Electrolyte and preparation method thereof, potassium ion battery and application

Abstract

The application provides an electrolyte, a preparation method thereof, a potassium ion battery and application. The electrolyte comprises a potassium salt, water and an organic solvent. The concentration of the potassium salt is 1 mol / kg to 8 mol / kg. The donor number of the organic solvent is 10 kcal / mol to 30 kcal / mol. The molar ratio of the organic solvent to water is 1:5 to 5:1. The electrolyte formed by the organic solvent, the potassium salt and water molecules has a three-dimensional ordered eutectic network. The eutectic network realizes significant inhibition of water molecule activity through a synergistic enhancement mechanism of physical anchoring and electronic effect regulation. The electrolyte has a wide electrochemical stability window, and has the advantages of low cost, high safety and wide temperature domain adaptability.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, specifically to an electrolyte and its preparation method, a potassium-ion battery, and its applications. Background Technology

[0002] With the rapid development of clean energy, the demand for large-scale energy storage technology has surged. While lithium-ion batteries offer excellent performance, the scarcity and high cost of lithium resources limit their application in large-scale energy storage. Potassium, with its similar chemical properties to lithium and abundant, low-cost resources, makes potassium-ion batteries an ideal alternative. Among them, aqueous potassium-ion batteries have attracted much attention due to their high safety, environmental friendliness, and low cost, showing broad application prospects in low-speed electric vehicles, data center base stations, and other scenarios. However, aqueous potassium-ion battery electrolytes suffer from problems such as a narrow electrochemical stability window, high cost, and poor adaptability over a wide temperature range, affecting the practical application of potassium-ion batteries. Summary of the Invention

[0003] The first aspect of this application provides an electrolyte comprising a potassium salt, water, and an organic solvent; wherein the concentration of the potassium salt is 1 mol / kg to 8 mol / kg; the number of donors of the organic solvent is 10 kcal / mol to 30 kcal / mol; and the molar ratio of the organic solvent to the water is 1:5 to 5:1.

[0004] In some embodiments of this application, the organic solvent includes at least one selected from sulfolane, sulfolane, succinate, hexanetrionitrile, and acetamide.

[0005] In some embodiments of this application, the potassium salt includes at least one of potassium trifluoromethanesulfonate, potassium hexafluorophosphate, potassium bis(fluorosulfonyl)imide, and potassium bis(trifluoromethanesulfonyl)imide.

[0006] In some embodiments of this application, the concentration of the potassium salt is 1 mol / kg to 5 mol / kg; preferably, the concentration of the potassium salt is 2.45 mol / kg to 5 mol / kg.

[0007] In some embodiments of this application, the molar ratio of the organic solvent to the water is 1:3 to 3:1.

[0008] In some embodiments of this application, the molar ratio of the potassium salt to the organic solvent is from 1:7.34 to 1:0.92; preferably, the molar ratio of the potassium salt to the organic solvent is from 1:3 to 1:1.

[0009] In some embodiments of this application, the electrolyte satisfies at least one of the following conditions: (1) The electrochemical stability window of the electrolyte is 3V~4V; (2)The electrolyte is in a liquid state under the condition that the temperature is from -20°C to 60°C.

[0010] The second aspect of the present application provides a preparation method of the electrolyte provided in the first aspect of the present application, including: Performing a first mixing process on the potassium salt and the organic solvent to obtain a first mixed solution, wherein the temperature of the first mixing process is 50°C to 80°C, and the time of the first mixing process is 0.5 h to 2 h; Performing a second mixing process on the first mixed solution and water to obtain a second mixed solution, wherein the temperature of the second mixing process is 40°C to 60°C, and the time of the second mixing process is 0.5 h to 1 h; Bubbling an inert gas into the second mixed solution to obtain the electrolyte.

[0011] In some embodiments of the present application, the preparation method of the electrolyte satisfies at least one of the following conditions: (1)In the first mixed solution, the molar ratio of the potassium salt to the organic solvent is from 1:7.34 to 1:0.92; preferably, the molar ratio of the potassium salt to the organic solvent is from 1:3 to 1:1; (2)In the second mixed solution, the molar ratio of the organic solvent to water is from 1:5 to 5:1.

[0012] The third aspect of the present application provides a potassium ion battery, which includes the electrolyte provided in the first aspect of the present application or the electrolyte prepared by the method provided in the second aspect of the present application.

[0013] In some embodiments of the present application, the potassium ion battery includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes at least one of a Prussian blue analogue, KVPO4F, and K z V2O5; wherein, the chemical formula of the Prussian blue analogue is K x M[Fe(CN)6] 1-y ·nH2O, where M includes at least one of Mn, Fe, Cu, Ni, Co, and Zn, 0 < x ≤ 2, 0 < y ≤ 1, 0 < n ≤ 1, 0 < z ≤ 1; the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes at least one of an organic material and a polyanion compound.

[0014] In some embodiments of this application, the organic material includes at least one of 3,4,9,10-perylenetetracarboxylic diimide and 1,4,5,8-naphthalenetetracarboxylic anhydride, and the polyanionic compound includes potassium titanium phosphate.

