Sodium supplement, preparation method thereof, positive active material, positive electrode sheet, and battery

Abstract

The application discloses a kind of sodium supplement agent and preparation method thereof, positive active material, positive pole piece and battery, and sodium supplement agent includes sodium supplement particle, sodium supplement particle has core-shell structure, sodium supplement particle includes sodium supplement core and the sodium supplement shell that is coated in the outside of sodium supplement core, the material of sodium supplement shell includes organic sodium supplement agent, the material of sodium supplement core includes inorganic sodium supplement agent, inorganic sodium supplement agent includes Na x M y O z Wherein x, y and z are all greater than 0, x / y>1, M includes at least one transition metal element. According to the sodium supplement agent of the embodiment of the application, the active sodium ions can be supplemented, and the problems of reducing the battery capacity and energy density and the cycle performance due to the consumption of sodium ions by the solid electrolyte interface (SEI) film can be solved; by forming the core-shell structure of the organic sodium supplement agent wrapping the inorganic sodium supplement agent, the influence of water and oxygen in the air on the inorganic sodium supplement agent can be reduced, and the structural stability of the inorganic sodium supplement agent can also be played, to prevent the structure from collapsing.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a sodium supplement agent and its preparation method, a positive electrode active material, a positive electrode sheet, and a battery. Background Technology

[0002] In related technologies, during the cycling process of sodium-ion batteries, the solid electrolyte interface (SEI) film formed consumes the active sodium in the cathode material, reducing the energy density, battery capacity, and cycle stability of the sodium-ion battery.

[0003] Currently, sodium replenishment methods are mainly divided into positive electrode sodium replenishment and negative electrode sodium replenishment. Positive electrode sodium replenishment typically uses organic or inorganic sodium replenishing agents. However, after organic sodium replenishing agents react and release active sodium ions, the lack of a structural framework leads to the structural collapse of the positive electrode material. Inorganic sodium replenishing agents, on the other hand, are unstable in air and easily react with water and oxygen to produce alkaline substances with a high pH value, causing the slurry to become jelly-like and uncoatable. Therefore, it is necessary to ensure good isolation between the inorganic sodium replenishing agent and air during the processing and preparation of inorganic sodium replenishing agents, which makes the processing and preparation of inorganic sodium replenishing agents difficult. Therefore, improvements are needed. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, one objective of this invention is to provide a sodium replenishing agent for positive electrode active materials, which can replenish active sodium ions during battery charging and discharging, solving the problem of reduced battery capacity, energy density, and cycle performance caused by sodium ion consumption at the solid electrolyte interphase (SEI) membrane. By encapsulating an inorganic sodium replenishing agent with an organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can be enhanced, preventing structural collapse and improving the battery's energy density, battery capacity, and cycle performance.

[0005] The present invention also proposes a method for preparing the above-mentioned sodium supplement.

[0006] The present invention also proposes a positive electrode active material having the above-mentioned sodium supplement.

[0007] The present invention also proposes a positive electrode sheet having the above-mentioned positive active material.

[0008] The present invention also proposes a battery having the above-mentioned positive electrode.

[0009] According to a first aspect of the present invention, a sodium-replenishing agent for a positive electrode active material comprises sodium-replenishing particles having a core-shell structure. The sodium-replenishing particles include a sodium-replenishing core and a sodium-replenishing shell covering the core. The material of the sodium-replenishing shell comprises an organic sodium-replenishing agent, and the material of the sodium-replenishing core comprises an inorganic sodium-replenishing agent, wherein the inorganic sodium-replenishing agent includes Na. x M y O z , where x, y and z are all greater than 0, x / y > 1, and M includes at least one transition metal element.

[0010] According to embodiments of the present invention, the sodium replenishing agent for positive electrode active materials can replenish active sodium ions during battery charging and discharging, solving the problem of reduced battery capacity, energy density, and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film. By encapsulating the inorganic sodium replenishing agent with an organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can be utilized to prevent structural collapse, thereby improving the battery's energy density, battery capacity, and cycle performance.

[0011] According to some embodiments of the present invention, 1 < x / y ≤ 5, 0.5 < x / z < 5.

[0012] According to some optional embodiments of the present invention, the chemical formula Na x M y O z In this context, x = 2, 5, or 6, y = 1, z = 2 or 4, and M includes one or more of the elements Zn, Ni, Cu, Fe, Mn, Cr, and Al.

