Positive electrode material, positive plate comprising positive electrode material, electrochemical device and electronic equipment

Abstract

The invention discloses a positive electrode material, a positive plate comprising the positive electrode material, an electrochemical device and electronic equipment, and relates to the technical field of electrochemical energy storage. The positive electrode material provided by the invention is obtained by coating a sodium manganese titanium phosphate core with a nitrogen-doped carbon (NC) material. The nitrogen-doped carbon coating has good electronic conductivity, chemical inertness in electrolyte and good mechanical toughness. In addition, the positive electrode and the positive electrode-electrolyte interface layer are sewn through the polar nitrogen-doped carbon coating, so that the conductivity of the positive electrode material and the stability of a solid-liquid interface can be effectively improved. The positive electrode material is high in capacity, good in cycling stability and good in high temperature resistance, and the battery can stably operate at the high temperature of 80 DEG C and has relatively high first discharge capacity and good capacity retention ratio. In addition, the positive electrode material is controllable in preparation process, stable in coating layer structure, controllable in thickness, short in synthesis period and suitable for batch production, and has remarkable practical value and good application potential.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a cathode material and a cathode sheet, electrochemical device and electronic device including the cathode material. Background Technology

[0002] In the field of rechargeable batteries, the choice of cathode material directly affects battery performance, cost, and safety. Currently, most mainstream batteries use lithium cathode materials, which, while offering high energy density, struggle to meet the future demand for affordable TWh-level energy storage due to insufficient lithium resources in the Earth's crust and high raw material costs. In contrast, sodium-ion batteries (SIBs), with their high sodium abundance, relatively uniform resource distribution, and low cost (sodium compounds cost less than 1 / 20th the price of lithium salts), have become one of the ideal energy storage technologies to replace lithium-ion batteries.

[0003] Among sodium-ion battery cathode materials, polyanionic cathode materials have emerged as a promising candidate: compared to layered oxides, polyanionic cathode materials exhibit superior structure and thermal stability, and are cost-effective as they do not contain cobalt or nickel; compared to Prussian blue, polyanionic cathode materials do not suffer from structural defects caused by water of crystallization and are free of cyanide toxicity; furthermore, due to their relatively high operating potential, they can achieve high energy densities up to 400 Wh / kg. However, polyanionic cathode materials suffer from insufficient intrinsic conductivity, with electronic conductivity (~10)... -10 S / cm) and ionic conductivity (~10) -9 The sodium ion has a low S / cm ratio; secondly, because the radius of sodium ions (1.02 Å) is much larger than that of lithium ions (0.76 Å), sodium ions are more prone to causing more significant lattice distortion and volume expansion when they are inserted into or extracted in electrode materials, which exacerbates the pulverization of the electrode structure and the side reactions of the electrolyte, especially at high temperatures. These defects seriously hinder the industrial application of sodium-ion batteries with polyanionic cathode materials.

[0004] Therefore, it is of great significance to solve the problems of insufficient conductivity, easy side reactions with electrolyte, and poor high-temperature interface stability of current sodium ion cathode materials. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a positive electrode material and a positive electrode sheet, electrochemical device, and electronic device including the same, aiming to solve the problems of insufficient conductivity, easy side reactions with electrolyte, and poor high-temperature interface stability of current sodium ion positive electrode materials.

[0006] In a first aspect, this application proposes a cathode material comprising a core and a coating layer covering the surface of the core; the core comprises a sodium manganese titanium phosphate compound, and the coating layer comprises a nitrogen-doped carbon material.

[0007] The cathode material according to the embodiments of this application has at least the following beneficial effects: This application proposes a cathode material obtained by coating a sodium manganese titanium phosphate core with nitrogen-doped carbon (NC) material, with the nitrogen-doped carbon (NC) coating in situ coated on the surface of the sodium manganese titanium phosphate particles. The nitrogen-doped carbon (NC) coating has good electronic conductivity, chemical inertness in the electrolyte, and good mechanical toughness. Furthermore, this coating can significantly enhance the interaction between itself and the core sodium manganese titanium phosphate material and electrolyte components (such as ethylene carbonate (EC)), forming a stable cathode / carbon layer / cathode-electrolyte interface film. This interfacial contact can effectively improve the transport of electrons / sodium ions, induce a uniform distribution of local charges, thereby alleviating the continuous decomposition and recombination of the electrode-electrolyte membrane (CEI) during cycling. Simultaneously, the enhanced stability of the cathode / carbon layer / cathode-electrolyte structure can also suppress the dissolution of transition elements and cathode side reactions, ensuring the long-term stability of the sodium-ion battery at high temperatures. Ultimately, the aforementioned polar nitrogen-doped carbon-coated sodium manganese titanium phosphate cathode material possesses advantages such as a high voltage plateau, good cycle performance, and good high-temperature performance. It can meet the requirements of sodium-ion battery cathodes, including high electronic conductivity, good interface control, and mechanical toughness, thereby improving battery cycle stability and high-temperature performance. The battery can operate stably at 80°C and has a high initial discharge capacity and good capacity retention. Furthermore, it can meet the needs of long-life electronic devices in both ordinary and special scenarios, and has extremely broad application prospects in the field of rechargeable batteries.

[0008] In some embodiments, the core has the chemical formula Na. 3+2x Mn 1+x Ti 1-x (PO4)3; where 0 ≤ x ≤ 0.5.

[0009] In some embodiments, the core has the chemical formula Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3.

[0010] In some embodiments, at least one of the following (a1) to (a4) is included: (a1) The median particle size D of the kernel 50 The range is 3~10 μm; (a2) The thickness of the coating layer is in the range of 2~5 nm; (a3) In the cathode material, the coating layer accounts for 8-12% of the mass; (a4) In the nitrogen-doped carbon material, the mass ratio of nitrogen element is 2~5%.

[0011] A second aspect of this application also provides a method for preparing the above-mentioned cathode material, comprising the following steps: Sodium source, manganese source, titanium source, phosphate and carbon source materials are dissolved in water and mixed evenly to obtain solution A; Nitrogen-doped carbon source was dissolved in water and mixed thoroughly to obtain solution B; After mixing solutions A and B evenly, the mixture is stirred continuously under predetermined condition one until it transforms into a wet gel. Then, after drying under predetermined condition two, the precursor powder is obtained. The precursor powder is calcined under predetermined condition three, ground after cooling, and then calcined again under predetermined condition four to obtain the cathode material.

