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

Abstract

The invention relates to the technical field of electrochemical energy storage, in particular to a polymer electrolyte, a preparation method and application thereof, a solid-state lithium battery and a preparation method thereof. The polymer electrolyte comprises a polymer matrix and a lithium salt, wherein the polymer matrix has the following structural unit: # imgabs0 #; wherein n ranges from 13 to 300. According to the method, the polymer electrolyte is prepared only by initiating the beta-propiolactone monomer to polymerize through the lithium salt, an additional catalyst or additive does not need to be added, the electrolyte has excellent lithium salt solubility, a polar group ester group and Li < + > form weak coordination, Li < + > conduction is promoted, the room-temperature ionic conductivity and the ionic transference number of the polymer electrolyte are improved, and the service life of the polymer electrolyte is prolonged. Furthermore, the concentration polarization phenomenon at the interface in the circulation process is reduced, the growth of lithium dendrites is inhibited, and the uniform deposition of Li < + > is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a polymer electrolyte and a preparation method and application thereof, as well as a solid-state lithium battery and a preparation method thereof. Background Art

[0002] Among the numerous battery technologies, lithium-ion batteries (LIBs) have been widely used in portable appliances, transportation, and large-scale power storage facilities due to their advantages such as high energy density, long cycle life, low self-discharge rate, and wide operating temperature range. However, traditional liquid lithium-ion batteries use high-temperature-intolerant diaphragms and unstable organic electrolytes, which pose great safety risks. Solid electrolytes have stable physical and chemical properties and can effectively solve safety problems such as leakage and thermal runaway in liquid lithium-ion batteries. At the same time, solid electrolytes matched with lithium metal negative electrodes can greatly increase the energy density of batteries.

[0003] Compared with inorganic solid electrolytes, solid polymer electrolytes have the advantages of easy processing, light weight, low production cost, high flexibility, low interfacial resistance, and their shape can change with the volume of the electrode during battery charging and discharging. All-solid polymer electrolytes are composed of polymer matrix materials that can dissolve lithium salts and lithium salts, and do not require the addition of liquid plasticizers. With the deepening of research on solid polymer electrolytes, the types of polymers that can be used as matrix materials have gradually increased, such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF) and polycarbonates. Each material exhibits different characteristics due to the difference in functional groups, but the comprehensive performance is still difficult to meet the needs of lithium batteries, especially in terms of room temperature ionic conductivity. Taking PEO, which has been studied for the longest time and the most in-depth, as an example, its flexible main chain structure and low glass transition temperature are considered to be the most promising polymer electrolyte for commercialization. However, the semi-crystalline nature of PEO-based electrolytes at room temperature and the large number of polar groups on the main chain that form strong coordination with Li+ hinder Li + conduction, resulting in its low room temperature ionic conductivity (10 -6 -10 -7 S cm -1 ) limits its large-scale use. Summary of the invention

[0004] At present, most polymer electrolytes face complex ex-situ preparation methods. This technology is complicated to operate and easily causes poor contact at the cathode-electrolyte interface, making it difficult to apply to actual industrial production; the subsequent membrane preparation and solvent evaporation steps are not only complicated but also pollute the environment. Therefore, the development of new polymer matrices that match high-performance lithium batteries and their simple preparation methods are of great significance to the development and application of lithium-ion batteries.

[0005] The object of the present invention is to overcome the problems of low ionic conductivity and complex preparation methods of polymer electrolytes under room temperature conditions in the prior art, and to provide a polymer electrolyte, a preparation method and an application thereof, and a solid-state lithium battery and a preparation method thereof. The polymer electrolyte used as an electrolyte for a solid-state lithium battery has good interfacial stability and compatibility, high room-temperature ionic conductivity and lithium-ion transference number, and a wide electrochemical stability window.

[0006] To achieve the above object, in the first aspect of the present invention, a polymer electrolyte is provided. The polymer electrolyte includes a polymer matrix and a lithium salt, and the polymer matrix has the following structural unit: ;

[0007] wherein, n is 13 - 300.

[0008] In the second aspect of the present invention, a preparation method of a polymer electrolyte is provided. The preparation method includes: under an inert atmosphere, directly mixing β -propiolactone with a lithium salt for a polymerization reaction.

[0009] In the third aspect of the present invention, an application of the polymer electrolyte described in the first aspect in the preparation of a solid-state lithium battery is provided.

[0010] In the fourth aspect of the present invention, a solid-state lithium battery is provided. The solid-state lithium battery includes the polymer electrolyte described in the first aspect.

