A negative electrode material, a preparation method thereof, a negative electrode sheet, and a sodium-ion battery

Abstract

This application relates to an anode material and its preparation method, an anode electrode sheet, and a sodium-ion battery, specifically relating to the field of electrochemical energy storage technology. The anode material comprises: an anode material matrix; and a hydrophobic modification layer disposed on at least a portion of the surface of the anode material matrix, the hydrophobic modification layer being composed of an array of long-chain organic molecules arranged perpendicularly to or inclined to the surface of the anode material matrix. The anode material provided by this application can solve the problems of gas expansion and performance degradation caused by hydrogen evolution in aqueous sodium-ion battery anodes in related technologies, as well as the contradiction between efficient water blocking and rapid sodium-ion conduction in existing surface coating technologies.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a negative electrode material and its preparation method, a negative electrode sheet, and a sodium-ion battery. Background Technology

[0002] Aqueous sodium-ion batteries are considered an important development direction in large-scale energy storage due to their advantages such as low cost, high safety, and abundant resources. However, the operating potential of their anode materials (such as NaTi2(PO4)3, etc.) is approximately 2.1 V vs. Na + The hydrogen evolution potential (HEP) of the negative electrode (Na) is very close to that of water. During charging, water molecules are easily reduced on the surface of the negative electrode, generating hydrogen gas. This not only causes an increase in internal battery pressure, leading to swelling and even the risk of explosion, but also disrupts the electrolyte pH balance and significantly reduces coulombic efficiency and cycle life.

[0003] Unlike lithium-ion batteries that use organic electrolytes, aqueous systems struggle to form a dense and stable solid electrolyte interfacial film on the negative electrode surface to effectively block water molecules. Current common solutions to the hydrogen evolution problem involve introducing a coating layer on the negative electrode surface, but this often presents a contradiction between water resistance and sodium conductivity: traditional carbon coatings, while possessing some conductivity, typically contain hydrophilic groups on their surface, failing to effectively repel water molecules; while thick polymer coatings, although enhancing water resistance, severely hinder sodium ion migration, leading to a sharp increase in interfacial impedance and deterioration in battery performance.

[0004] Therefore, there is an urgent need to develop a negative electrode interface modification strategy that can selectively block water and efficiently conduct sodium, thereby suppressing the hydrogen evolution reaction at the source and promoting the practical application of aqueous sodium-ion batteries. Summary of the Invention

[0005] This application provides a negative electrode material and its preparation method, a negative electrode sheet, and a sodium-ion battery to solve the problems of gas expansion and performance degradation caused by hydrogen evolution in the negative electrode of aqueous sodium-ion batteries in related technologies, as well as the contradiction that existing surface coating technologies cannot simultaneously achieve efficient water blocking and rapid sodium ion conduction.

[0006] The technical solution provided by this invention is as follows: In a first aspect, this application provides a negative electrode material, the negative electrode material comprising: Negative electrode material matrix; and, A hydrophobic modification layer is disposed on at least a portion of the surface of the negative electrode material substrate, the hydrophobic modification layer being composed of an array of long-chain organic molecules arranged perpendicularly to or inclined to the surface of the negative electrode material substrate.

[0007] The negative electrode material provided in this application constructs a hydrophobic modification layer on the surface of the negative electrode material substrate, which is formed by long-chain organic molecules arranged in an orderly manner in a vertical or inclined manner to form a "bristle"-like structure. By utilizing the steric hindrance effect of the molecular brush structure and the synergistic effect of the hydrophobic field, it can effectively block water molecules and hydrated sodium ions from contacting the active surface of the electrode, thereby suppressing the occurrence of hydrogen evolution side reactions. At the same time, the nano-micro channels formed by this ordered array structure allow desolvated sodium ions to pass through efficiently, achieving excellent hydrophobic protection while ensuring good ion transport dynamics. This solves the problem of difficulty in balancing water blocking and sodium conduction in traditional coating technology, thereby improving the cycle stability of aqueous sodium-ion batteries.

[0008] In some embodiments, the hydrophobic modified layer is anchored to the surface of the negative electrode material substrate by chemical bonds. The chemical bonding strengthens the bond strength and stability between the hydrophobic modified layer and the negative electrode material substrate, ensuring that it is not easily detached or degraded during long-term charge-discharge cycles and electrolyte immersion. This maintains the durable and ordered structure of the long-chain organic molecular array, thus continuously exerting its water-blocking and ion-sieving functions, which is beneficial for improving the cycle stability of aqueous sodium-ion batteries.

[0009] In some embodiments, the chemical bonds include at least one of Ti-O-Si bonds, Ti-OC bonds, and C-Ti bonds. By using the above-mentioned covalent bonds to firmly anchor the hydrophobic modified layer to the surface of the negative electrode material substrate, on the one hand, the structural stability of the hydrophobic modified layer under long-term electrochemical cycling and electrolyte wetting can be ensured, effectively preventing coating peeling; on the other hand, it is conducive to the formation of a dense and ordered molecular arrangement, further enhancing its spatial barrier and hydrophobic properties, thereby inhibiting the hydrogen evolution reaction in an aqueous environment and ensuring the long-term electrochemical stability of the negative electrode interface.

