Sodium supplementing agent, sodium ion battery and preparation method of sodium supplementing agent

Abstract

The invention provides a sodium supplementing agent, a sodium ion battery and a preparation method of the sodium supplementing agent, and belongs to the technical field of secondary batteries, and the sodium supplementing agent comprises an inner core and a coating layer. Wherein the inner core comprises a sodium supplementing material and a lithium supplementing material; the coating layer includes a carbon material. The sodium supplementing agent provided by the invention effectively improves the gram volume development and cycle life of the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a sodium supplement agent, a sodium ion battery and a preparation method of the sodium supplement agent. BACKGROUND

[0002] In recent years, energy storage technology has developed rapidly, among which lithium ion batteries are the most representative. Lithium ion batteries have long cycle life, high energy density and other characteristics, and are widely used in consumer electronics, new energy vehicles and aerospace fields.

[0003] While the lithium battery industry is developing rapidly, the price of lithium salt is also rising rapidly, resulting in a sharp increase in raw material costs, which limits the further development and application of lithium ion batteries. Sodium ion batteries have attracted attention due to their competitive cost advantage and sustainable resource supply, and are expected to become a substitute for lithium ion batteries.

[0004] Similar to lithium ion batteries, sodium ion batteries also have some irreversible reactions such as the formation of SEI film on the surface of the negative electrode, which causes the loss of active sodium in the system, resulting in low charge-discharge capacity and poor cycle performance of sodium ion batteries in the actual charge-discharge process, which seriously affects the commercialization process of sodium ion batteries.

[0005] Therefore, it is necessary to design a sodium supplement agent, a sodium ion battery and a preparation method of the sodium supplement agent to improve the above problems. SUMMARY

[0006] The present application provides a sodium supplement agent, a sodium ion battery and a preparation method of the sodium supplement agent to improve the technical problems of low charge-discharge capacity and poor cycle performance of sodium ion batteries.

[0007] In a first aspect, the present application provides a sodium supplement agent, which includes a core and a coating layer.

[0008] The core includes a sodium supplement material and a lithium supplement material; the coating layer includes a carbon material.

[0009] In an example of the present application, the sodium supplement material includes at least one of Na2CO3, Na2NiO2, NaCrO2, Na2S, CH3COONa, Na2C4O4 and Na2C2O4.

[0010] In an example of the present application, the lithium supplement material includes at least one of Li5FeO4, Li2NiO2 and LiCoO2.

[0011] In an example of the present application, the decomposition potential of the sodium supplement material is higher than that of the lithium supplement material.

[0012] In an example of the present application, the D50 particle size of the sodium supplement material is less than or equal to 5 μm, the D50 particle size of the lithium supplement material is greater than the D50 particle size of the sodium supplement material, and the difference between the D50 particle size of the lithium supplement material and the D50 particle size of the sodium supplement material is greater than or equal to 2 μm. In an example of the present application, the D50 particle size of the sodium supplement material is 3-5 μm.

[0013] In an example of the present application, the D50 particle size of the lithium supplement material is less than or equal to 15 μm.

[0014] In an example of the present application, the D50 particle size of the lithium supplement material is 7-15 μm.

[0015] In an example of the present application, the mass content of the lithium supplement material in the inner core is greater than or equal to 20%.

[0016] In an example of the present application, the mass content of the lithium supplement material in the inner core is 20%-60%.

[0017] In an example of the present application, the mass content of the inner core in the sodium supplement agent is 85%-98%, and the mass content of the coating layer in the sodium supplement agent is 2%-15%.

[0018] In an example of the present application, the carbon material includes at least one of graphene, carbon nanotube, hard carbon, soft carbon, carbon fiber and conductive carbon.

[0019] In an example of the present application, the coating layer is doped with non-metal atoms, and the non-metal atoms include at least one of N, B, S and P.

[0020] In an example of the present application, the coating layer includes metal atoms, and the metal atoms include at least one of noble metal atoms and transition metal atoms.

[0021] In an example of the present application, the noble metal atoms include at least one of Ir, Rh, Ru and Pd.

[0022] In an example of the present application, the transition metal atoms include at least one of Ni, Co, Mn and Fe.

[0023] In a second aspect, the present application further provides a preparation method of a sodium supplement agent, which comprises: providing a coating material, wherein the coating material includes a carbon material; mixing the sodium supplement material and the lithium supplement material uniformly according to a preset mass ratio to obtain an inner core material; mixing and grinding the inner core material and the coating material to obtain a sodium supplement agent.

[0024] In a third aspect, the present application also provides a sodium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer comprises the sodium supplementing agent described in any one of the above examples or prepared by the preparation method described in any one of the above examples.

[0025] The sodium supplementing agent provided by the present application comprises an inner core and a carbon coating layer, and the inner core comprises a sodium supplementing material and a lithium supplementing material. The sodium supplementing agent is prepared by introducing the lithium supplementing material into the inner core, so that lithium ions are released in advance of sodium ions in the initial charging decomposition process, and the lithium ions dissolved in the electrolyte first participate in the formation of a lithium-containing SEI film on the surface of the negative electrode, thereby reducing the loss of active sodium ions in the sodium supplementing agent due to participation in the formation of the SEI film. The SEI film formed has better stability and can reduce the consumption of active sodium ions due to repeated dissolution and regeneration of the film during charging and discharging, thereby effectively improving the specific capacity of the sodium ion battery and the cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application. It is apparent that the accompanying drawings in the following description are only some embodiments of the present application, and other embodiments can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0027] In the drawings: Figure 1 FIG. 1 is a structural schematic diagram of a sodium supplementing agent according to an embodiment of the present application; Figure 2 FIG. 2 is a flowchart of a preparation method of a sodium supplementing agent according to an embodiment of the present application.

[0028] The reference signs are as follows: 10, inner core; 11, sodium supplementing material; 12, lithium supplementing material; 20, coating layer; 21, carbon material; 22, non-metallic atom; 23, metallic atom. DETAILED DESCRIPTION

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of the present invention is for describing specific implementation schemes and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0030] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as part of the scope of the invention.

[0031] In this specification, the median particle size (D50) can be defined as the equivalent diameter of the particle corresponding to the cumulative particle size distribution curve reaching 50%. The median particle size (D50) can be measured, for example, by laser diffraction. D50 can be obtained using a HELOS-RODOS type dry laser particle size analyzer. Laser diffraction can typically measure particle sizes from the submicron range to several millimeters, thus providing highly reproducible and high-resolution results.

