A method for preparing a low-cost potassium-ion battery cathode material using iron elements

Abstract

The application provides a method for preparing a low-cost positive electrode material of a potassium ion battery by using iron elements, and belongs to the field of new energy materials.The specific implementation steps of the method are as follows: (1) performing solvent thermal treatment on raw material powder; (2) performing pre-calcination on the powder obtained in step 1; (3) performing tabletting treatment on the product obtained in step (2); and (4) performing high-temperature calcination on the product obtained in step (3).The positive electrode material prepared by the method has a non-layered structure, and has the advantages of simple process, low cost and suitability for large-scale production, and the electrochemical performance of the positive electrode material applied to the potassium ion battery has great research value.

Description

Technical Field

[0001] This invention relates to the field of new energy materials, and in particular to a non-layered cathode material compound designed and synthesized using iron, a transition metal element that is abundant and inexpensive, and its application as a cathode material in potassium-ion batteries. Background Technology

[0002] In recent years, the use of lithium-ion batteries has expanded from portable electronic products to large-scale energy storage systems, consistently maintaining its dominant position in the energy storage market. However, as market demand for lithium-ion batteries increases, the low abundance and uneven distribution of lithium in the Earth's crust have become increasingly apparent, resulting in very high raw material costs. Furthermore, with the continuous depletion of lithium resources, the market price of lithium is expected to continue rising. Under these circumstances, the academic community has focused extensively on potassium, an element in the same group as lithium. Potassium possesses similar physicochemical properties to lithium, and compared to lithium, it is abundant, evenly distributed, and inexpensive in nature, making it a promising alternative to lithium-ion batteries in energy storage.

[0003] Because the radius of potassium ions is much larger than that of transition metal ions, some transition metals that are not electrochemically active in lithium-ion batteries exhibit electrochemical activity in potassium-ion batteries. Iron, abundant and inexpensive in the Earth's crust, has a variety of valence states, such as +2, +3, +4, and +5, with +4 and +5 being observed during electrochemical processes. For example, the spatial framework composed of K₂O₆ octahedrons and FeO₄ tetrahedrons can serve as a basis for K₂O. + The insertion and extraction of these components provide ample space, potentially enabling the synthesis of electrochemically active, pure iron-based potassium-ion batteries, distinct from common layered materials. These batteries are represented by the chemical formula K0. x Fe y O z Non-layered compound cathode materials. Meanwhile, the above K... x Fe y O z Two-phase composite modification strategies in material systems can further improve their electrochemical performance.

[0004] Current research on pure iron-based materials as cathode materials for potassium-ion batteries indicates that this technology is in its early stages of development, with many issues remaining to be resolved. Among these, the most significant problem is the K... + With a large radius, K... + Repeated insertion and extraction can cause irreversible collapse and distortion of the material structure, which in turn leads to rapid capacity decay and poor cycle performance. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides a method for preparing a low-cost cathode material for potassium-ion batteries using iron elements. The preparation method of the present invention has a simple process and low cost, is suitable for large-scale production, and has great research value for the electrochemical performance exhibited by the cathode material for potassium-ion batteries.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a low-cost cathode material for potassium-ion batteries using iron elements, the method comprising the following steps:

[0008] (1) According to the chemical composition K x FeO2, where 0 < x < 1, calculate the mass ratio, weigh the raw materials K2CO3 and Fe2O3 and put them into a polytetrafluoroethylene inner liner for solvothermal pretreatment to obtain a precursor, react at 190 - 200 °C for 8 - 10 h, and dry the sample after centrifugation;

[0009] (2) Put the powder dried in step (1) into a mortar and grind it evenly, then put it into a crucible and place it in a muffle furnace for pre-calcination in an air atmosphere, heat up to 340 - 350 °C and keep warm for 2.5 - 3 h;

[0010] (3) Mix the powder obtained in step (2) evenly again, perform tablet pressing, and put the pressed tablet into a porcelain boat;

[0011] (4) Put the porcelain boat in step (3) into a muffle furnace and calcine it in an air atmosphere, heat up to 850 - 950 °C and keep warm for 8 - 12 h to obtain a KFeO2 / K x Fe y O z biphasic composite or KFeO2-phase cathode material for potassium-ion batteries; the cathode material for potassium-ion batteries is a non-layered structure.