[0011] In the fifth aspect of the present invention, a preparation method of the solid-state lithium battery described in the fourth aspect is provided. The preparation method includes: (1) mixing β -propiolactone with a lithium salt to obtain an electrolyte precursor; (2) injecting the electrolyte precursor described in step (1) between a positive electrode and a negative electrode for in-situ polymerization.

[0012] Through the above technical solutions, the present invention has the following advantages: The present invention only needs to initiate the polymerization of β -propiolactone monomers by a lithium salt to prepare a polymer electrolyte, without adding additional catalysts or additives. The electrolyte has excellent lithium salt solubility, and the polar group ester group forms a weak coordination with Li + to help promote Li + conduction, improve the room-temperature ionic conductivity and ion transference number of the polymer electrolyte, thereby reducing the concentration polarization phenomenon at the interface during the cycling process, inhibiting the growth of lithium dendrites, and promoting the uniform deposition of Li +

[0013] The polymer electrolyte of the present invention used as an electrolyte for a solid-state lithium battery has good interfacial stability and compatibility, high room-temperature ionic conductivity (2.21×10​-4 S cm -1 -8.23×10 -4 S cm -1 ),(0.45 - 0.70) for the lithium ion transference number, and a wide electrochemical stability window (4.85 - 5.36 V), and can extend the battery service life.

[0014] The present invention prepares the electrolyte of the solid-state battery through a simple in-situ polymerization method. The electrolyte precursor solution has large fluidity. Injecting the precursor solution into the battery can extend the electrolyte / electrode interface to the gaps between electrode particles, forming a tight and well-compatible interfacial property. The process is simple and can be quantitatively produced. Detailed implementation manners

[0015] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0016] The present invention provides a polymer electrolyte, which includes a polymer matrix and a lithium salt. The polymer matrix has the following structural units: ;

[0017] wherein, n is 13 - 300.

[0018] The present invention only needs to initiate β the polymerization of β-propiolactone monomers to prepare the polymer electrolyte without adding additional catalysts or additives. This electrolyte has excellent lithium salt solubility. The polar group ester group forms a weak coordination with Li + which helps to promote the conduction of Li + , improve the room-temperature ionic conductivity and ion transference number of the polymer electrolyte, and further reduce the concentration polarization phenomenon at the interface during the cycling process, inhibit the growth of lithium dendrites, and promote the uniform deposition of Li + .

[0019] According to a preferred embodiment of the present invention, the mass ratio of the polymer matrix to the lithium salt in the polymer electrolyte is 1.5 - 20:1, for example, it can be 2.5:1, 6.5:1, 9.5:1, 10.5:1, 15:1, 17.5:1. By adopting the foregoing preferred scheme, the lithium salt solubility can be further improved to promote the conduction of Li +Conduction, improve the room-temperature ionic conductivity and ion transference number of the polymer electrolyte, thereby reducing the concentration polarization phenomenon at the interface during cycling, inhibiting the growth of lithium dendrites, and promoting Li + uniform deposition.

[0020] To further improve the solubility of the lithium salt and promote Li + conduction, improve the room-temperature ionic conductivity and ion transference number of the polymer electrolyte, thereby reducing the concentration polarization phenomenon at the interface during cycling, inhibiting the growth of lithium dendrites, and promoting Li + uniform deposition, according to a preferred embodiment of the present invention, the mass ratio of the polymer matrix to the lithium salt in the polymer electrolyte is 2.5 - 6.5:1, for example, it can be 3.5:1, 5:1.

[0021] According to a preferred embodiment of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium tetrafluoroborate, and lithium hexachlorophosphate. By adopting the foregoing preferred scheme, the room-temperature ionic conductivity and ion transference number of the polymer electrolyte can be further improved.

[0022] To further improve the room-temperature ionic conductivity and ion transference number of the polymer electrolyte, according to a preferred embodiment of the present invention, the lithium salt is lithium hexafluorophosphate.

[0023] In the present invention, as long as the object of the present application can be achieved, there is no special requirement for the number-average molecular weight of the polymer matrix. According to a preferred embodiment of the present invention, the number-average molecular weight of the polymer matrix is 1000 - 19000 g / mol.

[0024] The present invention provides a method for preparing the polymer electrolyte as described above. The preparation method includes: under an inert atmosphere, β -propiolactone and the lithium salt are directly mixed for a polymerization reaction.

[0025] The present invention prepares the polymer electrolyte by a simple polymerization method. The electrolyte precursor solution has high fluidity. Injecting the precursor solution into the battery can extend the electrolyte / electrode interface to the gaps between electrode particles, forming a tight and well-compatible interfacial property. Its process is simple and can be quantitatively produced.

