Layered cathode materials for potassium-ion batteries and their preparation methods and potassium-ion batteries

Abstract

This invention belongs to the field of potassium-ion battery technology, specifically relating to a layered cathode material for potassium-ion batteries, its preparation method, and a potassium-ion battery. The preparation method includes the following steps: uniformly mixing a potassium source and an M source, sintering the mixture, and then rapidly cooling it at a rate greater than or equal to 15°C / min after sintering to obtain the layered cathode material for potassium-ion batteries. The M source includes at least one of a transition metal compound, an alkaline earth metal compound, an Al compound, a Sn compound, and a Sb compound. The preparation method provided by this invention, by rapidly cooling at a rate greater than or equal to 15°C / min after sintering, results in a low surface residual alkali content in the prepared layered cathode material, solving the problem of easy gelation in the slurry and improving the cycle stability of the potassium-ion battery prepared from this layered cathode material.

Description

Technical Field

[0001] This invention belongs to the field of potassium-ion battery technology, specifically relating to a layered cathode material for potassium-ion batteries, its preparation method, and a potassium-ion battery. Background Technology

[0002] In recent years, with the rapid development of the new energy industry, lithium resources for producing lithium-ion batteries have fallen far short of meeting the explosive growth in demand. Emerging potassium-ion batteries, due to abundant potassium resources, low cost, and similar physicochemical properties to lithium, have attracted widespread attention from researchers. Potassium-ion batteries hold promising application prospects in energy storage, hybrid power, and replacing lead-acid batteries. Because the standard redox potential of potassium (-2.94 V vs. SHE) falls between that of sodium (-2.73 V vs. SHE) and lithium (-3.04 V vs. SHE), potassium-ion batteries can operate at higher voltages. While graphite has very limited ability to intercalate and deintercalate sodium ions as an anode material in sodium-ion batteries, potassium ions can intercalate into graphite to form a KC8 structure (i.e., the theoretical potassium storage capacity of graphite is 279 mAh / g). This means that commercial graphite can be directly used as an anode material for potassium-ion batteries, reducing battery costs. Based on this, potassium-ion batteries have attracted increasing attention from researchers in recent years.

[0003] Because of the large radius of potassium ions, repeated insertion and extraction within the cathode material can easily cause structural collapse, leading to a degradation in electrical performance. Therefore, developing suitable cathode materials is crucial for the large-scale application of potassium-ion batteries. Currently, layered transition metal oxides are considered the most promising cathode materials for potassium-ion batteries due to their high capacity and high compaction density.

[0004] In existing methods for preparing potassium-ion layered oxide cathode materials, the potassium content is appropriately increased to compensate for potassium volatilization during high-temperature calcination. This results in a small amount of K2O remaining on the surface of the final potassium-ion layered oxide material. K2O adsorbs CO2 and H2O from the air to form KOH and K2CO3, resulting in a high amount of residual alkali (KOH and K2CO3) on the surface of the potassium-ion layered oxide material. Furthermore, K is more alkaline than Na and Li, so the alkalinity of potassium-ion cathode materials is much higher than that of lithium-ion and sodium-ion cathode materials. For example, patent CN109713295A discloses a method for preparing potassium-ion battery cathode materials, and the potassium-ion battery cathode materials prepared by this method have a high amount of residual alkali on the surface. The high residual alkali content on the surface of potassium ion layered oxide materials will have a serious impact on the performance of the materials: (1) the materials are extremely prone to moisture absorption and deterioration, resulting in poor slurry dispersibility and stability, easy gelation, and low product yield; (2) the residual alkali remaining on the surface of potassium ion layered oxides will decompose under high temperature conditions, producing carbon dioxide gas and water, which will ultimately seriously affect the cycle stability of potassium-ion batteries using potassium ion layered oxide materials as positive electrode materials. Therefore, researching a method for preparing potassium-ion battery layered positive electrode materials with low surface residual alkali (KOH and K2CO3) content is an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned shortcomings in the existing technology, the present invention aims to provide a layered cathode material for potassium-ion batteries, a method for preparing the same, and a potassium-ion battery. The preparation method provided by the present invention involves rapid cooling at a rate greater than or equal to 15°C / min after sintering, resulting in a low surface residual alkali content in the prepared layered cathode material for potassium-ion batteries. This solves the problem of easy gelation of the slurry and improves the cycle stability of the potassium-ion battery prepared from the layered cathode material.

