Electropolymerized construction of polymer electrolyte, preparation method thereof and lithium battery

Abstract

The application provides a polymer electrolyte constructed by electro-polymerization, a preparation method thereof and a lithium battery, and the preparation method comprises the following steps: S1, uniformly mixing an alkali metal salt, an electrolyte solvent, a positive electrode additive and a polymer monomer to obtain an electrolyte precursor; S2, injecting the electrolyte precursor between a positive electrode and a negative electrode to assemble a battery; and S3, performing a pre-circulation process of "constant current charging-constant voltage charging-constant current discharging" on the battery to obtain the polymer electrolyte; wherein the polymer monomer comprises an electro-polymerizable cyclosiloxane compound, and the voltage of the constant voltage charging is 4.5-4.7 V. In the application, the electro-polymerizable cyclosiloxane compound is subjected to ring-opening polymerization at a high voltage, and cooperates with the positive electrode additive lithium difluoro(oxalato)borate and the like, so that a dense and stable polymer electrolyte layer is constructed in situ at the positive electrode interface at a high voltage, solvent oxidation and electrode side reactions are significantly inhibited, and the battery still maintains excellent cycle stability and safety at a high voltage.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery fabrication technology, and in particular to an electropolymerized polymer electrolyte, its preparation method, and a lithium battery. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles, portable electronic devices, and high-energy-density energy storage systems, high-voltage lithium-ion batteries capable of stable operation above 4.5-4.7 V have become a key technological requirement. High-nickel layered ternary cathode materials (such as NCM811 and NCA), with their high specific capacity and high operating voltage, are driving battery energy density breakthroughs exceeding 300 Wh / kg. -1 The core path. However, despite the significant capacity expansion potential of cathode materials, current commercial electrolyte systems struggle to meet their high-voltage requirements, becoming a major bottleneck restricting the further development of high-energy-density batteries. Currently widely used carbonate-based electrolytes exhibit good stability below 4.2 V, but when the voltage increases to the 4.3-4.6 V range, both the solvent and lithium salt undergo significant electrochemical oxidation and decomposition. The fundamental reason is that carbonate solvents readily undergo electron extraction at high-potential cathode surfaces; simultaneously, high-nickel cathodes release lattice oxygen in a deeply delithiated state, further raising the interface potential and creating a strongly oxidizing environment that accelerates electrolyte degradation. Solvent decomposition produces active species such as CO2, carboxylates, and free radicals. LiPF6 also decomposes into corrosive substances like PF5 and HF at high voltages, continuously interacting with the cathode surface and escalating interfacial side reactions.

[0003] During this process, a stable CEI film is difficult to form on the cathode surface. Instead, an uneven, loose, and easily reconfigurable interfacial layer is generated, allowing the electrolyte to continuously penetrate into the cathode particles, inducing structural degradation. Secondary particle microcracks gradually expand under repeated stress, while transition metal dissolution and migration also occur simultaneously, leading to capacity decay, increased polarization, and a continuous accumulation of safety risks. Furthermore, the intense interfacial reactions induced by high voltage weaken the layered structure within the cathode, promoting the formation of local rock salt phases and further reducing lithium-ion transport efficiency. Therefore, the inherent oxidation intolerance of carbonate-based electrolytes under high voltage is the fundamental problem limiting the high-voltage performance of high-nickel ternary cathodes. Based on this, polymer electrolytes, due to their ability to reduce the content of oxidizable solvents, improve interfacial mechanical stability, and to some extent construct a stable protective layer, are considered an important direction for solving high-voltage interfacial instability. While commonly used in-situ thermosetting or photocuring polymer electrolytes can improve electrolyte stability, they still suffer from problems in practical applications, such as uneven interface coverage, the need to undergo high-temperature catalytic environment before cycling, and lack of interfacial selectivity in polymerization reactions. These issues prevent them from effectively blocking early interfacial instability processes and make it difficult to achieve directional passivation of high-energy active sites, thus limiting their application potential in the 4.5-4.7 V high-voltage range.

[0004] Therefore, a more direct and effective response to high voltage is needed, so that the activation of relevant protection mechanisms can truly target the problems caused by high voltage, thus becoming a better strategy for building a high voltage stability system. Summary of the Invention

[0005] In view of this, the present invention proposes an electropolymerized polymer electrolyte, its preparation method, and a lithium battery. The present invention utilizes electropolymerizable cyclosiloxane compounds to undergo ring-opening polymerization at high voltage, synergistically with cathode additives, to form a stable and dense inorganic-organic composite polymer network. This solves the technical problems of existing polymer electrolytes being susceptible to oxidation at high voltages of 4.5-4.7 V, and the structural collapse of high-nickel layered cathode materials at high cutoff voltages, leading to rapid capacity decay due to the dissolution of highly oxidized transition metal ions. The invention achieves in-situ construction of a dense and stable polymer electrolyte layer at the high-voltage cathode interface, significantly suppressing solvent oxidation and electrode side reactions, and improving the battery's excellent cycle stability and safety even at high voltages.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a polymer electrolyte constructed by electropolymerization, comprising the following steps: S1, mixing an alkali metal salt, an electrolyte solvent, a positive electrode additive and a polymer monomer to obtain an electrolyte precursor; S2. Encapsulate the electrolyte precursor to obtain a battery; S3. Perform a pre-cycle process of "constant current charging - constant voltage charging - constant current discharging" on the battery to obtain the polymer electrolyte; The polymer monomer includes electropolymerizable cyclosiloxane compounds, and the constant voltage charging voltage is between 4.5 and 4.7V.

