A sodium-ion battery positive electrode material, a positive electrode sheet, and a secondary battery

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to a sodium ion battery positive electrode material. n Mn 1‑x‑ y M x A y O2, wherein M is at least one of Li, Mg, Cu, Ni, Ca, Zn, Fe, Cr, Al, A is at least one of Ta, Mo, W, Nb, Si, Sn, V, wherein 0.4<=x<=0.8, 0

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a sodium-ion battery cathode material, cathode sheet, and secondary battery. Background Technology

[0002] With the rapid development of vehicle electrification, the demand for lithium-ion power batteries is increasing, leading to a tightening supply of lithium resources and persistently high prices. Since lithium-ion batteries dominate energy storage, the rapid development of the energy storage industry is also exacerbating the rapid depletion of lithium resources and the supply-demand imbalance. Therefore, the development of new energy storage batteries based on non-lithium-ion batteries is urgently needed. Sodium-ion batteries have significant advantages such as low cost, abundant resources, good safety, and environmental friendliness, making them suitable for large-scale energy storage. For sodium-ion batteries, developing suitable cathode materials is crucial. Manganese-based linear materials have advantages such as high capacity, good rate performance, and long cycle life, making them suitable for use as cathode materials in sodium-ion batteries.

[0003] Compared to layered cathode materials for lithium-ion batteries, layered materials used in sodium-ion batteries are more complex. They are prone to phase transitions and lattice oxygen loss even at lower charging voltages, and readily absorb moisture and carbon dioxide from the air, resulting in strong surface alkalinity. Currently, layered materials used as cathodes in sodium-ion batteries generally use manganese (Mn) as the basic framework, contributing capacity by doping with active elements such as Ni, Fe, and Cu, and stabilizing the lattice with inactive elements. Among manganese-based layered cathode materials, O3-type materials have the advantage of high capacity, but they are prone to phase transitions during cycling, causing lattice distortion and resulting in poor cycle performance. Furthermore, layered materials are unstable in air, leading to strong surface alkalinity, which in turn causes gelation of the slurry and gas buildup in the battery.

[0004] Therefore, a technical method to solve the above problems is urgently needed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a sodium-ion battery cathode material that has good structural stability, electrochemical performance, and good cycle stability, addressing the shortcomings of existing technologies.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A sodium-ion battery cathode material includes a manganese-based oxide material and a coating layer covering the manganese-based oxide material, wherein the general chemical formula of the manganese-based oxide material is Na. n Mn 1-x-y M x A yO2, where M is at least one of Li, Mg, Cu, Ni, Ca, Zn, Fe, Cr, Al, A is at least one of Ta, Mo, W, Nb, Si, Sn, V, where 0.4 ≤ x ≤ 0.8, 0 < y ≤ 0.1, 0.85 ≤ n ≤ 1, and the coating layer comprises a polyanionic material.

[0008] Preferably, the positive electrode material of the sodium-ion battery has a single crystal structure, and the particle size of the positive electrode material of the sodium-ion battery is 2 - 10 μm.

[0009] Preferably, the manganese-based layered oxide material is in the O3 phase.

[0010] Preferably, the thickness of the coating layer is 10 - 200 nm.

[0011] Preferably, the mass ratio of the manganese-based layered oxide material to the coating layer is 90 - 110:1 - 10.

[0012] Preferably, the preparation method of the polyanionic material is to mix a metal source material and an anion group-containing material, and obtain the polyanionic material through a solid-phase reaction. The solid-phase reaction temperature is 500°C - 1000°C, the reaction time is 1 - 10 hours, and the reaction atmosphere is a reducing atmosphere.

[0013] Preferably, the preparation method of the polyanionic material further includes a modification treatment. The modification treatment specifically is to mix the prepared polyanionic material and an oxidant in a solvent, grind, centrifuge, and vacuum dry to obtain a modified polyanionic material.

[0014] Preferably, the weight part ratio of the polyanionic material to the oxidant is 0.1 - 10:1 - 3.

[0015] The second object of the present invention is: aiming at the deficiencies of the prior art, to provide a positive electrode sheet with good electrochemical performance and cycle stability.

[0016] To achieve the above object, the present invention adopts the following technical solutions:

[0017] A positive electrode sheet includes the above-mentioned positive electrode material of the sodium-ion battery.

[0018] The third object of the present invention is: aiming at the deficiencies of the prior art, to provide a secondary battery with good electrochemical performance and cycle stability.