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

[0007] In a first aspect, the present invention provides a method for preparing a layered cathode material for potassium-ion batteries, the method comprising the following steps:

[0008] After the potassium source and the M source are mixed evenly, they are sintered. After sintering, they are rapidly cooled at a rate of 15°C / min or higher to obtain a layered cathode material for potassium-ion batteries. The M source includes at least one of the following: a compound of a transition metal element, a compound of an alkaline earth metal element, a compound of Al, a compound of Sn, and a compound of Sb.

[0009] The preparation method provided by the present invention involves rapid cooling at a rate of 15°C / min or higher after sintering, which results in a low residual alkali content on the surface of the prepared potassium-ion battery layered cathode material. This solves the problem of easy gelation of the slurry and improves the cycle stability of the potassium-ion battery prepared from the layered cathode material.

[0010] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, after sintering, the material is rapidly cooled to room temperature at a rate greater than or equal to 15°C / min, for example, at a rate of 15-30°C / min (e.g., 15°C / min, 20°C / min, 25°C / min, or 30°C / min, etc.).

[0011] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the transition metal element includes at least one of Ni, Co, Mn, Cu, Fe, Zn, Zr, V, Ti, Nb, W, Mo, and Ce.

[0012] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the M source includes at least one of the following: Ni compounds, Co compounds, Mn compounds, Cu compounds, Fe compounds, Mg compounds, Zn compounds, Sn compounds, Zr compounds, Ca compounds, Al compounds, V compounds, Ti compounds, Nb compounds, W compounds, Mo compounds, Ce compounds, Sr compounds, and Sb compounds.

[0013] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the potassium source includes at least one of potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), potassium hydroxide, potassium acetate (CH2COOK), potassium phosphate, potassium nitrate (KNO3), and potassium sulfate (K2SO4).

[0014] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the general chemical formula of the layered cathode material for potassium-ion batteries is K. x MO y Where x > 0.4, y ≥ 2, and M includes at least one of transition metal elements, alkaline earth metal elements, Al, Sn, and Sb.

[0015] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, 0.5 <x<0.9,y=2。

[0016] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, M includes at least one of Ni, Co, Mn, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb.

[0017] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, M includes Mn and M1, wherein M1 includes at least one of Ni, Co, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb, and the general chemical formula of the layered cathode material for potassium-ion batteries is K. x Mn z M1 (1-z) O y Where x > 0.4 (e.g., 0.5) <x<0.9),y≥2,0.5≤z≤0.9。

[0018] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the sintering temperature is 600-1000℃, for example, 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 840℃, 880℃, or 900℃.

[0019] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the sintering heating rate is 2 to 10 °C / min, for example, the heating rate is 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min.

[0020] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the sintering atmosphere is an air atmosphere or an oxygen atmosphere.

[0021] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the sintering time is 10-20 hours, for example, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, or 20 hours.

[0022] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the potassium source and the M source are mixed by dry ball milling.

[0023] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the equipment used for ball milling is a planetary ball mill, wherein the ball milling medium is zirconia balls, the ball milling speed is 200-600 r / min (for example, 200 r / min, 400 r / min, 600 r / min), and the ball milling time is 2-10 h (for example, 2 h, 4 h, 6 h, 8 h, 10 h, etc.).

[0024] In the above-mentioned method for preparing layered cathode material for potassium-ion batteries, as a preferred embodiment, the amount of the M source is calculated according to stoichiometry. For example, the theoretical amount of M source required to prepare 1 mol of layered cathode material for potassium-ion batteries is 1 mol, so the amount of the M source is 1 mol. The amount of potassium source used is 1-10% more than the amount calculated according to stoichiometry. For example, the theoretical amount of potassium source required to prepare 1 mol of layered cathode material for potassium-ion batteries is 1 mol, so the amount of potassium source used is 1.01-1.1 mol.