[0015] In some embodiments of this application, the positive current collector includes at least one of titanium mesh, carbon cloth, carbon felt, and graphite paper; the negative current collector includes at least one of carbon-coated aluminum foil, carbon felt, graphite paper, and carbon-coated copper foil.

[0016] The fourth aspect of this application provides an application of the potassium-ion battery provided in the third aspect of this application in an energy storage system.

[0017] The beneficial effects of this application are: This application provides an electrolyte, its preparation method, a potassium-ion battery, and its application. The electrolyte comprises a potassium salt, water, and an organic solvent; the concentration of the potassium salt is 1 mol / kg to 8 mol / kg; the donor number of the organic solvent is 10 kcal / mol to 30 kcal / mol; and the molar ratio of the organic solvent to water is 1:5 to 5:1. The aforementioned electrolyte has a wide electrochemical stability window while also possessing the advantages of low cost, high safety, and wide temperature range adaptability. Attached Figure Description

[0018] Figure 1 The results are obtained by differential scanning voltammetry (DSC) testing of the first mixed solution prepared in Examples 14, 12, 1, and 11 of this application.

[0019] Figure 2 The Fourier transform infrared (FTIR) spectrometry results are those of the electrolyte prepared in Example 1 of this application.

[0020] Figure 3 These are photographs of the flammability testing process of the electrolyte prepared in Example 1 of this application and the commercial organic electrolyte. Detailed Implementation

[0021] The embodiments of this application are described in detail below. The embodiments described below are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] In the development of aqueous potassium-ion batteries, the high-concentration salt strategy, represented by water-in-salt (WIS) electrolytes, can broaden the electrochemical stability window (ESW) of aqueous electrolytes from 2V to around 3V. However, high-concentration WIS electrolytes are limited by high cost and a still relatively narrow electrochemical stability window, and the tendency of this electrolyte to salt out at low temperatures will inevitably limit the applicable temperature range of potassium-ion batteries.

[0024] The first aspect of this application provides an electrolyte comprising a potassium salt, water, and an organic solvent; wherein the concentration of the potassium salt is 1 mol / kg to 8 mol / kg; the number of donors of the organic solvent is 10 kcal / mol to 30 kcal / mol; and the molar ratio of the organic solvent to the water is 1:5 to 5:1.

[0025] In some embodiments of this application, the concentration of the potassium salt is 1 mol / kg to 5 mol / kg; preferably, the concentration of the potassium salt is 2.45 mol / kg to 5 mol / kg.

[0026] In some embodiments of this application, the molar ratio of the organic solvent to the water is 1:3 to 3:1.

[0027] As an example, the concentration of potassium salt can be 1 mol / kg, 2 mol / kg, 3 mol / kg, 4 mol / kg, 5 mol / kg, 6 mol / kg, 7 mol / kg, 8 mol / kg, or a range of any two of these values.

[0028] As an example, the number of organic solvent donors can be 10 kcal / mol, 12 kcal / mol, 14 kcal / mol, 16 kcal / mol, 18 kcal / mol, 20 kcal / mol, 22 kcal / mol, 24 kcal / mol, 26 kcal / mol, 28 kcal / mol, 30 kcal / mol, or a range of any two of these values.

[0029] As an example, the molar ratio of organic solvent to water in the electrolyte can be 1:5, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, or a range of any two of these values.

[0030] By adding an organic solvent with a donor number ranging from 10 kcal / mol to 30 kcal / mol to the electrolyte, and adjusting the molar ratio of the organic solvent to water to be within the range of 1:5 to 5:1, while simultaneously adjusting the potassium salt concentration to be between 1 mol / kg and 8 mol / kg, a stable deep eutectic system is obtained. It should be noted that a deep eutectic system (DES) refers to a binary or multi-component eutectic mixture formed by mixing at least one hydrogen bond acceptor (such as an alkali metal salt) and at least one hydrogen bond donor (such as a solvent with a high donor number) in a specific molar ratio, through hydrogen bonding, ionic dipole interactions, or van der Waals forces. Its melting point is significantly lower than the individual melting points of each component. Due to the formation of the eutectic network, there are almost no free solvent molecules in the system; therefore, DES typically exhibits a homogeneous and transparent liquid state at room temperature, possessing characteristics such as high ionic conductivity, a wide electrochemical window, and high thermal stability. When the added water molecules do not exceed the "hydration limit", they can be embedded in the eutectic system as structural water to form a "hydrated deep eutectic electrolyte". At this time, the water molecules are "fixed" through hydrogen bonds, and their electrochemical activity is significantly suppressed, thereby broadening the electrochemical stability window of the electrolyte. Figure 2 The FTIR test results of the electrolyte in one embodiment of this application are from... Figure 2 It can be seen that the OH stretching peak (3100~3500 cm⁻¹) corresponds to the strong hydrogen bond of free water. - ¹) The hydrogen bond peaks almost disappear, and the peaks with no hydrogen bond and weak hydrogen bond dominate, which is a typical characteristic of water molecules being "fixed" in the eutectic network.