[0012] Further, when calculating the mass of the raw materials in step (1), the actual amount of K used is 5% more than the theoretical calculation.

[0013] More preferably, x = 0.3 in the chemical composition in step (1) is the best.

[0014] Further, the solvent used in the solvothermal treatment in step (1) is anhydrous ethanol, methanol or ethylene glycol, and the solvent dosage is 80% of the volume of the polytetrafluoroethylene inner liner.

[0015] More preferably, the solvent in step (1) is anhydrous ethanol as the best.

[0016] Further, the drying condition in step (1) is to dry at a temperature of 80 - 90 °C for 10 - 12 h.

[0017] Furthermore, the heating rate of the pre-calcination in step (2) is 3-5℃ / min.

[0018] Furthermore, in step (3), the tableting process should be carried out under pressure of 0.6-0.8 MPa for 2-8 minutes.

[0019] More preferably, the pressure in step (3) is 0.6 MPa.

[0020] More preferably, the pressure holding time in step (3) is 5 minutes.

[0021] Furthermore, the heating rate in step (4) is 5-10℃ / min.

[0022] More preferably, the heating temperature in step (4) is 850°C.

[0023] More preferably, the heat preservation time in step (4) is 8 hours.

[0024] This invention also provides the application of the cathode material prepared by the method, specifically the KFeO2 / K x Fe y O z Dual-phase composite or KFeO2 phase materials are used to make positive electrode sheets for potassium-ion batteries;

[0025] When preparing the positive electrode sheet, KFeO2 / K x Fe y O z The mass ratio of the dual-phase composite or KFeO2 phase material, the mass of acetylene black, and the mass of the binder is 6-7:0.8-1:0.8-1.

[0026] Furthermore, the adhesive is polyvinylidene fluoride (PVDF), and N-methyl-2-pyridinyl ketone (NMP) with a mass fraction of 4-6 wt% is used as the solvent.

[0027] More preferably, KFeO2 / K x Fe y O z The mass ratio of the duplex composite or KFeO2 phase material, the mass of acetylene black, and the mass of the binder is 7:1:1.

[0028] The present invention also provides the positive electrode sheet for fabricating a CR2032 coin cell, wherein the positive electrode sheet is coated onto an aluminum foil current collector during fabrication, with a loading of 0.7-0.9 mg / cm³. 2 .

[0029] More preferably, when assembled into a CR2032 coin cell, the positive electrode material loading is 0.8 mg / cm³. 2 .

[0030] The beneficial technical effects of this invention are as follows:

[0031] 1. This invention obtains KO columns of different combinations of KO6 octahedrons and FeO4 tetrahedra by simply controlling the potassium content and applying an appropriate synthesis method. x Fe y O z Phase materials, such as KFeO2, KFe 11 O 17 The aim is to obtain a series of novel pure iron-based non-layered potassium-ion battery cathode materials with excellent electrochemical performance, including K5FeO4, KFe5O8, K4Fe2O5, K2Fe4O7, K3FeO3, K4Fe2O5, and K3FeO2.

[0032] 2. This invention provides an improved and optimized high-temperature solid-state method combined with a solvothermal method for preparing low-cost iron-based potassium-ion battery cathode materials. Using Fe2O3 as the iron source and K2CO3 as the potassium source, a precursor is first prepared via a solvothermal method, then the precursor is pre-calcined, and finally the pre-sintered sample is pressed into tablets and calcined at high temperature.

