Positive electrode material and secondary battery, electric device

Abstract

This application relates to the field of batteries, disclosing a positive electrode material, a secondary battery, and an electrical device. The positive electrode material of this application includes a core and a shell. The core includes P2-type sodium-ion oxide and O3-type sodium-ion oxide, and the shell includes a metal carbide. The metal in the metal carbide includes metal elements from groups IVB, VB, and VIB. This application improves cycle stability by coating P2-type / O3-type sodium-ion oxide with metal carbide, thereby mitigating the phase transition that occurs in the layered positive electrode material during the charging and discharging process of sodium-ion batteries, preventing the destruction of the layered positive electrode material structure and the cracking of electrode particles. Furthermore, the additional addition of sodium manganese oxide can synergistically enhance the long-term cycle stability of the sodium-ion battery and reduce the contact area between the layered positive electrode material and the electrolyte, preventing irreversible capacity decay caused by excessive dissolution of transition metals.

Description

Technical Field

[0001] This application relates to the field of sodium-ion batteries, and more particularly to a cathode material, a secondary battery, and an electrical device. Background Technology

[0002] Layered cathode materials for sodium-ion batteries are mainly classified into O3-type and P2-type, possessing high energy density and promising applications in high-energy-density sodium-ion battery systems. However, during the charge and discharge process of layered sodium-ion batteries, sodium ions repeatedly intercalate and deintercalate from the interlayer of the cathode material, causing phase transitions in both P2-type and O3-type cathode materials. Since phase transitions are accompanied by volume changes, stress accumulates continuously during repeated expansion-contraction-expansion-contraction, eventually leading to structural damage and electrode particle cracking. This exacerbates side reactions between the electrode material and the electrolyte, and in severe cases, electrode pulverization occurs. A large number of electrode particles lose electrical contact with the current collector, reducing the content of effective active material and resulting in a decline in electrochemical performance.

[0003] Obtaining layered cathode materials with excellent stability and cycle performance remains a challenge for current sodium-ion batteries. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a cathode material that can significantly improve the cracking phenomenon caused by phase transition during the charging and discharging process of layered cathode materials, thereby improving the cycle performance and gas generation performance of sodium-ion batteries.

[0005] Another objective of this application is to provide a secondary battery and electrical device based on the aforementioned cathode material.

[0006] In order to solve the above-mentioned technical problems / achieve the above-mentioned objectives, or at least partially solve the above-mentioned technical problems / achieve the above-mentioned objectives, as a first aspect of this application, a positive electrode material is provided, the positive electrode material comprising a core and a shell, the core comprising a composite material composed of P2 type sodium ion oxide and O3 type sodium ion oxide, the shell comprising a metal carbide, wherein the metal in the metal carbide comprises a metal element from groups IVB, VB, or VIB.

[0007] Optionally, the outer shell further includes sodium manganese oxide, with the metal carbide distributed inside and / or on the surface of the sodium manganese oxide. More preferably, the molar ratio of the sodium manganese oxide to the metal carbide is 1:(0.05–0.1), and the sodium manganese oxide includes Na… p MnO2, 0.05 < p ≤ 0.55.

[0008] Optionally, the metal carbide includes at least one of WC, TiC, TaC, NbC, and HfC.

[0009] Optionally, the content of the metal carbide is 0.5% to 3% based on the mass of the cathode material.

[0010] Optionally, the chemical formula of the composite material includes Na. x MO2, where M includes at least one of Fe, Ni, Li, Cu, Zn, Co, Ti, and Mn, and 1.1 ≥ x ≥ 0.5;

[0011] Further optionally, the space group of the O3-type sodium ion oxide is R-3m, and the cell parameter is 2.8. The space group of the P2 type sodium ion oxide is P63 / mmc, and the unit cell parameters are...

[0012] As a second aspect of this application, a secondary battery is provided, including a negative electrode, a separator, an electrolyte, and a positive electrode containing the positive electrode material described in this application.

[0013] As a third aspect of this application, an electrical device is provided, including the secondary battery described in this application, wherein the secondary battery provides electrical energy to the electrical device.

