A method for preparing a high-stability manganese-based oxide potassium-ion battery cathode material

Abstract

This invention provides a method for preparing a high-stability manganese-based oxide potassium-ion battery cathode material, comprising the following steps: S1, taking 1.12g of K2CO3 and 1.9275g of MnO2, and mixing and grinding the two chemicals for 15min; S2, loading the uniform powder obtained from grinding into an alumina crucible, and then placing it in a muffle furnace, adjusting the heating rate to 5℃min. ‑1 The temperature was raised to 700℃ and held for 5 hours. This invention provides a method for preparing a high-stability manganese-based oxide potassium-ion battery cathode material. The KMO@C0.2 potassium-ion battery electrode prepared by this invention has high stability. The KMO@C0.2 composite material has excellent specific capacity, cycle life, and rate performance. The carbon coating can protect the KMO cathode surface for a long time from the influence of electrolyte side reactions, reduce irreversible interfacial reactions and interfacial kinetics, and ball milling reduces the particle size, increases the specific surface area of ​​the material and the active sites for K+ diffusion, thereby greatly increasing the specific capacity.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage device technology, and relates to a method for preparing a potassium-ion battery cathode material, specifically a method for preparing KMO@C0.2 potassium-ion battery cathode material by solid-state reaction and high-energy ball milling. Background Technology

[0002] Solid-state reaction is the most common method for preparing layered manganese dioxide (δ-MnO2) cathodes. It is a simple method involving the physical mixing (sometimes solution mixing) of potassium and transition metal precursors (oxides or acetates) and sintering to obtain the final product. For example, Kim... [1] P3-K0.5MnO2 was synthesized via a conventional solid-state route using K2CO3 and Mn2O3 precursors. The stoichiometrically mixed powder was ground and then calcined at 800 °C for 12 h. By selecting suitable precursors and controlling the calcination temperature, the desired phase structure and crystallinity can be obtained. Liu [2] K was prepared by a simplified solid-state method 0.45 Mn 0.8 Fe 0.2 O2. Stoichiometric amounts of K2CO3, Mn2O3, and Fe2O3 powders were mixed with ethanol in air for 12 h using a wet planetary ball milling method. These pellets were then calcined in air at 850 °C for 15 h to obtain K. 0.45 Mn 0.8 Fe 0.2 O2 sample. This technology also uses a simple hot sintering scheme, and the raw materials are also inexpensive K2CO3 and Mn2O3, but it adopts a two-step process. The second step is to process K2CO3 and Mn2O3. 0.28 MnO2· 0.29 H2O (KMO) and Ketjen black (KB) are coated onto the surface of KMO using a high-energy ball milling process to obtain KMO@C0.2 material.

[0003] In various energy storage systems, lithium-ion batteries (LIBs) have become the primary power source for consumer electronics and smart wearable devices due to their high energy density, long cycle life, and ease of maintenance. However, LIBs alone may not be able to meet future energy demands associated with the rapid growth of the electric vehicle market and stationary energy storage systems. Lithium is scarce and unevenly distributed in the Earth's crust, raising concerns about soaring lithium prices and the sustainability of lithium in meeting future energy needs. Therefore, potassium-ion batteries (PIBs) are a promising alternative or complement to lithium-ion batteries because potassium is abundant. It is well known that cathode materials are one of the keys to the excellent electrochemical performance of potassium-ion batteries. They can be broadly classified into organic compounds, layered transition metal oxides (LTMOs), Prussian blue analogues (PBAs), and polyanionic compounds (PACs). In particular, layered transition metal oxides (LTMOs), due to their high theoretical energy density, structural stability, and low cost, have made KxMO2 (M = transition metal) one of the most promising cathodes among PIBs and have attracted attention.

[0004] Constructing a suitable coating matrix is ​​an effective way to prevent direct contact between the electrode and the organic electrolyte. Suppressing side reactions can improve interfacial stability and cycle stability. Surface coating effectively avoids direct contact between the cathode material and the electrolyte, inhibiting electrolyte corrosion of the cathode material and dissolution of transition metals, and is an effective surface modification method. An effective and direct strategy is to use a soft conductive matrix to buffer the volume changes during potassicization / depotassicization. Carbon coating can improve the conductivity between particles while avoiding direct contact between the electrolyte and the electrode, thus improving rate performance and cycle stability. We adopted two strategies. First, we synthesized δ-MnO2 particles using a simple solid-state reaction route, which is a low-cost and high-yield synthesis method. Then, water molecules from deionized water were embedded into the interlayer of δ-MnO2 as water of crystallization to synthesize potassium-type birnessite (KMO). Second, a conductive amorphous carbon coating was coated onto the KMO powder using a physical method through high-energy ball milling. This coating not only provides a suitable conductive network to improve electronic conductivity, but also buffers the volume expansion of KMO particles and reduces agglomeration. Therefore, the KMO@C0.2 composite material, composed of flexible, conductive amorphous carbon and KMO particles, is expected to exhibit excellent performance in PIBs.