[0012] In some embodiments, the method for preparing the cathode material includes at least one of the following (b1) to (b10): (b1) The molar ratio of the sodium source, manganese source, titanium source, phosphate, and carbon source materials is (3.2~3.6):(1.0~1.4):(0.6~1.0):(2.5~3.5):(0.5~0.7); (b2) The sodium source is selected from sodium acetate, the manganese source is selected from manganese acetate tetrahydrate, the titanium source is selected from dihydroxybis(ammonium lactate)titanium(IV), the phosphate is selected from ammonium dihydrogen phosphate, and the carbon source material is selected from citric acid; (b3) The concentration of sodium ions in solution A is 0.05~1 mol / L; (b4) The nitrogen-doped carbon source is selected from at least one of polyvinylpyrrolidone, melamine, gelatin, or nylon-66; (b5) In solution B, the concentration of the nitrogen-doped carbon source is 6~30 g / L; (b6) The predetermined condition is: stirring under a constant temperature water bath, with a temperature of 60~90℃ and a rotation speed of 200~800r / min; (b7) The second predetermined condition is: drying in a forced-air drying oven at a temperature of 80~120℃ for 10~14 hours; (b8) The predetermined condition three is: calcination at 300~450℃ for 3~5h in an inert gas, with a heating rate of 3~5℃ / min; (b9) The fourth predetermined condition is: calcination at 550~750℃ for 10~15h in an inert gas, with a heating rate of 3~5℃ / min; (b10) When (b8) or (b9) is included, the inert gas is selected from nitrogen or argon.

[0013] A third aspect of this application also provides a positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer comprises the positive electrode material described above or the positive electrode material prepared by the preparation method described above.

[0014] A fourth aspect of this application also proposes a battery cell comprising a negative electrode and the aforementioned positive electrode.

[0015] A fifth aspect of this application also proposes an electrochemical device comprising the aforementioned battery cell.

[0016] A sixth aspect of this application also proposes an electronic device comprising the aforementioned electrochemical device. Attached Figure Description

[0017] Figure 1 The positive electrode materials Na prepared in Comparative Examples 1 and 2 and Examples 1, 2 and 3 are... 3.4 Mn 1.2 Ti 0.8 (PO4)3, Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / C, Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC, Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-1, Na 3.4 Mn 1.2 Ti 0.8 XRD pattern of (PO4)3 / NC-2.

[0018] Figure 2 The cathode material Na in Comparative Example 1 3.4 Mn 1.2 Ti 0.8 Cycling curves of sodium cathode prepared by (PO4)3 at 200 mA / g and 25℃.

[0019] Figure 3 The cathode material Na in Comparative Example 2 3.4 Mn 1.2 Ti 0.8 Schematic diagram of SEM and TEM results of sodium cathode prepared by (PO4)3 / C.

[0020] Figure 4 The cathode material Na in Comparative Example 2 3.4 Mn 1.2 Ti 0.8The charge-discharge curves of the sodium cathode prepared by (PO4)3 / C at 50 mA / g and 25 °C.

[0021] Figure 5 The cathode material Na in Comparative Example 2 3.4 Mn 1.2 Ti 0.8 Cycling curves of sodium cathode prepared by (PO4)3 / C at 1000 mA / g and different temperatures (25℃ and 80℃).

[0022] Figure 6 The positive electrode material Na in Example 1 3.4 Mn 1.2 Ti 0.8 Schematic diagram of SEM and TEM results of sodium cathode prepared by (PO4)3 / NC.

[0023] Figure 7 The positive electrode material Na in Example 1 3.4 Mn 1.2 Ti 0.8 The charge-discharge curves of the sodium cathode prepared by (PO4)3 / NC at 50 mA / g and 25 °C.

[0024] Figure 8 The positive electrode material Na in Example 1 3.4 Mn 1.2 Ti 0.8 Cycling curves of sodium cathode prepared by (PO4)3 / NC at 1000 mA / g and different temperatures (25℃ and 80℃).

[0025] Figure 9 Na is the positive electrode material in Example 2. 3.4 Mn 1.2 Ti 0.8 Rate curve of sodium cathode prepared by (PO4)3 / NC-1.

[0026] Figure 10 The positive electrode material Na in Example 3 3.4 Mn 1.2 Ti 0.8 Rate curve of sodium cathode prepared by (PO4)3 / NC-2.

[0027] Figure 11 The cathode material Na in Comparative Example 2 3.4 Mn 1.2 Ti 0.8 The sodium-ion cathode prepared by (PO4)3 / C and the cathode material Na from Example 1 3.4 Mn 1.2 Ti 0.8A schematic diagram of the TEM results of the sodium cathode prepared by (PO4)3 / NC after cycling for 3 cycles at 50 mA / g and 25 °C.

[0028] Figure 12 The cathode material Na in Comparative Example 2 3.4 Mn 1.2 Ti 0.8 The sodium-ion cathode prepared by (PO4)3 / C and the cathode material Na from Example 1 3.4 Mn 1.2 Ti 0.8 A schematic diagram of the TEM results of the sodium cathode prepared by (PO4)3 / NC after 50 cycles at 50 mA / g and 25 °C.

[0029] Figure 13 The cathode material Na in Comparative Example 2 3.4 Mn 1.2 Ti 0.8 The sodium-ion cathode prepared by (PO4)3 / C and the cathode material Na from Example 1 3.4 Mn 1.2 Ti 0.8 A schematic diagram of the TEM results of the sodium cathode prepared by (PO4)3 / NC after 500 cycles at 1000 mA / g and 80 °C. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0031] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0032] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate small variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the terms may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two values ​​is less than or equal to ±10% of the average of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two values ​​can be considered "substantially" the same.

[0033] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0034] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0035] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0036] In the following description, all figures disclosed in this application are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit (RL) and an upper limit (RU) is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable ranging from 1% to 100% with a 1% increment, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed.

[0037] Throughout this specification, references to “implementation,” “partial implementation,” “one implementation,” “another approach,” “specific approach,” or “partial approach” mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0038] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0039] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

[0040] The term "polymer" refers to a polymeric compound prepared by polymerizing the same or different types of monomers. The general term "polymer" includes the terms "homopolymer," "copolymer," "trimer," and "interpolymer."

[0041] The term "coating" refers to one or more layers applied to one or both sides of a porous substrate material. Functional coatings comprise a mixture of at least one organic binder and at least one inorganic filler. In addition to the organic binder and inorganic filler, the protective porous layer may also include one or more additives. Functional coatings can be single-layer, double-layer, or multi-layer structures.

[0042] The term "binder" refers to a substance used to bond inorganic fillers to or to each other in a porous substrate material. Any organic binder that can bond inorganic fillers to or to each other in a porous substrate material may be used herein. Some non-limiting examples of organic binders include polyesters, polyamides, polyacrylic acid, polyethers, polyimides, polyolefins, rubbers, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, cellulose, cellulose derivatives, latexes, and combinations thereof.

[0043] The term "inorganic filler" refers to a non-conductive material. Some non-limiting examples of inorganic fillers include metal oxides, as well as non-oxide materials and non-metallic materials. Some non-limiting examples of metal oxides include alumina, zirconium oxide, barium titanate, lead zirconate titanate, ferrites, zinc oxide, and combinations thereof. Some non-limiting examples of non-oxide materials and non-metallic materials include silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium boride, molybdenum silicide, and combinations thereof.

[0044] The term "water-soluble polymer" refers to a high molecular weight polymer that is soluble in water or uniformly dispersed in water.