[0033] 3. The precursor material prepared by this method under high temperature and high pressure using a solvothermal method has a nanoscale particle size, which increases the contact area between raw materials; the pre-calcination method is used to reduce impurities on the material surface; and the tableting process is used to shorten the reaction distance of ions and enhance the crystallinity of the material.

[0034] 4. The KFeO2 / K prepared by this invention x Fe y O z The precursor of dual-phase composite or KFeO2 phase cathode material is obtained by solvothermal treatment of raw materials. This method can reduce the particle size of the material, increase the porosity between materials, and thus improve the structural stability.

[0035] 5. The present invention provides a satisfactory first-cycle discharge capacity and structural stability by assembling a half-cell using potassium foil as the negative electrode material, which is sufficient to prove the feasibility of iron-based materials as positive electrode materials for potassium-ion batteries and has great research value.

[0036] 6. The raw material used in this invention is Fe, a transition metal that is abundant in the Earth's crust and inexpensive, used to prepare KFeO2 / K x Fe y O z The application of dual-phase composite or KFeO2 phase materials in potassium-ion batteries breaks the status quo of traditional high-cost cathode materials, proving the feasibility of low-cost iron-based cathode materials. Furthermore, the preparation process is simple and highly controllable, meeting the requirements of the low-cost, large-scale energy storage market. Attached Figure Description

[0037] Figure 1 To prepare KFeO2 / K x Fe y O z Process flow diagram of dual-phase composite or KFeO2 phase cathode materials;

[0038] Figure 2 The image shows the XRD pattern of the cathode material prepared in Example 1 of this invention.

[0039] Figure 3 This is a SEM image of the cathode material prepared in Example 1 of this invention;

[0040] Figure 4 The first-cycle discharge capacity diagram of the positive electrode material prepared in Example 1 of this invention;

[0041] Figure 5 This is a cycling diagram of the positive electrode material prepared in Example 1 of this invention;

[0042] Figure 6 The image shows the XRD pattern of the cathode material prepared in Example 2 of this invention.

[0043] Figure 7 This is a SEM image of the cathode material prepared in Example 2 of this invention;

[0044] Figure 8 The first-cycle discharge capacity diagram of the positive electrode material prepared in Example 2 of this invention;

[0045] Figure 9 This is a cycling diagram of the positive electrode material prepared in Example 2 of this invention;

[0046] Figure 10 The image shows the XRD pattern of the cathode material prepared in Example 3 of this invention.

[0047] Figure 11 This is a SEM image of the cathode material prepared in Example 3 of this invention;

[0048] Figure 12 This is a diagram showing the first-cycle discharge capacity of the cathode material prepared in Example 3 of this invention;

[0049] Figure 13 This is a cycling diagram of the positive electrode material prepared in Example 3 of this invention;

[0050] Figure 14 The image shows the XRD pattern of the cathode material prepared in Example 4 of this invention.

[0051] Figure 15 This is a SEM image of the cathode material prepared in Example 4 of this invention;

[0052] Figure 16 This is a diagram showing the first-cycle discharge capacity of the cathode material prepared in Example 4 of this invention;

[0053] Figure 17 This is a cycling diagram of the positive electrode material prepared in Example 4 of this invention;

[0054] Figure 18 The image shows the XRD pattern of the cathode material prepared in Example 5 of this invention.

[0055] Figure 19 This is a SEM image of the cathode material prepared in Example 5 of this invention;

[0056] Figure 20 This is a diagram showing the first-cycle discharge capacity of the cathode material prepared in Example 5 of this invention;

[0057] Figure 21 This is a cycling diagram of the positive electrode material prepared in Example 5 of this invention;

[0058] Figure 22 The image shows the XRD pattern of the cathode material prepared in Example 6 of this invention.

[0059] Figure 23 This is a SEM image of the cathode material prepared in Example 6 of this invention;

[0060] Figure 24 This is a diagram showing the first-cycle discharge capacity of the cathode material prepared in Example 6 of this invention;

[0061] Figure 25 This is a cycling diagram of the positive electrode material prepared in Example 6 of this invention;

[0062] Figure 26 The image shows the XRD pattern of the cathode material prepared in Example 7 of this invention.

