbent having less than 40 micrometers of particle size based on total weight of the electrolyte film excluding liquid electrolyte in dry state, polymer bonding agent and 30-90 wt.% of ionic conductive liquid electrolyte relative to total weight of the electrolyte including the liquid electrolyte. The absorbent is at least one selected from mineral particles, synthetic oxide particles and mesoporous molecular sieve.

Description

Solid electrolyte for secondary battery and manufacturing method thereof {Solid Electrolytes for Secondary Cell and Methods for Preparing Them}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte film for use in secondary cells, and more particularly, to a liquid film and a lithium salt (or both liquids) in an electrolyte film containing an inorganic absorbent. Electrolyte) to provide a movement path of ions moving between the positive electrode and the negative electrode during the charge and discharge of the secondary battery.

A battery has three basic components: a positive electrode, a negative electrode, and an electrolyte. The material of the negative electrode is often a compound in which lithium metal or lithium ions can be intercalated, preferably a carbon material or Polymeric materials can be used. The material of the positive electrode is a material capable of intercalating lithium ions, and preferably lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (Li _x NiO ₂ ), or lithium nickel cobalt oxide (Li _x Ni _y Co). Oxide or polymer materials such as _1-y O ₂ ), spinel type lithium manganese oxide (Li _x Mn ₂ O ₄ ), manganese dioxide (MnO ₂ ), and the like may be used. By introducing a liquid electrolyte into the electrolyte membrane, an ion conductive matrix can be formed.

The battery using the polymer electrolyte has a lower risk of leakage and excellent electrochemical stability than the battery using the liquid electrolyte, and thus, various types of assembly are possible and automation of the manufacturing process is easy.

Therefore, since it was discovered that a polymer such as polyoxyethylene may have conductivity of a metal ion when it contains a polar heterogeneous element capable of electrical interaction with the metal ion, the ion conductive polymer, that is, the polymer electrolyte Research has been actively conducted. However, only pure polymer of polyoxyethylene has very low ion conductivity of about 10 ^-8 S / cm at room temperature, so that the temperature of about 100 ° C is necessary to show a conductivity of 10 ^-4 S / cm applicable to the battery. Because of the problem of reaching, the main flow of polymer electrolyte research was to improve conductivity.

As it has been found that the conduction of ions in the polymer electrolyte requires the movement of the polymer chain, attempts to improve the conductivity of the ions have been made in the direction of increasing the flexibility of the polymer chain. Blonsky et al. Have introduced an phosphazene bond into the polymer backbone to produce an electrolyte with improved conductivity of 10 ^-5 S / cm ( J. Am. Chem. Soc. , 106 , 6854 ( 1984)), the electrolyte had poor conductivity and mechanical strength.

In addition, various attempts have been made to modify the structure of the polymer or to add an inorganic material to lower the crystallinity of the polymer. However, a pure polymer electrolyte (not including a liquid electrolyte) composed of only a polymer and a metal salt does not exhibit sufficient conductivity. There is a situation.

In contrast, the gel-type electrolyte of US Pat. No. 5,219,679 contains a liquid electrolyte in the polymer backbone, and exhibits properties of the polymer in terms of mechanical properties and has conductivity close to that of the liquid electrolyte. It suggests practical possibilities. That is, there is no separate activation process for adding a liquid electrolyte, and a part of the liquid electrolyte is already contained in the process of preparing the polymer electrolyte (casting a mixture of the polymer solution and the liquid electrolyte). However, the electrolyte of US Pat. No. 5,219,679 includes a polymer such as polyacrylonitrile that is reactive toward lithium metal, so that reaction products accumulate between the electrolyte and the lithium electrode during storage and use of the battery. As a result, the interface resistance is continuously increased.

On the other hand, Scrosati et al . Prepared a polyelectrolyte in the form of a gel using polymethylmethacrylate, which is less reactive with lithium metal ( Electrochim. Acta , 140 , 991 (1995)). The electrolyte, which uses polymethyl methacrylate as a polymer component, has a low reactivity with the lithium surface and has a slight increase in resistance at the electrode surface during storage, but exhibits a weakness in mechanical strength and is sufficient to form a film. In order to obtain strength, the content of the polymer must be increased, and in this process, the conductivity drops to 10 ^-4 S / cm or less. In addition, since the gel-type electrolyte contains a large amount of liquid components, vaporization of the liquid components occurring on the surface of the electrolyte is inevitable, so that the change of composition and the decrease in conductivity due to the loss of the liquid components during the storage period are only concerned. In addition, the lithium salt contained in the liquid electrolyte is decomposed by reacting with moisture in the air, which has the disadvantage of requiring an extremely dehumidifying atmosphere with extremely low moisture.