[0032] The applicant's research found that during the charging and discharging process of sodium-ion batteries, the SEI film (Solid Electrolyte Interface) formed on the negative electrode surface is mainly composed of sodium-containing organic and inorganic compounds. Compared to the SEI film in lithium-ion batteries, this SEI film has stronger solubility in the electrolyte and poorer stability at high temperatures. The unstable SEI film in sodium-ion batteries continuously dissolves and regenerates during charging and discharging, thus continuously consuming active sodium ions in the battery. This makes it difficult for sodium-ion batteries to meet energy storage requirements in practical applications in terms of charge / discharge capacity and cycle life.

[0033] Currently, while the industry uses sodium-replenishing materials to replenish active sodium in sodium-ion batteries to reduce the adverse effects of active sodium loss, these methods, though effective in compensating for the energy density deficiency caused by sodium deficiency in the cathode material, cannot prevent the unstable SEI film on the anode surface from continuously consuming active sodium ions. This results in suboptimal sodium replenishment and fails to effectively improve the charge / discharge capacity and cycle life of sodium-ion batteries.

[0034] To address the aforementioned issues, this application provides a sodium replenishing agent. This agent introduces lithium replenishing material into the core, utilizing the characteristic that lithium ions have lower resistance to separation than sodium ions. During the initial decomposition process, lithium ions are preferentially released to participate in the formation of the SEI film on the negative electrode surface, thereby reducing the loss of sodium ions released by the sodium replenishing agent due to their participation in SEI film formation. Simultaneously, by introducing lithium elements into the SEI film, the stability of the SEI film is improved, reducing the risk of dissolution during charge and discharge, and minimizing the loss of active sodium caused by repeated dissolution and regeneration of the SEI film during charge and discharge. This effectively enhances the specific capacity and cycle life of the sodium-ion battery.

[0035] like Figure 1 As shown, in a first aspect, the sodium replenishing agent provided in this application includes a core 10 and a coating layer 20. The core 10 includes a sodium replenishing material 11 and a lithium replenishing material 12. The coating layer 20 covers the outside of the core 10 and includes a carbon material 21.

[0036] Based on the characteristic that lithium ions have a smaller radius than sodium ions and therefore lower extraction resistance, a lithium replenishing material 12 is introduced into the core 10 of the sodium replenishing agent to work in conjunction with the sodium replenishing material 11. This reduces the extraction resistance of active ions in the sodium replenishing agent at low voltages, lowers the decomposition potential of the sodium replenishing agent, and increases the specific capacity of the sodium replenishing agent during the first charge. Furthermore, during the first charge, the lithium replenishing material 12 in the sodium replenishing agent decomposes and releases lithium ions before the sodium replenishing material 11. The preferentially released lithium ions dissolve in the electrolyte and participate in the formation of the SEI film on the negative electrode surface before sodium ions. This effectively reduces the amount of sodium ions lost in the sodium replenishing agent due to participation in the formation of the SEI film, further improving the specific charging capacity of the sodium replenishing agent.

[0037] Furthermore, compared to SEI films formed solely by sodium ions, SEI films formed by lithium ions exhibit better electrochemical stability. The resulting SEI film is less likely to dissolve in the electrolyte during charge and discharge, reducing the amount of active sodium ions consumed by repeated dissolution and regeneration during charge and discharge, thereby effectively improving the charge and discharge capacity and cycle life of sodium-ion batteries.

[0038] It should be noted that the type of sodium-supplementing material 11 contained in the core 10 of the sodium supplement is not limited, and sodium-supplementing materials 11 commonly used in the art can be selected. For example, in some embodiments, the sodium-supplementing material 11 contained in the core 10 can be selected from at least one of Na2CO3, Na2NiO2, NaCrO2, Na2S, CH3COONa, Na2C4O4, and Na2C2O4. The sodium-supplementing material 11 can be any one of the materials listed above, such as Na2CO3, Na2NiO2, NaCrO2, Na2S, CH3COONa, Na2C4O4, or Na2C2O4. The sodium-supplementing material 11 can also be any combination of two or more of the materials listed above. For example, the sodium-supplementing material 11 can be a combination of Na2CO3 and Na2O2, or a combination of Na2CO3 and Na2O, or a combination of Na2O2 and Na2O, or a combination of Na2CO3 and Na2NiO2, or a combination of NaCrO2 and Na2S, or a combination of CH3COONa and Na2C2O4, or a combination of Na2CO3, Na2O2, and CH3COONa, or a combination of Na2CO3, Na2O, and Na2C2O4, etc., and so on. When the sodium-supplementing material 11 is a combination of two or more materials, the proportion of each material within the combination is not limited and can be mixed in any proportion. In other embodiments, the sodium-supplementing material 11 can also be a material not listed above.

[0039] In the sodium replenishing agent, the type of lithium replenishing material 12 contained in the core 10 is not limited, and commonly used lithium replenishing materials 12 in the art can be selected. For example, in some embodiments, the lithium replenishing material 12 contained in the core 10 can be selected from at least one of Li5FeO4, Li2NiO2, and LiCoO2. That is, the lithium replenishing material 12 can be any one of the materials listed above, such as Li5FeO4, Li2NiO2, or LiCoO2; the lithium replenishing material 12 can also be any combination of two or more of the materials listed above, for example, the lithium replenishing material 12 is a combination of Li5FeO4 and Li2NiO2, or a combination of Li5FeO4 and LiCoO2, or a combination of Li2NiO2 or LiCoO2, or a combination of Li5FeO4, Li2NiO2, or LiCoO2, etc., which will not be listed here one by one. When the lithium replenishing material 12 is a combination of two or more materials, the proportion of each material in the combination is not limited, and they can be mixed in any proportion. In other embodiments, the lithium replenishing material 12 can also be a material not listed above.

[0040] In some embodiments, in the core 10, the decomposition potential of the sodium replenishing material 11 is higher than that of the lithium replenishing material 12, so as to further increase the number of lithium ions that are released before sodium ions in the sodium replenishing agent, thereby further reducing the amount of active sodium consumed in the formation of the SEI film on the negative electrode surface, improving the sodium replenishing efficiency of the sodium replenishing agent, enhancing the electrochemical stability of the SEI film formed on the negative electrode surface, and improving the cycle performance of the battery.

[0041] Furthermore, in the sodium replenishing agent, the coating layer 20 located outside the core 10, based on the high conductivity of the carbon material 21, can effectively reduce the migration resistance of electrons in the sodium replenishing agent, further reducing the decomposition potential of the sodium replenishing agent and improving the sodium replenishment efficiency. At the same time, the coating layer 20 can also effectively reduce the direct contact between the core 10 and the external environment, improving the air stability of the sodium replenishing agent.

