A solid electrolyte membrane, its preparation method and application

Abstract

This application relates to a solid electrolyte membrane, a preparation method and an application thereof, belonging to the technical field of solid-state batteries; the composition of the solid electrolyte membrane includes: a polymer and a first lithium salt, and the first lithium salt includes an inorganic lithium salt and an organic lithium salt; the inorganic lithium salt is dispersed in the thin film and forms a spatial network skeleton, and the organic lithium salt and the polymer jointly form a flexible spatial network for connecting the spatial network skeleton, so that lithium ions can be conducted through the spatial network skeleton and can also be conducted through the branched veins formed by the organic lithium salt on the thin film, increasing the transmission path of lithium ions in the thin film to improve the conductivity of the thin film; in other words, the cooperation of the organic lithium salt and the inorganic lithium salt is more conducive to providing freely shuttling ions during the electrolysis process and conducting ions in the flexible spatial network to enhance the conductivity of the composite solid electrolyte thin film at room temperature.

Description

Technical Field

[0001] This application relates to the technical field of solid-state batteries, and in particular, to a solid-state electrolyte membrane, a preparation method thereof, and an application thereof. Background Art

[0002] To eliminate range anxiety and revolutionize the new energy vehicle market, the performance characterization of solid-state batteries is the goal of the development of power batteries. Solid-state batteries, also known as the new development direction of future lithium batteries, are batteries in which there is no liquid electrolyte between the positive and negative electrodes of the battery, greatly improving the safety of the battery system and achieving a simultaneous increase in energy density. Among various new battery systems, solid-state batteries are the next-generation technology closest to industrialization, which has become the consensus of the industry and the scientific community.

[0003] In the prior art, it has been proposed to perform isostatic pressing step by step, so that the mechanical strength requirements for the sulfide electrolyte membrane are very low. Therefore, a thinner electrolyte membrane can be used, greatly reducing the amount of electrolyte and the length of the lithium ion transfer path during the operation of the battery, reducing impedance, and reducing the requirements for the bonding strength and the range of types of the binder, which is beneficial to reducing the cost of the battery cell and realizing the leap from a mold battery to a soft-pack battery cell. However, the conductivity of this solid-state battery cell is low, especially at room temperature. It has also been proposed to simultaneously introduce a flexible conductive carbon material and a flexible polymer solid electrolyte on the sulfur cathode to form a uniform ion / electron conductive path, which can comprehensively improve the flexibility of the electrode, and the overall preparation method is simple, energy-efficient, and more practical; the electronic conductivity of this battery itself is very low, especially in a low-temperature environment, the battery almost becomes a non-conductive insulator.

[0004] In summary, the low ionic conductivity of the current all-solid-state electrolyte, poor low-temperature working stability, and still relatively high production cost are the main factors restricting the commercial application of solid-state batteries. Summary of the Invention

[0005] This application provides a solid-state electrolyte membrane, a preparation method thereof, and an application thereof to improve the conductivity of the solid-state electrolyte membrane.

[0006] In a first aspect, this application provides a solid-state electrolyte membrane, and the components of the solid-state electrolyte membrane include: a polymer and a first lithium salt, and the first lithium salt includes an inorganic lithium salt and an organic lithium salt.

[0007] As an optional implementation manner, the inorganic lithium salt includes at least one of lithium sulfide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate; and / or

[0008] The organic lithium salt includes at least one of lithium dodecylsulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0009] As an alternative embodiment, the mass of the first lithium salt is 2% to 6% of the mass of the polymer; and / or

[0010] The mass ratio of the organic lithium salt to the inorganic lithium salt is 1:(2 - 5).

[0011] As an alternative embodiment, the polymer includes a polyethylene oxide polymer; and / or

[0012] The composition of the solid electrolyte membrane further includes: a plasticizer; the plasticizer includes at least one of dibutyl phthalate, a carbonate - based mixed plasticizer dimethyl carbonate - ethylene carbonate, ethylene carbonate - diethyl carbonate - methyl ethyl carbonate, and ethylene carbonate - propylene carbonate; the mass of the plasticizer is 0.5% to 1% of the mass of the polymer.