U.S. Patent No. 5,296,318, U.S. Patent No. 5,418,091, etc., provide a hybrid polymer electrolyte system to supplement the above problems. Hybrid polymer electrolytes are liquid electrolytes that are sensitive to the effects of moisture while retaining the advantages of gel-type polymer electrolytes (containing a large amount of liquid electrolyte and having conductivity similar to that of liquid electrolyte because conduction of lithium ions proceeds through the liquid phase). By adding the battery just before packaging, it was possible to minimize the influence of moisture in the electrolyte manufacturing process. However, since the liquid electrolyte is added after preparing the electrolyte membrane, a site for sucking the liquid component or a driving force for penetrating the liquid component into the electrolyte membrane is required in the electrolyte membrane. To this end, dibutyl phthalate was added as a plasticizer in the preparation of the electrolyte membrane, and after the battery assembly was completed, the plasticizer was extracted with an organic solvent such as alcohol or ether to make a place for the liquid component to be inhaled. However, since the process of extracting dibutyl phthalate uses a chemical method, it has a fatal disadvantage of low reproducibility, low battery yield, and difficulty in automating for mass production.

Accordingly, the present inventors add an absorbent capable of absorbing a liquid electrolyte into the polymer matrix in Korean Patent Application No. 98-57030 to configure the electrolyte membrane, and the liquid electrolyte is in the activation process after completion of battery assembly. In order to solve the problems of the prior art, by introducing.

The invention of the patent application discloses a number of absorbents that can be used in the formation of electrolyte membranes, and the present inventors are urgently required to develop absorbents that exhibit better properties when used in the formation of electrolyte membranes of secondary batteries, in particular. Recognition and the same series of studies have been conducted.

Accordingly, the present invention seeks to develop a solid electrolyte containing an absorbent having excellent mechanical, thermal, and electrochemical stability among the absorbents added during the formation of the electrolyte membrane, which exhibits superior physical properties during battery production.

The present invention also seeks to develop a secondary battery exhibiting excellent characteristics using such a solid electrolyte.

1 is a view showing the experimental results according to the linear potential scanning method to measure the electrochemical stability of the solid electrolyte of the present invention,

FIG. 2 is a view showing a change in discharge capacity of a battery using a solid electrolyte of the present invention containing an inorganic absorbent compared with a case of a battery using a polymer absorbent.

The solid electrolyte for a secondary battery of the present invention includes a powdery inorganic absorbent, a polymer binder, and an ion conductive liquid electrolyte having a particle size of 40 μm or less, and the inorganic absorbent includes mineral particles, synthetic oxide particles, and mesoporous molecular sieves ( one or two or more kinds of particles selected from the group consisting of mesoporous molecular sieves, added at 30 to 95% by weight based on the total weight of the dry electrolyte membrane containing no liquid electrolyte, wherein the ion conductive liquid electrolyte is a liquid electrolyte It is characterized in that added to 30 to 90% by weight based on the total weight of the total electrolyte including.

In the present specification, the electrolyte membrane refers to an electrolyte membrane which is in a dry state and does not contain a liquid electrolyte, and the solid electrolyte means to include ionic conductivity by including a liquid electrolyte in the electrolyte membrane. Although not a complete solid state as it contains a liquid electrolyte, the basic backbone originates from the electrolyte membrane in the solid state, and is also referred to as a solid electrolyte in order to refer to a concept distinct from the liquid electrolyte. In addition, the said absorbent means the substance which can absorb the liquid electrolyte, or the substance which can improve the absorption power with respect to the liquid electrolyte of a solid electrolyte.

The solid electrolyte of the present invention is prepared by introducing an inorganic absorbent into the polymer binder to prepare an electrolyte membrane and then injecting a liquid electrolyte. The solid electrolyte has a lithium ion conductivity of 10 ⁻⁴ S / cm or more at room temperature.