[0031] In the application, the organic solvent molecule not only acts as a hydrogen bond acceptor to form weak hydrogen bonds with water molecules, but more importantly, the organic solvent reacts with K... + Stable coordination bonds are formed between the molecules through ion-dipole interactions, while intermolecular interactions also exist between organic solvent molecules. Together, these three elements constitute a three-dimensional ordered eutectic network. This eutectic network synergistically inhibits the activity of water through the following two mechanisms: (1) Physical anchoring: Water molecules are fixed in the cavity around organic solvent molecules through hydrogen bonds, forming a "hydration shell", which prevents them from moving freely to the electrode surface to participate in electrochemical side reactions.

[0032] (2) Electronic effect regulation: Due to the presence of strong polar groups in the deep eutectic system, the OH bond of water molecules is further polarized and enhanced, and the water splitting energy is greatly increased, thereby significantly inhibiting the hydrogen evolution and oxygen evolution reactions.

[0033] In summary, the core technology of this application does not lie in simply introducing organic solvents, but in constructing a holistic deep eutectic system that uniformly locks potassium salts, organic solvents, and water molecules within the same eutectic network. This deep eutectic system exhibits a synergistic enhancement effect in inhibiting water molecules, far exceeding the scope of the technical concept of "organic solvents inhibiting water activity."

[0034] Furthermore, due to the dual anchoring of water molecules by the deep eutectic network, the electrolyte of this application can induce the formation of an inorganic-rich interfacial film on the electrode surface even without the addition of traditional film-forming additives, further stabilizing the electrode-electrolyte interface. In contrast, mixed electrolytes that only use organic co-solvents to suppress water activity often require complex additives or sacrifice ionic conductivity to achieve a wide electrochemical window. This application achieves a relatively wide electrochemical stability window and high ionic conductivity even at low salt concentrations, thanks to the unique advantages of the deep eutectic network. Simultaneously, the system remains liquid and exhibits stable battery performance across a wide temperature range of -20℃ to 60℃, further demonstrating the thorough suppression effect of the deep eutectic network on free water. Therefore, the inventiveness of this application stems not only from "organic solvent suppression of water activity" but also from the first application of the deep eutectic concept to the design of aqueous potassium-ion battery electrolytes. Through the overall network structure, precise control of water molecule activity is achieved, significantly broadening the electrochemical stability window of the electrolyte, resulting in significant progress and unpredictable technical effects.

[0035] Meanwhile, compared to the WIS electrolyte in related technologies, the concentration of potassium salt in this application is only 1mol / kg to 8mol / kg. On the one hand, the overall viscosity of the electrolyte is lower, the fluidity is excellent, the wetting effect on the electrodes and separator is good, the resistance to potassium ion migration is small, and the ionic conductivity of the electrolyte is higher, which is conducive to improving the battery's rate charge and discharge performance. On the other hand, there is no need to use a large amount of high-cost fluorinated potassium salt, the raw material cost is controllable, the electrolyte preparation process is simple, the salt component has low solubility pressure, and the problem of salt crystal precipitation is not easy to occur during storage and use, which greatly improves the wide temperature range adaptability of potassium-ion batteries.

[0036] In summary, the synergistic effect of potassium salt, water, and organic solvent in the electrolyte provided in this application significantly broadens the electrochemical stability window of the electrolyte, while also taking into account low cost, high safety, and wide temperature range adaptability.

[0037] In some embodiments of this application, the organic solvent includes at least one of cyclobutene sulfone (Bds, donor number 12.8 kcal / mol), cyclobutene sulfone (donor number 14.6 kcal / mol), succinic anionyl (donor number 12.4 kcal / mol), hexanetrionitrile (donor number 10.5 kcal / mol), and acetamide (donor number 27 kcal / mol). The electrolyte prepared by organic solvents within the above range with potassium salt and water forms a stable deep eutectic system. Furthermore, the strongly polar functional groups (sulfone group -SO2-, nitrile group -C≡N, amide group -CONH2) of the organic solvents within the above range form weak hydrogen bonds with water molecules, disrupting the strong hydrogen bond network between water molecules. This converts "free water" with a strong hydrogen bond network into "fixed water" limited by the organic solvents of this application, thereby significantly inhibiting water activity, broadening the electrochemical stability window, and maintaining the non-flammable properties and wide temperature range adaptability of the electrolyte.

[0038] In some embodiments of this application, the potassium salt includes at least one selected from potassium trifluoromethanesulfonate (KOTF), potassium hexafluorophosphate (KPF6), potassium bis(fluorosulfonyl)imide (KFSI), and potassium bis(trifluoromethanesulfonyl)imide (KTFSI). Potassium salts within the above range all contain fluoride anions, exhibiting strong polarization capabilities and readily dissociating K+ in the electrolyte. + It exhibits good compatibility with the organic solvents and water used in this application, and has excellent solubility, which is beneficial for further broadening the electrochemical stability window while maintaining the non-flammable properties and wide temperature range adaptability of the electrolyte.