[0042] It should be noted that the specific form of the carbon material 21 in the coating layer 20 is not limited and may include morphological carbon and amorphous carbon. In some embodiments, the carbon material 21 in the coating layer 20 may be selected from at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon. That is, the carbon material 21 can be any one of the materials listed above, such as graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, or conductive carbon; the carbon material 21 may also be any combination of two or more of the materials listed above, for example, a combination of graphene and carbon nanotubes, or a combination of graphene and carbon fiber, or a combination of conductive carbon and carbon nanotubes, or a combination of hard carbon and conductive carbon, or a combination of graphene, carbon nanotubes, and conductive carbon, or a combination of hard carbon, graphene, and conductive carbon, etc., which will not be listed here. When the carbon material 21 is a combination of two or more materials, the proportion of each material within the combination is not limited and can be mixed in any proportion. In other embodiments, the carbon material 21 may also be a material not listed above.

[0043] like Figure 1 As shown, in some embodiments, the D50 particle size of the sodium-supplementing material 11 particles in the core 10 is less than or equal to 5 μm. When the D50 particle size of the sodium-supplementing material 11 particles in the core 10 is reduced to the above range, the diffusion distance of sodium ions in the sodium-supplementing material 11 can be effectively shortened, the extraction resistance of sodium ions in the sodium-supplementing material 11 can be reduced, the decomposition potential of the sodium-supplementing material 11 can be reduced, thereby improving the charging capacity of the sodium-supplementing material 11.

[0044] like Figure 1As shown, in some embodiments, the D50 particle size of the lithium-supplementing material 12 is larger than that of the sodium-supplementing material 11. The sodium-supplementing agent is mixed in the core 10 with the larger-particle-size lithium-supplementing material 12 and the smaller-particle-size sodium-supplementing material 11. This avoids the spontaneous agglomeration of the smaller-particle-size sodium-supplementing material 11 into larger-particle-size particles when forming the core 10 with the lithium-supplementing material 12, thus effectively maintaining the improvement effect of the smaller-particle-size sodium-supplementing material 11 on the sodium-supplementing agent's desodium removal rate at low potentials. Furthermore, based on the characteristic that the lithium-supplementing material 12 is mainly composed of solid-phase decomposition products, the solid-phase products of the larger-particle lithium-supplementing material 12 effectively support the structure of the core 10 after the sodium-supplementing material 11 decomposes and releases a large amount of gas, preventing the sodium-supplementing agent from collapsing within the positive electrode after decomposition and affecting the structural stability of the positive electrode sheet.

[0045] In the core 10, the D50 particle size difference between the lithium replenishing material 12 and the sodium replenishing material 11 is greater than or equal to 2 μm. Optionally, the D50 particle size difference between the lithium replenishing material 12 and the sodium replenishing material 11 can be any value in the range of 2 to 20 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, or 20 μm. When there is a sufficient particle size difference between the lithium replenishing material 12 and the sodium replenishing material 11, it can be ensured that the lithium replenishing material 12 effectively supports the structure of the coating layer 20 after the sodium replenishing agent is desodiumed, maintaining the integrity of the sodium replenishing agent particle structure. If the difference in D50 particle size between lithium replenishing material 12 and sodium replenishing material 11 is less than 2 μm, the particle size of lithium replenishing material 12 in the core 10 is too small, which affects the support effect of its own decomposition products on the coating layer 20 and increases the risk of collapse after sodium replenishing agent particles are desodiumed.

[0046] In some embodiments, the D50 particle size of the sodium supplement material 11 is any value in the range of 1 to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm. Optionally, in one embodiment, the D50 particle size of the sodium supplement can be any value in the range of 3 to 5 μm, for example, it can be 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0047] In some embodiments, the D50 particle size of the lithium replenishing material 12 is less than or equal to 15 μm. When the D50 particle size of the lithium replenishing material 12 is within the above range, the negative impact of large-diameter particles on the lithium removal rate of the lithium replenishing material 12 can be reduced, and the number of lithium ions preferentially removed during the decomposition of the sodium replenishing agent can be avoided from decreasing significantly, thereby ensuring the improvement effect of introducing the lithium replenishing material 12 into the core 10 on the sodium replenishing efficiency of the sodium replenishing agent. If the D50 particle size of the lithium replenishing material 12 is too large, it will cause the decomposition potential of the lithium replenishing material 12 to increase, which will reduce the proportion of lithium ions removed before sodium ions during the decomposition of the core 10, increase the amount of active sodium lost in the formation of the SEI film on the negative electrode surface, reduce the charging capacity of the sodium replenishing agent, affect the sodium replenishing effect of the sodium replenishing agent on the battery, and also reduce the stability of the negative electrode SEI film, which will have a negative impact on the battery capacity and cycle life.

[0048] Optionally, the D50 particle size of the lithium replenishment material 12 can be any value in the range of 7 to 15 μm, for example, it can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0049] Further optionally, in one embodiment, the D50 particle size of the lithium replenishing material 12 is any value in the range of 5 to 10 μm, for example, it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm.

[0050] In some embodiments, the mass content of the core 10 in the sodium supplement is any value in the range of 85% to 98%, for example, the mass content of the core 10 can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or 98%.

[0051] In some embodiments, the mass content of the coating layer 20 in the sodium supplement is any value in the range of 2% to 15%, for example, the mass content of the coating layer 20 can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0052] In some embodiments, the mass content of lithium supplement material 12 in the core 10 is greater than or equal to 20%. Optionally, in some embodiments, the mass content of lithium supplement material 12 in the core 10 is any value in the range of 20% to 60%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%; the mass content of sodium supplement material 11 in the core 10 is any value in the range of 40% to 80%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

[0053] like Figure 1 As shown, in some embodiments, the carbon material 21 of the coating layer 20 is doped with non-metallic atoms 22. The non-metallic atoms 22 are chemically bonded to the carbon material 21 to break the electronic symmetry of the carbon material 21 and introduce more active sites into the coating layer 20. The active sites introduced by the doping of non-metallic atoms 22 (such as pyridine nitrogen, graphitic nitrogen, thiophene sulfur, etc.), based on their own electron-deficient structure, can effectively adsorb the gas generated by the decomposition of the sodium supplementing material 11, including active oxygen; on the other hand, they can further promote the transfer of electrons in the sodium supplementing agent based on the highly conductive carbon material 21, improve the decomposition ability of the sodium supplementing agent under low voltage, and reduce the decomposition potential of the sodium supplementing agent.

