Polymer solid electrolyte, preparation method thereof and solid-state battery

Abstract

The invention relates to the technical field of solid-state batteries, and discloses a polymer solid-state electrolyte and a preparation method thereof, and a solid-state battery, the polymer solid-state electrolyte is formed by complexing a fluorine-containing compound and lithium ions, the structural formula of the fluorine-containing compound is shown in the specification, 1 < = n < = 20, 1 < = x < = 50, 1 < = y < = 50, the molar ratio of the fluorine-containing compound to the lithium ions is (1-10): 1. The polymer solid electrolyte provided by the invention has relatively high room-temperature conductivity, relatively wide electrochemical window, excellent lithium stability and good electrochemical compatibility with a high-voltage positive electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and in particular to a polymer solid-state electrolyte and a preparation method thereof, and a solid-state battery. Background Art

[0002] Lithium-ion batteries using graphite anodes are mainly used in electric vehicles, portable devices and large energy storage devices, but the development of energy density has reached a bottleneck. The theoretical capacity of lithium metal anode is 3860mAh g -1 , which can provide higher energy density after replacing carbon / graphite negative electrodes. However, serious interfacial side reactions between the electrolyte and the lithium metal negative electrode can lead to a rapid decrease in the capacity of the lithium-ion battery, lithium dendrite short circuits and safety issues caused by electrolyte leakage during battery cycling. Using solid electrolytes to replace flowing liquid electrolytes can alleviate various interfacial side reactions and thermal runaway problems of high-voltage lithium metal batteries. Therefore, designing a solid electrolyte with stable properties can achieve an electrolyte / electrode interface with excellent electrochemical compatibility, ensuring the cycling stability and safety of high-voltage lithium metal batteries.

[0003] Solid electrolytes are mainly divided into sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes and polymer solid electrolytes. Compared with the other three inorganic solid electrolytes, polymer solid electrolytes have the advantages of good flexibility, light weight and easy large-scale industrialization. The soft nature of polymer electrolytes enables them to have good interfacial contact with electrodes and low interfacial impedance. In addition, the synthesis of polymer electrolytes by in situ polymerization can further reduce the electrolyte / electrode interface impedance and improve the electrochemical performance of the battery. However, as a typical polyether electrolyte, polyethylene oxide (PEO) polymer electrolyte has limited its commercialization process due to its low room temperature conductivity and poor electrochemical compatibility with high-voltage positive electrode materials.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a polymer solid electrolyte and a preparation method thereof, and a solid-state battery, so as to solve the problem of poor electrochemical compatibility between the existing polymer solid electrolyte and high-voltage positive electrode materials.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] In a first aspect of the present invention, a polymer solid electrolyte is provided. The polymer solid electrolyte is formed by complexing a fluorine-containing compound with lithium ions. The structural formula of the fluorine-containing compound is:

[0008]

[0009] Wherein, 1≤n≤20, 1≤x≤50, 1≤y≤50, and the molar ratio of the fluorine-containing compound to the lithium ion is (1-10):1.

[0010] Preferably, 2≤n≤10, 20≤x≤50, 20≤y≤50.

[0011] Preferably, the structural formula of the fluorine-containing compound monomer is one of the following structural formulas:

[0012]

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned polymer solid electrolyte, the preparation method comprising the following steps:

[0014] mixing a lithium salt, an initiator, a comonomer, and a fluorinated polymer monomer to obtain a precursor solution;

[0015] impregnating the precursor solution on the diaphragm to perform an in-situ polymerization reaction to obtain the polymer solid electrolyte;

[0016] Wherein, the comonomer is polyethylene glycol diglycidyl ether PEGDE or glycerol triglycidyl ether GTE, and the fluorinated polymer monomer is glycidyl 2,2,3,3-tetrafluoropropyl ether TFE.

[0017] Preferably, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, and lithium hexafluorophosphate.

[0018] Preferably, the initiator is selected from one of lithium tetrafluoroborate, lithium hexafluorophosphate, stannous fluoride, lithium difluorooxalatoborate, aluminum trifluoromethanesulfonate and the like.

[0019] Preferably, the diaphragm is selected from one of Celgard 2500, Celgard 2340, PE diaphragm, PET non-woven fabric, and Polyimide membrane.

[0020] Preferably, in the precursor solution, the mass proportion of lithium salt is 10 wt%-50 wt%, the mass proportion of comonomer is 70 wt%-90 wt%, and the mass proportion of fluorinated polymer monomer is 2 wt%-50 wt%.

[0021] Preferably, the in-situ polymerization reaction is carried out at a temperature of 40-80° C. and for a time of 3-10 h.

[0022] A third aspect of the present invention provides a solid-state battery, comprising the above-mentioned polymer solid electrolyte or a polymer solid electrolyte prepared by the above-mentioned preparation method.