[0019] To achieve the above object, the present invention adopts the following technical solutions:

[0020] A secondary battery includes the above-mentioned positive electrode sheet.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The layered cathode material of the present invention uses Mn element as the basic framework, suppresses harmful phase transitions during charge and discharge through lattice doping, and forms a coating layer by combining surface coating modification, further stabilizing the lattice of the material during charge and discharge, improving the stability in air, reducing the surface alkalinity, increasing the cycle life of the material, and improving the processing performance of the electrode and suppressing the gas evolution of the battery. Brief Description of the Drawings

[0022] Figure 1 It is the XRD pattern of the cathode material of the sodium-ion battery prepared in Example 1 of the present invention.

[0023] Figure 2 It is the low-magnification scanning electron microscope image of the cathode material of the sodium-ion battery prepared in Example 1 of the present invention.

[0024] Figure 3 It is the high-magnification scanning electron microscope image of the cathode material of the sodium-ion battery prepared in Example 1 of the present invention.

[0025] Figure 4 It is the energy spectrum surface scan image of the cathode material of the sodium-ion battery prepared in Example 1 of the present invention and V element.

[0026] Figure 5 It is the charge-discharge curve of the cathode material of the sodium-ion battery prepared in Example 1 of the present invention.

[0027] Figure 6 It is the cycle life diagram of the cathode material of the sodium-ion battery prepared in Example 1 of the present invention.

[0028] Figure 7 It is the cycle life diagram of the layered cathode material prepared in Comparative Example 1. Detailed Embodiments

[0029] The present invention will be further described in detail below in conjunction with the specific embodiments and the drawings of the specification, but the embodiments of the present invention are not limited thereto.

[0030] A cathode material for a sodium-ion battery includes a manganese-based layered oxide material and a coating layer coated on the manganese-based layered oxide material. The chemical general formula of the manganese-based layered oxide material is Na n Mn 1-x-y M x A y O2. In the formula, M is at least one of Li, Mg, Cu, Ni, Ca, Zn, Fe, Cr, Al, and A is at least one of Ta, Mo, W, Nb, Si, Sn, V, where 0.4 ≤ x ≤ 0.8, 0 < y ≤ 0.1, 0.85 ≤ n ≤ 1, and the coating layer includes a polyanion material.

[0031] In the molecular formula of the sodium-ion battery cathode material of the present invention, Mn serves as the basic framework. Preferably, M contains at least one electrochemically active element, including Cu, Ni, Fe, and Cr. Electrochemical activity refers to the ability to contribute to capacity through valence changes. Preferably, element M is uniformly doped. More preferably, M contains at least one electrochemically inactive element, including Li, Mg, Cu, Ca, Zn, and Al. Electrochemical inactivity refers to the ability to not contribute to capacity through valence changes, but only to stabilize the crystal lattice. More preferably, the inactive element contains Li, as low-valence Li doping is beneficial for improving the valence state of manganese, the sodium content, and the material's capacity. In the molecular formula of the sodium-ion battery cathode material of the present invention, A is a high-valence inactive element. Preferably, A is selected from at least one of Ta, Mo, W, Nb, Si, Sn, and V. Preferably, element A is uniformly doped. Studies have shown that doping with element A can not only improve lattice stability but also increase the working voltage of the battery and reduce the surface alkalinity of the material. The studies also show that co-doping of inactive elements in A and M can produce a synergistic effect, which can stabilize the lattice and increase the working voltage.

[0032] In this invention, Na n Mn 1-x-y M x Surface coating of AyO2 particles improves the stability of layered materials in air, reduces surface alkalinity, and inhibits slurry gelation and battery gas expansion. Furthermore, surface coating can also enhance the Na... n Mn 1-x-y M x A y The interface stability between O2 and electrolyte is improved, surface lattice distortion is suppressed, and the cycling stability of the material is enhanced.

[0033] Preferably, the coating layer is made of sodium-based polyanionic material. Polyanionic materials are air-stable, hydrophobic, and carbon dioxide-repellent, thereby reducing or eliminating sodium content. n Mn 1-x-y M x A y The surface of O2 is alkaline; in addition, the polyanionic material itself is a sodium storage material and a sodium ion conductor, and its coating does not affect the specific capacity of the material or the diffusion of sodium ions.

[0034] Preferably, the polyanionic material is selected from, but not limited to, NaFePO4, NaTi2PO4, Na3V2(PO4)3, Na3V2(PO4)2F3, Na3(VOPO4)2F, Na4MnV(PO4)3, and NaFeSO4F.

[0035] The polyanionic materials include Na3Fe2(PO4)P2O7, Na4Fe3(PO4)2(P2O7), Na2Fe2(SO4)3, NaVPO4F, Na2FePO4F, and NaFe2PO4(SO4)2; the polyanionic materials also include their derivatives, which include dopants at F-site, Mn-site, V-site, and Fe-site, wherein the doping amount is 0.5% to 10%.