[0054] Furthermore, although the carbon material 21 in the coating layer 20 can promote electron transfer in the sodium replenishing agent and reduce its decomposition potential, the hydrophobic properties of the carbon material 21 surface hinder the wetting of the sodium replenishing agent by the electrolyte. This makes it difficult for the lower ion conductivity of the sodium replenishing agent surface to match its higher electron conductivity, thereby exacerbating the polarization risk of the sodium replenishing agent and affecting its sodium replenishment efficiency. The sodium replenishing agent of this application forms porous structures and hydrophilic groups on the surface of the carbon material 21 by doping non-metallic atoms 22 into it. These include nitrogen doping introducing pyridine nitrogen, graphitic nitrogen, and quaternary nitrogen; phosphorus doping forming CPO, COP, and C3-P=O; and sulfur doping forming thiophene and SO42-SO ... y (0 < y < 6), etc. Hydrophilic groups introduced by doping non-metallic heteroatoms 22. The hydrophilic groups introduced onto the carbon material 21 can improve the wettability of the coating layer 20 to the electrolyte, accelerate the extraction rate of sodium ions from the sodium supplement, inhibit the polarization of the sodium supplement during decomposition, and further improve the specific capacity of the sodium supplement. Furthermore, carbon materials 21 doped with non-metallic atoms 22 also exhibit better mechanical properties. For example, boron-doped carbon nanotubes are harder, tougher, and have higher compressive strength than pure carbon nanotubes; sulfur-doped carbon nanotubes have good toughness and flexural modulus; and nitrogen-doped carbon nanotubes have high mechanical strength and heat resistance.

[0055] In some embodiments, the mass content of non-metallic atoms 22 in the coating layer 20 is 4% to 15%, for example, it can be 4%, 5%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. When the mass content of non-metallic atoms 22 in the coating layer 20 is within the above range, the improvement effect of non-metallic atom doping on the electronic conductivity and surface wettability of the sodium supplement can be ensured, and excessive doping can be avoided from causing excessive damage to the carbon layer, thereby affecting the protective effect of the coating layer 20 on the core 10.

[0056] In some embodiments, the non-metallic atom 22 includes at least one of N, B, S, and P. That is, the non-metallic atom 22 doped in the coating layer 20 can be any one of the materials listed above, such as N, B, S, or P; the non-metallic atom 22 doped in the coating layer 20 can also be any combination of two or more of the materials listed above, for example, the non-metallic atom 22 can be a combination of N and S, or a combination of N and P, or a combination of B and P, or a combination of S and B, or a combination of N, B, and P, or a combination of N, B, S, and P, etc., and will not be listed one by one here. When the non-metallic atom 22 is a combination of two or more materials, the proportion of each material in the combination is not limited, and they can be mixed in any proportion. In other embodiments, the non-metallic atom 22 can also be a material not listed above.

[0057] like Figure 1 As shown, in some embodiments, the coating layer 20 includes metal atoms 23, which include at least one of noble metal atoms and transition metal atoms. The metal atoms 23 are supported in the carbon material 21 in single-atom form. Based on their unique electronic structure and quantum size effect, the single metal atoms 23 effectively enhance the catalytic activity of the sodium supplementer with a lower loading amount through high metal atom utilization, thereby improving the reaction kinetics of the sodium supplementer and reducing its decomposition potential. Furthermore, the metal atoms 23 supported in the carbon material 21, as a highly active catalyst, can efficiently adsorb various molecules, thus effectively adsorbing the gas released by the sodium supplementer 11 during its decomposition, reducing the gas production during the decomposition of the sodium supplementer.

[0058] In some embodiments, the mass content of metal atoms 23 in the coating layer 20 is any value within the range of 0.1% to 1%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%. Based on its high atomic utilization, the metal atoms 23, when loaded in the coating layer 20 at the above-mentioned mass content range, can effectively improve the catalytic efficiency for the decomposition of sodium-supplementing material 11 without significantly affecting the energy density of the sodium-supplementing agent.

[0059] In some embodiments, the transition metal atom 23 is selected from at least one of Ni, Co, Mn, and Fe. That is, the transition metal atom can be any one of the materials listed above, such as Ni, Co, Mn, or Fe; the transition metal atom can also be any combination of two or more of the materials listed above, for example, a combination of Ni and Co, or a combination of Ni and Mn, or a combination of Mn and Fe, or a combination of Mn and Co, or a combination of Ni, Fe, and Co, or a combination of Ni, Co, Mn, and Fe, etc., and so on. When the transition metal atom is a combination of two or more materials, the proportion of each material within the combination is not limited, and they can be mixed in any proportion. In other embodiments, the transition metal atom can also be a material not listed above.

[0060] In some embodiments, the noble metal atom 23 is selected from at least one of Ir, Rh, Ru, and Pd. That is, the noble metal atom can be any one of the materials listed above, such as Ir, Rh, Ru, or Pd; the noble metal atom can also be any combination of two or more of the materials listed above, for example, a combination of Ir and Rh, or a combination of Ir and Ru, or a combination of Pd and Rh, or a combination of Pd and Ru, or a combination of Rh, Ru, and Pd, or a combination of Ir, Rh, Ru, and Pd, etc., and so on, without further listing. When the noble metal atom is a combination of two or more materials, the proportion of each material within the combination is not limited, and they can be mixed in any proportion. In other embodiments, the noble metal atom can also be a material not listed above.

[0061] It should be noted that, in the above embodiments, the heteroatom-doped carbon material 21 can be prepared by various methods, such as physical grinding and mixing, chemical vapor deposition, arc discharge, laser evaporation, etc.

[0062] like Figure 1 As shown, in some embodiments, the coating layer 20 simultaneously contains non-metallic atoms 22 and metallic atoms 23, which can be selected from the atom types in the above embodiments. The metallic atoms 23 and non-metallic atoms 22 in the coating layer 20 work synergistically to effectively capture the gases released from the decomposition of the sodium supplement material 11, reduce the gas production from the decomposition of the sodium supplement, and improve the catalytic activity and conductivity of the sodium supplement, thereby further reducing the decomposition potential of the sodium supplement. In addition, the non-metallic atoms 22 doped in the coating layer 20 help anchor the active metal atoms 23, increasing the loading and stability of the metal atoms 23 in the coating layer 20, thereby enhancing the catalytic effect of the metal atoms 23 on the sodium supplement material 11 and the adsorption effect on the gas produced by the sodium supplement material 11.

[0063] In a second aspect, the present invention also provides a method for preparing the sodium supplement in any of the above embodiments, such as... Figure 2 As shown, the preparation method of this sodium supplement includes the following steps: S1. Provide a coating material, wherein the coating material includes a carbon material; S2. Mix the sodium-supplementing material and the lithium-supplementing material evenly according to the preset mass ratio to obtain the core material; S3. Mix and grind the core material and the coating material to obtain a sodium supplement.

[0064] In some embodiments, in step S1, the carbon material is selected from at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon.

[0065] In some embodiments, step S1 further includes the step of doping the carbon material with non-metallic atoms, specifically by mixing and sintering the carbon material with non-metallic element raw materials, thereby doping the carbon material with non-metallic atoms to obtain a doped modified material. For example, in one instance, the carbon material and non-metallic element raw materials are mixed and ball-milled for 12 to 48 hours to obtain a mixed powder; then, under a protective atmosphere, the mixed powder is sintered at a temperature of 600°C to 1200°C for 4 to 6 hours to obtain a carbon material doped with non-metallic atoms.

