CN112786950B - Composite solid electrolyte, preparation method thereof and solid battery - Google Patents

Composite solid electrolyte, preparation method thereof and solid battery Download PDF

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CN112786950B
CN112786950B CN201911071763.4A CN201911071763A CN112786950B CN 112786950 B CN112786950 B CN 112786950B CN 201911071763 A CN201911071763 A CN 201911071763A CN 112786950 B CN112786950 B CN 112786950B
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layer
lithium
ion conductor
fast ion
lithium salt
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CN112786950A (en
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缪永华
缪颖培
周炫名
靳承铀
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Zhongtian Energy Storage Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0088—Composites
    • H01M2300/0094—Composites in the form of layered products, e.g. coatings
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The invention provides a composite solid electrolyte, a preparation method thereof and a solid battery. The composite solid electrolyte comprises a three-layer laminated structure consisting of a core layer and a surface layer, wherein the core layer mainly consists of a mixture containing polyvinylidene fluoride, a fast ion conductor and lithium salt, and the surface layer mainly consists of a mixture containing polycarbonate, the fast ion conductor and the lithium salt. The composite solid electrolyte provided by the invention has the main body of a polyvinylidene fluoride/fast ion conductor/lithium salt mixture, the interface wetting layer of a polycarbonate/fast ion conductor/lithium salt mixture, and the problem of interface bonding between positive and negative electrodes of a solid battery and the electrolyte is solved by utilizing the self-wetting action of in-situ gelation of the polycarbonate.

Description

Composite solid electrolyte, preparation method thereof and solid battery
Technical Field
The invention relates to the technical field of batteries, in particular to a composite solid electrolyte, a preparation method thereof and a solid battery.
Background
The rapid development of new energy automobiles has prompted the increasing demand for high performance energy storage power supplies. However, the recent auto-ignition events of electric vehicles occurring in succession still suggest that safety is one of the core problems that the power supply technology needs to solve. The use of solid electrolytes instead of liquid electrolytes is the fundamental approach to solving the safety problem of lithium ion batteries. The design and development of a solid electrolyte with high ionic conductivity, the improvement of electrode/electrolyte interface combination and the improvement of the multiplying power and the cycle performance of a battery are always core subjects in the research field of solid lithium ion batteries. In recent years, both inorganic solid electrolytes and polymer solid electrolytes have made remarkable progress, and solid batteries have good application prospects. Compared with inorganic solid electrolytes and pure polymer solid electrolytes, the organic/inorganic composite solid electrolyte combines the advantages of inorganic and organic components, synergistically improves the mechanical and electrochemical properties of the solid electrolyte, has good interface compatibility and the like, and is expected to become a preferred electrolyte material of a high-performance solid lithium ion battery. Researchers have made many studies in the aspects of finding lithium salts, modifying polymers, adding inorganic fillers to polymer electrolytes, and the like, in order to improve comprehensive electrochemical properties of such electrolytes, such as room-temperature ionic conductivity, lithium ion migration number, electrochemical window, and the like. However, due to solid state electricityThe electrolyte is required to have certain rigidity, the surfaces of electrodes (including a positive electrode and a negative electrode) are uneven, ideal surface-surface contact, usually point-point contact, is difficult to form between the electrodes and the electrolyte, particularly, the volume of the electrodes is changed during charging and discharging, the electrolyte is not changed, so that the stress of the electrode/solid electrolyte interface is increased, the interface structure is damaged, the physical contact is worse, high interface resistance is caused, the transmission of lithium ions is inhibited, and the growth of lithium dendrites is promoted by the uneven current distribution on the surface of the negative electrode during charging and discharging. Due to Li+The difference in chemical potentials in the electrode and electrolyte may cause Li+Redistribution at the interface of the positive electrode and the electrolyte generates a space charge layer, further increasing the Li ion transport barrier. It is these interfacial problems that inhibit ion transport capabilities that tend to result in solid-state batteries with low coulombic efficiency, power density, and rapid capacity fade.
