Polymer additives and electrolytes and lithium metal battery applications

Abstract

The application relates to a polymer additive, an electrolyte and a lithium metal battery application, which has lipophilic and hydrophilic groups and can self-assemble to form vesicles in the electrolyte, and the chemical structural formula is as follows: the copolymer prepared by the application can self-assemble to form vesicles in the electrolyte, can induce lithium metal to present an equiaxed crystal morphology, and then develop into a dense columnar crystal morphology, realize flat and dense deposition of the lithium metal, maximally ensure the integrity of the electrode, and then improve the conductivity of the electrode and the service life of the full battery.

Description

Technical Field

[0001] This invention relates to a technology in the field of lithium battery manufacturing, specifically a polymer additive, its electrolyte, and its application in lithium metal batteries. Background Technology

[0002] In recent years, lithium metal anodes have been considered key anode materials for next-generation high-energy-density batteries due to their very high theoretical specific capacity (3860 mAh / g) and the lowest electrochemical potential (3.04 V compared to the standard hydrogen electrode). However, when lithium metal is used as an anode, the growth of lithium dendrites can lead to several problems. On the one hand, it can cause lithium anode pulverization, increasing the battery's internal resistance and reducing its cycle performance. On the other hand, dendrites piercing the separator can cause internal short circuits, potentially leading to safety accidents such as combustion and explosion. Although recent studies have shown that optimizing electrolytes (Nat. Mater. 2022, 21, 445-454), substrate modification (Nat. Energy 2020, 5, 299-308), artificial SEI (Nat. Mater. 2019, 18, 384-389), and controlling temperature (Science 2018, 359, 1513-1516) and pressure (Nat. Energy 2021, 6, 987-994) can, to some extent, help suppress lithium dendrite growth and regulate the deposition morphology of lithium metal, maintaining the integrity of the electrode during repeated lithium metal deposition / dissolution remains a significant challenge. Summary of the Invention

[0003] This invention addresses the problem of lithium dendrite growth during lithium deposition in lithium metal batteries, which remains unresolved in existing technologies. It proposes a polymer additive, its electrolyte, and its application in lithium metal batteries. The resulting copolymer can self-assemble into vesicles in the electrolyte, inducing lithium metal to exhibit an equiaxed crystal morphology, which then develops into a dense columnar crystal morphology. This achieves smooth and dense deposition of lithium metal, maximizing electrode integrity and thus improving electrode conductivity and the lifespan of the entire battery.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a polymer additive having lipophilic and hydrophilic groups, capable of self-assembling into vesicles in an electrolyte, and its chemical structural formula is as follows:

[0006]

[0007] Where: x:y = 0:100~150:100, y:z = 100:10~0:10, k = 30~150, m = 10~50, n = 5~25, x, y, z, k, m, and n are all natural numbers, and R1 and R2 are each an independent hydrocarbon group with 1 to 20 carbon atoms.

[0008] This invention relates to a method for preparing the above-mentioned polymer additive, which is obtained by free radical polymerization of short-chain alkyl polyethylene glycol methacrylate, long-chain alkyl polyethylene glycol methacrylate, and polyurethane methacrylate analogs.

[0009] The chemical structural formula of the short-chain alkyl polyethylene glycol methacrylate is as follows: Wherein: k is an integer from 30 to 150, R1 is a hydrocarbon group with 1 to 20 carbon atoms, preferably R1 is methyl or ethyl.

[0010] The chemical structural formula of the long-chain alkyl polyethylene glycol methacrylate is as follows: Wherein: m is an integer from 10 to 50, R2 is a hydrocarbon group with 1 to 20 carbon atoms, preferably, R2 is dodecyl or hexadecyl.

[0011] The chemical structural formula of the polyurethane methacrylate analog is as follows:

[0012] Where: n is an integer from 5 to 25.

[0013] The preparation method specifically includes:

[0014] Step 1) Dissolve methyl polyethylene glycol and triethylamine in a solvent, add methacryloyl chloride dropwise and react under stirring. The resulting reaction product is extracted, filtered and rotary evaporated to obtain methyl polyethylene glycol methacrylate.