[0026] According to a preferred embodiment of the present invention, the conditions of the polymerization reaction include: the temperature is 40 - 110°C; and / or the time is 2 - 12 h; and / or β the molar ratio of -propiolactone to the lithium salt is 3 - 36. By adopting the foregoing preferred scheme, the solubility of the lithium salt can be further enhanced, and the interfacial stability and compatibility of the electrolyte can be improved.

[0027] In order to further improve the solubility of lithium salts and enhance the interfacial stability and compatibility of electrolytes, according to a preferred embodiment of the present invention, the conditions for the polymerization reaction include: the temperature is 50 - 70 °C; and / or the time is 4 - 8 h; and / or β The molar ratio of β-propiolactone to lithium salt is 5 - 12.

[0028] In the present invention, as long as the object of the present application can be achieved, the inert atmosphere can be a conventional choice in the art. According to a preferred embodiment of the present invention, the inert atmosphere is an argon atmosphere and / or a nitrogen atmosphere, preferably an argon atmosphere.

[0029] In the present invention, as long as the object of the present invention can be achieved, there is no special requirement for the mixing method. According to a preferred embodiment of the present invention, the mixing method is magnetic stirring.

[0030] According to a preferred embodiment of the present invention, the magnetic stirring time is 2 - 8 h.

[0031] The present invention provides an application of the polymer electrolyte in the preparation of solid-state lithium batteries.

[0032] The polymer electrolyte of the present invention used as an electrolyte for solid-state lithium batteries has good interfacial stability and compatibility, high room-temperature ionic conductivity (2.21×10 -4 -8.23×10 -4 S cm -1 ), lithium-ion transference number (0.45 - 0.70), wide electrochemical stability window (4.85 - 5.36 V), and can extend the battery service life.

[0033] The present invention provides a solid-state lithium battery, which includes the polymer electrolyte described above.

[0034] According to a preferred embodiment of the present invention, the room-temperature ionic conductivity of the solid-state lithium battery is 2.21×10 -4 -8.23×10 -4 S cm -1 ; and / or the lithium-ion transference number of the solid-state lithium battery is 0.45 - 0.70; and / or the electrochemical stability window of the solid-state lithium battery is 4.85 - 5.36 V.

[0035] The present invention provides a preparation method of the solid-state lithium battery described above. The preparation method includes: (1) mixing β-propiolactone and lithium salt to obtain an electrolyte precursor; (2) injecting the electrolyte precursor obtained in step (1) between the positive electrode and the negative electrode for in-situ polymerization. β β-propiolactone and lithium salt to obtain an electrolyte precursor; (2) injecting the electrolyte precursor obtained in step (1) between the positive electrode and the negative electrode for in-situ polymerization.

[0036] The solid-state lithium battery of the present invention is prepared by an in-situ polymerization method, and its process is simple and can be mass-produced.

[0037] According to a preferred embodiment of the present invention, step (2) includes: under an inert atmosphere condition, infiltrating the electrolyte precursor into the separator and then placing it between the positive electrode and the negative electrode for polymerization reaction.

[0038] In the present invention, as long as the object of the present invention can be achieved, the separator can be a conventional choice in the art. According to a preferred embodiment of the present invention, the separator is at least one of a cellulose acetate separator, a PP film, and a glass cellulose film.

[0039] According to a preferred embodiment of the present invention, a standing treatment is performed before the polymerization reaction in step (2), and the standing treatment time is 6 - 24 h.

[0040] In the present invention: The assembly of the solid-state lithium-ion battery includes the following structure: positive electrode case - positive electrode material - polymer electrolyte - negative electrode material - stainless steel gasket - spring sheet - negative electrode case; Using the stainless steel gasket as the blocking electrode, an assembled button cell (SS|PPL-SPE|SS) is used to obtain electrochemical impedance data by means of EIS. According to the formula σ = L / SR, where L is the thickness of the polymer electrolyte, S is the area of the stainless steel sheet, and R is the measured impedance value, the room-temperature ionic conductivity is calculated; among them, the numerical values of each parameter in the above formula are defined according to the experimental test requirements.

[0041] Using a lithium metal sheet as the electrode, an assembled button cell (Li|PPL-SPE|Li) is used to obtain a steady-state current by means of chronoamperometry. According to the formula , I0 and I ss are the initial current and the steady-state current (A) respectively, R0 and R ss are the initial impedance and the steady-state impedance (Ω) respectively, and is the applied polarization voltage (V), and the lithium-ion transference number is calculated; among them, the numerical values of each parameter in the above formula are defined according to the experimental test requirements.