[0025] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the potassium source and the M source are mixed uniformly in a molar ratio of K:M = ax:1, wherein 1.01 ≤ a ≤ 1.1, and x > 0.4, for example, 0.5. <x<0.9。

[0026] In the above-mentioned method for preparing the layered cathode material for potassium-ion batteries, as a preferred embodiment, the preparation method further includes post-processing of the layered cathode material for potassium-ion batteries, the post-processing including:

[0027] The potassium-ion battery layered cathode material was mixed with potassium difluorophosphate (KPO2F2) in a non-aqueous solvent to obtain a suspension;

[0028] The suspension is subjected to solid-liquid separation to obtain a solid, which is then washed with the non-aqueous solvent and finally dried to obtain the processed potassium-ion battery layered cathode material.

[0029] This invention utilizes potassium difluorophosphate solution to wash the layered cathode material of potassium-ion batteries, which can further reduce the residual alkali content on the surface and improve the high-temperature storage performance and cycle stability of potassium-ion batteries prepared from this layered cathode material.

[0030] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the non-aqueous solvent includes at least one of methanol, ethanol, ethylene glycol, n-propanol, and isopropanol.

[0031] In the above-mentioned method for preparing the layered cathode material for potassium-ion batteries, as a preferred embodiment, the molar ratio of potassium difluorophosphate (KPO2F2) to the residual alkali on the surface of the layered cathode material for potassium-ion batteries is 0.5:1 to 9.0:1. For example, the molar ratio can be 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, 6.0:1, 7.0:1, 8.0:1, or 9.0:1.

[0032] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the residual alkali includes at least one of KOH and K2CO3.

[0033] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, the mixing temperature during the post-processing is 25-80°C (for example, it can be 25°C, 35°C, 45°C, 60°C, or 80°C).

[0034] In the above-mentioned method for preparing layered cathode materials for potassium-ion batteries, as a preferred embodiment, in the post-processing, the mixing method is to use a magnetic stirrer for stirring and mixing. The stirring speed is 100-1000 rpm (e.g., 100 rpm, 300 rpm, 600 rpm, 800 rpm, or 1000 rpm, etc.), and the stirring time is 0.5-5.0 h (e.g., 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, or 5.0 h).

[0035] In a second aspect, the present invention provides a potassium-ion battery layered cathode material, wherein the potassium-ion battery layered cathode material is prepared by the preparation method of the potassium-ion battery layered cathode material provided in the first aspect.

[0036] Thirdly, the present invention provides a potassium-ion battery, the potassium-ion battery comprising the layered positive electrode material of the potassium-ion battery as described in the second aspect.

[0037] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0038] (1) The preparation method provided by the present invention rapidly cools the potassium-ion battery layered cathode material at a rate of greater than or equal to 15°C / min after sintering, which results in a low surface residual alkali content, solves the problem of easy gelation of slurry, and improves the cycle stability of potassium-ion battery prepared from the potassium-ion battery layered cathode material.

[0039] (2) By using potassium difluorophosphate solution to wash the layered cathode material of potassium-ion battery, the present invention can further reduce the residual alkali content on the surface and improve the high-temperature storage performance and cycle stability of potassium-ion battery prepared from the layered cathode material. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0042] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0043] In this invention, unless otherwise specified and / or stated, all values ​​relating to component amounts are in parts by weight. Process parameters in the following examples that do not specify specific conditions are generally performed under conventional conditions. Unless otherwise specified, the experimental reagents used in the following examples are conventional biochemical reagents; and unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations.