[0063] Figure 27 This is a SEM image of the cathode material prepared in Example 7 of this invention;

[0064] Figure 28 The first-cycle discharge capacity diagram of the positive electrode material prepared in Example 7 of this invention;

[0065] Figure 29 This is a cycling diagram of the positive electrode material prepared in Example 7 of this invention;

[0066] Figure 30 The image shows the XRD pattern of the cathode material prepared in Example 8 of this invention.

[0067] Figure 31 This is a SEM image of the cathode material prepared in Example 8 of this invention;

[0068] Figure 32 This is a diagram showing the first-cycle discharge capacity of the cathode material prepared in Example 8 of this invention;

[0069] Figure 33 This is a cycling diagram of the positive electrode material prepared in Example 8 of this invention;

[0070] Figure 34 The image shows the XRD pattern of the cathode material prepared in Example 9 of this invention.

[0071] Figure 35 This is a SEM image of the cathode material prepared in Example 9 of this invention.

[0072] Figure 36 This is a diagram showing the first-cycle discharge capacity of the cathode material prepared in Example 9 of this invention;

[0073] Figure 37 This is a cycling diagram of the positive electrode material prepared in Example 9 of this invention; Detailed Implementation

[0074] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0075] Example 1:

[0076] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0077] (1) According to the chemical composition K 0.1 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (0.1451 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 ml polytetrafluoroethylene liner. 40 mL of anhydrous ethanol was added, and the mixture was reacted at 190 °C for 8 h by rotation. After centrifugation, the sample was dried in an 80 °C oven for 10 h.

[0078] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. The temperature is raised to 340℃ and held for 2.5h. The pre-calcine heating rate is 3℃ / min.

[0079] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.6 MPa for 2 minutes.

[0080] (4) Place the porcelain boat from step (3) into a muffle furnace and calcine it in air atmosphere. Heat the furnace to 850℃ and hold for 8 hours to obtain KFeO2 / KFe. 11 O 17 The dual-phase composite potassium-ion battery cathode material has a heating rate of 5℃ / min.

[0081] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0082] Weigh out KFeO2 / KFe according to a mass ratio of 6:1:1. 11 O 17 A black, viscous slurry was formed by thoroughly mixing a biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, or NMP, as a solvent). The resulting active material was then uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.7 mg / cm³. 2 KFeO2 / KFe can then be obtained. 11 O 17 The above experiments were all conducted in a glove box for the positive electrode sheet of potassium-ion batteries made of dual-phase composite materials.

[0083] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0084] The XRD and SEM characterization of the material obtained in Example 1 are as follows: Figure 2 , 3 As shown, the capacity and 200 cycles are as follows: Figure 4 , 5 As shown.

[0085] Example 2:

[0086] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0087] (1) According to the chemical composition K 0.2 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (0.2902 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 mL polytetrafluoroethylene liner. 40 mL of methanol was added, and the mixture was reacted at 195 °C for 9 h using a rotary reaction apparatus. After centrifugation, the sample was dried in an 85 °C oven for 11 h.

[0088] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. The temperature is raised to 345℃ and held for 2.75h. The pre-calcine heating rate is 4℃ / min.

[0089] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.7 MPa for 5 minutes.

[0090] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 900℃ and hold it for 10 hours to obtain the KFeO2 / K5FeO4 dual-phase composite potassium-ion battery cathode material. The heating rate is 7.5℃ / min.

[0091] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0092] KFeO2 / K5FeO4 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 7:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.8 mg / cm³. 2 Thus, the positive electrode of potassium-ion battery made of KFeO2 / K5FeO4 dual-phase composite material can be obtained. All the above experiments were carried out in a glove box.