[0023] Advantages:

[0024] The application discloses a polymer solid electrolyte and a preparation method and a solid-state battery thereof.

[0025] The preparation method is simple in process, low in cost, and high in production efficiency, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A structural schematic diagram of the polymer solid electrolyte prepared for the application example 1 is shown in the figure.

[0027] Figure 2 The lithium ion transference number of the polymer solid electrolyte prepared for the application example 1 is shown in the figure.

[0028] Figure 3 The lithium stability test of the polymer solid electrolyte prepared for the application example 1 is shown in the figure.

[0029] Figure 4 The battery cycle of the polymer solid electrolyte prepared for the application example 1 matched with the high-voltage positive electrode is shown in the figure. DETAILED DESCRIPTION

[0030] The application provides a polymer solid electrolyte and a preparation method and a solid-state battery thereof, in order to make the purpose, technical scheme and effect of the application more clear and definite, the application is further described in detail below.

[0031] Based on this, the application example provides a polymer solid electrolyte, the polymer solid electrolyte is formed by complexing fluorine-containing compound and lithium ion, the structural formula of the fluorine-containing compound is as follows:

[0032]

[0033] Wherein, 1≤n≤20, 1≤x≤50, 1≤y≤50, the molar ratio of the fluorine-containing compound and the lithium ion is (1-10): 1.

[0034] The introduction of the fluorinated component enhances the interaction between the electrolyte structure and the anion in the lithium salt, inhibits the movement of the anion, and enhances the free movement of lithium ions. In addition, the introduction of the fluorinated component can also reduce the crosslinking degree of the polymer solid electrolyte, improve the free movement of the polymer chain segment, and promote the transmission of lithium ions; and, benefiting from the strong electron-withdrawing effect of the fluorinated component, the fluorinated component promotes the formation of an electrolyte interface film in the battery cycle, inhibits the growth of lithium dendrites, and improves the stability of the polymer solid electrolyte to lithium. In a common polymer solid electrolyte system, decomposition is prone to occur when matched with a high-voltage positive electrode during cycling, and a relatively thick positive electrode electrolyte interface layer is generated, but the introduction of the fluorinated molecule changes the composition of the positive electrode electrolyte interface layer, and the inorganic positive electrode electrolyte interface layer rich in fluorinated lithium is relatively stable, thereby maintaining the stability of the system during the battery cycle.

[0035] In addition, the embodiment of the present application also complexes the fluorine-containing compound with lithium ions, and doping lithium ions in the polyether solid electrolyte can improve the room temperature conductivity and broaden the electrochemical window.

[0036] The embodiment of the present application provides a preparation method of the above-mentioned polymer solid electrolyte, and the preparation method comprises the following steps:

[0037] The lithium salt, the initiator, the comonomer and the fluorinated polymer monomer are mixed to obtain a precursor solution;

[0038] The precursor solution is infiltrated on a diaphragm to perform an in-situ polymerization reaction, so as to obtain the polymer solid electrolyte.

[0039] The preparation method provided by the embodiment of the present application is simple in process, low in cost, high in production efficiency, and suitable for large-scale industrial production.

[0040] In some embodiments, in the precursor solution, the mass percentage of the lithium salt is 10wt%-50wt%, the mass percentage of the comonomer is 70wt%-90wt%, and the mass percentage of the fluorinated polymer monomer is 2wt%-50wt%

[0041] An appropriate amount of lithium salt can provide the required lithium ions in the system, the comonomer in the system is mainly a carrier for lithium ion conduction, too much will cause the lithium ion conductivity to decrease, and too little will not be able to exhibit good oxidation resistance. The fluorinated polymer monomer is mainly to improve the oxidation resistance of the electrolyte film, too little will not be obvious, and too much will have low lithium ion conductivity, thereby reducing the battery performance

[0042] In some preferred embodiments, in the precursor solution, the mass percentage of the lithium salt is 20wt%, the mass percentage of the comonomer is 60wt%, and the mass percentage of the fluorinated polymer monomer is 20wt%.

[0043] In some embodiments, the in-situ polymerization reaction has a temperature of 40-80℃ and a time of 3-10h.

[0044] This temperature range is the initiation temperature of the initiator, and a lower temperature will prolong the polymerization time, and a higher temperature will make the polymerization rate too fast, causing the polymer solid electrolyte to have more micro-bubbles.

[0045] The selection of polymerization time mainly considers that too short polymerization time will cause some unreacted monomers (comonomers, fluorinated polymer monomers) in the polymer solid electrolyte, and these residual monomers have some side reactions with the electrode. After the polymerization is completed, it can be tested, and it is not necessary to polymerize for too long a time.

