An in-situ polymerized sodium-ion battery and a preparation method thereof

Abstract

The application discloses an in-situ polymerization sodium ion battery and a preparation method thereof, and relates to the technical field of sodium ion batteries.The method comprises the following steps: firstly, through mediation of a silane coupling agent, a thiol-containing initiator derivative is covalently grafted on the surface of a solid-state electrolyte; then, a phenyl polymerization monomer is mixed with an electrolyte to prepare an in-situ polymerization liquid; subsequently, the solid-state electrolyte grafted with the initiator on the surface is prepared into a composite positive electrode sheet together with a positive electrode material, and the positive electrode sheet is assembled into an electric core together with a negative electrode sheet; finally, the in-situ polymerization liquid is injected, and in-situ polymerization is initiated through heating, so that the sodium ion battery is prepared. Through chemical grafting, the application realizes site-specific and directional initiation of a polymerization reaction, forms a stable and firm polymer electrolyte layer on the positive electrode interface, and significantly improves the energy density, rate performance, cycle life and safety of the battery, and effectively solves the problem of gas generation in the charging and discharging process.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to an in-situ polymerization sodium ion battery and a preparation method thereof. BACKGROUND

[0002] Sodium ion batteries (SIBs) are considered as an important supplement and alternative to lithium ion batteries (LIBs) in large-scale energy storage and other fields due to their abundant resources, low cost, and environmental friendliness. However, the commercialization process is still constrained by key performance shortfalls such as energy density, safety, and cycle life. Specifically, sodium ion batteries and lithium ion batteries have similar working principles and components, but the sodium ion radius (0.102 nm) is much larger than that of lithium ion (0.076 nm), which not only slows down the sodium ion insertion / extraction dynamics in the electrode, but also exacerbates the electrode structure stress, leading to material damage and degradation during charging and discharging, and thus causing cell gas production, which not only affects the cycle stability, but also increases the safety risk. Traditional sodium ion batteries use liquid organic electrolytes, which have high ionic conductivity, but have double hidden dangers: first, the organic electrolyte is flammable and easy to leak, and the battery is prone to leakage, combustion, and even explosion when subjected to pressure, puncture, or heating; second, the excess electrolyte is required in the energy storage scenario, and the low theoretical specific capacity of the positive electrode material directly leads to low battery energy density.

[0003] In-situ polymerization technology, as a new electrolyte preparation method, provides a new idea for solving the above problems. This technology directly polymerizes liquid monomers into solid or gel electrolytes inside the battery, which can form a uniform electrolyte layer in close contact with the electrode surface, significantly improving the interface compatibility and reducing the interface impedance. Compared with the traditional solution casting method, in-situ polymerization avoids the complex preparation process and solvent evaporation problem, and can obtain a thinner and more uniform electrolyte layer, improving the energy density of the battery. In addition, the in-situ polymerized electrolyte also has good mechanical properties and thermal stability, which can effectively inhibit the growth of sodium dendrites, improve the cycle life and safety performance of the battery.

[0004] Although the existing in-situ polymerization sodium ion battery has advantages, it has obvious shortfalls, which are mainly reflected in three aspects: first, the ionic conductivity is low and the internal resistance is high, the polymer network hinders ion transmission, and the rate performance is worse at low temperature, even if the polymer skeleton can assist sodium ion migration, the efficiency is far inferior to that of liquid electrolyte; second, the high-rate charging and discharging performance is insufficient, the sodium ion transmission rate is difficult to meet the high current demand, which will also cause concentration polarization, heating, and exacerbate electrolyte decomposition and interface instability; third, the temperature dependence is strong, the conductivity drops sharply at low temperature, causing performance deterioration, and at high temperature, the liquid component is prone to volatilization and decomposition, which will accelerate the degradation of the electrode and the interface side reaction, and destroy the cycle stability. SUMMARY

[0005] The present application aims to solve the problems of low energy density, flammable electrolyte, easy leakage, poor electrochemical stability of the existing sodium ion battery, and low ionic conductivity, unstable interface, poor high and low temperature and rate performance of the sodium ion battery prepared by the existing in-situ polymerization technology, and provides a preparation method of an in-situ polymerization sodium ion battery, which can improve the ionic conductivity and interface stability, thereby effectively improving the energy density, safety and rate performance of the sodium ion battery, and the prepared sodium ion battery is not prone to gas production. The present application also discloses a sodium ion battery prepared by the above-mentioned preparation method of an in-situ polymerization sodium ion battery.

[0006] The purpose of the present application is mainly achieved by the following technical solutions:

[0007] A preparation method of an in-situ polymerization sodium ion battery, comprising the following steps:

[0008] Step S1, solid-state electrolyte and silane coupling agent mediated covalent grafting initiator: the surface hydroxyl of the solid-state electrolyte is activated and treated, then modified with a silane coupling agent, and then a thiol-containing initiator derivative is covalently grafted on the surface of the solid-state electrolyte to obtain a solid-state electrolyte covalently grafted with an initiator on the surface;

[0009] Step S2, preparation of in-situ polymerization liquid: phenyl polymer monomer and electrolyte are mixed to prepare an in-situ polymerization liquid; wherein the addition amount of phenyl polymer monomer during preparation of the in-situ polymerization liquid is 2-5 wt.% of the total mass of the phenyl polymer monomer and electrolyte mixture;

[0010] Step S3, preparation of composite positive electrode and negative electrode: the positive electrode active material, conductive agent, binder and the surface covalently grafted initiator of the solid-state electrolyte obtained in step S1 are mixed to prepare a composite positive electrode slurry, and a composite positive electrode sheet is prepared; the negative electrode active material, conductive agent and binder are mixed to prepare a negative electrode slurry, and a negative electrode sheet is prepared;

[0011] Step S4, battery assembly and in-situ polymerization: a separator and the composite positive electrode sheet and negative electrode sheet prepared in step S3 are used to assemble a soft package cell, then the in-situ polymerization liquid is injected into the soft package cell, and then the soft package cell is placed in a 30-80℃ oven for 3-5 hours, the free radicals generated by the thermal decomposition of the composite positive electrode sheet initiate the polymerization of the phenyl polymer monomer, the in-situ polymerization liquid changes from liquid to solid, and finally an in-situ polymerization semi-solid sodium ion battery is prepared. In the specific implementation of the present application, step S2 is not limited to the above defined order, as long as the in-situ polymerization liquid is prepared before step S4 is implemented.

