Positive electrode active material, method for producing positive electrode active material, and potassium ion battery

Abstract

The application provides a positive electrode active material, a preparation method of the positive electrode active material and a potassium ion battery, and relates to the field of secondary batteries. The positive electrode active material comprises a core and a carbon layer covering the core, and the chemical formula of the core is K 3+x V 3‑x Ni x (PO4)4, 0.05<=x<=0.5. In the application, Ni 2+ is doped in the KVP material, so that the structural stability and the electrochemical performance of the positive electrode active material are effectively improved. Specifically, by doping Ni 2+ , the product purity and the crystalline integrity of the positive electrode active material are significantly improved, the structural stability of the product is enhanced, and the problems of low product purity and many impurities in the existing preparation method are solved. Moreover, the reaction kinetics and the cycle performance of the positive electrode active material are synergistically optimized.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, and more particularly to a positive electrode active material, a method for preparing the positive electrode active material, and a potassium-ion battery. Background Technology

[0002] With the advancement of global "dual-carbon" goals, renewable energy storage technology has become a research hotspot. Potassium-ion batteries, due to their abundant potassium resources, standard electrode potential close to that of lithium, and the availability of graphite as a low-cost anode, are considered one of the ideal alternatives to lithium-ion batteries. The cathode material, as the core component of potassium-ion batteries, directly determines the battery's energy density, cycle life, and operating voltage. Vanadium-based phosphate materials (such as K3V3(PO4)4, or KVP for short) have become a research hotspot for potassium-ion battery cathode materials due to their structural stability and the rich variations in vanadium valence states.

[0003] However, existing KVP materials have significant technical defects: first, the capacity is low, with the actual specific capacity being far lower than the theoretical value, and the reaction kinetics are slow with insufficient potassium ion diffusion efficiency; second, the cycling stability is poor, especially at high current densities, where the capacity decays rapidly.

[0004] While existing methods for modifying KVP include metal ion doping, these methods often suffer from numerous side reactions and limited performance improvements. They fail to simultaneously address the need for synergistic optimization of capacity and cycle performance, thus limiting the application of KVP materials in high-energy-density potassium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide a positive electrode active material, a method for preparing the positive electrode active material, and a potassium-ion battery to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution: A positive electrode active material, the positive electrode active material comprising a core and a carbon layer coating the core, the core having the chemical formula K. 3+x V 3-x Ni x (PO4)4, 0.05≤x≤0.5.

[0007] According to an embodiment of this application, the carbon content in the positive electrode active material is 4.5wt%~5.5wt%.

[0008] This application also provides a method for preparing the positive electrode active material as described above, comprising: A vanadium source and a chelating agent are added to water to obtain a first mixed solution; wherein the vanadium source includes V 5+ The chelating agent contains carbon; A potassium source and a nickel source are added to the first mixed solution to obtain a second mixed solution; A phosphorus source was added to the second mixed solution to obtain a wet gel; The wet gel was dehydrated to obtain a dry gel. The dry gel was calcined to obtain a positive electrode active material.

[0009] According to an embodiment of this application, the vanadium source includes ammonium metavanadate; The potassium source includes potassium carbonate; The nickel source includes at least one of nickel nitrate hexahydrate, nickel nitrate, nickel acetate tetrahydrate, and nickel acetate; The phosphorus source includes ammonium dihydrogen phosphate; The chelating agent includes at least one of citric acid, glucose, and oxalic acid.

[0010] According to an embodiment of this application, the preparation method further includes: feeding vanadium source, nickel source and phosphorus source according to the stoichiometric ratio in the core chemical formula, wherein the amount of potassium source fed is 1.1-1.2 times the molar amount of potassium element in the stoichiometric ratio; The molar ratio of the chelating agent to the total molar ratio of metal ions in the vanadium and nickel sources is (1~1.5):1.