[0014] In this application, metal carbides from groups IVB, VB, and VIB possess high hardness and high melting point. As a coating layer component of the cathode material, they improve the mechanical strength of the cathode material. During repeated Na+ insertion and extraction, the metal carbides enhance the particle structure stability of the cathode material, effectively suppressing the formation of microcracks during charging and discharging, thus ensuring the long-term cycle stability of the cathode material. Furthermore, metal carbides from groups IVB, VB, and VIB exhibit corrosion resistance, effectively resisting electrolyte corrosion and mitigating its corrosive effect on the cathode material, further ensuring the stability of the cathode material in the battery system. Additionally, metal carbides are excellent electrical conductors, reducing the impedance of the cathode material and improving the rate performance of the secondary battery. Therefore, adding metal carbides from groups IVB, VB, and VIB to the outer casing can improve the mechanical and electrical properties of the cathode material, effectively increasing battery life and charging / discharging efficiency. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0016] Figure 1 The diagram shown is a structural schematic of a positive electrode material according to an embodiment of this application;

[0017] Figure 2The diagram shown is a structural schematic of a positive electrode material according to another embodiment of this application. Detailed Implementation

[0018] This application discloses a positive electrode material, a secondary battery, and electrical equipment. Those skilled in the art can refer to the content of this document and appropriately improve the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The product described in this application has been described through preferred embodiments. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the product described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0019] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0020] In the first aspect of this application, a positive electrode material is provided, comprising a core and a shell. The core comprises a composite material composed of P2-type sodium ion oxide and O3-type sodium ion oxide, and the shell comprises a metal carbide. The metal in the metal carbide comprises metal elements from groups IVB, VB, and VIB. A schematic diagram of its structure is shown below. Figure 1 .

[0021] Specifically, P2-type sodium oxide generally exhibits better rate capability and stability, while O3-type sodium oxide shows higher theoretical capacity. Therefore, using a composite material of P2-type and O3-type sodium oxide as the core of the cathode material can balance the energy density and cycle stability of the cathode material. Meanwhile, group IVB, VB, and VIB metal carbides, on the other hand, possess high hardness and high melting point. As a coating layer component of the cathode material, they improve the mechanical strength of the cathode material. + During repeated insertion and extraction processes, metal carbides enhance the particle structure stability of the cathode material, effectively suppressing the formation of microcracks during charging and discharging, thus ensuring the long-term cycle stability of the cathode material. Furthermore, group IVB, VB, and VIB metal carbides possess corrosion resistance, effectively resisting electrolyte corrosion and mitigating its corrosive effects on the cathode material, further ensuring the stability of the cathode material within the battery system. Additionally, metal carbides are excellent electrical conductors, reducing the impedance of the cathode material and improving the rate performance of the secondary battery. Therefore, adding group IVB, VB, and VIB metal carbides to the casing can improve the mechanical and electrical properties of the cathode material, effectively increasing battery life and charging / discharging efficiency.

[0022] In some embodiments of this application, the metal carbide comprises metal elements from groups IVB, VB, and VIB, such as Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W. Compared to carbides of other transition metals, carbides of group IVB, VB, and VIB metals exhibit high hardness, high melting point, and high corrosion resistance, and further enhance their effectiveness in preventing cracking caused by sodium ion oxide phase transformation and improving long-cycle performance. In other embodiments of this application, the metal carbide comprises at least one of WC, TiC, TaC, NbC, and HfC.

[0023] In some embodiments of this application, the content of the metal carbide is 0.5% to 3% based on the mass of the cathode material; in other embodiments, the content of the metal carbide is a range of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or 3%, or any two of these ranges. In some embodiments, the content of the metal carbide can be 1.2% to 2.3% based on the mass of the cathode material. The metal carbide content within the above range provides strong mechanical support for the cathode material and improves its conductivity. Furthermore, within this range, the relative content of sodium oxide ions is avoided, thus preventing an impact on the battery capacity.

[0024] In some embodiments of this application, in order to further synergistically improve the electrode cracking phenomenon caused by the phase transition of the layered cathode material and enhance the electrochemical performance of the cathode material, the outer shell also includes sodium manganese oxide, and the metal carbide is distributed inside and / or on the surface of the sodium manganese oxide. A schematic diagram of the structure is shown below. Figure 2 In other embodiments of this application, the sodium manganese oxide has a nanorod-like structure with a length of 2–5 μm and a diameter of 100–400 nm; or a nanoribbon-like structure with a length of 5–10 μm, a width of 50–200 nm, and a thickness of 20–100 nm. The structure of the sodium manganese oxide can improve the tightness of the outer shell, which is beneficial for blocking the electrolyte. The aforementioned size range is beneficial for providing sodium ion channels of suitable width, which is beneficial for reducing impedance.