[0012] The present application utilizes the reaction of the hydroxyl (-OH) on the surface of the solid-state electrolyte treated by surface hydroxyl activation with silane coupling agent to introduce active groups on the surface of the solid-state electrolyte, then introduces a thiol-containing initiator derivative, utilizes click reaction to graft the initiator to the surface of the solid-state electrolyte, so that the solid-state electrolyte has thermal initiation in-situ polymerization initiator activity. Subsequently, the solid-state electrolyte after chemical grafting is added to the sodium ion positive electrode material slurry (including positive electrode active material, conductive agent and binder) to prepare a composite positive electrode with initiator activity. The present application also mixes a phenyl polymerization monomer with an electrolyte to prepare a phenyl-containing in-situ polymerization liquid. After assembling the battery cell with the composite positive electrode with initiator activity and the negative electrode, the phenyl-containing in-situ polymerization liquid is injected, and the active groups on the surface of the solid-state electrolyte of the composite positive electrode are decomposed into free radicals by heating, which initiates the polymerization of the phenyl monomer in the in-situ polymerization liquid, and finally realizes the conversion of the liquid electrolyte into a solid state to prepare a semi-solid sodium ion battery.

[0013] Further, the surface hydroxyl activation treatment of the solid-state electrolyte in step S1 includes the following steps: soaking the solid-state electrolyte in an acidic solution for 1-3 hours to increase the surface hydroxyl density, and then washing with deionized water to obtain a hydroxyl-activated solid-state electrolyte. The present application can significantly increase the surface hydroxyl density through acid treatment, providing more anchoring sites for subsequent silanization reaction, and ensuring high grafting density.

[0014] Further, the modification of the solid-state electrolyte with silane coupling agent in step S1 includes the following steps: immersing the solid-state electrolyte treated by surface hydroxyl activation in an ethanol aqueous solution containing 1-3 wt.% silane coupling agent, and reacting at 40-60°C for 1-4 hours to obtain a silane-modified solid-state electrolyte; wherein the volume fraction of the ethanol aqueous solution is 90%-97%. In specific implementation of the present application, the combination of the silane coupling agent and the solid-state electrolyte generates silanol (-SiOH) by hydrolysis of the alkoxy group (-OR), which reacts with the hydroxyl group (-OH) on the surface of the solid-state electrolyte to form a firm Si-O-M (M is a metal ion on the surface of the solid-state electrolyte) covalent bond.

[0015] Further, the covalent grafting of the thiol-containing initiator derivative on the surface of the solid-state electrolyte in step S1 includes the following steps: adding the solid-state electrolyte modified with silane coupling agent to a toluene solution containing thiol-containing initiator derivative, grafting the initiator to the surface by click chemistry, and obtaining the solid-state electrolyte covalently grafted with the initiator on the surface after cleaning and drying; wherein the amount of thiol-containing initiator derivative added is 0.2-0.5 wt.% of the total mass of the thiol-containing initiator derivative and toluene mixture.

[0016] Further, the mass ratio of the positive active material, the conductive agent, the binder and the solid-state electrolyte of the surface covalent grafting initiator in the preparation of the composite positive electrode slurry in step S3 is 97-X:1.8:1.2:X, wherein X is the solid-state electrolyte additive amount of the surface covalent grafting initiator, 2≤X≤5.

[0017] The mass ratio of the negative active material, the conductive agent and the binder in the preparation of the negative electrode slurry in step S3 is 95:3:2.

[0018] Further, the solid-state electrolyte adopts a NASICON structure solid-state electrolyte or a β''-aluminum oxide electrolyte. The NASICON structure solid-state electrolyte and the β''-aluminum oxide electrolyte are both high-phase ion conductive solid-state electrolytes, which, as an initiator carrier, not only realize the initiation function, but also can construct a fast sodium ion transmission "highway" in the positive electrode, and form a synergistic ion conduction effect with the polymer electrolyte to improve the rate performance of the battery.

[0019] Further, the silane coupling agent adopts any one of KH-550, KH-560, KH-570 and A-171. These silane coupling agents have an alkoxy group capable of reacting with the surface hydroxyl group of the solid-state electrolyte at one end, and an active group amino, epoxy, methacryloyloxy, vinyl group at the other end, respectively. These active groups can efficiently react with the initiator derivative containing a mercapto group (-SH) through click chemistry, ensuring that the initiator can be fixed through a firm covalent bond, avoiding its dissolution or migration in the electrolyte, and ensuring the long-term stability of the initiation activity. The silane coupling agent should "fix" the initiator molecules on the surface of the solid-state electrolyte through chemical bonding, without damaging the characteristics of the thermal decomposition active center of the initiator.

[0020] The initiator derivative containing a mercapto group in the application has the characteristics of a free radical in-situ polymerization initiator (thermal decomposition produces free radicals, forms a monomer free radical with a polymer monomer, and follows the free radical chain initiation-chain growth-chain termination polymerization path), and can be covalently combined with the silane coupling agent to form a "silane-initiator" bridging structure. Further, the initiator derivative containing a mercapto group adopts any one of azobisisobutyronitrile-mercapto derivative, benzoyl peroxide-mercapto derivative and dimethyl azobis isobutyrate-mercapto derivative. Among them, azobisisobutyronitrile-mercapto derivative, benzoyl peroxide-mercapto derivative and dimethyl azobis isobutyrate-mercapto derivative are mercapto derivatives of classic azo or peroxide initiators. They retain the original ability to thermally initiate free radicals, while introducing mercapto groups, so as to efficiently react with the unsaturated bond (such as C=C of KH-570) on the silane coupling agent through sulfur-alkene click chemistry.

[0021] Further, the chemical formula of the phenyl polymerization monomer is:

[0022]

[0023] In the formula, R1 is a bridging group connecting the phenyl group and the double bond, and is a direct bond, -CH2-, -O- or -CH2O-; R2 is a substituent on the double bond, and is H or CH3. The chemical formula of the phenyl polymerization monomer in the application meets three core elements: a polymerizable carbon-carbon double bond (a free radical polymerization site), a phenyl group (providing stability) and a functional group (promoting sodium ion transmission or interface compatibility), so that after polymerization, a structure of “polymer backbone + movable sodium ions” is formed, providing a transmission channel for sodium ions, and the conjugated structure of the phenyl group can improve the stability of the backbone. The phenyl polymerization monomer in the application contains a polymerizable double bond, a phenyl group and a functional group, the conjugated effect of the phenyl group can improve the electrochemical stability and mechanical strength of the polymer and inhibit gas production; and the adjustable R1 and R2 groups can optimize the polymerization activity of the monomer, the glass transition temperature (Tg) of the final polymer and the interaction ability with sodium ions. For example, when R1 is -O- or -CH2O-, the ether bond functional group can assist sodium ion transmission and possibly create new sodium storage sites on the negative electrode surface through coordination.

[0024] Further, the positive active material in the step S3 is any one of a polyanion type positive electrode, a layered oxide type positive electrode and a Prussian blue type positive electrode material; and the negative active material in the step S3 is hard carbon. The method has universality and can be widely applied to mainstream sodium battery positive electrode materials such as polyanion type (such as NFPP, stable structure), layered oxide (high capacity) and Prussian blue type (low cost), and is not dependent on a specific positive electrode, and has broad industrial application prospects.