[0039] In some embodiments of this application, the molar ratio of the potassium salt to the organic solvent is from 1:7.34 to 1:0.92; preferably, the molar ratio of the potassium salt to the organic solvent is from 1:3 to 1:1. For example, the molar ratio of the potassium salt to the organic solvent can be 1:7.34, 1:5, 1:4, 1:3, 1:2, 1:1, 1:0.92, or a range consisting of any two of these values. By controlling the molar ratio of the potassium salt to the organic solvent within the above range, it is beneficial for the electrolyte to form a stable three-dimensional ordered eutectic network, further suppressing the activity of water molecules in the electrolyte, thereby further broadening the electrochemical stability window of the electrolyte, while also taking into account low cost, high safety, and wide temperature range adaptability.

[0040] In some embodiments of this application, the electrochemical stability window of the electrolyte is 3V~4V. The electrolyte prepared in this application has a wide electrochemical stability window, which is beneficial for improving the operating voltage and energy density of potassium-ion batteries, and can also be adapted to more high-performance positive and negative electrode active materials.

[0041] In some embodiments of this application, the electrolyte is in a liquid state at temperatures ranging from -20°C to 60°C. The electrolyte prepared in this application is a deep eutectic system with an extremely low melting point, and the potassium salt concentration in the electrolyte is low, making it less prone to salting out at low temperatures. Therefore, the electrolyte in this application can maintain a homogeneous liquid state at temperatures ranging from -20°C to 60°C, which is beneficial for improving the wide temperature range adaptability of potassium-ion batteries.

[0042] The second aspect of this application provides a method for preparing the electrolyte provided in the first aspect of this application, comprising: The potassium salt and the organic solvent are subjected to a first mixing treatment to obtain a first mixed solution. The temperature of the first mixing treatment is 50℃~80℃, and the time of the first mixing treatment is 0.5h~2h. For example, the temperature of the first mixing treatment can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃ or any two of these values, and the time of the first mixing treatment can be 0.5h, 1h, 1.5h, 2h or any two of these values. The first mixed solution is subjected to a second mixing treatment with the water to obtain a second mixed solution. The temperature of the second mixing treatment is 40℃~60℃, and the time of the second mixing treatment is 0.5h~1h. For example, the temperature of the second mixing treatment can be 40℃, 45℃, 50℃, 55℃, 60℃ or any two of these values, and the time of the second mixing treatment can be 0.5h, 0.6h, 0.7h, 0.8h, 1h or any two of these values. The second mixed solution is bubbled with an inert gas to obtain the electrolyte.

[0043] In the preparation of the electrolyte in this application, potassium salt and organic solvent are first mixed to obtain a deep eutectic solution of potassium salt and organic solvent. Then, a certain amount of water is introduced to form a hydrated eutectic electrolyte, which reduces the viscosity of the electrolyte and increases its ionic conductivity. Simultaneously, the strong polar functional groups of the organic solvent form weak hydrogen bonds with water molecules, disrupting the strong hydrogen bond network between water molecules and converting the "free water" with a strong hydrogen bond network into "fixed water" restricted by the organic solvent, forming a three-dimensional eutectic network that significantly inhibits water activity. Finally, an inert gas is introduced for bubbling to remove dissolved oxygen from the electrolyte. The electrolyte prepared by this method can broaden the electrochemical stability window while maintaining its non-flammable properties and wide temperature range adaptability. Furthermore, the preparation method of the electrolyte provided in this application is simple, the reaction conditions are mild, and the cost is low, making it suitable for large-scale industrial application.

[0044] In some embodiments of this application, the molar ratio of the potassium salt to the organic solvent in the first mixed solution is from 1:7.34 to 1:0.92; preferably, the molar ratio of the potassium salt to the organic solvent is from 1:3 to 1:1. For example, the molar ratio of the potassium salt to the organic solvent can be 1:7.34, 1:5, 1:3, 1:2, 1:1, 1:0.92, or a range of any two of these values. By adjusting the molar ratio of the potassium salt and the organic solvent within the range of this application, the resulting first mixed solution can be a deep eutectic system with a low melting point.

[0045] In some embodiments of this application, the molar ratio of the organic solvent to the water in the second mixed solution is 1:5 to 5:1. For example, the molar ratio of the organic solvent to the water can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, or any range of two of these values. By adjusting the molar ratio of the organic solvent to the water within the range of this application, the resulting second mixed solution can be a hydrated deep eutectic system, which is beneficial for reducing the viscosity of the electrolyte and increasing the ionic conductivity of the electrolyte. At the same time, it is beneficial for the strong polar functional groups of the organic solvent to form weak hydrogen bonds with water molecules, thereby significantly inhibiting the activity of water.

[0046] A third aspect of this application provides a potassium-ion battery, which includes the electrolyte provided in the first aspect of this application or the electrolyte prepared by the method provided in the second aspect of this application. Since the potassium-ion battery of this application includes the aforementioned electrolyte, it possesses all the advantages of the aforementioned electrolyte, which will not be elaborated further here.