[0036] Preferably, the polyanionic material is selected from sodium-deficient polyanionic materials, and the sodium deficiency is 5% to 30%. Sodium deficiency is beneficial for spontaneous absorption of residual sodium on the surface of the layered positive electrode, thereby further reducing the surface alkalinity.

[0037] Further optimization involves sand milling the polyanionic material. After sand milling, the particle size is reduced to 10-200 nanometers. The sand-milled nanoscale polyanionic material is more likely to achieve complete and uniform coating of layered materials.

[0038] The sodium-ion battery cathode material of this invention includes a layered material synthesis method and a surface modification method. The layered material preparation includes direct solid-state reaction, co-precipitation, and sol-gel methods. The direct solid-state reaction method refers to the direct preparation of Na+ through a high-temperature solid-state reaction. n Mn 1xy M x A y In the synthesis of O2, compounds containing elements Na, Mn, M, and A are uniformly mixed using processes such as ball milling, sand milling, or high-speed mixing, and then subjected to a solid-state reaction. The compounds are selected from nitrates, acetates, carbonates, oxalates, oxides, hydroxides, hydroxyoxides, etc., containing these elements. Preferably, the solid-state reaction temperature is 600℃~1000℃, the reaction time is 5~20 hours, the reaction atmosphere is selected from air, oxygen, or compressed air, and the reaction equipment is selected from box furnaces, roller kilns, rotary kilns, etc. After high-temperature calcination, further steps such as crushing, sorting, and iron removal are required. The crushing includes ball milling, air jet milling, etc.

[0039] The coprecipitation method mentioned above refers to the process of synthesizing Na. n Mn 1xy M x A yIn the O2 process, soluble salts containing Mn and M are dissolved in deionized water to prepare a salt solution. Then, under the action of a precipitating agent and a complexing agent, a co-precipitation reaction is performed to obtain a solid precursor. This precursor is then mixed with a sodium-containing compound and synthesized into the final product through a solid-phase reaction. Preferably, the salt solution is selected from chlorides, sulfates, nitrates, etc.; the complexing agent is selected from ammonia, sodium citrate, sodium ethylenediaminetetraacetate, etc.; the precipitating agent is selected from sodium hydroxide, potassium hydroxide, sodium oxalate, potassium oxalate, sodium carbonate, potassium carbonate, etc.; and the sodium-containing compound is selected from sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, sodium hydroxide, sodium acetate, etc. When elements M and A readily co-precipitate, they are introduced as a precursor; when elements M and A do not readily co-precipitate, they are introduced together with the sodium-containing compound. Preferably, the co-precipitation reaction temperature is 40℃~70℃, the solid-phase reaction temperature is 600℃~1000℃, the reaction time is 5~20 hours, the reaction atmosphere is air, oxygen, or compressed air, and the reaction equipment is selected from box furnace, roller kiln, rotary kiln, etc. After high-temperature calcination, it still needs to undergo crushing, sorting, and iron removal steps, including ball milling and air jet milling.

[0040] The sol-gel method mentioned above refers to the synthesis of Na n Mn 1-x-y M x A y In the O2 process, nitrates, sulfates, or organic salts containing Na, Mn, M, and A are dissolved in water, and after mixing, a sol is formed. A complexing agent such as citric acid is then added, and the mixture is stirred at a certain temperature to obtain a gel. The final product is then obtained through a solid-phase reaction. Preferably, the stirring temperature is 50℃~90℃, the solid-phase reaction temperature is 600℃~1000℃, the reaction time is 5~20 hours, the reaction atmosphere is air, oxygen, or compressed air, and the reaction equipment is selected from box furnaces, roller kilns, rotary kilns, etc. After high-temperature calcination, further steps such as crushing, sorting, and iron removal are required. The crushing includes ball milling, air jet milling, etc.

[0041] After coating, heat treatment is required. Preferably, the heat treatment temperature is 500℃~800℃, the heat treatment time is 0.5~5 hours, and the heat treatment atmosphere is an inert atmosphere or a reducing atmosphere. After heat treatment, it is beneficial for the residual sodium on the surface of the layered material to spontaneously implant into the sodium-deficient polyanionic material, thereby reducing the surface alkalinity of the material.

[0042] This invention also discloses a method for preparing sodium-deficient, nanoscale polyanionic materials, the specific steps of which are as follows:

[0043] (1) Containing Na + Fe 2+ or Fe 3+ Mn 2+ or Mn3+ Ti 4+ V 3+ or V 4+ or V 5+ PO4 3- SO4 2- F - The compound is used to synthesize the polyanionic material through a solid-state reaction. Preferably, the solid-state reaction temperature is 500℃~1000℃, the reaction time is 1~10 hours, and the reaction atmosphere is a reducing atmosphere.