[0025] A sodium ion battery is prepared by using the above-mentioned in-situ polymerization sodium ion battery preparation method. The battery prepared by the application has a unique “electrode-electrolyte” interface structure and a bulk polymer network formed by chemical grafting and in-situ polymerization, so that the battery has a series of performance characteristics different from traditional liquid batteries and conventional in-situ polymerization batteries, such as higher energy density, excellent cycle life and no gas swelling appearance.

[0026] In summary, compared with the prior art, the application has the following beneficial effects:

[0027] (1) The present application converts liquid electrolyte into solid state by in-situ polymerization, eliminating the risk of leakage and combustion. More importantly, the "physical barrier layer" and "chemical stable layer" formed on the surface of the positive electrode material by the solid-state electrolyte of the surface grafted initiator atomically isolate the direct contact between the positive active material and the electrolyte, effectively inhibiting the oxygen release from the positive electrode material lattice and the related side reactions during charging and discharging, thereby fundamentally solving the gas swelling problem of the battery cell.

[0028] (2) The unique "chemical grafting guided directional polymerization" strategy of the present application enables the polymerization reaction to occur preferentially at the positive electrode interface, forming an efficient and continuous ion transport channel. The present application constructs a "solid-state electrolyte skeleton-polymer network" dual high-speed ion transport path, significantly reducing the interface impedance, making the battery have excellent rate performance and low temperature performance.

[0029] (3) In the present application, the initiator is firmly grafted on the surface of the solid-state electrolyte by covalent bond, and the polymerization network initiated thereby has a much higher bonding strength with the electrode than physical adsorption. This strong interface structure can effectively buffer the volume change of the electrode during charging and discharging, preventing the interface from falling off and failing, thereby ensuring that the battery can still maintain high capacity retention rate after long cycle, greatly prolonging the service life.

[0030] (4) The phenyl-containing polymer monomer used in the present application can form π-Na + adsorption after polymerization due to the conjugation effect of the phenyl group, and the functional groups (such as ether bonds) on the polymer chain can anchor sodium ions through "chemical bonding", which is equivalent to creating new sodium storage sites on the surface and inside of the hard carbon negative electrode, thereby improving the specific capacity of the hard carbon negative electrode, and ultimately achieving effective improvement of the energy density of the full battery. BRIEF DESCRIPTION OF DRAWINGS

[0031] The drawings described herein are used to provide further understanding of the embodiments of the present application, constitute a part of the present application, and do not constitute a limitation on the embodiments of the present application. In the drawings:

[0032] Figure 1 is a flow chart of the preparation method of the present application;

[0033] Figure 2 is a schematic diagram of the rate test results of Example 1 and Example 2, and the comparative example of the present application;

[0034] Figure 3 is a schematic diagram of the long cycle test results of Example 1 and Example 2, and the comparative example of the present application;

[0035] Figure 4 is a physical picture of the battery cell after cycling of Example 1 and the comparative example of the present application. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0037] like Figure 1 As shown, a method for preparing an in-situ polymerized sodium-ion battery includes the following steps: Step S1, solid electrolyte and silane coupling agent mediated covalent grafting of initiator: the surface hydroxyl group of the solid electrolyte is activated, then modified with a silane coupling agent, and then a mercapto-containing initiator derivative is covalently grafted onto the surface of the solid electrolyte to obtain a solid electrolyte with a surface covalently grafted initiator; Step S2, preparation of in-situ polymerization liquid: phenyl polymer monomers are mixed with electrolyte to prepare an in-situ polymerization liquid; wherein, the amount of phenyl polymer monomers added when preparing the in-situ polymerization liquid is 2-5 wt.% of the total mass of the phenyl polymer monomer and electrolyte mixture; Step S3, preparation of composite positive and negative electrodes: positive electrode active material, conductive... A composite positive electrode slurry is prepared by mixing a solid electrolyte containing an agent, a binder, and a surface covalent graft initiator obtained in step S1, and then fabricating a composite positive electrode sheet. A negative electrode slurry is prepared by mixing a negative electrode active material, a conductive agent, and a binder, and then fabricating a negative electrode sheet. Step S4, battery assembly and in-situ polymerization: A soft-pack battery cell is assembled using a separator and the composite positive and negative electrode sheets prepared in step S3. Then, an in-situ polymerization solution is injected into the soft-pack battery cell. The soft-pack battery cell is then placed in an oven at 30-80℃ and left to stand for 3-5 hours. The phenyl monomer is polymerized by using the free radicals of the composite positive electrode sheet under heat decomposition, thereby realizing the transformation of the in-situ polymerization solution from liquid to solid state. Finally, an in-situ polymerized semi-solid sodium-ion battery is prepared.

[0038] The solid electrolyte of this invention is a NASICON-structured solid electrolyte or a β″-alumina electrolyte. The silane coupling agent is any one of KH-550 (γ-aminopropyltriethoxysilane), KH-560 (γ-glycidyl etheroxypropyltrimethoxysilane), KH-570 (γ-methacryloyloxypropyltrimethoxysilane), and A-171 (vinyltrimethoxysilane). The positive electrode active material is any one of polyanionic positive electrode, layered oxide positive electrode, and Prussian blue-based positive electrode material; the negative electrode active material is hard carbon. The thiol-containing initiator derivative is any one of azobisisobutyronitrile-thiol derivative (AIBN-SH), benzoyl peroxide-thiol derivative (BPO-SH), and dimethyl azobisisobutyrate-thiol derivative (AIBME-SH).

[0039] In the specific implementation of the present application, azobisisobutyronitrile-mercapto derivative (AIBN-SH), benzoyl peroxide-mercapto derivative (BPO-SH) and dimethyl azobisisobutyrate-mercapto derivative (AIBME-SH) can be synthesized online. Among them, the synthesis path of azobisisobutyronitrile-mercapto derivative is as follows: 4,4'-azobis(4-cyanopentanoic acid) is used as raw material, the carboxyl group thereof is subjected to amidation reaction with 3-mercapto-1-propanamine in the presence of condensing agent N,N'-dicyclohexyl carbodiimide (DCC) and catalyst 4-dimethylamino pyridine (DMAP) at room temperature in anhydrous dichloromethane solvent, and then azobisisobutyronitrile-mercapto derivative is obtained after post-treatment and purification. The derivative retains the thermal initiation characteristics of azobisisobutyronitrile, and the terminal mercapto group thereof can be used for click chemistry reaction with silane coupling agent. The synthesis path of benzoyl peroxide-mercapto derivative is as follows: 4-carboxy benzoyl peroxide is used as raw material, and the first step is to react with thionyl chloride to generate the corresponding acyl chloride intermediate; then, the intermediate is subjected to esterification reaction with 1,3-propanedithiol in the presence of pyridine in anhydrous tetrahydrofuran solvent to generate an intermediate containing a disulfide bond; finally, the intermediate is selectively reduced by triphenylphosphine, and then benzoyl peroxide-mercapto derivative is obtained after post-treatment and purification. The derivative retains the thermal initiation characteristics of benzoyl peroxide, and the terminal mercapto group thereof can be used for click chemistry reaction with silane coupling agent. The synthesis path of dimethyl azobisisobutyrate-mercapto derivative (AIBME-SH) is as follows: azobisisobutyric acid is used as raw material, the carboxyl group thereof is subjected to amidation reaction with 2-aminoethanethiol in the presence of condensing agent N,N'-dicyclohexyl carbodiimide (DCC) and catalyst 4-dimethylamino pyridine (DMAP) at room temperature in anhydrous dichloromethane solvent, and then dimethyl azobisisobutyrate-mercapto derivative is obtained after post-treatment and purification. The derivative retains the thermal initiation characteristics of dimethyl azobisisobutyrate, and the terminal mercapto group thereof can be used for click chemistry reaction with silane coupling agent.

