Positive electrode material, secondary battery, and electric device

Abstract

A positive electrode material, a secondary battery, and an electric device in the technical field of batteries. The positive electrode material comprises a sodium-ion layered oxide having sodium vacancies; further, the sodium-ion layered oxide comprises a doping element distributed in the sodium vacancies; the valence of the doping element in the sodium-ion layered oxide is greater than or equal to 3. By using the positive electrode material, the cycle performance and rate capability of batteries can be improved.

Description

Positive electrode material, secondary battery and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 26, 2023, with application number 202310928367.9 and invention name “A positive electrode material, secondary battery and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode material, a secondary battery, and an electrical device. Background Art

[0003] Sodium ion cathode materials can be divided into P2 and O3 types based on their crystal structures. P2O3 mixed-phase cathode materials have attracted widespread attention due to their high rated voltage and high energy density. However, due to the twinning growth of the P2 and O3 phases, the interlayer spacing of the cathode material decreases, resulting in poor rate performance and cycle life.

[0004] Summary of the Invention

[0005] To this end, the embodiments of the present application provide a positive electrode material, a secondary battery, and an electrical device, aiming to improve the rate performance and cycle performance of sodium ion batteries.

[0006] In a first aspect, the present application provides a positive electrode material, the positive electrode material comprising a sodium ion layered oxide, wherein the sodium ion layered oxide has sodium vacancies;

[0007] The sodium ion layered oxide includes a doping element, wherein the doping element is at least partially distributed in the sodium vacancies, and the valence of the doping element in the sodium ion layered oxide is ≥3.

[0008] Furthermore, the sodium vacancies account for 10% to 40% of the total sodium content of the sodium ion layered oxide.

[0009] Furthermore, the sodium ion layered oxide comprises an O3 phase structure and a P2 phase structure.

[0010] Furthermore, the chemical formula of the sodium ion layered oxide includes Na x M y A z O2, wherein 0.5≤x≤1.1, 0<y<1, 0<z<1, M includes at least one element selected from Fe, Ni, Li, Cu, Zn, Co, Ti, and Mn, and A is the doping element.

[0011] Furthermore, the ionic radius r of the doping element is

[0012] Furthermore, the doping element includes at least one of tungsten, molybdenum, niobium, ruthenium, and antimony.

[0013] Furthermore, the space group of the O3 phase structure is R-3m, accounting for 2% to 98%; the space group of the P2 phase structure is P63 / mmc, accounting for 2% to 98%.

[0014] Furthermore, the positive electrode material includes spherical particles and / or quasi-spherical particles, and the particle size Dv50 of the positive electrode material is 1 μm to 20 μm.

[0015] In a second aspect, the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises the positive electrode material provided in the first aspect.

[0016] In a third aspect, the present application provides an electrical device comprising the secondary battery as described in the second aspect.

[0017] One of the above technical solutions has the following advantages or beneficial effects:

[0018] The positive electrode material of the present application comprises a sodium ion layered oxide having sodium vacancies; the sodium ion layered oxide also comprises a doping element, the doping element being at least partially distributed in the sodium vacancies, and the valence of the doping element in the sodium ion layered oxide being greater than or equal to 3. Since the positive electrode material has a large number of sodium vacancies in its crystal structure, the sodium vacancies constitute three-dimensional channels for sodium ion transmission, thereby effectively promoting the insertion and extraction of sodium ions in the positive electrode material. At the same time, the doping element with a higher valence increases the interlayer spacing of the positive electrode material, further improving the sodium ion extraction efficiency. Furthermore, the doping element with a higher valence can improve the stability of the positive electrode material and can suppress the transition from the O3 phase to the OP2 phase, which has a poor reversibility, during the charge and discharge process. Therefore, the cycle performance and rate performance of the battery using the positive electrode material of the present application can be improved. DETAILED DESCRIPTION

[0019] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

[0020] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] In addition, the term "and / or" in this application is simply a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application, unless otherwise specified, generally indicates that the related objects are in an "or" relationship.

