A potassium ion battery positive electrode active material, a positive electrode material, and a preparation method and application thereof

Abstract

The application provides a potassium ion battery positive electrode active material, a positive electrode material and a preparation method and application thereof. x A 1‑y‑z B y C z O 2‑m F m , 0 < x < 1, 0 <= y <= 0.5, 0 <= z <= 0.5, 0 <= m <= 0.5, and m and y, z are not 0 at the same time; A is selected from at least one of Co and Mn; B is selected from at least one of Zn, Ni, Mg and Cu; and C is selected from at least one of Cr, Fe, Ti and Li. The potassium ion battery positive electrode material prepared by using the positive electrode active material provided by the application can effectively solve the problems of unstable structure, complex phase change and capacity attenuation of the K x AO2 type potassium ion battery positive electrode material, and the positive electrode active material has wide application prospect and advantages. The potassium ion battery provided by the application is expected to be a new type of energy storage device, is suitable for large-scale energy storage equipment, and has good commercial application prospect.

Description

Technical Field

[0001] The present invention relates to the field of positive electrode materials for rechargeable batteries, and particularly to a positive electrode active material for potassium ion batteries, a positive electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] At present, lithium ion batteries have characteristics such as high capacity, high energy density and long cycle life, and are widely used in fields such as portable electronic devices and electric vehicles. However, the resource reserves of lithium element in the earth's crust are limited and the regional distribution is uneven, making the production cost of lithium ion batteries increasingly expensive, and the application of lithium ion batteries in large-scale energy storage systems is severely restricted. Therefore, developing new rechargeable batteries with the advantages of rich resources and low prices has become the key to promoting the practical application of rechargeable batteries in large-scale energy storage devices. Compared with lithium element, which accounts for 0.0017wt% of the total amount of crustal elements, potassium element, which accounts for 2.09wt% of the total amount of crustal elements, has rich resource reserves, revealing the potential price advantage of rechargeable potassium ion batteries. At the same time, the oxidation-reduction potential of K

[0004] / K is about -2.93V vs. standard hydrogen electrode, which is very close to the oxidation-reduction potential of Li + / Li (-3.04V vs. standard hydrogen electrode). Therefore, potassium ion batteries can provide a relatively high energy density.

[0003] The positive electrode material of potassium ion batteries is a layered transition metal oxide. During the charge and discharge process, continuous insertion / extraction of potassium ions usually causes severe slippage of the transition metal layer, inducing a complex phase transition process, thereby causing irreversible structural damage to the positive electrode material, which severely restricts the development and application of this type of positive electrode material. Taking the layered transition metal oxide K x MnO2 (0 < x < 1) as an example, it has advantages such as high specific capacity, high energy density, environmental friendliness, and low price. However, during the charge and discharge process, this type of positive electrode material has a complex phase transition process, which is likely to cause serious structural damage and rapid capacity decay. The complex phase transition process is mainly caused by the continuous insertion / extraction of potassium ions with a relatively large ionic radius in the material. During the insertion / extraction process of potassium ions, the volume change is relatively large, which is likely to cause severe slippage of the transition metal layer and even serious structural decay. Especially, the high-spin Mn 3+ in the transition metal layer has a strong Jahn-Teller effect, which will cause severe lattice distortion, reduce the stability of the lattice structure, and is prone to complex phase transitions. Therefore, the complex phase transition process and irreversible structural decay are the main challenges faced by the positive electrode materials of potassium ion batteries.

[0004] To solve the problems of unstable structure, complex phase transformation, and capacity decay of layered transition metal oxide cathode active materials in existing potassium-ion batteries, cation doping or substitution in the transition metal layer is an effective method to stabilize the lattice structure, inhibit phase transformation, and improve electrochemical performance. However, the relatively large K + radius usually causes drastic changes in the unit cell parameters, and it is still difficult to completely inhibit the phase transformation process at high potentials even if doping or substitution of transition metals (such as Fe, Co, etc.) is successfully achieved. For example, in the P2-type K 0.65 Fe 0.5 Mn 0.5 O2 cathode material, there are still multiple phase transformation processes of complex P2 phase, OP4 phase, and O2 phase during charge and discharge. Especially the generation of the O2 phase is usually accompanied by drastic slip of the transition metal layer, which is extremely likely to cause irreversible decay of the lattice structure, resulting in rapid capacity decay. SUMMARY OF THE INVENTION

[0005] The present invention provides a cathode active material for a potassium-ion battery, a cathode material, and a preparation method and application thereof.

