Surface modified negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a surface-modified negative electrode material as well as a preparation method and application thereof, and relates to the technical field of sodium-ion battery electrode materials. The surface modified negative electrode material comprises negative electrode particles and a mixed ion / electron conductor layer coating the surfaces of the negative electrode particles, wherein the mixed ion / electron conductor layer comprises polyphosphates and a sodium-containing polymer; the molecular formula of the multi-phosphate is NaxMaNbPO4, x / (a + b) is more than or equal to 0.4 and less than or equal to 0.7, x + n1a + n2b is equal to 3, n1 is the valence of M, n2 is the valence of N, the molar ratio of M to N is z, and z is more than or equal to 1 and less than or equal to 3. According to the surface modified negative electrode material, the specific mixed ion / electron conductor layer is adopted to coat the negative electrode material, so that the effect of an artificial SEI film can be achieved, co-intercalation of a solvent is prevented, surface side reaction can be effectively inhibited, formation of an interface layer which is not beneficial to sodium ion / electron transmission is inhibited, the high-temperature performance of a battery is improved, and the long cycle life of the battery is prolonged.

Description

Technical Field

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

[0002] Currently, lithium-ion batteries (LIBs) dominate the secondary battery market due to their high energy density and mature technology. However, the uneven geographical distribution of lithium resources and their extremely low crustal reserves severely restrict their large-scale application in energy storage. With the rapid development of vehicle electrification, the low-altitude economy, and robotics, the demand for large-scale secondary batteries is increasing rapidly, necessitating the urgent development of non-lithium-ion battery energy storage systems, represented by high-efficiency, low-cost sodium-ion batteries (SIBs).

[0003] Sodium-ion batteries operate on a similar mechanism to lithium-ion batteries. However, due to the larger radius of sodium ions and their incompatibility with graphite layers, graphite, widely used as the anode in lithium-ion batteries, is generally unsuitable for sodium-ion batteries. Therefore, developing suitable non-graphite anodes is a key factor in the development of sodium-ion batteries.

[0004] Similar to lithium-ion batteries, sodium-ion batteries also form an SEI (solid electrolyte membrane) on the surface of the negative electrode. However, the SEI film in sodium-ion batteries contains a lower content of inorganic components (such as NaF and Na2CO3) and a higher proportion of organic polymers (such as polycarbonate). Organic components have high solubility in the electrolyte, especially under high pressure or high temperature conditions, easily dissolving and causing the SEI layer to fail, triggering continuous side reactions and consuming active sodium. If PTFE (polytetrafluoroethylene) is used as a binder for the negative electrode, these side reactions will be exacerbated. Therefore, it is necessary to study reasonable modification of the negative electrode surface to suppress electrolyte damage to the SEI film, improve the initial coulombic efficiency of the negative electrode, and enhance the cycle and storage performance of sodium-ion batteries at both room temperature and high temperature.

[0005] Patent application CN118198310A discloses a hard carbon composite anode material with a core-shell structure, comprising a core, an outer shell, and an intermediate layer. The core is phosphorus-doped porous hard carbon, the intermediate layer is phosphorus sulfide, and the outer shell contains a fast ion conductor and a conductive agent. This gives the hard carbon composite anode material better fast-charging performance. However, this solution has not yet been able to further improve the battery's initial efficiency and high-temperature cycle performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects and shortcomings of existing anode materials and provide a surface-modified anode material that can effectively suppress the occurrence of side reactions, improve the initial coulombic efficiency of the anode, and has high high-temperature stability and long cycle life.

[0007] Another objective of this invention is to provide a method for preparing surface-modified negative electrode materials.