The interface problem of the solid-state battery is solved, and more work is focused on modifying the surface of the negative electrode by adopting an interface transition layer, such as Al2O3Inorganic oxides or metals such as Al, Si, Ge, ZnO, etc. have been proposed and used, but these processes are complicated and costly, and poor ductility and plasticity cannot ensure good cycle performance. In recent years, carbon microspheres, CNTs, graphene, C fibers, fluorides, nitrides, phosphates, SiO2The @ PMMA composite particle layer, the CNTs/LLZO 3D network, the polymer layer, the ZnO/CNTS composite layer, the LiF/graphene composite layer and the like are sequentially applied to the Li cathode, and certain effects are shown in the aspects of inhibiting the growth of Li dendrites and regulating and controlling the uniform deposition of Li. The modification work on the aspect of the positive electrode is less, and researchers try to respectively coat a LATP fast ion conductor layer and a poly (acrylonitrile-butadiene) copolymer coating layer on the surface of a ternary electrode material, so that the problems of a space charge layer and interface contact between the positive electrode material and a solid electrolyte in a solid-state battery are improved to a certain extent. However, in the whole, the current interface design rule and principle are still fuzzy, an ideal interface layer is still difficult to determine, and the ion transport capability of the solid-state battery cannot be fundamentally improved by adopting a single measure to solve the interface problem existing in the solid-state electrolyte.The enhancement method for the stable and reliable interface ion transmission needs to be further researched and researched. The modification is carried out on the Li metal surface with extremely strong activity, the operation is inconvenient, and the cost is high. A simple, convenient and effective soft interface preparation method is needed to be found, a rigid and flexible high-ductility functional transition layer is respectively formed on an anode/electrolyte interface and a cathode/electrolyte interface, and the problems of poor physical contact of the electrode/electrolyte interface, high interface impedance, growth of a space charge layer and lithium dendrites and the like are solved. A method of simultaneously constructing transition layers directly on both sides of an electrolyte membrane to form a three-layer structure has attracted attention of researchers. Researchers have coated a layer of gel polymer electrolyte on each side of the LLZO inorganic solid electrolyte membrane, and the interfacial resistance between the positive electrode and the electrolyte is changed from the original 6.5X 104The ohm is reduced to 208 ohm, and the impedance of the cathode/electrolyte interface is reduced from 1.45 multiplied by 103And the ohm drops to 214 ohms. The method has obvious effect of improving the interface ion transmission, but Li metal is unstable to all organic electrolyte systems, and lithium dendrite still inevitably occurs after repeated cycles, especially under the condition of large-current charge and discharge. Meanwhile, a large amount of organic solvent permeates into the positive electrode, so that part of active substances are easy to fall off, and then the ion-conducting and electron-insulating polymer permeates into the periphery of the active substances along with the organic solvent to reduce the electron conductivity of the electrode, thereby influencing the multiplying power and the cycle performance of the electrode and the utilization rate of the active substances.
Disclosure of Invention
In view of the above, there is a need to provide an improved composite solid electrolyte having interfacial self-wetting function.
The technical scheme provided by the invention is as follows: a composite solid electrolyte comprises a three-layer laminated structure consisting of a core layer and a surface layer, wherein the core layer mainly consists of a mixture containing polyvinylidene fluoride, a fast ion conductor and lithium salt, and the surface layer mainly consists of a mixture containing polycarbonate, the fast ion conductor and lithium salt.
Furthermore, the mass percentage of the polyvinylidene fluoride in the core layer is 60-80%, the mass percentage of the fast ion conductor is 5-30%, and the mass percentage of the lithium salt is 5-30%.
Furthermore, the mass of the polycarbonate in the surface layer accounts for 60-80%, the mass of the fast ion conductor accounts for 5-30%, and the mass of the lithium salt accounts for 5-30%.
Further, the thickness of the core layer is 10-100 microns; each of the skin layers has a thickness of 5-20 microns.
Further, the polycarbonate comprises one of polypropylene carbonate, polyethylene carbonate and polybutylene carbonate; the fast ion conductor comprises one of lithium lanthanum zirconium oxygen, lithium lanthanum titanium oxygen and lithium lanthanum niobium oxygen; the lithium salt comprises one of lithium perchlorate, lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide.