[0044] (2) The above-mentioned polyanionic material and oxidant are mixed in deionized water and subjected to sand milling treatment. Preferably, the sand milling time is 5 minutes to 5 hours. Preferably, the oxidant is selected from ammonium persulfate, sodium persulfate, tetrafluoroborate, potassium dichromate, or sodium dichromate. Preferably, the molar ratio of polyanionic material to oxidant is 0.1 to 10: 1 to 3.

[0045] (3) The sand milling product is centrifuged and vacuum dried to obtain a sodium-deficient, nano-sized polyanionic material. Preferably, the drying temperature is 80℃~120℃.

[0046] The sodium-deficient polyanionic material is a surface-deficient polyanionic material, which is more likely to absorb residual alkali on the surface of the layered material due to its sodium-deficient surface.

[0047] Preferably, the Na n Mn 1-x-y M x A y O2 has a single-crystal structure with a particle size of 2–10 micrometers. Within this particle size range, it is beneficial to increase the compaction density of the electrode, reduce the exposed area of ​​air or electrolyte, reduce surface alkalinity, improve the processing performance of the electrode, and enhance the interfacial stability between the material and the electrolyte, thereby increasing cycle life.

[0048] Preferably, the surface coating method is selected from atomic layer deposition, sol-gel method, magnetron sputtering method, and mechanical fusion method; even more preferably, the surface coating method is selected from mechanical fusion method, which can achieve uniform and complete coating, and has a simple process, low cost, and can realize large-scale production.

[0049] In some embodiments, the sodium-ion battery cathode material has a single-crystal structure, and the particle size of the sodium-ion battery cathode material is 2–10 μm. Within this particle size range, it is beneficial to increase the compaction density of the electrode, reduce the exposed area of ​​air or electrolyte, reduce surface alkalinity, improve the processing performance of the electrode, and improve the interfacial stability between the material and the electrolyte, thereby improving cycle life.

[0050] In some embodiments, the manganese-based morphological oxide material is an O3 phase. Among manganese-based morphological cathode materials, O3-type materials have the advantage of high capacity, but they are prone to phase transition during cycling. Therefore, it is necessary to dope and coat the O3 phase.

[0051] In some embodiments, the thickness of the coating layer is 10–200 nm. Specifically, the thickness of the coating layer is 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, or 200 nm.

[0052] In some embodiments, the mass ratio of the manganese-based morphological oxide material to the coating layer is 90–110:1–10. The mass ratios of the manganese-based morphological oxide material to the coating layer are 90:1, 90:5, 90:10, 93:2, 95:8, and 99:10.

[0053] In some embodiments, the preparation method of the polyanionic material involves mixing a metal source material and a material containing anionic groups, followed by a solid-state reaction to obtain the polyanionic material. The solid-state reaction temperature is 500℃~1000℃, the reaction time is 1~10 hours, and the reaction atmosphere is a reducing atmosphere. Preferably, the solid-state reaction temperature is 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, or 1000℃; and the reaction time is 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0054] In some embodiments, the preparation method of the polyanionic material further includes a modification treatment, wherein the modification treatment specifically involves mixing the prepared polyanionic material and an oxidant in a solvent, grinding, centrifuging, and vacuum drying to obtain the modified polyanionic material.

[0055] In some embodiments, the weight ratio of the polyanionic material to the oxidant is 0.1–10:1–3. The weight ratios of the polyanionic material to the oxidant are 0.1:1, 0.8:3, 2:1, 4:1, 6:1, 7:4, 8:3, 9:1, and 10:1.

[0056] A positive electrode sheet comprising the aforementioned sodium-ion battery positive electrode material. The positive electrode sheet of the present invention exhibits excellent electrochemical performance and cycle stability.

[0057] A secondary battery includes the aforementioned positive electrode. The secondary battery can be a sodium-ion battery, lithium-ion battery, magnesium-ion battery, calcium-ion battery, potassium-ion battery, etc. Preferably, the following secondary battery uses a sodium-ion battery as an example. The sodium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. The separator separates the positive and negative electrodes, and the casing is used to house the positive electrode, negative electrode, separator, and electrolyte. The secondary battery of the present invention has good electrochemical performance and cycle stability.

[0058] The positive electrode sheet adopts the above-mentioned positive electrode sheet, wherein the positive electrode current collector is usually a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in sodium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0059] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector can be any material suitable for use as a negative electrode current collector in sodium-ion batteries. For example, the negative electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil. The negative electrode active material includes soft carbon, hard carbon, metal oxides, etc.

[0060] The sodium-ion battery also includes an electrolyte, using an organic solution containing an organic solvent, a sodium salt, and additives as the organic electrolyte. The sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, and sodium bis(oxalato)borate. The organic solvent includes at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl ethyl carbonate.