[0008] Another object of the present invention is to provide an application of the above-mentioned surface-modified negative electrode material in the preparation of sodium-ion batteries.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a surface-modified negative electrode material, comprising negative electrode particles and a mixed ion / electron conductor layer coated on the surface of the negative electrode particles, wherein the mixed ion / electron conductor layer comprises a polyphosphate and a sodium-containing polymer. The molecular formula of the polyphosphate is Na. x M a N b PO4; In the formula, M is selected from at least one of Ti, Si, Sn, Zr, Ce, Ge, Ta, Nb, W or Mo; N is selected from at least one of Li, Mg, Ca, Sr, Ba, Zn, Al, La or Fe; wherein 0.4≤x / (a+b)≤0.7, x+n1a+n2b=3, n1 is the valence of M, n2 is the valence of N, and the molar ratio of M and N (M / N) is z, and satisfies 1≤z≤3; The sodium-containing polymer is selected from one or more of sodium carboxymethyl cellulose, sodium lignosulfonate, sodium polyacrylate, or sodium alginate.

[0010] The surface-modified negative electrode material of this invention employs a specific mixed ion / electron conductor layer to coat the negative electrode material. The polyphosphate acts as an ion / electron transporter, while the sodium-containing polymer provides adhesion and coating, and also possesses a certain ion-conducting capability. The two work together to form a mixed ion / electron conductor layer, which functions as an artificial SEI film, achieving a desolvation effect, preventing solvent co-intercalation, and effectively suppressing surface side reactions and the formation of interface layers that are detrimental to sodium ion / electron transport. Simultaneously, it maintains the stability of the SEI film on the negative electrode surface under high temperature, long cycle, or overcharge / discharge conditions, improving the battery's high-temperature performance and long cycle life.

[0011] Specifically, the polyphosphate of this invention further optimizes the ratio of each component. When 0.4 ≤ x / y ≤ 0.7, the mixed ionic / electronic conductor exhibits a large ionic conductivity. Simultaneously, by optimizing the z molar ratio, and in conjunction with optimizing the molar ratio x / (a+b) of Na, M, and N ions, higher ionic and electronic conductivity can be obtained, thereby achieving rapid sodium ion transport and electrode reaction kinetics.

[0012] Optionally, the oxidation state n1 of M is +3 to +6; the oxidation state n2 of N is +1 to +3.

[0013] In some implementations, 0.4 ≤ x / (a+b) ≤ 0.52, 1 ≤ z ≤ 2.6.

[0014] In the mixed ionic / electronic conductor Preferably, M is selected from at least one of Ti, Zr, and Nb.

[0015] Preferably, the N is selected from at least one of Li, Mg or Al.

[0016] Alternatively, 0.2≤x≤0.6, 0.3≤a≤0.7, and 0.1≤b≤0.5.

[0017] In some embodiments, the mass fraction of the mixed ion / electron conductor layer to the negative electrode particles is 1-5 wt.%.

[0018] In some embodiments, the mass ratio of the polyphosphate to the sodium-containing polymer is (20-95):(5-80). Preferably, it is (75-90):(10-25).

[0019] This invention further optimizes the proportion of polyphosphates. An excessively high proportion leads to decreased coating density and reduced effectiveness in inhibiting SEI film dissolution. Conversely, an excessively low proportion reduces the ion permeability of the coating layer, limiting sodium ions' passage through the mixed ion / electron conductor layer. This invention utilizes a specific amount of polyphosphates to interact with the polymer chains, promoting sodium dissociation from the polymer chains and improving ionic conductivity.

[0020] In some embodiments, the polyphosphate is synthesized by a solid-state method. The synthesis method is as follows: the precursors of each element (Na source, M metal source, N metal source and phosphate source) are mixed uniformly by ball milling according to the stoichiometric ratio, wherein the ball milling time is 2 to 10 hours, and the mixture is calcined in an atmosphere at 800 to 1000°C for 5 to 20 hours. Finally, the polyphosphate is obtained by pulverization.

[0021] The negative electrode particles of the present invention may be selected from conventional negative electrode materials in the field of sodium-ion batteries. Specifically, the negative electrode particles include, but are not limited to, one or more of hard carbon, soft carbon, graphite, tin, bismuth or phosphorus.