[0007] Based on the above technical solutions, the electropolymerizable cyclosiloxane compound further includes one or two of the following: decamethylcyclopentasiloxane, octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane.

[0008] Based on the above technical solutions, the electropolymerizable cyclic siloxane compound further includes one or two of the following: a mixture of polydimethylsiloxane and cyclic siloxane, and a mixture of cyclic methylsiloxane and cyclic polysiloxane.

[0009] The aforementioned cyclosiloxane compounds possess a stable Si-O-Si cyclic structure, maintaining electrochemical inertness under conventional voltages. However, they can be selectively activated under high voltage conditions of 4.5-4.7 V to undergo controlled ring-opening polymerization, thereby constructing a highly antioxidant polymer network in situ at the cathode interface. The resulting Si–O–Si framework structure not only exhibits excellent chemical stability but also effectively anchors high-oxidation-state transition metal ions, suppressing interfacial side reactions. By introducing cyclosiloxane precursors with different substituents, the polymerization reactivity and interfacial compatibility can be further controlled, which is beneficial for improving the cycle stability and safety of the battery under high voltages.

[0010] Based on the above technical solution, step S1 further includes adding and mixing an alkali metal salt, an electrolyte solvent, a positive electrode additive and a polymer monomer in sequence to obtain an electrolyte precursor.

[0011] Based on the above technical solutions, the electrolyte solvent further includes one or more of ethylene carbonate, propylene carbonate, butene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and dipropyl carbonate.

[0012] Based on the above technical solution, step S2 further includes: injecting the electrolyte precursor between the positive electrode and the negative electrode, so that the electrolyte precursor fully wets the positive electrode, the negative electrode and the separator, and then encapsulating it to obtain the battery.

[0013] Based on the above technical solutions, the pre-cycle process of "constant current charging-constant voltage charging-constant current discharging" further includes: A1. At a first current density, the battery is charged with constant current until the voltage of the battery reaches a preset charging cutoff voltage, wherein the charging cutoff voltage is 4.5~4.7 V. A2. Maintain the charging cutoff voltage and perform constant voltage charging on the battery until the charging current decays to the second current density; A3. Discharge the battery at a constant current density until the battery voltage drops to a preset discharge cutoff voltage. Repeat the cycle A1~A3 2~5 times.

[0014] Based on the above technical solution, further, the first current density is 0.05C~0.2C, the second current density is 0.005C~0.02C, and the discharge cutoff voltage is 2.5V~3.0V.

[0015] Based on the above technical solutions, the positive electrode additive further includes at least one of lithium difluorooxalate borate, lithium difluorooxalate borate, and lithium tetrafluoroborate.

[0016] Based on the above technical solution, the mass ratio of the positive electrode additive to the polymer monomer is further 1:(0.69~6.9).

[0017] When the amount of cathode additive is too low, the number of effective interfacial regulation species (such as BF3-type Lewis acids and inorganic / organic composite products containing BO structures) generated by its decomposition under high voltage conditions is insufficient, making it difficult to form a continuous and dense protective layer on the cathode surface. On the one hand, it cannot effectively inhibit the oxidative decomposition of the electrolyte under high voltage, leading to an aggravation of interfacial side reactions; on the other hand, the insufficient number of Lewis acids also makes it difficult to fully trigger the ring-opening polymerization of cyclosiloxane precursors, resulting in a loose polymer network structure and a limited number of active sites, thereby weakening its anchoring ability for high oxidation state transition metal ions and harmful byproducts, ultimately manifesting as insufficient cycle stability and high voltage tolerance.

[0018] When the amount of cathode additive is too high, its extensive decomposition under high voltage will generate excessive Lewis acidic species and inorganic salt byproducts (such as LiF, boron-containing amorphous phases, etc.), which can easily form an excessively thick and non-uniform interface layer on the cathode surface. On the one hand, this interface layer will significantly increase the lithium-ion transport impedance and affect the electrode kinetic performance; on the other hand, an excessively strong Lewis acid environment may induce non-selective rapid polymerization or localized excessive cross-linking of cyclosiloxanes, leading to an increase in polymer network structure defects, and even causing localized gelation or phase separation of the electrolyte, which is detrimental to the long-term stability of the interface.

[0019] Based on the above technical solutions, the polymer monomer further accounts for 5-20% of the total volume of the electrolyte precursor.