[0010] In some embodiments, the negative electrode material matrix includes at least one of sodium titanate, sodium titanium phosphate, hard carbon, and organic negative electrode materials. These negative electrode material matrices are chosen because they exhibit relatively stable performance in aqueous sodium-ion batteries and their costs are relatively controllable. Furthermore, their surfaces are relatively easy to chemically modify, facilitating subsequent grafting processes.

[0011] In some embodiments, the long-chain organic molecules include at least one of perfluoroalkylsilanes, long-chain alkyl thiols, and aryl diazonium salts. By selecting the above-mentioned specific modifying molecules, the interfacial performance can be controlled based on their different chemical properties. For example, using perfluoroalkylsilanes can impart extremely strong hydrophobicity to the surface (contact angle >135°), which can improve the hydrogen evolution overpotential; using aryl diazonium salts can form a highly dense and firmly bonded C-Ti bonded layer through electrochemical grafting, enhancing interfacial stability; and alkyl thiols of different chain lengths can adjust the spatial density and arrangement order of the hydrophobic modified layer. These molecules can all be firmly bonded to the surface of the negative electrode material matrix through corresponding chemical reactions (such as hydrolysis condensation, electrochemical reduction, and self-assembly), forming a stable and functionally designable "molecular brush" interface. While ensuring efficient ion transport, this solves problems such as negative electrode hydrogen evolution and interfacial corrosion in aqueous environments, which is beneficial to improving the cycle stability of the battery.

[0012] In some embodiments, the thickness of the hydrophobic modified layer is 3-6 nm. This thickness range can balance water-blocking ability and sodium ion transport performance.

[0013] Secondly, this application provides a method for preparing the aforementioned negative electrode material, comprising the following steps: Surface activation treatment is performed on the negative electrode material substrate; The activated negative electrode material matrix is ​​mixed with a reaction solution containing a hydrophobic modifier and subjected to surface grafting treatment to form a hydrophobic modified layer on at least a portion of the surface of the negative electrode material matrix. The grafted material is then post-processed to obtain the negative electrode material.

[0014] The preparation method provided in this application first activates the surface of the negative electrode material matrix to expose abundant reaction sites, and then performs a controllable surface grafting reaction with a specific hydrophobic modifier, which can construct a dense and firmly bonded hydrophobic modified layer in situ on the surface of the negative electrode material matrix.

[0015] In some embodiments, the hydrophobic modifier includes at least one of perfluoroalkylsilane, long-chain alkyl thiol, and aryl diazonium salt.

[0016] Thirdly, this application provides a negative electrode sheet, which includes the negative electrode material described above or the negative electrode material prepared according to the method described above.

[0017] The negative electrode sheet prepared using the aforementioned hydrophobic molecular brush modified negative electrode material possesses a highly hydrophobic and ion-sieving intelligent interface. During battery operation, this negative electrode sheet effectively suppresses hydrogen evolution side reactions caused by water molecules contacting the electrode active surface, thus avoiding volume expansion, performance degradation, and safety hazards due to gas generation during battery cycling. Simultaneously, its unique interface structure ensures efficient sodium ion transport, giving the electrode sheet excellent water resistance, high ionic conductivity, and structural stability, thereby improving the cycle stability of aqueous sodium-ion batteries.

[0018] Fourthly, this application provides a sodium-ion battery, which includes the negative electrode sheet described above.

[0019] Sodium-ion batteries employing the aforementioned negative electrode sheet can suppress hydrogen evolution side reactions during charging due to the selective water-blocking and highly efficient sodium-conducting properties of the molecular brush structure on the negative electrode surface. This significantly reduces the risk of battery gas expansion, maintains electrolyte pH stability, and improves the battery's coulombic efficiency and cycle life. Simultaneously, this design ensures low impedance and rapid ion transport at the negative electrode interface, enabling the battery to maintain high safety while also exhibiting excellent rate performance and long-term cycle stability. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the "molecular brush" interface sieving mechanism in an embodiment of this application.

[0022] Figure 2 This is a comparison diagram of the water contact angle between Example 1 and Comparative Example 1.

[0023] Figure 3 The graphs show the hydrogen evolution polarization curves of the negative electrode sheets in Example 1 and Comparative Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] The inventors discovered that a key challenge limiting the performance improvement and long-term stable operation of aqueous sodium-ion batteries lies in the hydrogen evolution problem at the negative electrode / electrolyte interface. Taking the commonly used negative electrode material NaTi2(PO4)3 as an example, its operating potential is approximately 2.1 V (vs. Na + The potential of Na ( / Na) is very close to that of water's reduction decomposition potential.

[0026] 1. Hydrogen evolution reaction (HER) is difficult to avoid: During battery charging, water molecules on the negative electrode surface readily gain electrons and are reduced to produce hydrogen gas (2H₂O + 2e⁻). - → H2 + 2OH - This not only leads to increased internal battery pressure, causing bulging and even safety risks, but also results in electrolyte pH imbalance and a significant decrease in coulombic efficiency.