[0061] The separator can be any material suitable for sodium-ion battery separators in the art, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0062] Preferably, the shell is made of one of stainless steel, aluminum shell, or aluminum-plastic film.

[0063] Example 1

[0064] Press Na 0.92 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.39 Nb 0.01The material was prepared using a direct solid-state reaction method with an O2 stoichiometric ratio. First, Na2CO3, MnO2, MgO, Fe2O3, NiO, Li2CO3, and Nb2O5 were mixed uniformly according to the stoichiometric ratio. The mixture was then ball-milled for 15 hours at 350 rpm to obtain a precursor. The precursor was then placed in a muffle furnace and calcined at 850°C in air for 15 hours to obtain O3-type Na. 0.92 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.39 Nb 0.01 O2 layered material; XRD analysis of the product showed it to be an O3 phase. (See...) Figure 1 A solid-state method, combined with sand milling in a sodium persulfate environment, was used to prepare sodium-deficient Na₂S₀ particles with a particle size of 100 nanometers. 3-x V2(PO4)3. The above layered material is combined with surface-deficient sodium-containing nano-sized Na... 3-x V2(PO4)3 was mixed evenly and then mechanically fused using a fusion machine, in which Na... 0.92 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.39 Nb 0.01 O2 and Na 3-x The weight ratio of V2(PO4)3 was 100:1. SEM analysis showed that the particle size of the coated product was 210 micrometers, and the Na... 3-x V2(PO4)3 will Na 0.92 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.39 Nb 0.01 O2 is evenly and completely coated, see Figures 2-4 The product has a pH of 9.1. Using the layered material prepared in this example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a NaPF6 propylene carbonate (PC) / ethyl methyl carbonate (EMC) solution as the electrolyte, along with 4% by weight of fluorinated ethylene carbonate (FEC) added to the electrolyte, a button cell was assembled and charged / discharge tested. The current density was 75 mA / g, and the voltage range was 1.9–4.1 V. The charge / discharge curves are shown below. Figure 5 As shown, the specific capacity is 133.5 mAh / g, the median voltage is 3.14 V, and the capacity retention is 95.8% after 100 cycles. Figure 6 After the above charge-discharge cycles, the battery did not swell with gas.

[0065] Example 2

[0066] Press Na 0.88 [Li 0.03 Mg 0.03 Ni 0.22 Fe 0.31 Mn 0.40 Mo 0.01 The precursor was prepared using a coprecipitation method based on the stoichiometric ratio of O2, and the material was then prepared using a high-temperature solid-state reaction method. First, a mixed solution of NiSO4, FeSO4, and MnSO4 was prepared according to the stoichiometric ratio of Ni:Fe:Mn = 0.22:0.31:0.40. The coprecipitated precursor was then obtained via coprecipitation. Next, the coprecipitated precursor was mixed with Na2CO3, Li2CO3, MgO, and MoO3. After high-speed mixing, the mixture was placed in a muffle furnace and calcined at 840°C in air for 15 hours to obtain O3-type Na. 0.88 [Li 0.03 Mg 0.03 Ni 0.22 Fe 0.31 Mn 0.40 Mo 0.01 O2 layered material, the product was analyzed by XRD and found to be O3 phase. A sodium-deficient surface type with a particle size of 100 nm was prepared using a solid-state method combined with sand milling in a potassium persulfate environment. 3-x V2(PO4)2F3. The above layered material is combined with surface-deficient sodium-containing nano-sized Na... 3-x V2(PO4)2F3 was mixed evenly and then mechanically fused using a fusion machine, in which Na... 0.88 [Li 0.03 Mg 0.03 Ni 0.22 Fe 0.31 Mn 0.40 Mo 0.01 O2 and Na 3-x The weight ratio of V2(PO4)2F3 was 100:1.5. SEM analysis showed that the particle size of the coated product was 2–10 micrometers, and the Na... 3-x V2(PO4)2F3 will Na 0.88 [Li 0.03 Mg 0.03 Ni 0.22 Fe 0.31 Mn 0.40 Mo 0.01The O2 layer was uniformly and completely coated. The pH of the product was 9.3. Using the layered material prepared in this embodiment as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a NaPF6 PC / EMC solution as the electrolyte, along with 4% FEC by weight of the electrolyte, a button cell was assembled and subjected to charge-discharge tests. The current density was 75 mA / g, the voltage range was 1.9–4.1 V, the specific capacity was 135.1 mAh / g, and the median voltage was 3.15 V. After 100 cycles, the capacity retention was 94.5%. The battery did not exhibit gas buildup after the above charge-discharge cycles.