[0011] According to an embodiment of this application, the preparation of the first mixed solution includes: adding a vanadium source and a chelating agent to water, stirring at a temperature of 75~85°C for 30-50 minutes to obtain the first mixed solution; And / or, the preparation of the second mixed solution includes: adding a potassium source and a nickel source to the first mixed solution, stirring at a temperature of 75~85°C for 30-50 min to obtain the second mixed solution; And / or, the preparation of wet gel includes: adding a phosphorus source to the second mixed solution and stirring at a temperature of 75~85°C until it becomes a viscous, non-flowing state to obtain a wet gel.

[0012] According to an embodiment of this application, the temperature of the dehydration treatment is 110~130℃, and the time of the dehydration treatment is 3~5h.

[0013] According to an embodiment of this application, the calcination treatment is carried out in a mixed atmosphere of Ar and H2; The volume ratio of Ar to H2 in the mixed atmosphere is (90-95):(5-10).

[0014] According to an embodiment of this application, the calcination treatment includes a first stage and a second stage performed sequentially; The first stage includes: heating to 320-380℃ at a heating rate of 4-6℃ / min, and then holding at that temperature for 3-5 hours; The second stage includes: heating to 750-850℃ at a heating rate of 4-6℃ / min, and then holding at that temperature for 10-14 hours.

[0015] This application also provides a potassium-ion battery, which includes the positive electrode active material described above or the positive electrode active material prepared by the preparation method described above.

[0016] Compared with the prior art, the beneficial effects of this application include: This application will be related to V 3+ Similar ionic radii (Ni) 2+ It is 0.72 Å, V 3+ Ni (0.74 Å) 2+ Doping with KVP materials effectively improves the structural stability and electrochemical performance of the positive electrode active material. Specifically, this is achieved by doping with Ni. 2+ This significantly improves the purity and crystal integrity of the cathode active material, enhances its structural stability, and addresses the issues of low product purity and numerous impurity phases in existing preparation methods. Furthermore, the cathode active material of this application achieves synergistic optimization of reaction kinetics and cycling performance. The cathode active material of this application achieves substantial improvements in reaction kinetics: reducing charge transfer resistance and increasing the potassium ion diffusion coefficient, significantly improving electron transport and ion diffusion efficiency; the capacity of this application shows almost no decay after cycling at high current densities, overcoming the problem of rapid capacity decay under high current in existing materials.

[0017] This application uses the sol-gel method to prepare positive electrode active materials. This method has the advantages of simple operation and low production cost, and is suitable for large-scale production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0019] Figure 1 XRD comparison images of the positive electrode active materials of the examples and comparative examples; Figure 2 This is a TEM image of the positive electrode active material in Example 1; Figure 3 This is a SEM image of the positive electrode active material in Example 1; Figure 4 Here is a SEM image of the positive electrode active material in Example 3; Figure 5 The rate performance diagram for the comparative example KVP; Figure 6 This is a rate performance diagram for Example 2; Figure 7 This is a rate performance diagram for Example 1; Figure 8 This is a rate performance diagram for Example 3; Figure 9 This is a graph showing the long-cycle performance of Example 2 at a high current density of 10C; Figure 10 The graph shows the long-cycle performance of Comparative Example 1 at a high current density of 10C. Detailed Implementation

[0020] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0021] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0022] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0023] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0024] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0025] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0026] A positive electrode active material, the positive electrode active material comprising a core and a carbon layer coating the core, the core having the chemical formula K. 3+x V 3-x Ni x (PO4)4, 0.05≤x≤0.5.

[0027] This application utilizes Ni 2+ With V 3+ Similar ionic radii (Ni) 2+ It is 0.72 Å, V 3+ Given the properties of 0.74 Å, electrochemically inert Ni was chosen. 2+ Doping of vanadium sites in KVP materials with Ni 2+ It acts as a "structural pillar" in the crystal lattice, which can suppress the decomposition of materials under high pressure, while not introducing additional redox reactions to interfere with it, thus ensuring the stability of electrochemical performance.

[0028] The positive electrode active material of this application also achieves a significant improvement in high-voltage stability, overcoming the defect of existing KVP materials being prone to failure under high voltage, and providing a possibility for the application of high-energy-density batteries.