[0045] The term "oil-soluble polymer" refers to a high molecular weight polymer that is insoluble in water but can be uniformly dispersed in an organic polar solvent, including but not limited to N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

[0046] Positive electrode active material: As used herein and in the claims, the term "positive electrode active material" (also known as cathode active material) is defined as a material that is electrochemically active in a positive electrode or cathode. Active material should be understood as a material capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.

[0047] <Cathode Materials> In a first aspect, this application proposes a cathode material comprising a core and a coating layer covering the surface of the core; the core comprises a sodium manganese titanium phosphate compound, and the coating layer comprises a nitrogen-doped carbon material.

[0048] The cathode material according to the embodiments of this application has at least the following beneficial effects: This application proposes a cathode material obtained by coating a sodium manganese titanium phosphate core with nitrogen-doped carbon (NC) material, with the nitrogen-doped carbon (NC) coating in situ coated on the surface of the sodium manganese titanium phosphate particles. The nitrogen-doped carbon (NC) coating has good electronic conductivity, chemical inertness in the electrolyte, and good mechanical toughness. Furthermore, this coating can significantly enhance the interaction between itself and the core sodium manganese titanium phosphate material and electrolyte components (e.g., ethylene carbonate (EC)), forming a stable cathode / carbon layer / cathode-electrolyte interface film. This interfacial contact can effectively improve electron / sodium ion transport, induce a uniform distribution of local charges, thereby mitigating the continuous decomposition and recombination of the electrode-electrolyte (CEI) membrane during cycling. Simultaneously, the enhanced stability of the cathode / carbon layer / cathode-electrolyte structure can also suppress the dissolution of transition elements and cathode side reactions, ensuring the long-term stability of the sodium-ion battery at high temperatures. Ultimately, the aforementioned polar nitrogen-doped carbon-coated sodium manganese titanium phosphate cathode material possesses advantages such as a high voltage plateau, good cycle performance, and good high-temperature performance. It can meet the requirements of sodium-ion battery cathodes, including high electronic conductivity, good interface control, and mechanical toughness, thereby improving battery cycle stability and high-temperature performance. The battery can operate stably at 80°C and has a high initial discharge capacity and good capacity retention. Furthermore, it can meet the needs of long-life electronic devices in both ordinary and special scenarios, and has extremely broad application prospects in the field of rechargeable batteries.

[0049] In some implementations, the core has the chemical formula Na. 3+2x Mn 1+x Ti 1-x (PO4)3; where 0 ≤ x ≤ 0.5. For example, the value of x can be 0.1, 0.2, 0.3, 0.4, 0.5, or within the range of any two of the above values.

[0050] In some implementations, the core has the chemical formula Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3.

[0051] In some embodiments, nitrogen-doped carbon (NC) material is in situ coated onto the surface of sodium manganese titanium phosphate particles, forming a nitrogen-doped carbon (NC) coating layer. This coating layer possesses good electrical conductivity, chemical inertness in electrolytes, improved interfacial compatibility, and the ability to promptly mitigate the valence-change dissolution of transition metal elements. Its electronic conductivity is typically 10⁻⁶. 3 ~10 5 It has a S / cm ratio, a stable structure, and a simple preparation process, and can be widely used in the coating of polyanionic cathode materials.

[0052] In some implementations, the median particle size D of the kernel 50 The range is 3 to 10 μm; for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or within the range of any two of the above values.

[0053] In some embodiments, the thickness of the coating layer ranges from 2 to 5 nm; for example, it can be 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, or within any two of the above values.

[0054] In some embodiments, the coating layer accounts for 8 to 12% of the mass of the cathode material; for example, it can be 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, or within any two of the above values.

[0055] In some embodiments, the mass percentage of nitrogen in the nitrogen-doped carbon material is 2 to 5%; for example, it can be 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or within any two of the above values.

[0056] In one specific embodiment of this application, a positive electrode material is provided, including a core and a coating layer covering the surface of the core; the core includes sodium manganese titanium phosphate compound Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3, the coating layer includes nitrogen-doped carbon (NC) material. The above-mentioned polar nitrogen-doped carbon coating provided in this application coats sodium manganese titanium phosphate cathode material (Na). 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC), nitrogen-doped carbon (NC) coatings exhibit good electronic conductivity, chemical inertness in electrolytes, and good mechanical toughness; simultaneously, nitrogen-doped carbon (NC) coatings can significantly enhance their affinity for Na+. 3.4 Mn 1.2 Ti 0.8The interaction between the (PO4)3 core material and the electrolyte components (e.g., ethylene carbonate (EC)) forms a stable cathode / carbon layer / cathode-electrolyte interface film. This interfacial contact effectively improves electron / sodium ion transport and induces a uniform distribution of local charges, thereby mitigating the continuous decomposition and recombination of the electrode-electrolyte (CEI) membrane during cycling. Furthermore, the enhanced structural stability of the cathode / carbon layer / cathode-electrolyte also suppresses the dissolution of transition elements and cathode side reactions, ensuring the long-term stability of the sodium-ion battery at high temperatures. This cathode material exhibits an initial discharge specific capacity of approximately 159 mAh / g at 50 mA / g and 25 °C, and approximately 168 mAh / g at 50 mA / g and 80 °C, with good cycle performance. Importantly, it can operate stably at 80 °C. This solves the problems of poor electronic conductivity, severe transition metal dissolution, and poor high-temperature interface stability found in existing polyanionic sodium battery cathode materials. Ultimately, the aforementioned polar Na… 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC cathode material has advantages such as high voltage platform, good cycle performance and good high temperature performance. It can meet the requirements of sodium-ion battery cathode such as high electronic conductivity, good interface control and mechanical toughness, improve battery cycle stability and high temperature performance, and the battery can operate stably at a high temperature of 80℃. It can also meet the needs of long-life electronic devices in both ordinary and special scenarios, and has extremely broad application prospects in the field of secondary batteries.

[0057] A second aspect of this application provides a method for preparing the aforementioned cathode material, comprising the following steps: S100. Dissolve sodium source, manganese source, titanium source, phosphate and carbon source materials in water, mix them evenly to obtain solution A; S200. Dissolve the nitrogen-doped carbon source in water and mix thoroughly to obtain solution B; S300. After mixing solution A and solution B evenly, stir continuously under predetermined condition one until it transforms into a wet gel, and then dry under predetermined condition two to obtain precursor powder. S400. The precursor powder is calcined under predetermined condition three, ground after cooling, and then calcined again under predetermined condition four to obtain the above-mentioned cathode material.