[0013] According to some embodiments of the present invention, Na x M y O z The materials formed after releasing active sodium ions include: Na w M y O z , where 0 < w < x.

[0014] In some optional embodiments of the present invention, the general chemical formula Na... w M y O z In this context, 0 < w ≤ 1, y = 1, z = 2, and M includes one or more of Zn, Ni, Cu, Fe, Mn, Cr, and Al.

[0015] According to some embodiments of the present invention, the ratio of the thickness of the sodium-supplementing shell to the particle size of the sodium-supplementing core ranges from 0.02 to 0.5; and / or, the thickness of the sodium-supplementing shell ranges from 0.1 micrometers to 2 micrometers, and the particle size of the sodium-supplementing core ranges from 0.5 micrometers to 5 micrometers.

[0016] According to some embodiments of the present invention, the organic sodium supplement includes Na i A a B b D c Where A is one of the elements C, O, N, F, P and H, B is one of the elements C, O, N, F, P and H, D is one of the elements C, O, N, F, P and H, i is greater than 1, and at least one of a, b and c is greater than 0.

[0017] According to some optional embodiments of the present invention, the organic sodium supplement includes at least one of Na3C6H5O7, Na2C2O4, Na3N, Na3F, Na3P, Na2C4O4, Na2C3O3, Na2C5O5, and Na2C6O6.

[0018] According to a second aspect of the present invention, a method for preparing a sodium supplement is provided, wherein the sodium supplement is the sodium supplement described in the first aspect of the present invention. The method for preparing the sodium supplement includes: dispersing an inorganic sodium supplement in an organic solvent and adding an organic sodium supplement to the organic solvent; performing a solvothermal reaction at a set temperature for a set time to generate the sodium supplement particles having a core-shell structure; and separating the sodium supplement particles from the organic solvent by centrifugation, vacuum drying, or filtration.

[0019] The preparation method of the sodium supplement according to the embodiments of the present invention is simple and easy to control.

[0020] According to some embodiments of the present invention, the molar ratio of the organic sodium supplement to the inorganic sodium supplement added to the organic solvent is 0.05 to 0.5.

[0021] According to a third aspect of the present invention, a positive electrode active material includes: a main material; and a sodium supplement, wherein the sodium content of the sodium supplement is greater than the sodium content of the main material, and the sodium supplement is a sodium supplement according to the first aspect of the present invention described above.

[0022] According to embodiments of the present invention, by setting the positive electrode active material to include the above-mentioned sodium replenishing agent, active sodium ions can be replenished during battery charging and discharging, solving the problem of reduced battery capacity, energy density, and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film; by encapsulating the inorganic sodium replenishing agent with an organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can also be utilized to prevent structural collapse, thereby improving the battery's energy density, battery capacity, and cycle performance.

[0023] According to some embodiments of the present invention, the sodium supplement has a sodium content of more than 30%, and the sodium content of the main material is less than 25%; and / or, the mass ratio of the sodium supplement to the main material is in the range of 0.01 to 0.3.

[0024] According to some embodiments of the present invention, the main material includes polyanionic compounds or transition metal oxides.

[0025] According to a fourth aspect of the present invention, a positive electrode sheet includes: a positive current collector; and a positive electrode material, wherein the positive electrode material includes a positive active material according to the third aspect of the present invention, and the positive electrode material covers the positive current collector.

[0026] According to the positive electrode sheet of the present invention, by setting the positive electrode material of the positive electrode sheet to include the above-mentioned positive electrode active material, active sodium ions can be replenished during the charging and discharging process of the battery, which solves the problem of reduced battery capacity, energy density and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film; by encapsulating the inorganic sodium replenishing agent with the organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can also be utilized to prevent structural collapse and improve the energy density, battery capacity and cycle performance of the battery.

[0027] A battery according to a fifth aspect embodiment of the present invention includes: a positive electrode sheet according to the fourth aspect embodiment of the present invention described above.

[0028] According to the battery of the present invention, by setting the above-mentioned positive electrode plate, active sodium ions can be replenished during the charging and discharging process of the battery, which solves the problem of reduced battery capacity, energy density and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film; by encapsulating the inorganic sodium supplement with the organic sodium supplement to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium supplement can be reduced, and the structural stability of the inorganic sodium supplement can also be utilized to prevent structural collapse, thereby improving the energy density, battery capacity and cycle performance of the battery.