[0029] When x in the kernel chemical formula is within the above range, high-purity K can be generated. 3+x V 3-x Ni xXRD analysis of (PO4)4 showed that the main body of the positive electrode active material is a pure-phase Pnna type layered structure, with only a weak Ni3V2O3 impurity peak observed, indicating high crystal integrity, which is beneficial to improving the electrochemical performance of the positive electrode active material. The positive electrode active material of this application also possesses excellent high-voltage stability, good cycle stability, balanced reaction kinetics, and high coulombic efficiency. If the x in the core chemical formula is too small, the amount of Ni doping in the core is too low, and its role as a "structural pillar" in the crystal lattice is insufficient. Under high voltage, the crystal lattice is prone to distortion, resulting in poor high-voltage stability and fewer active sites, making it unable to effectively reduce the potassium ion migration barrier. If the x in the core chemical formula is too large, the amount of Ni doping in the core is too high. Excess Ni exceeds the lattice capacity limit and cannot stably occupy V sites, thus forming an impurity phase, destroying the original layered structure, hindering ion and electron transport, and thus reducing the electrochemical performance of the positive electrode active material.

[0030] The positive electrode active material of this application belongs to the Pnna-type layered structure, which is formed by connecting V / NiO6 octahedra and PO4 tetrahedra to form an XZ plane. The interlayer space is a potassium ion transport channel. 3+x V 3-x Ni x Coating the surface of (PO4)4 with a carbon layer can improve the electronic conductivity of the material.

[0031] In some embodiments, the carbon in the carbon layer is an amorphous carbon layer.

[0032] According to embodiments of this application, the carbon content in the positive electrode active material is 4.5 wt% to 5.5 wt%. For example, the carbon content in the positive electrode active material is any value between 4.5 wt%, 4.6 wt%, 4.7 wt%, 4.8 wt%, 4.9 wt%, 5 wt%, 5.1 wt%, 5.2 wt%, 5.3 wt%, 5.4 wt%, 5.5 wt%, or 4.5 wt% to 5.5 wt%.

[0033] This application also provides a method for preparing the positive electrode active material as described above, comprising: A vanadium source and a chelating agent are added to water to obtain a first mixed solution; wherein the vanadium source includes V 5+ The chelating agent contains carbon; A potassium source and a nickel source are added to the first mixed solution to obtain a second mixed solution; A phosphorus source was added to the second mixed solution to obtain a wet gel; The wet gel was dehydrated to obtain a dry gel. The dry gel was calcined to obtain a positive electrode active material.

[0034] According to an embodiment of this application, the vanadium source includes ammonium metavanadate (NH4VO3). The potassium source includes potassium carbonate (K2CO3); The nickel source includes nickel nitrate hexahydrate (Ni(NO3)2). At least one of the following: 6H2O, nickel nitrate (Ni(NO3)2), nickel acetate tetrahydrate, and nickel acetate; The phosphorus source includes ammonium dihydrogen phosphate (NH4H2PO4). The chelating agent includes at least one selected from citric acid (C6H8O7), glucose, and oxalic acid. These chelating agents can also serve as carbon sources. After high-temperature decomposition, the chelating agent generates a carbon layer that coats the outer surface of the core.

[0035] According to an embodiment of this application, the preparation method further includes: feeding vanadium source, nickel source and phosphorus source according to the stoichiometric ratio in the core chemical formula, wherein the amount of potassium source fed is 1.1-1.2 times (e.g., any value between 1.1 times, 1.2 times or 1.1-1.2 times) of the molar amount of potassium element in the stoichiometric ratio. The amount of potassium source fed in this application is excessive relative to the stoichiometry. This design can, on the one hand, compensate for the loss of potassium ions due to volatilization during calcination, avoid lattice defects caused by potassium deficiency, and ensure the integrity of the chemical formula of the product; on the other hand, the additional introduction of a small amount of migratory potassium ions can increase the storage sites of potassium ions in the material and improve the specific capacity; in addition, this design can also optimize the lattice structure parameters, reduce the potassium ion migration barrier, and improve the reaction kinetics performance.

[0036] The molar ratio of the chelating agent to the total molar ratio of metal ions in the vanadium and nickel sources is (1~1.5):1. For example, the molar ratio of the chelating agent to the total molar ratio of metal ions in the vanadium and nickel sources is any value between 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or (1~1.5):1.

