Polymer electrolyte, method for preparing the same, and lithium metal battery

Abstract

The application provides a polymer electrolyte, a preparation method thereof and a lithium metal battery, and belongs to the technical field of lithium metal batteries.The polymer electrolyte comprises a polymer and a lithium salt distributed in the polymer, and monomers for synthesizing the polymer comprise at least one of silane acrylate compounds with structures as shown in Formula I, wherein R1, R2 and R3 comprise at least one of an alkyl group, an alkoxy group, a halogenated alkyl group and a siloxane group.The application selects specific types of monomers, so that the room temperature ionic conductivity of the polymer electrolyte exceeds 1*10 ‑4 S / cm, the electrochemical window exceeds 5V, and the polymer electrolyte also has good stability for matching high-voltage positive electrodes and lithium metal negative electrodes.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a polymer electrolyte, its preparation method, and a lithium metal battery. Background Technology

[0002] Lithium-ion rechargeable batteries have become a hot research topic in the energy storage field due to their high energy density and cycle performance. While lithium-ion batteries, when paired with lithium-ion metal anodes, can significantly increase energy density, the high reactivity of lithium metal makes it prone to continuous side reactions with traditional liquid electrolytes. This leads to a continuous thickening of the solid electrolyte interphase (SEI) film on the surface, increasing impedance with each cycle and causing rapid capacity decay. Furthermore, uneven lithium-ion deposition on the anode side can lead to lithium metal dendrite growth, increasing the risk of short circuits and even fires and explosions. Therefore, to reduce capacity decay during cycling and improve the safety of lithium-ion batteries, solid polymer electrolytes have emerged as a replacement for traditional liquid electrolytes.

[0003] However, current polymer electrolytes still have some problems, mainly including low room-temperature ionic conductivity, narrow electrochemical window, difficulty in simultaneously achieving high-voltage cathode stability and lithium metal anode stability, and poor contact between the polymer electrolyte and the electrode. For example, although the widely reported polyoxyethylene (PEO) polymer system has good lithium metal stability, its room-temperature ionic conductivity is only 10. -6 S / cm and at 3.9V (vs Li + Polymer electrolytes decompose at around 1000 L / L, making them unsuitable for high-voltage cathodes such as lithium nickel manganese cobalt oxide, lithium nickel manganese oxide, and lithium cobalt oxide. While current polymer systems such as polyacrylate (PMMA) and polyacrylonitrile (PAN) are relatively stable for high-voltage cathodes, their stability on the lithium metal anode side is poor, with numerous side reactions and difficulty in achieving long-term cycling. Furthermore, since most polymer electrolytes are currently prepared using non-in-situ methods, this not only results in poor contact between the polymer electrolyte and the electrode and high interfacial contact impedance, but also increases the difficulty of battery assembly. Therefore, there is an urgent need to develop a polymer electrolyte, its preparation method, and a lithium metal battery. This polymer electrolyte should have high room-temperature ionic conductivity, a wide electrochemical window, good stability for both high-voltage and low-voltage anodes, and good contact with the electrode. Summary of the Invention

[0004] This invention aims to at least partially address one of the technical problems in related technologies. To this end, this invention proposes a polymer electrolyte, its preparation method, and a lithium metal battery. The polymer electrolyte exhibits high room-temperature ionic conductivity and a wide electrochemical window, while also maintaining high-voltage performance at the positive electrode and stability at the lithium metal negative electrode. Furthermore, the preparation method improves the contact between the polymer electrolyte and the electrode.

[0005] This invention provides a polymer electrolyte comprising a polymer and a lithium salt distributed in the polymer, wherein the monomers for synthesizing the polymer comprise at least one silane acrylate compound with the structure shown in Formula I.

[0006]

[0007] R1, R2, and R3 include at least one of alkyl, alkoxy, haloalkyl, and siloxane.

[0008] The advantages and technical effects of the polymer electrolyte of the present invention are as follows:

[0009] (1) By selecting a compound with the structural formula of Formula I as a monomer, the present invention enables the room temperature ionic conductivity of the polymer electrolyte to exceed 1×10⁻⁶. -4 The S / cm has a wide electrochemical window, exceeding 5V. At the same time, the polymer electrolyte also has good stability when matched with high-voltage cathodes and lithium metal anodes.

[0010] (2) The polymer electrolyte of the present invention includes the lithium salt, which not only provides the polymer electrolyte with the required lithium ions, but also acts as an activator to induce the monomer to undergo a polymerization reaction.

[0011] Preferably, the silane acrylate compound comprises at least one selected from 3-trimethoxysilane propyl acrylate, (3-acryloyloxy)dimethylmethoxysilane, 2-acrylic acid 3-(diethoxymethylsilyl), 3-(methacryloyloxy)propyltrimethoxysilane, methacryloyloxypropyltris(trimethylsiloxane), acryloyloxyethoxytrimethylsilane, (3-acryloyloxy)methylbis(trimethylsiloxy)silane, 3-acryloyloxypropylmethyldichlorosilane, 2-(trimethylsiloxy)ethyl methacrylate, (3-acryloyloxypropyl)tris(trimethylsiloxy)silane, 3-methacryloyloxypropyldimethylethoxysilane, and 3-(triallylsilyl)propyl acrylate.