[0047] In some embodiments of this application, the potassium-ion battery includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, such as a Prussian blue analogue, KVPO4F, or K... z At least one of V2O5; wherein the chemical formula of the Prussian blue analogue is K x M[Fe(CN)6] 1-y·nH2O, where M includes at least one of Mn, Fe, Cu, Ni, Co, and Zn, 0 < x ≤ 2, 0 < y ≤ 1, 0 < n ≤ 1, 0 < z ≤ 1; the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes at least one of an organic material and a polyanion compound. Preferably, the organic material includes at least one of 3,4,9,10-perylene tetracarboxylic diimide (PTCDI) and 1,4,5,8-naphthalene tetracarboxylic dianhydride (PNTCDA), and the polyanion compound includes potassium titanium phosphate (KTi2(PO4)3); more preferably, the negative electrode active material includes 3,4,9,10-perylene tetracarboxylic diimide (PTCDI).

[0048] The above positive electrode active material and negative electrode active material are electrochemically compatible with the relatively wide electrochemical stability window of the electrolyte of the present application, and can be adapted to the system environment with a low potassium salt concentration; at the same time, the advantage of the low viscosity of the low potassium salt electrolyte matches the excellent potassium ion insertion and extraction kinetics of the positive electrode active material and the negative electrode active material, synergistically reducing battery polarization, reducing the decomposition and consumption of the electrolyte, and being beneficial to improving the comprehensive electrochemical performance.

[0049] In the present application, the positive electrode active material includes at least one of a Prussian blue analogue, KVPO4F, and K z at least one of V2O5. The Prussian blue analogue has an open framework structure, rich potassium ion transport channels, low structural deformation degree, and excellent cycle stability; KVPO4F has a strong antioxidant ability and a relatively high working voltage due to its polyanion structure, which can effectively improve the energy density of the battery; K z V2O5 is a layered vanadium-based oxide with a high potassium storage specific capacity and excellent potassium ion insertion and extraction kinetics. The negative electrode active material includes at least one of an organic material and a polyanion compound. Among them, organic materials such as PTCDI and PNTCDA reversibly store potassium ions relying on carbonyl groups, have good molecular structure flexibility, small charge-discharge volume stress, and are suitable for the aqueous electrolyte environment; KTi2(PO4)3 has a three-dimensional conductive framework, a fast potassium ion diffusion rate, a stable potassium insertion potential, and excellent structural rigidity.

[0050] The positive electrode active material and negative electrode active material of the present application can be purchased or prepared. The present application does not particularly limit the preparation method of the positive electrode active material or the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the Prussian blue analogue K x M[Fe(CN)6] 1-ynH2O can be prepared by co-precipitation: First, prepare an aqueous solution of potassium ferrocyanide to obtain solution A; then prepare a salt solution containing element M to obtain solution B. Mix solutions A and B, then allow to stand for aging, centrifuge, and dry to obtain the Prussian blue analogue K. x M[Fe(CN)6] 1-y ·nH2O.

[0051] In some embodiments of this application, the positive electrode current collector includes at least one selected from titanium mesh, carbon cloth, carbon felt, and graphite paper; the negative electrode current collector includes at least one selected from carbon-coated aluminum foil, carbon felt, graphite paper, and carbon-coated copper foil. Preferably, the positive electrode current collector includes titanium mesh, and the negative electrode current collector includes carbon-coated aluminum foil. The positive electrode current collector provided in this application has high chemical inertness and is not easily oxidized or corroded at the high positive electrode potential of potassium-ion batteries. Furthermore, it is not prone to side reactions with the electrolyte of this application, exhibiting stable electrochemical performance, thereby contributing to improved cycle life and safety of potassium-ion batteries. The negative electrode current collector provided in this application, while meeting electrochemical stability requirements, has low manufacturing costs and is suitable for industrial applications.

[0052] In this application, the positive electrode includes a positive electrode film layer located on at least one side of the positive electrode current collector. The phrase "positive electrode film layer located on at least one side of the positive electrode current collector" means that the positive electrode film layer can be disposed on one surface of the positive electrode current collector along its thickness direction, or on two surfaces of the positive electrode current collector along its thickness direction. It should be noted that "surface" here can be the entire surface area of ​​the positive electrode current collector, or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the thickness of the positive electrode film layer and the positive electrode current collector, as long as the purpose of this application is achieved. For example, the thickness of the single-sided positive electrode material layer is 10 μm to 500 μm, and the thickness of the positive electrode current collector is 10 μm to 200 μm.

[0053] In this application, the positive electrode film layer also includes a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fiber. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode film layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0054] In this application, there are no particular limitations on the preparation method of the positive electrode sheet, as long as it achieves the purpose of this application. For example, it can be prepared by the following method: mixing positive electrode active material, positive electrode conductive agent, and positive electrode binder, and adding N-methylpyrrolidone (NMP) and stirring evenly. The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector, and after drying, a positive electrode sheet coated with a positive electrode film layer is obtained. Then, it is cold-pressed and cut to obtain the positive electrode sheet.

[0055] In this application, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The phrase "the negative electrode film layer is located on at least one side of the negative current collector" means that the negative electrode film layer can be disposed on one surface of the negative current collector along its thickness direction, or on two surfaces of the negative current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative current collector, or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the thickness of the negative electrode film layer and the negative current collector, as long as the purpose of this application is achieved. For example, the thickness of the single-sided negative electrode material layer is 10 μm to 500 μm, and the thickness of the negative current collector is 10 μm to 200 μm.