[0013] In a second aspect, the present application provides a solid - state battery cell, and the solid - state battery cell includes the solid electrolyte membrane described in the first aspect.

[0014] As an alternative embodiment, the solid - state battery cell further includes a positive electrode sheet, the positive electrode sheet includes a second lithium salt, and the second lithium salt is the same as the inorganic lithium salt of the solid electrolyte membrane.

[0015] As an alternative embodiment, the positive electrode sheet further includes a conductive agent and a binder; the mass ratio of the conductive agent, the binder, and the second lithium salt is 100:(2 - 5):(1 - 3).

[0016] In a third aspect, the present application provides a solid - state battery, and the solid - state battery includes the solid - state battery cell described in the second aspect.

[0017] In a fourth aspect, the present application provides a method for preparing a solid electrolyte membrane, and the method includes:

[0018] Dissolving the components of the solid electrolyte membrane in a solvent to obtain a mixed solution, where the components of the solid electrolyte membrane include: a polymer and a first lithium salt, and the first lithium salt includes an inorganic lithium salt and an organic lithium salt;

[0019] Placing the mixed solution in a mold and then drying to remove the solvent to obtain the solid electrolyte membrane.

[0020] In a fifth aspect, the present application provides a method for preparing a solid - state battery cell, and the method includes:

[0021] Obtaining a positive electrode sheet, a negative electrode sheet, and a solid electrolyte membrane;

[0022] Assembling the positive electrode sheet, the negative electrode sheet, and the solid electrolyte membrane to obtain the solid - state battery cell.

[0023] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0024] The solid electrolyte membrane provided by the embodiments of the present application has a composition including a polymer and a first lithium salt. The first lithium salt includes an inorganic lithium salt and an organic lithium salt. The inorganic lithium salt is dispersed in the thin film and forms a spatial network skeleton. The organic lithium salt and the polymer jointly form a flexible spatial network for connecting the spatial network skeleton, so that lithium ions can be conducted through the spatial network skeleton and can also be conducted through the branched veins formed by the organic lithium salt on the thin film, increasing the transmission path of lithium ions in the thin film to improve the conductivity of the thin film; in other words, the cooperation of the organic lithium salt and the inorganic lithium salt is more conducive to providing freely shuttling ions during the electrolysis process and conducting ions in the flexible spatial network to enhance the conductivity of the composite solid electrolyte thin film at room temperature. Description of the Drawings

[0025] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0026] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a flowchart of the method provided by the embodiments of the present application. Detailed Embodiments

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0029] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present application can all be obtained through market purchases or can be prepared by existing methods.

[0030] Currently, the low ionic conductivity, poor low-temperature working stability, and still relatively high production cost of all-solid-state electrolytes are the main factors restricting the commercial application of solid-state batteries. During the invention process, the inventors found that the reasons for the low conductivity of the solid electrolyte membrane may be as follows: 1. In the solid electrolyte thin film, PEO / Li + in the solid polymer electrolyte, Li + cannot move freely at room temperature like Li in liquid electrolytes + , so it is necessary to rely on high temperature to achieve electron transition to realize the function of conduction; 2. The conduction process between Li + and the conductive agent between the solid electrolyte thin film and the positive electrode sheet is not smooth, which may be due to the fact that Li + is restricted by PEO.

[0031] An embodiment of the present application provides a solid electrolyte membrane, and the components of the solid electrolyte membrane include: a polymer and a first lithium salt, and the first lithium salt includes an inorganic lithium salt and an organic lithium salt.

[0032] The components of the solid electrolyte membrane include a polymer and a first lithium salt, and the first lithium salt includes an inorganic lithium salt and an organic lithium salt. The inorganic lithium salt is dispersed in the thin film and forms a spatial network skeleton. The organic lithium salt and the polymer jointly form a flexible spatial network for connecting the spatial network skeleton, so that lithium ions can be conducted through the spatial network skeleton and also through the branched veins formed by the organic lithium salt on the thin film, increasing the transmission path of lithium ions in the thin film to improve the conductivity of the thin film; in other words, the cooperation of the organic lithium salt and the inorganic lithium salt is more conducive to providing freely shuttling ions during the electrolysis process and conducting ions in the flexible spatial network to enhance the conductivity of the composite solid electrolyte thin film at room temperature.