[0022] According to a first aspect of the present application, a positive electrode material is provided, which includes a sodium ion layered metal oxide, wherein the sodium ion layered metal oxide has sodium vacancies; at the same time, the sodium ion layered metal oxide includes a doping element, the doping element is at least partially distributed in the sodium vacancies, and the valence of the doping element in the sodium ion layered oxide is ≥3.

[0023] The sodium ion layered metal oxide in the positive electrode material of the present application has sodium vacancies, which constitute three-dimensional channels for sodium ion transmission. Therefore, it can effectively promote the insertion and extraction of sodium ions during the charge and discharge process. At the same time, the higher valence doping elements increase the interlayer spacing of the positive electrode material. In addition, the higher valence doping elements can improve the stability of the positive electrode material, further improve the sodium ion extraction efficiency, and inhibit the transformation process from the O3 phase to the OP2 phase, which has a poor reversibility during the charge and discharge process. Therefore, the cycle performance of the battery using the positive electrode material of the present application can be improved.

[0024] In some embodiments of the present application, sodium vacancies account for 10% to 40% of the total sodium content of the sodium ion layered oxide, for example, a range of 10%, 18%, 22%, 29%, 36%, 40%, or any two of these. Controlling the number of sodium vacancies in the positive electrode material within the above range allows the positive electrode material to have suitable three-dimensional sodium ion transport channels, effectively promoting the insertion and extraction of sodium ions into and out of the positive electrode material during the charge and discharge process of the battery, thereby improving the battery's rate performance.

[0025] It should be noted that the doping element content ranges from 2% to 5% based on the total amount of metal elements in the positive electrode material excluding sodium. For example, the content can be in the range of 2%, 2.3%, 2.8%, 3.2%, 3.7%, 4.5%, 5%, or any two of these. By controlling the doping element content within the above range, the appropriate amount of doping element can be used to improve the battery's cycling performance while ensuring a high energy density.

[0026] In some embodiments of the present application, the sodium ion layered oxide comprises an O3 phase structure and a P2 phase structure. The sodium ion layered oxide comprising an O3 phase structure and a P2 phase structure can enable the positive electrode material to exert a higher gram capacity while taking into account higher structural stability. At the same time, the proportion of the O3 phase structure and the P2 phase structure in the positive electrode material can be adjusted by the molar percentage of the sodium element in the sodium ion layered oxide, and the proportion of the O3 phase structure increases with the increase of the molar percentage of the sodium element. The greater the molar percentage of the sodium element in the positive electrode material, the greater the proportion of the O3 phase structure; the smaller the molar percentage of the sodium element, the greater the proportion of the P2 phase structure.

[0027] In some embodiments of the present application, the chemical formula of the sodium ion layered oxide includes Na x M y A z O2, wherein 0.5≤x≤1.1, 0<y<1, 0<z<1, for example, x can be in the range of one or any two of 0.5, 0.7, 0.9, 1.1, y can be in the range of one or any two of 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, and z can be in the range of one or any two of 0.1, 0.3, 0.5, 0.6, 0.8, 0.9. In some embodiments, M includes at least one element selected from iron (Fe), nickel (Ni), lithium (Li), copper (Cu), zinc (Zn), cobalt (Co), titanium (Ti), and manganese (Mn), and A is the aforementioned doping element. The sodium ion layered oxide further includes at least one element selected from iron (Fe), nickel (Ni), lithium (Li), copper (Cu), zinc (Zn), cobalt (Co), titanium (Ti), and manganese (Mn), which can further improve the energy density and stability of the positive electrode material, and has a positive effect on the cycle stability and capacity improvement of the battery.

[0028] In some embodiments of the present application, the ionic radius r of the doping element is The doping elements have a larger metal ion radius, which increases the interlayer spacing of the positive electrode material, is conducive to the embedding and extraction of sodium ions between the layers during charging and discharging, and improves the rate performance of the battery.