[0012] Preferably, the lithium salt comprises at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium oxalate borate, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0013] Preferably, the total mass of the polymer electrolyte is 100%, the polymer content is 40.4-51.5%, and the lithium salt content is 27.4-42.9%.

[0014] Preferably, the polymer electrolyte has a weight-average molecular weight of 10-20w.

[0015] This invention also provides a method for preparing a polymer electrolyte, comprising the following steps:

[0016] (1) First, the monomer, organic solvent and lithium salt are mixed to obtain a prepolymer, and then the prepolymer and thermal initiator are mixed to obtain the precursor liquid;

[0017] (2) The membrane is impregnated with the precursor solution, and then the positive electrode and the negative electrode are attached to both sides of the impregnated membrane respectively. The precursor solution is polymerized in situ to form the polymer electrolyte.

[0018] The advantages and technical effects of the preparation method of the polymer electrolyte of the present invention are as follows:

[0019] (1) Step (1) of the present invention is to dissolve the lithium salt in the monomer to prepare the prepolymer, and then mix the prepolymer and the thermal initiator to obtain the precursor liquid. This can ensure that the lithium salt can participate in the subsequent polymerization process, so that the lithium salt can be evenly distributed in the gel network, which helps the transfer of lithium ions in the polymer electrolyte.

[0020] (2) In step (2) of the present invention, after impregnating the separator with the precursor liquid, the positive and negative electrode sheets are directly attached to both sides of the separator, so that the precursor liquid can fully wet the separator, the positive electrode active material and the negative electrode active material, and the polymer electrolyte grows in situ between these three. Therefore, it can effectively improve the wettability between the electrolyte and the electrode, reduce the interfacial impedance between the two, reduce the overall internal resistance of the lithium metal battery, and simplify the battery assembly process.

[0021] Preferably, in step (1), the viscosity of the precursor liquid is 5-10 mP·s.

[0022] Preferably, in step (1), the organic solvent is ethylene glycol dimethyl ether; and / or the thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecanoyl peroxide, potassium persulfate, and ammonium persulfate.

[0023] Preferably, in step (1), the volume ratio of the monomer to the organic solvent is 1:0.5-1:1; and / or the concentration of the lithium salt in the prepolymer is 3-8 mol / L; and / or the mass of the thermal initiator is 0.1-0.5% of the mass of the prepolymer.

[0024] The present invention also provides a lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and a polymer electrolyte of the present invention or a polymer electrolyte obtained by the preparation method of the present invention.

[0025] The advantages and technical effects of the lithium metal battery of the present invention are as follows: the lithium metal battery of the present invention has excellent cycle stability and safety. Attached Figure Description

[0026] Figure 1 The image shows the LSV test results of the Li / Al asymmetric battery assembled from the polymer electrolyte prepared in Example 1.

[0027] Figure 2 The image shows the cycle life curve of the polymer electrolyte prepared in Example 1 in an NCM811 / Li battery.

[0028] Figure 3 The image shows the LSV test results of the Li / Al asymmetric battery assembled from the polymer electrolyte prepared in Example 2.

[0029] Figure 4 The image shows the cycle life curve of the polymer electrolyte prepared in Example 2 in an NCM811 / Li battery.

[0030] Figure 5 The image shows the LSV test results of the Li / Al asymmetric battery assembled from the polymer electrolyte prepared in Example 3.

[0031] Figure 6 The image shows the cycle life curve of the polymer electrolyte prepared in Example 3 in an NCM811 / Li battery.

[0032] Figure 7 The image shows the LSV test results of the Li / Al asymmetric battery assembled from the polymer electrolyte prepared in Example 4.

[0033] Figure 8 The image shows the cycle life curve of the polymer electrolyte prepared in Example 4 in an NCM811 / Li battery.

[0034] Figure 9 The image shows the LSV test results of the Li / Al asymmetric battery assembled from the polymer electrolyte prepared in Example 5.

[0035] Figure 10 The image shows the cycle life curve of the polymer electrolyte prepared in Example 5 in an NCM811 / Li battery. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0037] This invention provides a polymer electrolyte comprising a polymer and a lithium salt distributed in the polymer, wherein the monomers for synthesizing the polymer comprise at least one silane acrylate compound with the structure shown in Formula I.

[0038]

[0039] R1, R2, and R3 include at least one of alkyl, alkoxy, haloalkyl, and siloxane.