[0006] The present invention provides the following technical solutions:

[0007] The present invention provides a cathode active material, and the chemical formula of the cathode active material is: K x A 1-y-z B y C z O 2-m F m , where 0 < x < 1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ m ≤ 0.5, and m, y, and z are not simultaneously 0. In the present invention, m, y, and z not being simultaneously 0 means that when m is 0, y and z are not 0; when y and z are 0, m is not 0.

[0008] Preferably, the cathode active material is a P2-type layered transition metal oxide.

[0009] According to an embodiment of the present invention, A is selected from at least one of Co and Mn. Preferably, A is selected from Mn.

[0010] According to an embodiment of the present invention, B is selected from at least one of Zn, Ni, Mg, and Cu. Preferably, B is selected from Ni and / or Mg. Preferably, B is selected from Ni.

[0011] According to an embodiment of the present invention, C is selected from at least one of Cr, Fe, Ti, and Li. Preferably, C is selected from Fe and / or Ti. Preferably, C is selected from Ti. <0000​According to an embodiment of the present invention, 0.2 ≤ x ≤ 0.8. Preferably, 0.4 ≤ x ≤ 0.7. More preferably, 0.6 ≤ x ≤ 0.7.

[0013] According to an embodiment of the present invention, 0.05 ≤ y ≤ 0.3. Preferably, 0.08 ≤ y ≤ 0.2. Preferably, 0.1 ≤ y ≤ 0.12.

[0014] According to an embodiment of the present invention, 0.02 ≤ z ≤ 0.25. Preferably, 0.05 ≤ y ≤ 0.15. More preferably, 0.08 ≤ y ≤ 0.12.

[0015] According to an embodiment of the present invention, 0.01 ≤ m ≤ 0.3. Preferably, 0.02 ≤ m ≤ 0.2. Preferably, 0.05 ≤ m ≤ 0.15.

[0016] According to an embodiment of the present invention, the crystal phase structure of the positive electrode active material is a hexagonal P2 phase with a space group of P63 / mmc.

[0017] According to an embodiment of the present invention, the particle size of the positive electrode active material is 0.1-1 μm.

[0018] According to an embodiment of the present invention, the lattice spacing of the positive electrode active material is For example,

[0019] According to an exemplary embodiment of the present invention, the positive electrode active material is K. 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O2, K 0.67 Mn 0.78 Ni 0.22 O2, K 0.67 Mn 0.78 Ti 0.22 O2, K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.98 F 0. 02 K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.95 F 0.05 K 0.67 Mn0.78 Ni 0.11 Ti 0.11 O 1.92 F 0.08 、or K 0.67 Mn 0.78 Ni 0.11 Ti 0.1 1O 1.85 F 0.15 .

[0020] The present invention also provides a method for preparing the above-mentioned positive electrode active material, the method comprising the following steps:

[0021] The positive electrode active material is prepared by mixing, pressing, and calcining the raw materials.

[0022] According to an embodiment of the present invention, the raw materials include metal carbonates, metal hydroxides, metal oxides, and / or metal fluorides. Preferably, the feed ratio (e.g., molar ratio) of the raw materials satisfies the stoichiometry required for each element in the positive electrode active material, wherein the positive electrode active material has the definition described above.

[0023] Preferably, the metal carbonate is selected from alkali metal carbonates. Exemplarily, the metal carbonate is selected from potassium carbonate and / or lithium carbonate.

[0024] Preferably, the metal hydroxide is selected from alkali metal hydroxides. For example, the metal hydroxide is selected from potassium hydroxide.

[0025] Preferably, the metal oxide includes an oxide of metal A, an oxide of metal B, and / or an oxide of metal C.

[0026] Preferably, the metal fluoride includes a fluoride of metal A.

[0027] Preferably, the oxide of metal A is selected from oxides of manganese and / or oxides of cobalt. Exemplarily, the oxide of metal A is selected from at least one of manganese trioxide, manganese dioxide, and cobalt tetroxide.

[0028] Preferably, the oxide of metal B is selected from at least one of zinc oxide, nickel oxide, magnesium oxide, and copper oxide.

[0029] Preferably, the oxide of metal C is selected from at least one of chromium oxide, iron oxide, ferrous oxide, and titanium dioxide.