[0029] In some embodiments of the present application, the doping element includes at least one of tungsten (W), molybdenum (Mo), niobium (Nb), ruthenium (Ru), and antimony (Sb).6+ The ionic radius is Molybdenum ion Mo 6+ The ionic radius is Niobium ion Nb 5+ The ionic radius is Ruthenium ion 5+ The ionic radius is Antimony ion Sb 3+ The ionic radius is 0.76. The above metal elements doped in the positive electrode material have a higher metal valence and a larger ionic radius. Doping in the positive electrode material can increase the interlayer spacing of the positive electrode material and improve the structural stability of the positive electrode material, so that the battery has better rate performance and capacity retention.

[0030] In some embodiments of the present application, the space group of the O3 phase structure is R-3m, accounting for 2% to 98%, for example, it can be one of 2%, 18%, 22%, 33%, 40%, 45%, 60%, 69%, 80%, 88%, 95%, 98% or any two of the range values; in another embodiment, the space group of the P2 phase structure is P63 / mmc, accounting for 2% to 98%, for example, it can be one of 2%, 18%, 22%, 33%, 45%, 58%, 69%, 80%, 88%, 95%, 98% or any two of the range values.

[0031] The proportion of O3 phase structure and P2 phase structure is controlled within the above range, so that the material has higher gram capacity and structural stability. Preferably, the proportion of O3 phase structure is 40% to 60%. At the same time, the range of the unit cell parameter c1 of the P2 phase structure in the sodium ion layered oxide is The range of the unit cell parameter c2 of the O3 phase structure is Larger unit cell parameters can make the positive electrode material have a larger interlayer spacing. A larger interlayer spacing is beneficial to the embedding and extraction of sodium ions between the positive electrode material layers during the charge and discharge process of the battery, thereby improving the battery's rate performance.

[0032] In some embodiments of the present application, the positive electrode material includes spherical particles and / or quasi-spherical particles, and the particle size Dv50 of the positive electrode material is 1 μm to 20 μm, wherein Dv50 is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%. Preferably, the particle size Dv50 of the positive electrode material is 5 μm to 8 μm. By controlling the particle size of the positive electrode material within the above range, the positive electrode material can obtain moderate surface activity, effectively reducing the gas production of the battery during the charge and discharge process, while allowing sodium ions to have a moderate migration path, so that the battery has better rate performance.

[0033] According to a second aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises the positive electrode material of the first aspect.

[0034] The aforementioned secondary battery was subjected to a charging test. When the charging voltage of the secondary battery was between 4.0V and 4.3V, no OP2 phase was generated in the positive electrode material. This indicates that the positive electrode material of the present application can effectively inhibit the transformation process from the O3 phase to the OP2 phase, slowing down the secondary battery's cycle capacity decay rate, resulting in the secondary battery having better cycle performance and service life. In this embodiment, the secondary battery comprises a sodium ion battery.

[0035] According to a third aspect of the present application, there is provided an electric device comprising the above-mentioned secondary battery, wherein the secondary battery serves as a power supply for the electric device.

[0036] The present application is further described below through specific examples.

[0037] Example 1

[0038] Cathode material:

[0039] 1) Preparation of precursor materials: Under room temperature, a certain amount of 0.5 mol / LNiSO4·6H2O, 0.5 mol / LFeSO4·7H2O, and 1 mol / LMnSO4·H2O were dissolved in distilled water, wherein the molar ratio of Ni:Fe:Mn was 0.4:0.2:0.4, and stirred at 100 rpm for 2 h to obtain a mixed solution. A certain amount of NaOH solid was added to the mixed solution to make the concentration of NaOH 1 mol / L, and then stirred at 200 rpm for 12 h. The resultant was filtered and dried to obtain the precursor material Ni 0.4 Fe 0.2 Mn 0.4 (OH)2.

[0040] 2) Preparation of positive electrode materials: The precursor material, NaOH, and Nb2O5 solids were placed in a ball mill and milled at 300 rpm for 12 hours to form a powder precursor, wherein the molar ratio of Na: (Ni+Fe+Mn+Nb) = 0.8:1, and Nb: (Ni+Fe+Mn) = 0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 12 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula Na 0.8 Ni 0.38 Fe 0.19 Mn 0.38 Nb 0.05 O2 P2O3 mixed phase positive electrode material.