The invention also relates to a preparation method of the composite solid electrolyte, which comprises the following steps:
dissolving polyvinylidene fluoride, a fast ion conductor and lithium salt in a first solvent according to a preset proportion to form a first colloid;
dissolving polycarbonate, a fast ion conductor and lithium salt in a second solvent according to a preset proportion to form a second colloid;
sequentially forming a first film layer, a core film and a second film layer on a substrate by the second colloid, the first colloid and the second colloid through coating and heating layer by layer to obtain a three-layer structure composite film;
and placing the composite membrane in a vacuum drying oven for heating treatment to obtain the composite solid electrolyte.
Further, the dissolving step and the subsequent stirring operation were carried out for 2 hours.
Further, in the step of coating and heating layer by layer, the heating temperature is 60 ℃, and the heating time is 5-15 minutes.
Further, the thickness of the first film layer or the second film layer is 50-150 micrometers, and the thickness of the core film is 50-300 micrometers.
The invention also provides a solid-state battery, which comprises a positive electrode, a negative electrode and the composite solid-state electrolyte between the positive electrode and the negative electrode, wherein the negative electrode is metal lithium, and the positive electrode comprises one of lithium iron phosphate, lithium cobaltate or lithium nickel cobalt manganese.
Compared with the prior art, the composite solid electrolyte provided by the invention has the advantages that the main body is a polyvinylidene fluoride/fast ion conductor/lithium salt mixture, the interface wetting layer is a polycarbonate/fast ion conductor/lithium salt mixture, and the problem of interface bonding between the positive electrode and the negative electrode of the solid battery and the electrolyte is solved by utilizing the self-wetting effect of in-situ gelation of the polycarbonate.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is a schematic structural diagram of a composite solid electrolyte according to an embodiment of the present invention, in which a core layer a is a mixture of polyvinylidene fluoride/fast ion conductor/lithium salt, which is a main body of the composite solid electrolyte, a surface layer B is a mixture of polycarbonate/fast ion conductor/lithium salt, which is a self-wetting layer of the composite solid electrolyte.
Fig. 2 is a scanning electron micrograph of a cross section of the composite solid electrolyte shown in fig. 1.
Fig. 3 is a graph showing the change in the impedance of the battery before and after self-wetting before and after applying the composite solid electrolyte shown in fig. 1.
Fig. 4 is a graph showing the coulombic efficiency and the charge-discharge cycle of a battery using the composite solid electrolyte shown in fig. 1.
Description of reference numerals:
none.
The following detailed description further illustrates embodiments of the invention in conjunction with the above-described figures.
Detailed Description
So that the manner in which the above recited objects, features and advantages of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. In addition, the features of the embodiments of the present application may be combined with each other without conflict.
In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the invention, and the described embodiments are merely a subset of embodiments of the invention, rather than a complete embodiment. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the embodiments of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present invention belong. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the invention.
The invention provides a composite solid electrolyte which has a self-wetting function and can form ideal surface-to-surface contact with a positive electrode or a negative electrode of a battery. The composite solid electrolyte comprises a three-layer laminated structure consisting of a core layer and a surface layer, wherein the core layer mainly consists of a mixture containing polyvinylidene fluoride, a fast ion conductor and lithium salt, and the surface layer mainly consists of a mixture containing polycarbonate, the fast ion conductor and the lithium salt.
In a specific embodiment, the mass ratio of the polyvinylidene fluoride in the core layer is 60-80%, the mass ratio of the fast ion conductor is 5-30%, and the mass ratio of the lithium salt is 5-30%. Wherein the fast ion conductor comprises one of lithium lanthanum zirconium oxygen, lithium lanthanum titanium oxygen and lithium lanthanum niobium oxygen; the lithium salt comprises one of lithium perchlorate, lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide. The thickness of the core layer is 10-100 microns.