[0044] In a first aspect, the present invention provides a method for preparing a layered cathode material for a potassium ion battery. The preparation method includes the following steps: After uniformly mixing a potassium source and an M source, sintering is carried out, and after the sintering is completed, rapid cooling is carried out at a rate of 15-30 °C / min to room temperature to obtain a layered cathode material for a potassium ion battery. Among them, the M source includes at least one of compounds of Ni, Co, Mn, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb; the potassium source includes at least one of potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), potassium hydroxide, potassium acetate (CH2COOK), potassium phosphate, potassium nitrate (KNO3), and potassium sulfate (K2SO4); the chemical general formula of the layered cathode material for a potassium ion battery is K x MO y , where 0.5 < x < 0.9, y = 2, and M includes at least one of Ni, Co, Mn, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb; M includes Mn and M1, and M1 includes at least one of Ni, Co, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb. The chemical general formula of the layered cathode material for a potassium ion battery is K x Mn z M1 (1-z) O yWhere x > 0.4, y ≥ 2, 0.5 ≤ z ≤ 0.9; the sintering temperature is 600–1000℃, the sintering heating rate is 2–10℃ / min, the sintering atmosphere is air or oxygen, and the sintering time is 10–20 h; the potassium source and the M source are mixed by dry ball milling, the ball milling equipment is a planetary ball mill, the ball milling media is zirconia balls, the ball milling speed is 200–600 r / min, and the ball milling time is 2–10 h; the potassium source and the M source are mixed uniformly according to a molar ratio of K:M = ax:1, where 1.01 ≤ a ≤ 1.1, x > 0.4; the preparation method further includes post-processing the potassium-ion battery layered cathode material, the post-processing including: the potassium-ion battery layered cathode material... The positive electrode material and potassium difluorophosphate (KPO2F2) are mixed in a non-aqueous solvent at 25–80°C to obtain a suspension. The suspension is then subjected to solid-liquid separation to obtain a solid. The solid is then washed with the non-aqueous solvent and finally dried to obtain the treated potassium-ion battery layered positive electrode material. The non-aqueous solvent includes at least one of methanol, ethanol, ethylene glycol, n-propanol, and isopropanol. The molar ratio of potassium difluorophosphate (KPO2F2) to the residual alkali on the surface of the potassium-ion battery layered positive electrode material is 0.5:1 to 9.0:1. The residual alkali includes at least one of KOH and K2CO3. The mixing method is to use a magnetic stirrer to stir and mix at a speed of 100–1000 rpm for 0.5–5.0 h.

[0045] In a second aspect, the present invention provides a potassium-ion battery layered cathode material, wherein the potassium-ion battery layered cathode material is prepared by the preparation method of the potassium-ion battery layered cathode material provided in the first aspect.

[0046] Thirdly, the present invention provides a potassium-ion battery, the potassium-ion battery comprising the layered positive electrode material of the potassium-ion battery as described in the second aspect.

[0047] To further understand the present invention, the following detailed description of the potassium-ion battery layered cathode material, its preparation method, and the potassium-ion battery provided by the present invention is provided in conjunction with embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0048] In the following embodiments and comparative examples:

[0049] Room temperature: 25℃-30℃.

[0050] Method for testing residual alkali content on the surface of layered cathode materials for potassium-ion batteries: The KOH and K2CO3 content (mass percentage) on the surface of the layered cathode materials for potassium-ion batteries is determined by potentiometric titration. First, 50g of the material is weighed and placed in 50mL of deionized water, stirred for 30min, and filtered to obtain a clear liquid. 10mL of this clear liquid is taken and titrated with a 0.05mol / L HCl standard solution to calculate the KOH and K2CO3 content. Residual alkali content on the surface of the layered cathode material for potassium-ion batteries = KOH content + K2CO3 content.

[0051] Example 1

[0052] The method for preparing the layered cathode material for potassium-ion batteries provided in this embodiment includes the following steps:

[0053] S1. According to the molar ratio of K:Mn:Cu = 0.7:0.8:0.2, K2CO3, Mn2O3, and CuO are sequentially placed into a planetary ball mill and ball-milled at a speed of 600 r / min for 6 hours. The ball milling media is zirconia balls. The molar ratio of K in K2CO3, Mn in Mn2O3, and Cu in CuO is 0.7:0.8:0.2.

[0054] S2. The mixed material from step S1 is transferred to a furnace with a high concentration of oxygen (oxygen content ≥ 98.5%) and heated to 900℃ at a heating rate of 5℃ / min for sintering for 15 hours. Then, it is rapidly cooled to room temperature at a rate of 25℃ / min. After coarse crushing with a roller crusher and fine grinding with an air jet mill, it is sieved through a 400-mesh standard sieve to obtain potassium ion layered oxide (potassium ion battery layered cathode material) K. 0.67 Mn 0.8 Cu 0.2 O2 (abbreviated as KMCO).