[0025] In some other embodiments of this application, the molar ratio of the sodium manganese oxide to the metal carbide is 1:[0.05 to 0.1], for example, it can be one or any two of the following: 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09 or 1:0.1.

[0026] In some embodiments of this application, the sodium manganese oxide includes Na. p MnO2, 0.05 < p ≤ 0.55. In some other embodiments of this application, the sodium manganese oxide can be Na. 0.1 MnO2, Na 0.3 MnO2, Na 0.44 MnO2, Na 0.55 MnO2; preferably Na 0.44 MnO2, Na 0.44 MnO2 has advantages such as abundant raw materials, simple synthesis methods, non-toxicity and environmental friendliness, stability to water and oxygen, high structural stability and high ion conductivity. When used together with metal carbides to coat layered cathode materials, it can further improve the environmental stability, cycle stability and processing performance of layered cathode materials.

[0027] In some embodiments of this application, the chemical formula of the composite material is Na. x MO2, where M includes at least one of Fe, Ni, Li, Cu, Zn, Co, Ti, and Mn, and 1.1 ≥ x ≥ 0.5; in other embodiments of this application, x = 0.9, 0.98, 0.74, 0.67, 1.05, 0.53, 1.1, or 0.5.

[0028] In some embodiments of this application, M includes Ni, and at least one of Fe, Cu, Co, and Mn; in some other embodiments of this application, M includes Ni and Mn; or Ni and Fe; or Ni and Cu; or Ni, Co, and Mn. In some other embodiments of this application, the composite material includes Na. 0.9 Ni 0.7 Mn 0.3 O2, Na 0.74 Ni 0.7 Mn 0.3 O2, Na 0.98 Ni 0.8 Fe 0.2 O2, Na 0.67 Ni 0.8 Fe 0.2 O2, Na 1.05 Ni 0.7 Cu 0.3 O2, Na 0.53 Ni 0.7 Cu 0.3 O2, Na 1.1 Ni 0.6 Co 0.2 Mn 0.2 O2, Na 0.5 Ni 0.6 Co 0.2 Mn 0.2 At least one of O2.

[0029] In some embodiments of this application, the space group of the O3-type sodium ion oxide is R-3m, and the cell parameters are... The space group of the P2 type sodium ion oxide is P63 / mmc, and the unit cell parameters are...

[0030] In some embodiments of this application, the composite material of the positive electrode material comprises a spherical or spherical particle structure with a particle size of 1 μm to 20 μm, or 5 μm to 12 μm; a shell covers the surface of the spherical or spherical particles, and the thickness of the shell is 10 to 1000 nm. In other embodiments of this application, the specific surface area of ​​the positive electrode material is 0.005 m². 2 / g~10m 2 / g, or 1m 2 / g~5m 2 / g; the tap density of the positive electrode material is 1g / cm³. 3 ~3g / cm 3 The compacted density is 2 g / cm³ 3 ~5g / cm 3 The true density is 2 g / cm³. 3 ~4g / cm3 .

[0031] This application also provides a method for preparing the cathode material, including:

[0032] S1, after the first sodium source and the M source are mixed evenly, a sintering is performed once to obtain O3 type sodium ion oxide;

[0033] S2, annealing the O3 type sodium ion oxide to partially convert the O3 type sodium ion oxide into the P2 type sodium ion oxide, thus obtaining the composite material;

[0034] S3. The composite material, metal carbide and manganese source solution are mixed and heated and stirred at a certain temperature to evaporate the solvent in the manganese source solution to obtain a mixed powder.

[0035] S4. The mixed powder is sintered a second time to obtain the positive electrode material.

[0036] In some embodiments of this application, the first sodium source includes a sodium salt capable of providing sodium ions, such as sodium carbonate, sodium sulfate, sodium nitrate, etc., and the M source is one or more of oxides of Fe, Ni, Li, Cu, Zn, Co, Ti, Mn. In other embodiments of this application, the M source includes NiO, MnO2, etc.