In a specific embodiment, the mass ratio of the polycarbonate in the surface layer is 60-80%, the mass ratio of the fast ion conductor is 5-30%, and the mass ratio of the lithium salt is 5-30%. Wherein the polycarbonate comprises one of polypropylene carbonate, polyethylene carbonate and polybutylene carbonate; the fast ion conductor comprises one of lithium lanthanum zirconium oxygen, lithium lanthanum titanium oxygen and lithium lanthanum niobium oxygen; the lithium salt comprises one of lithium perchlorate, lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide. Each of the skin layers has a thickness of 5-20 microns.
The preparation method of the composite solid electrolyte comprises the following steps:
step S1: dissolving polyvinylidene fluoride, a fast ion conductor and lithium salt in a first solvent according to a preset proportion to form a first colloid.
In a specific embodiment, the mass ratio of the polyvinylidene fluoride is 60-80%, the mass ratio of the fast ion conductor is 5-30%, and the mass ratio of the lithium salt is 5-30%; wherein the fast ion conductor comprises one of lithium lanthanum zirconium oxygen, lithium lanthanum titanium oxygen and lithium lanthanum niobium oxygen; the lithium salt comprises one of lithium perchlorate, lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide. The first solvent includes N, N-dimethylformamide or N-methylpyrrolidone. The dissolving process of the step is accompanied by stirring operation, and the stirring time is 2 hours.
Step S2: and dissolving the polycarbonate, the fast ion conductor and the lithium salt in a second solvent according to a preset proportion to form a second colloid.
In a specific embodiment, the mass ratio of the polycarbonate is 60-80%, the mass ratio of the fast ion conductor is 5-30%, and the mass ratio of the lithium salt is 5-30%. Wherein the polycarbonate comprises one of polypropylene carbonate, polyethylene carbonate and polybutylene carbonate; the fast ion conductor comprises one of lithium lanthanum zirconium oxygen, lithium lanthanum titanium oxygen and lithium lanthanum niobium oxygen; the lithium salt comprises one of lithium perchlorate, lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide. The second solvent is N, N-dimethylformamide or N-methylpyrrolidone. The dissolving process of the step is accompanied by stirring operation, and the stirring time is 2 hours.
Step S3: and sequentially forming a first film layer, a core film and a second film layer on the substrate by the second colloid, the first colloid and the second colloid through coating and heating layer by layer to obtain the three-layer structure composite film.
In a specific embodiment, in the step of coating and heating layer by layer, the heating temperature is 60 ℃, and the heating time is 5-15 minutes. The thickness of the first film layer or the second film layer is 50-150 microns, and the thickness of the core film is 50-300 microns. The substrate comprises a stainless steel plate or a polytetrafluoroethylene plate. The more concrete step-by-step steps are as follows:
step S31: and (3) uniformly coating the second colloid on a stainless steel plate or a polytetrafluoroethylene plate by using a scraper to form a uniform first film layer B with the thickness of 50-150 microns, and heating for 5-10 minutes at the temperature of 60 ℃.
Step S33: and continuously and uniformly coating the first colloid on the surface of the first film layer B by using a scraper to form a uniform core film A with the thickness of 50-300 microns, and heating for 10-15 minutes at the temperature of 60 ℃.
Step S35: and (3) continuously and uniformly coating the second colloid B on the surface of the core film A by using a scraper to form a uniform second film layer B with the thickness of 50-150 microns, and heating for 5-10 minutes at 60 ℃ to obtain the three-layer structure composite film.
Step S4: and placing the composite membrane in a vacuum drying oven for heating treatment to obtain the composite solid electrolyte.
In a specific embodiment, step S4 is to heat the composite membrane in a vacuum drying oven at 100 ℃ for 12-24 hours to obtain a three-layer structure composite solid electrolyte.
The composite solid electrolyte can be applied to a solid battery by combining with a positive electrode and a negative electrode, the positive electrode can be ternary lithium iron phosphate, lithium cobaltate and lithium nickel cobalt manganese, the negative electrode is metal lithium, the composite solid electrolyte has the characteristics of dissolving metal salt and transferring ion migration of a liquid electrolyte, particularly, the surface layer contains polycarbonate, in-situ gelation occurs under the conditions of heating, voltage application or interface reaction, the interface combination and wetting effect of an electrolyte main body (a core layer) and the positive and negative electrodes are greatly improved, the ideal surface-surface contact requirement is met while the gel layer is prevented from being directly added, the resistance caused by poor interface contact is greatly reduced, and the electrical property of the battery is effectively improved.