[0005] Therefore, it is necessary to provide a method for preparing a highly stable manganese-based oxide potassium-ion battery cathode material to solve the above-mentioned technical problems. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a method for preparing KMO@C0.2 potassium-ion battery cathode materials through solid-state reaction and high-energy ball milling. The potassium-ion battery cathode material KMO@C0.2 prepared by this method has a smaller particle size than KMO, which can increase the active sites for K+ diffusion, facilitate electrolyte penetration, and reduce electrode polarization during electrochemical reactions, thereby enabling high-capacity charge and discharge of the battery.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a highly stable manganese-based oxide potassium-ion battery cathode material, comprising the following steps:

[0008] S1. Take 1.12g of K2CO3 and 1.9275g of MnO2, and grind the two drugs together for 15 minutes.

[0009] S2. Place the uniform powder obtained from grinding into an alumina crucible, then place it in a muffle furnace, and adjust the heating rate to 5℃ min. -1 Heat to 700℃ and keep warm for 5 hours;

[0010] S3. Wait for the muffle furnace to cool down to room temperature. Use a circulating water vacuum pump to filter the black powder from the solid-phase reaction with a large amount of deionized water to remove unreacted K2CO3 and impurities such as potassium manganate.

[0011] S4. Place the washed powder into a vacuum drying oven at 80℃ and dry for at least 8 hours to obtain the precursor material K from the first step of the process. 0.28 MnO2· 0.29 H2O (KMO);

[0012] S5. The second step of the process uses high-energy ball milling. A certain amount of KMO powder and Ketjen Black (KB) powder are mixed and loaded into a ball milling jar. Then, agate balls with an appropriate ball-to-material ratio are added.

[0013] S6. Set the rotation speed and time parameters of the planetary ball mill to ball mill KMO and KB to obtain the final product KMO@C0.2;

[0014] S7, KMO@C0.2, acetylene black, and polyvinylidene fluoride are mixed and dispersed in n-methyl-2-pyridone (NMP), and then ground to form a uniform slurry. The resulting slurry is uniformly coated on the surface of a clean aluminum foil treated with anhydrous ethanol and dried overnight in a vacuum oven at 80°C to obtain a potassium-ion battery positive electrode sheet.

[0015] S8. Using a manual button cell slicing machine, the electrodes were punched into 14 mm diameter discs. The effective mass loading of the cathode was approximately 1.0–2.0 mg cm⁻² per electrode. Metallic potassium, 1 M KPF₆ (EC:DEC = 1:1 Vol%), and glass fiber were used as the anode, electrolyte, and separator, respectively. CR₂O₃₂ coin cells were assembled in an argon-filled glove box, and the electrochemical performance of the prepared electrodes was evaluated.

[0016] Preferably, in step S1, the molar ratio of K2CO3 to MnO2 is 0.7:1, and 5wt% K2CO3 is added to compensate for the potassium source lost at high temperature.

[0017] Preferably, the protective gas is any one or more of argon, nitrogen, helium, and neon.

[0018] Preferably, in step S5, the mass of KMO is 0.8g and the mass of KB is 0.2g.

[0019] Preferably, in step S7, the mass ratio of KMO@C0.2 to the conductive agent and the binder is 8:1:1.

[0020] Compared with related technologies, the preparation method of a high-stability manganese-based oxide potassium-ion battery cathode material provided by the present invention has the following beneficial effects:

[0021] (1) The KMO@C0.2 potassium ion battery electrode prepared by the present invention has high stability. The KMO@C0.2 composite material has excellent specific capacity, cycle life and rate performance. The carbon coating can protect the KMO cathode surface for a long time and is not affected by electrolyte side reactions. It reduces irreversible interfacial reactions and interfacial kinetics. Ball milling reduces the particle size, increases the specific surface area of ​​the material and the active sites for K+ diffusion, thereby greatly increasing the specific capacity.

[0022] (2) The KMO@C0.2 potassium ion battery cathode prepared by the present invention has a discharge specific capacity of 137.9 mA h g-1 at a current density of 20 mA g-1, and has excellent energy storage properties.

[0023] (3) The KMO@C0.2 potassium ion battery cathode prepared by the present invention has excellent cycle performance, and the battery capacity retention rate is ≥81% in 300 cycles.