[0040] The polymer electrolyte of the present invention comprises a polymer network and a lithium salt distributed within the polymer network. Because the polymer network is prepared using monomers of a specific type containing both silicon-oxygen and acrylate functional groups, the polymer electrolyte of the present invention exhibits a lithium content exceeding 1 × 10⁻⁶. -4 It boasts a room-temperature ionic conductivity of S / cm and a wide electrochemical window exceeding 5V, while also achieving both high-voltage resistance to the cathode and stability against lithium metal.

[0041] Preferably, the silane acrylate compound includes at least one selected from 3-trimethoxysilane propyl acrylate, (3-acryloyloxy)dimethylmethoxysilane, 2-acrylate 3-(diethoxymethylsilyl), 3-(methacryloyloxy)propyltrimethoxysilane, methacryloyloxypropyltris(trimethylsiloxane), acryloyloxyethoxytrimethylsilane, (3-acryloyloxy)methylbis(trimethylsiloxy)silane, 3-acryloyloxypropylmethyldichlorosilane, (methacryloyloxyethyloxy)trimethylsilane, (3-acryloyloxypropyl)tris(trimethylsiloxy)silane, 3-methacryloyloxypropyldimethylethoxysilane, and 3-(triallylsilyl)propyl acrylate. The polymer electrolyte formed by polymerizing the above-mentioned silane acrylate compounds exhibits higher room temperature ionic conductivity and a wider electrochemical window. Furthermore, it possesses excellent antioxidant properties and can better bind to the high-voltage cathode.

[0042] The lithium salt not only provides the required lithium ions to the polymer electrolyte but also acts as an activator, inducing the polymerization reaction of the monomers. This invention does not impose specific limitations on the type of lithium salt, as long as it performs the above-mentioned functions. For example, the lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium oxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF6), and lithium tetrafluoroborate (LiBF4).

[0043] Preferably, based on the total mass of the polymer electrolyte (100%), the polymer has a mass fraction of 40.4-51.5%, and the lithium salt has a mass fraction of 27.4-42.9%. If the mass fraction of the polymer is too low and the lithium salt content is too high, it will be difficult to form a sufficient polymer network, which is detrimental to improving the room temperature ionic conductivity of the polymer electrolyte. Similarly, if the mass fraction of the polymer is too high and the lithium salt content is too low, it will also be detrimental to the transfer of lithium ions in the polymer electrolyte.

[0044] Preferably, the weight-average molecular weight of the polymer electrolyte is 10-20 W. If the weight-average molecular weight of the polymer electrolyte is too small, the room-temperature ionic conductivity of the polymer electrolyte decreases, which is detrimental to the transfer of lithium ions in the polymer electrolyte. If the weight-average molecular weight of the polymer electrolyte is too large, the interfacial wettability between the polymer electrolyte and the electrode deteriorates, which is not conducive to reducing the contact resistance between the electrolyte and the electrode, resulting in an increase in the overall internal resistance of the lithium metal battery.

[0045] This invention also provides a method for preparing a polymer electrolyte, comprising the following steps:

[0046] (1) First, the monomer, organic solvent and lithium salt are mixed to obtain a prepolymer, and then the prepolymer and thermal initiator are mixed to obtain the precursor liquid;

[0047] (2) The membrane is impregnated with the precursor solution, and then the positive electrode and the negative electrode are attached to both sides of the impregnated membrane respectively. The precursor solution is polymerized in situ to form the polymer electrolyte.

[0048] In step (1) of the preparation method of the present invention, the lithium salt is dissolved in the monomer to obtain the prepolymer, and then the prepolymer and the thermal initiator are mixed to obtain the precursor solution. This ensures that the lithium salt can participate in the subsequent polymerization process, so that the lithium salt can be uniformly distributed in the gel network, which helps the transfer of lithium ions in the polymer electrolyte. In addition, since the precursor solution in step (2) can fully wet the separator, the positive electrode active material particles and the negative electrode lithium metal, the polymer electrolyte can grow in situ among these three. Therefore, it can effectively improve the wettability between the electrolyte and the electrode, reduce the interfacial impedance between them, reduce the overall internal resistance of the lithium metal battery, and simplify the battery assembly process.

[0049] Although the silane acrylate compounds can achieve bulk self-polymerization, their polymerization energy barrier is high, resulting in a slow polymerization rate at room temperature and making overall control difficult. Therefore, it is necessary to introduce the thermal initiator into the precursor solution to facilitate effective control of the polymerization reaction.

[0050] The preparation method of the present invention does not have specific limitations on the specific type of the thermal initiator, as long as it can achieve the above-mentioned effects. For example, the thermal initiator may include at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecanoyl peroxide, potassium persulfate, and ammonium persulfate. Preferably, the thermal initiator is azobisisobutyronitrile. Azobisisobutyronitrile is more soluble in the monomer, thereby better initiating the polymerization reaction of the monomer.