[0020] By introducing polymerizable cyclosiloxane monomers into the electrolyte system and synergistically interacting with alkali metal salts, cathode additives, and organic solvents, electrochemical ring-opening polymerization of cyclosiloxanes can be selectively induced by Lewis acid species generated from the decomposition of cathode additives and lithium salts under high voltage conditions, thus constructing a stable polymer network with a Si-O-Si backbone in situ. This polymer network can form reversible coordination channels with lithium ions to ensure ion transport performance, and can also effectively suppress high-voltage oxidative decomposition of electrolyte solvents and dissolution of transition metals, thereby significantly improving the cycle stability and safety of the battery under high-voltage conditions.

[0021] When the amount of polymerizable monomer is too small, the number of precursors that can participate in electrochemical polymerization under high voltage conditions is limited, making it difficult to form a continuous and dense polymer network structure at the cathode interface. This results in incomplete interface coverage, insufficient number of Si–O–Si active sites, and inability to effectively anchor high oxidation state transition metal ions and electrolyte oxidation byproducts, thereby weakening the suppression effect on high voltage side reactions and resulting in limited improvement in cycle stability.

[0022] Conversely, when the amount of polymerizable monomer is excessive, localized overly rapid or non-selective polymerization can easily occur during electrochemically induced polymerization, forming excessively thick or uneven polymer layers. This not only increases lithium-ion transport impedance but may also cause localized gelation or phase separation of the electrolyte, compromising the uniformity and long-term stability of the electrode / electrolyte interface. By controlling the amount of polymerizable monomer within a reasonable range, synergistic optimization of the polymerization reaction rate, network structure density, and ion transport performance can be achieved, thereby obtaining an electrochemical system that combines high voltage tolerance with excellent cycle stability.

[0023] Based on the above technical solution, the volume ratio of the polymer monomer to the electrolyte solvent is further 1:(4~20).

[0024] Secondly, the present invention provides a polymer electrolyte prepared by the aforementioned preparation method.

[0025] Thirdly, the present invention also provides a lithium battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the aforementioned polymer electrolyte.

[0026] Based on the above technical solutions, the active material of the positive electrode further includes any one of ternary materials, lithium cobalt oxide, lithium manganese oxide, and layered oxides, and the active material of the negative electrode includes lithium metal sheets.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses cyclosiloxane compounds containing a siloxane skeleton as electropolymerizable polymer monomers. These monomers have multiple Si-O bonds and can undergo ring-opening polymerization at high voltages. Combined with cathode additives, they form a stable and dense inorganic-organic composite polymer network, which significantly suppresses solvent oxidation and electrode side reactions, allowing the battery to maintain excellent cycle stability even at a high voltage of 4.7 V. Experimental verification shows that the polymer electrolyte formed by this invention enables the battery to achieve higher cycle stability in high-voltage regions.

[0028] (2) The cyclosiloxane compounds selected in this invention have flexible Si-O backbones, which form highly cross-linked and flexible polysiloxane networks after electropolymerization. This network can effectively restrict the free migration of liquid electrolyte molecules, improve the thermal stability of the electrolyte, and reduce parasitic reactions between the electrolyte and high-voltage cathodes (such as NCM811, LNMO, etc.). At the same time, the inorganic SiOx regions in the polysiloxane network can improve the mechanical strength and voltage resistance of the film, enabling the battery to exhibit better stability under high voltage conditions. The polymerized interface film prepared by this invention significantly delays interfacial oxidative decomposition, resulting in a significant improvement in its cycle life at 4.7 V.

[0029] (3) The cyclosiloxane compounds used in this invention can be selectively polymerized under a voltage of 4.5-4.7 V. Within this voltage range, the high potential environment at the cathode interface promotes the decomposition of lithium salts and the dehydrogenation of carbonates in the electrolyte to generate active intermediates with Lewis acidity. Under the action of an electric field, these intermediates coordinate and activate with the Si-O bonds in the cyclosiloxane molecules, thereby lowering their ring-opening polymerization energy barrier. This induces the cyclosiloxanes to undergo ring-opening and further condensation in the cathode interface region, forming a gel or solid polymer structure with Si-O-Si as the backbone. This electropolymerized electrolyte has higher oxidation resistance and can be matched with high-voltage cathode materials. At the same time, the Si-O-Si backbone generated during the polymerization process can effectively anchor the highly oxidized Ni. 4+ Ions. The electropolymerized electrolyte system of this invention significantly suppresses the generation of interfacial gases and structural damage under high voltage, enabling solid-state / semi-solid-state batteries to exhibit superior safety and stability under high voltage.

[0030] (4) The present invention also provides a lithium battery based on an electrolyte constructed by electropolymerization. The battery assembled with NCM811 cathode and lithium metal anode can form a stable and uniform polymer crosslinking network after constant voltage electropolymerization treatment at 4.5-4.7 V, which enables the battery to exhibit significantly improved cycle life under high voltage operation. In addition, when the cathode is replaced with other high voltage materials (such as high voltage lithium manganese oxide, nickel-rich layered oxide), the electropolymerized electrolyte system of the present invention can also significantly improve high voltage stability, thereby expanding its application prospects in various types of high energy density batteries.