Preferred examples of the mineral particles in the inorganic absorbent may include mineral particles having a phyllosilicate structure such as clay, paragonite, montmorillonite, mica, and the like. Preferred examples of the synthetic oxide particles include zeolite, porous silica, alumina, and the like. Examples of the mesoporous molecular sieve include 2 to 30 nm of an oxide material such as silica. And those having a pore diameter of. The mineral particles, synthetic oxide particles and mesoporous molecular sieves may be in the form of a mixture of two or more of the kinds described as examples.

Absorbents used in the formation of electrolyte membranes include polypropylenes, polyethylenes, and polystyrenes in which porosity is introduced by controlling macromolecules with bulky functional groups introduced into the side chains or by controlling variables in the manufacturing process. Porous polymers such as polystyrene, polyurethane, etc., and natural polymers such as wood flour, pulp, cellulose, cork, and the like may be used.

However, since the organic absorbents are less mechanically, thermally and electrochemically stable than the inorganic absorbents, it has been confirmed by the present inventors that the secondary batteries using the organic absorbents have poor characteristics of the batteries compared to the secondary batteries using the inorganic absorbers. .

That is, when assembling the positive electrode and the negative electrode by pressing or laminating method in assembling the battery, the organic material absorbent has different mechanical and thermal behaviors from the polymer binder of the electrolyte membrane or the electrode plate, and thus the inorganic material in the repeated charging and discharging process of the battery. It was confirmed that the reduction of the discharge capacity was greater than in the case of using the absorbent. For example, absorbents made of organic materials, such as polymers with low melting points or low mechanical strength, may lose their absorbency during pressing or laminating. In other words, when an organic absorbent such as a polymer is used, the electrolyte membrane or the solid electrolyte may exhibit good performance. However, when the battery is assembled by pressing or laminating, it may be difficult to maintain the original performance.

In addition, as described above, in the general polymer electrolyte, since the conductivity of ions is directly affected by the movement of the polymer chain, the temperature influence on the ion conductivity is very large. In particular, since the polymer chain is slowed at a low temperature and the ion conductivity is greatly reduced, the performance of the battery becomes very bad. However, in the case of using the absorbent as in the present invention, the ion conductivity is improved, and if the inorganic absorbent which is less affected by the temperature is used in a large amount, unlike the characteristics of the general polymer electrolyte, the temperature may be less affected by the temperature. . In addition, the inorganic material is contained in a large amount, it is also possible to obtain an advantage that the resistance to ignition or explosion is improved compared to the electrolyte containing an excessive amount of organic matter such as a polymer.

Therefore, it was confirmed that the use of the inorganic absorbent in the electrolyte membrane of the secondary battery is preferable to the use of the organic absorbent.

The amount of the inorganic absorbent added is 30 to 95% by weight, more preferably 50 to 90% by weight, based on the weight of the dry electrolyte membrane containing no liquid electrolyte as described above. If the added amount is 95% by weight or more, the mechanical strength of the formed electrolyte membrane is lowered, and if it is 30% by weight or less, there is a problem that the ability to absorb the liquid electrolyte is lowered.

In order not to reduce the mechanical strength and uniformity of the electrolyte membrane to be formed, the inorganic absorber preferably has a particle size of 40 µm or less, more preferably 20 µm or less, as described above.

The polymer binder may include polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and maleic anhydride, and polyvinyl chloride (polyvinylchloride), polymethyl methacrylate, polymethacrylate, cellulose triacetate, polyurethane, polysulfone, polyether, polyolefin such as polyethylene or polypropylene ), Polyethylene oxide, polyisobutylene, polybutyldiene, polyvinylalcohol, polyacrylonitrile, polyimide, polyvinyl formal, Acrylonitrilebutyldiene rubber, ethylene propylene diene monomer (ethyle one or two or more mixtures selected from the group consisting of ne-propylene-diene-monomer), tetra (ethylene glycol) diacrylate, polydimethylsiloxane, polycarbonate and polysilicone; or These copolymers are preferable.

The solvent of the polymer binder, which is a solvent for dissolving the polymer binder, is N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile ), Cyclohexanone, chloroform, dichloromethane, hexamethylphosphoramide, dimethylsulfoxide, acetone, and dioxane Preference is given to one or a mixture of two or more selected.

The liquid electrolyte to be absorbed in the electrolyte membrane containing the inorganic absorbent is prepared by dissolving lithium salt in an organic solvent. In this specification, the absorption of the liquid electrolyte into the electrolyte membrane is defined as activation.