[0051] With the addition of the thermal initiator, the precursor solution is prone to polymerization in step (1), which is not conducive to the formation of a polymer electrolyte with good wettability between the electrodes in step (2). Therefore, it is necessary to introduce an appropriate amount of the organic solvent into the precursor solution to suppress the polymerization rate in step (1). In addition, although the lithium salt is soluble in the monomer, the viscosity of the precursor obtained after the lithium salt is dissolved is high, which is not conducive to obtaining a uniform polymer electrolyte film in step (2). In particular, high concentrations of lithium salt will greatly increase the viscosity of the precursor. Therefore, it is also necessary to introduce the organic solvent into the precursor solution in step (1) to appropriately reduce the viscosity of the precursor solution and facilitate the obtaining of a uniform polymer electrolyte film.

[0052] Preferably, in step (1), the viscosity of the precursor solution is 5-10 mP·s. If the viscosity of the precursor solution is too low, the adhesion to the membrane is weak, which is not conducive to the in-situ growth of a polymer electrolyte membrane with strong adhesion in step (2). If the viscosity of the precursor solution is too high, it is also not conducive to the in-situ growth of a uniform polymer electrolyte membrane in step (2).

[0053] The preparation method of this invention does not have specific limitations on the type of organic solvent, as long as it can achieve the above-mentioned effects. For example, the organic solvent may include at least one of ethers, cyclic carbonates, linear carbonates, lactones, and lactams. Preferably, the organic solvent is ethylene glycol dimethyl ether. Ethylene glycol dimethyl ether has better compatibility with lithium metal anodes and is beneficial to lithium ion migration in the polymer.

[0054] In step (1), by controlling the proportions of each reactant, the effective occurrence of the polymerization reaction can be ensured, guaranteeing a suitable reaction rate and product conversion rate, which helps to reduce costs and increase efficiency. A detailed analysis follows:

[0055] Preferably, in step (1), the volume ratio of the monomer to the organic solvent is 1:0.5-1:1, for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, etc. If the volume ratio of the monomer to the organic solvent is too small, the excess organic solvent will have an excessive inhibitory effect on the polymerization reaction, which is not conducive to the smooth polymerization reaction of the precursor liquid in step (2). If the volume ratio of the monomer to the organic solvent is too large, it may lead to excessive viscosity of the precursor liquid, which is also not conducive to the formation of a uniform polymer electrolyte film in step (2).

[0056] Preferably, in step (1), the concentration of the lithium salt in the prepolymer is 3-8 mol / L, such as 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, etc. If the concentration of the lithium salt is too low, it is not conducive to improving the room temperature ionic conductivity of the polymer electrolyte. If the concentration of the lithium salt is too high, the proportion of polymer in the polymer electrolyte is too low, and a sufficient polymer network cannot be formed, which is also not conducive to improving the room temperature ionic conductivity of the polymer electrolyte.

[0057] Preferably, in step (1), the mass of the thermal initiator is 0.1-0.5% of the mass of the prepolymer, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc. If the mass of the thermal initiator is too small compared to the mass of the prepolymer, it will be detrimental to reducing the self-polymerization energy barrier of the silane acrylate compound and will be detrimental to in-situ growth at room temperature. If the mass of the thermal initiator is too large compared to the mass of the prepolymer, its effect on reducing the self-polymerization energy barrier of the silane acrylate compound will be insignificant, and it will also increase production costs.

[0058] Regarding the specific method of impregnating the diaphragm with the precursor solution in step (2), the preparation method of the present invention does not have any particular limitations, as long as complete impregnation can be ensured. For example, the precursor solution can be dripped onto the diaphragm, or the diaphragm can be impregnated in the precursor solution.

[0059] The polymerization time in step (2) depends on the temperature conditions. If the polymerization is carried out at room temperature, it requires 6-12 hours. If the polymerization is carried out at 40-70℃, the reaction rate is greatly accelerated, and the polymerization time is only 0.5-2 hours. The degree of polymerization can be preliminarily judged by the state of the precursor liquid in the reagent bottle. For example, when there is no flowing liquid, the polymerization reaction is basically complete, and the polymerization time can be determined accordingly.

[0060] The present invention also provides a lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and a polymer electrolyte of the present invention or a polymer electrolyte obtained by the preparation method of the present invention. The lithium metal battery exhibits excellent cycle stability and safety.

[0061] Preferably, the positive electrode active material used in the positive electrode sheet is LiNi. 0.8 Co 0.1 Mn 0.1 O2, the negative electrode active material used is lithium metal sheet. The polymer electrolyte has high compatibility with the above-mentioned positive and negative electrodes, which helps to improve the compatibility between the electrodes.