[0093] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0094] The XRD and SEM characterization of the material obtained in Example 2 are as follows: Figure 6 , 7 As shown, the capacity and 200 cycles are as follows: Figure 8 , 9 As shown.

[0095] Example 3:

[0096] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0097] (1) According to the chemical composition K 0.3The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (0.4353 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 ml polytetrafluoroethylene liner. 40 mL of ethylene glycol was added, and the mixture was reacted at 200 °C for 10 h using a rotary evaporator. After centrifugation, the sample was dried in a 90 °C oven for 12 h.

[0098] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. Heat it to 350℃ and hold it for 3 hours. The pre-calcine heating rate is 5℃ / min.

[0099] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.8 MPa for 8 minutes.

[0100] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 950℃ and hold it for 12 hours to obtain the KFeO2 / KFe5O8 dual-phase composite potassium-ion battery cathode material. The heating rate is 10℃ / min.

[0101] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0102] KFeO2 / KFe5O8 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 8:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.9 mg / cm³. 2 Thus, the positive electrode sheet for potassium-ion batteries made of KFeO2 phase material can be obtained. All the above experiments were carried out in a glove box.

[0103] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0104] The XRD and SEM characterization of the material obtained in Example 3 are as follows: Figure 10 , 11 As shown, the capacity and 200 cycles are as follows: Figure 12 , 13 As shown.

[0105] Example 4:

[0106] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0107] (1) According to the chemical composition K 0.4 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (0.5804 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 ml polytetrafluoroethylene liner. 40 mL of anhydrous ethanol was added, and the mixture was reacted at 190 °C for 8 h by rotation. After centrifugation, the sample was dried in an 80 °C oven for 10 h.

[0108] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. The temperature is raised to 345℃ and held for 2.5h. The pre-calcine heating rate is 3℃ / min.

[0109] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.6 MPa for 2 minutes.

[0110] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 850℃ and hold it for 8 hours to obtain the KFeO2 / K4Fe2O5 dual-phase composite potassium-ion battery cathode material. The heating rate is 5℃ / min.

[0111] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0112] KFeO2 / K4Fe2O5 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 6:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.7 mg / cm³. 2 Thus, the positive electrode of potassium-ion battery made of KFeO2 / K4Fe2O5 dual-phase composite material can be obtained. All the above experiments were carried out in a glove box.

[0113] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0114] The XRD and SEM characterization of the material obtained in Example 4 are as follows: Figure 14 , 15 As shown, the capacity and 200 cycles are as follows: Figure 16 , 17 As shown.

[0115] Example 5:

[0116] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0117] (1) According to the chemical composition K 0.5 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (0.7256 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 mL polytetrafluoroethylene liner. 40 mL of methanol was added, and the mixture was reacted at 195 °C for 9 h using a rotary reaction apparatus. After centrifugation, the sample was dried in an 85 °C oven for 11 h.

[0118] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. The temperature is raised to 345℃ and held for 2.75h. The pre-calcine heating rate is 4℃ / min.

[0119] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.7 MPa for 5 minutes.

[0120] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 900℃ and hold it for 10 hours to obtain the KFeO2 / K2Fe4O7 dual-phase composite potassium-ion battery cathode material. The heating rate is 7.5℃ / min.

[0121] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0122] KFeO2 / K2Fe4O7 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 7:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.8 mg / cm³. 2 Thus, the positive electrode of potassium-ion battery made of KFeO2 / K2Fe4O7 dual-phase composite material can be obtained. All the above experiments were carried out in a glove box.

[0123] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0124] The XRD and SEM characterization of the material obtained in Example 5 are as follows: Figure 18 , 19 As shown, the capacity and 200 cycles are as follows: Figure 20 ,21 As shown.

[0125] Example 6:

[0126] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0127] (1) According to the chemical composition K 0.6 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (0.8706 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 mL polytetrafluoroethylene liner. 40 mL of ethylene glycol was added, and the mixture was reacted at 200 °C for 10 h using a rotary reactor. After centrifugation, the sample was dried in a 90 °C oven for 12 h.