[0056] The negative electrode material layer also includes a negative electrode conductive agent and a negative electrode binder. This application does not impose any particular limitation on the types of negative electrode conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), or carboxymethyl chitosan (CMCS). This application does not impose any particular limitation on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode film layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. In some embodiments of this application, the negative electrode film layer may further include a thickener. This application does not particularly limit the type of thickener, as long as it achieves the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode film layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0057] In this application, there are no particular restrictions on the preparation method of the negative electrode sheet, as long as it achieves the purpose of this application. For example, it can be prepared by the following method: adding negative electrode active material, negative electrode conductive agent, and negative electrode binder to deionized water and stirring evenly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on the surface of the negative electrode current collector, and after drying, a negative electrode sheet coated with a negative electrode film layer is obtained. Then, it is cold-pressed and cut to obtain the negative electrode sheet.

[0058] In this application, the potassium-ion battery also includes a separator. There are no particular limitations on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), and glass fiber. The separator type may include at least one of woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, or spun membrane. In this application, there are no particular limitations on the separator thickness, as long as it achieves the purpose of this application; for example, the separator thickness may be from 10 μm to 1000 μm.

[0059] In this application, the potassium-ion battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of potassium-ion batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc. Specifically, the potassium-ion battery described in this application can be a button cell, a pouch cell, or a cylindrical cell; this application does not impose any particular limitation, as long as it achieves the purpose of this application.

[0060] The preparation process of the potassium-ion battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the potassium-ion battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a potassium-ion battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a potassium-ion battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the potassium-ion battery.

[0061] The fourth aspect of this application provides an application of the potassium-ion battery provided in the third aspect of this application in an energy storage system.

[0062] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0063] Example 1 <Preparation of Electrolyte> 3 mmol KFSI (0.658 g) and 9 mmol (1.065 g) cyclobutene sulfone (donor number 12.8 kcal / mol) were weighed and heated at 70 °C for 1 h to obtain a transparent solution. This solution was then allowed to stand at room temperature for 12 h to obtain a first mixed solution. Next, 9 mmol (0.162 g) of deionized water was added to the first mixed solution, and the solution was shaken at 60 °C for 1 h to obtain a clear and transparent second mixed solution. This second mixed solution was cooled to room temperature and purged with high-purity argon gas at a rate of 6 mL / min for 1 h to remove dissolved oxygen, yielding the electrolyte. In this example, the concentration of potassium salt KFSI in the electrolyte was 2.45 mol / kg, and the molar ratio of cyclobutene sulfone to water was 1:1.

[0064] <Preparation of Positive Electrode Active Materials> First, 12 mmol of K₄Fe(CN)₆·3H₂O was added to 350 ml of deionized water and dissolved by stirring at 60 °C to form a transparent, pale yellow solution A. Next, 7.8 mmol of MnSO₄·H₂O, 4.2 mmol of FeSO₄·7H₂O, and 100 mmol of CH₃COOK were dissolved in another 350 ml of deionized water to form solution B. Then, solution B was slowly added dropwise to solution A at a rate of 10 ml / min, and the mixture was stirred continuously at 60 °C for 12 h. After the reaction was complete, the mixture was allowed to stand at 60 °C for 12 h to age. The pale blue precipitate was collected by centrifugation and washed twice each with deionized water and ethanol to remove impurities. Finally, the washed precipitate was dried under vacuum at 80 °C for 12 h to obtain the KMnFePBA positive electrode active material, with the chemical formula K₄FePBA. 1.92 Fe 0.33 Mn 0.67 [Fe(CN)6] 0.98 0.78H2O.

[0065] <Preparation of the positive electrode> The above-prepared positive electrode active material KMnFePBA, conductive carbon black Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was thoroughly mixed to form a uniform positive electrode slurry with a solid content of 70%. The positive electrode slurry was uniformly coated onto a 300 μm thick, 100-mesh titanium mesh, dried at 60°C for 6 hours, and then vacuum dried at 110°C for 12 hours. The resulting electrode sheet was rolled and then punched to obtain a positive electrode sheet with a diameter of 12 mm and a positive electrode film thickness of 30 μm (positive electrode active material loading of 1.6 mg / cm). 2 ).

[0066] Assembly of the three-electrode system Using the positive electrode sheet prepared above as the working electrode, activated carbon as the counter electrode, Ag / AgCl as the reference electrode, and the electrolyte prepared above as the electrolyte, a three-electrode system is assembled.

[0067] <Preparation of Negative Electrode Sheets> PTCDI (anode active material), conductive carbon black (conductive agent), and PVDF (binder) were mixed in a 7:2:1 mass ratio, with NMP added as a solvent. The mixture was thoroughly mixed to form a uniform anode slurry with a solid content of 60%. The anode slurry was then uniformly coated onto a 16 μm thick carbon-coated aluminum foil and vacuum-dried at 110°C for 12 hours. The resulting electrode sheet was then rolled and punched to obtain a 14 mm diameter anode sheet with a 25 μm anode film thickness (anode active material loading of 1.4 mg / cm³). 2 ).