The organic solvent is preferred to have high polarity and no reactivity with lithium metal in order to enhance dissociation of ions by increasing the polarity of the electrolyte and to facilitate conduction of ions by lowering the local viscosity around the ions. Examples of such organic solvents are ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone ), Dimethylsulfoxide, 1,3-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, N, N-dimethylformamide (N, N-dimethylformamide), diglyme, triglyme, tetraglyme and the like. In particular, it is preferable to use two or more mixed solutions composed of a high viscosity solvent and a low viscosity solvent as the organic solvent.

It is preferable that the lithium salt has a small lattice energy and a large dissociation degree. Examples of such lithium salts include one or two or more selected from the group consisting of LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiSCN LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) ₃ . There is a mixture. The concentration of the lithium salt is preferably 0.5M to 2M.

The liquid electrolyte is added in an amount of 30 to 90% by weight based on the total amount of the total electrolyte including the liquid electrolyte, but more preferably in an amount of 40 to 85% by weight, as described above.

The solid electrolyte of the present invention is easier to manufacture than the conventional polymer electrolyte, has a high mechanical, thermal, and electrochemical stability, and has high ion conductivity because conduction of lithium ions proceeds through the liquid phase, and a liquid electrolyte. It is characterized by not being affected by moisture or temperature until it is absorbed, that is, activated.

The present invention also relates to a method of making such a solid electrolyte.

The solid electrolyte of the present invention is prepared through four steps of mixing the inorganic absorbent and the polymer binder, dissolving, casting and drying the mixture, and activating the bar, and mixing, dissolving, and casting to obtain a dry solid electrolyte membrane. And an activation step of absorbing the liquid electrolyte.

That is, after dissolving the mixture of the inorganic absorbent and the polymer binder in the solvent of the polymer binder, casting it in the form of a membrane and drying it to form an electrolyte membrane having a thickness of 10 to 200㎛, ions in the dry electrolyte membrane Prepared by absorbing the conductive liquid electrolyte.

If such a manufacturing method in more detail as follows.

First, the powdery inorganic absorbent (particle size of 40 μm or less) and the polymer binder are dry mixed in a sealed container.

Such inorganic absorbents and polymeric binders are dissolved in the solvent of the polymeric binder. The solid content of the mixed solution (solid content) is preferably 5 to 50% by weight based on the total weight, the mechanical strength of the electrolyte membrane after drying is less than 5% by weight, if more than 50% by weight polymer binder is not sufficiently dissolved or The problem of very high viscosity of the mixed solution may occur.

In order to facilitate the dissolution of the polymer binder and to prevent the absorbents from sticking together, a magnetic stirrer, a mechanical stirrer, a planetary mixer, a high speed disperser, etc. may be used. Stir. In this process, an ultrasonic stirrer may be used to prevent the absorbents from agglomerating with each other and to prevent bubbles from forming during mixing. In some cases, defoaming and filtering may also be performed.

After the polymeric binder is completely dissolved and homogeneously mixed with the absorbent, it is poured into a flat plate such as a glass plate or a Teflon plate and applied to a uniform thickness. At this time, the thickness of the film is preferably adjusted to 10 to 200㎛. If the thickness of the membrane is 10 μm or less, the mechanical strength is lowered. If the thickness is 200 μm or more, the ion conductivity decreases, which is not preferable.

The resulting membrane is completely dried and then a liquid electrolyte is introduced.

The invention also relates to a secondary battery, in particular a lithium secondary battery, using the solid electrolyte as an electrolyte.

The assembling process of the battery refers to bonding by a method such as lamination, pressing, etc. together with a positive electrode and a negative electrode separately prepared with an electrolyte membrane interposed therebetween. When the electrolyte membrane is prepared in the above manner, since the liquid electrolyte is added after the battery assembly, the limitation of the dehumidification conditions in the process can be minimized. In addition, since a position capable of absorbing the liquid electrolyte is already made at the stage of preparing the electrolyte membrane and no extraction process such as a plasticizer is required, the process can be simplified, thereby lowering the manufacturing cost, as well as facilitating automation and yield. There is an advantage to increase.