[0029] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 This is a transmission electron microscope (TEM) image of sodium-supplementing particles of a sodium supplement according to some embodiments of the present invention. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0033] The following is for reference. Figure 1 A sodium supplement agent for a positive electrode active material is described according to an embodiment of the present invention.

[0034] According to a first aspect of the present invention, a sodium replenishing agent for a positive electrode active material includes sodium replenishing particles, the particle size of which can be less than 10 micrometers. This sodium replenishing agent can be added to the positive electrode active material, and during battery charging and discharging, the agent can replenish active sodium ions, solving the problem of reduced battery capacity, energy density, and cycle performance caused by sodium ion consumption at the solid electrolyte interphase (SEI) film.

[0035] The sodium-supplementing particles have a core-shell structure, comprising a sodium-supplementing core and a sodium-supplementing shell covering the core. The shell is made of an organic sodium-supplementing agent, while the core is made of an inorganic sodium-supplementing agent. Both organic and inorganic sodium-supplementing agents can release active sodium ions, thus supplementing the positive electrode material with sodium. This allows the sodium-supplementing particles to provide a greater number of active sodium ions, improving their sodium-supplementing effect. Furthermore, by coating the inorganic sodium-supplementing agent with the organic agent, the inorganic agent is effectively isolated from the outside air, reducing the impact of water and oxygen in the air. Simultaneously, after releasing active sodium ions, the inorganic sodium-supplementing agent retains its framework structure, preventing structural collapse and maintaining structural stability for the overall structure. Using this sodium-supplementing agent to supplement the positive electrode active material can improve the battery's energy density, capacity, and cycle performance.

[0036] Reference Figure 1 , Figure 1 The images shown are transmission electron microscopy (TEM) images of sodium-supplementing particles according to some embodiments of the present invention. TEM images were obtained using a JEOL JEM-2100 TEM at an accelerating voltage of 200 kV and a scale bar spacing of 1 μm. Observation reveals that the particle size (D50) of the sodium-supplementing particles ranges from 1 to 8 μm, and the particles exhibit an irregular granular shape. Specifically, the outer sodium-supplementing shell has a thickness of 0.16–0.27 μm, and the inner sodium-supplementing core has a particle size of approximately 2–3 μm.

[0037] Furthermore, inorganic sodium supplements include Na x M y O zWhere x, y, and z are all greater than 0, x / y > 1, and M includes at least one transition metal element. For example, M may include one transition metal element, or M may include two or more transition metal elements.

[0038] Optionally, 1 < x / y ≤ 5, 0.5 < x / z < 5.

[0039] By setting the inorganic sodium supplement to include the above-mentioned Na x M y O z It can not only provide more active sodium ions, but also has a high sodium content. The material formed after releasing active sodium ions to replenish sodium can also be used as the main material of positive electrode active material. Thus, while achieving the sodium replenishment function, it can further improve the energy density, battery capacity and cycle performance of the battery.

[0040] According to embodiments of the present invention, the sodium replenishing agent for positive electrode active materials can replenish active sodium ions during battery charging and discharging, solving the problem of reduced battery capacity, energy density, and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film. By encapsulating the inorganic sodium replenishing agent with an organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can be utilized to prevent structural collapse, thereby improving the battery's energy density, battery capacity, and cycle performance.

[0041] According to some optional embodiments of the present invention, the above-mentioned chemical formula Na x M y O z In this context, x = 2, 5, or 6; y = 1; z = 2 or 4; and M is one or more of the elements Zn, Ni, Cu, Fe, Mn, Cr, and Al. For example, when M is Ni, Na... x M y O z It can be Na₂NiO₂; for example, when M is element Cr, Na x M y O z It can be Na₂CrO₂; for example, when M is the element Cu, Na x M y O z It can be Na₂CuO₂; for example, when M is element Fe, Na x M y O z It can be Na5FeO4; for example, when M is the element Co, Na x M y O z It can be Na6CoO4; for example, when M is element Al, Nax M y O z It can be Na2AlO2.

[0042] According to some embodiments of the present invention, Na x M y O z The materials formed after releasing active sodium ions include: Na w M y O z , where 0 < w < x. Na x M y O z The materials formed after releasing active sodium ions include: Na w M y O z Material Na w M y O z It can be used as the main material for positive electrode active materials.