[0033] In some embodiments, the inorganic lithium salt includes at least one of lithium sulfide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate; the organic lithium salt includes at least one of lithium dodecylsulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. During the invention process, the inventors found that the effect is better when the inorganic lithium salt is lithium sulfide. The inventors analyzed the reason may be that the molecular structure of lithium sulfide is symmetrically stable, which is more conducive to forming a stable spatial network skeleton. At the same time, the effect is better when the organic lithium salt is lithium dodecylsulfonate. The inventors analyzed the reason may be that the molecular chain of lithium dodecylsulfonate is longer and it is easier to form a flexible spatial network with the PEO polymer than other organic lithium salts. In addition, the sulfonic acid group in lithium dodecylsulfonate serves as an efficient lithium-philic functional site, promoting the uniform distribution of lithium ions in the spatial network and contributing to the conduction of lithium ions.

[0034] In some embodiments, the mass of the first lithium salt is 2% to 6% of the mass of the polymer; the mass ratio of the organic lithium salt to the inorganic lithium salt is 1:(2 - 5).

[0035] By increasing the concentration of lithium ions in the solid electrolyte membrane, the nuclear distance between two adjacent lithium elements is made close enough to enable electron transition at room temperature, thus achieving a conductive effect similar to that of a liquid electrolyte.

[0036] In some embodiments, the polymer includes a polyethylene oxide polymer.

[0037] In some embodiments, the composition of the solid electrolyte membrane further includes: a plasticizer; the plasticizer includes at least one of dibutyl phthalate, the carbonate-based mixed plasticizer dimethyl carbonate - ethylene carbonate, ethylene carbonate - diethyl carbonate - methyl ethyl carbonate, and ethylene carbonate - propylene carbonate; the mass of the plasticizer is 0.5% to 1% of the mass of the polymer.

[0038] The embodiment of the present application provides a solid-state battery cell, and the solid-state battery cell includes the solid electrolyte membrane provided above.

[0039] This solid-state battery cell is realized based on the above solid electrolyte membrane. The specific content of the solid electrolyte membrane can be referred to the above embodiments. Since this solid-state battery cell adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0040] In some embodiments, the solid-state battery cell further includes a positive electrode sheet, and the positive electrode sheet includes a second lithium salt, and the second lithium salt is the same as the inorganic lithium salt of the solid electrolyte membrane.

[0041] This solid-state battery cell includes a first lithium salt and a second lithium salt. The first lithium salt is used in the solid electrolyte membrane, and the second lithium salt is used in the positive electrode sheet. Moreover, the inorganic lithium salts in the second lithium salt and the first lithium salt are the same, and the two can be used as initiators for the solid electrolyte film and the positive electrode sheet to conduct electricity, thereby improving the conductivity of the solid-state battery cell.

[0042] In some embodiments, the positive electrode sheet further includes a conductive agent and a binder; the mass ratio of the conductive agent, the binder, and the second lithium salt is 100:(2 - 5):(1 - 3).

[0043] Specifically, the conductive agent can be selected from one or more of carbon black conductive agents, graphite conductive agents, and graphene conductive agents. The carbon black conductive agents include acetylene black, 350G, carbon fiber (VGCF), carbon nanotubes (CNT), and Ketjen black. The graphite conductive agents include KS-6, KS-15, SFG-6, and SFG-15. The binder can be selected from one or more of vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and styrene-butadiene rubber (SBR).

[0044] An embodiment of the present application provides a solid-state battery, and the solid-state battery includes the solid-state battery cell provided above.

[0045] This solid-state battery is implemented based on the above solid-state battery cell. The specific content of the solid-state battery cell can be referred to the above embodiment. Since this solid-state battery adopts some or all of the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be elaborated here one by one.