[0068] Assembly of Potassium-ion Batteries In an air atmosphere, the positive electrode sheet, separator (Whatman (GF / D), with a thickness of 500 μm) and negative electrode sheet prepared above are stacked in sequence and fixed with tape, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role in isolation. The battery is then encapsulated with an aluminum-plastic film, injected with the electrolyte prepared above, and vacuum sealed to obtain a single-layer soft-pack battery.

[0069] Examples 2 to 5 Except for the section on <Preparation of Electrolyte>, where the types of organic solvents were adjusted according to Table 1, the rest was the same as in Example 1. The donor numbers for sulfolane were 14.6 kcal / mol, for succinate 12.4 kcal / mol, for hexanetrionitrile 10.5 kcal / mol, and for acetamide 27 kcal / mol.

[0070] Examples 6 to 8 Except for adjusting the type of potassium salt according to Table 1 in the <Preparation of Electrolyte> section, and keeping the concentration of potassium salt unchanged, the rest is the same as in Example 1.

[0071] Examples 9 to 15 Except for the preparation of the electrolyte, in which the concentration of potassium salt KFSI and the molar ratio of potassium salt to organic solvent were adjusted according to Table 1, and the molar ratio of organic solvent to water was kept constant, the rest was the same as in Example 1.

[0072] Examples 16 to 19 Except for the preparation of the electrolyte, in which the molar ratio of organic solvent to water and the molar ratio of potassium salt to organic solvent were adjusted according to Table 1, and the potassium salt concentration was kept constant, the rest was the same as in Example 1.

[0073] Comparative Example 1 <Preparation of Electrolyte> Weigh 3 mmol (0.658 g) of KFSI and add it to 1.227 g of deionized water. The solution is incubated at 60 °C with shaking for 1 h to obtain a clear, transparent, homogeneous solution. Cool the solution to room temperature and purge it with high-purity argon gas at a rate of 6 mL / min for 1 h to remove dissolved oxygen, thus obtaining the electrolyte. The electrolyte obtained in this comparative example has a potassium salt KFSI concentration of 2.45 mol / kg, and the solvent is water only.

[0074] Except for the preparation of the electrolyte, in which the electrolyte is obtained according to the above process, the rest is the same as in Example 1.

[0075] Comparative Example 2 Except for the section on <Preparation of Electrolyte>, where the potassium salt concentration was adjusted according to Table 1, the rest is the same as Comparative Example 1.

[0076] Comparative Examples 3 to 5 Except for the section on <Preparation of Electrolyte>, where the relevant parameters were adjusted according to Table 1, the rest is the same as in Example 1.

[0077] Differential scanning voltammetry (DSC) test The first mixed solutions prepared in Examples 14, 12, 1, and 11 were subjected to DSC testing to determine the lowest melting point of the first mixed solution. The test results are as follows: Figure 1 As shown.

[0078] In Example 14, the molar ratio of potassium bis(fluorosulfonyl)imide (KFSI) to the organic solvent cyclobutene sulfone (Bds) in the first mixed solution was 1:1; in Example 12, the molar ratio of KFSI to Bds in the first mixed solution was 1:2; in Example 1, the molar ratio of KFSI to Bds in the first mixed solution was 1:3; and in Example 11, the molar ratio of KFSI to Bds in the first mixed solution was 1:4. Figure 1 As can be seen, the melting points of the first mixed solutions in the above embodiments are significantly lower than those of potassium difluorosulfonylimide (melting point 102℃) and cyclobutene sulfone (melting point 65℃), indicating that the first mixed solutions in the above embodiments are deep eutectic systems. Furthermore, the first mixed solution in Example 1 exhibits a unique lowest melting point, indicating that the complete coordination and charge delocalization effect between KFSI and Bds has reached the optimal state.

[0079] Fourier transform infrared spectroscopy (FTIR) test The electrolyte prepared in Example 1 was subjected to FTIR testing, and the test results are as follows: Figure 2 As shown. From Figure 2 It can be seen that the OH stretching peak (3100 cm⁻¹) corresponds to the strong hydrogen bond of free water. -1 ~3500cm -1 The presence of almost no hydrogen bonds and the dominance of peaks with no hydrogen bonds and weak hydrogen bonds indicate that the activity of water molecules in the electrolyte of this application is significantly suppressed, which is a typical characteristic of water molecules being "fixed" in the eutectic network.

[0080] Linear sweep voltammetry (LSV) test Using the Xinwei Battery Testing Equipment, the three-electrode systems assembled in the examples and comparative examples were subjected to linear sweep voltammetry (LSV) testing at a scan rate of 5 mV / s. The electrochemical stability window (EWS) of the electrolytes in the examples and comparative examples was measured, and the test results are detailed in Table 2.

[0081] The potassium-ion batteries assembled in the aforementioned embodiments and comparative examples were subjected to constant current charge-discharge tests using Xinwei Battery Testing Equipment. The test results are shown in Table 2.