As an example of the manufacturing method of the secondary battery using the solid electrolyte of this invention, the electrolyte membrane obtained from the said process is centered in the center, and a positive electrode and a negative electrode are bonded together and a battery is comprised. An inorganic absorbent powder is contained in the electrolyte membrane, the positive electrode is electrically connected to the positive electrode current collector, and the negative electrode is electrically connected to the negative electrode current collector. After the activation step of absorbing the liquid electrolyte in the assembly thus constructed is manufactured in a state capable of operating as a battery.

The manufacturing process of the positive electrode or the negative electrode is as follows. The positive electrode or the negative electrode consists of a current collector and an active material layer, respectively. The active material layer generally includes an active material, a conducting material, a binding material, and the like. In addition, various additives may be introduced for the purpose of improving battery performance. The current collector, the conductive material, the binder, and the additive included in the positive electrode or the negative electrode may be the same or different depending on the purpose.

The current collector is to provide a migration path of electrons generated in the oxidation / reduction reaction in the anode or cathode. As the current collector, a grid, a foil, a punching foil, an etching foil, or the like is generally used, and may be selected according to the performance of a battery or a manufacturing process. If the grid is used, the active material filling rate may be increased, but the manufacturing process may be tricky. If the foil is used, the battery performance may be improved and the manufacturing process may be simplified, but the filling rate of the active material may be lowered. Copper, aluminum, nickel, titanium, stainless steel, carbon, etc. are used as an electrical power collector. Generally, aluminum is used for the positive electrode and copper is used for the negative electrode.

The active material is a material in which the charge / discharge reaction (or oxidation / reduction reaction) of the battery actually occurs, and is the most important factor that determines the performance of the battery. Moreover, it is a component with the largest content in an active material layer. As the positive electrode active material, an oxide, a sulfide, an organic compound, a high molecular compound, or the like of a transition metal may be used. Preferably, lithium cobalt oxide (Li _x CoO ₂ ) and lithium nickel oxide (Li) are used. oxides or polymer materials such as _x NiO ₂ ), lithium nickel cobalt oxide (Li _x Ni _y Co _1-y O ₂ ), spinel type lithium manganese oxide (Li _x Mn ₂ O ₄ ), manganese dioxide (MnO ₂ ), etc. have. Alkali metal, alkali earth metal, carbon, transition metal oxides / sulfides, organic compounds, high molecular compounds and the like may be used as the negative electrode active material, and preferably carbon materials or polymer materials may be used. . It is good to select an active material according to the performance and a use of a battery.

A conductive material is a material added to the positive electrode or the negative electrode for the purpose of improving conductivity, and generally used is carbon. Among them, graphite, cokes, activated carbon, carbon black are preferred, and graphite and carbon black are most preferred. One or more conductive materials selected from the group may be used, and may be manufactured or natural materials. The conductive material is added at 3% by weight to 15% by weight of the total weight of the electrode material, and when the amount of the conductive material is reduced to about 3% by weight or less, there is a problem that the overvoltage occurs because the electrical conductivity is lowered, which is more than 15% by weight. In this case, there is a problem that the energy density per unit volume is reduced and side reactions caused by the conductive material are intensified.

The binder is added to strengthen the bonding of the active material layer and a high molecular compound is generally used. The polymer compound used when preparing the solid electrolyte membrane may be used as a binder, and it is preferable to use the same polymer as that of the electrolyte membrane or one having miscibility. The binder is added up to 15% by weight of the total weight of the electrode material. When the addition amount of the binder is small there may be a problem that the bonding strength of the electrode is lowered, when more than 15% by weight there is a problem that the workability and porosity of the electrode is inferior.

An additive is a material added for the purpose of improving the performance of a battery or an electrode, and can be variously selected according to the target performance or use. Improve the bonding force inside the electrode plate or the current collector, induce the porosity or amorphousness of the electrode plate, improve the dispersity of the electrode plate material or the efficiency of the electrode manufacturing process, suppress the overcharge / over-discharge of the active material, Side reaction products are added for the purpose of improving performance, such as by recombination or removal, or by improving liquid electrolyte absorption. Generally, salts, organic / inorganic compounds, inorganic materials, and high molecular compounds may be used, and an absorbent added to the electrolyte membrane may be selected.

Hereinafter, the lithium secondary battery of the present invention will be described in more detail.