[0040] The chemical general formula of the phenyl polymer monomer in the present application is as follows:

[0041]

[0042] Among them, R1 is a bridging group connecting the phenyl group and the double bond, and the role is to adjust the distance between the phenyl group and the functional group, and direct bond, -CH2-, -O- or -CH2O- is adopted; R2 is a substituent on the double bond, and H or CH3 is adopted. In the specific implementation of the present application, the phenyl polymer monomer can adopt styrene (R1 is directly connected, and the benzene ring is directly connected with the carbon atom on the vinyl group; R2 is H), phenyl methacrylate (R1 is -O-, and R2 is CH3), p-methyl styrene (R1 is directly connected, R2 is H, and there is a methyl group at the para position of the benzene ring), and vinyl benzyl ether (R1 is -CH2O-, and R2 is H).

[0043] The'solid-state electrolyte and silane coupling agent mediated covalent grafting initiator' described in the application refers to a process in which the initiator molecule is grafted to the surface of the solid-state electrolyte through covalent bonding by using silane coupling agent as a chemical bridge. Specifically, it includes:

[0044] Activation of the surface hydroxyl group of the solid-state electrolyte; modification of the activated solid-state electrolyte with silane coupling agent to introduce active groups (such as double bonds) on its surface that can react with the initiator; using click chemistry to covalently graft thiol-containing initiator derivatives to the surface of the modified solid-state electrolyte, ultimately obtaining a solid-state electrolyte with covalently grafted initiators on its surface.

[0045] In the preparation of in-situ polymerization liquid, the phenyl polymer monomer is mixed and stirred with the electrolyte, and defoaming treatment is performed. The application limits the addition amount of phenyl polymer monomer to 2-5wt.% based on the trade-off between'solidification degree' and 'ionic conductivity', with a lower limit of 2% to ensure that a sufficient and strong three-dimensional polymer network can be formed after polymerization, effectively'solidifying' the liquid electrolyte, and providing sufficient π-Na + adsorption sites to improve the capacity of hard carbon, and avoid the formation of a polymer network with insufficient strength when the content is less than 2%, which cannot effectively fix the electrolyte; the upper limit is 5% to avoid excessive monomer content, which can cause the polymer network to be too dense, hindering the migration of sodium ions, leading to increased battery resistance and decreased rate performance. At the same time, excessive polymer can also generate a large internal stress during the cycle process.

[0046] In the preparation of in-situ polymerization liquid, the electrolyte uses commercial electrolyte, and the electrolyte includes sodium salt and organic solvent; wherein the sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6) and sodium perchlorate (NaClO4); the organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC).

[0047] In the preparation of the composite positive electrode slurry, the positive electrode active material, the conductive agent, the binder, and the surface covalently grafted initiator solid-state electrolyte are high-speed mixed and stirred to obtain the initiator active composite positive electrode slurry. The prepared initiator active composite positive electrode slurry is coated onto an aluminum foil by an extrusion coater, and then subjected to drying, rolling, slitting, and cutting processes to prepare the initiator active composite positive electrode sheet.

[0048] In the preparation of the negative electrode slurry, the negative electrode active material, the conductive agent, and the binder are high-speed mixed and stirred to prepare the negative electrode slurry. The prepared hard carbon negative electrode slurry is coated onto an aluminum foil by an extrusion coater, and then subjected to drying, rolling, slitting, and cutting processes to prepare the negative electrode sheet.

[0049] In the specific implementation of the present application, the conductive agent is selected from at least one of acetylene black, Super P, Ketjen black, carbon nanotubes and graphene; and the binder is selected from at least one of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

[0050] The soft package battery cell is prepared in a stacking mode when the diaphragm, the composite positive electrode sheet and the negative electrode sheet are assembled, and specifically includes the following sub-steps.

[0051] Preparation of the electrode sheet and the diaphragm: the prepared initiator active composite positive electrode sheet and the negative electrode sheet are punched into a preset size (for example, 100mm x 70mm in length x width). At the same time, a commercial diaphragm slightly larger in size than the electrode sheet (for example, a glass fiber diaphragm or a polyolefin porous diaphragm commonly used in sodium ion batteries) is prepared.

[0052] Stacking assembly: in a dry environment (such as a glove box with a dew point lower than -40℃) or a dry room, the stacking operation is performed in the following order: first, lay a layer of the diaphragm as the bottom layer, place a piece of the negative electrode sheet in the center on the diaphragm, cover a layer of the diaphragm on the negative electrode sheet, and then place a piece of the composite positive electrode sheet in the center on the layer of the diaphragm. Repeat the above stacking process to sequentially stack the negative electrode sheet, the diaphragm and the positive electrode sheet, until the designed number of layers (for example, 10 to 20 layers) is reached, and finally end with a layer of the diaphragm to form a multi-layer stacked battery cell structure of "positive electrode-diaphragm-negative electrode-diaphragm-positive electrode...". It should be particularly noted that the composite positive electrode sheet and the negative electrode sheet are isolated from each other by the diaphragm and are arranged alternately in the stacking process, and the area of the positive electrode sheet is slightly smaller than or equal to the area of the negative electrode sheet, so as to ensure the safety of the battery during charging and discharging.

[0053] Soft package: the stacked multi-layer structure is moved into a punch-formed aluminum-plastic film packaging bag. A top sealing device is used to heat seal the three edges of the aluminum-plastic film except the liquid injection port to form a soft package battery cell with a reserved liquid injection port.

[0054] The surface hydroxyl activation treatment of the solid electrolyte in step S1 of the present application includes the following steps: soaking the solid electrolyte in an acidic solution for 1-3 hours to increase the surface hydroxyl density, and then washing with deionized water to obtain a hydroxyl activated solid electrolyte. In the specific implementation of the present application, the acidic solution is a weak acidic aqueous solution with a pH value of 3-4; preferably, it is dilute acetic acid, dilute hydrochloric acid or citric acid buffer with a concentration of 0.1 mol / L-2 mol / L. Using a weak acid and treating in this pH range can effectively increase the surface hydroxyl density of the solid electrolyte while minimizing the corrosion of the strong acid to the bulk structure, ensuring the basis of the subsequent grafting reaction and the ionic conductivity of the material itself.