[0015] The reaction is carried out at a temperature of 0–50°C for a time of 1–20 h.

[0016] Step 2) Dissolve dodecyl polyethylene glycol and triethylamine in another solvent, add methacryloyl chloride dropwise and react under stirring. The resulting reaction product is extracted, filtered and rotary evaporated to obtain dodecyl polyethylene glycol methacrylate.

[0017] The reaction is carried out at a temperature of 0–50°C for a time of 1–20 h.

[0018] Step 3) Dissolve isophorone diisocyanate, diethylene glycol, and triethylenediamine catalyst in another solvent, add ethyl isocyanate methacrylate dropwise and react under stirring conditions. The resulting reaction product is obtained by rotary evaporation to obtain polyurethane methacrylate.

[0019] The reaction is carried out at a temperature of 30–80°C for a time of 1–30 hours.

[0020] Step 4) Dissolve the methyl polyethylene glycol methacrylate, dodecyl polyethylene glycol methacrylate, polyurethane methacrylate and photoinitiator obtained in steps 1)-3) in solvents respectively, mix them evenly, and react them under ultraviolet light to obtain polymer additives.

[0021] The solvent is dichloromethane, trichloromethane, tetrachloromethane, tetrahydrofuran, or a combination thereof.

[0022] The photoinitiator is 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone or 2-dimethylamino-2-benzyl-1-[4-(4-morpholinyl)phenyl]-1-butanone.

[0023] The amount of the photoinitiator is 2-10 wt% of the monomer;

[0024] This invention relates to an application of the above-mentioned polymer additive in the preparation of an electrolyte, specifically: dispersing the polymer additive in the electrolyte and stirring at room temperature for 1 to 4 hours to obtain a vesicle electrolyte.

[0025] The amount of the polymer additive used is 0.1 to 15 wt% of the total mass.

[0026] The vesicle electrolyte comprises an organic solvent, a lithium salt, and a polymer additive, wherein: the organic solvent is diethyl carbonate (DEC), fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), or a combination thereof; and the lithium salt is lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), or a combination thereof.

[0027] This invention relates to a lithium metal battery, comprising: a positive electrode, a negative electrode, a separator, and the aforementioned vesicle electrolyte.

[0028] The negative electrode is preferably a lithium foil with a thickness of 10 to 100 μm.

[0029] Technical effect

[0030] The copolymer of this invention possesses lipophilic and hydrophilic groups and is capable of conducting lithium ions. As an additive in lithium metal battery electrolytes, it can self-assemble into vesicles within the electrolyte, thereby obtaining a vesicle electrolyte that induces the deposition of lithium metal in a dendrite-free equiaxed crystal form, which then develops into a dense columnar crystal morphology. This achieves dense deposition of lithium metal, which helps to suppress the pulverization of the lithium metal anode and maximizes the integrity of the lithium metal electrode, thus significantly improving the cycle life of the full battery under this vesicle electrolyte system. The preparation method of this invention is simple, can be mass-produced, and is inexpensive. Attached Figure Description

[0031] Figure 1 This is a diagram of the vesicle structure formed by the self-assembly of the copolymer of the present invention dispersed in diethyl carbonate (DEC);

[0032] Figure 2 The images show a comparison of the morphology of lithium copper batteries deposited at different current densities in Example 1 and Comparative Example 1.

[0033] In the figure: ad is 0.1 mA / cm 2 1mA / cm 2 5mA / cm 2 10mA / cm 2 Deposition morphology of lithium metal in the vesicle electrolyte mentioned in Example 1 at current density; h1 and h2 are 0.1 mA / cm². 2 1mA / cm 2 5mA / cm 2 10mA / cm 2 Deposition morphology of lithium metal in the electrolyte mentioned in Comparative Example 1 at current density;

[0034] Figure 3 The graph shows a comparison of the cycle performance of the ternary NCM811 cathode systems in Example 1 and Comparative Example 1.

[0035] Figure 4 For the lithium copper batteries in Example 3 and Comparative Example 3, at 0.5 mA / cm 2 Comparison of morphology of current density deposition;

[0036] In the figure: a and b are SEM planar and cross-sectional views of the deposits in the vesicle electrolyte mentioned in Example 3, respectively; c and d are SEM planar and cross-sectional views of the deposits in the electrolyte mentioned in Comparative Example 3, respectively.