[0027] 2. Lack of stable SEI film: Unlike systems using organic electrolytes, aqueous electrolytes are unlikely to spontaneously form a dense, stable solid electrolyte interface (SEI) film on the negative electrode surface that can effectively block water molecules from approaching, resulting in the negative electrode active surface being directly exposed to the water environment for a long time.

[0028] 3. Existing surface modification technologies face contradictions: To suppress hydrogen evolution, conventional surface coating strategies often compromise one aspect for another. For example, while traditional carbon coatings possess a certain degree of conductivity, their surfaces typically contain a large number of hydrophilic functional groups (-OH, -COOH), which cannot effectively repel water molecules. On the other hand, although thick polymer coatings can improve water resistance, they often severely hinder the migration of sodium ions, leading to a sharp increase in electrode interfacial impedance and deteriorating the battery's rate performance.

[0029] In view of this, this application provides a negative electrode material and its preparation method, a negative electrode sheet and a sodium-ion battery, to solve the problems of gas expansion and performance degradation caused by hydrogen evolution in the negative electrode of aqueous sodium-ion batteries in related technologies, as well as the contradiction that existing surface coating technologies cannot simultaneously achieve efficient water blocking and rapid sodium ion conduction.

[0030] In a first aspect, this application provides a negative electrode material, which, according to embodiments of this application, comprises: Negative electrode material matrix; and, A hydrophobic modification layer is disposed on at least a portion of the surface of the negative electrode material substrate, the hydrophobic modification layer being composed of an array of long-chain organic molecules arranged perpendicularly to or inclined to the surface of the negative electrode material substrate.

[0031] The negative electrode material provided in this application, by constructing a hydrophobic modification layer on the surface of the negative electrode material matrix, consisting of long-chain organic molecules arranged in an orderly manner in a vertical or inclined manner to form a "bristle"-like structure, enables the electrode surface to exhibit superhydrophobic properties with a high water contact angle, thereby effectively repelling the adhesion and contact of free water molecules at the electrode interface. Simultaneously, this ordered array structure forms ion sieving channels with steric hindrance and a hydrophobic field, selectively allowing desolvated sodium ions to pass through efficiently, but blocking larger hydrated sodium ions ([Na(H2O)]). n ] + The free water molecules approach the active surface of the electrode, thereby inhibiting the hydrogen evolution reaction at the source and achieving a unified function of both blocking water and conducting sodium, which can improve the cycle stability of aqueous sodium-ion batteries.

[0032] In some embodiments provided in this application, the hydrophobic modified layer is anchored to the surface of the negative electrode material substrate by chemical bonds. The hydrophobic modified layer is firmly anchored to the surface of the negative electrode material substrate by chemical bonds, which enhances the bonding strength and stability between the hydrophobic modified layer and the negative electrode material substrate. This ensures that it is not easily detached or degraded during long-term charge-discharge cycles and electrolyte immersion, thereby maintaining the durable and ordered structure of the long-chain organic molecular array and continuously exerting its water-blocking and ion-sieving functions, which is beneficial to improving the cycle stability of aqueous sodium-ion batteries.

[0033] In some embodiments provided in this application, the chemical bonds include at least one of Ti-O-Si bonds, Ti-OC bonds, and C-Ti bonds. By using the above-mentioned covalent bonds to firmly anchor the hydrophobic modified layer to the surface of the negative electrode material substrate, on the one hand, the structural stability of the hydrophobic modified layer under long-term electrochemical cycling and electrolyte wetting can be ensured, effectively preventing coating peeling; on the other hand, it is conducive to the formation of a dense and ordered molecular arrangement, further enhancing its spatial barrier and hydrophobic properties, thereby inhibiting the hydrogen evolution reaction in an aqueous environment and ensuring the long-term electrochemical stability of the negative electrode interface.

[0034] In some embodiments provided in this application, the negative electrode material matrix includes at least one of sodium titanate, sodium titanium phosphate, hard carbon, and organic negative electrode materials. The above-mentioned negative electrode material matrices are selected because, on the one hand, they exhibit relatively stable performance in aqueous sodium-ion batteries, and their costs are relatively controllable. On the other hand, their surfaces are relatively easy to chemically modify, facilitating subsequent grafting processes.

[0035] In some embodiments provided in this application, the long-chain organic molecules include at least one of perfluoroalkylsilanes, long-chain alkyl thiols, and aryl diazonium salts. By selecting the above-mentioned specific modifying molecules, the interfacial performance can be controlled based on their different chemical properties. For example, using perfluoroalkylsilanes can impart extremely strong hydrophobicity to the surface (contact angle >135°), which can improve the hydrogen evolution overpotential; using aryl diazonium salts can form a highly dense and firmly bonded C-Ti bonded layer through electrochemical grafting, enhancing interfacial stability; and alkyl thiols of different chain lengths can adjust the spatial density and arrangement order of the hydrophobic modified layer. These molecules can all be firmly bonded to the surface of the negative electrode material matrix through corresponding chemical reactions (such as hydrolysis condensation, electrochemical reduction, and self-assembly), forming a stable and functionally designable "molecular brush" interface. While ensuring efficient ion transport, this solves problems such as negative electrode hydrogen evolution and interfacial corrosion in aqueous environments, which is beneficial to improving the cycle stability of the battery.