After dissolving the mixture of the absorbent and the polymeric binder in the solvent of the polymeric binder, casting it in the form of a membrane and drying it to form an electrolyte membrane having a thickness of 10 to 200㎛, form the battery together with the positive and negative electrodes prepared separately It is prepared by absorbing the liquid electrolyte after assembling. In order to be a solid electrolyte having sufficient ion conductivity for use, an activation step of absorbing the liquid electrolyte must be performed. After the activation step, the battery can be operated as a battery. If the activation step is not performed, the room temperature ion conductivity is very low, and thus cannot be used as an electrolyte by itself.

The manufacturing process of the positive electrode and / or negative electrode to be combined with the electrolyte membrane is as follows. A mixture of the positive or negative electrode materials is made into a slurry, and then formed into a thin film by casting, coating, screen printing, etc., followed by pressing or laminating. It is produced by combining with the current collector, or by molding directly on the current collector.

On the electrode produced by the above method, a solid electrolyte slurry composed of an absorbent, a polymer binder, and a solvent may be directly cast to form an electrolyte membrane, or may be separately manufactured and laminated or pressed. If the former method is used, the adhesion between the electrode and the electrolyte membrane can be improved, but if the conditions of the manufacturing process of the electrode and the electrolyte membrane are inconsistent, or if the electrode or the electrolyte membrane is contaminated or its performance is easily damaged during the process. it's difficult. Although the latter method of separately fabricating and assembling is disadvantageous, the adhesion between the electrode and the electrolyte membrane may be weakened, but the advantages of simple performance management, simple process design, and simple installation are more preferable.

In addition, the electrolyte membrane prepared from the present invention has an advantage that the mechanical strength is greater than that of a pure electrolyte membrane, a gel-type polymer electrolyte or an electrolyte membrane to which a plasticizer is added because the absorbent is included. Therefore, since the shape change is extremely small and the reproducibility is large in the pressing or laminating process, the defect rate is low and mass production is possible. That is, the electrolyte membrane produced from the present invention can be said to have a feature that is more suitable for the pressing or laminating method which is advantageous in terms of performance management, process design, and equipment.

Hereinafter, the solid electrolyte according to the present invention containing an inorganic absorbent and a method for manufacturing a battery using the solid electrolyte will be described in detail. First of all, the manufacturing and performance investigation of the solid electrolyte were carried out. In addition, the process of fabricating the battery by combining the positive electrode and the negative electrode together with the solid electrolyte and examining the performance thereof was described. However, these examples do not limit the contents of the present invention, and modifications may be made without departing from the basic spirit of the present invention.

Example 1

The absorbent and the binder powder were put in a 20 ml vial, followed by dry mixing for about 5 minutes in a magnetic stirrer. 4 ml of NMP was added thereto and stirring continued until the binder was completely dissolved. Ultrasonic agitation was performed for 30 minutes during stirring to prevent the absorbent particles from agglomerating with each other. The mixed solution prepared by the above method was coated on a glass plate so as to have a thickness of about 100 μm, and then dried at room temperature for about 2 hours and further dried by a vacuum dryer for 6 hours. At this time, the temperature of the vacuum dryer was adjusted to about 50 ℃. The electrolyte membrane prepared by the above method was immersed in the liquid electrolyte solution for about 10 minutes, and then the weight change before and after the liquid electrolyte was completely absorbed was measured, and the conductivity was measured using the AC impedance method.

The characteristics and conductivity of the solid electrolyte according to the type and content ratio of the absorbent and the binder are summarized in Table 1 below. In order to compare the ability of the electrolyte membrane to absorb the liquid electrolyte, the sorption capacity (Δ _ab ) was defined as follows.

Δ _ab = [amount of absorbed liquid electrolyte (mg)] / [weight of electrolyte membrane (mg)]