Example one
(1) Dissolving 1g of polyvinylidene fluoride, 0.2g of lithium lanthanum zirconium oxygen fast ion conductor powder and 0.2g of lithium bis (trifluoromethyl) sulfonyl imide in 50g N N-dimethylformamide, and stirring for 2 hours to form uniform first colloid;
(2) 1g of polypropylene carbonate, 0.2g of lithium lanthanum zirconium oxygen fast ion conductor powder and 0.2g of lithium bis (trifluoromethyl) sulfonyl imide are dissolved in N, N-dimethylformamide and stirred for 2 hours to form uniform second colloid;
(3) uniformly coating the first colloid on a stainless steel plate by using a scraper to form a uniform electrolyte wet film, namely a first film layer B, wherein the thickness of the wet film is 150 microns, and heating for 10 minutes at 60 ℃;
(4) on the basis of the step (3), continuously and uniformly coating the first colloid on the surface of the first film layer B by using a scraper to form a uniform electrolyte wet film, namely a core film A, wherein the thickness of the wet film is 200 microns, and heating for 15 minutes at 60 ℃;
(5) on the basis of the step (4), continuously and uniformly coating the second colloid on the surface of the core film A by using a scraper to form a uniform electrolyte wet film, namely a second film layer B, wherein the thickness of the wet film is 150 microns, and heating the film for 10 minutes at 60 ℃ to obtain a three-layer structure composite film;
(6) and (3) heating the composite membrane in a vacuum drying oven at 100 ℃ for 24 hours to obtain a three-layer structure composite electrolyte membrane product, namely the composite solid electrolyte.
The results show that the prepared composite solid electrolyte has a layered structure, as shown in fig. 1 and 2, wherein the thickness of the core layer is about 75 microns, the mass percentage of polyvinylidene fluoride is 71.4%, the mass percentage of the fast ion conductor is 14.3%, and the mass percentage of the lithium salt is 14.3%; the thicknesses of the upper surface layer and the lower surface layer (wetting layer) are respectively about 20 microns, the mass percentage of the polypropylene carbonate is 71.4%, the mass percentage of the fast ion conductor is 14.3%, and the mass percentage of the lithium salt is 14.3%. The composite solid electrolyte, a lithium iron phosphate anode and a lithium metal cathode form a solid battery, the battery impedance is obviously reduced after the solid battery is heated and activated for 12 hours at the temperature of 80 ℃, and as shown in fig. 3, the interface wettability is enhanced (wherein, the abscissa represents the impedance of the battery, the larger the impedance is, the worse the interface wettability is, and conversely, the smaller the impedance is, the better the interface wettability is); FIG. 4 shows the cell cycling at 0.5C for 300 cycles with a specific capacity retention of 120 mAh/g; the battery is not subjected to interface modification, so that the impedance is too high, and the battery cannot run; if the electrolyte is added for wetting, the specific capacity of the invention can be designed to be achieved, but the cycle period is not as good as that of the invention, and the electrolyte is not wetted in situ, so that the implementation effect is different from that of the invention.
Example two
(1) Dissolving 1g of polyvinylidene fluoride, 0.1g of lithium lanthanum titanium oxygen fast ion conductor powder and 0.4g of lithium perchlorate in 50g N-methyl pyrrolidone, and stirring for 2 hours to form uniform first colloid;
(2) dissolving 1g of polypropylene carbonate, 0.1g of lithium lanthanum titanium oxide fast ion conductor powder and 0.4g of lithium perchlorate in N-methylpyrrolidone, and stirring for 2 hours to form uniform second colloid;
(3) uniformly coating the second colloid on a stainless steel plate by using a scraper to form a uniform electrolyte wet film, namely a first glue film B, wherein the thickness of the wet film is 50 micrometers, and heating for 5 minutes at 60 ℃;
(4) on the basis of the step (3), continuously and uniformly coating the first colloid on the surface of the first adhesive film B by using a scraper to form a uniform electrolyte wet film, namely a core film A, wherein the thickness of the wet film is 120 microns, and heating for 10 minutes at 60 ℃;
(5) on the basis of the step (4), continuously and uniformly coating the second colloid on the surface of the core film A by using a scraper to form a uniform electrolyte wet film, namely a second adhesive film B, wherein the thickness of the wet film is 50 micrometers, and heating the film for 5 minutes at 60 ℃ to obtain a three-layer structure composite film;
(6) and (3) heating the composite membrane in a vacuum drying oven at 100 ℃ for 12 hours to obtain a three-layer structure composite electrolyte membrane product, namely the composite solid electrolyte.