[0128] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. Heat it to 350℃ and hold it for 3 hours. The pre-calcine heating rate is 5℃ / min.

[0129] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.8 MPa for 3 minutes.

[0130] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 950℃ and hold it for 12 hours to obtain the KFeO2 / K3FeO3 dual-phase composite potassium-ion battery cathode material. The heating rate is 10℃ / min.

[0131] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0132] KFeO2 / K3FeO3 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 8:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.9 mg / cm³. 2 Thus, the positive electrode of potassium-ion battery made of KFeO2 / K3FeO3 dual-phase composite material can be obtained. All the above experiments were carried out in a glove box.

[0133] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0134] The XRD and SEM characterization of the material obtained in Example 6 are as follows: Figure 22 , 23 As shown, the capacity and 200 cycles are as follows: Figure 24 , 25 As shown.

[0135] Example 7:

[0136] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0137] (1) According to the chemical composition K 0.7 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (1.0158 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 mL polytetrafluoroethylene liner. 40 mL of anhydrous ethanol was added, and the mixture was reacted at 190 °C for 8 h by rotation. After centrifugation, the sample was dried in an 80 °C oven for 10 h.

[0138] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. The temperature is raised to 340℃ and held for 2.5h. The pre-calcine heating rate is 3℃ / min.

[0139] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.6 MPa for 2 minutes.

[0140] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 850℃ and hold it for 8 hours to obtain the KFeO2 / K4Fe2O5 dual-phase composite potassium-ion battery cathode material. The heating rate is 5℃ / min.

[0141] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0142] KFeO2 / K4Fe2O5 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 6:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.7 mg / cm³. 2 Thus, the positive electrode of potassium-ion battery made of KFeO2 / K4Fe2O5 dual-phase composite material can be obtained. All the above experiments were carried out in a glove box.

[0143] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0144] The XRD and SEM characterization of the material obtained in Example 7 are as follows: Figure 26 , 27 As shown, the capacity and 200 cycles are as follows: Figure 28 , 29 As shown.

[0145] Example 8:

[0146] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0147] (1) According to the chemical composition K 0.8 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (1.1608 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 mL polytetrafluoroethylene liner. 40 mL of methanol was added, and the mixture was reacted at 195 °C for 9 h by rotation. After centrifugation, the sample was dried in an 85 °C oven for 11 h.

[0148] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. The temperature is raised to 345℃ and held for 2.75h. The pre-calcine heating rate is 4℃ / min.

[0149] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.7 MPa for 5 minutes.

[0150] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 900℃ and hold it for 10 hours to obtain the KFeO2 / K3FeO2 dual-phase composite potassium-ion battery cathode material. The heating rate is 7.5℃ / min.

[0151] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0152] KFeO2 / K3FeO2 biphase composite material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 7:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.8 mg / cm³. 2Thus, the positive electrode of potassium-ion battery made of KFeO2 / K3FeO2 dual-phase composite material can be obtained. All the above experiments were carried out in a glove box.

[0153] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0154] The XRD and SEM characterization of the material obtained in Example 8 are as follows: Figure 30 , 31 As shown, the capacity and 200 cycles are as follows: Figure 32 , 33 As shown.

[0155] Example 9:

[0156] I. This embodiment provides a method for preparing low-cost, non-layered potassium-ion battery cathode materials using iron. The specific steps are as follows: Figure 1 As shown:

[0157] (1) According to the chemical composition K 0.9 The calculated mass ratio of FeO2 (K excess 5%) was determined. Pre-dried K2CO3 (1.3059 g) and Fe2O3 (1.5969 g) were weighed and placed in a 50 mL polytetrafluoroethylene liner. 40 mL of ethylene glycol was added, and the mixture was reacted at 200 °C for 10 h using a rotary evaporator. After centrifugation, the sample was dried in a 90 °C oven for 12 h.