[0037] Figure 5 This is a SEM cross-sectional image of spherical crystals of lithium metal deposited in a vesicle electrolyte. Detailed Implementation

[0038] Example 1

[0039] This embodiment relates to a novel polymer additive and its electrolyte, and the preparation of a battery based on the electrolyte, including the following steps:

[0040] Step 1) Dissolve 5.0 g of polyethylene glycol monomethyl ether with a molecular weight of 5000 and 0.3 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 0.3 g of methacryloyl chloride dropwise to the solution and stir at 35 °C for 4 h. Transfer the solution obtained after the reaction to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain methyl polyethylene glycol methacrylate by rotary evaporation.

[0041] Step 2) Dissolve 5.0 g of dodecyl polyethylene glycol with a molecular weight of 1300 and 0.8 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 0.8 g of methacryloyl chloride dropwise to the solution and stir at 35 °C for 4 h. Transfer the resulting solution to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain dodecyl polyethylene glycol methacrylate by rotary evaporation.

[0042] Step 3) Dissolve 10g of isophorone diisocyanate, 5.3g of diethylene glycol, and 5mg of triethylenediamine catalyst in 100ml of tetrahydrofuran. Add 0.8g of ethyl isocyanate methacrylate dropwise. Under argon protection and stirring at 70℃, react for 12h and then stop heating. During the reaction, keep the mixture under reflux. After cooling to room temperature, remove tetrahydrofuran and unreacted substances by rotary evaporation to obtain polyurethane methacrylate.

[0043] Step 4) Dissolve 1.6g of methyl polyethylene glycol methacrylate, 1.6g of dodecyl polyethylene glycol methacrylate and 1.0g of polyurethane methacrylate in 20ml of anhydrous dichloromethane and stir for 2h. Then add 0.21g of photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone and mix. React at room temperature under ultraviolet light for 4h. After removing the solvent by rotary evaporation, the polymer additive is obtained.

[0044] In this embodiment, the chemical structure of the additive prepared is x:y:z = 31:110:33, and n = 10.

[0045] Step 5) The electrolyte formulation is: 0.2 mol / L LiPF6, 0.2 mol / L LiBF4, 0.8 mol / L LiDFOB, and the organic solvent is fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 1:2, with 1 wt% of the above polymer additives added.

[0046] Step 6) Uses a 20μm thick lithium foil, a Celgard 2400 separator, and an areal load of 4mAh / cm². 2 A full cell was assembled using a ternary NCM811 cathode and the aforementioned vesicle electrolyte containing polymer additives, with the electrolyte-to-cathode capacity ratio controlled at 2.65 gAh. -1 Long-term cycling tests were conducted at a rate of 0.2C. A lithium-copper battery was assembled using 50μm thick lithium foil, a Celgard 2400 separator, copper foil, and the aforementioned vesicle electrolyte containing polymer additives. A 0.1mAh / cm³ electrolyte was deposited at different current densities. 2 The capacity.

[0047] Example 2

[0048] This embodiment relates to a novel polymer additive and its electrolyte, and the preparation of a battery based on the electrolyte, including the following steps:

[0049] Step 1) Dissolve 10.0g of polyethylene glycol monomethyl ether with a molecular weight of 2000 and 1.5g of triethylamine in 50ml of dichloromethane and stir for 1h. Then add 1.5g of methacryloyl chloride dropwise to the solution and stir at 40℃ for 4h. Transfer the solution obtained after the reaction to a separatory funnel, add 50ml of 0.5mol / L sodium bicarbonate aqueous solution, shake for 10min and let stand for 8h. Take the lower organic phase and obtain methyl polyethylene glycol methacrylate by rotary evaporation.

[0050] Step 2) Dissolve 5.0 g of hexadecyl polyethylene glycol with a molecular weight of 1500 and 1.0 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 0.8 g of methacryloyl chloride dropwise to the solution and stir at 35 °C for 5 h. Transfer the resulting solution to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain hexadecyl polyethylene glycol methacrylate by rotary evaporation.