[0062] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0063] Example 1

[0064] A method for preparing a polymer electrolyte and a lithium metal battery includes the following steps:

[0065] (1) Place 1 mL of 3-trimethoxysilane propylene acrylate (monomer) in a culture bottle. Add 0.5 mL of ethylene glycol dimethyl ether (organic solvent) to the 3-trimethoxysilane propylene acrylate (monomer) to reduce the viscosity of the precursor solution under high-concentration lithium salt dissolution conditions. Add lithium difluorosulfonyl imide (LiFSI) to the mixture of 3-trimethoxysilane propylene acrylate (monomer) and ethylene glycol dimethyl ether (organic solvent), and stir magnetically at room temperature for 10 min to fully dissolve the lithium salt, obtaining a prepolymer with a concentration of 3 mol / L of lithium difluorosulfonyl imide (LiFSI). Add 0.3% (by mass) of azobisisobutyronitrile (a thermal initiator) to the prepolymer, and stir magnetically at room temperature for 10 min to completely dissolve the thermal initiator, thus obtaining a precursor solution with a viscosity of 6 mP·s.

[0066] (2) 100 μL of precursor solution was added to the PE separator, and the impregnated separator was attached to the surface of the aluminum foil. Then, a Li metal sheet was placed on top of the PE separator and a coin cell was assembled. The cell was allowed to stand at room temperature of 25°C for 12 h for in-situ growth, thus obtaining a Li / Al asymmetric cell including a polymer electrolyte. The Li / Al asymmetric cell was subjected to LSV testing.

[0067] (3) Add 100 μL of precursor solution to the PE membrane, and then attach the wetted membrane to the NCM811 positive electrode (LiNi). 0.8 Co 0.1 Mn 0.1 The O2 surface was then covered, and a Li metal sheet was placed on top of the PE separator to assemble a coin cell. In-situ growth was performed by allowing it to stand at 25°C for 12 hours, resulting in an NCM811 / Li battery containing a polymer electrolyte. High-voltage cathode testing was then conducted on the NCM811 / Li battery.

[0068] (4) 200 μL of precursor solution was added to the GF / A separator, and the impregnated separator was attached to the surface of a stainless steel sheet. Then, another identical stainless steel sheet was placed on top of the separator and a coin cell was assembled. The cell was allowed to stand at room temperature (25°C) for 12 hours for in-situ growth, thus obtaining a symmetrical cell. The room temperature ionic conductivity of the symmetrical cell was then tested.

[0069] The polymer electrolyte obtained by the above preparation method comprises 51.5% polymer and 27.4% lithium salt distributed in the polymer, based on the total mass of the polymer electrolyte as 100%. The monomer for synthesizing the polymer is 3-trimethoxysilane propylene acrylate, and the weight average molecular weight of the polymer electrolyte is 15-20w.

[0070] Figure 1 The image shows the LSV test results of the Li / Al asymmetric cell prepared in Example 1. Figure 1 It can be seen that within the scanning range of 3-4.5V, the current passing through is on the order of 10. -6 A indicates that the polymer electrolyte prepared in Example 1 has good high-voltage resistance and can be matched and applied to high-voltage cathode materials. Figure 2 The high-voltage cathode test results for the NCM811 / Li battery prepared in Example 1 are shown in the figure. The test voltage range was 2.7-4.4V, the test rate was 0.2C charge-discharge, the capacity retention rate after 150 cycles was 80%, and the average coulombic efficiency exceeded 99.3%. The room temperature ionic conductivity values ​​of the polymer electrolyte prepared in Example 1 are listed in Table 1, and its lithium-ion conductivity is greater than 1×10⁻⁶. -4 S / cm.

[0071] Example 2

[0072] Compared with Example 1, the preparation method of this embodiment increases the concentration of lithium bisfluorosulfonylimide (LiFSI) in the prepolymer to 6 mol / L, the concentration of the precursor solution is 8 mP·s, and other conditions are exactly the same as in Example 1.

[0073] The polymer electrolyte obtained by the above preparation method comprises 47.1% polymer and 33.4% lithium salt distributed in the polymer, based on the total mass of the polymer electrolyte as 100%. The monomer for synthesizing the polymer is 3-trimethoxysilane propylene acrylate, and the weight-average molecular weight of the polymer electrolyte is 15-18w.

[0074] Figure 3 The image shows the LSV test results of the Li / Al asymmetric cell prepared in Example 2. Figure 3 It can be seen that within the 3-5V scanning range, the current passing through is on the order of 10. -6 A indicates that the polymer electrolyte prepared in Example 2 has good high-voltage resistance and can be matched and applied to high-voltage cathode materials. Figure 4 The high-voltage cathode test results of the NCM811 / Li battery prepared in Example 2 are shown in the figure. The test voltage range was 2.7-4.4V, the test rate was 0.2C charge-discharge, the capacity retention rate after 280 cycles was 80%, and the average coulombic efficiency exceeded 99.8%. The room temperature ionic conductivity values ​​of the polymer electrolyte prepared in Example 2 are listed in Table 1, and its lithium-ion conductivity is greater than 1×10⁻⁶. -4 S / cm.

[0075] Example 3

[0076] Compared with Example 2, the preparation method of this embodiment replaces 3-trimethoxysilane propylene acrylate with (3-acryloyloxy)dimethylmethoxysilane, the concentration of the precursor solution is 7 mP·s, and other conditions are exactly the same as in Example 2.