[0046] A solid-state battery generally includes a housing, an end cap, several solid-state battery cells, and electrode tabs, etc. Among them, the housing is composed of a double-layer shell, and there is a cavity between the double-layer shells. The cavity is filled with an inert gas. The housing is made of a metal sheet wrapped with polyethylene; several of the solid-state battery cells are inserted inside the housing, and a flame retardant is filled between several solid-state battery cells; the end cap is embedded at one end of the housing; the electrode tabs are welded to several solid-state battery cells, and the electrode tabs pass through the end cap.

[0047] An embodiment of the present application provides a method for preparing a solid-state electrolyte membrane, and the method includes:

[0048] S1. Dissolve the components of the solid-state electrolyte membrane in a solvent to obtain a mixed solution. The components of the solid-state electrolyte membrane include: a polymer and a first lithium salt, and the first lithium salt includes an inorganic lithium salt and an organic lithium salt;

[0049] Specifically, in this embodiment, a PEO (polyethylene oxide) polymer, a first lithium salt, and a plasticizer are dissolved in an organic solvent of tetrahydrofuran and acetone according to a certain metering ratio. Through magnetic stirring and ultrasonic dispersion at 40-60 °C, the lithium salt and the polymer are uniformly dissolved in the solvent to obtain a mixed solution.

[0050] S2. Place the mixed solution in a mold and then dry it to remove the solvent to obtain a solid-state electrolyte membrane.

[0051] Specifically, in this embodiment, the obtained mixed solution is poured onto a polytetrafluoroethylene (PTFE) mold and placed in a drying and normal-pressure purging device to volatilize the solvent (or volatilize naturally at room temperature). Finally, it is vacuum-dried in a vacuum drying oven for 10 - 24 h to remove a small amount of residual solvent, thus obtaining the solid electrolyte membrane.

[0052] In other embodiments, the preparation method of the solid electrolyte membrane can also be: dissolving a certain amount of polymer powder in a lithium salt liquid electrolyte, usually stirring at 40 °C for 1 - 2 h to obtain a homogeneous and clear solution, then gradually adding a cross-linking agent and stirring evenly. The mixed solution is filled into a sealed glass container, and using the photo-initiated cross-linking theory, it is subjected to radiation cross-linking reaction at a certain temperature with a certain irradiation source to obtain the gel polymer electrolyte membrane.

[0053] The embodiment of the present application provides a preparation method of a solid-state battery cell, and the method includes:

[0054] S1. Obtaining a positive electrode sheet, a negative electrode sheet, and a solid electrolyte membrane;

[0055] Specifically, in this embodiment, the preparation of the positive electrode sheet includes: coating a positive electrode active paste including a conductive agent, a binder, and a second lithium salt on a copper foil current collector through a vacuum spray coater, drying it with a vacuum desiccant, and then compacting it with a roll press to obtain the positive electrode sheet; the preparation of the negative electrode sheet includes: coating a negative electrode active paste including graphene on a copper-lithium metal sheet, and then compacting it with a roll press to obtain the negative electrode sheet; the solid electrolyte membrane is prepared by using the method provided above.

[0056] S2. Assembling the positive electrode sheet, the negative electrode sheet, and the solid electrolyte membrane to obtain a solid-state battery cell.

[0057] Specifically, in this embodiment, the positive electrode sheet, the composite solid electrolyte, and the negative electrode sheet are stacked to form a solid-state battery cell

[0058] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. For the experimental methods without specific conditions noted in the following embodiments, they are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0059] Examples 1 - 8 and Comparative Examples 1 - 2

[0060] A preparation method of a solid-state battery cell includes the following steps:

[0061] S1. Preparation of the positive electrode sheet

[0062] The positive electrode active paste including a conductive agent, a binder, and a first lithium salt is coated on a copper foil current collector by a vacuum spray coater, dried with a vacuum desiccator, and then compacted with a pair of rollers to obtain a positive electrode sheet;

[0063] S2. Preparation of the negative electrode sheet

[0064] The negative electrode active paste including graphene is coated on a copper-lithium metal sheet, and then compacted with a pair of rollers to obtain a negative electrode sheet;