[0031] (5) This invention achieves the transformation from a liquid system to a highly stable polymer electrolyte by rationally screening electropolymerizable polymer monomers, optimizing the precursor ratio of polymer monomers / alkali metal salts / cathode additives / electrolyte solvents, and employing a constant-voltage triggered in-situ electropolymerization process. This method combines the advantages of in-situ, integrated assembly and compatibility with high-voltage cathodes, and can be widely applied to advanced lithium battery systems. The constructed silicon-oxygen crosslinked network not only has excellent electrochemical stability and interface protection capabilities, but also has the potential to be further extended to sodium batteries and other metal battery systems, showing significant prospects for industrial application. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a linear sweep voltammetry (LSV) curve of the electrolyte precursor in Example 1; Figure 2 This is a time-voltage curve of the pre-cycle process of "constant current charging-constant voltage charging-constant current discharging" in Example 2; Figure 3 The graph shows the cycle performance of the solid-state battery assembled with the polymer electrolyte prepared in Example 3, NCM9055 positive electrode, and lithium metal negative electrode at a charging cutoff voltage of 4.7 V. Figure 4 This is a comparison of the cycle performance of the solid-state batteries in Example 2 and Comparative Example 1 at a charging cutoff voltage of 4.7 V; Figure 5 This is a comparison of the cycle performance of the solid-state battery in Example 2 and Comparative Example 2 at a charging cutoff voltage of 4.7 V; Figure 6 This is a comparison of the cycle performance of solid-state batteries in Examples 2, 9, and 10 at a charging cutoff voltage of 4.7 V. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] In the following specific embodiments, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane was purchased from TCI, catalog number T2523, with a purity of 97.0% (GC); Cyclopentasiloxane (decamethylcyclopentasiloxane) was purchased from Maclean's, catalog number D833862, with a purity of 98%. 2,4,6-Trivinyl-2,4,6-trimethylcyclotrisiloxane was purchased from TCI, catalog number T3745, with a purity of 95.0% (GC). Cyclotridimethylsiloxane (hexamethylcyclotrisiloxane) was purchased from TCI, catalog number H0725, with a purity of 98.0% (GC). Octamethylcyclotetrasiloxane (octamethylcyclotetrasiloxane) was purchased from TCI, catalog number O0142, with a purity of 98.0% (GC). 1,1,3,3,5,5-Hexamethoxy-1,3,5-trisilycyclohexane (methylcyclosiloxane) was purchased from Aladdin, catalog number H157319, with a purity of ≥90%. Cyclomethyl silicone was purchased from Maclean, catalog number C823972, with a purity of 98%. The polydimethylsiloxane was purchased from Aladdin, catalog number C194626, with a purity of ≥98%. The purity of propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene carbonate, and butene carbonate is 99.95% min, and the moisture content is 20ppm max.

[0036] In the following specific embodiments, the mass ratio of the positive electrode additive to the polymer monomer refers to the mass of the active material (lithium difluorooxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate).

[0037] Example 1 This embodiment provides an electropolymer electrolyte constructed by electropolymerization, a method for preparing the same, and a lithium battery.

[0038] The method for preparing the electropolymer electrolyte includes the following steps: S1. Prepare 150 mL of electrolyte precursor: Measure 50 mL of ethylene carbonate (EC) and 50 mL of dimethyl carbonate (DMC) and mix them in a 1:1 volume ratio. Then add a 1 mol / L solution of lithium hexafluorophosphate (LiPF6) and stir at 25°C for 30 min until completely dissolved. Then add lithium difluorooxalate borate (LiDFOB) as a positive electrode additive with a concentration of 0.2 mol / L, and stir at 25°C for 2 h until completely dissolved; Then add 20 mL of the polymer monomer 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (TVD4), and make up the remainder with dimethyl carbonate to 150 mL. Stir at 25 °C for 10 h until completely dissolved to obtain a homogeneous electrolyte precursor. The final concentration of the alkali metal salt LiPF6 in the electrolyte precursor is 1 mol / L, and the mass ratio of the positive electrode additive to the polymer monomer is 1:5. The volume of the polymer monomer accounts for 7.5% of the total volume of the electrolyte precursor. The volume ratio of the polymer monomer to the electrolyte solvent is 1:5.

[0039] S2. Drop 15 μL of electrolyte precursor onto the Al positive electrode, then cover it with a polypropylene separator. Add another 15 μL of electrolyte precursor to wet the polypropylene separator. Then, stack the negative electrode, lithium metal sheet, nickel foam, etc. Perform linear sweep voltammetry (LSV) testing on the Chenhua electrochemical workstation. The scanning potential range is from open circuit voltage to 7 V, and the scan rate is 5 mV / s.

[0040] The results are as follows Figure 1 The results show that the oxidation concentration region of the system is 4.5~4.7 V. Based on the electrochemical oxidation polymerization mechanism, the constant voltage potential is set at 4.5~4.7 V.

[0041] Example 2 This embodiment provides an electropolymer electrolyte constructed by electropolymerization, a method for preparing the same, and a lithium battery.