[0043] In some optional embodiments of the present invention, the above-mentioned chemical formula Na w M y O z In this context, 0 < w ≤ 1, y = 1, z = 2, and M includes one or more of Zn, Ni, Cu, Fe, Mn, Cr, and Al. For example, when M is the element Ni, Na... w M y O z It can be NaNiO2; for example, when M is element Cu, Na w M y O z It can be NaCuO2; for example, when M is element Fe, Na w M y O z It can be NaFeO2; for example, when M includes the elements Fe, Co, and Mn, Na w M y O z It can be NaNi 0.33 Fe 0.33 Mn 0.33 O2; for example, when M includes elements Fe, Co, and Mn, Na w M y O z It can also be NaNi 0.5 Fe 0.25 Mn 0.25 O2.

[0044] For example, after releasing active sodium ions to replenish sodium, Na₂NiO₂ can form NaNiO₂, which can be used as the main material for the positive electrode active material. Similarly, after releasing active sodium ions, Na₅FeO₄ can form NaFeO₂, which can also be used as the main material for the positive electrode active material.

[0045] According to some embodiments of the present invention, the organic sodium supplement includes Na i A a B b D c Where A, B, and D are elements C, O, N, F, P, and H, i is greater than 1, and at least one of a, b, and c is greater than 0. Optionally, the organic sodium supplement package may include at least one of Na3C6H5O7, Na2C2O4, Na3N, Na3F, Na3P, Na2C4O4, Na2C3O3, Na2C5O5, and Na2C6O6.

[0046] According to some embodiments of the present invention, with reference to Figure 1 The ratio of the thickness of the sodium-supplementing shell to the particle size of the sodium-supplementing core should range from 0.02 to 0.5. If the ratio is too small, the shell is too thin, which is detrimental to the protection of the inner inorganic sodium-supplementing agent and may lead to its failure. If the ratio is too large, the shell is too thick. Since the inner inorganic sodium-supplementing agent has a higher theoretical specific capacity and contains more active sodium sources than the outer organic sodium-supplementing agent, an excessively thick shell will result in a decrease in the active sodium content.

[0047] By setting the ratio of the thickness of the sodium-supplementing shell to the particle size of the sodium-supplementing core within the range of 0.02–0.5, the inner inorganic sodium-supplementing agent can be better protected to prevent its failure. Furthermore, a higher proportion of the inorganic sodium-supplementing agent results in a higher content of active sodium in the sodium-supplementing particles, thus enhancing their sodium-supplementing effect. Additionally, ensuring a large volumetric proportion of the inner inorganic sodium-supplementing agent within the sodium-supplementing particles contributes to their structural stability. Even after the particles release active sodium ions for sodium supplementation, a relatively stable framework structure remains to provide support, better preventing structural collapse.

[0048] According to some embodiments of the present invention, with reference to Figure 1The thickness of the sodium-supplementing shell ranges from 0.1 μm to 2 μm, and the particle size of the sodium-supplementing core ranges from 0.5 μm to 5 μm. By setting the thickness range of the sodium-supplementing shell to 0.1 μm to 2 μm and the particle size range of the sodium-supplementing core to 0.5 μm to 5 μm, the overall particle size range of the sodium-supplementing particles is made more suitable. This avoids the difficulty in preparing sodium-supplementing particles that are too small, and also avoids the situation where excessively large sodium-supplementing particles lead to insufficient reaction of the inner inorganic sodium-supplementing agent and incomplete release of the active sodium source, resulting in poor sodium-supplementing effect. In short, this makes the preparation of sodium-supplementing particles easier and allows the inner inorganic sodium-supplementing agent to fully release the sodium source, thereby improving the sodium-supplementing effect.

[0049] Furthermore, by setting the thickness of the sodium-supplementing shell to 0.1 μm to 2 μm and the particle size of the sodium-supplementing core to 0.5 μm to 5 μm, the inner inorganic sodium-supplementing agent can be better protected to prevent its failure. This also allows for a higher proportion of the inorganic sodium-supplementing agent, resulting in a higher content of active sodium in the sodium-supplementing particles and thus a more effective sodium-supplementing effect. Additionally, ensuring a large volumetric proportion of the inner inorganic sodium-supplementing agent within the sodium-supplementing particles contributes to structural stability. Even after the particles release active sodium ions for sodium supplementation, they retain a relatively stable framework structure for support, better preventing structural collapse.