[0051] Step 3) Dissolve 5g of isophorone diisocyanate, 2.7g of diethylene glycol, and 10mg of triethylenediamine catalyst in 100ml of tetrahydrofuran. Add 0.8g of ethyl isocyanate methacrylate dropwise. Under argon protection and stirring at 80℃, react for 20h and then stop heating. During the reaction, keep the mixture under reflux. After cooling to room temperature, remove tetrahydrofuran and unreacted substances by rotary evaporation to obtain polyurethane methacrylate.

[0052] Step 4) Dissolve 2.0g of methyl polyethylene glycol methacrylate, 1.2g of hexadecyl polyethylene glycol methacrylate and 1.0g of polyurethane methacrylate in 20ml of anhydrous dichloromethane and stir for 2h. Then add 0.17g of 1-hydroxycyclohexylphenyl ketone and mix. React at room temperature under ultraviolet light for 4h. After removing the solvent by rotary evaporation, the polymer additive is obtained.

[0053] In this embodiment, the chemical structure of the additive prepared is x:y:z = 93:73:33, and n = 5.

[0054] Step 5) The electrolyte formulation is: 0.2 mol / L LiPF6, 0.2 mol / L LiBF4, 0.8 mol / L LiDFOB, and the organic solvent is fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 1:2, with 2 wt% of the above polymer additives added.

[0055] Step 6) Uses a 20μm thick lithium foil, a Celgard 2400 separator, and an areal load of 1.67mAh / cm². 2 A full cell was assembled using a lithium cobalt oxide cathode and the aforementioned vesicle electrolyte containing polymer additives, with the electrolyte-to-cathode capacity ratio controlled at 4.58 gAh. -1 Long cycles were performed at a 0.5C rate.

[0056] Example 3

[0057] This embodiment relates to a novel polymer additive and its electrolyte, and the preparation of a battery based on the electrolyte, including the following steps:

[0058] Step 1) Dissolve 5.0 g of polyethylene glycol monomethyl ether with a molecular weight of 5000 and 0.3 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 0.3 g of methacryloyl chloride dropwise to the solution and stir at 35 °C for 4 h. Transfer the solution obtained after the reaction to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain methyl polyethylene glycol methacrylate by rotary evaporation.

[0059] Step 2) Dissolve 5.0 g of dodecyl polyethylene glycol with a molecular weight of 1300 and 0.8 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 0.8 g of methacryloyl chloride dropwise to the solution and stir at 40 °C for 4 h. Transfer the resulting solution to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain dodecyl polyethylene glycol methacrylate by rotary evaporation.

[0060] Step 3) Dissolve 10g of isophorone diisocyanate, 5.3g of diethylene glycol, and 5mg of triethylenediamine catalyst in 100ml of tetrahydrofuran. Add 0.8g of ethyl isocyanate methacrylate dropwise. Under argon protection and stirring at 70℃, react for 12h and then stop heating. During the reaction, keep the mixture under reflux. After cooling to room temperature, remove tetrahydrofuran and unreacted substances by rotary evaporation to obtain polyurethane methacrylate.

[0061] Step 4) Dissolve 1.6g of methyl polyethylene glycol methacrylate, 1.6g of dodecyl polyethylene glycol methacrylate and 1.0g of polyurethane methacrylate in 20ml of anhydrous dichloromethane and stir for 2h. Then add 0.4g of photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone and mix. React at room temperature under ultraviolet light for 4h. After removing the solvent by rotary evaporation, the polymer additive is obtained.

[0062] In this embodiment, the chemical structure of the additive prepared is x:y:z = 31:110:33, and n = 10.

[0063] Step 5) The electrolyte formulation is: 1 mol / L LiPF6, the organic solvent is ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, and 1 wt% of the above polymer additive is added.

[0064] Step 6) Uses a 50μm thick lithium foil, a Celgard 2400 separator, and an areal load of 4mAh / cm². 2 A full cell was assembled using a ternary NCM811 cathode and the aforementioned vesicle electrolyte containing polymer additives, with the electrolyte-to-cathode capacity ratio controlled at 2.65 gAh. -1 Long-term cycling tests were conducted at a rate of 0.5C. A lithium-copper battery was assembled using 50μm thick lithium foil, a Celgard 2400 separator, copper foil, and the aforementioned vesicle electrolyte containing polymer additives. The battery was tested at 0.5mA / cm². 2 Deposition was carried out at a current density.