[0042] The method for preparing the electropolymer electrolyte includes the following steps: S1. Prepare 250 mL of electrolyte precursor: Measure 50 mL of propylene carbonate, then add a 1 mol / L solution of lithium hexafluorophosphate (LiPF6), and stir at 25 °C for 30 min until completely dissolved. Then add lithium dioxalate borate, a positive electrode additive with a concentration of 0.2 mol / L, and stir at 25°C for 2 h until completely dissolved; Then add 25 mL of the polymer monomer cyclopentadimethylsiloxane, and make up the remainder with dimethyl carbonate to 250 mL. Stir at 25 °C for 10 h until completely dissolved to obtain a homogeneous electrolyte precursor. The final concentration of the alkali metal salt LiPF6 in the electrolyte precursor is 0.5 mol / L, and the mass ratio of the positive electrode additive to the polymer monomer is 1:0.69.

[0043] The volume of the polymer monomer accounts for 10% of the total volume of the electrolyte precursor.

[0044] The volume ratio of the polymer monomer to the electrolyte solvent is 1:2.

[0045] S2. 15 μL of the electrolyte precursor is injected and dropped onto LiNi. 0.90 Co 0.05 Mn 0.05 On the positive electrode of O2 (NCM9055), a polypropylene separator is placed on top, and then 15 μL of electrolyte precursor is added to wet the polypropylene separator. Then, negative electrode lithium metal sheet, nickel foam, etc. are stacked on top. The packaged battery is set on the Xinwei charge-discharge instrument with a pre-cycle step of "constant current charging-constant voltage charging-constant current discharging" to initiate electrochemical polymerization and obtain a high-voltage polymer-based solid battery.

[0046] The pre-cycle step parameters are set as follows: constant current charging to 4.5 V at a current density of 0.1 C, followed by constant voltage charging for 1 hour at the cutoff voltage of the constant current charging with a cutoff current density of 0.01 C, and then constant current discharging to 2.8 V at a current density of 0.1 C. This process is repeated three times. The charge-discharge curves of the pre-cycle process are shown below. Figure 2 As shown.

[0047] The obtained high-voltage polymer solid-state battery was then subjected to charge-discharge cycles at a rate of 1 C in the range of 2.8 V to 4.7 V on a Newway charge-discharge instrument.

[0048] Test results as follows Figure 3 As shown, the obtained high-voltage polymer solid-state battery can achieve 80% capacity retention after 307 cycles at a high charging cutoff voltage of 4.7 V.

[0049] Example 3 This embodiment provides an electropolymer electrolyte constructed by electropolymerization, a method for preparing the same, and a lithium battery.

[0050] The method for preparing the electropolymer electrolyte includes the following steps: S1. Prepare 20 mL of electrolyte precursor: Measure 10 mL of the electrolyte solvent ethylene carbonate, then add a 1 mol / L solution of the alkali metal salt lithium hexafluorophosphate (LiPF6), and stir at 25 °C for 30 min until completely dissolved; Then add lithium tetrafluoroborate, a positive electrode additive with a concentration of 0.2 mol / L, and stir at 25°C for 2 h until completely dissolved; Then add 1 mL of the polymer monomer 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, and make up the remainder with dimethyl carbonate to 20 mL. Stir at 25 °C for 10 h until completely dissolved to obtain a homogeneous electrolyte precursor. The final concentration of the alkali metal salt LiPF6 in the electrolyte precursor is 2 mol / L, and the mass ratio of the positive electrode additive to the polymer monomer is 1:6.9.

[0051] The volume of the polymer monomer accounts for 5% of the total volume of the electrolyte precursor.

[0052] The volume ratio of the polymer monomer to the electrolyte solvent is 1:10.

[0053] S2. 15 μL of the electrolyte precursor is injected and dropped onto LiNi. 0.90 Co 0.05 Mn 0.05 On the positive electrode of O2 (NCM9055), a polypropylene separator is placed on top, and then 15 μL of electrolyte precursor is added to wet the polypropylene separator. Then, negative electrode lithium metal sheet, nickel foam, etc. are stacked on top. The packaged battery is set on the Xinwei charge-discharge instrument with a pre-cycle step of "constant current charging-constant voltage charging-constant current discharging" to initiate electrochemical polymerization and obtain a high-voltage polymer-based solid battery.

[0054] The pre-cycle step parameters are set as follows: constant current charging to 4.6V at a current density of 0.05 C, followed by constant voltage charging for 0.5 h at the cutoff voltage of constant current charging with a cutoff current density of 0.005 C, and then constant current discharging to 2.5 V at a current density of 0.05 C. This process is repeated twice.

[0055] Example 4 The difference between this embodiment and Embodiment 2 is that: in step S1, the alkali metal salt is lithium bis(trifluoromethanesulfonylimide), the electrolyte solvent is butene carbonate, and the polymer monomer is cyclotripolydimethylsiloxane.