[0055] The present application places the soft-pack battery cell into a 30-80℃ oven for 3-5 hours, wherein the lower limit of the temperature, 30℃, is the required thermal decomposition starting temperature of the initiator used to generate free radicals to start polymerization. The upper limit of the temperature, 80℃, is to avoid excessive temperature causing the initiator to decompose too quickly, resulting in a local polymerization rate that is too high, forming an uneven electrolyte membrane, and also preventing thermal damage to other battery components (such as separators, adhesives). The time limit of 3-5 hours is to ensure that the monomer has enough time to diffuse throughout the entire battery cell and be fully initiated to polymerize, achieving complete and uniform conversion from liquid to solid state.

[0056] In step S1 of the present application, the initiator is covalently grafted on the surface of the solid-state electrolyte, so that the initiation sites are precisely "anchored" around the positive electrode material. This ensures that during the heating and polymerization process in step S4, the polymerization reaction preferentially starts at the positive electrode interface and forms a more tightly and uniformly combined polymer electrolyte interface layer with the electrode. This "directed initiation" mechanism effectively reduces the interface impedance and avoids the problem of uneven ion transport channels caused by random polymerization, enabling the prepared battery to achieve excellent rate performance and cycle stability.

[0057] In step S1 of the present application, the silane coupling agent is used to modify the surface of the solid-state electrolyte, including the following steps: immersing the solid-state electrolyte with surface hydroxyl activation treatment into an ethanol aqueous solution containing 1-3wt.% silane coupling agent, and reacting at 40-60℃ for 1-4 hours to obtain a silane-modified solid-state electrolyte; wherein the volume fraction of the ethanol aqueous solution is 90%-97%. In specific implementation, the present application reacts at 40℃ for 4 hours or at 60℃ for 1 hour, which provides sufficient energy and time for silane hydrolysis and condensation reaction with surface hydroxyl groups, ensuring the formation of a firm covalent bond layer. Excessive temperature (>60℃) or time (>4 hours) will accelerate the self-condensation of silane coupling agent molecules, forming unstable siloxane oligomers, affecting the grafting efficiency and uniformity of the layer. The present application limits the volume fraction of the ethanol aqueous solution to 90%-97%, and the ethanol at this concentration range as a cosolvent can effectively regulate the proportion of water, ensuring the appropriate hydrolysis of the silane coupling agent for grafting reaction, while inhibiting its self-condensation due to excessive hydrolysis, thereby ensuring the high efficiency and directionality of the modification reaction.

[0058] The step S1 of covalently grafting the thiol-containing initiator derivative on the surface of the solid-state electrolyte includes the following steps: adding the solid-state electrolyte modified by the silane coupling agent into a toluene solution containing the thiol-containing initiator derivative, grafting the initiator to the surface by click chemistry, and obtaining the solid-state electrolyte with the surface covalently grafted initiator after cleaning and drying; wherein the addition amount of the thiol-containing initiator derivative is 0.2-0.5wt.% of the total mass of the thiol-containing initiator derivative and toluene mixture. In the specific implementation of the present application, the thiol-containing initiator derivative is dissolved in toluene in a glove box, and stirring is performed until complete dissolution. Then the solid-state electrolyte modified by silane is added to the solution for stirring, and the addition reaction (click chemistry) between the double bond (-C=C-) of silane and the thiol group (-SH) of the initiator derivative occurs to form a C-S covalent bond, so that the initiator derivative is grafted to the surface. Finally, the unreacted initiator derivative is removed by toluene cleaning, vacuum drying, and finally obtaining the solid-state electrolyte with the surface covalently grafted initiator. The present application limits the addition amount of the thiol-containing initiator derivative to 0.2-0.5wt.% of the total mass of the thiol-containing initiator derivative and toluene mixture, the lower limit of 0.2% ensures that the solid-state electrolyte surface has a high enough initiator grafting density, so that enough radicals can be generated when heated to effectively initiate monomer polymerization; the upper limit of 0.5% avoids the possibility of homopolymerization of the initiator in the solution due to too high initiator concentration, rather than grafting to the surface of the solid-state electrolyte, resulting in waste and possibly introducing impurities.

[0059] In the step S3 of preparing the composite positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid-state electrolyte with the surface covalently grafted initiator is 97-X:1.8:1.2:X, wherein X is the addition amount of the solid-state electrolyte with the surface covalently grafted initiator, and 2≤X≤5. In the preparation of the composite positive electrode slurry, the mass ratio is limited to ensure a high active material content while introducing a functional solid-state electrolyte. 92%-95% of the positive electrode active material maintains a very high active material ratio, which is the basis for achieving high energy density; 1.8% of the conductive agent and 1.2% of the binder are the conventional and optimized ratios for sodium ion battery cathodes, which are sufficient to build an efficient electron conduction network and provide sufficient bonding strength. Among them, the addition amount of the solid-state electrolyte is 2%-5% of the total mass of the positive electrode slurry, which is based on the balance between "interface effect" and "energy density". The setting of this range is based on the following considerations: when the addition amount is less than 2%, a complete and effective interface protection layer cannot be formed on the surface of the positive electrode material to inhibit the generation of gas in the positive electrode; and when the addition amount exceeds 5%, the positive electrode active material is excessively diluted, resulting in a decrease in battery energy density. By controlling the addition amount within this range, the present application achieves the best balance between interface stability and high energy density.

[0060] The mass ratio of the negative electrode active material, the conductive agent and the binder is 95:3:2 in the preparation of the negative electrode slurry in step S3 of the present application. The present application maximizes the sodium storage capacity of the negative electrode by 95% of the negative electrode active material, matches with the high-capacity positive electrode, compensates for the insufficient conductivity of the hard carbon itself by 3% of the conductive agent, and ensures the good rate performance, and ensures the integrity of the electrode structure when the volume changes in the charging and discharging process by 2% of the binder.

[0061] The present application also discloses a sodium ion battery prepared by the above-mentioned in-situ polymerization sodium ion battery preparation method.

[0062] The present application introduces an initiator on the surface of the solid-state electrolyte by the chemical grafting method, and prepares a composite positive electrode, realizes the atomic-level combination of the solid-state electrolyte and the surface of the positive electrode active material in the form of in-situ polymerization, forms a "physical barrier layer" and a "chemical stable layer", effectively avoids the direct contact of the active oxygen in the positive electrode material and the electrolyte, and buffers the volume change of the positive electrode in the charging and discharging process, reduces the interface stress, and greatly reduces the gas production of the positive electrode material in the charging and discharging process.