[0058] The method for preparing the cathode material according to the embodiments of this application has at least the following beneficial effects: The preparation method of this application utilizes a sol-gel method combined with a high-temperature annealing process to carbonize a nitrogen-doped carbon source (e.g., polyvinylpyrrolidone (PVP-K30)) to obtain a nitrogen-doped carbon (NC) coating, which is then in situ coated onto the surface of sodium manganese titanium phosphate particles to obtain a high-temperature resistant polar nitrogen-doped carbon-coated sodium manganese titanium phosphate cathode material. The above preparation method is simple, the coating thickness is controllable, and the production efficiency is high, making it suitable for industrial-scale production. The obtained cathode material has advantages such as a high voltage platform, good cycle performance, and good high-temperature performance. It can meet the requirements of high electronic conductivity, good interface control, and mechanical toughness for sodium phosphate battery cathodes, and can meet the needs of long-life electronic devices in both ordinary and special scenarios. It solves the problems of poor conductivity, rate performance, and high-temperature performance of sodium phosphate battery cathode materials in application, and has extremely broad application prospects in the field of secondary batteries.

[0059] In some implementations, the core has the chemical formula Na. 3+2x Mn 1+x Ti 1-x (PO4)3; where 0 ≤ x ≤ 0.5. For example, the value of x can be 0.1, 0.2, 0.3, 0.4, 0.5, or within the range of any two of the above values.

[0060] In some implementations, the core has the chemical formula Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3.

[0061] In some embodiments, the sodium source is selected from sodium acetate, but is not limited thereto.

[0062] In some embodiments, the manganese source is selected from manganese acetate tetrahydrate, but is not limited thereto.

[0063] In some embodiments, the titanium source is selected from dihydroxybis(ammonium lactate)titanium (IV), but is not limited thereto.

[0064] In some embodiments, the phosphate is selected from, but is not limited to, ammonium dihydrogen phosphate.

[0065] In some embodiments, the carbon source material is selected from citric acid, but is not limited thereto.

[0066] In some embodiments, the molar ratio of sodium source, manganese source, titanium source, phosphate and carbon source materials is (3.2~3.6):(1.0~1.4):(0.6~1.0):(2.5~3.5):(0.5~0.7), preferably 3.4:1.2:0.8:3:0.6.

[0067] Specifically, the molar ratio of sodium acetate, manganese acetate tetrahydrate, dihydroxybis(lactic acid)titanium(IV)dihydroxybis(lactic acid)titanium(IV)), ammonium dihydrogen phosphate, and citric acid is (3.2~3.6):(1.0~1.4):(0.6~1.0):(2.5~3.5):(0.5~0.7), preferably 3.4:1.2:0.8:3:0.6.

[0068] In some embodiments, the concentration of sodium ions in solution A is 0.05~1 mol / L, preferably 0.05~0.5 mol / L.

[0069] In some embodiments, the nitrogen-doped carbon source includes, but is not limited to, at least one of polyvinylpyrrolidone (PVP-K30), melamine, gelatin, or nylon-66.

[0070] In some embodiments, the concentration of the nitrogen-doped carbon source in solution B is 6-30 g / L, preferably 10-15 g / L.

[0071] In some embodiments, in step S300, solution A and solution B are stirred for 1 to 3 hours to mix evenly, preferably for 2 hours.

[0072] In some implementations, the predetermined condition is: stirring under a constant temperature water bath at a temperature of 60~90℃ and a rotation speed of 200~800 r / min.

[0073] Preferably, the constant temperature water bath is a single-station constant temperature stirring water bath.

[0074] Preferably, the stirring temperature is 80℃.

[0075] Preferably, the stirring speed is 400 r / min.

[0076] In some embodiments, the second predetermined condition is: drying in a forced-air drying oven at a temperature of 80~120°C for 10~14 hours, preferably 12 hours.

[0077] In some embodiments, the predetermined condition three is: calcination at 300~450°C for 3~5 hours in an inert gas at a heating rate of 3~5°C / min; preferably, calcination at 350°C for 4 hours at a heating rate of 5°C / min.

[0078] In some embodiments, the predetermined condition four is: calcination at 550~750°C for 10~15h in an inert gas at a heating rate of 3~5°C / min; preferably, calcination at 650°C for 12h at a heating rate of 5°C / min.

[0079] In some embodiments, the inert gas is selected from nitrogen or argon. Specifically, the inert gas is selected from nitrogen with a purity of 99.999% or argon with a purity of 99.999%.

[0080] In some embodiments, the grinding time in step S400 is 15 to 45 minutes.

[0081] Finally, this application demonstrates that nitrogen-doped carbon-coated sodium manganese titanium phosphate cathode materials with different thicknesses can be prepared using sol-gel and high-temperature annealing processes. The specific preparation method includes: (1) mixing manganese source, titanium source, phosphoric acid source, carbon source and sodium source in proportion and treating with sol-gel method to obtain precursor; (2) placing the precursor in a tube furnace and calcining at high temperature under inert gas protection to finally obtain nitrogen-doped carbon-coated sodium manganese titanium phosphate products with different thicknesses.

[0082] In one specific embodiment of this application, a cathode material Na is provided. 3.4 Mn 1.2 Ti 0.8 The preparation method of (PO4)3 / NC includes the following steps: (1) Synthesis of sodium manganese titanium phosphate precursor (Na 3.4 Mn 1.2 Ti 0.8 (PO4)3) solution: Sodium acetate, manganese acetate tetrahydrate, dihydroxybis(ammonium lactate)titanium (IV), ammonium dihydrogen phosphate, and citric acid were added to a certain amount of deionized water and dissolved by thorough stirring at room temperature to obtain a homogeneous mixed solution A, namely the sodium manganese titanium phosphate precursor (Na). 3.4 Mn 1.2 Ti 0.8 (PO4)3) solution; (2) Synthesis of nitrogen-doped carbon-coated sodium manganese titanium phosphate (Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC) precursor: Polyvinylpyrrolidone (PVP-K30) was added to a certain amount of deionized water to obtain solution B; Solution A and solution B were mixed and stirred thoroughly for 2 hours, then stirred continuously in a water bath until a wet gel was formed. The gel was then dried in a forced-air oven at 120°C for 12 hours to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC precursor; (3) Synthesis of nitrogen-doped carbon-coated sodium manganese titanium phosphate (Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC): The powdered precursor obtained in step (2) was calcined at 350°C for 4 hours in an inert gas atmosphere. After cooling to room temperature, it was ground and then calcined again at 650°C for 12 hours in an inert gas atmosphere to obtain the final product, nitrogen-doped carbon-coated sodium manganese titanium phosphate (Na). 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC), which is the cathode material mentioned above.

[0083] This application also provides the application of the above-mentioned cathode materials and / or preparation methods in sodium-ion batteries.

[0084] <Positive Electrode Tablets> A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer comprises the positive electrode material described above or the positive electrode material prepared by the preparation method described above.