[0056] Step S2: 15 μL of the electrolyte precursor is injected and dropped onto LiNi. 0.90 Co 0.05 Mn 0.05On the positive electrode of O2 (NCM9055), a polypropylene separator is placed on top, and then 15 μL of electrolyte precursor is added to wet the polypropylene separator. Then, negative electrode lithium metal sheet, nickel foam, etc. are stacked on top. The packaged battery is set on the Xinwei charge-discharge instrument with a pre-cycle step of "constant current charging-constant voltage charging-constant current discharging" to initiate electrochemical polymerization and obtain a high-voltage polymer-based solid battery.

[0057] The pre-cycle step parameters are set as follows: constant current charging to 4.7V at a current density of 0.2 C, followed by constant voltage charging for 2 hours at the cutoff voltage of constant current charging with a cutoff current density of 0.02 C, and then constant current discharging to 3.0V at a current density of 0.2 C. This process is repeated 5 times.

[0058] Example 5 The difference between this embodiment and Example 2 is that the alkali metal salt is lithium bis(fluorosulfonyl)imide, the electrolyte solvent is diethyl carbonate, and the polymer monomer is octamethylcyclotetrasilyl ether.

[0059] Example 6 The difference between this embodiment and Example 2 is that the alkali metal salt is a mixture of lithium hexafluorophosphate and lithium tetrafluoroborate in a mass ratio of 1:1, the electrolyte solvent is ethyl methyl carbonate, and the polymer monomer is 1,1,3,3,5,5-hexamethoxy-1,3,5-trisilycyclohexane.

[0060] Example 7 The difference between this embodiment and Embodiment 2 is that the polymer monomer is cyclomethylsilicon.

[0061] Example 8 The difference between this embodiment and Embodiment 2 is that the polymer monomer is polydimethylsiloxane.

[0062] Example 9 The difference between this embodiment and Embodiment 2 is that the volume of the polymer monomer accounts for 5% of the total volume of the electrolyte precursor.

[0063] The batteries described above were then subjected to charge-discharge cycles at a rate of 1 C within the range of 2.8 V to 4.7 V using a Newway charge-discharge tester. The test results are as follows: Figure 6 As shown, the battery assembled in this embodiment can achieve 80% capacity retention after 171 cycles at a high charging cutoff voltage of 4.7 V.

[0064] Example 10 The difference between this embodiment and Embodiment 2 is that the volume of the polymer monomer accounts for 15% of the total volume of the electrolyte precursor.

[0065] Comparative Example 1 The difference between this comparative example and Example 2 is that it does not contain polymer monomers.

[0066] The obtained high-voltage polymer solid-state battery was then subjected to charge-discharge cycles at a rate of 1 C within the range of 2.8 V to 4.7 V using a Newway charge-discharge tester. The test results are as follows: Figure 4 As shown, the battery assembled in this comparative example can only achieve 80% capacity retention after 90 cycles at a high charging cutoff voltage of 4.7 V, which is worse than the cycle stability of Example 2.

[0067] Comparative Example 2 The difference between this comparative example and Example 2 is that the pre-cycle step of "constant current charging-constant voltage charging-constant current discharging" is not performed in step S2.

[0068] The packaged battery was directly subjected to charge-discharge cycles at a rate of 1 C within the range of 2.8 V to 4.7 V on a Newway charge-discharge tester. The results are as follows... Figure 5 As shown, the battery assembled in this embodiment can only achieve 80% capacity retention after 120 cycles at a high charging cutoff voltage of 4.7 V. This is worse than the cycle stability after polymerization.

[0069] Comparative Example 3 The difference between this comparative example and Example 2 is that the amount of polymer monomer used is too small, and its volume accounts for only 1% of the total volume of the electrolyte precursor shown, which is 1.5 mL.

[0070] Comparative Example 4 The difference between this comparative example and Example 2 is that the amount of polymer monomer used is excessive, accounting for 30% of the total volume of the electrolyte precursor shown, which is 45 mL.

[0071] Comparative Example 5 The difference between this comparative example and Example 2 is that in step S2, the device is charged to 4.0V at a constant current density of 0.1 C, then charged at a constant voltage for 1 h at the cutoff voltage of the constant current charge with a cutoff current density of 0.01 C, and then discharged at a constant current density of 0.1 C to 2.8 V. This process is repeated three times.

[0072] Comparative Example 6 The difference between this comparative example and Example 2 is that in step S2, the device is charged to 5.0V at a constant current density of 0.1 C, then charged at a constant voltage for 1 h at the cutoff voltage of the constant current charge with a cutoff current density of 0.01 C, and then discharged at a constant current density of 0.1 C to 2.8 V. This process is repeated three times.

[0073] Comparative Example 7 The difference between this comparative example and Example 2 is that the positive electrode additive is too small, and the mass ratio of the positive electrode additive to the polymer monomer is 0.5:5.

[0074] Comparative Example 8 The difference between this comparative example and Example 2 is that: there is too much positive electrode additive, and the mass ratio of the positive electrode additive to the polymer monomer is 2:5.