[0065] Example 4

[0066] This embodiment relates to a novel polymer additive and its electrolyte, and the preparation of a battery based on the electrolyte, including the following steps:

[0067] Step 1) Dissolve 5.0 g of polyethylene glycol monoethyl ether with a molecular weight of 2000 and 0.3 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then, add 0.3 g of methacryloyl chloride dropwise to the solution and stir at 35 °C for 4 h. Transfer the resulting solution to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min, and let stand for 8 h. Take the lower organic phase and obtain ethyl polyethylene glycol methacrylate by rotary evaporation.

[0068] Step 2) Dissolve 20g of isophorone diisocyanate, 10.6g of diethylene glycol, and 10mg of triethylenediamine catalyst in 100ml of tetrahydrofuran. Add 0.8g of ethyl isocyanate methacrylate dropwise. Under argon protection and stirring at 50℃, react for 12h and then stop heating. During the reaction, keep the mixture under reflux. After cooling to room temperature, remove tetrahydrofuran and unreacted substances by rotary evaporation to obtain polyurethane methacrylate.

[0069] Step 3) Dissolve 1.6g of ethyl polyethylene glycol methacrylate and 1.0g of polyurethane methacrylate in 20ml of anhydrous dichloromethane and stir for 2h. Then add 0.2g of photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone and mix. React under ultraviolet light at room temperature for 4h. After removing the solvent by rotary evaporation, the polymer additive is obtained.

[0070] In this embodiment, the chemical structure of the additive prepared has x:z = 80:33 and n = 20.

[0071] Step 4) The electrolyte formulation is: 0.2 mol / L LiPF6, 0.2 mol / L LiBF4, 0.8 mol / L LiDFOB, and the organic solvent is fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 1:2, with 10 wt% of the above polymer additives added.

[0072] Step 5) Uses a 100μm thick lithium foil, a Celgard 2400 separator, and an areal load of 4mAh / cm². 2 A full cell was assembled using a ternary NCM811 cathode and the aforementioned vesicle electrolyte containing polymer additives, with the electrolyte-to-cathode capacity ratio controlled at 5 gAh. -1 Long-term cycling was performed at a rate of 0.5C. A lithium-copper battery was assembled using 100μm thick lithium foil, a Celgard 2400 separator, copper foil, and the aforementioned vesicle electrolyte containing polymer additives. Deposition at different current densities was carried out at 0.5mAh / cm³. 2 The capacity.

[0073] Example 5

[0074] This embodiment relates to a novel polymer additive and its electrolyte, and the preparation of a battery based on the electrolyte, including the following steps:

[0075] Step 1) Dissolve 3.0 g of polyethylene glycol monoethyl ether with a molecular weight of 3000 and 0.4 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 0.3 g of methacryloyl chloride dropwise to the solution and stir at 35 °C for 4 h. Transfer the resulting solution to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain ethyl polyethylene glycol methacrylate by rotary evaporation.

[0076] Step 2) Dissolve 5.0 g of dodecyl polyethylene glycol with a molecular weight of 2000 and 1.0 g of triethylamine in 50 ml of dichloromethane and stir for 1 h. Then add 1.2 g of methacryloyl chloride dropwise to the solution and stir at 40 °C for 5 h. Transfer the resulting solution to a separatory funnel, add 50 ml of 0.5 mol / L sodium bicarbonate aqueous solution, shake for 10 min and let stand for 8 h. Take the lower organic phase and obtain dodecyl polyethylene glycol methacrylate by rotary evaporation.

[0077] Step 3) Dissolve 10g of isophorone diisocyanate, 5.3g of diethylene glycol, and 5mg of triethylenediamine catalyst in 100ml of tetrahydrofuran. Add 0.53g of ethyl isocyanate methacrylate dropwise. Under argon protection and stirring at 70℃, react for 12h and then stop heating. During the reaction, keep the mixture under reflux. After cooling to room temperature, remove tetrahydrofuran and unreacted substances by rotary evaporation to obtain polyurethane methacrylate.