[0066] In some embodiments, the non-metallic element raw material is a precursor material containing a non-metallic element, which is at least one of N, B, S, and P. For example, the nitrogen source in the non-metallic element raw material can be selected from at least one of urea, polyacrylonitrile, melamine, or aminomethylphosphonic acid; the boron source in the non-metallic element raw material can be selected from at least one of boric acid, boron oxide, or sodium tetraborate; the sulfur source in the non-metallic element can be selected from at least one of sulfur powder, ferrous sulfate, or potassium sulfate; and the phosphorus source in the non-metallic element raw material can be selected from at least one of red phosphorus, sodium dihydrogen phosphate, or tripotassium phosphate.

[0067] In some embodiments, step S1 further includes the step of introducing metal atoms into the doped modified material. Specifically, the doped modified material is mixed and sintered with a metal element raw material to obtain a coating material, wherein the coating material is a doped modified material loaded with single metal atoms. For example, in one example, the metal element raw material and the doped modified material are placed in a solvent at a preset mass ratio and stirred for 8 to 12 hours to obtain a mixed solution; then the mixed solution is centrifuged and dried to obtain a composite powder, wherein the composite powder is a non-metallic carbon material containing the metal element raw material; finally, under a protective atmosphere, the composite powder is sintered at a temperature of 600°C to 1200°C for 2 to 4 hours to obtain the coating material.

[0068] In step S2, the sodium-supplementing material and the lithium-supplementing material are mixed according to a preset mass ratio, and then ball-milled for 12 to 48 hours to obtain the core material. The mass ratio of the sodium-supplementing material to the lithium-supplementing material is (40~80):(20~40).

[0069] In step S3, the coating material and the core material are mixed according to a preset mass ratio, and then thoroughly ground to coat the core surface with the coating material, thereby producing a sodium supplement; wherein the mass ratio of the core material to the coating material is (85~98):(2~15). For example, in one example, after mixing the core material and the coating material according to the preset mass ratio, ball milling is continued for 12 to 48 hours to obtain the sodium supplement.

[0070] In a third aspect, the present invention also provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive electrode material, a positive electrode conductive agent, a positive electrode binder, and a sodium supplement agent as described in any of the above embodiments, or a sodium supplement agent prepared by the preparation method described in any of the above embodiments. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative electrode material, a negative electrode conductive agent, a thickener, and a negative electrode binder. The positive and negative electrode materials can intercalate and deintercalate sodium ions to achieve energy storage and release. The electrolyte is the carrier for sodium ion transport between the positive and negative electrodes. The separator is permeable to sodium ions but non-conductive, thereby separating the positive and negative electrodes to prevent short circuits.

[0071] Because the sodium-ion battery incorporates the aforementioned sodium replenishing agent into its positive electrode, lithium ions from the sodium replenishing agent participate in the formation of the SEI film on the surface of the negative electrode when the sodium-ion battery is at 100% charge after initial charging. The lithium-containing SEI film has higher electrochemical stability and is less likely to undergo side reactions with the electrolyte, thus consuming the active sodium in the electrolyte. This effectively improves the high-temperature storage life and cycle life of the sodium-ion battery.

[0072] It should be noted that the preparation of the positive electrode, negative electrode, separator, electrolyte, and assembly of the electrochemical device in a sodium-ion battery can be carried out using conventional methods in this field. The following is an example description of the preparation method for a sodium-ion battery: Preparation of positive electrode sheet: The positive electrode material, a composite material containing sodium supplement (the sodium supplement has a mass content of 0.5%~10% in the composite material), a positive electrode conductive agent, and a positive electrode binder are mixed in a weight ratio of (90~98):(1~4):(1~4), optionally 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred under vacuum until the system is homogeneous and transparent to obtain a positive electrode slurry. This positive electrode slurry is uniformly coated onto a positive electrode current collector aluminum foil, which is then air-dried at room temperature and transferred to an oven for further drying. Finally, the foil is cold-pressed and slit to obtain the positive electrode sheet.

[0073] The cathode material includes sodium-containing compounds, specifically NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaMn2O4, NaNi 1 / 2Mn 3 / 2 O2, NaFePO4, Na4Fe3(PO4)2P2O7 (NFPP for short), NaMnPO4, NaCoPO4, Na2FePO4F, Na2MnPO4F, Na2CoPO4F, Na3PS4, P2-Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 The cathode material can be one or at least two of the materials listed above, such as NaFeO2 or Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, or Na2FePO4F, etc.; or any combination of two or more of the materials listed above, such as a combination of NaFeO2 and NaCoO2, or a combination of NaCrO2, NaMnO2 and NaNiO2, or a combination of Na2FePO4F and Na2MnPO4F, or NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2 and Na 2 / 3 Fe 1 / 3 Mn 2 / 3Compositions of O2, etc., will not be listed here. It should be noted that the positive electrode material can also be any positive electrode active material not listed above. When the positive material is a combination of two or more, there is no restriction on the ratio between the components in the composition, and they can be mixed in any proportion.

[0074] The positive electrode conductive agent can be selected from at least one of conductive materials such as carbon black (Super P), acetylene black, nano metal powder, carbon nanotubes (CNT), graphene, and carbon nanofibers (VGCF); the positive electrode binder can be selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), for example, PVDF can be selected as the positive electrode binder.

[0075] Negative electrode preparation: Negative electrode material, negative electrode conductive agent, negative electrode binder, and negative electrode dispersant are mixed in a mass ratio of (93~98):(0.2~1.5):(1~3):(0.01~1.5). N-methylpyrrolidone or deionized water is added as a solvent, and the mixture is thoroughly stirred under vacuum to obtain a negative electrode slurry. This negative electrode slurry is uniformly coated onto a negative electrode current collector, which is then air-dried at room temperature and transferred to an oven for further drying. Finally, the negative electrode is cold-pressed and slit to obtain the negative electrode sheet.