[0055] Example 2

[0056] The preparation method of the potassium-ion battery layered cathode material provided in this embodiment is basically the same as that in Example 1, except that in step S2, the rapid cooling rate is 15°C / min, specifically including the following steps:

[0057] S1. According to the molar ratio of K:Mn:Cu = 0.7:0.8:0.2, K2CO3, Mn2O3, and CuO are sequentially placed into a planetary ball mill and ball-milled at a speed of 600 r / min for 6 hours. The ball milling media is zirconia balls. The molar ratio of K in K2CO3, Mn in Mn2O3, and Cu in CuO is 0.7:0.8:0.2.

[0058] S2. The mixed material from step S1 is transferred to a furnace with a high concentration of oxygen (oxygen content ≥ 98.5%) and heated to 900℃ at a heating rate of 5℃ / min for sintering for 15 hours. Then, it is rapidly cooled to room temperature at a rate of 15℃ / min. After coarse crushing with a roller crusher and fine grinding with an air jet mill, it is sieved through a 400-mesh standard sieve to obtain potassium ion layered oxide (potassium ion battery layered cathode material) K. 0.67 Mn 0.8 Cu 0.2 O2 (abbreviated as KMCO).

[0059] Example 3

[0060] The preparation method of the potassium-ion battery layered cathode material provided in this embodiment is basically the same as that in Example 1, except that in step S2, the rapid cooling rate is 30°C / min, specifically including the following steps:

[0061] S1. According to the molar ratio of K:Mn:Cu = 0.7:0.8:0.2, K2CO3, Mn2O3, and CuO are sequentially placed into a planetary ball mill and ball-milled at a speed of 600 r / min for 6 hours. The ball milling media is zirconia balls. The molar ratio of K in K2CO3, Mn in Mn2O3, and Cu in CuO is 0.7:0.8:0.2.

[0062] S2. The mixed material from step S1 is transferred to a furnace with a high concentration of oxygen (oxygen content ≥ 98.5%) and heated to 900℃ at a heating rate of 5℃ / min for sintering for 15 hours. Then, it is rapidly cooled to room temperature at a rate of 30℃ / min. After coarse crushing with a roller crusher and fine grinding with an air jet mill, it is sieved through a 400-mesh standard sieve to obtain potassium ion layered oxide (potassium ion battery layered cathode material) K. 0.67 Mn 0.8 Cu 0.2 O2 (abbreviated as KMCO).

[0063] Example 4

[0064] The method for preparing the layered cathode material for potassium-ion batteries provided in this embodiment includes the following steps:

[0065] S1. K2CO3, Mn2O3, and CuO are sequentially placed into a planetary ball mill and mixed at a speed of 400 r / min for 8 hours according to a molar ratio of K:Mn:Cu = 0.7:0.8:0.2. The ball milling media are zirconia balls. The molar ratio of K in K2CO3, Mn in Mn2O3, and Cu in CuO is 0.7:0.8:0.2.

[0066] S2. The mixed material from step S1 is transferred to a furnace with a high concentration of oxygen (oxygen content ≥ 98.5%) and heated to 700℃ at a heating rate of 3℃ / min for sintering for 20 hours. Then, it is rapidly cooled to room temperature at a rate of 25℃ / min. After coarse crushing with a roller crusher and fine grinding with an air jet mill, it is sieved through a 400-mesh standard sieve to obtain potassium ion layered oxide (potassium ion battery layered cathode material) K. 0.67 Mn 0.8 Cu 0.2 O2 (abbreviated as KMCO).

[0067] Example 5

[0068] The preparation method of the potassium-ion battery layered cathode material provided in this embodiment is basically the same as that in Embodiment 1, except that after step S2, a post-processing of the potassium-ion battery layered cathode material is further included, specifically including the following steps:

[0069] S1. According to the molar ratio of K:Mn:Cu = 0.7:0.8:0.2, K2CO3, Mn2O3, and CuO are sequentially placed into a planetary ball mill and ball-milled at a speed of 600 r / min for 6 hours. The ball milling media is zirconia balls. The molar ratio of K in K2CO3, Mn in Mn2O3, and Cu in CuO is 0.7:0.8:0.2.