[0067] Example 3

[0068] Press Na 0.88 [Cu 0.02 Mg 0.02 Ni 0.22 Fe 0.32 Mn 0.40 Ta 0.02 The precursor was prepared using the sol-gel method with a stoichiometric ratio of O2, and the material was then prepared by high-temperature solid-state reaction. First, NaNO3, Mn(NO3)2, Ni(NO3)2, Cu(NO3)2, Mg(NO3)2, Fe(NO3)2, and C were added according to the stoichiometric ratio. 10 H 25 O5Ta was mixed in deionized water and stirred to obtain a sol. Citric acid was then added, and the mixture was stirred thoroughly at 70°C to obtain a gel precursor. The precursor was thoroughly dried, ball-milled, and then placed in a muffle furnace and calcined at 855°C in air for 12 hours to obtain O3-type Na. 0.88 [Cu 0.02 Mg 0.02 Ni 0.22 Fe 0.32 Mn 0.40 Ta 0.02 O2 layered material, the product was analyzed by XRD and found to be O3 phase. A sodium-deficient surface type with a particle size of 100 nm was prepared by solid-state method combined with sand milling in a sodium persulfate environment. 3-x (VOPO4)2F. The above layered material is combined with surface-deficient sodium-containing nano-sized Na... 3-x (VOPO4)2F was mixed evenly and then mechanically fused using a fusion machine, in which Na... 0.88 [Cu 0.02 Mg 0.02 Ni 0.22 Fe 0.32 Mn 0.40 Ta 0.02 O2 and Na 3-x The weight ratio of (VOPO4)2F was 100:2. SEM analysis showed that the particle size of the coated product was 2–10 micrometers, and the Na...3-x (VOPO4)2F will contain Na 0.88 [Cu 0.02 Mg 0.02 Ni 0.22 Fe 0.32 Mn 0.40 Ta 0.02 The O2 is uniformly and completely coated. The pH value of the product is 9.5. Using the layered material prepared in this embodiment as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a NaPF6 PC / EMC solution as the electrolyte, and adding 4% FEC by weight of the above electrolyte, a button cell was assembled and charged and discharged. The current density was 75 mA / g, the voltage range was 1.9–4.1 V, the specific capacity was 134.1 mAh / g, the median voltage was 3.12 V, and the capacity retention rate was 92.7% after 100 cycles. After the above charge and discharge cycles, the battery did not swell.

[0069] Example 4

[0070] Press Na 0.89 [Al 0.01 Mg 0.04 Ni 0.23 Fe 0.32 Mn 0.39 Sn 0.01 The material was prepared using a direct solid-state reaction method with a stoichiometric ratio of O2. First, Na2CO3, Mn2O3, Fe2O3, NiO, MgO, Al2O3, and SnO2 were mixed uniformly according to the stoichiometric ratio. The mixture was then ball-milled for 15 hours at 350 rpm to obtain a precursor. The precursor was then placed in a muffle furnace and calcined at 850°C in air for 12 hours to obtain O3-type Na. 0.89 [Al 0.01 Mg 0.04 Ni 0.23 Fe 0.32 Mn 0.39 Sn 0.01 O2 layered material, the product was XRD analysis showed to be O3 phase. A sodium-deficient surface type with a particle size of 100 nm was prepared by solid-state method combined with sand milling in a tetrafluoroborate-nitric acid environment. 3-x Fe2(PO4)P2O7. The above layered material is combined with surface-deficient sodium-containing nano-sized Na... 3-x Fe2(PO4)P2O7 was mixed evenly and then mechanically fused using a fusion machine, in which Na... 0.89 [Al 0.01 Mg 0.04 Ni 0.23 Fe 0.32 Mn 0.39 Sn 0.01 O2 and Na3-x The weight ratio of Fe2(PO4)P2O7 was 100:1. SEM analysis showed that the particle size of the coated product was 2–10 micrometers, and the Na... 3* x Fe2(PO4)P2O7 will Na 0.89 [Al 0.01 Mg 0.04 Ni 0.23 Fe 0.32 Mn 0.39 Sn 0.01 The O2 layer was uniformly and completely coated. The pH of the product was 9.4. Using the layered material prepared in this embodiment as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a NaPF6 PC / EMC solution as the electrolyte, along with 4% FEC by weight of the electrolyte, a button cell was assembled and subjected to charge-discharge tests. The current density was 75 mA / g, the voltage range was 1.9–4.1 V, the specific capacity was 136.2 mAh / g, and the median voltage was 3.14 V. After 100 cycles, the capacity retention was 93.1%. The battery did not exhibit gas buildup after the above charge-discharge cycles.

[0071] Example 5

[0072] The difference from Example 1 is that the mass ratio of the manganese-based morphological oxide material to the coating layer is 97:2.

[0073] The rest is the same as in Example 1, and will not be repeated here.