[0036] In some embodiments provided in this application, the thickness of the hydrophobic modified layer is 3-6 nm. This thickness range can balance water-blocking ability and sodium ion transport performance.

[0037] Secondly, this application provides a method for preparing the aforementioned negative electrode material, comprising the following steps: Surface activation treatment is performed on the negative electrode material substrate; The activated negative electrode material matrix is ​​mixed with a reaction solution containing a hydrophobic modifier and subjected to surface grafting treatment to form a hydrophobic modified layer on at least a portion of the surface of the negative electrode material matrix. The grafted material is then post-processed to obtain the negative electrode material.

[0038] This preparation method constructs abundant reaction sites on the negative electrode material matrix through surface activation, and uses liquid-phase self-assembly grafting to orient hydrophobic modifier molecules at the interface and form covalent bonds with the matrix, thereby constructing a stable and orderly monolayer-level hydrophobic modified layer.

[0039] As an example, the hydrophobic modifier includes at least one of perfluoroalkylsilane, long-chain alkyl thiol, and aryl diazonium salt.

[0040] Thirdly, this application provides a negative electrode sheet, which includes the negative electrode material described above or the negative electrode material prepared according to the method described above.

[0041] The negative electrode sheet prepared using the aforementioned hydrophobic molecular brush modified negative electrode material possesses a highly hydrophobic and ion-sieving intelligent interface. During battery operation, this negative electrode sheet effectively suppresses hydrogen evolution side reactions caused by water molecules contacting the electrode active surface, thus avoiding volume expansion, performance degradation, and safety hazards due to gas generation during battery cycling. Simultaneously, its unique interface structure ensures efficient sodium ion transport, giving the electrode sheet excellent water resistance, high ionic conductivity, and structural stability, thereby improving the cycle stability of aqueous sodium-ion batteries.

[0042] Fourthly, this application provides a sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an aqueous electrolyte, wherein the negative electrode includes a negative electrode sheet as described above.

[0043] Sodium-ion batteries employing the aforementioned negative electrode sheet can suppress hydrogen evolution side reactions during charging due to the selective water-blocking and highly efficient sodium-conducting properties of the molecular brush structure on the negative electrode surface. This significantly reduces the risk of battery gas expansion, maintains electrolyte pH stability, and improves the battery's coulombic efficiency and cycle life. Simultaneously, this design ensures low impedance and rapid ion transport at the negative electrode interface, enabling the battery to maintain high safety while also exhibiting excellent rate performance and long-term cycle stability.

[0044] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Example 1 This embodiment provides a method for preparing a negative electrode material with surface-grafted perfluorosilanes, the specific steps of which are as follows: 1. Surface Activation Treatment: Weigh 5.0 g of sodium titanium phosphate (NaTi2(PO4)3) powder and place it in a 250 mL beaker. Add 100 mL of 5% hydrogen peroxide solution and mechanically stir continuously at 300 rpm for 30 minutes at room temperature to increase the concentration of hydroxyl groups (-OH) on the surface, serving as grafting sites. After the reaction, transfer the mixture to a centrifuge tube and centrifuge at 8000 rpm for 5 minutes, discarding the supernatant. Wash the collected solid precipitate three times with deionized water, centrifuging after each wash. Transfer the washed solid to a vacuum drying oven and dry at 80°C for 4 hours to obtain activated sodium titanium phosphate powder with a surface rich in hydroxyl groups.

[0045] 2. Preparation of the grafting reaction solution: Measure 95 mL of anhydrous ethanol and 5 mL of deionized water, mix thoroughly to prepare an ethanol-water mixed solvent. Add 1.0 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (F-TEOS) to this mixed solvent and stir until initially dissolved. Then, add glacial acetic acid dropwise to adjust the pH of the solution to 4.0, and let it stand at room temperature for 30 minutes to allow the silane reagent to fully hydrolyze.

[0046] 3. Self-assembly grafting reaction: The activated sodium titanium phosphate powder obtained in step 1 is added to the grafting reaction solution prepared in step 2. The mixture is transferred to a three-necked flask equipped with a reflux condenser and placed in a constant temperature oil bath at 60°C. Under nitrogen protection, the mixture is stirred and refluxed at a rate of 200 rpm for 6 hours. During this process, the silane hydrolysis products undergo dehydration condensation with the titanium hydroxyl groups (Ti-OH) on the surface of sodium titanium phosphate to form Ti-O-Si covalent bonds, allowing the perfluoroalkyl chains to be grafted onto the material surface in a self-assembly manner.

[0047] 4. Post-treatment and curing: After the reaction is complete, the reaction system is cooled to room temperature. The solid product is collected by centrifugation and ultrasonically washed three times with anhydrous ethanol for 10 minutes each time to completely remove physically adsorbed residual reagents. The washed product is placed in a clean petri dish and transferred to a forced-air drying oven for heat treatment at 120°C for 2 hours to promote the complete condensation reaction and form a stable siloxane network.