[0030] Preferably, the fluoride of metal A is selected from potassium fluoride.

[0031] According to an embodiment of the present invention, the mixing specifically includes uniformly mixing the raw materials by high-energy ball milling. Preferably, the high-energy ball milling is carried out in a high-energy ball mill.

[0032] Preferably, during ball milling, the radius of the milling beads is 1-8 mm, more preferably 3-6 mm, for example 5 mm.

[0033] Preferably, the high-energy ball mill has a rotational speed of 100-1200 r / min, more preferably 300-900 r / min, for example 450 r / min.

[0034] Preferably, the ball milling time is 2-24 hours, more preferably 6-15 hours, for example 12 hours.

[0035] Preferably, the high-energy ball milling is carried out in an atmosphere of any one of air, argon, nitrogen, and oxygen, preferably air or oxygen, for example, oxygen.

[0036] According to an embodiment of the present invention, the tableting specifically includes pressing the mixed raw materials into tablets using a tableting machine. Preferably, the tablets are round tablets. Preferably, the diameter of the round tablets is 6-15 mm, more preferably 10 mm. Preferably, the thickness of the round tablets is 0.5-5 mm, more preferably 2 mm.

[0037] According to an embodiment of the present invention, the calcination specifically includes calcining the compressed tablet. Preferably, the calcination is carried out in a muffle furnace, more preferably in a programmed temperature-controlled muffle furnace. Preferably, the heating rate of the calcination is 1-10°C / min, more preferably 2-5°C / min, for example, 3°C / min.

[0038] Preferably, the calcination temperature is 200-1500℃, more preferably 400-1300℃, for example 400℃, 600℃, 800℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, or 1300℃. More preferably, the calcination temperature is 900-1100℃.

[0039] Preferably, the calcination time is 6-24 hours, and more preferably 12 hours.

[0040] The present invention also provides the application of the above-mentioned positive electrode active material in energy storage devices, for example, in the positive electrode material of energy storage devices. Preferably, the energy storage device is a potassium-ion battery.

[0041] The present invention also provides a positive electrode material, wherein the positive electrode material comprises the above-mentioned positive electrode active material.

[0042] According to an embodiment of the present invention, the positive electrode material further includes a conductive agent and a binder.

[0043] According to an embodiment of the present invention, the conductive agent is selected from at least one of Super-P, Ketjen Black-300, Ketjen Black-600, superconducting carbon black, and acetylene black, preferably Ketjen Black-600.

[0044] According to an embodiment of the present invention, the adhesive is selected from at least one of polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), preferably polyvinylidene fluoride (PVDF).

[0045] According to embodiments of the present invention, the present invention does not specify a particular mass ratio for the positive electrode active material, conductive agent, and binder; a mass ratio commonly used by those skilled in the art can be adopted, as long as it meets the performance requirements of the positive electrode material. For example, the mass ratio of the positive electrode active material, conductive agent, and binder is 8:1:1.

[0046] According to an exemplary embodiment of the present invention, the positive electrode material undergoes no phase change during charge and discharge within a voltage window of 1.5-4.2V, thus achieving a fully solid solution reaction.

[0047] According to an exemplary embodiment of the present invention, the positive electrode material contains K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 Positive electrode active material. Preferably, the positive electrode material has a reversible capacity of 132.5 mAh / g at a current density of 10 mA / g. Preferably, the positive electrode material has a reversible capacity of 75.6 mAh / g after 100 cycles at a current density of 100 mA / g.

[0048] The present invention also provides a positive electrode sheet, which includes the above-described positive electrode material and a current collector. Preferably, the current collector is an aluminum foil.

[0049] The present invention also provides a method for preparing the above-mentioned positive electrode sheet, including slurry preparation and drying.

[0050] According to an embodiment of the present invention, the slurry preparation includes dissolving the above-mentioned positive electrode material in a solvent to prepare a homogeneous slurry. The present invention does not specifically limit the solvent in the slurry, as long as a homogeneous slurry can be obtained. Preferably, the solvent is N-methylpyrrolidone (NMP).

[0051] According to an embodiment of the present invention, the drying process includes uniformly coating the slurry onto the current collector, and drying to obtain the positive electrode material.

[0052] Preferably, the slurry loading on the current collector is 1-5 mg / cm³. 2 Preferably 1-2 mg / cm2 .

[0053] Preferably, the drying conditions include drying at 100°C for 24 hours.