[0076] The negative electrode material can be hard carbon. The negative electrode conductive agent can be selected from at least one conductive material such as carbon black (Super P), acetylene black carbon nanotubes (CNT), nano-silver powder, graphene, and carbon nanofiber (VGCF). The negative electrode binder is selected from at least one binder such as polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR). The thickener is selected from carboxymethyl cellulose, which can be sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0077] Electrolyte preparation: In this application, the electrolyte can be any conventional type of electrolyte in the art. For example, in an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC) and dimethyl carbonate (DMC) are uniformly mixed at a volume ratio of 1:1 to obtain an organic solvent. Then, fluoroethylene carbonate (FEC) additives accounting for 5% of the mass fraction of ethylene carbonate (EC) and dimethyl carbonate (DMC) are added to the organic solvent. Next, fully dried sodium salt NaClO4 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0078] Membrane preparation: The membrane is selected from conventional porous polymer membranes in the art. For example, the membrane material can be selected from one or more combinations of polyvinylidene fluoride, polystyrene, polyarylether sulfone, polyvinyl chloride, polypropylene, polyethylene, polyamide, polyimide, polyacrylic acid, polyacetal, polycarbonate, polyester, polyetherimide, polyimide, polyketone, polyphenylene ether, polyphenylene sulfide, polymethylpentene, polysulfone nonwoven glass, glass fiber materials, ceramics, metal oxides, and composites of organic and inorganic substances. For example, in one instance, the diaphragm is a porous polyethylene (PE) or polypropylene (PP) membrane, optionally a PP / PE / PP porous membrane, with a thickness of 9 μm to 18 μm, such as 9 μm, 12 μm, 16 μm or 18 μm; an air permeability of 180 s / 100 mL to 380 s / 100 mL, such as 180 s / 100 mL, 280 s / 100 mL or 380 s / 100 mL; and a porosity of 30% to 50%, such as 30%, 40% or 50%.

[0079] Battery Assembly: Battery assembly is carried out according to conventional methods. For example, after preparation, the negative electrode, separator, and positive electrode are stacked in sequence and placed in an aluminum-plastic film to obtain a bare cell. The bare cell is then placed in a casing and thoroughly baked to ensure that its water content is below 450 ppm. The prepared electrolyte is injected into the dry cell and sealed. After formation, venting, and aging, a sodium-ion battery with the preset capacity is obtained.

[0080] The conditions for formation, venting, and aging are as follows: charging to the cutoff voltage at a rate of 0.1 to 0.33 C, venting vacuum of -40 to -98 kPa, and venting time of more than 10 seconds; aging temperature of 40 to 50 °C and aging time of 24 to 72 hours.

[0081] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by conventional methods in the art.

[0082] Example 1 This embodiment provides a sodium supplement agent comprising a core and a coating layer surrounding the core. The core comprises 90% by mass and includes sodium-supplementing material Na2CO3 and lithium-supplementing material Li5FeO4 (LFO). The sodium-supplementing material comprises 60% by mass and the lithium-supplementing material comprises 40% by mass. The D50 particle size of the sodium-supplementing material is 3 μm and the D50 particle size of the lithium-supplementing material is 7 μm. The coating layer comprises 10% by mass and includes carbon material, specifically carbon nanotubes.

[0083] The preparation process of this sodium supplement is as follows: (1) The sodium-supplementing material and the lithium-supplementing material were mixed evenly at a mass ratio of 6:4, and ball-milled for 12 hours to obtain the core material; (2) Using carbon material as the coating material, the core material and carbon material are mixed evenly at a mass ratio of 9:1 and ball-milled for 24 hours to obtain sodium supplement.

[0084] Example 2 This embodiment provides a sodium supplement with the same system as in Example 1. The difference between this embodiment and Example 1 is that the coating layer of the sodium supplement is doped with non-metallic atoms, the non-metallic atom being N, and the mass content of non-metallic atoms in the coating layer is 6%.

[0085] The preparation process of this sodium supplement is as follows: (1) The sodium-supplementing material and the lithium-supplementing material were mixed evenly at a mass ratio of 6:4 and ball-milled for 12 hours to obtain the core material.

[0086] (2) The carbon material and the nitrogen source urea are mixed evenly at a mass ratio of 7.5:1, and the mixture is ball-milled for 24 hours to obtain a mixed powder. The mixed powder is then placed in a furnace, and the furnace environment is heated to 900°C at a rate of 5°C / min under a nitrogen atmosphere. The mixture is heated at 900°C for 5 hours and then cooled to obtain a coating material. The coating material is a carbon material doped with nitrogen atoms.

[0087] (3) Mix the core material and the coating material evenly at a mass ratio of 9:1, and ball mill for 24 hours to obtain the sodium supplement.

[0088] Example 3 This embodiment provides a sodium supplement with the same system as in Example 1. The difference between this embodiment and Example 1 is that the coating layer of the sodium supplement is doped with metal atoms, the metal atom is Pd, and the mass content of the metal atoms in the coating layer is 0.2%.

[0089] The preparation process of this sodium supplement is as follows: (1) The sodium-supplementing material and the lithium-supplementing material were mixed evenly at a mass ratio of 6:4 and ball-milled for 12 hours to obtain the core material.

[0090] (3) Add carbon material and palladium chloride, a metal element raw material, to deionized water and stir until homogeneous to obtain a mixed solution; centrifuge and dry the mixed solution to obtain a composite powder, which is a carbon material containing a metal element raw material; place the composite powder in a furnace and heat the furnace environment to 1000°C at a rate of 5°C / min under a nitrogen atmosphere, and heat it at 900°C for 3 hours. After cooling, a coating material is obtained, which is a carbon material loaded with Pd atoms.

[0091] (3) Mix the core material and the coating material evenly at a mass ratio of 9:1, and ball mill for 24 hours to obtain the sodium supplement.

[0092] Example 4 This embodiment provides a sodium supplement with the same system as in Example 2. The difference between this embodiment and Example 2 is that the coating layer of the sodium supplement also contains metal atoms, the metal atoms are Pd, and the mass content of the metal atoms in the coating layer is 0.2%.

[0093] The preparation process of this sodium supplement is as follows: (1) The sodium-supplementing material and the lithium-supplementing material were mixed evenly at a mass ratio of 6:4 and ball-milled for 12 hours to obtain the core material.

[0094] (2) The carbon material and the nitrogen source urea were mixed evenly at a mass ratio of 7.5:1, and the mixture was ball-milled for 24 hours to obtain a mixed powder. The mixed powder was then placed in a furnace, and the furnace environment was heated to 900°C at a rate of 5°C / min under a nitrogen atmosphere. The mixture was heated at 900°C for 5 hours and then cooled to obtain a doped modified material. The doped modified material was a carbon material doped with nitrogen atoms.

[0095] (3) Add the doped modified material and the metal element raw material palladium chloride to deionized water and stir evenly to obtain a mixed solution; centrifuge and dry the mixed solution to obtain a composite powder, which is a doped modified material containing the metal element raw material; finally, place the composite powder in a furnace, and under a nitrogen atmosphere, raise the furnace environment to 1000°C at a rate of 5°C / min, and heat it at 900°C for 3 hours. After cooling, obtain a coating material, which is a doped modified material loaded with Pd atoms.

[0096] (4) Mix the core material and the coating material evenly at a mass ratio of 9:1, and ball mill for 24 hours to obtain the sodium supplement.

[0097] Example 5 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the D50 particle size of the sodium supplement material is 1 μm, and the D50 particle size of the lithium supplement material is 5 μm.