[0048] Final product: The obtained material is sodium titanium phosphate anode material with perfluoroalkyl chains grafted on the surface. The surface of this material exhibits superhydrophobic properties, and the perfluorosilane molecules are firmly bonded to the surface through Ti-O-Si covalent bonds.

[0049] Example 2 This embodiment provides a method for surface modification of negative electrode materials using an electrochemical grafting method, the specific steps of which are as follows: 1. Electrode preparation: Weigh 85 parts by weight of sodium titanium phosphate (NaTi2(PO4)3) active material, 10 parts by weight of acetylene black conductive agent, and 5 parts by weight of polyvinylidene fluoride (PVDF) binder. Add an appropriate amount of N-methylpyrrolidone (NMP) as a solvent. Mix and stir at 2000 rpm for 4 hours in a planetary mixer to obtain a uniform negative electrode slurry. Use an automatic coating machine to uniformly coat the slurry onto a pretreated copper foil current collector, controlling the coating density at 10±1 mg / cm². Then, place the coated electrode in a vacuum drying oven, pre-dry at 80℃ for 2 hours, and then vacuum dry at 120℃ for 12 hours. Finally, use a roller press to cold press at 5 MPa pressure and cut into circular pieces with a diameter of 12 mm to obtain the sodium titanium phosphate working electrode.

[0050] 2. Preparation of the electrochemical grafting solution: Measure 100 mL of anhydrous acetonitrile as the solvent, add 0.0853 g (0.5 mmol) of tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte, and stir until completely dissolved. Then add 0.0208 g (0.075 mmol) of p-trifluoromethylbenzenediazotetrafluoroborate, and sonicate for 10 minutes to ensure complete dissolution, obtaining a 5 mM electrochemical grafting solution. The entire preparation process was carried out in a nitrogen-protected glove box.

[0051] 3. Electrochemical grafting reaction: Electrochemical grafting was carried out using a standard three-electrode system: the sodium titanium phosphate electrode prepared in step one was used as the working electrode, and the platinum sheet electrode was used as the counter electrode, Ag / Ag + A 0.01 M AgNO3 solution in acetonitrile was used as the reference electrode. The three-electrode system was immersed in the grafting solution prepared in step two, and cyclic voltammetry was performed using an electrochemical workstation. The scan potential range was 0 V to -0.5 V (vs. Ag / Ag). + The scan rate was 50 mV / s, and a total of 5 cyclic scans were performed. The experiment was conducted at room temperature under nitrogen protection.

[0052] 4. Post-treatment and cleaning: After electrochemical grafting, the working electrode was removed and immediately immersed in fresh anhydrous acetonitrile solution for 5 minutes. Then, the electrode was transferred to a beaker containing acetone and treated in an ultrasonic cleaner at 40 kHz and 100 W for 10 minutes. The acetonitrile immersion and acetone ultrasonic cleaning steps were repeated three times each. Finally, the electrode was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain a modified electrode with an aryl hydrophobic layer grafted onto its surface.

[0053] Reaction Mechanism and Phenomenon Analysis: During cyclic voltammetry scanning, the diazonium salt cation (ArN2) + Electrochemical reduction occurs on the surface of the working electrode, generating highly reactive aryl radicals. These radicals rapidly react with titanium or oxygen atoms on the electrode surface to form strong covalent bonds (C-Ti or CO bonds). Cyclic voltammetry curves show a distinct reduction current peak in the range of -0.2 V to -0.3 V during the first scan, corresponding to the reduction process of the diazonium salt. In subsequent scans, this reduction peak current significantly decays until it almost disappears, indicating that the electrode surface is covered by a dense organic layer, and the reaction exhibits self-limiting characteristics.

[0054] Final product: A dense aryl hydrophobic layer is formed on the surface of the modified electrode, which is firmly bonded to the electrode substrate through C-Ti covalent bonds.

[0055] Example 3 This embodiment provides a method for preparing a negative electrode material by constructing a polymer brush layer using surface-initiated atom transfer radical polymerization (SI-ATRP) technology. The specific steps are as follows: 1. Surface anchoring of the initiator: 3.0 g of sodium titanium phosphate (NaTi2(PO4)3) powder was placed in a 100 mL three-necked flask, 60 mL of anhydrous toluene was added, and the mixture was ultrasonically dispersed for 30 minutes. Then, 0.3 mL of 3-aminopropyltriethoxysilane (APTES) was added, and the mixture was refluxed at 80 °C for 12 hours under nitrogen protection, allowing the silane coupling agent to bond to the material surface via a hydrolysis-condensation reaction. After the reaction was complete, the mixture was centrifuged and washed three times with toluene and ethanol to obtain the aminated sodium titanium phosphate.

[0056] The above-mentioned aminated material was redispersed in 40 mL of anhydrous tetrahydrofuran (THF), and 0.4 g of 2-bromoisobutyryl bromide (BiB) and 0.3 mL of triethylamine were added. After reacting for 2 hours in an ice-water bath, the temperature was raised to room temperature and the reaction was continued for 10 hours. The solid was collected by centrifugation, thoroughly washed with THF, and then vacuum dried to obtain sodium titanium phosphate material with ATRP initiator bonded to its surface.