[0054] According to an embodiment of the present invention, the positive electrode sheet is prepared in an inert atmosphere. Preferably, the inert atmosphere is an argon atmosphere.

[0055] According to an exemplary embodiment of the present invention, the positive electrode sheet is prepared in an argon atmosphere glove box (O2 < 0.1 ppm, H2O < 0.1 ppm).

[0056] The present invention also provides an energy storage element, the energy storage element comprising at least one of the above-mentioned positive electrode active material, the above-mentioned positive electrode material, or the above-mentioned positive electrode sheet.

[0057] According to an embodiment of the present invention, the energy storage element further includes an electrolyte. Preferably, the electrolyte is an organic electrolyte.

[0058] Preferably, the organic electrolyte comprises a potassium salt and an organic solvent. The organic solvent is selected from at least one of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), preferably with an EC:DEC ratio of 1:1 (volume ratio). The potassium salt is selected from one or more of potassium bis(fluorosulfonyl)imide (KFSI), potassium hexafluorophosphate (KPF6), and potassium bis(trifluoromethyl)sulfonyl)imide (KTFSI), preferably potassium hexafluorophosphate (KPF6).

[0059] The concentration of potassium salt in the organic electrolyte is 0.2-2 mol / L, preferably 0.8 mol / L.

[0060] According to an embodiment of the present invention, the energy storage element is preferably a potassium-ion battery. The operating temperature of the potassium-ion battery is preferably 25°C.

[0061] According to an embodiment of the present invention, the assembly of the energy storage element is carried out in an inert atmosphere. The inert atmosphere has the definition described above.

[0062] According to an exemplary embodiment of the present invention, the energy storage element is assembled in an argon atmosphere glove box (O2 < 0.1 ppm, H2O < 0.1 ppm).

[0063] Beneficial effects:

[0064] This invention provides a potassium-ion battery cathode material, its preparation method, and its application. Compared to K... xThe AO2 type positive electrode active material, by introducing a certain amount of metals B and C with similar ionic radii to metal A, can effectively suppress the Jahn-Teller effect, improve the structural stability of the material, completely suppress the phase transition process during charging and discharging, and achieve a fully solid solution reaction. Furthermore, by introducing a certain amount of anion F to partially replace O, this invention optimizes the electron configuration of the layered structure, expands the interlayer spacing, and is beneficial to K... + The rapid and stable transmission of this material enhances its cycle stability. The cathode material of this invention boasts advantages such as abundant raw material resources, low cost, non-toxicity, environmental friendliness, and good cycle stability, making it well-suited for large-scale energy storage applications.

[0065] The inventors discovered that the positive electrode active material of this invention optimizes the crystal structure through cation doping / substitution. Specifically, the introduction of B and C effectively stabilizes the crystal structure, suppresses the Jahn-Teller effect, inhibits transition metal layer slippage caused by potassium ion insertion / extraction, suppresses the formation of OP4 and O2 phases, and improves the cycle stability of the electrode material. Furthermore, the introduction of F can partially replace O, optimize the electronic arrangement of the layered structure, expand the interlayer spacing, and facilitate K... + The rapid and stable transport of these materials improves their cycling stability. Therefore, the positive electrode active material of this invention completely suppresses the phase transition process during charging and discharging, achieving a full solid solution reaction within the charging and discharging range of 1.5-4.2V. For example, the positive electrode active material K... 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.8 9F 0.11 It exhibits a high reversible capacity of 132.5 mAh / g at a current density of 10 mA / g, and retains a reversible capacity of 75.6 mAh / g after 100 cycles at a current density of 100 mA / g, while undoped / substituted K 0.67 After cycling, only 29.4 mAh / g of reversible capacity remains in MnO2.

[0066] The potassium-ion battery cathode material prepared using the cathode active material of this invention can effectively solve the K... x The AO2 type potassium-ion battery cathode material suffers from unstable structure, complex phase transition, and capacity decay. The cathode active material described above has broad application prospects and advantages.

[0067] The potassium-ion battery of this invention is expected to serve as a novel energy storage device, suitable for large-scale energy storage equipment, and has good prospects for commercial application. Attached Figure Description

[0068] Figure 1 K in Example 1 0.67 Mn 0.78 Ni0.11 Ti 0.11 O 1.89 F 0.11 X-ray diffraction (XRD) pattern of the positive electrode active material.