[0042] Using lithium metal as the negative electrode and a stainless steel gasket as the positive electrode, an assembled button cell (SS|PPL-SPE|Li) is used to measure the electrochemical stability window by cyclic voltammetry.

[0043] The present invention will be described in detail below through examples. Unless otherwise specified, the raw materials are all commercially available products.

[0044] Example 1 (1) In a glove box filled with argon, β-propiolactone (β-PL) (0.216 g, 3 mmol) and lithium hexafluorophosphate (0.040 g, 0.3 mmol) were added to a beaker and magnetically stirred for 5 h until homogeneous to obtain an electrolyte precursor.

[0045] (2) In a glove box filled with argon, using a cellulose acetate membrane as the separator, the electrolyte precursor was injected into the battery case to soak the cellulose acetate membrane, which was clamped between the electrodes to assemble a battery. It was left standing for 12 h, and then the battery was placed in an oven at 60 °C and heated for 6 h to initiate in-situ polymerization of the electrolyte, and a solid-state lithium battery was obtained after the reaction. The polymer matrix in the electrolyte has the following structural units: ;

[0046] In the formula, n is 190.

[0047] The polymer obtained by in-situ polymerization was characterized: 1 H NMR (400 MHz, CDCl3, δ, ppm): 4.30 (t, 2H), 2.61 (t, 2H); 13 C NMR (400 MHz, CDCl3, δ, ppm): 32 (-CH2CH2COO-), 59 (-OCH2-), 170 (-C=O); By analyzing the assembled battery, the room-temperature ionic conductivity, lithium-ion transference number, and electrochemical stability window of the polymer electrolyte were calculated, and the results are shown in Table 1.

[0048] Example 2 According to the method of Example 1, except that the feeding amount of β-propiolactone was changed so that the molar ratio of β-PL to the lithium salt was 5:1. By analyzing the assembled battery, the room-temperature ionic conductivity, lithium-ion transference number, and electrochemical stability window of the polymer electrolyte were calculated, and the results are shown in Table 1.

[0049] Example 3 According to the method of Example 1, except that the feeding amount of β-propiolactone was changed so that the molar ratio of β-PL to the lithium salt was 15:1. By analyzing the assembled battery, the room-temperature ionic conductivity, lithium-ion transference number, and electrochemical stability window of the polymer electrolyte were calculated, and the results are shown in Table 1.

[0050] Example 4 According to the method of Example 1, except that the feeding amount of β-propiolactone was changed so that the molar ratio of β-PL to the lithium salt was 25:1. By analyzing the assembled battery, the room-temperature ionic conductivity, lithium-ion transference number, and electrochemical stability window of the polymer electrolyte were calculated, and the results are shown in Table 1.

[0051] Example 5 According to the method of Example 1, the difference is that the separator is a PP membrane. By analyzing the assembled battery, the room temperature ionic conductivity, lithium ion transference number and electrochemical stability window of the polymer electrolyte are calculated, and the results are shown in Table 1.

[0052] Example 6 According to the method of Example 1, the difference is that the separator is a glass cellulose membrane. By analyzing the assembled battery, the room temperature ionic conductivity, lithium ion transference number and electrochemical stability window of the polymer electrolyte are calculated, and the results are shown in Table 1.

[0053] Example 7 According to the method of Example 1, the difference is that the lithium salt is lithium perchlorate. By analyzing the assembled battery, the room temperature ionic conductivity, lithium ion transference number and electrochemical stability window of the polymer electrolyte are calculated, and the results are shown in Table 1.

[0054] Example 8 According to the method of Example 1, the difference is that the lithium salt is lithium bis(oxalato)borate. By analyzing the assembled battery, the room temperature ionic conductivity, lithium ion transference number and electrochemical stability window of the polymer electrolyte are calculated, and the results are shown in Table 1.

[0055] Example 9 According to the method of Example 1, the difference is that the reaction temperature is 40 °C. By analyzing the assembled battery, the room temperature ionic conductivity, lithium ion transference number and electrochemical stability window of the polymer electrolyte are calculated, and the results are shown in Table 1.

[0056] Example 10 According to the method of Example 1, the difference is that the reaction temperature is 80 °C. By analyzing the assembled battery, the room temperature ionic conductivity, lithium ion transference number and electrochemical stability window of the polymer electrolyte are calculated, and the results are shown in Table 1.