[0057] 2. Surface-initiated ATRP polymerization: In a nitrogen-filled glove box, 100 mg of the initiator material prepared in step one was placed in a reaction tube, along with 3 mL of methyl methacrylate (MMA) monomer, 2 mL of methanol / water mixed solvent (volume ratio 3:1), 15 mg of cuprous bromide (CuBr), and 32 μL of N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA). After sealing the reaction tube, it was placed in a 70°C oil bath and stirred at 300 rpm for 4 hours.

[0058] 3. Polymerization Termination and Post-treatment: After the reaction is complete, remove the reaction tube and quickly open it to expose it to air to terminate the polymerization. Add 20 mL of tetrahydrofuran to dilute the reaction system, and collect the solid product by centrifugation. Clean the obtained material sequentially with tetrahydrofuran, acetone, and ethanol using ultrasonication three times each, for 10 minutes each time, to thoroughly remove unreacted monomers, catalyst, and physically adsorbed polymers. Finally, dry the material in a vacuum oven at 60°C for 8 hours.

[0059] Final product: A sodium titanium phosphate anode material with PMMA polymer brushes grafted onto its surface was obtained. The thickness of the polymer brush layer (approximately 5 nm) was precisely controlled using SI-ATRP technology.

[0060] Comparative Example 1 This comparative example provides a raw, untreated sodium titanium phosphate material as the negative electrode material. The specific steps are as follows: Take 5.0 g of commercially available sodium titanium phosphate (NaTi2(PO4)3, purity ≥99%, D50 particle size 1μm~5 μm), without any chemical treatment, dry it in a vacuum oven at 100℃ for 12 hours, and then use it for subsequent operations.

[0061] Comparative Example 2 This comparative example provides a sodium titanium phosphate anode material modified by physical adsorption of perfluorosilane.

[0062] This comparative example is basically the same as Example 1, except that: this comparative example does not perform hydrogen peroxide surface activation treatment on sodium titanium phosphate, nor does it perform subsequent 120°C heat curing treatment. Instead, it directly mixes sodium titanium phosphate powder with a reaction solution containing perfluorosilane, so that perfluorosilane molecules adhere to the surface of sodium titanium phosphate through physical adsorption.

[0063] The specific steps are as follows: 5.0 g of sodium titanium phosphate powder was weighed and added to a mixed solvent consisting of 95 mL of anhydrous ethanol and 5 mL of deionized water. Then, 1.0 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane was added, and the mixture was stirred and dispersed for 30 min. The mixture was then stirred for another 2 h at room temperature to allow the perfluorosilane molecules to adsorb onto the surface of the sodium titanium phosphate particles. After the reaction was complete, the solid product was collected by centrifugation and washed three times with anhydrous ethanol. The product was then vacuum dried at 60 °C for 4 h to obtain the sodium titanium phosphate anode material modified by physical adsorption of perfluorosilane.

[0064] Comparative Example 3 This comparative example provides a sodium titanium phosphate anode material with thick polymer hydrophobic coating.

[0065] The difference between this comparative example and Example 3 is that Example 3 forms a nanoscale polymer brush layer through surface-initiated polymerization, while this comparative example uses a conventional solution coating method to form a thicker polymer hydrophobic layer on the surface of sodium titanium phosphate.

[0066] The specific steps are as follows: 5.0 g of sodium titanium phosphate powder was weighed and dispersed in 100 mL of N-methylpyrrolidone. 0.8 g of polyvinylidene fluoride-hexafluoropropylene copolymer was added, and the mixture was stirred at room temperature for 4 h to allow the polymer to fully dissolve and coat the surface of the sodium titanium phosphate particles. Subsequently, the mixture was stirred at 80 °C to evaporate the solvent, the solid product was collected, and then vacuum dried at 120 °C for 8 h to obtain a thick polymer hydrophobically coated sodium titanium phosphate material.

[0067] Performance testing 1. The anode materials obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to interfacial physicochemical property tests, specifically testing the water contact angle, bonding force, and interfacial impedance. The specific test steps are as follows: Water contact angle test: The negative electrode materials prepared in each embodiment and comparative example were pressed into discs with a diameter of 12 mm, or prepared into negative electrode sheets according to the same formula and fixed on the sample stage. The test was conducted using a contact angle meter at 25°C. 3 μL of deionized water was dropped onto the sample surface using a micro-syringe. After the droplet stabilized for 5 seconds, the droplet morphology was photographed, and the static water contact angle was calculated using the instrument's built-in software. Five different locations were randomly selected for testing on each sample, and the average value was taken as the water contact angle of that sample.