[0022] This invention protects a method for preparing a surface-modified negative electrode material, comprising the following steps: S1, thoroughly pulverize the polyphosphates; S2, the polyphosphate, sodium-containing polymer and aminosilane coupling agent are mixed and dispersed evenly in an aqueous solvent system to obtain a coating solution; S3, the coating solution is mixed evenly with the negative electrode particles and spray-dried to obtain a coated mixture; S4. Under an inert atmosphere, the coating mixture is heat-treated at 60~130℃ to obtain the surface-modified negative electrode material.

[0023] Optionally, in step S1, the polyphosphate is pulverized to a particle size of D50 = 100~500 nm.

[0024] In some embodiments, the weight ratio of the aminosilane coupling agent to the sodium-containing polymer is (0.1~1):100. The aminosilane coupling agent connects the polyphosphate and the sodium-containing polymer. Furthermore, a specific amount of silane coupling agent allows for more uniform dispersion of the polyphosphate in the sodium-containing polymer and fixes the polyphosphate particles onto the polymer. The amino groups in the amino-containing silane coupling agent also form hydrogen bonds with the oxygen-containing groups on the negative electrode surface, resulting in a tighter and more robust coating of the negative electrode particles by the polyphosphate and the sodium-containing polymer.

[0025] In some embodiments, the aminosilane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, or 3-aminopropyltrimethoxysilane.

[0026] Optionally, in step S2, the solid-liquid mass ratio of the solid-phase system of the polyphosphate, sodium-containing polymer and aminosilane coupling agent in water is 1:(4~10).

[0027] Optionally, in step S3, the mass ratio of the coating solution to the negative electrode particles is 1:(1.7~20).

[0028] Optionally, the inert gas in the inert atmosphere is selected from argon, nitrogen, or helium.

[0029] Optionally, the heat treatment time is 1-2 hours.

[0030] This invention protects the application of a surface-modified negative electrode material in the preparation of sodium-ion batteries.

[0031] Specifically, the surface-modified negative electrode material of the present invention is used in negative electrode sheets containing binder polytetrafluoroethylene (PTFE).

[0032] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a surface-modified anode material that employs a specific mixed ion / electron conductor layer to coat the anode material. The polyphosphate acts as an ion / electron transporter, while the sodium-containing polymer provides adhesion and coating, while also possessing a certain ion-conducting capability. The two work together to form the mixed ion / electron conductor layer, which functions as an artificial SEI film, achieving a desolvation effect, preventing solvent co-intercalation, and effectively suppressing surface side reactions and the formation of interface layers that are detrimental to sodium ion / electron transport. Simultaneously, it maintains the stability of the SEI film on the anode surface under high temperature, long cycle, or overcharge / discharge conditions, improving the battery's high-temperature performance and cycle life. Furthermore, this surface-modified anode material reduces side reactions between PTFE and the anode, thereby enabling the application of PTFE-containing anode sheets in sodium-ion batteries. Attached Figure Description

[0033] Figure 1 This is a scanning electron microscope (SEM) image of the surface-modified negative electrode material prepared in Example 1 of the present invention.

[0034] Figure 2 This is a SEM image of the simple negative electrode material of Comparative Example 1 of the present invention.

[0035] Figure 3 This is an energy dispersive spectral scan of the surface-modified negative electrode material prepared in Example 1 of the present invention.

[0036] Figure 4 Comparison of residual capacity of batteries prepared from surface-modified negative electrode materials according to various embodiments of the present invention after storage at 60°C for 7 days. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way.

[0038] Example 1 A surface-modified negative electrode material includes negative electrode particles and a mixed ion / electron conductor layer coated on the surface of the negative electrode particles. The mixed ion / electron conductor layer comprises a polyphosphate and a sodium-containing polymer. The molecular formula of the polyphosphate is Na. 0.34 Ti 0.38 Al 0.38 PO4; The sodium-containing polymer is sodium alginate.