[0158] (2) Grind and disperse the centrifugally dried material evenly, put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere. Heat it to 350℃ and hold it for 3 hours. The pre-calcine heating rate is 5℃ / min.

[0159] (3) Mix the powder obtained in step (2) again until uniform, and then compress it into tablets. Place the compressed tablets into a ceramic boat and press them at 0.8 MPa for 8 minutes.

[0160] (4) Place the ceramic boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat it to 950℃ and hold it for 12 hours to obtain the KFeO2 phase potassium ion battery cathode material. The heating rate is 10℃ / min.

[0161] II. This embodiment also provides a method for using the above-mentioned materials to manufacture the positive electrode sheet of a potassium-ion battery, the specific steps of which are as follows:

[0162] KFeO2 phase material, acetylene black, and PVDF (using 5 wt% N-methyl-2-pyridinyl ketone, i.e., NMP, as solvent) were weighed according to a mass ratio of 8:1:1. After thoroughly stirring to form a black, viscous slurry, the resulting active material was uniformly loaded onto a vacuum-dried aluminum foil current collector, with a loading of approximately 0.9 mg / cm³. 2 Thus, the positive electrode sheet for potassium-ion batteries made of KFeO2 phase material can be obtained. All the above experiments were carried out in a glove box.

[0163] A CR2032 coin cell was assembled using a potassium sheet as the negative electrode and potassium hexafluorophosphate as the electrolyte, and its structure and electrochemical characterization were performed.

[0164] The XRD and SEM characterization of the material obtained in Example 9 are as follows: Figure 34 , 35 As shown, the capacity and 200 cycles are as follows: Figure 36 , 37 As shown.

[0165] Test example:

[0166] (1) The XRD patterns of the cathode materials obtained from Examples 1 to 9 show that when x = 0.3-0.8, the ratio of KFeO2 / K x Fe y O z In the two-phase composite, when x = 0.9, only the KFeO2 phase exists.

[0167] (2) SEM images of the cathode materials obtained in Examples 1 to 9 show that the sample surfaces are smooth and have good crystallinity. With the increase of the stoichiometric ratio of potassium (K), the primary grains of the material gradually become larger and thicker. Larger grains increase the K content during charging and discharging. + This reduces the diffusion path and diffusion resistance, thereby decreasing the discharge specific capacity and cycle performance of the cathode material.

[0168] (3) Electrical performance test: When loading the battery, the potassium sheet is used as the negative electrode and the positive electrode material is used to form a potassium-ion battery. The loaded potassium-ion battery is subjected to the following performance tests.

[0169] Capacity test: During the test, the battery is at room temperature. The loaded battery is then mounted on the LAND battery test system. The charge and discharge voltage range is set to 1.5-4.0V and the current density is 20mA / g.

[0170] Cyclic testing: During testing, the battery is kept at room temperature. The loaded battery is then mounted on the LAND battery testing system. The charge and discharge voltage range is set to 1.5-4.0V, and the main test current density is 20mA / g.

[0171] The test results are as follows:

[0172] Example 1 provides an initial discharge capacity of 88 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 80.1% after 200 cycles.

[0173] Example 2 provides an initial discharge capacity of 86 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 81% after 200 cycles.

[0174] Example 3 provides an initial discharge capacity of 91 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 83.5% after 200 cycles.

[0175] Example 4 provides an initial discharge capacity of 84 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 77% after 200 cycles.

[0176] Example 5 provides an initial discharge capacity of 81 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 74.3% after 200 cycles.

[0177] Example 6 provides an initial discharge capacity of 85 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 76.8% after 200 cycles.

[0178] Example 7 provides an initial discharge capacity of 79 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 69.5% after 200 cycles.

[0179] Example 8 provides an initial discharge capacity of 82 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 68.4% after 200 cycles.