[0074] Example 6

[0075] The difference from Example 1 is that the mass ratio of the manganese-based morphological oxide material to the coating layer is 90:1.

[0076] The rest is the same as in Example 1, and will not be repeated here.

[0077] Example 7

[0078] The difference from Example 1 is that the mass ratio of the manganese-based morphological oxide material to the coating layer is 96:3.

[0079] The rest is the same as in Example 1, and will not be repeated here.

[0080] Example 8

[0081] The difference from Example 1 is that the mass ratio of the manganese-based morphological oxide material to the coating layer is 102:5.

[0082] The rest is the same as in Example 1, and will not be repeated here.

[0083] Example 9

[0084] The difference from Example 1 is that the mass ratio of the manganese-based morphological oxide material to the coating layer is 104:7.

[0085] The rest is the same as in Example 1, and will not be repeated here.

[0086] Example 10

[0087] The difference from Example 1 is that the mass ratio of the manganese-based morphological oxide material to the coating layer is 110:9.

[0088] The rest is the same as in Example 1, and will not be repeated here.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that Na was not performed. 2.5 V2(PO4)3 coating. The material has a pH of 12.1 and, under the same test conditions as in Example 1, exhibits a capacity retention of 85.1% after 100 cycles. See [link to Example 1]. Figure 7 And the battery is bloated.

[0091] The rest is the same as in Example 1, and will not be repeated here.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that sodium persulfate was not added during the milling process, meaning the layered material was coated with non-sodium-deficient Na3V2(PO4)3. The material had a pH of 10.3, and under the same test conditions as Example 1, after 100 cycles, the capacity retention was 91.1%, and the battery did not swell.

[0094] The rest is the same as in Example 1, and will not be repeated here.

[0095] Comparative Example 3

[0096] The difference from Example 1 is that the coating material is a common oxide, V₂O₃, instead of Na. 2.5 V2(PO4)3. The material has a pH of 11.4. Under the same test conditions as in Example 1, after 100 cycles, the capacity retention rate is 87.2%, and the battery does not swell.

[0097] The rest is the same as in Example 1, and will not be repeated here.

[0098] Comparative Example 4

[0099] The difference from Example 1 is that Li was not added during the preparation process; the Li was partially replaced by Mg to obtain Na. 0.88 [Mg 0.08 Ni 0.20 Fe 0.32 Mn 0.39Nb 0.01 O2, the pH value of the material is 9.8. Under the same test conditions as in Example 1, the specific capacity is 121.4 mAh / g, the median voltage is 3.10 V, and after 100 cycles, the capacity retention is 85.3%, and the battery does not swell.

[0100] The rest is the same as in Example 1, and will not be repeated here.

[0101] Comparative Example 5

[0102] The difference from Example 1 is that Nb was not doped during the preparation process; the Nb portion was replaced by Mn, thus yielding Na. 0.93 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.40 O2, the pH value of the material is 10.2. Under the same test conditions as in Example 1, with a median voltage of 3.06V, after 100 cycles, the capacity retention was 87.6%, and the battery was bloated.

[0103] The rest is the same as in Example 1, and will not be repeated here.

[0104] Comparative Example 6

[0105] The difference from Example 1 is that Nb was not added during the preparation process; the Nb portion was replaced by the trivalent element Co, thus yielding Na. 0.94 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.39 Co 0.01 O2, the pH value of the material is 9.7. Under the same test conditions as in Example 1, with a median voltage of 3.03V, after 100 cycles, the capacity retention was 86.4%, and the battery was bloated.

[0106] The rest is the same as in Example 1, and will not be repeated here.

[0107] Performance testing: The secondary batteries manufactured above were subjected to performance testing, and the test results are recorded in Table 1.

[0108] Table 1

[0109]

[0110] As shown in Table 1 above, the secondary battery prepared by this invention exhibits better performance than the secondary batteries of Comparative Examples 1-6, with a capacity retention rate as high as 95.8%. A comparison of Examples 1-4 reveals that when Li, Mg, Ni, and Fe elements are used for doping of type M elements, and Nb element is used for doping of type A elements, and Na is used as the doping agent… 0.92 [Li 0.05 Mg 0.03 Ni 0.20 Fe 0.32 Mn 0.39 Nb 0.01 The secondary battery prepared with O2 stoichiometry has better performance, with a capacity retention rate of 95.8%.

[0111] A comparison of Example 1 and Comparative Example 1 shows that when a coating layer is used to coat the layered positive electrode material, stability is effectively increased, capacity retention is improved, and the capacity protection rate is increased from 85.1% to 95.8%, while also preventing battery gas buildup. This is because the polyanionic material in the coating layer has air stability, hydrophobicity, and carbon dioxide repellency, thereby reducing or eliminating Na+. n Mn 1-x-y M x A y The alkalinity of the O2 surface improves the stability of layered materials in air, inhibits surface lattice distortion, and suppresses slurry gelation and battery gas expansion.