[0070] S2. The mixed material from step S1 is transferred to a furnace with a high concentration of oxygen (oxygen content ≥ 98.5%) and heated to 900℃ at a heating rate of 5℃ / min for sintering for 15 hours. Then, it is rapidly cooled to room temperature at a rate of 25℃ / min. After coarse crushing with a roller crusher and fine grinding with an air jet mill, it is sieved through a 400-mesh standard sieve to obtain potassium ion layered oxide (potassium ion battery layered cathode material) K. 0.67 Mn 0.8 Cu 0.2 O2 (abbreviated as KMCO).

[0071] S3. At room temperature, KPO2F2 is added to a glass beaker containing ethanol solvent. The mixture is stirred with a magnetic stirrer at 500 rpm for 60 min to obtain a homogeneous ethanol solution containing KPO2F2. The molar volume concentration of KPO2F2 in the ethanol solvent is 0.1 mol / L.

[0072] The potassium ion layered oxide prepared in step S2 was added to an ethanol solution containing KPO2F2, and stirred at 400 rpm for 3.0 h using a magnetic stirrer to obtain a uniform suspension. The molar ratio of KPO2F2 to residual alkali (KOH and K2CO3) on the surface of the potassium ion layered oxide was 1:1 (the ratio of the number of moles of KPO2F2 to the sum of the number of moles of KOH and K2CO3 on the surface of the potassium ion layered oxide was 1:1). The stirring temperature was controlled at 25℃.

[0073] S4. Centrifuge the uniform suspension obtained in step S3 at 2000 rpm for 15 min. Then wash the precipitate after centrifugation three times with ethanol solvent. Filter the washed material and transfer the filter cake to a vibrating dryer with a vacuum degree of -80 kPa. Dry it under vacuum at 90°C for 12 h. Then sieve it through a 325-mesh standard sieve to obtain the processed potassium ion layered oxide.

[0074] Example 6

[0075] The preparation method of the potassium-ion battery layered cathode material provided in this embodiment is basically the same as that in Example 5, except that in step S3, the molar ratio of KPO2F2 to the residual alkali on the surface of the potassium-ion layered oxide is 1.5:1.

[0076] Example 7

[0077] The preparation method of the potassium-ion battery layered cathode material provided in this embodiment is basically the same as that in Example 5, except that in step S3, the mixture is stirred at a speed of 400 rpm for 2.0 h, and the stirring temperature is controlled at 45°C.

[0078] Comparative Example 1

[0079] The preparation method of the potassium-ion battery layered cathode material provided in this comparative example is basically the same as that in Example 1, except that in step S2, after sintering for 15 hours, it is cooled to room temperature in the furnace.

[0080] Comparative Example 2

[0081] The preparation method of the potassium-ion battery layered cathode material provided in this comparative example is basically the same as that in Example 1, except that in step S2, after sintering for 15 h, it is rapidly cooled to room temperature at a rate of 10 °C / min.

[0082] Comparative Example 3

[0083] The preparation method of the potassium-ion battery layered cathode material provided in this comparative example is basically the same as that in Example 5, except that KPO2F2 is not added in step S3. Specifically, it includes the following steps:

[0084] S1-S2: Same as steps S1-S2 in Example 5.

[0085] S3. Add the potassium ion layered oxide prepared in step S2 to ethanol, and stir with a magnetic stirrer at a speed of 400 rpm for 3.0 h to obtain a uniform suspension. The volume of ethanol is the same as the volume of the ethanol solution containing KPO2F2 in step S3 of Example 5, and the mass of potassium ion layered oxide is the same as the mass of potassium ion layered oxide in Example 5. The stirring temperature is controlled at 25°C.

[0086] S4. Centrifuge the uniform suspension obtained in step S3 at 2000 rpm for 15 min. Then wash the precipitate after centrifugation three times with ethanol solvent. Filter the washed material and transfer the filter cake to a vibrating dryer with a vacuum degree of -80 kPa. Dry it under vacuum at 90°C for 12 h. Then sieve it through a 325-mesh standard sieve to obtain the processed potassium ion layered oxide.