[0039] The preparation method of the surface-modified negative electrode material includes the following steps: S1, preparation and pulverization of polyphosphates; Specifically, Na₂CO₃, TiO₂, Al₂O₃, and NH₄H₂PO₄ are used as raw materials, mixed according to stoichiometric ratios, and ball-milled in ethanol until homogeneous. The mixture is then reacted at 900°C under an air atmosphere for 10 hours to obtain Na₂CO₃. 0.34 Ti 0.38 Al 0.38 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0040] S2, Preparation of coating solution for mixed ionic / electronic conductors: Specifically, in this embodiment, the sodium-containing polymer is sodium alginate, and the pulverized Na... 0.34 Ti 0.38 Al 0.38 PO4 and sodium alginate were mixed at a mass ratio of 90:10. γ-aminopropyltriethoxysilane was then added at a mass ratio of 0.2:100 to sodium alginate. Deionized water was then added at a solid-liquid ratio of 1:5, and the mixture was thoroughly mixed to form a coating solution.

[0041] S3, Preparation of coating mixture: Specifically, commercial hard carbon particles are used as the negative electrode particles. The coating solution is mixed with the commercial hard carbon particles at a mass ratio of 1:5. Simultaneously, the solution is uniformly sprayed into the airflow system through an atomizing nozzle, controlling the airflow velocity at 20 m / s and the airflow temperature at 80°C to obtain the coated mixture. In this embodiment, dynamic airflow dispersion can avoid powder agglomeration. Combined with precise spray feeding, the coating layer thickness can be controlled at the submicron level, achieving uniform, complete, and tight coating of the negative electrode particles.

[0042] S4. Under an argon atmosphere, the coating mixture is heat-treated at 100°C for 1 hour to obtain the surface-modified negative electrode material.

[0043] Example 2 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.48 Ti 0.54 Mg 0.18 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, TiO₂, MgO, and NH₄H₂PO₄ as raw materials, the ingredients were prepared according to stoichiometric ratios, ball-milled and mixed uniformly in ethanol, and then reacted at 800℃ under an air atmosphere for 20 hours to obtain a mixed ionic / electronic conductor Na. 0.48 Ti 0.54 Mg 0.18 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0044] Example 3 A surface-modified negative electrode material, which differs from Example 1 in that the sodium-containing polymer in this example is an equal amount of sodium polyacrylate.

[0045] Example 4 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.33 Zr 0.55 Mg 0.19 Li 0.08 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Na₂CO₃, ZrO₂, MgO, LiOH, and NH₄H₂PO₄ were used as raw materials, and the mixture was prepared according to stoichiometric ratios. The mixture was then ball-milled in ethanol until homogeneous, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.33 Zr 0.55 Mg 0.19 Li 0.08 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0046] Example 5 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.50 Nb 0.03 Si 0.50 Mg 0.16 Li 0.03 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, ZrO₂, MgO, LiOH, and NH₄H₂PO₄ as raw materials, the ingredients were prepared according to stoichiometric ratios, ball-milled and mixed evenly in ethanol, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.50 Nb 0.03 Si 0.50 Mg 0.16 Li 0.03 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0047] Example 6 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.38 Ti 0.43 Al 0.30 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, ZrO₂, MgO, LiOH, and NH₄H₂PO₄ as raw materials, the ingredients were prepared according to stoichiometric ratios, ball-milled and mixed evenly in ethanol, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.38 Ti 0.43 Al 0.30 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0048] Example 7 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.36 Ti 0.51 Al 0.20 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, ZrO₂, MgO, LiOH, and NH₄H₂PO₄ as raw materials, the ingredients were prepared according to stoichiometric ratios, ball-milled and mixed evenly in ethanol, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.36 Ti 0.51 Al 0.20 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0049] Example 8 A surface-modified anode material, which differs from Example 1 in that: this example uses commercial soft carbon particles as anode particles.

[0050] Example 9 A surface-modified negative electrode material, which differs from Example 1 in that: the sodium-containing polymer in this example is an equal amount of sodium lignosulfonate.

[0051] Comparative Example 1 A negative electrode material differs from that of Example 1 in that the surface of the negative electrode material in this comparative example is not coated with a mixed ion / electron conductor layer.