[0112] Comparing Example 1 and Comparative Example 2, it can be seen that when a sodium-deficient polyanionic material with a coating layer is used, the surface alkalinity can be further reduced. This is because sodium deficiency is conducive to its spontaneous absorption of residual sodium on the surface of the layered positive electrode, thereby further reducing the surface alkalinity. Preferably, the amount of sodium deficiency is 5% to 30%.

[0113] Comparing Example 1 and Comparative Example 3, it can be seen that when the coating material is a conventional oxide such as oxide V2O3, the coating does not significantly improve the structural stability of the core cathode material, and the battery still exhibits gas expansion. This indicates that polyanionic materials can effectively improve the structural stability of the cathode material, preventing harmful phase transitions from occurring during multiple charge-discharge cycles and improving battery cycle performance.

[0114] A comparison of Example 1 and Comparative Example 4 shows that when Li is used as the doping element in the positive electrode layered material, low-valence Li doping is beneficial for improving the valence state of manganese, the content of sodium, and the capacity of the material. Simultaneously, using lithium doping can also improve the cycle stability of the battery and prevent battery gas buildup.

[0115] Comparing Example 1 and Comparative Example 5, it is evident that when the positive electrode layered material lacks Nb doping and is replaced by Mn (i.e., only M-type elements are doped), the prepared positive electrode material exhibits low capacity retention, and the battery is prone to gas buildup. The A-type elements of this invention are high-valence inactive elements. Doping with element A not only improves lattice stability but also increases the battery's operating voltage and reduces the material's surface alkalinity. Furthermore, co-doping with both A-type and M-type elements produces a synergistic effect, stabilizing the lattice and increasing the operating voltage.

[0116] A comparison of Example 1 and Comparative Example 6 shows that when Nb is replaced by Co in the positive electrode layered material, the capacity retention of the prepared positive electrode material is low, and the battery is prone to gas buildup. This invention selects Nb as a doping element in Class A elements, resulting in a positive electrode material with good stability and preventing battery gas buildup.

[0117] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A sodium-ion battery cathode material, characterized in that, A manganese-based layered oxide material having a general formula of Na n Mn 1-x-y M x A y O2, wherein M is at least one of Li, Mg, Cu, Ni, Ca, Zn, Fe, Cr, Al, A is at least one of Ta, Mo, W, Nb, Si, Sn, V, wherein 0.4≤x≤0.8, 0<y≤0.1, 0.85≤n≤1, and a coating layer coated on the manganese-based layered oxide material, the coating layer comprising a polyanion material, the material of the coating layer being a sodium-based polyanion material. The sodium ion battery cathode material is a single crystal structure; the polyanion material and the oxidizing agent are mixed in deionized water, sand milling treatment is carried out to obtain a sand milling product, and then the sand milling product is subjected to centrifugal separation and vacuum drying to obtain a surface sodium-deficient nanoscale polyanion material, the polyanion material is selected from a surface sodium-deficient polyanion material, and the sodium deficiency is 5% to 30%; after the manganese-based layered oxide material is coated, it needs to be subjected to heat treatment; after the heat treatment, it is beneficial to spontaneously implant the residual sodium on the surface of the layered material into the surface sodium-deficient polyanion material, thereby reducing the alkalinity of the material surface.

2. The sodium-ion battery cathode material of claim 1, wherein, The particle size of the sodium ion battery cathode material is 2 to 10 microns.

3. The sodium-ion battery cathode material of claim 1, wherein, The manganese-based layered oxide material is in an O3 phase.

4. The sodium-ion battery cathode material of claim 1, wherein, The thickness of the coating layer is 10 to 200 nanometers.

5. The sodium-ion battery cathode material of any one of claims 1-4, wherein, The mass ratio of the manganese-based layered oxide material to the coating layer is 90 to 110: 1 to 10.

6. The sodium-ion battery cathode material of claim 5, wherein, The preparation method of the polyanion material is to mix a metal source material and an anion group-containing material, and to obtain a polyanion material through solid-phase reaction, the solid-phase reaction temperature is 500 to 1000 degrees Celsius, the reaction time is 1 to 10 hours, and the reaction atmosphere is a reducing atmosphere.

7. The sodium-ion battery cathode material of claim 1, wherein, The weight ratio of the polyanion material to the oxidizing agent is 0.1 to 10: 1 to 3.

8. A positive electrode sheet characterized by comprising: The sodium ion battery cathode material of any one of claims 1 to 7.

9. A secondary battery characterized by comprising: The positive electrode sheet of claim 8.

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