[0085] The positive electrode sheet according to the embodiments of this application has at least the following beneficial effects: The positive electrode sheet provided in this application uses nitrogen-doped carbon (NC) material to coat sodium manganese titanium phosphate positive electrode material, and the nitrogen-doped carbon (NC) coating is in situ coated on the surface of sodium manganese titanium phosphate particles. The nitrogen-doped carbon (NC) coating has good electronic conductivity, chemical inertness in the electrolyte, and good mechanical toughness. Moreover, this coating can significantly enhance the interaction between itself and the core sodium manganese titanium phosphate material and electrolyte components (such as ethylene carbonate (EC)), forming a stable positive electrode / carbon layer / positive electrode-electrolyte interface film. This interfacial contact can effectively improve the transport of electrons / sodium ions, induce a uniform distribution of local charges, thereby alleviating the continuous decomposition and recombination of the electrode-electrolyte membrane (CEI) during cycling. At the same time, the enhanced stability of the positive electrode / carbon layer / positive electrode-electrolyte structure can also suppress the dissolution of transition elements and cathode side reactions, ensuring the long-term stability of sodium-ion batteries at high temperatures. Ultimately, the aforementioned polar nitrogen-doped carbon-coated sodium manganese titanium phosphate cathode material possesses advantages such as a high voltage plateau, good cycle performance, and good high-temperature performance. It can meet the requirements of sodium-ion battery cathodes, including high electronic conductivity, good interface control, and mechanical toughness, thereby improving battery cycle stability and high-temperature performance. The battery can operate stably at 80°C and has a high initial discharge capacity and good capacity retention. Furthermore, it can meet the needs of long-life electronic devices in both ordinary and special scenarios, and has extremely broad application prospects in the field of rechargeable batteries.

[0086] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent.

[0087] In some embodiments, the mass percentage of each component, taking the positive electrode material, conductive agent, and binder as a whole, is as follows: positive electrode material 70-98%, conductive agent 1-20%, and binder 1-10%.

[0088] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer.

[0089] The positive electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery positive electrode binders.

[0090] In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0091] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0092] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0093] In some embodiments, the preparation method of the positive electrode sheet includes the following steps: thoroughly mixing the positive electrode material, conductive agent, binder, and solvent according to a mass ratio, coating the mixture onto the positive electrode current collector, and then drying, cold pressing, and stamping to obtain the positive electrode sheet. The preparation method of the positive electrode sheet can adopt conventional methods in the industry, and this application does not limit it.

[0094] <Battery Cell> A fourth aspect of this application also proposes a battery cell comprising a negative electrode and the aforementioned positive electrode.

[0095] Since the battery cell adopts all the technical solutions of the positive electrode sheet in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions in the above embodiments. That is, it has good high battery cycle stability and high temperature performance, the battery can operate stably at a high temperature of 80°C, and has high initial discharge capacity and good capacity retention rate, thus having extremely broad application prospects.

[0096] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0097] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil or an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0098] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0099] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0100] In some embodiments, the negative electrode active material may include hard carbon, but is not limited thereto, and may also include other materials that can be used as negative electrode active materials for sodium-ion batteries.

[0101] In some embodiments, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0102] In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0103] In some embodiments, a method for preparing the above-mentioned negative electrode sheet is also provided, including the steps of: thoroughly mixing the negative electrode active material, conductive agent, and binder according to a mass ratio, coating the mixture onto the negative electrode current collector, and then drying, cold pressing, and stamping to obtain the negative electrode sheet. The preparation method of the negative electrode sheet can adopt conventional methods in the industry, and this application does not limit it.

[0104] <Electrochemical Device> A fifth aspect of this application also proposes an electrochemical device comprising the aforementioned battery cell.

[0105] The electrochemical device provided in this application includes any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, and specific, non-limiting examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a sodium secondary battery, including sodium-ion secondary batteries, sodium polymer secondary batteries, or sodium-ion polymer secondary batteries.

[0106] In some embodiments, the electrochemical device includes a sodium-ion battery.

[0107] In some embodiments, the electrochemical device includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive and negative electrodes.

[0108] The separator separates the negative and positive electrodes and provides a pathway for sodium ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in sodium secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures. Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate. In some embodiments, the porous substrate is, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0109] In some embodiments, the coating is disposed on one side of the substrate. In some embodiments, the coating is disposed on both sides of the substrate.

[0110] In some embodiments, the coating includes inorganic fillers and adhesives.

[0111] In some embodiments, the inorganic filler comprises Al2O3, SiO2, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, TiN, AlN, Na2O·mTiO2, K2O·nTiO2, BaO x MTiO3 and combinations thereof, wherein m is 3 or 6, n is 1, 2, 4, 6 or 8, x is 1 or 2, and M is Ba, Sr or Ca. Inorganic fillers may be spherical, plate-like, disc-like, needle-like, cylindrical, irregular or other known particle shapes.

[0112] In some embodiments, the inorganic filler includes one or more of alumina, hydrated alumina, boehmite, magnesium hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, and barium sulfate.

[0113] In some implementations, the binder is a water-soluble polymer.

[0114] In some implementations, the water-soluble polymer is a homopolymer or copolymer.

[0115] In some embodiments, the water-soluble binder includes at least one of polyamide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose, cyanoethyl cellulose, nitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0116] In some implementations, the binder is an oil-soluble polymer.

[0117] In some embodiments, non-limiting examples of oil-soluble polymers include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyester, polyether, polyvinyl compounds, polyolefins, rubber, polyvinylpyrrolidone, polystyrene, nitrile rubber (NBR), styrene-butadiene rubber (SBR), latex, acrylonitrile-styrene-butadiene copolymer, halogenated polymers, fluorinated polymers, chlorinated polymers, unsaturated polymers, conjugated diene polymers, and combinations thereof.

[0118] In some embodiments, the electrolyte may include at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.

[0119] In some embodiments, the liquid electrolyte may include a non-aqueous solvent and a sodium salt.

[0120] In some embodiments, the sodium salt may include at least one of NaPF6, NaBF4, NaClO4, NaF, NaCl, NaTFSI, NaFSI, NaOTf, and CH3COONa.

[0121] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0122] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0123] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0124] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0125] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0126] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0127] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0128] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0129] In one specific embodiment of this application, the electrochemical device is a sodium-ion battery. The preparation method of the sodium-ion battery includes the following steps: adding 1.0 M NaClO4 to ethylene carbonate (EC) and propylene carbonate (PC) (EC:PC = 1:1 mass ratio), and adding 5 wt.% fluorinated ethylene carbonate (FEC) as the electrolyte; using a sodium sheet or spherical hard carbon (HC) as the negative electrode, and the above-mentioned positive electrode sheet as the positive electrode.

[0130] Specifically, spherical hard carbon (HC) is prepared by the following method: commercial spherical hard carbon is ultrasonically purified, acidified with 2 mol / L hydrochloric acid solution, and then vacuum dried to serve as the negative electrode.

[0131] Specifically, the vacuum drying process takes 8 to 12 hours.

[0132] In some embodiments, the positive and negative electrode capacity ratio (N / P) of the above-mentioned positive electrode material to spherical hard carbon (HC) is 1.05 to 1.3.

[0133] <Electronic Devices> A sixth aspect of this application provides an electronic device comprising the aforementioned electrochemical device.