[0050] According to a second aspect embodiment of the present invention, a method for preparing a sodium supplement, wherein the sodium supplement is the sodium supplement described in the first aspect embodiment of the present invention, and the method for preparing the sodium supplement includes:

[0051] The inorganic sodium supplement is dispersed in an organic solvent, and the organic sodium supplement is added to the organic solvent. The organic solvent may include one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide.

[0052] At a set temperature, a solvothermal reaction is carried out for a set time. The dispersed inorganic sodium supplement is used as the growth nucleus, and the organic sodium supplement grows and coats the outside of the inorganic sodium supplement, generating sodium supplement particles with a core-shell structure. The set temperature can be 70℃~90℃, for example, the set temperature can be 80℃, and the set time can be 2h~48h. By adjusting the above set temperature and set time, sodium supplement particles with the required particle size can be produced.

[0053] Sodium-supplemented particles are separated from organic solvents by centrifugation, vacuum drying, or filtration.

[0054] The preparation method of the sodium supplement according to the embodiments of the present invention is simple and easy to control.

[0055] According to some embodiments of the present invention, the molar ratio of the organic sodium supplement to the inorganic sodium supplement added to the organic solvent is 0.05 to 0.5. By setting the molar ratio of the organic sodium supplement to the inorganic sodium supplement added to the organic solvent to 0.05 to 0.5, the thickness of the sodium supplement shell and the particle size of the sodium supplement core of the grown sodium supplement particles can be within a suitable range. For example, the ratio of the thickness of the sodium supplement shell to the particle size of the sodium supplement core of the grown sodium supplement particles can be in the range of 0.02 to 0.5.

[0056] For example, the material of the sodium-supplementing shell of the sodium-supplementing particles is Na3C6H5O7, and the material of the sodium-supplementing core of the sodium-supplementing particles is Na2NiO2. During the preparation of the sodium-supplementing agent, the molar ratio of the organic sodium-supplementing agent to the inorganic sodium-supplementing agent added to the organic solvent is 0.3. The obtained sodium-supplementing particles have a coating thickness of 0.2 micrometers for the sodium-supplementing shell and a particle size of 1.5 micrometers for the sodium-supplementing core.

[0057] For example, the material of the sodium-supplementing shell of the sodium-supplementing particles is Na3C6H5O7, and the material of the sodium-supplementing core of the sodium-supplementing particles is Na2NiO2. In the preparation process of the sodium-supplementing agent, the molar ratio of the organic sodium-supplementing agent to the inorganic sodium-supplementing agent added to the organic solvent is 0.01, and other parameters are the same. The obtained sodium-supplementing particles have a coating thickness of 20nm to 100nm for the sodium-supplementing shell and a particle size of 3μm to 15μm for the sodium-supplementing core.

[0058] For example, the material of the sodium-supplementing shell of the sodium-supplementing particles is Na3C6H5O7, and the material of the sodium-supplementing core of the sodium-supplementing particles is Na2NiO2. In the preparation process of the sodium-supplementing agent, the molar ratio of the organic sodium-supplementing agent to the inorganic sodium-supplementing agent added to the organic solvent is 2, and other parameters are the same. The obtained sodium-supplementing particles have a coating thickness of 0.5 micrometers to 2 micrometers for the sodium-supplementing shell and a particle size of 0.5 micrometers to 3 micrometers for the sodium-supplementing core.

[0059] The positive electrode active material according to a third aspect embodiment of the present invention includes: a main material and a sodium supplement, wherein the sodium content of the sodium supplement is greater than the sodium content of the main material, and the sodium supplement is the sodium supplement of the first aspect embodiment of the present invention described above. For example, the sodium content of the sodium supplement is greater than 30%, and the sodium content of the main material is less than 25%.

[0060] According to embodiments of the present invention, by setting the positive electrode active material to include the above-mentioned sodium replenishing agent, active sodium ions can be replenished during battery charging and discharging, solving the problem of reduced battery capacity, energy density, and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film; by encapsulating the inorganic sodium replenishing agent with an organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can also be utilized to prevent structural collapse, thereby improving the battery's energy density, battery capacity, and cycle performance.

[0061] According to some embodiments of the present invention, the mass ratio of sodium supplement to main material ranges from 0.01 to 0.3. If the mass ratio of sodium supplement to main material is too small, it indicates that the amount of sodium supplement is too low, thus failing to achieve a good sodium supplementation effect; if the mass ratio of sodium supplement to main material is too high, it indicates that the amount of sodium supplement is too large, which will make the sodium supplement difficult to decompose, thus failing to fully release active sodium. Furthermore, the decomposition of excessive outer layer of the sodium supplement (including organic sodium supplement) will damage the electrode structure and increase side reactions.