[0041] Positive electrode sheet: the above positive electrode material (Na 0.8 Ni 0.38 Fe 0.19 Mn 0.38 Nb 0.05 O2), polyvinylidene fluoride (PVDF), and conductive carbon black were mixed in a stirring tank at a mass ratio of 85:7.5:7.5, and an appropriate amount of N-methylpyrrolidone (NMP) was added to adjust the viscosity to obtain a positive electrode active slurry. The positive electrode active slurry was evenly coated on both surfaces of the current collector (aluminum foil), dried, rolled, and cut to obtain a positive electrode sheet with an area density of 15 mg / cm 2 .

[0042] Negative electrode sheet: Add the negative electrode active material graphite, conductive agent acetylene black (SuperP) and binder (SBR) in a mass ratio of 94:3:3 into a stirring tank, and add an appropriate amount of deionized water for stirring to evenly disperse it into a black negative electrode active slurry. Use a coater to apply the negative electrode active slurry on both surfaces of the negative electrode collector (copper foil). After baking, rolling and cutting, the negative electrode sheet is obtained.

[0043] Separator: A three-layer polypropylene / polyethylene / polypropylene separator (PP / PE / PP) is used as the separator.

[0044] Electrolyte: An organic electrolyte is used, including an organic solvent and a sodium salt, wherein the organic solvent is a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DMC) in a mass ratio of 3:3:4, and the sodium salt is sodium hexafluorophosphate (NaPF6), and the concentration of the sodium salt is 1.0 mol / L.

[0045] Secondary battery: Assemble the positive electrode, separator, and negative electrode, bake and dry them, inject electrolyte, and perform static infiltration, formation, and capacity separation operations to obtain a secondary battery.

[0046] Example 2

[0047] Compared with Example 1, Example 2 has the same configuration as Example 1 except that the preparation of the positive electrode material is different.

[0048] Preparation of positive electrode materials: The precursor material, NaOH, and Nb2O5 solids were placed in a ball mill and ball-milled at 300 rpm for 18 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Nb)=0.84:1, and Nb:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 9 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula of Na 0.84 Ni 0.38 Fe 0.19 Mn 0.38 Nb 0.05 O2 P2O3 mixed phase positive electrode material.

[0049] Example 3

[0050] Compared with Example 1, Example 3 has the same configuration as Example 1 except that the preparation of the positive electrode material is different.

[0051] Preparation of positive electrode materials: The precursor material, NaOH, and Nb2O5 solids were placed in a ball mill and milled at 300 rpm for 18 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Nb)=0.88:1, and Nb:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 9 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula Na 0.88 Ni 0.38 Fe 0.19 Mn 0.38 Nb 0.05 O2 P2O3 mixed phase positive electrode material.

[0052] Example 4

[0053] Compared with Example 1, Example 4 has the same configuration as Example 1 except that the preparation of the positive electrode material is different.

[0054] Preparation of positive electrode materials: The precursor material, NaOH, and Nb2O5 solids were placed in a ball mill and ball-milled at 300 rpm for 12 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Nb)=0.76:1, and the molar ratio of Nb:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 12 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula of Na 0.76 Ni 0.38 Fe 0.19 Mn 0.38 Nb 0.05 O2 P2O3 mixed phase positive electrode material.

[0055] Example 5

[0056] Compared with Example 1, Example 5 is similar to Example 1 except that the preparation of the positive electrode material is different.

[0057] Preparation of positive electrode materials: The precursor material, NaOH, and Nb2O5 solids were placed in a ball mill and milled at 300 rpm for 10 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Nb)=0.72:1, and the molar ratio of Nb:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 15 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula of Na 0.72 Ni 0.38 Fe 0.19 Mn 0.38 Nb 0.05 O2 P2O3 mixed phase positive electrode material.

[0058] Example 6

[0059] Compared with Example 1, Example 6 has the same configuration as Example 1 except that the preparation of the positive electrode material is different.