Example Absorbent Binder Liquid electrolyte Δ _ab Ion Conductivity (mS / cm) Mechanical strength Kinds g Kinds g a Paragonite 0.13 PVdF 0.28 EC / PC 1M LiPF ₆ 0.5 0.01 Very good b 〃 0.17 〃 0.26 〃 0.7 0.02 Very good c 〃 0.72 〃 0.24 〃 0.9 0.17 Very good d 〃 1.06 〃 0.26 〃 1.5 0.19 Great e 〃 1.51 〃 0.25 〃 2.2 0.39 Great f 〃 2.00 〃 0.26 〃 5.0 0.63 Great g 〃 1.98 〃 0.25 EC / DMC 1M LiPF ₆ 5.5 0.75 Good h Zeolite 1.37 〃 0.60 〃 4.7 0.68 Great i 〃 1.50 〃 0.38 〃 5.5 0.85 Great j 〃 1.65 〃 0.29 〃 5.8 0.91 Good k Montmorillonite 1.34 〃 0.58 〃 4.4 0.70 Great l 〃 1.50 〃 0.38 〃 5.8 0.82 Great m Silica 1.35 〃 0.59 〃 5.6 0.75 Great n Polypropylene 1.35 〃 0.60 〃 5.7 0.80 Great o Wood flour 1.35 〃 0.60 〃 5.5 0.79 Great p Paragonite 2.00 P (VdF-HFP) 0.26 〃 5.1 0.76 Great q 〃 1.95 PAN 0.25 〃 5.0 0.74 Great r 〃 2.00 PU 0.26 〃 5.3 0.72 Great s 〃 1.98 PVC 0.25 〃 5.5 0.78 Great t 〃 2.00 P (VdF-HFP) 0.26 〃 5.4 0.75 Great u Zeolite 2.00 P (VdF-HFP) 0.26 〃 5.3 0.78 Great v 〃 1.95 PAN 0.25 〃 5.1 0.74 Good w 〃 2.00 PU 0.26 〃 5.2 0.72 Great x 〃 1.98 PVC 0.25 〃 5.4 0.78 Great y 〃 2.00 P (VdF-HFP) 0.26 〃 5.3 0.75 Great

Example 2 (comparative example)

An electrolyte membrane was prepared in the same manner as in Example 1- (f), except that no absorbent was added to investigate the influence of the inorganic absorbent added when preparing the electrolyte membrane. The prepared electrolyte membrane was transparent and had excellent mechanical strength. However, the electrolyte membrane was immersed in the liquid electrolyte solution at room temperature for 10 hours, but the weight of the electrolyte membrane before and after impregnation was the same within the measurement error. In addition, the ionic conductivity of the solid electrolyte thus prepared could not be measured by the alternating current impedance method.

Example 3

In order to measure the electrochemical stability of a solid electrolyte containing an inorganic absorbent, linear sweep voltammetry was performed using stainless steel (# 304) as a working electrode and lithium metal as a counter electrode and a reference electrode. The potential scan range was from the open circuit voltage to 5.4 V (vs. Li / Li ⁺ ) and the potential scan speed was 10 mV / sec. The results of the linear potential scanning method for the solid electrolyte prepared by the method of Example 1- (g), 1- (i) and 1- (l) are shown as A, B and C in FIG.

Example 4

In order to test the performance of a battery using a solid electrolyte containing an inorganic absorbent, a battery composed of an oxide positive electrode, a carbon negative electrode, and a solid electrolyte obtained according to the present invention was constructed to perform a charge and discharge test. The constructed cell has a lamination form, and after laminating the positive electrode, the electrolyte membrane, and the negative electrode to make an assembly, the liquid electrolyte was finally absorbed. The constant current at the rate of charging the reversible capacity in two hours (C / 2 rate) is applied until the battery voltage reaches 4.2 V, and again charged until the current decreases to C / 10 mA by applying the 4.2 V electrostatic potential. It was. It was then discharged at a current of two hours discharge rate to 2.5 V or 2.75 V (C / 2 rate). The charging and discharging were repeated to observe a change in discharge capacity according to the number of charge and discharge cycles. The battery configuration and test results are summarized in Table 2 below and shown in FIG. 2. As disclosed in Table 2, the solid electrolyte shows a state in which the liquid electrolyte is absorbed into the electrolyte membrane.

Example anode cathode Solid electrolyte city Active material Conductive material Binder additive Active material Conductive material Binder additive z LiCoO ₂ Carbon black PVdF Zeolite Graphite Carbon black PVdF Zeolite Example 1- (f) 3-D aa LiCoO ₂ Carbon black PVdF Zeolite Graphite Carbon black PVdF Zeolite Example 1- (j) 3-E bb LiCoO ₂ Carbon black PVdF Zeolite Graphite Carbon black PVdF Zeolite Example 1- (n) Figure 3-F cc LiCoO ₂ Carbon black PU Zeolite Graphite Carbon black PU Zeolite Example 1- (r) 3-G dd LiMn ₂ O ₄ Carbon black P (VdF-HFP) Zeolite Graphite Carbon black P (VdF-HFP) Zeolite Example 1- (u) 3-H