[0134] The electronic device described in this application is not particularly limited and may be any electronic device known in the prior art. The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. Some embodiments of this application include electronic devices such as mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0135] Unless otherwise specified in the following examples, the techniques or conditions described in the literature in this field or in accordance with the product instructions shall apply. All reagents or instruments without a specified manufacturer are commercially available conventional products.

[0136] Example 1 (1) 17 mmol sodium acetate powder, 6 mmol manganese acetate tetrahydrate powder, 15 mmol ammonium dihydrogen phosphate, 4 mmol dihydroxybis(ammonium lactate)titanium(IV) and 3 mmol citric acid were added to 50 mL of deionized water and dissolved by stirring at room temperature for 1 h to obtain a homogeneous mixed solution A with a sodium salt molar concentration of 0.34 mol / L; (2) Add 0.5 g of polyvinylpyrrolidone (PVP-K30) to 40 mL of deionized water to form solution B. Mix solutions A and B prepared in step (1) and stir for 2 h. The mixed solution is then continuously stirred in a water bath at 80 °C for about 6 h at a stirring speed of 400 r / min; the solution transforms into a wet gel. Finally, dry in a forced-air oven at 80 °C for 12 h to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC precursor C; (3) Place the powdered precursor C obtained in step (2) in a tube furnace, introduce 99.999% pure argon gas into the tube furnace, and heat it to 350℃ at a rate of 5℃ / min for 4 hours. After cooling to room temperature, grind it, and then heat it to 650℃ at a rate of 5℃ / min for 12 hours to obtain powder D, denoted as Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC.

[0137] Example 2 (1) 17 mmol sodium acetate powder, 6 mmol manganese acetate tetrahydrate powder, 15 mmol ammonium dihydrogen phosphate, 4 mmol dihydroxybis(ammonium lactate)titanium(IV) and 3 mmol citric acid were poured into 20 mL of deionized water and dissolved by stirring at room temperature for 1 h to obtain a homogeneous mixed solution A with a sodium salt molar concentration of 0.85 mol / L; (2) Add 0.2 g of polyvinylpyrrolidone (PVP-K30) to 30 mL of deionized water to form solution B. Mix solutions A and B prepared in step (1) and stir for 1 h. The mixed solution is continuously stirred in a water bath at 60 °C for about 14 h at a stirring speed of 800 r / min; the solution transforms into a wet gel. Finally, dry in a forced-air oven at 90 °C for 14 h to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-1 precursor C; (3) Place the powdered precursor C obtained in step (2) in a tube furnace, introduce 99.999% pure argon gas into the tube furnace, and heat it to 300℃ at a rate of 3℃ / min for 5 hours. After cooling to room temperature, grind it, and then heat it to 550℃ at a rate of 3℃ / min for 15 hours to obtain powder D, denoted as Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-1.

[0138] Example 3 (1) 17 mmol sodium acetate powder, 6 mmol manganese acetate tetrahydrate powder, 15 mmol ammonium dihydrogen phosphate, 4 mmol dihydroxybis(ammonium lactate)titanium(IV) and 3 mmol citric acid were added to 100 mL of deionized water and dissolved by stirring at room temperature for 1 h to obtain a homogeneous mixed solution A with a sodium salt molar concentration of 0.17 mol / L; (2) Add 0.8 g of polyvinylpyrrolidone (PVP-K30) to 30 mL of deionized water to form solution B. Mix solutions A and B prepared in step (1) and stir for 3 h. The mixed solution is then continuously stirred in a water bath at 90 °C for about 10 h at a stirring speed of 200 r / min; the solution transforms into a wet gel. Finally, dry in a forced-air oven at 120 °C for 10 h to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-2 precursor C; (3) Place the powdered precursor C obtained in step (2) in a tube furnace, introduce 99.999% pure argon gas into the tube furnace, and heat it to 450℃ at a rate of 4℃ / min for 3 hours. After cooling to room temperature, grind it, and then heat it to 750℃ at a rate of 4℃ / min for 10 hours to obtain powder D, denoted as Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-2.

[0139] Comparative Example 1 (1) 17 mmol sodium acetate powder, 6 mmol manganese acetate tetrahydrate powder, 15 mmol ammonium dihydrogen phosphate powder and 4 mmol dihydroxybis(ammonium lactate)titanium(IV) were poured into 50 mL of deionized water and dissolved by stirring at room temperature for 1 h to obtain a homogeneous mixed solution A with a sodium salt molar concentration of 0.34 mol / L. (2) Mixed solution A was continuously stirred in a water bath at 80℃ for about 6 hours at a stirring speed of 400 r / min; the solution transformed into a wet gel. Finally, it was dried in a forced-air oven at 80℃ for 12 hours to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 precursor B; (3) Place the powdered precursor B obtained in step (2) in a tube furnace, introduce 99.999% pure argon gas into the tube furnace, and heat it to 350°C at a rate of 5°C / min for 4 hours. After cooling to room temperature, grind it, and then heat it to 650°C at a rate of 5°C / min for 12 hours to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 powder.

[0140] Comparative Example 2 (1) 17 mmol sodium acetate powder, 6 mmol manganese acetate tetrahydrate powder, 15 mmol ammonium dihydrogen phosphate powder, 4 mmol dihydroxybis(ammonium lactate)titanium(IV) and 3 mmol citric acid powder were poured into 50 mL of deionized water and dissolved by stirring thoroughly at room temperature for 1 h to obtain a homogeneous mixed solution A with a sodium salt molar concentration of 0.34 mol / L; (2) Add 3 mmol of glucose to 30 mL of deionized water to form solution B. Mix solutions A and B prepared in step (1) and stir for 2 h. The mixed solution is then continuously stirred in a water bath at 80 °C for about 6 h at a stirring speed of 400 r / min; the solution transforms into a wet gel. Finally, dry in a forced-air oven at 80 °C for 12 h to obtain Na.3.4 Mn 1.2 Ti 0.8 (PO4)3 / C precursor C; (3) Place the powdered precursor C obtained in step (2) in a tube furnace, introduce 99.999% pure argon gas into the tube furnace, and heat it to 350°C at a rate of 5°C / min for 4 hours. After cooling to room temperature, grind it, and then heat it to 650°C at a rate of 5°C / min for 12 hours to obtain Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / C powder.

[0141] Test case Sodium-ion secondary batteries were prepared using the cathode materials of Examples 1-3 and Comparative Examples 1-2, respectively: (1) Preparation of positive electrode sheet The positive electrode materials of Examples 1-3 and Comparative Examples 1-2, the conductive agent Ketjen black, and the binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 70:20:10. The mixture was then coated onto the positive electrode current collector Al foil, dried, cold-pressed, and stamped to obtain the positive electrode sheet.

[0142] (2) Preparation of negative electrode The negative electrode active material hard carbon, conductive agent Ketjen black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methylpyrrolidone (NMP) solvent system at a mass ratio of 80:10:10. The mixture is then coated onto the negative electrode current collector Cu foil, dried, cold-pressed, and stamped to obtain the negative electrode sheet.

[0143] (3) Preparation of the separating membrane: Whatman's GF series filter paper (GF / A) was used as the separating membrane.