[0037] According to an embodiment of this application, the preparation of the first mixed solution includes: adding a vanadium source and a chelating agent to water, and stirring at a temperature of 75-85°C (e.g., 75°C, 77°C, 80°C, 82°C, 85°C, or any value between 75-85°C) for 30-50 minutes (e.g., 30 minutes, 40 minutes, 50 minutes, or any value between 30-50 minutes) to obtain the first mixed solution; under these conditions, the vanadium source V can be chelated. 5+ Restore to V 4+ .

[0038] The preparation of the second mixed solution includes: adding a potassium source and a nickel source to the first mixed solution, and stirring at a temperature of 75~85℃ (e.g., 75℃, 77℃, 80℃, 82℃, 85℃ or any value between 75~85℃) for 30-50 min (e.g., 30 min, 40 min, 50 min or any value between 30-50 min) to obtain the second mixed solution; The preparation of wet gel includes: adding a phosphorus source to the second mixed solution and stirring at a temperature of 75~85℃ (e.g., 75℃, 77℃, 80℃, 82℃, 85℃ or any value between 75~85℃) until it becomes viscous and non-flowing, thus obtaining wet gel.

[0039] According to an embodiment of this application, the temperature of the dehydration treatment is 110~130℃, and the dehydration treatment time is 3~5h. For example, the dehydration treatment temperature is 110℃, 112℃, 115℃, 117℃, 120℃, 122℃, 125℃, 127℃, 130℃, or any value between 110~130℃; the dehydration treatment time is 3h, 4h, 5h, or any value between 3~5h.

[0040] In some embodiments, after dehydration and before calcination, the preparation method further includes: grinding the dehydrated product and calcining the resulting powder.

[0041] According to an embodiment of this application, the calcination treatment is carried out in a mixed atmosphere of Ar and H2; The volume ratio of Ar to H2 in the mixed atmosphere is (90-95):(5-10).

[0042] The H2 in the mixed atmosphere acts as a reducing agent, ensuring that V remains stable at V2. 3+ Valence state, to prevent V from being oxidized to V 4+ or V 5+ This, in turn, helps improve the electrochemical performance of the material; Ar gas isolates the material from air, preventing oxygen from participating in the reaction and generating impurity phases such as V2O5, while also preventing Ni from being oxidized, thus ensuring Ni's... 2+ The doping effect.

[0043] For example, the volume ratio of Ar to H2 in the mixed atmosphere is any value between 90:10, 91:9, 92:8, 93:7, 94:6, 95:5 or (90-95):(5-10).

[0044] According to an embodiment of this application, the calcination treatment includes a first stage and a second stage performed sequentially; The first stage includes: heating to 320-380℃ (e.g., 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, or any value between 4-6℃ / min) at a heating rate of 4-6℃ / min (e.g., 4℃ / min, 5℃ / min, 6℃ / min, or any value between 320-380℃), and then holding at that temperature for 3-5 hours (e.g., 3 hours, 4 hours, 5 hours, or any value between 3-5 hours); calcination at low temperature under the above conditions can achieve the decomposition of the chelating agent, the complete removal of moisture and organic impurities in the precursor, avoid side reactions caused by impurities during high-temperature calcination, and provide a pure environment for subsequent crystal growth; The second stage includes: heating at a rate of 4~6℃ / min (e.g., 4℃ / min, 5℃ / min, 6℃ / min, or any value between 4~6℃ / min) to 750~850℃ (e.g., 750℃, 770℃, 800℃, 820℃, 850℃, or any value between 750~850℃), and then holding at that temperature for 10~14h (e.g., 10h, 11h, 12h, 13h, 14h, or any value between 10~14h). High-temperature calcination under these conditions allows for the complete growth of the crystal structure and uniform coating of the carbon layer; specifically, at 750~850℃, the precursor can be completely decomposed, which is beneficial for obtaining a high-purity Pnna-type layered structure. If the calcination temperature in the second stage is too low, incomplete crystallization and numerous lattice defects will occur; if the calcination temperature in the second stage is too high, Ni will undergo side reactions with V and P, easily generating impurity phases, resulting in lower purity of the positive electrode active material. A calcination time of 10-14 hours provides sufficient time for the crystal structure to grow fully, which is beneficial to improving lattice integrity and crystallinity, reducing lattice defects, and also allows the chelating agent to fully decompose and form a uniformly coated carbon layer, thereby improving the electronic conductivity of the material.