[0052] Comparative Example 2 A surface-modified negative electrode material differs from Example 1 in that the mixed ion / electron conductor layer in this comparative example does not contain sodium polymer. Its preparation method directly uses Na... 0.34 Ti 0.38 Al 0.38 PO4 and negative electrode particles were ball-milled and coated at a mass ratio of 1:30 to form a coated mixture. Subsequent steps were the same as in Example 1.

[0053] Comparative Example 3 A surface-modified negative electrode material differs from Example 1 in that the comparative example mixed ion / electron conductor layer does not contain polyphosphates. In its preparation method, γ-aminopropyltriethoxysilane is added at a mass ratio of 0.2:100 to sodium alginate. Then, deionized water is added at a solid-liquid ratio of 1:5, and the mixture is stirred evenly to form a coating solution; subsequent steps are the same as in Example 1.

[0054] Comparative Example 4 A surface-modified negative electrode material differs from Example 1 in that: the comparative example mixed ion / electron conductor layer does not contain silane coupling agent.

[0055] Comparative Example 5 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.33 Ti 0.33 Al 0.45 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, TiO₂, Al₂O₃, and NH₄H₂PO₄ as raw materials, the ingredients were prepared according to stoichiometric ratio, ball-milled and mixed evenly in ethanol, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.33 Ti 0.33 Al 0.45 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0056] Comparative Example 6 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.28 Ti 0.50 Al 0.24 PO4; x / (a+b) < 0.4, The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, TiO₂, Al₂O₃, and NH₄H₂PO₄ as raw materials, the ingredients were prepared according to stoichiometric ratio, ball-milled and mixed evenly in ethanol, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.28 Ti 0.50 Al 0.24 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0057] Comparative Example 7 A surface-modified negative electrode material, differing from Example 1 in that: the polyphosphate in this example is Na. 0.34 Ti 0.67 PO4; The method for preparing polyphosphates in this embodiment includes the following steps: Using Na₂CO₃, TiO₂, and NH₄H₂PO₄ as raw materials, the mixtures were prepared according to stoichiometric ratios, ball-milled in ethanol until homogeneous, and then reacted at 1000℃ under air atmosphere for 5 hours to obtain Na₂CO₃. 0.34 Ti 0.67 PO4 was subjected to sand milling to reduce its particle size to 200 nm.

[0058] Performance testing The surface-modified anode materials of the above embodiments and comparative examples were subjected to the following performance tests: 1. Scanning electron microscopy (SEM) characterization like Figure 1 As shown, SEM analysis of the surface-modified anode material prepared in Example 1 indicates that the mixed ion / electron conductors are uniformly, completely, and conformally coated on the surface of the anode particles. In contrast, SEM analysis of the hard carbon material in Comparative Example 1... Figure 2 Its surface is flat and uncovered.

[0059] 2. Energy Dispersive Spectroscopy (EDS) surface scanning characterization like Figure 3 As shown, energy dispersive spectroscopy (EDS) analysis indicates that the elements in Example 1 are uniformly distributed, proving that the coating layer has high uniformity.

[0060] 3. Electrochemical performance characterization Sodium vanadium phosphate was used as the positive electrode, and the negative electrode materials obtained in the above examples and comparative examples were used as the negative electrode. The cells were assembled into a soft-pack full cell and tested within a voltage range of 1.5 to 3.6 V. The results are shown in Table 1.

[0061] (1) First efficiency test: During the first cycle of battery formation and capacity testing, the calculation formula is: First efficiency = First discharge capacity ÷ First charge capacity.

[0062] (2) Residual capacity ratio after 7 days of storage at 60℃: The battery was initially discharged at room temperature using a 0.2C rate test, and then stored at 60℃±2℃ for 7 days with a full charge of 3.6V. Finally, the battery was removed and discharged at 0.2C rate after returning to room temperature. The calculation formula is: Residual capacity ratio = Discharge capacity after test ÷ Initial discharge capacity.

[0063] (3) High-temperature cycling: The battery was charged and discharged at a rate of 1C at an environment of 60℃±2℃ until the discharge capacity was less than 80% of the initial discharge capacity. The high-temperature cycling capacity decay of Examples 1-4 and Comparative Examples 1-4 is as follows: Figure 4 As shown.