[0144] (4) Preparation of electrolyte A solution prepared by mixing sodium salt NaClO4 with a solvent (ethylene carbonate (EC): propylene carbonate (PC) = 1:1, by mass, with the addition of 5% fluoroethylene carbonate) is used as the electrolyte for sodium-ion secondary batteries. (5) Preparation of sodium-ion secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. The electrode assembly is then placed in the battery casing, electrolyte is injected, and the battery is sealed to obtain a sodium-ion secondary battery.

[0145] Performance testing methods 1. X-ray diffraction (XRD) The cathode sheets made from the cathode materials in the examples and comparative examples were subjected to XRD tests. XRD is mainly used to study the internal crystal structure of materials because X-rays have wavelengths similar to the interplanar spacing and have a certain penetrating power. A beam of X-rays passes through a crystal and diffracts; by analyzing the diffraction pattern, phase identification and structural analysis can be performed. Test conditions: Cu Kα radiation, operating current 250 mA, continuous scanning, operating voltage 40 kV, scanning range 2θ 15–70°, step size 0.02, scanning speed 10° / min.

[0146] 2. Scanning electron microscope (SEM) The cathode materials prepared in the examples and comparative examples were subjected to scanning electron microscopy (SEM) tests. SEM is mainly used to study the surface morphology and microstructure characteristics of materials. Because SEM can scan the sample surface point by point with a focused electron beam, it excites secondary electrons and backscattered electrons, etc. These signals are received by a detector and converted into electrical signals, generating a high-resolution image of the sample surface. This allows for the analysis of surface morphology, particle size and distribution, particle aggregation state, and interfacial bonding. Testing conditions: Field emission scanning electron microscope (FESEM) was used, with an accelerating voltage of 5–20 kV (adjusted according to the sample's conductivity), a working distance of 5–15 mm, secondary electron imaging mode, and a magnification range of 500–50,000x. The samples were sputter-coated with gold before testing to enhance conductivity.

[0147] 3. Transmission electron microscope (TEM) After preparing ultrathin samples from the cathode materials used in the examples and comparative examples, TEM tests were performed. TEM is mainly used to study the internal microstructure and fine crystal features of materials. Because high-energy electron beams have extremely short wavelengths and strong penetrating power, scattering and interference phenomena occur when the electron beam penetrates the ultrathin sample. By modulating and imaging these electron signals, information such as the sample's micromorphology, crystal lattice structure, grain size, grain boundary features, and internal defects (such as dislocations and vacancies) can be obtained. Selected area electron diffraction (SAED) can also be used for phase verification. Testing conditions: Field emission transmission electron microscopy was used, with an accelerating voltage of 200 kV and a point resolution ≤0.25 nm.

[0148] 4. Gram capacity test Five sodium-ion secondary batteries prepared from the cathode materials in the examples and comparative examples were taken respectively, and charged at a constant current of 50 mA / g at room temperature until the voltage reached 4.2V. Then, they were discharged at a constant current of 50 mA / g until the voltage reached 1.5V.

[0149] 5. Cyclic performance test Five sodium-ion secondary batteries prepared with the cathode materials from the examples and comparative examples were taken respectively. The sodium-ion secondary batteries were repeatedly charged and discharged using the following steps, and the cycle capacity retention rate was calculated: First, a constant current charge and discharge was performed at 50 mA / g until the upper limit voltage of 4.2V was reached. Then, a constant current discharge was performed at a discharge current of 50 mA / g until the final voltage of 1.5V was reached. The discharge capacity of the first cycle was recorded. For example, 500 charge and discharge cycles were performed, and the discharge capacity of the first and 500th cycles was recorded. Cycle capacity retention rate C 500 = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0150] Results Analysis The Na products of the examples and comparative examples were compared respectively. 3.4 Mn 1.2 Ti 0.8 (PO4)3 (Comparative Example 1), Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / C (Comparative Example 2), Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC (Example 1), Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-1 (Example 2) and Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-2 (Example 3) was characterized by XRD, and the results are as follows: Figure 1 As shown in the figure, Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 and Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / C, Na 3.4 Mn 1.2 Ti 0.8 The peak positions of (PO4)3 / NC are basically the same. This is because the ordinary carbon coating and the nitrogen-doped carbon coating only serve as a coating shell and do not change the internal crystal structure of sodium manganese titanium phosphate.

[0151] The product Na from Comparative Example 1 3.4 Mn 1.2 Ti 0.8 The electrochemical performance test results of sodium-ion batteries prepared from 3-micron (PO4) particles are as follows: Figure 2 As shown in the figure, Na 3.4 Mn1.2 Ti 0.8 The (PO4)3 electrode exhibits a specific capacity of 51.2 mAh / g after 443 cycles at 200 mA / g and 25 °C, with a capacity retention of 56.1%.

[0152] The product Na from Comparative Example 2 3.4 Mn 1.2 Ti 0.8 Scanning electron microscopy (SEM) results of (PO4)3 / C micron particles ( Figure 3 a) and transmission electron microscopy (TEM) characterization results ( Figure 3 (b) As shown in the figure, after the coating layer is formed by sol-gel and annealing treatment, Na 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / C particles exhibit a micron-sized morphology with a carbon layer covering their surface. The electrochemical performance test results of the prepared sodium-ion battery are as follows: Figure 4 and Figure 5 As shown: Figure 4 As shown, after being coated with a normal, undoped carbon layer, Na 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / C electrode exhibits a specific capacity of 133.2 mAh / g at 50 mA / g and 25 °C. Figure 5 As shown in (a), Na 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / C electrode exhibits a discharge specific capacity of 70.6 mAh / g after 2000 cycles at 1000 mA / g and 25°C, with a capacity retention of 70.2%. Figure 5 As shown in (b), Na 3.4 Mn 1.2 Ti 0.8 The discharge specific capacity of the (PO4)3 / C electrode after 500 cycles at 1000 mA / g and 80℃ is 63.0 mAh / g, with a capacity retention of 54.4%.

[0153] Product Na from Example 1 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC micron-sized particles were characterized by SEM. Figure 6 a) and TEM characterization ( Figure 6 (b) The result is as follows Figure 6 As shown in the figure, after the coating layer is formed through sol-gel and annealing treatment, Na 3.4 Mn 1.2 Ti 0.8The (PO4)3 / NC particles still exhibit an irregular micron-sized morphology, with a nitrogen-doped carbon layer coating the surface, making them more dense and uniform. The electrochemical performance test results of the prepared sodium-ion battery are as follows: Figure 7 and Figure 8 As shown: by Figure 7 It can be seen that, after using a suitable nitrogen-doped carbon layer coating, Na 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / NC electrode exhibits a discharge specific capacity of approximately 159 mAh / g at 50 mA / g and 25 °C; Figure 8 As shown in (a), Na 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / NC electrode exhibits a discharge specific capacity of 115.7 mAh / g after 2000 cycles at 1000 mA / g and 25°C, with a capacity retention of 97.8%. Figure 8 As shown in (b), Na 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / NC electrode exhibits a discharge specific capacity of approximately 127.2 mAh / g after 1000 cycles at 1000 mA / g and 80°C, with a capacity retention of 87.8%. Nitrogen-doped carbon-coated Na... 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / NC electrode exhibits superior battery performance.