[0062] By setting the mass ratio of sodium supplement to main material to a range of 0.01 to 0.3, the sodium supplement can achieve a better sodium supplementation effect, and it can also make the sodium supplement easy to grade, fully release active sodium, and reduce damage to the electrode structure.

[0063] According to some embodiments of the present invention, the main material may include polyanionic compounds or transition metal oxides.

[0064] For example, the main material may include a polyanionic compound with the chemical formula Na. g M h (X e O f ) j Z k M is one of the elements Ti, V, Cr, Mn, Fe, Co, Ni, Ca, Mg, Al, Nb, etc.; X is one of the elements Si, S, P, As, B, Mo, W, Ge; and Z is an element F or OH ion. For example, polyanionic compounds include Na3V2(PO4)3 and Na2FeP2O7, where the mass percentage of sodium is ≤0.2%.

[0065] For example, the main material may include transition metal oxides with the chemical formula Na. n MO2, where M is a transition metal element. For example, M can be one of the elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mg, Al, or Nb, where 0 < n ≤ 1. For instance, the transition metal oxide in the main material can be Na. n FeO2, Na n NiO2, Na n CoO2, Na n MnO2, Na n VO2, Na n CrO2, wherein the mass percentage of sodium is ≤0.23%.

[0066] According to a fourth aspect of the present invention, a positive electrode sheet includes: a positive current collector and a positive electrode material, wherein the positive electrode material includes a positive active material according to the third aspect of the present invention, and the positive electrode material covers the positive current collector.

[0067] According to the positive electrode sheet of the present invention, by setting the positive electrode material of the positive electrode sheet to include the above-mentioned positive electrode active material, active sodium ions can be replenished during the charging and discharging process of the battery, which solves the problem of reduced battery capacity, energy density and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film; by encapsulating the inorganic sodium replenishing agent with the organic sodium replenishing agent to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium replenishing agent can be reduced, and the structural stability of the inorganic sodium replenishing agent can also be utilized to prevent structural collapse and improve the energy density, battery capacity and cycle performance of the battery.

[0068] A battery according to a fifth aspect embodiment of the present invention includes: a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode according to the fourth aspect embodiment of the present invention.

[0069] According to the battery of the present invention, by setting the above-mentioned positive electrode plate, active sodium ions can be replenished during the charging and discharging process of the battery, which solves the problem of reduced battery capacity, energy density and cycle performance caused by sodium ion consumption by the solid electrolyte interphase (SEI) film; by encapsulating the inorganic sodium supplement with the organic sodium supplement to form a core-shell structure, the influence of water and oxygen in the air on the inorganic sodium supplement can be reduced, and the structural stability of the inorganic sodium supplement can also be utilized to prevent structural collapse, thereby improving the energy density, battery capacity and cycle performance of the battery.

[0070] The sodium supplement, positive electrode active material, positive electrode sheet, and battery of the present invention will be further described below with reference to several embodiments and comparative examples.

[0071] Example 1,

[0072] The positive electrode active material in this embodiment includes a main material and a sodium supplement agent. The sodium supplement agent includes sodium supplement particles. The sodium supplement shell of the sodium supplement particles is made of Na3C6H5O7, and the sodium supplement core of the sodium supplement particles is made of Na2NiO2. The coating thickness of the sodium supplement shell is 0.2 micrometers, and the particle size of the sodium supplement core is 1.5 micrometers.

[0073] The sodium-supplementing particles in this embodiment are prepared using the preparation method described in the second aspect of the embodiment above. The molar ratio of organic sodium supplement to inorganic sodium supplement is 0.3 during the preparation process.

[0074] Example 2,

[0075] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the material for the sodium-filled shell in this embodiment is Na2C6O6.

[0076] Example 3,

[0077] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the sodium-supplementing core in this embodiment is Na5FeO4.

[0078] Example 4,

[0079] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the particle size of the sodium-supplementing core in this embodiment is 0.5 micrometers.

[0080] Example 5,

[0081] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the particle size of the sodium-supplementing core in this embodiment is 3 micrometers.

[0082] Example 6,

[0083] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the particle size of the sodium-supplementing core in this embodiment is 5 micrometers.