[0024] (4) The KMO@C0.2 potassium ion battery cathode prepared by the present invention has excellent rate performance. The discharge specific capacity of the KMO@C0.2 cathode is 137.9, 121.1, 110.6, 94.9, 77.2 and 59.8 mAh g−1, respectively. When the applied current density gradually increases from 20, 50, 100, 200, 500 and 1000 mA g−1, the reversible capacity of the KMO@C0.2 composite electrode gradually decreases with the increase of current density. When the current density recovers to 20 mA g−1, the specific capacity recovers to 110.3 mAh g−1, showing excellent rate performance. Attached Figure Description

[0025] Figure 1 shows the process flow chart for preparing KMO@C0.2 as a potassium-ion battery electrode in Example 1 using a two-step process.

[0026] Figure 2 shows the specific capacity of KMO@C0.2 prepared as a potassium-ion battery electrode in Example 1 using a two-step process.

[0027] Figure 3 shows the cycling performance of KMO@C0.2 prepared in Example 1 as a potassium-ion battery electrode at a current density of 1000 mA / g.

[0028] Figure 4 shows the rate performance of KMO@C0.2 prepared in Example 1 as a potassium-ion battery electrode. Detailed Implementation

[0029] Please refer to the following: Figure 1-4 The preparation method of the high-stability manganese-based oxide potassium-ion battery cathode material includes the following steps:

[0030] S1. Take 1.12g of K2CO3 and 1.9275g of MnO2, and grind the two drugs together for 15 minutes.

[0031] S2. Place the uniform powder obtained from grinding into an alumina crucible, then place it in a muffle furnace, and adjust the heating rate to 5℃ min. -1 Heat to 700℃ and keep warm for 5 hours;

[0032] S3. Wait for the muffle furnace to cool down to room temperature. Use a circulating water vacuum pump to filter the black powder from the solid-phase reaction with a large amount of deionized water to remove unreacted K2CO3 and impurities such as potassium manganate.

[0033] S4. Place the washed powder into a vacuum drying oven at 80℃ and dry for at least 8 hours to obtain the precursor material K from the first step of the process. 0.28 MnO2· 0.29 H2O (KMO);

[0034] S5. The second step of the process uses high-energy ball milling. A certain amount of KMO powder and Ketjen Black (KB) powder are mixed and loaded into a ball milling jar. Then, agate balls with an appropriate ball-to-material ratio are added.

[0035] S6. Set the rotation speed and time parameters of the planetary ball mill to ball mill KMO and KB to obtain the final product KMO@C0.2;

[0036] S7, KMO@C0.2, acetylene black, and polyvinylidene fluoride are mixed and dispersed in n-methyl-2-pyridone (NMP), and then ground to form a uniform slurry. The resulting slurry is uniformly coated on the surface of a clean aluminum foil treated with anhydrous ethanol and dried overnight in a vacuum oven at 80°C to obtain a potassium-ion battery positive electrode sheet.

[0037] S8. Using a manual button cell slicing machine, the electrodes were punched into 14 mm diameter discs. The effective mass loading of the cathode was approximately 1.0–2.0 mg cm⁻² per electrode. Metallic potassium, 1 M KPF₆ (EC:DEC = 1:1 Vol%), and glass fiber were used as the anode, electrolyte, and separator, respectively. CR₂O₃₂ coin cells were assembled in an argon-filled glove box, and the electrochemical performance of the prepared electrodes was evaluated.

[0038] In step S1, the molar ratio of K2CO3 to MnO2 is 0.7:1, and 5wt% K2CO3 is added to compensate for the potassium source lost at high temperature.

[0039] The protective gas is any one or more of argon, nitrogen, helium, and neon.

[0040] In step S5, the mass of KMO is 0.8g and the mass of KB is 0.2g.

[0041] In step S7, the mass ratio of KMO@C0.2 to the conductive agent and the binder is 8:1:1.

[0042] This solution is low-cost and has a simple preparation process. First, the prepared KMO, compared to traditional δ-MnO2, introduces water of crystallization, which can enhance the cycle stability of the cathode material. This is a new trend in the development of manganese-based potassium ion cathode materials. Second, the modification method of carbon coating has made corresponding research progress in lithium-ion and sodium-ion batteries, but it is still a blank in potassium-ion batteries. The second step is to innovatively use high-energy ball milling to introduce carbon coating technology into potassium-ion batteries. High-energy ball milling makes KMO particles smaller, increases the specific surface area, and solves the problem of difficult capacity improvement in potassium-ion batteries. The carbon coating avoids direct contact between the electrolyte and KMO, which enhances the cycle stability and rate performance of the cathode material compared to a single solid-phase reaction.