[0046] In some preferred embodiments, the in-situ polymerization reaction has a temperature of 60℃ and a time of 8h.

[0047] The present application provides a solid-state battery comprising the polymer solid electrolyte described above or the polymer solid electrolyte prepared by the preparation method described above.

[0048] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments, and are only for illustrating the present application and by no means limit the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0049] Example 1

[0050] Preparation of precursor solution: 0.2352g LiTFSI and 2wt% LiBF4 were dissolved in 1.0g PEGDE and 0.3g TFE and stirred for 1 hour to obtain a uniform transparent precursor solution.

[0051] Preparation of solid-state battery, comprising the following steps:

[0052] Preparation of positive electrode sheet: 70wt% NCM622 positive electrode material, 10wt% Super-P conductive agent, 10wt% PVDF binder and 10wt% ionic liquid plasticizer were dissolved in N-pyrrolidone. After the above mixed slurry was mixed and stirred for 24 hours, the mixed slurry was coated on a carbon-coated aluminum foil, and the solvent was dried in a 100℃ oven.

[0053] Assembly of solid-state battery: the above prepared positive electrode NCM622 sheet was used as the positive electrode, lithium metal sheet was used as the negative electrode, Celgard 2500 was used as the separator of the polymer solid electrolyte, and the above prepared precursor solution was infiltrated on the separator to obtain a solid-state battery.

[0054] Performance detection experiment

[0055] The solid-state battery prepared in Example 1 was taken out for electrochemical test after being heated in a 60℃ oven for 8 hours. Among them, Figure 2 show the lithium ion transference number of the polymer solid-state electrolyte; Figure 3 show the lithium stability test of the polymer solid-state electrolyte; Figure 4 show the battery cycle of the polymer solid-state electrolyte matching high-voltage positive electrode.

[0056] The lithium ion transference number of the polymer solid-state electrolyte is 0.366, which is much larger than the lithium ion transference number of the basic PEO polymer electrolyte;

[0057] The polymer solid-state electrolyte shows excellent lithium stability, which is stably cycled for more than 2000h under a current density of 0.2mA cm -2 .

[0058] The polymer solid-state electrolyte shows good electrochemical compatibility with the high-voltage positive material single crystal NCM622, and the capacity retention rate after 200 cycles is 72.31% under the charge-discharge range of 3.0V-4.3V at the charge-discharge rate of 0.2C.

[0059] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A polymer solid electrolyte, characterized in that The polymer solid electrolyte is formed by complexing a fluorine-containing compound with lithium ions. The structural formula of the fluorine-containing compound is: Wherein, 1≤n≤20, 1≤x≤50, 1≤y≤50, and the molar ratio of the fluorine-containing compound to the lithium ion is (1-10):

1.

2. The polymer solid electrolyte according to claim 1, characterized in that in, 2≤n≤10, 20≤x≤50, 20≤y≤50.

3. The polymer solid electrolyte according to claim 1, characterized in that The structural formula of the fluorine-containing compound monomer is one of the following structural formulas:

4. A method for preparing a polymer solid electrolyte according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: mixing a lithium salt, an initiator, a comonomer, and a fluorinated polymer monomer to obtain a precursor solution; impregnating the precursor solution on the diaphragm to perform an in-situ polymerization reaction to obtain the polymer solid electrolyte; Wherein, the comonomer is polyethylene glycol diglycidyl ether or glycerol triglycidyl ether, and the fluorinated polymer monomer is glycidyl 2,2,3,3-tetrafluoropropyl ether.

5. The method for preparing a polymer solid electrolyte according to claim 4, wherein: The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, and lithium hexafluorophosphate.

6. The method for preparing a polymer solid electrolyte according to claim 4, characterized in that: The initiator is selected from one of lithium tetrafluoroborate, lithium hexafluorophosphate, stannous fluoride, lithium difluorooxalatoborate, aluminum trifluoromethanesulfonate and the like.

7. The method for preparing a polymer solid electrolyte according to claim 4, wherein: The diaphragm is selected from one of Celgard 2500, Celgard 2340, PE diaphragm, PET non-woven fabric, and Polyimide film.

8. The method for preparing a polymer solid electrolyte according to claim 4, wherein: In the precursor solution, the mass proportion of lithium salt is 10 wt%-50 wt%, the mass proportion of comonomer is 70 wt%-90 wt%, and the mass proportion of fluorinated polymer monomer is 2 wt%-50 wt%.

9. The method for preparing a polymer solid electrolyte according to claim 4, wherein: The in-situ polymerization reaction temperature is 40-80° C. and the reaction time is 3-10 hours.

10. A solid-state battery, characterized in that: The solid-state battery comprises the polymer solid electrolyte described in any one of 1-3 or the polymer solid electrolyte prepared by the preparation method described in any one of claims 4-9.

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