[0068] Adhesion test: The modified negative electrode material or modified negative electrode sheet was immersed in an aqueous electrolyte for 24 h, then removed and gently rinsed with deionized water. After drying, its water contact angle or surface element content was tested again. The adhesion stability between the hydrophobic modified layer and the substrate was characterized by the water contact angle retention rate or characteristic element retention rate before and after immersion. For perfluorosilane modified samples, the F element content can be determined by XPS; for aryl diazonium salt modified samples, the characteristic peaks of F or C elements can be determined by XPS; for polymer brush modified samples, the mass change or XPS characteristic element content can be used for evaluation. The adhesion force or modified layer retention rate is calculated according to the following formula: Modification layer retention rate = (feature signal intensity after immersion / feature signal intensity before immersion) × 100%.

[0069] Interfacial impedance testing: The modified negative electrode material was fabricated into a negative electrode sheet and assembled with a positive electrode and electrolyte to form a sodium-ion battery, or a three-electrode system was constructed using the negative electrode sheet as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode. The interface was allowed to stabilize for 2 hours before testing. AC impedance testing was performed using an electrochemical workstation with a frequency range of 100 kHz to 0.01 Hz and a perturbation voltage of 5 mV. The interfacial charge transfer impedance Rct was obtained by fitting a Nyquist plot and used to evaluate the effect of the hydrophobic modification layer on interfacial ion transport.

[0070] The specific test results are shown in Table 1: Table 1

[0071] As shown in Table 1, all three examples were able to form a stable hydrophobic modified layer on the surface of the negative electrode material, with a water contact angle significantly higher than that of Comparative Example 1. This indicates that the molecular brush modification of this application can significantly reduce the affinity of the negative electrode material surface for water.

[0072] Example 1 shows that Ti-O-Si bonds are formed by the condensation reaction of perfluorosilane with Ti-OH on the surface of activated sodium titanium phosphate. The water contact angle reaches 135° and the retention rate of the modified layer reaches 98%, indicating that chemical bond anchoring can significantly improve the stability of the hydrophobic layer.

[0073] Example 2 shows that an aryl hydrophobic layer was formed by electrochemical grafting of aryl diazonium salts. The retention rate of the modified layer reached 99%, indicating that electrochemical grafting can form a stable and dense organic layer.

[0074] Example 3 forms a polymer brush layer through surface-initiated polymerization. Although the water contact angle is slightly lower than that of Example 1, it still exhibits good interfacial stability and hydrophobic effect.

[0075] Comparative Example 1 is an unmodified sodium titanium phosphate material with a water contact angle of only 15°, indicating that its surface is highly hydrophilic and can easily come into direct contact with aqueous electrolytes.

[0076] Although Comparative Example 2 used the same perfluorosilane modifier as Example 1, since no surface activation and thermal curing treatment were performed, the perfluorosilane mainly adhered to the material surface through physical adsorption. After immersion, the water contact angle decreased significantly, and the retention rate of the modified layer was only 55%, indicating that the physical adsorption layer was not stable enough in the aqueous electrolyte.

[0077] Comparative Example 3 uses a thick polymer hydrophobic coating layer. Although the water contact angle is high, the interfacial impedance increases to 520Ω, indicating that an excessively thick hydrophobic layer will hinder the cross-interface transport of sodium ions, making it difficult to simultaneously achieve both water blocking and sodium conduction.

[0078] 2. Soft-pack sodium-ion batteries were prepared using the negative electrode materials of Examples 1-3 and Comparative Examples 1-3, respectively, and the electrochemical performance of the obtained sodium-ion batteries was tested. Specifically: Preparation of sodium-ion batteries: Taking the negative electrode material of Example 1 as an example, the perfluorosilane-modified sodium titanium phosphate negative electrode material obtained in Example 1, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 85:10:5. N-methylpyrrolidone was added as a solvent, and the mixture was stirred for 4 h to obtain a uniform negative electrode slurry. The negative electrode slurry was coated on the surface of a copper foil or aluminum foil current collector, and the areal density was controlled to be 10±1 mg / cm². After pre-drying at 80℃ for 2 h, it was vacuum dried at 120℃ for 12 h. After rolling and cutting, the negative electrode sheet was obtained.

[0079] The positive electrode material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 85:10:5, and N-methylpyrrolidone was added and stirred to form a positive electrode slurry. The positive electrode slurry was coated onto the surface of an aluminum foil current collector, and after drying, rolling, and cutting, the positive electrode sheet was obtained.

[0080] The positive electrode, separator, negative electrode, and aqueous electrolyte are assembled into a pouch sodium-ion battery. The aqueous electrolyte can be a 1 mol / L to 3 mol / L NaClO4 aqueous solution, Na2SO4 aqueous solution, or a buffer system thereof. After assembly, the battery is allowed to stand for 12 h to allow the electrolyte to fully wet the electrodes and separator, and then electrochemical tests are performed.

[0081] Hydrogen evolution onset potential: A linear scan voltammetry test was performed using a three-electrode system. The negative electrode prepared in each embodiment or comparative example was used as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte was a 1 mol / L Na₂SO₄ or 1 mol / L NaClO₄ aqueous solution. Nitrogen gas was purged for 30 min before the test to remove dissolved oxygen. The scan rate was 1 mV / s towards the negative potential, and the current density versus potential curve was recorded. The potential corresponding to a cathode current density of 0.1 mA / cm² was defined as the hydrogen evolution onset potential. The test results can be converted relative to Na / Na + The potential.