[0084] Example 7,

[0085] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the thickness of the sodium-filled shell in this embodiment is 0.5 micrometers.

[0086] Example 8,

[0087] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the thickness of the sodium-filled shell in this embodiment is 2 micrometers.

[0088] Example 9,

[0089] The only difference between the positive electrode active material in this embodiment and that in Example 1 is that the thickness of the sodium-filled shell in this embodiment is 5 micrometers.

[0090] Comparative Example 1,

[0091] The only difference between the positive electrode active material of this comparative example and that of Example 1 is that no sodium supplement was added to the positive electrode active material of this comparative example.

[0092] Comparative Example 2,

[0093] The only difference between the positive electrode active material of this comparative example and that of Example 1 is that the positive electrode active material of this comparative example only contains the inorganic sodium supplement Na2NiO2.

[0094] Comparative Example 3,

[0095] The only difference between the positive electrode active material of this comparative example and that of Example 1 is that the positive electrode active material of this comparative example only contains the organic sodium supplement Na3C6H5O7.

[0096] Batteries of Examples 1 to 9 and Comparative Examples 1 to 3 were prepared according to the following methods.

[0097] The coin cells used for testing in each embodiment and comparative example were prepared according to the following method:

[0098] 1. Preparation of the positive electrode sheet:

[0099] The positive electrode active material, conductive agent, and binder are mixed together in a predetermined ratio and dispersed in a solvent such as N-methylpyrrolidone (NMP). After stirring evenly, the mixture is uniformly coated onto the positive electrode current collector, which is made of aluminum foil. After drying, the foil is rolled and then punched to obtain the positive electrode sheet. The main material of the positive electrode active material is a layered metal oxide (Na₂O₃). n MO2).

[0100] 2. Preparation of the negative electrode sheet:

[0101] A 10 wt% aqueous carboxymethyl cellulose binder was fully dissolved in water, and 10 wt% carbon black conductive agent and 80 wt% of the above-mentioned hard carbon material were added to prepare a uniformly dispersed slurry. The slurry was uniformly coated onto the surface of the negative electrode current collector, which was a porous copper foil, and then transferred to a vacuum drying oven for complete drying. The resulting electrode was rolled and then punched to obtain the negative electrode sheet.

[0102] 3. Preparation of electrolyte:

[0103] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1, and then 5% FEC (fluoroethylene carbonate) was added. Then, fully dried lithium salt NaClO4 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.

[0104] 4. Preparation of the separating membrane:

[0105] A 260-micron glass fiber film was selected.

[0106] 5. Battery assembly:

[0107] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrolyte is then added, and the cells are assembled into a button cell.

[0108] The coin cells prepared in the above-described embodiments and comparative examples were subjected to electrochemical performance tests, including cycle performance tests and first-cycle charge specific capacity tests, wherein:

[0109] 1) Cyclic performance test

[0110] At 25°C, the batteries prepared in the examples and comparative examples were discharged to 2V at a rate of 0.1C and charged to 4V at a rate of 0.1C, and a full charge-discharge cycle test was performed until the battery capacity was less than 80% of the initial capacity, and the number of cycles was recorded.

[0111] 2) Specific capacity during the first charge cycle

[0112] At 25°C, the batteries prepared in the examples and comparative examples were charged from 1.5V to 4.5V at a rate of 0.1C, and the resulting charge specific capacity was the first charge specific capacity.

[0113] The cycle performance test parameters and first charge specific capacity test parameters of the coin cells prepared in the above embodiments and comparative examples, as well as the test results, are shown in Table 1 below.

[0114] Table 1

[0115]

[0116] As can be seen from Table 1 above, although Comparative Example 2 added an inorganic sodium supplement and Comparative Example 3 added an organic sodium supplement, their specific capacity and cycle performance were both poor, indicating a poor sodium supplementation effect. However, Examples 1 to 9 incorporated the sodium supplement of the present invention, resulting in significantly improved specific capacity and cycle performance compared to Comparative Examples 2 and 3, demonstrating a better sodium supplementation effect.

[0117] Table 1 also shows that in Examples 1 to 3, when the thickness of the sodium-supplementing shell, the particle size of the sodium-supplementing core, and the molar ratio of organic and inorganic sodium-supplementing agents during the preparation process are all the same, regardless of whether the sodium-supplementing shell is Na3C6H5O7 or Na2C6O6, or the sodium-supplementing core is Na2NiO2 or Na5FeO4, the specific capacity and cycle performance are all high, and the sodium-supplementing effect is excellent.