[0043] In this technical solution:

[0044] (1) The carbon coating material used is Ketjen Black;

[0045] (2) The mass ratio of KMO to Ketjen Black is 8:2;

[0046] (3) The rotation speed of the planetary ball mill is 300 rpm, with a forward rotation of 5 min, a pause of 60 s, a reverse rotation of 5 min, and a pause of 60 s;

[0047] (4) The total ball milling time is 6 hours;

[0048] (5) The mass ratio of large, medium and small natural agate balls is 1:1:1;

[0049] (6) The ball-to-material ratio is 20:1.

[0050] Through innovative material formulation and preparation processes, the electrochemical performance of the material is significantly improved while reducing production costs. Its unique microstructure design not only optimizes the material's physicochemical properties but also ensures excellent surface quality and shape stability in the finished product, meeting the comprehensive requirements of high-end applications for high performance, low cost, and aesthetics. Specific advantages are as follows:

[0051] (1) The KMO@C0.2 potassium ion battery electrode prepared by the present invention has high stability. The KMO@C0.2 composite material has excellent specific capacity, cycle life and rate performance. The carbon coating can protect the KMO cathode surface for a long time and is not affected by electrolyte side reactions. It reduces irreversible interfacial reactions and interfacial kinetics. Ball milling reduces the particle size, increases the specific surface area of ​​the material and the active sites for K+ diffusion, thereby greatly increasing the specific capacity.

[0052] (2) KMO@C0.2 particles promote rapid charge transfer through strong interfacial interaction with amorphous carbon via C=O bonds, thereby improving the structural stability of KMO@C0.2 composite electrode.

[0053] (3) The conductive carbon coating can not only provide a good conductive network and enhance the conductivity of electrons, but also buffer the volume expansion during the potassic / depotassic process and effectively reduce the agglomeration of KMO particles.

[0054] (4) The carbon coating prevents MnO2 from coming into direct contact with the electrolyte and inhibits the occurrence of side reactions.

[0055] (5) The two-step process still adheres to the original intention of low cost and high output, making it possible for inexpensive potassium-ion batteries to replace lithium-ion batteries in some energy storage fields.

[0056] (6) The preparation methods of manganese-based potassium ion batteries are no longer limited to transition metal element doping, two-step process and carbon coating, which enrich the modification methods of potassium ion cathode materials.

[0057] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a highly stable manganese-based oxide potassium-ion battery cathode material, characterized in that, Includes the following steps: S1. Take 1.12g of K2CO3 and 1.9275g of MnO2, and grind the two drugs together for 15 minutes. S2. Place the uniform powder obtained from grinding into an alumina crucible, then place it in a muffle furnace, and adjust the heating rate to 5℃ / min. -1 Heat to 700℃ and keep warm for 5 hours; S3. Wait for the muffle furnace to cool down to room temperature. Use a circulating water vacuum pump to filter the black powder from the solid-phase reaction with a large amount of deionized water to remove unreacted K2CO3 and potassium manganate impurities. S4. Place the washed powder into a vacuum drying oven at 80℃ and dry for at least 8 hours to obtain the precursor material K from the first step of the process. 0.28 MnO2· 0.29 H2O; S5. The second step of the process uses a high-energy ball milling process to process a certain amount of K. 0.28 MnO2· 0.29 H2O powder and Ketjen black powder are mixed and placed in a ball mill jar, followed by the addition of agate balls with an appropriate ball-to-material ratio. S6. Set the rotational speed and time parameters of the planetary ball mill, and set K... 0.28 MnO2· 0.29 H2O and Kotjen Black ball milling yielded the final product K. 0.28 MnO2· 0.29 H2O@C0.2; S7, K 0.28 MnO2· 0.29 H2O@C0.2, acetylene black, and polyvinylidene fluoride are mixed and dispersed in NMP, and then ground to form a uniform slurry. The resulting slurry is uniformly coated on the surface of a clean aluminum foil treated with anhydrous ethanol and dried overnight in a vacuum oven at 80°C to obtain a potassium-ion battery positive electrode sheet. S8. Use a manual button cell slicing machine to punch out circular pieces with a diameter of 14mm. The effective mass load of the cathode is 1.0-2.0 mg*cm per electrode. -2 A CR2032 coin cell was assembled in an argon-filled glove box using potassium metal, 1M KPF6, and glass fiber as the anode, electrolyte, and separator, respectively, and the electrochemical performance of the prepared electrode was evaluated.

2. The method for preparing the high-stability manganese-based oxide potassium-ion battery cathode material according to claim 1, characterized in that, In step S5, the K 0.28 MnO2· 0.29 The mass of H2O is 0.8g, and the mass of Ketjen Black is 0.2g.

3. The method for preparing the high-stability manganese-based oxide potassium-ion battery cathode material according to claim 1, characterized in that, In step S7, the K 0.28 MnO2· 0.29 The mass ratio of H2O@C0.2 to conductive agent and binder is 8:1:1.

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