The results showed that the prepared composite solid electrolyte had a layered structure as shown in fig. 1. Wherein the thickness of the middle layer (core layer) is about 10 microns, the mass ratio of the polyvinylidene fluoride is 66.7%, the mass ratio of the fast ion conductor is 6.7%, and the mass ratio of the lithium salt is 26.6%; the thicknesses of the upper surface layer and the lower surface layer (wetting layers) are respectively about 5 microns, the mass ratio of the polyethylene carbonate is 66.7%, the mass ratio of the fast ion conductor is 6.7%, and the mass ratio of the lithium salt is 26.6%. The composite solid electrolyte, a ternary NCM622 positive electrode and a metallic lithium negative electrode form a solid battery, the solid battery is heated and activated at the temperature of 80 ℃ for 12 hours, the impedance of the battery is obviously reduced, the coulombic efficiency gradually approaches 100% along with charge-discharge circulation, the interface wettability is enhanced, the battery circulates 100 circles at the temperature of 0.5 ℃, and the specific capacity is kept at 140 mAh/g.
EXAMPLE III
(1) Dissolving 1g of polyvinylidene fluoride, 0.4g of lithium lanthanum niobium oxygen fast ion conductor powder and 0.1g of lithium hexafluorophosphate in 50g N N-dimethylformamide, and stirring for 2 hours to form a uniform first colloid;
(2) 1g of polybutylene carbonate, 0.4g of lithium lanthanum niobium oxygen fast ion conductor powder and 0.1g of lithium hexafluorophosphate are dissolved in N, N-dimethylformamide and stirred for 2 hours to form uniform second colloid;
(3) uniformly coating the second colloid on a polytetrafluoroethylene plate by using a scraper to form a uniform electrolyte wet film, namely a first film layer B, wherein the thickness of the wet film is 100 microns, and heating for 10 minutes at 60 ℃;
(4) on the basis of the step (3), continuously and uniformly coating the first colloid on the surface of the first film layer B by using a scraper to form a uniform electrolyte wet film, namely a core film A, wherein the thickness of the wet film is 300 microns, and heating for 15 minutes at 60 ℃;
(5) on the basis of the step (4), continuously and uniformly coating the second colloid on the surface of the core film A by using a scraper to form a uniform electrolyte wet film, wherein the thickness of the second film layer B is 100 microns, and heating the second film layer B at 60 ℃ for 10 minutes to obtain a three-layer structure composite film;
(6) and (3) heating the composite membrane in a vacuum drying oven at 100 ℃ for 20 hours to obtain a three-layer structure composite electrolyte membrane product, namely the composite solid electrolyte.
The results show that the prepared composite solid electrolyte was in a layered structure, as shown in fig. 1. Wherein the thickness of the middle layer (core layer) is about 97 microns, the mass ratio of polyvinylidene fluoride is 66.7%, the mass ratio of the fast ion conductor is 22.6%, and the mass ratio of the lithium salt is 6.7%; the thicknesses of the upper surface layer and the lower surface layer (wetting layer) are respectively about 12 micrometers, the mass ratio of the polypropylene carbonate is 66.7%, the mass ratio of the fast ion conductor is 22.6%, and the mass ratio of the lithium salt is 6.7%. The composite solid electrolyte, a lithium cobaltate anode and a metallic lithium cathode form a solid battery, the solid battery is heated and activated for 24 hours at the temperature of 80 ℃, the coulombic efficiency gradually approaches 100 percent along with charge-discharge circulation, the interface wettability is enhanced, the battery is circulated for 200 circles at the temperature of 0.5 ℃, and the specific capacity is kept at 117 mAh/g.