[0075] Performance testing The batteries assembled in Examples 1-10 and Comparative Examples 1-6 were subjected to cycle performance tests, and the test results are shown in Table 1 below.

[0076]

[0077] As shown in Table 1, the polymer electrolyte provided by this invention enables the battery to maintain excellent cycle stability even at a high voltage of 4.7V.

[0078] A comparison of Example 2 and Comparative Example 1 shows that the battery cycle performance decreases when polymer monomers are absent. This is because when the electrolyte system lacks polymerizable monomers, it is difficult to construct a stable polymer interface network in situ during high-voltage cycling. The cathode / electrolyte interface is directly exposed to a strong oxidizing environment, leading to continuous oxidative decomposition of the electrolyte solvent and lithium salt, and the accumulation of unstable byproducts. On the one hand, the lack of coordination and anchoring of high-oxidation-state transition metal ions by a polymer layer based on Si-O-Si or similar frameworks makes it easier for metal ions such as nickel ions to dissolve and migrate, causing interface structure damage and impedance growth. On the other hand, unsuppressed side reactions continuously consume the electrolyte and generate gases or electrically insulating products, damaging the electrode / electrolyte contact, thereby accelerating capacity decay and causing a significant decrease in cycle stability.

[0079] A comparison of Example 2 and Comparative Example 2 shows that the battery cycle performance deteriorates when the pre-cycle step of "constant current charging-constant voltage charging-constant current discharging" is not performed. This is because without the pre-cycle step of "constant current charging-constant voltage charging-constant current discharging," the polymerizable monomers and cathode additives are difficult to be fully activated under controlled conditions during subsequent cycles, resulting in uneven or incomplete electrochemically induced polymerization reactions. This makes it difficult to construct a continuous and dense polymer network and a stable interface layer in situ at the cathode interface. Simultaneously, the lack of a constant voltage stage to maintain a stable high potential is detrimental to the slow decomposition of lithium salts and cathode additives and the generation of appropriate amounts of Lewis acidic species, thereby weakening the synergistic effect on the selective polymerization of cyclosiloxanes and interface regulation. Furthermore, the lack of the subsequent constant current discharge process is detrimental to the structural rearrangement and densification of the newly formed interface layer, easily leading to the accumulation of interface side reactions and rapid impedance growth, ultimately resulting in a significant decrease in the battery's cycle stability at high voltages.

[0080] A comparison of Example 2 and Comparative Example 3 shows that when the amount of polymer monomer is too small, the battery cycle performance decreases. This is because when the amount of polymer monomer is too small, the number of precursors that can participate in electrochemically induced polymerization under high voltage conditions is insufficient, making it difficult to form a continuous and dense polymer network structure in situ at the cathode interface. This results in incomplete interface coverage and a limited number of active Si-O-Si sites, thereby weakening its inhibitory effect on electrolyte oxidation side reactions and the dissolution of high oxidation state transition metal ions. At the same time, the polymer layer structure is loose, making it difficult to effectively isolate the strong oxidation environment and stabilize the cathode / electrolyte interface. Ultimately, this manifests as accelerated impedance growth and increased capacity decay during high-voltage cycling, leading to a decrease in battery cycle performance.

[0081] A comparison of Example 2 and Comparative Example 4 shows that excessive use of polymer monomers leads to a decrease in battery cycle performance. This is because excessive use of polymer monomers can easily cause localized, excessively rapid, or non-selective polymerization reactions under high-voltage electrochemical induction conditions, resulting in an excessively thick or uneven polymer layer at the positive electrode interface. On the one hand, overly cross-linked or dense polymer networks significantly increase lithium-ion migration resistance, weakening electrode reaction kinetics. On the other hand, excessive monomers may also induce localized gelation or phase separation of the electrolyte, disrupting the uniformity and structural stability of the electrode / electrolyte interface, thereby accelerating polarization and capacity decay during high-voltage cycling, ultimately leading to a decrease in battery cycle performance.

[0082] A comparison of Example 2 and Comparative Example 5 shows that when the constant voltage charging voltage is too low, the battery cycle performance deteriorates. This is because when the constant voltage charging voltage is too low, the high potential driving force required for the positive electrode interface is insufficient, making it difficult to effectively trigger the electrochemical activation process of polymerizable monomers and positive electrode additives. Consequently, polymer precursors such as cyclosiloxanes cannot undergo sufficient and selective electro-induced polymerization, making it difficult to construct a continuous, dense, and stable polymer interface layer in situ on the positive electrode surface. Simultaneously, the number of Lewis acidic species generated by the decomposition of lithium salts and positive electrode additives under low constant voltage conditions is limited, resulting in insufficient interface regulation. The electrolyte is more prone to continuous oxidative decomposition and transition metal dissolution during subsequent high-voltage cycles, ultimately manifesting as a rapid increase in interfacial impedance and a decrease in cycle stability.