[0180] Example 9 provides an initial discharge capacity of 85 mAh / g at a current density of 20 mA / g and a voltage range of 1.5–4 V; the capacity retention rate is 67.5% after 200 cycles.

[0181] Comparative example:

[0182] The inventors further simplified Example 9 by employing a single high-temperature solid-state method to prepare the KFeO2 phase material. Specifically, the solvothermal method for preparing the precursor was omitted. Instead, the raw materials K2CO3 and Fe2O3 were mixed and calcined under an Ar atmosphere, heated to 950°C and held for 12 hours to obtain the dark green KFeO2 phase potassium-ion battery cathode material. The heating rate was 10°C / min.

[0183] When the single KFeO2 phase material synthesized by the above-mentioned high-temperature solid-state method is used as a positive electrode material for potassium-ion batteries, its capacity is halved after only 50 cycles, and the retention rate is only 50%, making it impossible to cycle up to 200 cycles.

[0184] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, and for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for preparing low-cost potassium-ion battery cathode materials using iron, characterized in that, The method includes the following steps: (1) According to the chemical composition K x FeO2, where 0 < x < 1, calculate the mass ratio. Weigh the raw materials K2CO3 and Fe2O3 and put them into a polytetrafluoroethylene inner liner for solvothermal pretreatment to obtain a precursor. React at 190 - 200 °C for 8 - 10 h, dry the sample after centrifugation; (2) Grind the dried powder from step (1) into a mortar until uniform, then put it into a crucible, place it in a muffle furnace, and pre-calcine it in an air atmosphere, raising the temperature to 340-350℃ and holding it for 2.5-3 hours. (3) Mix the powder obtained in step (2) again until it is uniform, compress it into tablets, and put the compressed tablets into a ceramic boat. (4) Place the porcelain boat from step (3) into a muffle furnace and calcine it in an air atmosphere. Heat the furnace to 850-950℃ and hold for 8-12 hours to obtain KFeO2 / K x Fe y O z Dual-phase composite or KFeO2 phase potassium-ion battery cathode material; the potassium-ion battery cathode material has a non-layered structure.

2. The method according to claim 1, characterized in that, In step (1), when calculating the mass of the raw material, the actual amount of K used should be 5% more than the theoretically calculated amount.

3. The method according to claim 1, characterized in that, The solvent used in the solvent heat treatment in step (1) is anhydrous ethanol, methanol or ethylene glycol, and the amount of solvent used is 80% of the volume of the polytetrafluoroethylene liner.

4. The method according to claim 1, characterized in that, The drying conditions described in step (1) are drying at 80-90℃ for 10-12 hours.

5. The method according to claim 1, characterized in that, The heating rate for the pre-calcination in step (2) is 3-5℃ / min.

6. The method according to claim 1, characterized in that, When performing tablet compression in step (3), the pressure should be maintained at 0.6-0.8 MPa for 2-8 minutes.

7. The method according to claim 1, characterized in that, The heating rate in step (4) is 5-10℃ / min.

8. The application of the cathode material prepared by the method according to any one of claims 1-7, characterized in that, The prepared KFeO2 / K x Fe y O z Dual-phase composite or KFeO2 phase materials are used to make positive electrode sheets for potassium-ion batteries; When preparing the positive electrode sheet, KFeO2 / K x Fe y O z The mass ratio of the dual-phase composite or KFeO2 phase material, the mass of acetylene black, and the mass of the binder is 6-7:0.8-1:0.8-1.

9. The application according to claim 8, characterized in that, The adhesive is polyvinylidene fluoride (PVDF), and N-methyl-2-pyridinyl ketone (NMP) with a mass fraction of 4-6 wt% is used as the solvent.

10. The application according to claim 8, characterized in that, The positive electrode sheet is used to manufacture CR2032 coin cells. During preparation, the positive electrode sheet is coated onto an aluminum foil current collector with a loading of 0.7-0.9 mg / cm³. 2 .

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