[0064] Table 1

[0065] As shown in Table 1, the surface-modified anode material of this invention achieves an initial efficiency of over 89.5%, and retains over 92% of its capacity after 7 days of storage at 60°C. It exhibits high initial battery efficiency, high high-temperature stability, and long cycle life.

[0066] Compared to Example 1, Comparative Examples 1-3, which do not contain a mixed ionic / electronic conductor layer, or whose mixed ionic / electronic conductor layer contains only sodium polymer or polyphosphate, show a decrease in the initial efficiency and the capacity residual ratio after 7 days of storage at 60°C.

[0067] Comparative Example 5, which uses a polyphosphate with z < 1, Comparative Example 6, which uses a polyphosphate with x / (a+b) < 0.4, and Comparative Example 7, which uses a polyphosphate without metal N doping, all failed to effectively maintain the SEI film on the negative electrode surface, resulting in reduced initial efficiency and significantly decreased high-temperature stability of the material.

[0068] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A surface-modified negative electrode material, characterized by, The surface modified negative electrode material comprises negative electrode particles and a mixed ion / electron conductor layer coated on the surface of the negative electrode particles, wherein the mixed ion / electron conductor layer comprises a polybasic phosphate and a sodium-containing polymer, The polybasic phosphate has a molecular formula of Na x M a N b PO4; the M is selected from at least one of Ti, Si, Sn, Zr, Ce, Ge, Ta, Nb, W or Mo; the N is selected from at least one of Li, Mg, Ca, Sr, Ba, Zn, Al, La or Fe; wherein 0.4≤x / (a+b)≤0.7, x+n1a+n2b=3, n1 is the valence of M, n2 is the valence of N; the molar ratio of M and N is z, and satisfies 1≤z≤3; The sodium-containing polymer is selected from one or more than two of sodium carboxymethyl cellulose, sodium lignosulfonate, sodium polyacrylate or sodium alginate.

2. The surface-modified negative electrode material according to claim 1, characterized in that, 0.4≤x / (a+b)≤0.52, 1≤z≤2.

6.

3. The surface-modified negative electrode material according to claim 1, characterized in that, The mass fraction of the mixed ion / electron conductor layer in the negative electrode particles is 1-5 wt.%.

4. The surface-modified negative electrode material according to claim 1, characterized in that, The mass ratio of the polybasic phosphate to the sodium-containing polymer is (20-95):(5-80).

5. The surface-modified negative electrode material according to claim 1, characterized in that, The negative electrode particles are selected from one or more of hard carbon, soft carbon, graphite, tin, bismuth or phosphorus.

6. A method for producing the surface-modified negative electrode material according to any one of claims 1 to 5, characterized by, The method comprises the following steps: S1, sufficiently pulverizing a polybasic phosphate; S2, uniformly mixing and dispersing the polybasic phosphate, a sodium-containing polymer and an amino silane coupling agent in an aqueous solvent system to obtain a coating solution; S3, uniformly mixing the coating solution with negative electrode particles and spray drying to obtain a coated mixture; S4, under an inert atmosphere, heat treating the coated mixture at 60-130°C to obtain the surface modified negative electrode material.

7. The method for preparing the surface-modified negative electrode material according to claim 6, characterized in that, In step S2, the weight ratio of the amino silane coupling agent to the sodium-containing polymer is (0.1-1):

100.

8. The method for preparing the surface-modified negative electrode material according to claim 7, characterized in that, The amino silane coupling agent is selected from one or more than two of γ-aminopropyl triethoxysilane, N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane, N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane, γ-aminopropyl methyl diethoxysilane or 3-aminopropyl trimethoxysilane.

9. The method for preparing the surface-modified negative electrode material according to claim 6, characterized in that, In step S3, the mass ratio of the coating solution to the negative electrode particles is 1:(1.7-20).

10. Use of the surface modified negative electrode material of any one of claims 1-5 in the preparation of a sodium ion battery.

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