[0069] Figure 2 K in Example 1 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 Scanning electron microscope (SEM) image of the positive electrode active material.

[0070] Figure 3 K in Example 1 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 High-resolution transmission electron microscopy (HRTEM) image of the positive electrode active material.

[0071] Figure 4 K in Example 1 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 X-ray energy dispersive spectroscopy (EDS) diagram of the positive electrode active material.

[0072] Figure 5 K in Example 1 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 Charge-discharge curves of the positive electrode active material.

[0073] Figure 6 K in Example 1 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 Cyclic performance of the positive electrode active material.

[0074] Figure 7 K in Example 1 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 In-situ XRD pattern of the positive electrode active material. Detailed Implementation

[0075] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0076] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0077] Example 1

[0078] (I) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 Positive electrode active material

[0079] KOH, Mn2O3, NiO, TiO2, and KF in a molar ratio of 56:78:11:11:11 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at 450 r / min for 6 hours. The mixed raw material powder was then pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. These discs were then calcined at 1000 °C for 12 hours at a heating rate of 3 °C / min to obtain black discs, which is the K2O3 obtained in this embodiment. 0.6 Mn 0.8 Ni 0.1 Ti 0.1 O2 positive electrode active material.

[0080] (II) Structural and morphological characterization of the positive electrode active material prepared in this embodiment.

[0081] Figure 1 For K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 X-ray diffraction (XRD) pattern of the positive electrode active material. Figure 1 It can be seen that the K prepared in this embodiment 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The positive electrode active material is hexagonal, space group P63 / mmc, with the following unit cell parameters.

[0082] Figure 2 For K 0.67 Mn0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 Scanning electron microscope (SEM) images of the positive electrode active material, with particle sizes ranging from 0.1 to 1 μm.

[0083] Figure 3 For K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The high-resolution transmission electron microscope (HRTEM) image of the positive electrode active material shows a lattice spacing of [missing information].

[0084] Figure 4 For K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The X-ray energy dispersive spectroscopy (EDS) pattern of the positive electrode active material shows that elements such as K, Mn, Ni, Ti and O are uniformly distributed in the particles of the positive electrode active material.

[0085] (III) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 cathode materials

[0086] The positive electrode active material prepared in this embodiment was mixed with the binder polyvinylidene fluoride (PVDF) and Ketjen Black-600 at a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone (NMP) was added. The mixture was ground for 30 minutes in an argon atmosphere to prepare a slurry. Using aluminum foil as the current collector, the slurry was uniformly coated onto the aluminum foil and dried at 100°C for 24 hours to obtain a K-containing material. 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The positive electrode material has an active material loading of 1-2 mg / cm³. 2 .

[0087] (iv) Assembling potassium-ion batteries

[0088] The K-containing material prepared in this embodiment 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F0.11 A potassium-ion battery is assembled from the positive electrode material, separator, electrolyte (0.8M KPF6 EC / DEC (volume ratio 1:1) solution), potassium metal negative electrode, positive electrode shell and negative electrode shell.

[0089] Test Example 1

[0090] (1) Potassium-ion battery test

[0091] The test conditions for potassium-ion batteries are as follows: the test temperature is 25℃, and constant current charge-discharge tests are performed in the voltage range of 1.5-4.2V at current densities of 10mA / g and 100mA / g, respectively.

[0092] Figure 5 It is the one containing Example 1K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The constant current charge-discharge curves of a potassium-ion battery using the cathode material are shown at a current density of 10 mA / g. It can be seen that the battery has a high discharge specific capacity (132.5 mAh / g), and the second charge-discharge curve highly overlaps with the first, exhibiting high reversibility and high stability.

[0093] Figure 6 It is the one containing K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The cycling performance of the potassium-ion battery with the cathode material is shown in the figure. After 100 cycles at a current density of 100 mA / g, it still has a reversible capacity of 75.6 mAh / g, which shows excellent cycling stability.

[0094] (2) In-situ XRD testing of potassium-ion batteries

[0095] The above-prepared K-containing 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The positive electrode material, separator, electrolyte, and potassium metal negative electrode are assembled into a potassium-ion battery using a commercially customized mold (Bruker). The K-containing... 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.8 9F 0.11The charge-discharge curves of the positive electrode of the active material at a current density of 10 mA / g were obtained. At the same time, the structural information was tested using an X-ray diffractometer, and an XRD spectrum was obtained every 30 minutes to monitor the evolution of the lattice structure of the positive electrode material during the charge-discharge process.