[0078] Step 4) Dissolve 2.0g of ethyl polyethylene glycol methacrylate, 1.0g of dodecyl polyethylene glycol methacrylate and 1.5g of polyurethane methacrylate in 20ml of anhydrous dichloromethane and stir for 2h. Then add 0.3g of photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (HMPP) and mix. React at room temperature under ultraviolet light for 4h. After removing the solvent by rotary evaporation, the polymer additive is obtained.

[0079] In this embodiment, the chemical structure of the additive prepared is x:y:z = 63:47:33, and n = 15.

[0080] Step 5) The electrolyte formulation is: 0.2 mol / L LiPF6, 0.2 mol / L LiBF4, 0.8 mol / L LiDFOB, and the organic solvent is fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 1:2, with 4 wt% of the above polymer additives added.

[0081] Step 6) Uses a 20μm thick lithium foil, a Celgard 2400 separator, and an areal load of 4mAh / cm². 2 A full cell was assembled using a ternary NCM811 cathode and the aforementioned vesicle electrolyte containing polymer additives, with the electrolyte-to-cathode capacity ratio controlled at 2 gAh. -1 Long-term cycling tests were conducted at 1C rate. A lithium-copper battery was assembled using 50μm thick lithium foil, a Celgard 2400 separator, copper foil, and the aforementioned vesicle electrolyte containing polymer additives. A 0.1mAh / cm³ electrolyte was deposited at different current densities. 2 The capacity.

[0082] Comparative Example 1

[0083] The electrolyte and lithium metal battery were obtained according to the method in Example 1, except that 0 wt% electrolyte was used in this comparative example, i.e. no polymer additives were added.

[0084] like Figure 2 The figure shows a comparison of the morphology of lithium copper batteries deposited at different current densities in Example 1 and Comparative Example 1. As can be seen from the figure, the lithium metal in the vesicle electrolyte prepared by this technology exhibits dendrite-free equiaxed crystal deposition; while in the electrolyte without polymer additives, the lithium metal exhibits dendritic deposition.

[0085] Figure 3 The figure shows a comparison of the cycle performance of the ternary NCM811 cathode systems in Example 1 and Comparative Example 1. As can be seen from the figure, the high-load ternary NCM811 full cell assembled with the vesicle electrolyte system prepared by this technology has a better cycle life, and the capacity retention rate is 80% after 160 cycles. In contrast, the battery without polymer additives experienced rapid capacity decay after only 20 cycles.

[0086] Comparative Example 2

[0087] The electrolyte and lithium metal battery were obtained according to the method in Example 2, except that 0 wt% electrolyte was used in this comparative example, i.e. no polymer additives were added.

[0088] Comparative Example 3

[0089] The electrolyte and lithium metal battery were obtained according to the method in Example 3, except that 0 wt% electrolyte was used in this comparative example, i.e. no polymer additives were added.

[0090] like Figure 4 As shown, the lithium copper batteries in Example 3 and Comparative Example 3 operate at 0.5 mA / cm². 2The morphology comparison diagram of the current density deposition is shown in the figure. As can be seen from the figure, the lithium metal in the vesicle electrolyte prepared by this technology exhibits a dendrite-free, dense columnar crystal deposition, which maximizes the integrity of the electrode. In contrast, in the electrolyte without the addition of vesicle polymer additives, the lithium metal exhibits a loose and porous dendritic deposition, resulting in a large electrode volume expansion.

[0091] The technical effects of this invention include:

[0092] 1) This invention uses a simple ultraviolet light polymerization method to polymerize three monomers: methyl polyethylene glycol methacrylate, dodecyl polyethylene glycol methacrylate, and polyurethane methacrylate to obtain a copolymer. This copolymer can conduct lithium ions and has strong adhesion to lithium metal. In addition, the copolymer has oleophilic and hydrophilic groups and can self-assemble into vesicles in the electrolyte.