[0118] Table 1 also shows that in Examples 4 to 6, when the materials of the sodium-supplementing shell, the materials of the sodium-supplementing core, the thickness of the sodium-supplementing shell, and the molar ratio of organic sodium-supplementing agent and inorganic sodium-supplementing agent in the preparation process are all the same, the specific capacity and cycle performance are both high when the particle size of the sodium-supplementing core is in the range of 0.5 micrometers to 5 micrometers, and the sodium-supplementing effect is excellent.

[0119] Table 1 also shows that in Examples 7 to 9, when the materials of the sodium-supplementing shell, the materials of the sodium-supplementing core, the particle size of the sodium-supplementing core, and the molar ratio of organic and inorganic sodium-supplementing agents during the preparation process are all the same, the specific capacity and cycle performance are higher and the sodium-supplementing effect is better when the thickness of the sodium-supplementing shell is in the range of 0.2 μm to 2 μm; while when the thickness of the sodium-supplementing shell is 5 μm, the specific capacity and cycle performance are relatively lower than when the thickness of the sodium-supplementing shell is in the range of 0.2 μm to 2 μm, but the sodium-supplementing effect is still good.

[0120] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0121] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a sodium supplement, characterized in that, include: The inorganic sodium supplement is dispersed in an organic solvent, and the organic sodium supplement is added to the organic solvent; Sodium-supplementing particles with a core-shell structure are generated by a solvothermal reaction at a set temperature for a set duration. The sodium-supplementing particles are separated from the organic solvent by centrifugation, vacuum drying, or filtration. The inorganic sodium supplement includes Na x M y O z Where x, y, and z are all greater than 0, x / y > 1, and M includes one or more of the elements Zn, Ni, Cu, Fe, Mn, Cr, and Al; The organic solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide; The organic sodium supplement includes at least one of Na3C6H5O7 and Na2C6O6; The molar ratio of the organic sodium supplement to the inorganic sodium supplement added to the organic solvent is 0.05 to 0.5; The set temperature is 70℃~90℃; The set duration is 2 hours to 48 hours; The sodium supplement includes the sodium supplement particles, which have a core-shell structure. The sodium supplement particles include a sodium core and a sodium shell covering the sodium core. The material of the sodium core includes the inorganic sodium supplement.

2. The preparation method according to claim 1, characterized in that, 1<x / y≤5, 0.5<x / z<5.

3. The preparation method according to claim 2, characterized in that, Chemical formula Na x M y O z In the given information, x = 2, 5, or 6; y = 1; z = 2 or 4.

4. The preparation method according to claim 1, characterized in that, Na x M y O z The materials formed after releasing active sodium ions include: Na w M y O z , where 0 < w < x.

5. The preparation method according to claim 4, characterized in that, Chemical formula Na w M y O z In, 0<w≤1, y=1, z=2.

6. The preparation method according to claim 1, characterized in that, The ratio of the thickness of the sodium-supplementing shell to the particle size of the sodium-supplementing core ranges from 0.02 to 0.5; and / or, the thickness of the sodium-supplementing shell ranges from 0.1 micrometers to 2 micrometers, and the particle size of the sodium-supplementing core ranges from 0.5 micrometers to 5 micrometers.

7. A sodium supplement agent for positive electrode active materials, characterized in that, It is prepared by any one of the preparation methods according to claims 1-6.

8. A positive electrode active material, characterized in that, include: Main materials; A sodium supplement, wherein the sodium content of the sodium supplement is greater than the sodium content of the main material, and the sodium supplement is the sodium supplement according to claim 7.

9. The positive electrode active material according to claim 8, characterized in that, The sodium supplement has a sodium content greater than 30%, and the sodium content of the main material is less than 25%; and / or, the mass ratio of the sodium supplement to the main material is in the range of 0.01 to 0.

3.

10. The positive electrode active material according to claim 8, characterized in that, The main material includes polyanionic compounds or transition metal oxides.

11. A positive electrode plate, characterized in that, include: Positive current collector; A positive electrode material, the positive electrode material comprising a positive electrode active material according to any one of claims 8-10, the positive electrode material covering the positive electrode current collector.

12. A battery, characterized in that, The battery is a sodium-ion battery and includes: the positive electrode sheet according to claim 11.

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