Practice ofExample (b) Example 1 Example 2 Example 3
Initial capacity (mAh/g) 155 167 141
Current (C) 0.5 0.5 0.5
Cycle period (circle) 300 100 200
Residual capacity (mAh/g) 120 140 117
Coulombic efficiency 99.5％ 99.5％ 99.5％
In other embodiments of the present invention, the components and their contents of the core layer or the surface layer are not limited to those of the above embodiments, and it is verified that the coulombic efficiency of the product obtained within the reasonable range of the present invention is close to 100%, the interfacial wettability is good, and the cycle performance of the battery is excellent. When the composition of the core layer or the skin layer and the content thereof are out of the reasonable range of the present invention, the properties thereof may be deteriorated, particularly initial capacity and cycle life.
In conclusion, the invention greatly improves the interface combination and wetting effect of the electrolyte main body and the positive and negative electrodes by forming the three-layer structure composite electrolyte and utilizing the in-situ gelation of the upper layer polycarbonate and the lower layer polycarbonate under the conditions of heating, voltage application or interface reaction, and overcomes the defect of directly adding a gel layer. In addition, the preparation method of the composite solid electrolyte with the layered structure provided by the invention is directly carried out on the surface of the polymer electrolyte, and has the advantages of simple equipment and process, low cost and easy large-scale production.
Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the embodiments of the present invention.

Claims (8)

1. A composite solid electrolyte characterized by: the laminated structure comprises a core layer and a surface layer, wherein the core layer is mainly composed of a mixture containing polyvinylidene fluoride, a fast ion conductor and lithium salt, the mass ratio of polyvinylidene fluoride in the core layer is 60-80%, the mass ratio of the fast ion conductor is 5-30%, the mass ratio of lithium salt is 5-30%, the surface layer is mainly composed of a mixture containing polycarbonate, the fast ion conductor and lithium salt, the mass ratio of polycarbonate in the surface layer is 60-80%, the mass ratio of the fast ion conductor is 5-30%, and the mass ratio of lithium salt is 5-30%.
2. The composite solid-state electrolyte of claim 1, wherein: the thickness of the core layer is 10-100 microns; each of the skin layers has a thickness of 5-20 microns.
3. The composite solid-state electrolyte of claim 1, wherein: the polycarbonate comprises one of polypropylene carbonate, polyethylene carbonate and polybutylene carbonate; the fast ion conductor comprises one of lithium lanthanum zirconium oxygen, lithium lanthanum titanium oxygen and lithium lanthanum niobium oxygen; the lithium salt comprises one of lithium perchlorate, lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide.
4. A method of producing a composite solid electrolyte according to any one of claims 1 to 3, comprising the steps of:
dissolving polyvinylidene fluoride, a fast ion conductor and lithium salt in a first solvent according to a preset proportion to form a first colloid;
dissolving polycarbonate, a fast ion conductor and lithium salt in a second solvent according to a preset proportion to form a second colloid;
sequentially forming a first film layer, a core film and a second film layer on a substrate by the second colloid, the first colloid and the second colloid through coating and heating layer by layer to obtain a three-layer structure composite film;
and placing the composite membrane in a vacuum drying oven for heating treatment to obtain the composite solid electrolyte.
5. The method of claim 4, wherein: the dissolution step and its subsequent stirring operation were carried out for a period of 2 hours.
6. The method of claim 4, wherein: in the step of coating and heating layer by layer, the heating temperature is 60 ℃, and the heating time is 5-15 minutes.
7. The method of claim 4, wherein: the thickness of the first film layer or the second film layer is 50-150 microns, and the thickness of the core film is 50-300 microns.
8. A solid-state battery characterized by: the composite solid electrolyte according to any one of claims 1 to 3, comprising a positive electrode, a negative electrode and the composite solid electrolyte therebetween, wherein the negative electrode is metallic lithium, and the positive electrode comprises one of lithium iron phosphate, lithium cobaltate or lithium nickel cobalt manganese.
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