[0082] Volume expansion rate of the pouch cell after 50 cycles: The assembled pouch sodium-ion battery was cycled 50 times at 0.5C at 25℃. The volume of the pouch cell was measured before and after cycling using vernier calipers or the draining method. The volume expansion rate was calculated using the following formula: Volume expansion rate = (volume after cycle) (Initial volume) / Initial volume × 100%.

[0083] 500-cycle capacity retention: The soft-pack sodium-ion battery was subjected to constant current charge-discharge cycles at 25°C and a 1C rate. The discharge capacity C1 of the first cycle and the discharge capacity C2 of the 500th cycle were recorded. 500 Capacity retention is based on C. 500 Calculate using / C1×100%.

[0084] Coulomb efficiency: During the cyclic testing, the charging and discharging capacities are recorded for each cycle. Coulomb efficiency is calculated as discharging capacity / charging capacity × 100%. The average coulomb efficiency is the average of the coulomb efficiency from cycle 2 to cycle 500.

[0085] The specific test results are shown in Table 2: Table 2

[0086] As shown in Table 2, after constructing the molecular brush-type hydrophobic modified layer using chemical grafting or surface-initiated polymerization in Examples 1 to 3, the hydrogen evolution initiation potential was delayed compared to Comparative Example 1. The volume expansion rate of the soft pack after 50 cycles was less than 4%, the capacity retention rate after 500 cycles was not less than 89.5%, and the average coulombic efficiency was higher than 99.5%. These results demonstrate that the hydrophobic molecular brush interface of this application can effectively reduce the contact probability between water molecules and the negative electrode active surface, thereby inhibiting the hydrogen evolution reaction and circulating gas production.

[0087] Comparative Example 1 uses unmodified sodium titanium phosphate material, which has strong surface hydrophilicity. The aqueous electrolyte can easily come into direct contact with the negative electrode active surface, resulting in early hydrogen evolution reaction. The soft-pack battery showed severe gas swelling after 50 cycles, and the capacity retention rate decreased significantly after 500 cycles.

[0088] Comparative Example 2 was modified by physical adsorption of perfluorosilane. It had a certain degree of hydrophobicity in the initial stage, but due to the lack of stable chemical bonding, the hydrophobic molecules were easy to desorb during the wetting and circulation of the aqueous electrolyte, which led to a gradual weakening of the hydrogen evolution inhibition effect. The volume expansion rate and capacity decay of the soft package were still quite obvious.

[0089] Comparative Example 3 uses a thick polymer hydrophobic coating layer, which can reduce hydrogen evolution and soft pack expansion to some extent. However, due to the thick polymer layer and lack of ordered ion transport channels, the interfacial impedance increases significantly, resulting in a decrease in capacity retention after 500 cycles.

[0090] The above results demonstrate that the advantage of this application does not simply rely on hydrophobic materials or thick coatings, but rather on the formation of a nanoscale, orderly arranged hydrophobic molecular brush layer through chemical bonding, thereby inhibiting water molecules from contacting the negative electrode active surface while retaining the ability of sodium ions to transport across interfaces.

[0091] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0092] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0093] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A negative electrode material, characterized by, The negative electrode material includes: Negative electrode material matrix; and, A hydrophobic modification layer is disposed on at least a portion of the surface of the negative electrode material substrate, the hydrophobic modification layer being composed of an array of long-chain organic molecules arranged perpendicularly to or inclined to the surface of the negative electrode material substrate.

2. The negative electrode material as described in claim 1, characterized in that, The hydrophobic modified layer is anchored to the surface of the negative electrode material matrix by chemical bonds.

3. The negative electrode material as described in claim 2, characterized in that, The chemical bonds include at least one of Ti-O-Si bonds, Ti-OC bonds, and C-Ti bonds.

4. The negative electrode material as described in claim 1, characterized in that, The negative electrode material matrix includes at least one of sodium titanate, sodium titanium phosphate, hard carbon, and organic negative electrode materials.

5. The negative electrode material as described in claim 1, characterized in that, The long-chain organic molecules include at least one of perfluoroalkylsilanes, long-chain alkyl thiols, and aryl diazonium salts.

6. The negative electrode material as described in claim 1, characterized in that, The thickness of the hydrophobic modified layer is 3-6 nm.

7. A method for preparing the negative electrode material according to any one of claims 1-6, characterized in that, include: Surface activation treatment is performed on the negative electrode material substrate; The activated negative electrode material matrix is ​​mixed with a reaction solution containing a hydrophobic modifier and subjected to surface grafting treatment to form a hydrophobic modified layer on at least a portion of the surface of the negative electrode material matrix. The grafted material is then post-processed to obtain the negative electrode material.

8. The method as described in claim 7, characterized in that, The hydrophobic modifier includes at least one of perfluoroalkylsilane, long-chain alkyl thiol, and aryl diazonium salt.

9. A negative electrode sheet, characterized in that, Includes the negative electrode material as described in any one of claims 1-6 or the negative electrode material prepared by the method according to claim 7 or 8.

10. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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