[0077] The polymer electrolyte obtained by the above preparation method comprises 44.1% polymer and 35.4% lithium salt distributed in the polymer, based on the total mass of the polymer electrolyte as 100%. The monomer for synthesizing the polymer is (3-acryloyloxy)dimethylmethoxysilane, and the weight average molecular weight of the polymer electrolyte is 15-18w.

[0078] Figure 5 The image shows the LSV test results of the Li / Al asymmetric cell prepared in Example 3. Figure 5 It can be seen that within the 3-5V scanning range, the current passing through is on the order of 10. -6 A indicates that the polymer electrolyte prepared in Example 3 has good high-voltage resistance and can be matched and applied to high-voltage cathode materials. Figure 6The high-voltage cathode test results of the NCM811 / Li battery prepared in Example 3 are shown in the figure. The test voltage range was 2.7-4.4V, the test rate was 0.2C charge-discharge, the capacity retention rate after 210 cycles was 80%, and the average coulombic efficiency exceeded 99.5%. The room temperature ionic conductivity values ​​of the polymer electrolyte prepared in Example 3 are listed in Table 1, and its lithium-ion conductivity is greater than 1×10⁻⁶. -4 S / cm.

[0079] Example 4

[0080] Compared with Example 2, the preparation method of this embodiment replaces 3-trimethoxysilane propylene acrylate with 2-acrylic acid 3-(diethoxymethylsilyl) acrylate, the concentration of the precursor solution is 7.5 mP·s, and other conditions are exactly the same as in Example 2.

[0081] The polymer electrolyte obtained by the above preparation method comprises 45.9% polymer and 34.2% lithium salt distributed in the polymer, based on the total mass of the polymer electrolyte as 100%. The monomer for synthesizing the polymer is 2-acrylic acid 3-(diethoxymethylsilyl) and the weight average molecular weight of the polymer electrolyte is 15-18w.

[0082] Figure 7 The image shows the LSV test results of the Li / Al asymmetric cell prepared in Example 4. Figure 7 It can be seen that within the scanning range of 3-4.8V, the current passing through is on the order of 10. -6 A indicates that the polymer electrolyte prepared in Example 4 has good high-voltage resistance and can be matched and applied to high-voltage cathode materials. Figure 8 The high-voltage cathode test results of the NCM811 / Li battery prepared in Example 4 are shown in the figure. The test voltage range was 2.7-4.4V, the test rate was 0.2C charge-discharge, the capacity retention rate after 200 cycles was 80%, and the average coulombic efficiency exceeded 99.5%. The room temperature ionic conductivity values ​​of the polymer electrolyte prepared in Example 4 are listed in Table 1, and its lithium-ion conductivity is greater than 1×10⁻⁶. -4 S / cm.

[0083] Example 5

[0084] Compared with Example 2, the preparation method of this embodiment increases the concentration of lithium bisfluorosulfonylimide (LiFSI) in the prepolymer to 8 mol / L and the concentration of the precursor solution to 9.8 mP·s, while other conditions are exactly the same as in Example 2.

[0085] The polymer electrolyte obtained by the above preparation method comprises 40.4% polymer and 42.9% lithium salt distributed in the polymer, based on the total mass of the polymer electrolyte as 100%. The monomer for synthesizing the polymer is 3-trimethoxysilane propylene acrylate, and the weight-average molecular weight of the polymer electrolyte is 13-18w.

[0086] Figure 9 The image shows the LSV test results of the Li / Al asymmetric cell prepared in Example 5. Figure 9 It can be seen that within the scanning range of 0-5.5V, the current passing through is on the order of 10 -6 A indicates that the polymer electrolyte prepared in Example 5 has good high-voltage resistance and can be matched and applied to high-voltage cathode materials. Figure 10 The graph shows the high-voltage cathode test results of the NCM811 / Li battery prepared in Example 5. The test voltage range was 2.7-4.4V, the test rate was 0.2C charge-discharge, the capacity retention rate after 280 cycles was 80%, and the average coulombic efficiency exceeded 99.8%. The room-temperature ionic conductivity values ​​of the polymer electrolyte prepared in Example 5 are listed in Table 1, and its lithium-ion conductivity is greater than 1×10⁻⁶. -4 S / cm.

[0087] Example 6

[0088] Compared with Example 1, the preparation method of this embodiment is the same as that of Example 1, except that 2 mL of ethylene glycol dimethyl ether (organic solvent) is added, the concentration of the precursor solution is 3 mP·s, and after assembling the battery, it is allowed to stand at a constant temperature of 60°C for 1 h for in-situ growth. Other conditions are exactly the same as those of Example 1.

[0089] The polymer electrolyte obtained by the above preparation method comprises 42.5% polymer and 22.6% lithium salt distributed in the polymer, based on the total mass of the polymer electrolyte as 100%. The monomer for synthesizing the polymer is 3-trimethoxysilane propylene acrylate, and the weight-average molecular weight of the polymer electrolyte is 10-12w.