[0093] 2) In this invention, the copolymer prepared above is dispersed in an electrolyte. This polymer can self-assemble in the electrolyte to form a vesicle electrolyte. When this electrolyte is used to assemble a lithium metal battery with lithium metal, a positive electrode, and a separator, the vesicles induce the lithium metal to exhibit an equiaxed crystal morphology during lithium deposition, which then develops into a dense columnar crystal morphology. This achieves smooth and dense deposition of lithium metal, which helps to suppress the pulverization of the lithium metal negative electrode, maximizing the integrity of the electrode and thus improving the lifespan of the full battery. Even under harsh conditions such as low electrolyte-to-positive electrode capacity ratio and low negative-to-positive electrode areal capacity ratio, the vesicle electrolyte prepared using this method still exhibits superior cycle life in full batteries assembled with lithium metal sheets as the negative electrode and ternary NCM811 as the positive electrode.

[0094] In summary, the vesicle electrolyte prepared by this method can induce lithium metal to form spherical crystal deposition, which then evolves into a dense columnar crystal morphology without lithium dendrite growth. Thanks to its dense and flat deposition morphology, the high-load NCM811 full cell assembled using this vesicle electrolyte system exhibits superior cycle performance and service life.

[0095] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A polymer additive, characterized in that, Its chemical structural formula is: ， Where: x:y=0:100~150:100, y:z=100:10~0:10, k=30~150, m=10~50, n=5~25, x, y, z, k, m, n are all natural numbers, and R1 and R2 are each an independent hydrocarbon group with 1~20 carbon atoms.

2. A method for preparing the polymer additive of claim 1, characterized in that, It is obtained by free radical polymerization of short-chain alkyl polyethylene glycol methacrylate, long-chain alkyl polyethylene glycol methacrylate and polyurethane methacrylate analogs; The chemical structural formula of the short-chain alkyl polyethylene glycol methacrylate is as follows: Where: k is an integer from 30 to 150, and R1 is methyl or ethyl; The chemical structural formula of the long-chain alkyl polyethylene glycol methacrylate is as follows: Where: m is an integer from 10 to 50, and R2 is dodecyl or hexadecyl; The chemical structural formula of the polyurethane methacrylate analog is as follows: , where n is an integer from 5 to 25.

3. The method according to claim 2, characterized in that, specifically include: Step 1) Dissolve methyl polyethylene glycol and triethylamine in a solvent, add methacryloyl chloride dropwise and react under stirring. The resulting reaction product is extracted, filtered and rotary evaporated to obtain methyl polyethylene glycol methacrylate. Step 2) Dissolve dodecyl polyethylene glycol and triethylamine in another solvent, add methacryloyl chloride dropwise and react under stirring. The resulting reaction product is extracted, filtered and rotary evaporated to obtain dodecyl polyethylene glycol methacrylate. Step 3) Dissolve isophorone diisocyanate, diethylene glycol, and triethylenediamine catalyst in another solvent, add ethyl isocyanate methacrylate dropwise and react under stirring conditions. The resulting reaction product is obtained by rotary evaporation to obtain polyurethane methacrylate. Step 4) Dissolve the methyl polyethylene glycol methacrylate, dodecyl polyethylene glycol methacrylate, polyurethane methacrylate and photoinitiator obtained in steps 1)-3) in solvents respectively, mix them evenly, and react them under ultraviolet light to obtain polymer additives.

4. The method according to claim 3, characterized in that, The solvent is dichloromethane, trichloromethane, tetrachloromethane, tetrahydrofuran, or a combination thereof; the photoinitiator is 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, or 2-dimethylamino-2-benzyl-1-[4-(4-morpholinyl)phenyl]-1-butanone.

5. An application of a polymer additive prepared by the method described in claim 1 or any one of claims 2-4, characterized in that, It is used to prepare electrolytes, specifically by dispersing polymer additives in electrolytes and stirring at room temperature for 1-4 hours to obtain vesicle electrolytes.

6. The application according to claim 5, characterized in that, The amount of the polymer additive is 0.1 to 15 wt% of the total mass.

7. A lithium metal battery, characterized in that, include: Positive electrode, negative electrode, membrane, and vesicle electrolyte prepared according to the application of claim 5 or 6.

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