[0063] The present application prepares a phenyl-containing polymer by thermal initiation polymerization of a phenyl-containing polymer monomer. The conjugation effect of the phenyl group is utilized to form π-Na + adsorption, and the Na + is anchored by the "chemical bonding" mode based on the derived functional groups on the polymer molecular chain. The new sodium storage sites are increased on the surface and inside of the hard carbon negative electrode, so that the hard carbon negative electrode capacity is improved, and the energy density of the sodium ion battery is improved. The phenyl-containing polymer generated by in-situ polymerization interacts (physically adsorbs) with sodium ions (Na + ) through π electrons on the benzene ring on the molecular chain, and some specific functional groups (such as ether bonds-O-) on the chain may also coordinate with sodium ions (chemically anchor). These polymer networks penetrate inside the electrode and cover the surface of the hard carbon particles. Therefore, they are equivalent to "create" a new and effective sodium storage system in addition to the sodium storage sites in the body of the hard carbon material on its surface and in the surrounding space. This makes it possible to store and utilize more sodium ions in the same piece of hard carbon negative electrode, thereby directly improving the actual measured gram capacity. The unexpected effect of the present application compared with the traditional technology is that the in-situ generated phenyl-containing polymer network not only serves as an ion conduction matrix, but also becomes an effective sodium storage host through π-Na + adsorption and functional group coordination. This "secondary sodium storage" mechanism breaks the limitation of the traditional cognition that only the carbon material itself provides capacity, thereby improving the gram capacity of the hard carbon negative electrode.

[0064] The application introduces initiators on the surface of the solid-state electrolyte through click chemistry, and a polymerization network is formed on the surface of the solid-state electrolyte in a way of in-situ polymerization, which effectively shortens the transmission path of sodium ions in the positive electrode. Meanwhile, the solid-state electrolyte itself has the characteristics of high ionic conductivity and low electronic conductivity, which further increases the transmission rate of sodium ions on the positive electrode side, and effectively improves the rate and cycle performance of the battery cell.

[0065] Embodiment 1:

[0066] A preparation method of a sodium ion battery by in-situ polymerization, comprising the following steps:

[0067] Step S1: covalently grafting initiators on the surface of the solid-state electrolyte with the mediation of silane coupling agents;

[0068] S1.1: surface hydroxyl activation: selecting a NASICON structure solid-state electrolyte Na3Zr2Si2PO 12 Na3Zr2Si2PO 12 immersing in an acidic solution for 2 hours to increase the surface -OH density, and then washing with deionized water to obtain hydroxyl-activated Na3Zr2Si2PO 12 ;

[0069] S1.2: silane coupling agent modification: immersing the hydroxyl-activated Na3Zr2Si2PO 12 prepared in S1.1 in an ethanol solution containing 2wt.% KH-570, and reacting at 40℃ for 2 hours, so that the alkoxy group of KH-570 and the surface hydroxyl group of Na3Zr2Si2PO 12 form a covalent bond through condensation reaction to obtain a silane-modified solid-state electrolyte.

[0070] S1.3: initiator chemical grafting: in a glove box, dissolving azobisisobutyronitrile-mercapto derivative (AIBN-SH) in toluene and stirring until completely dissolved; wherein the addition amount of azobisisobutyronitrile-mercapto derivative (AIBN-SH) is 0.3wt.% of the total mass of the azobisisobutyronitrile-mercapto derivative (AIBN-SH) and toluene mixture. Then, the silane-modified solid-state electrolyte prepared in S1.2 is added to the solution for stirring, and the addition reaction (click chemistry) of the double bond (-C=C-) of silane and the mercapto group (-SH) of the initiator derivative occurs to form a C-S covalent bond, so that the initiator derivative is grafted to the surface; finally, the unreacted initiator derivative is removed by toluene cleaning, vacuum drying, and finally obtaining a surface covalently grafted initiator solid-state electrolyte.

[0071] Step S2: mix and stir the electrolyte with styrene (C8H8) polymerization monomer, and perform defoaming treatment to prepare an in-situ polymerization liquid; wherein the addition amount of the styrene (C8H8) polymerization monomer is 2 wt.% of the total mass of the electrolyte and the styrene (C8H8) polymerization monomer.

[0072] Step S3: preparation of the initiator-active composite positive electrode and the hard carbon negative electrode:

[0073] Step S3.1: select a polyanion positive electrode (NFPP), and high-speed mix and stir the NFPP, a conductive agent, a binder, and the surface covalent grafting initiator solid-state electrolyte prepared in S1.3 at a mass ratio of 95:1.8:1.2:2 to obtain an initiator-active composite positive electrode slurry.

[0074] Step S3.2: coat the initiator-active composite positive electrode slurry prepared in S3.1 onto an aluminum foil through an extrusion coater, and perform drying, rolling, slitting, and cutting processes to prepare an initiator-active composite positive electrode sheet.

[0075] Step S3.3: high-speed mix and stir a negative electrode active material (hard carbon), a conductive agent, and a binder at a mass ratio of 95:3:2 to prepare a hard carbon negative electrode slurry.

[0076] Step S3.4: coat the hard carbon negative electrode slurry prepared in S3.3 onto an aluminum foil through an extrusion coater, and perform drying, rolling, slitting, and cutting processes to prepare a hard carbon negative electrode sheet.

[0077] Step S4: prepare a soft-pack battery cell in a laminated manner by using the initiator-active composite positive electrode sheet prepared in step S3, the hard carbon negative electrode sheet, and a commercial separator, then inject the in-situ polymerization liquid prepared in step S2 into the soft-pack battery cell, and place the battery cell in a 60°C oven for 4 hours, so that the free radicals generated by the thermal decomposition of the composite positive electrode initiate the polymerization of the phenyl polymerization monomer, realizing the conversion of the in-situ polymerization liquid from a liquid state to a solid state, and preparing an in-situ polymerization sodium-ion battery cell.

[0078] Example 2:

[0079] An in-situ polymerization sodium-ion battery preparation method, comprising the following steps:

[0080] Step S1: solid-state electrolyte covalent grafting initiator mediated by silane coupling agent

[0081] S1.1 surface hydroxyl activation: select a β″-alumina electrolyte Na2O・5.33Al2O3, soak the Na2O・5.33Al2O3 in an acidic solution for 2 hours to increase the surface -OH density, and then wash with deionized water to obtain hydroxyl-activated Na2O・5.33Al2O3;

[0082] S1.2 Silane coupling agent modification: the hydroxyl-activated Na2O・5.33Al2O3 prepared in S1.1 is immersed in an ethanol solution containing 2wt.% KH-550, and reacted at 60℃ for 4 hours, so that the alkoxy group of KH-550 and the surface hydroxyl group of Na2O・5.33Al2O3 undergo condensation reaction to form covalent bonds, and a silane-modified solid-state electrolyte is obtained.