[0090] The room temperature ionic conductivity values ​​of the polymer electrolyte prepared in Example 6 are listed in Table 1, and its lithium-ion conductivity is greater than 1 × 10⁻⁶. -4 S / cm. However, if the precursor solution is left to stand at room temperature (25°C) for 12 hours, polymerization cannot occur. This indicates that when the volume of the organic solvent is higher than the volume of the monomer, the inhibitory effect on the polymerization rate of the silane acrylate compound is too great, and the precursor solution is unlikely to spontaneously form a polymer electrolyte at room temperature.

[0091] Comparative Example 1

[0092] A method for preparing a polymer electrolyte and a lithium metal battery includes the following steps:

[0093] (1) Place 1 mL of n-butyl acrylate (monomer) in a culture bottle. Add 0.5 mL of ethylene glycol dimethyl ether (organic solvent) to the n-butyl acrylate (monomer). Add lithium bis(fluorosulfonyl)imide (LiFSI) to the mixture of n-butyl acrylate (monomer) and ethylene glycol dimethyl ether (organic solvent), and stir magnetically at room temperature for 10 min to fully dissolve the lithium salt, obtaining a prepolymer with a LiFSI (lithium salt) concentration of 3 mol / L. Add 0.3% (by mass) of azobisisobutyronitrile (thermal initiator) to the prepolymer, and stir magnetically at room temperature for 10 min to completely dissolve the thermal initiator, thus obtaining the precursor solution.

[0094] (2) 100 μL of precursor solution was added to the PE separator, and the impregnated separator was attached to the surface of the aluminum foil. Then, a Li metal sheet was placed on top of the PE separator and a coin cell was assembled. The cell was allowed to stand at room temperature of 25°C for 12 h for in-situ growth, thus obtaining a Li / Al asymmetric cell including a polymer electrolyte. The Li / Al asymmetric cell was subjected to LSV testing.

[0095] (3) 100 μL of precursor solution was added to the PE separator, and the impregnated separator was attached to the surface of the positive electrode (NCM811). Then, a Li metal sheet was placed on top of the PE separator and a coin cell was assembled. The cell was allowed to stand at room temperature (25°C) for 12 hours for in-situ growth, thus obtaining the NCM811 / Li battery containing the polymer electrolyte. High-voltage positive electrode testing was performed on the NCM811 / Li battery.

[0096] (4) 200 μL of precursor solution was added to the GF / A separator, and the impregnated separator was attached to the surface of a stainless steel sheet. Then, another identical stainless steel sheet was placed on top of the separator and a coin cell was assembled. The cell was allowed to stand at room temperature (25°C) for 12 hours for in-situ growth, thus obtaining a symmetrical cell containing a polymer electrolyte. The room temperature ionic conductivity of the symmetrical cell was then tested.

[0097] Because the monomer structure used in Comparative Example 1 does not contain silicon-oxygen functional groups, the conductivity of lithium ions in the polymer network is low (<1×10⁻⁶). -4 Therefore, the polymer electrolyte of Comparative Example 1 is not suitable for the preparation and assembly of Li / NCM811 batteries (S / cm).

[0098] Comparative Example 2

[0099] Compared to Comparative Example 1, the preparation method of this comparative example replaced n-butyl acrylate with vinyltris(2-methoxyethoxy)silane. All other conditions remained identical to Comparative Example 1. After obtaining the precursor solution, it was found that polymerization failed after standing at room temperature (25°C) for 12 hours; similarly, it failed to polymerize after standing at 60°C for 1 hour. The experiment demonstrates that vinyltris(2-methoxyethoxy)silane, i.e., when the monomer lacks the acrylate functional group, cannot spontaneously form a polymer electrolyte at room temperature, nor can it form a polymer electrolyte under heating conditions. Therefore, the monomer of Comparative Example 2 is not suitable for the preparation and assembly of in-situ polymeric electrolytes.

[0100] Comparative Example 3

[0101] The preparation method of this comparative example is the same as that of Example 1, except that ethylene glycol dimethyl ether (an organic solvent) is not added. In this comparative example, it was found that the precursor solution underwent polymerization during the mixing and stirring stage, indicating that the polymerization barrier of the silane acrylate compound is greatly reduced under the thermal initiator environment, and it easily forms cross-linked polymers at room temperature. Therefore, without the addition of an organic solvent to the precursor solution to suppress the polymerization rate of the silane acrylate compound, the precursor solution of this comparative example is not suitable for the preparation and assembly of in-situ polymeric electrolytes, and the problem of wetting contact on the positive / negative electrode sides cannot be solved.

[0102] Comparative Example 4

[0103] A polymer electrolyte and lithium metal battery, the preparation method includes the following steps:

[0104] (1) Dissolve 60w molecular weight polyethylene oxide (PEO) powder in acetonitrile solution and add a certain amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to make [EO:Li] = 8:1. Stir magnetically until PEO and lithium salt are completely dissolved to obtain PEO-based polymer precursor solution.