[0154] Product Na from Example 2 3.4 Mn 1.2 Ti 0.8 Electrochemical performance testing of sodium-ion batteries prepared from (PO4)3 / NC-1 particles is as follows: Figure 9 As shown in the figure, after being coated with a thinner nitrogen-doped carbon layer, Na 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC-1 exhibits a discharge specific capacity of 142.2 mAh / g at a current density of 0.1 A / g, and still has a discharge specific capacity of 73.9 mAh / g when the current is increased to 2 A / g.

[0155] Product Na from Example 3 3.4 Mn 1.2 Ti 0.8 Electrochemical performance testing of sodium-ion batteries prepared from (PO4)3 / NC-2 particles is as follows: Figure 10 As shown in the figure, Na 3.4 Mn 1.2 Ti 0.8(PO4)3 / NC-2 exhibits a discharge specific capacity of 146.5 mAh / g at a current density of 0.1 A / g, and still has a discharge specific capacity of 84.9 mAh / g when the current is increased to 2 A / g.

[0156] The product Na from Example 1 was tested separately. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC and the product Na from Comparative Example 2 3.4 Mn 1.2 Ti 0.8 Sodium-ion batteries prepared by (PO4)3 / C were cycled several times and then characterized by transmission electron microscopy (TEM). The results are as follows: Figure 11 and Figure 12 As shown: by Figure 11 It can be seen that after three cycles at 50 mA / g and 25℃, CEI was uniformly deposited on Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / C and Na 3.4 Mn 1.2 Ti 0.8 The surface of (PO4)3 / NC maintains a complete crystal structure internally; by Figure 12 It can be seen that after 50 cycles, Na 3.4 Mn 1.2 Ti 0.8 The CEI on the (PO4)3 / C surface is loose and uneven in thickness, with local lattice distortions inside, while Na... 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / NC surface has a uniform and dense CEI, and the internal crystal structure is complete.

[0157] The product Na from Example 1 was tested separately. 3.4 Mn 1.2 Ti 0.8 (PO4)3 / NC and the product Na from Comparative Example 2 3.4 Mn 1.2 Ti 0.8 A sodium-ion battery prepared by (PO4)3 / C was cycled several times and then characterized by TEM. The results are as follows: Figure 13 As shown in the figure, after 500 cycles at 1000 mA / g and 80℃, Na 3.4 Mn 1.2 Ti 0.8 The CEI of (PO4)3 / C is loose and uneven in thickness, with some CEI originating from Na. 3.4 Mn 1.2 Ti 0.8The signs of surface detachment from (PO4)3 / C indicate that it has undergone severe reorganization and destruction. In contrast, Na... 3.4 Mn 1.2 Ti 0.8 The CEI on the (PO4)3 / NC surface is relatively intact and of uniform thickness, and the internal crystal structure is well protected.

[0158] In summary, the results of the comparative examples and embodiments show that the polar nitrogen-doped carbon coating introduced in this application enhances the performance of Na+. 3.4 Mn 1.2 Ti 0.8 The (PO4)3 / NC / CEI interface exhibits structural stability, and the excellent interfacial contact enhances electron / sodium ion transport, inducing a uniform distribution of local charges. This alleviates the continuous decomposition and recombination of CEI during cycling, significantly improving rate performance and cycling stability during electrochemical reactions.

[0159] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, It includes a core and a coating layer covering the surface of the core; the core includes a sodium manganese titanium phosphate compound, and the coating layer includes a nitrogen-doped carbon material.

2. The cathode material according to claim 1, characterized in that, The chemical formula of the kernel is Na. 3+2x Mn 1+x Ti 1-x (PO4)3; where 0 ≤ x ≤ 0.

5.

3. The cathode material according to claim 2, characterized in that, The chemical formula of the kernel is Na. 3.4 Mn 1.2 Ti 0.8 (PO4)3.

4. The cathode material according to any one of claims 1-3, characterized in that, Including at least one of the following (a1) to (a4): (a1) The median particle size D of the kernel 50 The range is 3~10 μm; (a2) The thickness of the coating layer is in the range of 2~5 nm; (a3) In the cathode material, the coating layer accounts for 8-12% of the mass; (a4) In the nitrogen-doped carbon material, the mass ratio of nitrogen element is 2~5%.

5. A method for preparing a positive electrode material as described in any one of claims 1-4, characterized in that, Including the following steps: Sodium source, manganese source, titanium source, phosphate and carbon source materials are dissolved in water and mixed evenly to obtain solution A; Nitrogen-doped carbon source was dissolved in water and mixed thoroughly to obtain solution B; After mixing solutions A and B evenly, the mixture is stirred continuously under predetermined condition one until it transforms into a wet gel. Then, after drying under predetermined condition two, the precursor powder is obtained. The precursor powder is calcined under predetermined condition three, ground after cooling, and then calcined again under predetermined condition four to obtain the cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that, Including at least one of the following (b1) to (b10): (b1) The molar ratio of the sodium source, manganese source, titanium source, phosphate, and carbon source materials is (3.2~3.6):(1.0~1.4):(0.6~1.0):(2.5~3.5):(0.5~0.7); (b2) The sodium source is selected from sodium acetate, the manganese source is selected from manganese acetate tetrahydrate, the titanium source is selected from dihydroxybis(ammonium lactate)titanium(IV), the phosphate is selected from ammonium dihydrogen phosphate, and the carbon source material is selected from citric acid; (b3) The concentration of sodium ions in solution A is 0.05~1 mol / L; (b4) The nitrogen-doped carbon source is selected from at least one of polyvinylpyrrolidone, melamine, gelatin, or nylon-66; (b5) In solution B, the concentration of the nitrogen-doped carbon source is 6~30 g / L; (b6) The predetermined condition is: stirring under a constant temperature water bath, with a temperature of 60~90℃ and a rotation speed of 200~800 r / min; (b7) The second predetermined condition is: drying in a forced-air drying oven at a temperature of 80~120℃ for 10~14 hours; (b8) The predetermined condition three is: calcination at 300~450℃ for 3~5h in an inert gas, with a heating rate of 3~5℃ / min; (b9) The fourth predetermined condition is: calcination at 550~750℃ for 10~15h in an inert gas, with a heating rate of 3~5℃ / min; (b10) When (b8) or (b9) is included, the inert gas is selected from nitrogen or argon.

7. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes the positive electrode material as described in any one of claims 1-4 or the positive electrode material prepared by the preparation method as described in any one of claims 5-6.

8. A battery cell, characterized in that, It includes a negative electrode and a positive electrode as described in claim 7.

9. An electrochemical device, characterized in that, Including the battery cell as described in claim 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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