Fig. 2 shows the respective discharge capacities obtained by repeating the charge / discharge test of the battery for each of the examples in comparison with the first discharge capacities. In view of the above test results, when using a solid electrolyte obtained from an inorganic absorbent (Example 4-z, aa, cc, dd) using a solid electrolyte containing an organic (polymer) absorbent (Example 4- It can be seen that the performance is better than bb). In other words, even if the electrolyte membrane or the solid electrolyte itself does not show a large difference in performance (ion conductivity, mechanical strength, etc.), the result of actual battery application is that an inorganic absorbent is used to further improve the overall battery performance (charge and discharge performance, etc.). You can see that it has an excellent effect.

The solid electrolyte of the present invention containing an inorganic absorbent has excellent mechanical strength and can be molded into a thin film, has a high ionic conductivity corresponding to a liquid electrolyte, and unlike a solid electrolyte in a gel form, even with a small amount of water. Since the decomposed lithium salt is not introduced during the preparation of the electrolyte membrane, no special dehumidification environment is required, and since the absorbent is electrochemically stable, it has a wide potential window, and the electrolyte manufacturing process is simple, so that automation for mass production is easy. It is characterized by. In addition, since the adhesion between the positive electrode and the negative electrode is excellent and the volume change due to the introduction of the liquid electrolyte is small, the interface resistance between the electrolyte and the electrode can be minimized. In addition, the mechanical, thermal, and electrochemical stability is better than that of the organic material absorbent, so that the discharge capacity decreases in the repeated charging and discharging process, which is suitable for use as an electrolyte for lithium secondary batteries.

Claims (4)

A powdery inorganic absorbent having a particle size of 40 μm or less, a polymer binder, and an ion conductive liquid electrolyte, the inorganic absorbent selected from the group consisting of mineral particles, synthetic oxide particles, and mesoporous molecular sieves One or two or more kinds of particles are added at 30 to 95% by weight based on the total weight of the dry electrolyte membrane containing no liquid electrolyte, and the ion conductive liquid electrolyte is 30 to 30% by weight of the total electrolyte including the liquid electrolyte. A solid electrolyte for a secondary battery, which is added at 90% by weight and has a thickness of 10 to 200 μm in a dry state without containing a liquid electrolyte. The method of claim 1, wherein the mineral particles are one or more mineral particles having a phyllosilicate structure such as clay, paragonite, montmorillonite, mica, etc., wherein the synthetic oxide particles are made of zeolite, porous silica and porous alumina. One or two or more mixtures selected from the group consisting of: the mesoporous molecular sieve has a pore diameter of 2 to 30 nm as an oxide material; The polymer binder is polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and maleic anhydride, polyvinyl chloride, polymethyl methacrylate, polymethacrylate , Cellulose triacetate, polyurethane, polysulfone, polyether, polyethylene, polypropylene, polyethylene oxide, polyisobutylene, polybutyldiene, polyvinyl alcohol, polyacrylonitrile, polyimide, polyvinyl formal, acrylo One or more mixtures or copolymers thereof selected from the group consisting of nitrile butyl diene rubber, ethylene propylene diene monomer, tetraethylene glycol diacrylate, polydimethylsiloxane, polycarbonate and silicone polymer; The ion conductive liquid electrolyte is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, 1,3-dioxene, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide In an organic solvent consisting of one or two or more mixtures selected from the group consisting of seed, sulfolane, N, N-dimethylformamide, diglyme, triglyme and tetraglyme, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiSCN Dissolving one or more lithium salts selected from the group consisting of LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) ₃ at a concentration of 0.5 to 2M; Solid electrolyte for a secondary battery, characterized in that. Characterized in that the mixture of the inorganic absorbent and the polymer binder is dissolved in the solvent of the polymer binder, cast it in the form of a membrane, and then dried to form an electrolyte membrane, and absorbing the ion conductive liquid electrolyte in the dried electrolyte membrane. The method for producing a solid electrolyte for secondary batteries according to claim 1. After dissolving the mixture of the inorganic absorbent and the polymeric binder in the solvent of the polymeric binder, casting it in the form of a membrane and drying it to form an electrolyte membrane, and then assembled into the form of a battery together with the positive and negative electrodes prepared separately, the ion conductive liquid Lithium secondary battery characterized in that the electrolyte is produced by absorbing.