[0105] (2) 200 μL of PEO-based polymer precursor solution was dispersed on a polytetrafluoroethylene (PTFE) plate. After evaporating and removing the acetonitrile solution by heat treatment at 60 °C, the PEO polymer electrolyte film was attached to the surface of an aluminum foil. Subsequently, a Li metal sheet was placed on top of the separator, and a coin cell was assembled to obtain a Li / Al asymmetric battery including a PEO-based polymer electrolyte film. It should be noted that the PEO polymer film is usually prepared by casting, and due to the large molecular weight of PEO used (60w), it is not suitable for dispersion on a PE film. The LSV test results of the Li / Al asymmetric battery showed that the PEO-based polymer electrolyte began to decompose at around 3.9 V in the 0-5.5 V scan range, indicating that this comparative example is not suitable for lithium metal batteries with high-voltage cathodes.

[0106] Table 1. Lithium-ion conductivity test results of Examples 1-6 and Comparative Example 1

[0107] Lithium-ion conductivity Example 1 <![CDATA[3×10 -4 S / cm]]> Example 2 <![CDATA[8×10 -4 S / cm]]> Example 3 <![CDATA[6.1×10 -4 S / cm]]> Example 4 <![CDATA[5.5×10 -4 S / cm]]> Example 5 <![CDATA[7×10 -4 S / cm]]> Example 6 <![CDATA[6.7×10 -4 S / cm]]> Comparative Example 1 <![CDATA[5.3×10 -5 S / cm]]>

[0108] The polymeric electrolytes of Examples 1-6 exhibit good stability when matched with high-voltage cathode materials, as well as stability against lithium metal. Linear sweep voltammetry (LSV) testing of Li / Al asymmetric cells also shows that the polymeric electrolytes of Examples 1-6 have a wide electrochemical window, exceeding 5V. Simultaneously, the room-temperature ionic conductivity of the polymeric electrolytes of Examples 1-6 exceeds 10. -4 S / cm, higher than the room temperature ionic conductivity of most polymer electrolytes currently available (10). -6 (S / cm); By assembling coin cells, it was found that the NCM811 / Li coin cell still retained 80% of its capacity after 150-280 cycles in the voltage range of 2.7-4.4V, indicating that it has good high-voltage cycling performance. Therefore, the polymer electrolyte of the present invention has broad application prospects in lithium metal batteries.

[0109] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0110] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium metal battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, It also includes a polymer electrolyte, which comprises a polymer and a lithium salt distributed in the polymer, wherein the monomers for synthesizing the polymer are at least one of silane acrylate compounds with the structure shown in Formula I. ， R1, R2, and R3 each independently include at least one of alkyl, alkoxy, haloalkyl, and siloxane; the polymer has a mass fraction of 40.4-51.5% based on the total mass of the polymer electrolyte as 100%.

2. The lithium metal battery according to claim 1, characterized in that, The silane acrylate compound includes at least one of 3-trimethoxysilane propyl acrylate, (3-acryloyloxy)dimethylmethoxysilane, (3-acryloyloxy)methylbis(trimethylsiloxy)silane, 3-acryloyloxypropylmethyldichlorosilane, and (3-acryloyloxypropyl)tri(trimethylsiloxy)silane.

3. The lithium metal battery according to claim 1, characterized in that, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium oxalate borate, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

4. The lithium metal battery according to claim 1, characterized in that, Based on the total mass of the polymer electrolyte as 100%, the mass fraction of the lithium salt is 27.4-42.9%.

5. The lithium metal battery according to claim 1, characterized in that, The polymer electrolyte has a weight-average molecular weight of 10-20w.

6. The lithium metal battery according to claim 1, characterized in that, The preparation method of the polymer electrolyte includes the following steps: (1) First, the monomer, organic solvent and lithium salt are mixed to obtain a prepolymer, and then the prepolymer and thermal initiator are mixed to obtain a precursor liquid; (2) The membrane is impregnated with the precursor solution, and then the positive electrode and the negative electrode are attached to both sides of the impregnated membrane respectively. The precursor solution is polymerized in situ to form the polymer electrolyte.

7. The lithium metal battery according to claim 6, characterized in that, In step (1), the viscosity of the precursor liquid is 5-10 mP·s.

8. The lithium metal battery according to claim 6, characterized in that, In step (1), the organic solvent is ethylene glycol dimethyl ether; and / or the thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecanoyl peroxide, potassium persulfate, and ammonium persulfate.

9. The lithium metal battery according to claim 6 or 8, characterized in that, In step (1), the volume ratio of the monomer to the organic solvent is 1:0.5-1:1; and / or, the concentration of the lithium salt in the prepolymer is 3-8 mol / L; and / or, the mass of the thermal initiator is 0.1-0.5% of the mass of the prepolymer.

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