[0045] In some embodiments, after the calcination treatment is completed, the preparation method further includes: cooling the calcined product to room temperature and grinding it to obtain a positive electrode active material.

[0046] The first and second stages work together to prepare positive electrode active materials with high purity, high crystal integrity, and excellent electrochemical performance. If the first stage of low-temperature calcination is omitted and the second stage of high-temperature calcination is carried out directly, it will lead to problems such as residual impurities, impurity phase formation, and incomplete crystallization, resulting in lower product purity and poorer electrochemical performance.

[0047] This application also provides a potassium-ion battery, including the positive electrode active material described above or the positive electrode active material prepared by the preparation method described above.

[0048] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0049] Example 1 Example 1 provides a positive electrode active material, the preparation method of which includes: 1. Press K 3.1 V 2.9 Ni 0.1 The stoichiometric ratio of (PO4)4 is calculated by weighing NH4VO3 and Ni(NO3)2. 6H2O, NH4H2PO4, K2CO3 and citric acid cause NH4VO3 to react with Ni(NO3)2 The molar ratio of 6H2O, NH4H2PO4, K2CO3, and citric acid is 2.9:0.1:4:1.705:3 (the amount of potassium source added is 1.1 times the molar amount of potassium in the stoichiometric ratio). Weigh out 0.580g of NH4VO3 and Ni(NO3)2. 0.05g of 6H2O, 0.787g of NH4H2PO4, 0.403g of K2CO3, and 0.985g of citric acid; 2. Add NH4VO3 and citric acid to 40 mL of deionized water and stir in an 80°C water bath for 30 min until a blue transparent solution is formed; 3. Then add K2CO3 and Ni(NO3)2 Stir at 80°C for 30 minutes in the presence of 6H₂O. 4. Then add NH4H2PO4 and continue stirring until it becomes a viscous, non-flowing state, to obtain a wet gel; The wet gel was dried in an oven at 120°C for 4 hours and then ground into a dry gel powder. 5. Place the dry gel powder into a ceramic boat, introduce a mixed atmosphere of Ar and H2 (the volume ratio of Ar to H2 in the mixed atmosphere is 95:5), heat to 350℃ at 5℃ / min, hold for 4h, then heat to 800℃ at a heating rate of 5℃ / min, hold for 12h, and after naturally cooling to room temperature, grind to obtain the positive electrode active material.

[0050] Example 1: The positive electrode active material (KVNP-0.1) comprises a core and a carbon layer coating the core. The chemical formula of the core is K. 3.1 V 2.9 Ni 0.1(PO4)4, the carbon content in the positive electrode active material is 4.5wt~5.5wt%.

[0051] Example 2 The difference between Example 2 and Example 1 is that: according to K 3.05 V 2.95 Ni 0.05 The stoichiometric ratio of (PO4)4 is calculated by weighing NH4VO3 and Ni(NO3)2. 6H2O, NH4H2PO4, K2CO3 and citric acid cause NH4VO3 to react with Ni(NO3)2 The molar ratio of 6H2O, NH4H2PO4, K2CO3, and citric acid is 2.95:0.05:4:1.678:3 (the amount of potassium source added is 1.1 times the molar amount of potassium in the stoichiometric ratio). Everything else is the same as in Example 1.

[0052] Example 2: The positive electrode active material (KVNP-0.05) comprises a core and a carbon layer coating the core. The chemical formula of the core is K. 3.05 V 2.95 Ni 0.05 (PO4)4, the carbon content in the positive electrode active material is 4.5wt~5.5wt%.