[0065] S3. Preparation of the composite solid electrolyte

[0066] S3.1. Dissolve PEO (polyethylene oxide) polymer, a second lithium salt, and a plasticizer in an organic solvent of tetrahydrofuran and acetone according to a certain metering ratio, and magnetically stir and ultrasonically disperse at 50 °C to uniformly dissolve the lithium salt and the polymer in the solvent to obtain a uniform and transparent liquid;

[0067] S3.2. Pour the obtained uniform and transparent liquid onto a polytetrafluoroethylene (PTFE) mold, and place it in a dry normal pressure purging device to volatilize the solvent (or naturally volatilize at room temperature), and finally vacuum dry in a vacuum drying oven to remove a small amount of residual solvent, that is, a prefabricated electrolyte film is prepared;

[0068] S4. Assembly: Stack the positive electrode sheet, the composite solid electrolyte, and the negative electrode sheet to form a solid-state battery cell.

[0069] The main parameters of each example and comparative example are controlled as shown in the following table:

[0070]

[0071]

[0072] After standing the assembled solid-state battery cell for 24 h, perform a lithium ion transference number test at a test temperature of room temperature (25 °C), and the results are shown in the following table:

[0073] Lithium ion transference number Example 1 0.89 Example 2 0.65 Example 3 0.76 Example 4 0.74 Example 5 0.79 Example 6 0.83 Example 7 0.71 Example 8 0.83 Comparative Example 1 0.51 Comparative Example 2 0.44

[0074] It can be seen from the above table that the lithium ion transference number of the solid-state battery cell prepared by the method provided in the application examples is greater than that of the solid-state battery cell prepared by the comparative examples. Among them, Example 1 using lithium sulfide as the inorganic lithium salt and lithium dodecylsulfonate as the organic lithium salt has significantly better effects than other examples. Perform a conductivity test at room temperature, and the result is 10 - 5 s·cm -1 , meeting the commercial requirements.

[0075] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the description of the range from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any recited number (fraction or integer) within the indicated range.

[0076] In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing direction in the drawings. Additionally, in the description of the specification of the present application, the terms "comprising", "including", etc. mean "including but not limited to".

[0077] In this document, relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this document, "and / or" describes the associated relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone. Where A and B may be singular or plural. In this document, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0078] The above description is only the specific implementation manners of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A solid-state battery cell, characterized in that, The solid-state battery cell includes a solid electrolyte membrane, a positive electrode sheet, and a negative electrode sheet. The solid electrolyte membrane is composed of the following components : a polymer, a first lithium salt, and a plasticizer. The first lithium salt includes an inorganic lithium salt and an organic lithium salt. The inorganic lithium salt is lithium sulfide, and the organic lithium salt is lithium dodecylsulfonate. The polymer is a polyethylene oxide polymer. The mass of the first lithium salt is 4% of the mass of the polymer. The mass ratio of the organic lithium salt to the inorganic lithium salt is 1:(3-5). The mass of the plasticizer is 0.5%-1% of the mass of the polymer. The positive electrode sheet includes a second lithium salt, a conductive agent, and a binder. The second lithium salt is the same as the inorganic lithium salt of the solid electrolyte membrane, and the mass ratio of the conductive agent, the binder, and the second lithium salt is 100:3:

2. The negative electrode sheet includes graphene and copper-lithium metal.

2. The solid-state battery cell according to claim 1, characterized in that, The plasticizer includes at least one of dibutyl phthalate, a carbonate-based mixed plasticizer dimethyl carbonate-ethylene carbonate, ethylene carbonate-diethyl carbonate-ethyl methyl carbonate, and ethylene carbonate-propylene carbonate.

3. A solid-state battery, characterized in that, The solid-state battery includes the solid-state battery cell according to claim 1.

4. A method for preparing a solid-state battery cell according to any one of claims 1-2, characterized in that, The method includes: obtaining a positive electrode sheet, a negative electrode sheet, and a solid electrolyte membrane; assembling the positive electrode sheet, the negative electrode sheet, and the solid electrolyte membrane to obtain a solid-state battery cell.

Images