[0037] In some embodiments of this application, the primary sintering temperature is 500–800°C, the time is 6–12 hours, the annealing temperature is 200–700°C, and the manganese source solution includes a manganese source and an organic solvent, wherein the manganese source includes manganese carbonate and the organic solvent includes ethanol.

[0038] In some embodiments of this application, the annealing process includes: heating the O3-type sodium ion oxide to 200-700°C at a heating rate of 1-5°C / min, and then performing a post-annealing treatment for 5-10 hours.

[0039] In a second aspect of this application, based on the positive electrode material provided above, a secondary battery is provided, including a negative electrode sheet, a separator, an electrolyte, and a positive electrode sheet containing the positive electrode material described in this application.

[0040] In some embodiments of this application, the positive electrode sheet comprises a metal foil and a positive electrode material layer, wherein the positive electrode material layer comprises the positive electrode material described in this application, as well as a binder and a conductive agent. The binder and conductive agent can be conventional materials, such as acetylene black (Super P) as the conductive agent, and polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR) as the binder, etc. In other embodiments of this application, the positive electrode material accounts for 80–96 wt%, the binder accounts for 2–10 wt%, and the conductive agent accounts for 2–5 wt%. In other embodiments of this application, the metal foil is aluminum foil with a thickness of 8–20 μm and an areal density of 3 mg / cm³. 2 ~10mg / cm 2 Compacted density 1g / cm³ 3 ~3g / cm 3 .

[0041] In some embodiments of this application, the electrolyte comprises an electrolyte sodium salt and a solvent; wherein the electrolyte sodium salt comprises one or both of NaPF6 or NaClO4, with a concentration of 0.5 to 3 mol / L; and the solvent comprises one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0042] In some embodiments of this application, the secondary battery is a pouch battery, a button battery, a half battery, or a full battery.

[0043] In a third aspect of this application, an electrical device is provided, including the secondary battery described in this application, which can be a variety of devices or equipment powered by the secondary battery, including but not limited to electric vehicles, electric cars, balance scooters, flatbed trucks, aircraft, lighting equipment, home appliances, etc.

[0044] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0045] The following provides a further description of a sodium-ion battery cathode material, a secondary battery, and an electrical device provided in this application.

[0046] Example 1:

[0047] S1. Raw materials Na2CO3, NiO, and MnO2 are mixed evenly to obtain a mixture, wherein the molar ratio of Na:Ni:Mn in the mixture is 0.9:0.44:0.56. The mixture is then sintered at 800℃ for 12 hours to obtain O3-type sodium ion oxide Na. 0.9 Ni 0.44 Mn0.56 O2, space group R-3m, cell parameters

[0048] S2, the O3-type sodium ion oxide is heated to 500℃ at a heating rate of 1-5℃ / min, and then annealed for 8 hours to partially convert the O3-type sodium ion oxide into the P2-type sodium ion oxide Na. 0.74 Ni 0.41 Mn 0.59 O2, space group P63 / mmc, cell parameters To obtain composite materials;

[0049] S3. After uniformly mixing the composite material and tungsten carbide (WC), a mixed powder is obtained;

[0050] S4. The mixed powder is subjected to secondary sintering at 900°C to obtain a positive electrode material, wherein the core of the positive electrode material is a P2 / O3 type layered composite material Na. 0.9 Ni 0.44 Mn 0.56 O2 and Na 0.74 Ni 0.41 Mn 0.59 O2, the outer shell includes WC (1.5%), and tungsten carbide accounts for 1.5% of the mass of the cathode material.

[0051] Example 2:

[0052] A cathode material is provided, and the preparation method is the same as in Example 1, except that the types of raw materials and the molar ratios of each element are adjusted in step S1 so that the core material obtained in step S2 is (O3 type) Na. 0.98 Ni 0.5 Fe 0.5 O2 and (P2 type) Na 0.67 Ni 0.5 Fe 0.5 O2.

[0053] Example 3:

[0054] A cathode material is provided, and the preparation method is the same as in Example 1, except that the types of raw materials and the molar ratios of each element are adjusted in step S1 so that the core material obtained in step S2 is (O3 type) Na. 1.05 Ni 0.6 Ti 0.4 O2 and (P2 type) Na 0.53 Ni 0.43 Ti 0.57 O2.