[0053] Example 3 The difference between Example 3 and Example 1 is that, according to K 3.5 V 2.5 Ni 0.5 The stoichiometric ratio of (PO4)4 is calculated by weighing NH4VO3 and Ni(NO3)2. 6H2O, NH4H2PO4, K2CO3 and citric acid cause NH4VO3 to react with Ni(NO3)2 The molar ratio of 6H2O, NH4H2PO4, K2CO3, and citric acid is 2.5:0.5:4:1.925:3 (the amount of potassium source added is 1.1 times the molar amount of potassium in the stoichiometric ratio). Everything else is the same as in Example 1.

[0054] Example 3: The positive electrode active material (KVNP-0.5) comprises a core and a carbon layer coating the core. The chemical formula of the core is K. 3.5 V 2.5 Ni 0.5 (PO4)4, the carbon content in the positive electrode active material is 0.06-0.07wt%.

[0055] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Ni(NO3)2 is not added. 6H2O. Everything else is the same as in Example 1.

[0056] II. Performance Testing XRD, SEM, and TEM tests were performed on the positive electrode active materials of the examples and comparative examples.

[0057] Figure 1 The XRD patterns of the positive electrode active materials in the examples and comparative examples are shown. XRD tests show that the positive electrode active material in Example 1 has a pure-phase Pnna-type layered structure, with only a weak Ni3V2O3 impurity peak observed. The positive electrode active material in Example 2 also has a pure-phase Pnna-type layered structure, with a Rietveld refinement error value Rwp = 7.41%. The XRD pattern of the positive electrode active material in Example 3 shows more impurity peaks, with Ni3V2O3 (PDF#74-1485) impurity peaks appearing near 15.7°, 26.8°, 29.2°, and 34.5°, and NiP3 (PDF#73-1242) impurity peaks appearing near 22.7° and 32.2°.

[0058] Appearance: SEM ( Figure 3 It was observed that the positive electrode active material in Example 1 had an irregular bulk agglomerate structure (size 5-10 μm) with a relatively smooth surface; TEM ( Figure 2 The positive electrode active material in Example 1 is shown to be amorphous with few surface impurities.

[0059] SEM ( Figure 4 It was observed that irregularly shaped objects (by-reaction products) adhered to the surface of the positive electrode active material in Example 3.

[0060] Structural parameters: Example 1: Cell parameters a = 10.73014 Å, b = 20.84266 Å, c = 6.50235 Å; cell volume V = 1454.216 Å. 3 ; Example 2: Cell parameters a = 10.73226 Å, b = 20.84566 Å, c = 6.50225 Å; cell volume V = 1454.690 Å. 3 ; Comparative Example 1 has unit cell parameters a = 10.7708 Å, b = 20.8928 Å, c = 6.5217 Å, and a unit cell volume V = 1467.59219 Å. 3 .

[0061] The positive electrode active materials of the examples and comparative examples were assembled into batteries under the same conditions, specifically including: using the materials prepared in the examples or comparative examples as positive electrode active materials, commercial porous carbon as negative electrode, 1M KPF6 / EC:PC (volume ratio 1:1) as electrolyte, glass fiber as separator, and assembling coin cells in an argon glove box (water and oxygen content are both below 0.1ppm).

[0062] The assembled batteries were subjected to electrochemical performance testing under the same conditions: a LAND CT2001A blue battery testing system was used at room temperature of 25±1℃ and a voltage window of 1.3-4.1 V (vs. K / K). + Using 1C=100 mA / g as a baseline, the discharge specific capacity and rate recovery performance at rates of 0.2C, 0.5C, 1C, 3C, 5C, and 10C were tested; the capacity retention rate was calculated after 200 cycles at a current density of 10C.

[0063] The assembled batteries were subjected to reaction kinetic tests under the same conditions: EIS was measured using a CHI660E electrochemical workstation, with a frequency range of 10. 6 -10 -2 Hz, AC amplitude 5 mV, the charge transfer resistance (Rct) was obtained by fitting; the Warburg impedance was fitted by EIS, and the potassium ion diffusion coefficient (D_K) was calculated. + ).

[0064] The performance test results of the examples and comparative examples are shown in Tables 1 and 2.

[0065] Table 1. Comparison of electrochemical performance between the examples and comparative examples.