[0060] Preparation of positive electrode material: The precursor material, NaOH and WO3 solids were placed in a ball mill and milled at 300 rpm for 12 hours to form a powder precursor, wherein the molar ratio of Na: (Ni + Fe + Mn + W) = 0.8:1, W: (Ni + Fe + Mn) = 0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800 ° C at a heating rate of 5 ° C / min. It was calcined in an air atmosphere at 800 ° C for 12 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula of Na0.8 Ni 0.38 Fe 0.19 Mn 0.38 W 0.05 O2 P2O3 mixed phase positive electrode material.

[0061] Example 7

[0062] Compared with Example 1, Example 7 has the same configuration as Example 1 except that the preparation of the positive electrode material is different.

[0063] Preparation of positive electrode materials: The precursor material, NaOH, and MoO3 solids were placed in a ball mill and ball-milled at 300 rpm for 12 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Mo)=0.8:1, and the molar ratio of Mo:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 12 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula of Na 0.8 Ni 0.38 Fe 0.19 Mn 0.38 Mo 0.05 O2 P2O3 mixed phase positive electrode material.

[0064] Example 8

[0065] Compared with Example 1, Example 8 has the same configuration as Example 1 except that the preparation of the positive electrode material is different.

[0066] Preparation of positive electrode materials: The precursor material, NaOH, and RuO2 solids were placed in a ball mill and milled at 300 rpm for 12 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Ru)=0.8:1, and Ru:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 12 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula Na 0.8 Ni 0.38 Fe 0.19 Mn 0.38 Ru 0.05 O2 P2O3 mixed phase positive electrode material.

[0067] Example 9

[0068] Compared with Example 1, Example 9 is similar to Example 1 except that the preparation of the positive electrode material is different.

[0069] Preparation of positive electrode materials: The precursor material, NaOH, and Sb2O5 solids were placed in a ball mill and milled at 300 rpm for 12 hours to form a powder precursor, wherein the molar ratio of Na:(Ni+Fe+Mn+Sb)=0.8:1, Sb:(Ni+Fe+Mn)=0.05:0.95. The powder precursor was pressed into a sheet, and the sheet precursor was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min. It was calcined in an air atmosphere at 800°C for 12 hours, cooled naturally to room temperature, crushed in a grinder, and sieved to obtain a material with the molecular formula of Na 0.8 Ni 0.38 Fe 0.19 Mn 0.38 Sb 0.05 O2 P2O3 mixed phase positive electrode material.

[0070] Examples 10 to 14

[0071] The preparation process of Examples 10 to 14 is the same as that of Example 1, except that the power of the pulverizer and the mesh size of the sieve are adjusted to obtain positive electrode materials with different particle sizes.

[0072] Examples 15 to 18

[0073] The preparation process of Examples 15 to 18 is the same as that of Example 1, except that the calcination temperature is adjusted to obtain positive electrode materials with different sodium vacancies. The higher the calcination temperature, the higher the sodium vacancy number.

[0074] Examples 19 to 22

[0075] The preparation process of Examples 19 to 22 is the same as that of Example 1, except that the addition ratio of the doping element compound is adjusted to obtain positive electrode materials with different doping element contents.

[0076] Comparative Example 1

[0077] The method is the same as Example 1, except that the calcination temperature is lowered to prepare a positive electrode material with element doping but no sodium vacancies.

[0078] Comparative Example 2

[0079] The same as Example 1, except that Nb2O5 is not added during the preparation of the positive electrode material.

[0080] Performance testing:

[0081] Crystal structure analysis: XRD analysis was performed on 5g of the cathode material over a scanning range of 10° to 120° at a scan rate of 1 min / degree. The resulting XRD patterns were refined using EXPGUI software, selecting R-3m for the O3 phase space group and P63 / mmc for the P2 phase space group. The refinement results revealed the proportions of the P2 and O3 phases, the unit cell parameter c, and the number of sodium vacancies.

[0082] OP2 phase generation test:

[0083] The positive electrode materials in the above-mentioned Examples 1-11 and Comparative Examples 1-2 were respectively combined with nanometal negative electrode materials to form button batteries, which were charged to a cutoff voltage of 4.0V at a rate of 1.0C. The button batteries were disassembled, the positive electrode sheets were taken out, and the positive electrode sheets were pasted into high-temperature resistant yellow glue. An XRD test was performed to obtain XRD pattern 1; the button batteries were charged to a cutoff voltage of 4.3V at a rate of 1.0C, the button batteries were disassembled, the positive electrode sheets were taken out, and the positive electrode sheets were pasted into high-temperature resistant yellow glue. An XRD test was performed to obtain XRD pattern 2. Analyze whether there are (0, -1, 5) crystal planes in patterns 1 and 2. If no (0, -1, 5) crystal planes are found, it is proved that no OP2 phase is generated.