[0055] Example 4:

[0056] A cathode material is provided, and the preparation method is the same as in Example 1, except that the types of raw materials and the molar ratios of each element are adjusted in step S1 so that the core material obtained in step S2 is (O3 type) Na. 1.1 Ni 0.6 Co 0.2 Mn 0.2 O2 and (P2 type) Na 0.5 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0057] Example 5:

[0058] A cathode material is provided, and the preparation method is the same as in Example 1, except that the metal carbide in step S3 is replaced with TiC.

[0059] Example 6:

[0060] A cathode material is provided, and the preparation method is the same as in Example 1, except that the metal carbide in step S3 is replaced with NbC.

[0061] Example 7:

[0062] A cathode material is provided, and the preparation method is the same as in Example 1, except that the metal carbide in step S3 is replaced with HfC.

[0063] Example 8:

[0064] A cathode material is provided, and the preparation method is the same as in Example 1, except that the metal carbide in step S3 is replaced with TaC.

[0065] Example 9:

[0066] A cathode material is provided, and the preparation method is the same as in Example 1, except that the amount of WC added is adjusted so that the proportion of WC in the cathode material is 0.5%.

[0067] Example 10:

[0068] A cathode material is provided, and the preparation method is the same as in Example 1, except that the amount of WC added is adjusted so that the proportion of WC in the cathode material is 1%.

[0069] Example 11:

[0070] A cathode material is provided, and the preparation method is the same as in Example 1, except that the amount of WC added is adjusted so that the proportion of WC in the cathode material is 2%.

[0071] Example 12:

[0072] A cathode material is provided, and the preparation method is the same as in Example 1, except that the amount of WC added is adjusted so that the proportion of WC in the cathode material is 3%.

[0073] Example 13:

[0074] A cathode material is provided, prepared according to Example 1, except that step S3 is replaced with "mixing the composite material, WC, and an ethanol solution of manganese carbonate, heating and stirring at 70°C, evaporating the ethanol to obtain a mixed powder". The resulting cathode material shell contains Na. 0.44 MnO2.

[0075] Example 14:

[0076] A cathode material is provided, prepared according to the method described in Example 13, except that the temperature of the secondary sintering in step S4 is adjusted, and the resulting cathode material shell contains Na. 0.55 MnO2.

[0077] Example 15:

[0078] A cathode material is provided, prepared according to the method described in Example 13, except that the temperature of the secondary sintering in step S4 is adjusted, and the resulting cathode material shell contains Na. 0.3 MnO2.

[0079] Example 16:

[0080] A positive electrode material is provided, and the preparation method is the same as in Example 13, except that the content of manganese carbonate in step S3 is adjusted to control the Na content. 0.44 The molar ratio of MnO2 to WC.

[0081] Example 17:

[0082] A positive electrode material is provided, and the preparation method is the same as in Example 13, except that the content of manganese carbonate in step S3 is adjusted to control the Na content. 0.44 The molar ratio of MnO2 to WC.

[0083] Comparative Example 1:

[0084] A positive electrode material is provided, and the preparation method is the same as in Example 1, except that WC is not added in step S3.

[0085] Comparative Example 2:

[0086] A cathode material is provided, and the preparation method is the same as in Example 1, except that WC in step S3 is replaced with SiC.

[0087] Comparative Example 3:

[0088] A cathode material is provided, and the preparation method is the same as in Example 1, except that WC in step S3 is replaced with Al₂O.

[0089] The characteristics of the cathode materials prepared in Examples 1-17 and Comparative Examples 1-3 are summarized in Table 1 below;

[0090] Table 1

[0091]

[0092]

[0093] The positive electrode materials of Examples 1-17 and Comparative Examples 1-3 were used as positive electrode active materials and assembled into 2025 type coin cells. The specific assembly process of the cells is as follows:

[0094] The above-mentioned positive electrode material, acetylene black and PVDF were dispersed and mixed in NMP solvent at a mass percentage of 96:2:2 to form a positive electrode slurry, which was uniformly coated on aluminum foil and dried at 100°C. Then it was cut into round pieces and transferred to a vacuum oven at 120°C to dry, thus obtaining the positive electrode sheet.