[0087] Performance testing:

[0088] Preparation method of positive electrode sheet: The positive electrode materials prepared in the examples and comparative examples are used as positive electrode active materials. The positive electrode active materials, conductive agent Super P and PVDF are mixed evenly in NMP at a mass ratio of 96:2:2 to prepare a positive electrode slurry. The evenly mixed slurry is then coated on aluminum foil and vacuum dried at 120°C for 13 hours. After rolling and die cutting, the positive electrode sheet of potassium ion battery is obtained.

[0089] Preparation method of negative electrode sheet: Hard carbon, acetylene black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed evenly in a mass ratio of 95.9:1.0:1.8:1.3 to prepare a negative electrode slurry. Then, the evenly mixed slurry is coated on copper foil and vacuum dried at 120°C for 13 hours. After rolling and die cutting, the negative electrode sheet of potassium ion battery is obtained.

[0090] Assembly of potassium-ion batteries: Positive and negative electrode sheets and a 9μm polypropylene separator (coated with alumina on one side as a ceramic layer) are stacked to obtain a cell. Then, electrolyte is injected to assemble and prepare a 4.5Ah soft pack battery. The electrolyte used is a 1mol / L KPF6 / EC+EMC+DMC (volume ratio of 1:1:1) electrolyte. After electrolyte injection, the battery is sealed and left to stand.

[0091] Potassium-ion battery cycle performance test: Under the temperature of 25℃, the battery was charged to 4.1V with constant current and constant voltage at 1C (cutoff current is 0.05C), and after standing for 5 minutes, it was discharged to 1.5V with constant current at 1C. The discharge capacity of the first cycle and the 300th cycle were recorded (capacity retention rate of 300 cycles = discharge capacity of the 300th cycle / discharge capacity of the 1st cycle). The test results are shown in Table 1.

[0092] The gelation performance of the cathode material slurry in the above embodiments and comparative examples was tested as follows: The prepared cathode slurry was placed in a sealed container at an ambient temperature of 25°C and a humidity of 80%. A beaker containing water was placed in the container to create a water-containing atmosphere. The gelation performance of the material was examined, and the experiment was conducted and recorded hourly to document the gelation status of the slurry. The test results are shown in Table 1.

[0093] Table 1

[0094]

[0095] At least the following points can be observed from Table 1:

[0096] (1) As can be seen from Examples 1-4 and Comparative Examples 1-2, the preparation method provided by the present invention rapidly cools the potassium-ion battery layered cathode material at a rate of greater than or equal to 15°C / min after sintering, resulting in a low surface residual alkali content, which solves the problem of easy gelation of slurry and improves the cycle stability of potassium-ion batteries prepared from the potassium-ion battery layered cathode material.

[0097] (2) As can be seen from Examples 1, 5 and 6, by using potassium difluorophosphate solution to wash the layered cathode material of potassium-ion battery, the residual alkali content on the surface can be further reduced, and the cycle stability of potassium-ion battery prepared from the layered cathode material can be improved. Moreover, as the amount of potassium difluorophosphate increases, the residual alkali content gradually decreases. The applicant speculates that the reason may be that sodium difluorophosphate reacts chemically with the residual alkali, so that the residual alkali content on the surface decreases as the amount of sodium difluorophosphate increases.

[0098] (3) As can be seen from Examples 5 and 7, increasing the stirring temperature can improve the rate of removing residual alkali.

[0099] (4) As can be seen from Examples 1, 5 and Comparative Example 3, washing the layered cathode material of potassium-ion battery with ethanol alone cannot significantly reduce the surface residual alkali content.