[0083] S1.3 Initiation chemical grafting: in a glove box, dissolve benzoyl peroxide-mercapto derivative (BPO-SH) in toluene and stir until completely dissolved; wherein the amount of benzoyl peroxide-mercapto derivative (BPO-SH) added is 0.2wt.% of the total mass of the benzoyl peroxide-mercapto derivative (BPO-SH) and toluene mixture. Then the silane-modified solid-state electrolyte prepared in S1.2 is added to the solution and stirred, using the double bond (-C=C-) of silane to undergo addition reaction (click chemistry) with the mercapto group (-SH) of the initiator derivative to form a C-S covalent bond, so that the initiator derivative is grafted to the surface; finally, the unreacted initiator derivative is removed by toluene cleaning, vacuum drying, and finally a solid-state electrolyte with surface covalent grafting of initiator is obtained.

[0084] Step S2: mix and stir the electrolyte with phenoxyethyl methacrylate polymer monomer, and perform defoaming treatment to prepare an in-situ polymerization liquid; wherein the amount of phenoxyethyl methacrylate polymer monomer added is 3wt.% of the total mass of the electrolyte and phenoxyethyl methacrylate polymer monomer.

[0085] Step S3: preparation of initiator-active composite positive electrode and hard carbon negative electrode:

[0086] Step S3.1: select a layered oxide type positive electrode, and mix and stir the positive electrode active material, conductive agent, binder, and surface covalent grafting initiator solid-state electrolyte prepared in S1.3 at a mass ratio of 96:1.8:1.2:1 to obtain an initiator-active composite positive electrode slurry.

[0087] Step S3.2: the initiator-active composite positive electrode slurry prepared in S3.1 is coated onto an aluminum foil by an extrusion coater, and the initiator-active composite positive electrode sheet is prepared through the processes of drying, rolling, slitting, and cutting.

[0088] Step S3.3: mix and stir the negative electrode active material (hard carbon), conductive agent, and binder at a mass ratio of 95:3:2 to prepare a hard carbon negative electrode slurry.

[0089] Step S3.4: the hard carbon negative electrode slurry prepared in S3.3 is coated onto an aluminum foil by an extrusion coater, and the hard carbon negative electrode sheet is prepared through the processes of drying, rolling, slitting, and cutting.

[0090] Step S4: The initiator active composite positive electrode sheet, hard carbon negative electrode sheet prepared in step S3 and commercial separator are prepared into a soft package battery in the form of a stack, then the in-situ polymerization liquid prepared in step S2 is injected into the soft package battery, and the battery is placed in an oven at 30-80℃ for 4 hours. The composite positive electrode is heated to decompose free radicals to initiate polymerization of the phenyl polymerization monomer, realizing the transformation of the in-situ polymerization liquid from liquid to solid, and preparing an in-situ polymerization sodium ion battery.

[0091] Comparative Example:

[0092] A traditional liquid sodium ion battery is prepared with NFPP as the positive electrode, which is used as a comparative example to compare with the in-situ polymerization sodium ion battery of the present application. Compared with the examples, the preparation steps of the traditional liquid sodium ion battery are as follows:

[0093] Step S1: A polyanion positive electrode (NFPP) is selected, and the NFPP, conductive agent and binder are mixed at a mass ratio of 97:1.8:1.2 to obtain a positive electrode slurry.

[0094] Step S2: The positive electrode slurry prepared in S1 is coated on an aluminum foil by an extrusion coater, and an initiator active positive electrode sheet is prepared after drying, rolling, slitting and cutting processes.

[0095] Step S3: A hard carbon negative electrode slurry is prepared by high-speed mixing and stirring the negative electrode active material (hard carbon), conductive agent and binder at a mass ratio of 95:3:2.

[0096] Step S4: The hard carbon negative electrode slurry prepared in S3 is coated on an aluminum foil by an extrusion coater, and a hard carbon negative electrode sheet is prepared after drying, rolling, slitting and cutting processes.

[0097] Step S5: The positive electrode sheet and the hard carbon negative electrode sheet prepared in steps S2 and S4, and the commercial separator are prepared into a soft package battery in the form of a stack, and an electrolyte is injected to obtain a traditional liquid sodium ion battery.

[0098] The energy density of the battery cells of the above examples and comparative examples is shown in Table 1

[0099] Table 1: Discharge energy, battery cell mass and energy density of the comparative examples and examples

[0100]

[0101] As can be seen from the preparation processes of Examples 1, 2, and the comparative example above, under the premise of the same positive and negative electrode materials, similar formulations, and similar cell weight, the energy density of Example 1 is 12.1 Wh / kg higher than that of Example 1. This indicates that the sodium-ion battery prepared by this invention has a higher energy density than that of a traditional liquid sodium-ion battery prepared under the same conditions. This is due to the unique conjugation effect of the phenyl-containing polymer prepared by thermally initiated polymerization using phenyl-containing monomers, forming π-Na + Adsorption, and anchoring of Na through "chemical bonding" based on derived functional groups on the polymer molecular chain. + New sodium storage sites are added to the surface and interior of the hard carbon anode. This allows more sodium ions to be inserted and extracted into the anode, thereby effectively increasing the specific capacity of the hard carbon anode and ultimately improving the overall energy density of the battery cell.

[0102] To verify that the in-situ polymerized sodium-ion battery of this invention has superior rate performance, the sodium batteries prepared in Examples 1, 2, and the comparative example were subjected to rate tests. All three groups of cells were charged at 0.5C and discharged at currents of 0.5C, 1C, 2C, 3C, 4C, and 5C, respectively. After the rate tests, a capacity recovery experiment was conducted at 0.5C to evaluate the cell's cycle reversibility. The test results are as follows: Figure 2 The initial 0.5C discharge capacity of the battery cell was used as the fixed capacity. The 0.5C capacity retention rate for Examples 1, 2, and the comparative example was 100%. The capacity retention rates for 1C, 2C, 3C, 4C, and 5C discharge rates for the battery cell in Example 1 were 97.5%, 96.9%, 95.7%, 95.3%, and 94.9%, respectively. The capacity retention rates for 1C, 2C, 3C, 4C, and 5C discharge rates for the battery cell in Example 2 were 95.7%, 94.6%, 94.1%, 93.7%, and 93.6%, respectively. The capacity retention rates of the comparative cell at 1C, 2C, 3C, 4C, and 5C discharge rates were 88.3%, 87%, 86.5%, 86.1%, and 85.9%, respectively. It can be seen that at different rates, the rate performance of Examples 1 and 2 is significantly better than that of the comparative cell. Because Examples 1 and 2 achieve a directional polymer network on the solid electrolyte surface through in-situ polymerization, the transport path of sodium ions within the positive electrode is effectively shortened, thus significantly increasing the cell's rate performance. Furthermore, after rate testing, a recovery experiment was conducted at a 0.5C current. The capacity retention rates of Examples 1 and 2 were both recovered to over 99.5%, while the comparative cell only recovered to 90%. The sodium-ion cell prepared through in-situ polymerization showed structural stability and no degradation after high-current testing, indicating higher cycle stability and reversibility.