[0096] Figure 7 For containing K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.89 F 0.11 The in-situ XRD pattern of the cathode material showed no characteristic peaks of any phase other than the P2 phase, indicating that the phase transition process was completely suppressed during charging and discharging, and a full solid solution reaction was achieved.

[0097] Example 2

[0098] (I) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O2 positive electrode active material

[0099] KOH, Mn2O3, NiO, and TiO2 in a molar ratio of 67:78:11:11 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 hours. The mixed raw material powder was pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 hours to obtain black discs, which are the positive electrode active material of this embodiment.

[0100] Other steps (ii)-(iv) are the same as in Example 1, and the positive electrode material and potassium-ion battery of this example are prepared.

[0101] Example 3

[0102] (I) Preparation of K 0.67 Mn 0.78 Ni 0.22 O2 positive electrode active material

[0103] KOH, Mn2O3, and NiO in a molar ratio of 67:78:22 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 hours. The mixed raw material powder was pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 hours to obtain black discs, which are the positive electrode active material of this embodiment.

[0104] Other steps (ii)-(iv) are the same as in Example 1, and the positive electrode material and potassium-ion battery of this example are prepared.

[0105] Example 4

[0106] (I) Preparation of K 0.67 Mn 0.78 Ti 0.22 O2 positive electrode active material

[0107] KOH, Mn2O3, and TiO2 in a molar ratio of 67:78:22 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 hours. The mixed raw material powder was pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 hours to obtain black discs, which are the positive electrode active material of this embodiment.

[0108] Other steps (ii)-(iv) are the same as in Example 1, and the positive electrode material and potassium-ion battery of this example are prepared.

[0109] Example 5

[0110] (I) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.98 F 0.02 Positive electrode active material

[0111] KOH, Mn2O3, NiO, TiO2, and KF in a molar ratio of 65:78:11:11:2 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 hours. The mixed raw material powder was then pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 hours to obtain black discs, which are the positive electrode active material of this embodiment.

[0112] Other steps (ii)-(iv) are the same as in Example 1, and the positive electrode material and potassium-ion battery of this example are prepared.

[0113] Example 6

[0114] (I) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.95 F 0.05 Positive electrode active material

[0115] KOH, Mn2O3, NiO, TiO2 and KF in a molar ratio of 62:78:11:11:5 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 h. The mixed raw material powder was pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 h to obtain black discs, which are the positive electrode active material of this embodiment.

[0116] Other steps (ii)-(iv) are the same as in Example 1, and the positive electrode material and potassium-ion battery of this example are prepared.

[0117] Example 7

[0118] (I) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.92 F 0.08 Positive electrode active material

[0119] KOH, Mn2O3, NiO, TiO2 and KF in a molar ratio of 59:78:11:11:8 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 hours. The mixed raw material powder was pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 hours to obtain black discs, which are the positive electrode active material of this embodiment.

[0120] Other steps (ii)-(iv) are the same as in Example 1, and the positive electrode material and potassium-ion battery of this example are prepared.

[0121] Example 8

[0122] (I) Preparation of K 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 1.85 F 0.15 Positive electrode active material

[0123] KOH, Mn2O3, NiO, TiO2, and KF in a molar ratio of 52:78:11:11:15 were accurately weighed as raw materials and placed in a high-energy ball mill. Under an oxygen atmosphere, the mixture was ball-milled at a speed of 450 r / min for 6 hours. The mixed raw material powder was pressed into discs with a diameter of 10 mm and a thickness of 1-3 mm under a pressure of 10 MPa. The discs were then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 hours to obtain black discs, which are the positive electrode active material of this embodiment.

[0124] For the other steps (ii)-(iv), they are the same as those in Example 1, and the cathode material and potassium-ion battery of this example are obtained.

[0125] Comparative Example 1

[0126] (i) Preparation of K 0.67 MnO2 cathode active material

[0127] Accurately weigh KOH and Mn2O3 with a molar ratio of 67:50 as raw materials, place them in a high-energy ball mill, under an oxygen atmosphere, ball mill for 6 h at a rotation speed of 450 r / min. The mixed raw material powder is pressed into a tablet under a pressure of 10 MPa to obtain a disc with a diameter of 10 mm and a thickness of 1 - 3 mm, and then heated to 1000 °C at a heating rate of 3 °C / min and calcined for 12 h to obtain a black disc, that is, the cathode active material of this example is obtained.