[0057] Comparative Example 1 According to the method of Example 1, the difference is that no lithium salt is added. By analyzing the polymer electrolyte, in the case of no addition of lithium salt, β-propiolactone monomer cannot undergo in-situ polymerization.

[0058] Comparative Example 2 According to the method of Example 1, the difference is that the reaction temperature is 30 °C. By analyzing the polymer electrolyte, under the condition of 30 °C, β-propiolactone monomer cannot undergo in-situ polymerization catalyzed by lithium salt to obtain the polymer electrolyte.

[0059] Comparative Example 3 According to the method of Example 1, except that assembling the battery in an argon - protected glove box is changed to assembling the battery in air. Through the analysis of the polymer electrolyte, in air, β - propiolactone monomers cannot be in - situ polymerized under the initiation and catalysis of lithium salts to obtain the polymer electrolyte.

[0060] Comparative Example 4 According to the method of Example 1, except that the monomer is selected as valerolactone. Through the analysis of the polymer electrolyte, valerolactone monomers cannot be in - situ polymerized under the initiation and catalysis of lithium salts to obtain the polymer electrolyte.

[0061] Comparative Example 5 According to the method of Example 1, except that the monomer is selected as caprolactone. Through the analysis of the polymer electrolyte, caprolactone monomers cannot be in - situ polymerized under the initiation and catalysis of lithium salts to obtain the polymer electrolyte.

[0062] Table 1

[0063] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and all fall within the protection scope of the present invention.

Claims

1. A polymer electrolyte, characterized in that, The polymer electrolyte comprises a polymer matrix and a lithium salt, and the polymer matrix has the following structural units: ； Wherein, n is 13 - 300.

2. The polymer electrolyte according to claim 1, wherein, The mass ratio of the polymer matrix to the lithium salt in the polymer electrolyte is 1.5 - 20:

1.

3. The polymer electrolyte according to claim 2, wherein, The mass ratio of the polymer matrix to the lithium salt in the polymer electrolyte is 2.5 - 6.5:

1.

4. The polymer electrolyte according to any one of claims 1 - 3, wherein, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium tetrafluoroborate, and lithium hexachlorophosphate.

5. The polymer electrolyte according to claim 4, wherein, The lithium salt is lithium hexafluorophosphate.

6. The polymer electrolyte according to any one of claims 1 - 5, wherein, The number-average molecular weight of the polymer matrix is 1000 - 19000 g / mol.

7. A method for preparing the polymer electrolyte according to any one of claims 1 - 6, characterized in that, The preparation method includes: under an inert atmosphere, β directly mixing β-propiolactone with a lithium salt for a polymerization reaction.

8. The preparation method according to claim 7, wherein, The conditions of the polymerization reaction include: The temperature is 40 - 110 °C; and / or the time is 2 - 12 h; and / or β The molar ratio of β-propiolactone to the lithium salt is 3 - 36.

9. The preparation method according to claim 8, wherein, The conditions of the polymerization reaction include: the temperature is 50 - 70 °C; and / or the time is 4 - 8 h; and / or β The molar ratio of β-propiolactone to the lithium salt is 5-12.

10. The preparation method according to any one of claims 7 - 9, wherein, The inert atmosphere is an argon atmosphere and / or a nitrogen atmosphere, preferably an argon atmosphere.

11. The application of the polymer electrolyte according to any one of claims 1 - 6 in the preparation of a solid - state lithium battery.

12. A solid - state lithium battery, characterized in that, The solid electrolyte of the solid-state lithium battery comprises the polymer electrolyte described in any one of claims 1 - 6.

13. The solid - state lithium battery according to claim 12, wherein, The room-temperature ionic conductivity of the solid-state lithium battery is 2.21×10 -4 -8.23×10 -4 S cm -1 ; and / or The lithium ion transference number of the solid-state lithium battery is 0.45 - 0.70; and / or The electrochemical stability window of the solid-state lithium battery is 4.85 - 5.36 V.

14. A method for preparing the solid - state lithium battery according to claim 12 or 13, characterized in that, The preparation method includes: (1) Mix β -propiolactone with a lithium salt to obtain an electrolyte precursor; β ​ (2) Injecting the electrolyte precursor described in step (1) between the positive electrode and the negative electrode for in-situ polymerization.

15. The preparation method according to claim 14, wherein, Step (2) includes: under an inert atmosphere condition, infiltrating the electrolyte precursor into the separator and then placing it between the positive electrode and the negative electrode for a polymerization reaction.

16. The preparation method according to claim 15, wherein, The separator is at least one of a cellulose acetate separator, a PP membrane, and a glass fiber membrane, preferably a cellulose acetate separator.

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