[0100] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a layered cathode material for potassium-ion batteries, characterized in that, The preparation method includes the following steps: After the potassium source and the M source are mixed evenly, they are sintered. After sintering, they are rapidly cooled at a rate of 15°C / min or higher to obtain a layered cathode material for potassium-ion batteries. The M source includes at least one of the following: a compound of a transition metal element, a compound of an alkaline earth metal element, a compound of Al, a compound of Sn, and a compound of Sb. The preparation method further includes post-processing of the potassium-ion battery layered cathode material, the post-processing including: The potassium-ion battery layered cathode material was mixed with potassium difluorophosphate in a non-aqueous solvent to obtain a suspension. The suspension is subjected to solid-liquid separation to obtain a solid, which is then washed with the non-aqueous solvent and finally dried to obtain the processed potassium-ion battery layered cathode material. During the post-processing, the mixing temperature is 35–80°C.

2. The method for preparing the layered cathode material for potassium-ion batteries according to claim 1, characterized in that, After sintering, the material is rapidly cooled to room temperature at a rate of 15-30℃ / min.

3. The method for preparing the layered cathode material for potassium-ion batteries according to claim 1, characterized in that, The transition metal element includes at least one selected from Ni, Co, Mn, Cu, Fe, Zn, Zr, V, Ti, Nb, W, Mo, and Ce; And / or, the M source includes at least one of the following: Ni compounds, Co compounds, Mn compounds, Cu compounds, Fe compounds, Mg compounds, Zn compounds, Sn compounds, Zr compounds, Ca compounds, Al compounds, V compounds, Ti compounds, Nb compounds, W compounds, Mo compounds, Ce compounds, Sr compounds, and Sb compounds; And / or, the potassium source includes at least one of potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium acetate, potassium phosphate, potassium nitrate, and potassium sulfate; And / or, the general chemical formula of the potassium-ion battery layered cathode material is K x MO y Where x > 0.4, y ≥ 2, and M includes at least one of transition metal elements, alkaline earth metal elements, Al, Sn, and Sb.

4. The method for preparing the layered cathode material for potassium-ion batteries according to claim 3, characterized in that, 0.5 <x<0.9,y=2; And / or, the M includes at least one of Ni, Co, Mn, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb; And / or, M includes Mn and M1, wherein M1 includes at least one of Ni, Co, Cu, Fe, Mg, Zn, Sn, Zr, Ca, Al, V, Ti, Nb, W, Mo, Ce, Sr, and Sb, and the general chemical formula of the potassium-ion battery layered cathode material is K. x Mn z M1 （1-z） O y Where x > 0.4, y ≥ 2, and 0.5 ≤ z ≤ 0.

9.

5. The method for preparing the layered cathode material for potassium-ion batteries according to claim 1, characterized in that, The sintering temperature is 600–1000℃; And / or, the heating rate of the sintering is 2 to 10 °C / min; And / or, the sintering atmosphere is an air atmosphere or an oxygen atmosphere; And / or, the sintering time is 10-20 h.

6. The method for preparing the layered cathode material for potassium-ion batteries according to claim 1, characterized in that, The potassium source and the M source are mixed by dry ball milling. The ball milling equipment is a planetary ball mill, wherein the ball milling media is zirconia balls, the ball milling speed is 200-600 r / min, and the ball milling time is 2-10 h. And / or, the potassium source and the M source are mixed uniformly in a molar ratio of K:M=ax:1, wherein 1.01≤a≤1.1 and x>0.

4.

7. The method for preparing the layered cathode material for potassium-ion batteries according to claim 1, characterized in that, The non-aqueous solvent includes at least one of methanol, ethanol, ethylene glycol, n-propanol, and isopropanol; And / or, the molar ratio of potassium difluorophosphate to residual alkali on the surface of the potassium-ion battery layered cathode material is 0.5:1 to 9.0:1, wherein the residual alkali includes at least one of KOH and K2CO3; And / or, in the post-processing, the mixing method is to use a magnetic stirrer to stir and mix, the stirring speed is 100 to 1000 rpm, and the stirring time is 0.5 to 5.0 h.

8. A layered cathode material for potassium-ion batteries, characterized in that, The potassium-ion battery layered cathode material is prepared by the method for preparing potassium-ion battery layered cathode material according to any one of claims 1-7.

9. A potassium-ion battery, characterized in that, The potassium-ion battery includes the layered positive electrode material of the potassium-ion battery as described in claim 8.

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