[0084] Rate performance:

[0085] At room temperature, the sodium ion battery is charged to 3.8V and discharged to 1.5V at a current density of 0.33C. The capacity of the sodium ion battery at this time is recorded as C1. The same sodium ion battery is charged to 3.8V at room temperature and discharged to 1.5V at a current density of 5.0C. The capacity of the sodium ion battery at this time is recorded as C2. The performance indicator of the discharge rate is the capacity retention rate, that is, C2 / C1.

[0086] Cycle performance:

[0087] At room temperature, the sodium-ion battery was charged to 3.8V at a current density of 1.0C, then discharged to 1.5V at a current density of 1.0C. The discharge capacity was recorded as C0. The battery was charged and discharged at 1.0C between 1.5V and 3.8V. The test was stopped when the discharge capacity reached 80%*C0, and the corresponding number of charge and discharge cycles was recorded.

[0088] The parameters of the positive electrode materials and the performance of the sodium ion batteries of the embodiments and comparative examples are shown in Table 1.

[0089] Table 1:

[0090] As can be seen from the data in Table 1, the introduction of high-valent doping elements and the introduction of suitable sodium vacancies in the positive electrode material are beneficial to the improvement of the battery cycle performance and rate performance. Specifically, from the data records of the embodiments and comparative examples in Table 1, it can be seen that when high-valent doping elements and sodium vacancies are simultaneously introduced into the positive electrode material, the discharge rate of the sodium ion battery is greater than 70%, and when the sodium ion discharge capacity decay value is 80% of the initial capacity, the number of cycles of the battery is greater than 1900. If no doping elements are introduced into the positive electrode material or no sodium vacancies are present, the discharge rate and cycle performance of the sodium ion battery are significantly reduced.

[0091] The above steps are merely provided to help understand the method, structure, and core concept of the present application. A person skilled in the art may make several improvements and modifications to the present application without departing from the principles of the present application, and such improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A positive electrode material, wherein: The positive electrode material includes a sodium ion layered oxide, wherein the sodium ion layered oxide has sodium vacancies; The sodium ion layered oxide includes a doping element, wherein the doping element is at least partially distributed in the sodium vacancies, and the valence of the doping element in the sodium ion layered oxide is ≥3.

2. The positive electrode material according to claim 1, wherein The sodium vacancies account for 10% to 40% of the total sodium content of the sodium ion layered oxide.

3. The positive electrode material according to claim 1, wherein The sodium ion layered oxide includes an O3 phase structure and a P2 phase structure.

4. The positive electrode material according to claim 3, wherein The chemical formula of the sodium ion layered oxide includes Na x M y A z O2, wherein 0.5≤x≤1.1, 0<y<1, 0<z<1, M includes at least one element selected from Fe, Ni, Li, Cu, Zn, Co, Ti, and Mn, and A is the doping element.

5. The positive electrode material according to claim 1, wherein The ionic radius r of the doping element is 6. The positive electrode material according to any one of claims 1 to 5, wherein The doping element includes at least one of tungsten, molybdenum, niobium, ruthenium and antimony.

7. The positive electrode material according to claim 3, wherein The space group of the O3 phase structure is R-3m, accounting for 2% to 98%; the space group of the P2 phase structure is P63 / mmc, accounting for 2% to 98%.

8. The positive electrode material according to claim 1, wherein The positive electrode material comprises spherical particles and / or quasi-spherical particles, and the particle size Dv50 of the positive electrode material is 1 μm to 20 μm.

9. A secondary battery, wherein: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 8.

10. An electrical device, wherein: The electrical device comprises the secondary battery according to claim 9, and the secondary battery serves as a power supply for the electrical device.

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