[0128] For the other steps (ii)-(iv), they are the same as those in Example 1, and the cathode material and potassium-ion battery of this comparative example are obtained.

[0129] Test Example 2

[0130] Perform electrical performance tests on the potassium-ion batteries of the above Examples 1 - 8 and Comparative Example 1. Refer to the constant current charge-discharge test in Test Example 1, and the test conditions are carried out at a current density of 100 mA / g. The test results are shown in Table 1.

[0131] Table 1

[0132]

[0133] In summary, the phase transition process is completely inhibited during the charge-discharge process of the cathode active material of the present invention, and a complete solid solution reaction within the voltage window of 1.5 - 4.2 V is achieved; the potassium-ion battery prepared by the present invention has high cycle stability, and the cathode active material mainly includes K x A 1-y-z B y C z O 2-m F m (0 < x < 1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ m ≤ 0.5). The cathode material of the present invention has the advantages of simple preparation method, rich raw material resources, low price, environmental friendliness, non-toxic and harmless, etc. Therefore, the potassium-ion battery of the present invention is expected to be used as a new type of energy storage device, suitable for large-scale energy storage equipment, and has good commercial application prospects.

[0134] The exemplary embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode active material, characterized in that, The chemical formula of the positive electrode active material is: K x Mn 1-y-z Ni y Ti z O 2- m F m , where 0.6≤x≤0.7, 0.1≤y≤0.12, 0.08≤z≤0.12, and 0.05≤m≤0.

15.

2. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material is a P2-type layered transition metal oxide; The chemical formula of the positive electrode active material is K. 0.67 Mn 0.78 Ni 0.11 Ti 0.11 O 2-m F m , 0.05≤m≤0.

15.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The positive electrode active material has a hexagonal P2 phase crystal structure and a space group of P63 / mmc. The particle size of the positive electrode active material is 0.1-1 μm; The lattice spacing of the positive electrode active material is 4. The method for preparing the positive electrode active material according to any one of claims 1-3, characterized in that, The method includes the following steps: The positive electrode active material is prepared by mixing, pressing, and calcining the raw materials. The raw materials include metal hydroxides, metal oxides, and metal fluorides; the feed ratio of the raw materials meets the stoichiometry required for each element in the positive electrode active material.

5. The preparation method according to claim 4, characterized in that, The metal hydroxide is selected from potassium hydroxide; The metal oxides include manganese oxides, nickel oxide, and titanium dioxide; The metal fluoride is selected from potassium fluoride.

6. The preparation method according to claim 4, characterized in that, The mixing specifically includes mixing the raw materials evenly through a high-energy ball mill; The high-energy ball milling is carried out in any one of the following atmospheres: air, argon, nitrogen, and oxygen; The tableting process specifically involves compressing the mixed raw materials into tablets using a tableting machine; The calcination specifically includes calcining the compressed tablet; the heating rate of the calcination is 1-10℃ / min; The calcination temperature is 200-1500℃; the calcination time is 6-24h.

7. The preparation method according to claim 4, characterized in that, The calcination is carried out in a muffle furnace; The heating rate for calcination is 2-5℃ / min.

8. The positive electrode active material according to any one of claims 1-3 is used in an energy storage element, wherein the energy storage element is a potassium-ion battery.

9. A positive electrode material, characterized in that, The positive electrode material includes the positive electrode active material according to any one of claims 1-3.

10. The cathode material according to claim 9, characterized in that, The positive electrode material also includes a conductive agent and a binder; The conductive agent is selected from at least one of Super-P, Ketjen Black-300, Ketjen Black-600, superconducting carbon black, and acetylene black; The adhesive is selected from at least one of polyvinyl alcohol, polyvinylidene fluoride, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

11. A positive electrode sheet, said positive electrode sheet comprising the positive electrode material and current collector as described in claim 9 or 10.

12. The method for preparing the positive electrode sheet according to claim 11, characterized in that, The process includes slurry preparation and drying; the slurry preparation includes dissolving the above-mentioned positive electrode material in a solvent to prepare a uniform slurry; the preparation of the positive electrode sheet is carried out in an inert atmosphere.

13. An energy storage element comprising at least one of the positive electrode active material according to any one of claims 1-3, the positive electrode material according to claim 9 or 10, or the positive electrode sheet according to claim 11.

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