[0103] Subsequently, cyclic tests were conducted on the battery cells of Examples 1, 2, and the comparative example using a 1C charging and 1C discharging regime. The test results are as follows: Figure 3 As shown in the figure, the comparison of cycle data shows that after 500 cycles, the capacity retention rate of the comparative cell is 85.62%; after 500 cycles, the capacity retention rate of the Example 1 cell reaches 95.78%; and after 500 cycles, the capacity retention rate of the Example 2 cell is 95.12%. With the progress of charge-discharge cycles, the capacity of the comparative cell decreases significantly, while the capacity decreases more slowly in Examples 1 and 2, demonstrating superior cycle life. Figure 3 The rightmost 0.5C value represents the recovery test after high-rate discharge, primarily determining whether irreversible capacity loss occurs internally after the cell has undergone high-rate discharge. A better 0.5C capacity retention rate indicates better cell stability. Simultaneously, the cell is visually inspected after 500 cycles, and the results are as follows... Figure 4 As shown. Figure 4 The left side shows the actual image of the comparative cell after cycling, and the right side shows the actual image of the Example 1 cell after cycling. It is clear from the images that the comparative cell exhibits significant bulging after 500 charge-discharge cycles, while the Example 1 cell shows virtually no bulging. Analysis of the cycling data reveals that the comparative cell suffers from significant gas generation during charge-discharge cycles, which is the main reason for its low capacity retention and short cycle life. In contrast, Example 1 does not exhibit gas generation during cycling, thus demonstrating good capacity retention and a longer cycle life. The specific reasons are as follows: The NFPP cathode material used in the comparative cell undergoes lattice distortion and structural collapse during charge-discharge, causing some oxygen atoms to escape and form oxygen. Simultaneously, this process increases the active sites on the material surface, accelerating side reactions with the electrolyte and producing gases such as carbon dioxide. Unlike the comparative cell, Example 1 coats the NFPP cathode material with a solid electrolyte material, effectively suppressing lattice distortion and structural collapse, thereby preventing oxygen generation. Furthermore, the directional polymerization network formed through click chemistry and in-situ polymerization can effectively isolate the contact between the cathode material and the electrolyte, preventing the active sites of the cathode material from reacting with the electrolyte to generate gas. In summary, the in-situ polymerized sodium-ion battery and its preparation method provided by this invention can effectively suppress gas generation in the battery cell and significantly improve the cycle life of the battery cell.

[0104] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ polymerized sodium-ion battery, characterized in that, Includes the following steps: Step S1: Solid electrolyte and silane coupling agent mediating covalent grafting of initiator: The solid electrolyte is activated by surface hydroxyl activation treatment, then modified with silane coupling agent, and then a mercapto-containing initiator derivative is covalently grafted onto the surface of the solid electrolyte to obtain a solid electrolyte with surface covalent grafting initiator. Step S2: Preparation of in-situ polymerization solution: The phenyl monomer is mixed with the electrolyte to prepare the in-situ polymerization solution; wherein, the amount of phenyl monomer added during the preparation of the in-situ polymerization solution is 2-5 wt.% of the total mass of the phenyl monomer and electrolyte mixture. Step S3: Preparation of composite positive and negative electrodes: The solid electrolyte of positive electrode active material, conductive agent, binder and surface covalent graft initiator obtained in step S1 is mixed to prepare composite positive electrode slurry and made into composite positive electrode sheet; the negative electrode active material, conductive agent and binder are mixed to prepare negative electrode slurry and made into negative electrode sheet. Step S4, Battery Assembly and In-situ Polymerization: The soft-pack battery cell is assembled using the separator and the composite positive and negative electrode sheets prepared in step S3. The in-situ polymerization liquid is then injected into the soft-pack battery cell. The soft-pack battery cell is then placed in an oven at 30-80℃ and left to stand for 3-5 hours. The phenyl monomer is polymerized by using the free radicals of the composite positive electrode sheet under heat decomposition, thereby realizing the transformation of the in-situ polymerization liquid from liquid to solid state. Finally, an in-situ polymerized semi-solid sodium-ion battery is prepared. The solid electrolyte is a NASICON structure solid electrolyte or a β″-alumina electrolyte; The silane coupling agent is any one of KH-550, KH-560, KH-570, and A-171; The thiol-containing initiator derivative is any one of azobisisobutyronitrile-thiol derivative, benzoyl peroxide-thiol derivative, and dimethyl azobisisobutyrate-thiol derivative. The general chemical formula of the phenyl polymer monomer is: Wherein, R1 is a bridging group connecting the phenyl group and the double bond, which can be a direct bond, -CH2-, -O- or -CH2O-; R2 is a substituent on the double bond, which can be H or CH3.

2. The method for preparing an in-situ polymerized sodium-ion battery according to claim 1, characterized in that, The surface hydroxyl activation treatment of the solid electrolyte in step S1 includes the following steps: soaking the solid electrolyte in an acidic solution for 1-3 hours to increase the surface hydroxyl density, and then washing it with deionized water to obtain the hydroxyl-activated solid electrolyte.

3. The method for preparing an in-situ polymerized sodium-ion battery according to claim 1, characterized in that, The modification of the solid electrolyte with silane coupling agent in step S1 includes the following steps: immersing the solid electrolyte with surface hydroxyl activation treatment in an ethanol aqueous solution containing 1-3 wt.% silane coupling agent, and reacting at 40-60°C for 1-4 hours to obtain the silane-modified solid electrolyte; wherein the volume fraction of the ethanol aqueous solution is 90%-97%.

4. The method for preparing an in-situ polymerized sodium-ion battery according to claim 1, characterized in that, The step S1 of covalently grafting a thiol-containing initiator derivative onto the surface of a solid electrolyte includes the following steps: adding a solid electrolyte modified with a silane coupling agent to a toluene solution containing a thiol-containing initiator derivative; grafting the initiator onto the surface via click chemistry; and obtaining a solid electrolyte with a surface covalently grafted initiator after washing and drying; wherein the amount of the thiol-containing initiator derivative added is 0.2-0.5 wt.% of the total mass of the mixture of the thiol-containing initiator derivative and toluene.

5. The method for preparing an in-situ polymerized sodium-ion battery according to claim 1, characterized in that, In step S3, when preparing the composite positive electrode slurry, the mass ratio of the positive electrode active material, conductive agent, binder, and surface covalent grafting initiator to the solid electrolyte is 97-X:1.8:1.2:X, where X is the amount of solid electrolyte added to the surface covalent grafting initiator, and 2≤X≤5. In step S3, when preparing the negative electrode slurry, the mass ratio of the negative electrode active material, conductive agent, and binder is 95:3:

2.

6. The method for preparing an in-situ polymerized sodium-ion battery according to claim 1, characterized in that, The positive electrode active material in step S3 is any one of polyanionic positive electrode, layered oxide positive electrode, and Prussian blue type positive electrode material; the negative electrode active material in step S3 is hard carbon.

7. A sodium-ion battery, characterized in that, The sodium-ion battery was prepared using any one of the in-situ polymerized sodium-ion batteries according to claims 1 to 6.

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