[0098] Example 6 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the D50 particle size of the sodium supplement material is 5 μm.

[0099] Example 7 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the D50 particle size of the sodium supplement material is 10 μm.

[0100] Example 8 This embodiment provides a sodium supplement agent with the same system as in Example 4. The difference between this embodiment and Example 4 is that the D50 particle size of the lithium supplement material is 15 μm.

[0101] Example 9 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of the lithium supplement material in the core is 20%, and the mass content of the sodium supplement material in the core is 80%.

[0102] Example 10 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of the lithium supplement material in the core is 60%, and the mass content of the sodium supplement material in the core is 40%.

[0103] Example 11 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of Pd atoms in the coating layer is 0.1%.

[0104] Example 12 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of Pd atoms in the coating layer is 1%, and the mass content of N atoms in the coating layer is 15%.

[0105] Example 13 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of N atoms in the coating layer is 4%.

[0106] Example 14 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of N atoms in the coating layer is 15%.

[0107] Example 15 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the metal atoms loaded in the coating layer of the sodium supplement are Fe. In step (2), by controlling the mass ratio of the doping modified material to the metal element raw material ferric acetate, the mass content of Fe atoms in the coating layer of the sodium supplement is 0.5%.

[0108] Example 16 This embodiment provides a sodium supplement agent with the same system as that in Embodiment 4. The difference between this embodiment and Embodiment 4 is that the metal atoms loaded in the coating layer of the sodium supplement agent are Co, and the non-metal atoms doped in the coating layer are S. In step (2), by controlling the mass ratio of carbon material to sulfur powder, the mass content of S atoms in the coating layer of the sodium supplement agent is 6%. In step (3), by controlling the mass ratio of doped modified material to cobalt acetate, the mass content of Co atoms in the coating layer of the sodium supplement agent is 0.5%.

[0109] Example 17 This embodiment provides a sodium supplement with the same system as in Embodiment 4. The difference between this embodiment and Embodiment 4 is that the non-metallic atoms doped in the coating layer are N and B, and the metallic atoms doped in the coating layer are Pd and Ni. In step (2), by controlling the mass ratio of carbon material to non-metallic raw materials urea and boric acid, the mass content of N atoms in the coating layer of the sodium supplement is 6% and the mass content of B atoms is 3%. In step (3), by controlling the mass ratio of doped modified material to metallic raw materials palladium chloride and nickel acetate, the mass content of Pd atoms in the coating layer of the sodium supplement is 0.2% and the mass content of Ni atoms is 0.5%.

[0110] Example 18 This embodiment provides a sodium supplement with the same system as in Embodiment 4. The difference between this embodiment and Embodiment 4 is that the non-metallic atoms doped in the coating layer are N and P, and the metallic atoms doped in the coating layer are Pd and Fe. In step (2), by controlling the mass ratio of carbon material to non-metallic raw materials urea and red phosphorus, the mass content of N atoms in the coating layer of the sodium supplement is 6% and the mass content of P atoms is 2%. In step (3), by controlling the mass ratio of doped modified material to metallic raw materials palladium chloride and ferric acetate, the mass content of Pd atoms in the coating layer of the sodium supplement is 0.2% and the mass content of Fe atoms is 0.5%.

[0111] Example 19 This embodiment provides a sodium supplement with the same system as in Example 4. The difference between this embodiment and Example 4 is that the mass content of the kernel in the sodium supplement is 85%.

[0112] Example 20 This embodiment provides a sodium supplement with the same system as that in Example 16. The difference between this embodiment and Example 15 is that the sodium supplement material is CH3COONa, and the mass content of the core in the sodium supplement is 97%.

[0113] Example 21 This embodiment provides a sodium supplement with the same system as that in Example 16. The difference between this embodiment and Example 16 is that the sodium supplement material is Na2C2O4, and the mass content of the core in the sodium supplement is 98%.

[0114] Example 22 This embodiment provides a sodium supplement agent with the same system as in Example 4. The difference between this embodiment and Example 4 is that the lithium supplement material is Li2NiO2.

[0115] Comparative Example 1 This comparative example provides a sodium supplement, which is the sodium supplement material in Example 1.

[0116] Comparative Example 2 This comparative example provides a sodium supplement, which is the sodium supplement material in Example 19.

[0117] Comparative Example 3 This comparative example provides a sodium supplement, which is the sodium supplement material in Example 20.

[0118] Comparative Example 4 This comparative example provides a sodium supplement with the same system as Example 1. The difference between this comparative example and Example 1 is that no lithium supplement material is introduced into the core.

[0119] Comparative Example 5 This comparative example provides a sodium supplement with the same system as Example 2. The difference between this comparative example and Example 2 is that no lithium supplement material is introduced into the core.

[0120] Comparative Example 6 This comparative example provides a sodium supplement with the same system as Example 3. The difference between this comparative example and Example 3 is that no lithium supplement material is introduced into the core.

[0121] Comparative Example 7 This comparative example provides a sodium supplement with the same system as Example 1. The difference between this comparative example and Example 1 is that the sodium supplement is not coated on the outside of the core, but only the lithium supplement material and the sodium supplement material are mixed.

[0122] The sodium supplements prepared in Examples 1 to 22 and Comparative Examples 1 to 7 were subjected to decomposition potential and specific capacity tests. The sodium-ion batteries provided in Examples 1 to 22 and Comparative Examples 1 to 7 were subjected to charge-discharge tests and storage gas generation tests to verify the efficacy of the present invention. The test results are shown in Table 2.

[0123] Sodium supplement capacity and decomposition potential test: The sodium supplement prepared above was mixed with conductive agent Super P and binder polyvinylidene fluoride (PVDF) in a weight ratio of 90:5:5. N-methylpyrrolidone (NMP) solvent was added and the mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was coated onto the positive electrode current collector aluminum foil and prepared by drying, cold pressing and slitting. Sodium metal was used as the negative electrode and assembled in the following order: positive electrode shell - electrode sheet - electrolyte - separator - electrolyte - sodium sheet - gasket - spring sheet - negative electrode shell. The battery was then sealed using a sealing machine to obtain a CR2032 button half cell.

[0124] At 25°C, the coin cell was charged to 4.25V with a constant current of 1mA, and the initial charge capacity and initial charge energy of the coin cell were measured. The initial charge capacity of the sodium supplement was obtained by dividing the initial charge capacity by the mass of the sodium supplement. The decomposition potential of the sodium supplement was obtained by dividing the initial charge energy by the initial charge capacity.