[0095] The negative electrode active materials, hard carbon, acetylene black and PVDF, were dispersed and mixed in NMP solvent at a mass percentage of 96:2:2 to form a negative electrode slurry. The slurry was uniformly coated on copper foil and dried at 100°C. It was then cut into round pieces and transferred to a vacuum oven at 120°C for drying to obtain the negative electrode sheet.

[0096] Place the positive electrode sheet into the positive electrode shell of the coin cell, add a glass fiber separator, add an appropriate amount of electrolyte (1 mol / L NaClO4, with EC and DEC in a volume ratio of 1:1), add the negative electrode sheet, add a gasket and a spring, cover with the negative electrode shell, and seal with a battery sealing machine to assemble the coin cell.

[0097] The performance of the prepared 2025-type button cells was tested, and the specific test details are as follows:

[0098] 1) Battery cycle performance test method:

[0099] (1) Under the condition of 25℃±3, the battery is charged to 4.0V at a constant current and constant voltage of 0.5C, and the cut-off current is 0.02C;

[0100] (2) Let it sit for 30 minutes;

[0101] (3) Under the condition of 25℃±3, discharge at 1C constant current to 1.5V, and record the capacity D1 at this time;

[0102] (4) Let it sit for 30 minutes;

[0103] (5) Repeat the above steps. When the capacity retention rate D = Dx / D1*100% < 80%, record the number of battery discharge cycles x.

[0104] 2) Battery rate performance test method:

[0105] (1) The experimental battery was charged to 4.0V at a constant current and constant voltage of 0.5C under the condition of 25℃±3℃, and the cut-off current was 0.02C;

[0106] (2) Let it sit for 30 minutes;

[0107] (3) Under the condition of 25℃±3, discharge at 1C constant current to 2.0V, and record the capacity D1 at this time;

[0108] (4) Let it sit for 30 minutes;

[0109] (5) Under the condition of 25℃±3, the battery is charged to 4.0V by constant current and constant voltage at 0.5C, and the cut-off current is 0.02C;

[0110] (6) Let it sit for 30 minutes;

[0111] (7) Under conditions of 25℃±3, discharge at a constant current of 5C to 2.0V;

[0112] Perform cycle charging and discharging on the battery using the above steps. When the capacity retention rate D = Dx / D1*100% < 80%, record the number of battery discharge cycles x. Record the test results in Table 2.

[0113] Table 2

[0114]

[0115]

[0116] As can be seen from the above experimental data, adding metal carbides to the surface of the cathode material can improve the cycle performance of the battery and maintain high cycle stability under high-rate charge and discharge conditions.

[0117] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises an inner core and an outer shell, the inner core comprises a composite material composed of P2 type sodium ion oxide and O3 type sodium ion oxide, the outer shell comprises metal carbide and sodium manganese oxide, the metal carbide is distributed in the interior and / or surface of the sodium manganese oxide, the metal in the metal carbide comprises metal elements in groups IVB, VB and VIB, and the metal elements comprise at least one of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W elements; The structure of the sodium manganese oxide comprises nanorods with a length of 2-5 μm and a diameter of 100-400 nm; or the structure of the sodium manganese oxide comprises nanobands with a length of 5-10 μm, a width of 50-200 nm and a thickness of 20-100 nm. The chemical formula of the composite material includes Na x MO2, wherein M is Ni, and one of Cu, Co, and Mn, and 1.1 ≥ x ≥ 0.

5.

2. The positive electrode material of claim 1, wherein, The metal carbide comprises at least one of WC, TiC, TaC, NbC and HfC.

3. The positive electrode material of claim 1, wherein, The content of the metal carbide is 0.5-3% based on the mass of the positive electrode material.

4. The positive electrode material of claim 1, wherein, The molar ratio of the sodium manganese oxide to the metal carbide is 1: [0.05-0.1].

5. The positive electrode material according to claim 1 or 4, characterized in that, The sodium manganese oxides include Na p Mn02, 0.05 < p < 0.

55.

6. The cathode material of claim 1, wherein, The space group of the O3 type sodium ion oxide is R-3m, the cell parameter is 2.8 Å 7. A secondary battery characterized by comprising: The secondary battery comprises the positive electrode material of any one of claims 1-6.

8. An electric device, characterized by The secondary battery of claim 7 provides electric energy for the electric device.

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