[0083] As can be seen from the comparison between Example 2 and Comparative Example 6, the battery cycle performance decreases when the constant voltage charging voltage is too high. This is because when the constant voltage charging voltage is too high, the positive electrode interface is in an excessively strong oxidizing environment, which easily triggers non-selective rapid decomposition of electrolyte solvent, lithium salt, and positive electrode additives, leading to the accumulation of a large number of unstable byproducts at the interface. On the one hand, excessively high potentials can cause polymerizable monomers to undergo excessive or uncontrolled electrochemical polymerization, forming polymer layers with many structural defects and uneven thickness, significantly increasing lithium-ion transport impedance. On the other hand, severe side reactions may also cause gas evolution, interface structure destruction, and accelerated dissolution of transition metals, thereby exacerbating polarization and capacity decay, ultimately resulting in a significant decrease in battery cycle stability.

[0084] A comparison of Example 2 and Comparative Example 7 shows that when the amount of cathode additive is too small, the battery cycle performance decreases. This is because when the amount of cathode additive is too small, the number of effective interfacial regulatory species generated by its preferential decomposition under high voltage conditions is insufficient, making it difficult to form a continuous and stable protective layer on the cathode surface. Furthermore, it cannot provide enough Lewis acid centers to synergistically induce the selective electrochemical polymerization of polymerizable monomers. On the one hand, the electrolyte solvent and lithium salt are more prone to continuous decomposition in a strong oxidizing environment, leading to the continuous accumulation of side reactions. On the other hand, the lack of effective anchoring and inhibition of high-oxidation-state transition metal ions results in intensified metal dissolution and unstable interfacial structure, ultimately manifesting as a rapid increase in interfacial impedance and a significant decrease in battery cycle performance.

[0085] As can be seen from the comparison between Example 2 and Comparative Example 8, the battery cycle performance decreases when there is too much positive electrode additive. This is because when the amount of positive electrode additive is too large, it will undergo excessive and rapid oxidative decomposition under high voltage conditions, generating a large number of Lewis acidic species and inorganic / organic byproducts, which easily form an excessively thick and non-uniform interface layer on the positive electrode surface. On the one hand, excessive decomposition products (such as LiF-rich, boron-containing or phosphorus-containing amorphous phases) will significantly increase the interfacial impedance, hinder the effective transport of lithium ions, and reduce the electrode reaction kinetics. On the other hand, an excessively strong Lewis acid environment may also induce non-selective or excessive polymerization of polymerizable monomers, leading to an increase in polymer network structure defects or even local gelation, thereby destroying the uniformity and long-term stability of the positive electrode / electrolyte interface, and ultimately causing a decrease in battery cycle performance.

[0086] In summary, this invention provides an electropolymerized polymer electrolyte, its preparation method, and a lithium battery. By injecting an electrolyte precursor into the battery through an electrochemical polymerization process, and then initiating electrochemical polymerization through a pre-cycling step of "constant current charging-constant voltage charging-constant current discharging," a polymer electrolyte suitable for high voltage and a high-voltage lithium battery can be obtained. This solves the technical problems of existing polymer electrolytes being susceptible to oxidation at a high voltage of 4.7 V, and the structural collapse of high-nickel layered cathode materials at high cutoff voltages, leading to rapid capacity decay due to the dissolution of highly oxidized transition metal ions.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an electropolymer electrolyte, characterized in that, The process includes the following steps: S1, mixing the alkali metal salt, electrolyte solvent, positive electrode additive and polymer monomer to obtain the electrolyte precursor; S2. The electrolyte precursor is injected between the positive and negative electrodes to assemble the battery. S3. Perform a pre-cycle process of "constant current charging - constant voltage charging - constant current discharging" on the battery to obtain the polymer electrolyte; The polymer monomer includes electropolymerizable cyclosiloxane compounds, and the constant voltage charging voltage is 4.5~4.7V; The electropolymerizable cyclosiloxane compounds include one or two of the following: decamethylcyclopentasiloxane, octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane. The positive electrode additive includes at least one of lithium difluorooxalate borate, lithium difluorooxalate borate, and lithium tetrafluoroborate. The mass ratio of the polymer monomer to the positive electrode additive is 1:(0.69~6.9). The polymer monomer accounts for 5-20% of the total volume of the electrolyte precursor.

2. The preparation method according to claim 1, characterized in that, The pre-cycle process of "constant current charging-constant voltage charging-constant current discharging" includes: A1. At a first current density, the battery is charged with constant current until the voltage of the battery reaches a preset charging cutoff voltage, wherein the charging cutoff voltage is 4.5~4.7 V; A2. Maintain the charging cutoff voltage and perform constant voltage charging on the battery until the charging current decays to the second current density; A3. Discharge the battery at a constant current density until the battery voltage drops to a preset discharge cutoff voltage. Repeat steps A1 to A3 2 to 5 times.

3. The preparation method according to claim 2, characterized in that, The first current density is between 0.05C and 0.2C, the second current density is between 0.005C and 0.02C, the third current density is between 0.05C and 0.2C, and the discharge cutoff voltage is between 2.5V and 3.0V.

4. A polymer electrolyte, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 3.

5. A lithium battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the polymer electrolyte according to claim 4.

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