[0125] The preparation process of sodium-ion batteries is as follows: The positive electrode material NFPP, a composite material containing sodium supplement (2% by mass), a positive electrode conductive agent, and a positive electrode binder are mixed at a weight ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred under vacuum until homogeneous. The slurry solid content is adjusted to 55% to obtain the positive electrode slurry. The positive electrode slurry is coated onto carbon aluminum foil, dried, and cold-pressed to form the positive electrode sheet. The negative electrode material hard carbon, the negative electrode conductive agent carbon black (Super P), the thickener sodium carboxymethyl cellulose (CMC-Na), and the negative electrode binder styrene-butadiene rubber (SBR) are mixed at a mass ratio of 96.6:0.8:1.2:1.4. Deionized water is added, and the slurry solid content is adjusted to 55%. The mixture is then thoroughly stirred under vacuum to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil, dried, and cold-pressed to form the negative electrode sheet. Using a 12μm thick porous PP membrane as the separator, the prepared positive electrode, separator, and negative electrode were stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film was wrapped around the separator, and the mixture was dried in a vacuum oven at 120 °C. After injecting 5.0 g / Ah of electrolyte, the mixture was sealed. Following processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, a 1 Ah soft-pack sodium-ion battery was finally obtained.

[0126] Sodium-ion battery gas production test: The prepared sodium-ion battery is placed in the test equipment, the equipment temperature is set to 25℃, and it is charged at a constant current and constant voltage of 0.33C to 4V (1C is the nominal capacity of the battery). After full charging, the initial volume V1 of the battery is measured. Then the sodium-ion battery is placed in a hot box at 60℃, and the volume change is measured every 30 days (using the "water displacement method"). The volume V2 of the battery taken out on the 60th day is recorded, and the gas production growth of the battery can be obtained as (V2-V1) / V1.

[0127] Table 1: Parameters of sodium supplements prepared in Examples 1 to 22 and Comparative Examples 1 to 7, and results of battery performance tests.

[0128] Table 2: Performance test results of sodium supplements prepared in Examples 1 to 22 and Comparative Examples 1 to 7

[0129] Comparing the test results of Example 1 and Comparative Example 1, Example 3 and Comparative Example 5, and Example 4 and Comparative Example 6, it can be seen that the sodium replenishing agent provided in this application introduces lithium replenishing material into the core and utilizes the introduced lithium ions to participate in the formation of the SEI film, thereby reducing the active sodium consumed in the battery due to the formation of the SEI film, improving the initial charge specific capacity of the sodium replenishing agent; and improving the stability of the SEI film formed in the battery, thereby reducing the gas generation rate of the battery during high-temperature storage, and effectively improving the cycle life of sodium-ion batteries.

[0130] Comparing the test results of Examples 1 and 2, it can be seen that doping the coating layer with non-metallic atoms can effectively improve the conductivity of the sodium supplement, reduce its decomposition potential, and increase its initial charge capacity. Simultaneously, the non-metallic atoms doped in the coating layer can effectively adsorb the gases produced by the decomposition of the sodium supplement material, thereby effectively inhibiting the growth of gas production from the decomposition of the sodium supplement.

[0131] Comparing the test results of Example 1 and Example 3, it can be seen that by loading metal atoms into the coating layer, the catalytic activity of the sodium supplement can be improved, the decomposition potential of the sodium supplement can be effectively reduced, and the initial charge capacity of the sodium supplement can be increased. At the same time, the metal atoms in the coating layer have a strong adsorption capacity for gas production of the core material, which can effectively inhibit the increase of decomposition gas production of the sodium supplement.

[0132] Comparing the test results of Examples 1 and 4, it can be seen that the sodium supplement provided in this application can improve the conductivity of the sodium supplement by utilizing the synergistic effect of metal atoms and non-metal atoms in the coating layer, further reducing the decomposition potential of the sodium supplement and increasing the initial charge capacity of the sodium supplement; and efficiently absorb the gas released by the decomposition of the core material, further reducing the gas production of the sodium supplement during decomposition.

[0133] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A sodium supplement, characterized in that, include: The core comprises sodium-supplementing materials and lithium-supplementing materials; A coating layer comprising a carbon material.

2. The sodium supplement according to claim 1, characterized in that, The sodium-supplementing material includes at least one of Na2CO3, Na2NiO2, NaCrO2, Na2S, CH3COONa, Na2C4O4, and Na2C2O4; the lithium-supplementing material includes at least one of Li5FeO4, Li2NiO2, and LiCoO2.

3. The sodium supplement according to claim 1 or 2, characterized in that, The decomposition potential of the sodium-supplementing material is higher than that of the lithium-supplementing material.

4. The sodium supplement according to claim 1, characterized in that, The D50 particle size of the sodium-supplementing material is less than or equal to 5 μm, the D50 particle size of the lithium-supplementing material is greater than the D50 particle size of the sodium-supplementing material, and the difference between the D50 particle size of the lithium-supplementing material and the D50 particle size of the sodium-supplementing material is greater than or equal to 2 μm.

5. The sodium supplement according to claim 4, characterized in that, The D50 particle size of the sodium supplement material is 3~5μm.

6. The sodium supplement according to claim 4, characterized in that, The D50 particle size of the lithium replenishment material is less than or equal to 15 μm.

7. The sodium supplement according to claim 6, characterized in that, The D50 particle size of the lithium replenishment material is 7~15μm.

8. The sodium supplement according to claim 1, characterized in that, The lithium replenishment material has a mass content of greater than or equal to 20% in the core.

9. The sodium supplement according to claim 8, characterized in that, The lithium replenishing material has a mass content of 20% to 60% in the core.

10. The sodium supplement according to claim 1, characterized in that, The core has a mass content of 85% to 98% in the sodium supplement; the coating layer has a mass content of 2% to 15% in the sodium supplement.

11. The sodium supplement according to claim 1, characterized in that, The carbon material includes at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon.

12. The sodium supplement according to claim 1, characterized in that, The coating layer is doped with non-metallic atoms, including at least one of N, B, S and P.

13. The sodium supplement according to claim 1, characterized in that, The coating layer includes metal atoms, which include at least one of noble metal atoms and transition metal atoms.

14. The sodium supplement according to claim 13, characterized in that, The noble metal atom includes at least one of Ir, Rh, Ru, and Pd, and the transition metal atom includes at least one of Ni, Co, Mn, and Fe.

15. A method for preparing the sodium supplement according to any one of claims 1 to 14, characterized in that, include: A coating material is provided, the coating material comprising a carbon material; The sodium-supplementing material and the lithium-supplementing material are mixed evenly according to a preset mass ratio to obtain the core material; The core material and the coating material are mixed and ground to obtain a sodium supplement.

16. A sodium-ion battery, characterized in that, The invention includes a positive electrode sheet, which comprises a positive current collector and a positive active material layer, wherein the positive active material layer comprises the sodium supplement agent according to any one of claims 1 to 14, or the sodium supplement agent prepared by the preparation method according to claim 15.

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