[0066] Table 2 Comparison of Reaction Kinetics between Examples and Comparative Examples

[0067] Example 1 operates stably within a voltage window of 1.3-4.2V, Example 2 can only be stabilized up to 4.1V (slight decomposition occurs at 4.2V), and Comparative Example 1 has a voltage window ≤4.0V (decomposition is easy above 4.0V).

[0068] Example 2 showed a capacity retention of 77% after 3000 cycles at a current density of 10C.

[0069] Depend on Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10As can be seen from Tables 1 and 2, Examples 1-3 simultaneously exhibit a low capacity decay rate, a high capacity retention rate, a high coulombic efficiency, a low charge transfer resistance Rct, and a high potassium ion diffusion coefficient D_K. + Its overall electrochemical performance is significantly better than that of Comparative Example 1.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0071] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material comprises a core and a carbon layer coating the core, wherein the core has the chemical formula K. 3+x V 3-x Ni x (PO4)4, 0.05≤x≤0.

5.

2. The positive electrode active material according to claim 1, characterized in that, The carbon content in the positive electrode active material is 4.5wt%~5.5wt%.

3. A method for preparing the positive electrode active material as described in claim 1 or 2, characterized in that, include: A vanadium source and a chelating agent are added to water to obtain a first mixed solution; wherein the vanadium source includes V 5+ The chelating agent contains carbon; A potassium source and a nickel source are added to the first mixed solution to obtain a second mixed solution; A phosphorus source was added to the second mixed solution to obtain a wet gel; The wet gel was dehydrated to obtain a dry gel. The dry gel was calcined to obtain a positive electrode active material.

4. The method for preparing the positive electrode active material according to claim 3, characterized in that, The vanadium source includes ammonium metavanadate; The potassium source includes potassium carbonate; The nickel source includes at least one of nickel nitrate hexahydrate, nickel nitrate, nickel acetate tetrahydrate, and nickel acetate; The phosphorus source includes ammonium dihydrogen phosphate; The chelating agent includes at least one of citric acid, glucose, and oxalic acid.

5. The method for preparing the positive electrode active material according to claim 4, characterized in that, The preparation method further includes: feeding vanadium source, nickel source and phosphorus source according to the stoichiometric ratio in the core chemical formula, wherein the amount of potassium source fed is 1.1-1.2 times the molar amount of potassium element in the stoichiometric ratio; The molar ratio of the chelating agent to the total molar ratio of metal ions in the vanadium and nickel sources is (1~1.5):

1.

6. The method for preparing the positive electrode active material according to claim 3, characterized in that, The preparation of the first mixed solution includes: adding the vanadium source and chelating agent to water, stirring at 75~85℃ for 30-50 min to obtain the first mixed solution; And / or, the preparation of the second mixed solution includes: adding a potassium source and a nickel source to the first mixed solution, stirring at a temperature of 75~85°C for 30-50 min to obtain the second mixed solution; And / or, the preparation of wet gel includes: adding a phosphorus source to the second mixed solution and stirring at a temperature of 75~85°C until it becomes a viscous, non-flowing state to obtain a wet gel.

7. The method for preparing the positive electrode active material according to claim 3, characterized in that, The dehydration treatment is carried out at a temperature of 110~130℃ for 3~5 hours.

8. The method for preparing the positive electrode active material according to claim 3, characterized in that, The calcination process was carried out in a mixed atmosphere of Ar and H2; The volume ratio of Ar to H2 in the mixed atmosphere is (90-95):(5-10).

9. The method for preparing the positive electrode active material according to any one of claims 3-8, characterized in that, The calcination process includes a first stage and a second stage performed sequentially. The first stage includes: heating to 320-380℃ at a heating rate of 4-6℃ / min, and then holding at that temperature for 3-5 hours; The second stage includes: heating to 750-850℃ at a heating rate of 4-6℃ / min, and then holding at that temperature for 10-14 hours.

10. A potassium-ion battery, characterized in that, The potassium-ion battery includes the positive electrode active material as described in claim 1 or 2, or the positive electrode active material prepared by the preparation method described in any one of claims 3-9.

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