[0082] (1) Potassium-ion battery energy density test: At 25℃, the potassium-ion battery was charged at a constant current of 0.15 A / g to a voltage of 2.5V, and then discharged at a constant current of 0.15 A / g to a voltage of 0V. The initial discharge capacity was recorded as Q1, and the average discharge voltage was recorded as V1. The energy density of the potassium-ion battery was calculated by the formula: energy density = Q1 × V1 / total mass of positive and negative electrode active materials.

[0083] (2) 1A / g cycle performance test: At 25℃, the potassium-ion battery was charged at a constant current of 1 A / g to a voltage of 2.5V, and then discharged at a constant current of 1 A / g to a voltage of 0V. The initial discharge capacity was recorded as P1. This constitutes one charge-discharge cycle. The above charge-discharge cycle was repeated for 2000 cycles, and the final discharge capacity was recorded as P2. The capacity retention rate after 2000 cycles of 1 A / g = P2 / P1 × 100%.

[0084] (3) Wide temperature range adaptability test: The potassium-ion battery was placed in a 25℃ oven and left to stand for 8 hours to reach a constant temperature. The potassium-ion battery was then charged at a constant current of 0.2 A / g to a voltage of 2.5V, and then discharged at a constant current of 0.2 A / g to a voltage of 0V. This constitutes one charge-discharge cycle. The above charge-discharge cycle was repeated for 5 cycles, and the discharge capacity of the fifth cycle was recorded as D1. Then, the potassium-ion battery was placed in a 60℃ oven and left to stand for 8 hours to reach a constant temperature. The potassium-ion battery was then charged at a constant current of 0.2 A / g to a voltage of 2.5V, and then discharged at a constant current of 0.2 A / g to a voltage of 0V. The above charge-discharge cycle was repeated for 5 cycles, and the discharge capacity of the fifth cycle was recorded as D2. The capacity retention rate R of the discharge capacity at 60℃ relative to the discharge capacity at 25℃ was also recorded. a Ra = D2 / D1 × 100%; Then, place the potassium-ion battery in a -20℃ oven and let it stand for 8 hours to reach a constant temperature. Charge the potassium-ion battery at a constant current of 0.2 A / g until the voltage reaches 2.5V, and then discharge it at a constant current of 0.2 A / g until the voltage reaches 0V. Repeat the above charge-discharge cycle 5 times. Record the discharge capacity of the 5th cycle as D3, and record the capacity retention rate R of the discharge capacity at -20℃ relative to the discharge capacity at 25℃. b R b =D3 / D1×100%; Then place the potassium-ion battery in a 25℃ oven and let it stand for 8 hours to allow it to reach a constant temperature. Charge the potassium-ion battery at a constant current of 0.2 A / g until the voltage reaches 2.5V, and then discharge it at a constant current of 0.2 A / g until the voltage reaches 0V. Repeat the above charge-discharge cycle 5 times. Record the discharge capacity of the 5th cycle as D4, and record the capacity retention rate R of the discharge capacity at 25℃ after returning to 25℃ relative to the initial 25℃ discharge capacity. c R c =D4 / D1×100%.

[0085] Flammability test Ignite a lit cotton swab and immerse it in a commercial organic electrolyte (potassium salt KFSI concentration of 1 mol / kg, organic solvents being ethylene carbonate EC and diethyl carbonate DEC, with a volume ratio of EC to DEC of 1:1) and the electrolyte prepared in Example 1, respectively. The commercial organic electrolyte ignited rapidly upon contact with the flame, and the flame continued to burn; the electrolyte prepared in Example 1 extinguished immediately upon contact with the flame, the cotton swab was completely extinguished, and no combustion was observed. The test results show that the electrolyte of this application has excellent non-flammable properties and its safety is significantly better than that of traditional organic electrolytes. For details of the test procedure, please refer to [link to test procedure]. Figure 3 .

[0086] The preparation parameters of each embodiment and comparative example are shown in Table 1, and the performance parameters of each embodiment and comparative example are shown in Table 2.

[0087] Table 1

[0088] Note: In Table 1, " / " indicates that no relevant preparation parameters are available. Table 2

[0089] As can be seen from Examples 1 to 19 and Comparative Examples 1 to 5, the electrolyte in the embodiments of this application includes an organic solvent with a donor number of 10 kcal / mol to 30 kcal / mol, and the molar ratio of the organic solvent to water is controlled to be 1:5 to 5:1, and the potassium salt concentration is 1 mol / kg to 8 mol / kg. The resulting electrolyte has a high electrochemical stability window. When applied to potassium-ion batteries, the energy density, cycle capacity retention rate of 1 A / g after 2000 cycles, Ra, Rb, and Rc of the potassium-ion battery are all high. This indicates that the electrolyte provided in this application has a wide electrochemical stability window, and the energy density, cycle performance, wide temperature range adaptability, and structural reversibility of the potassium-ion battery are all improved.

[0090] The electrolytes of Comparative Examples 1 and 2 did not contain the organic solvents of this application, the potassium salt concentration of Comparative Example 3 was less than 1 mol / kg, and the molar ratio of organic solvent to water in the electrolyte of Comparative Example 4 was less than 1:5. These electrolytes had narrow electrochemical stability windows, and the energy density, cycle capacity retention rate of 1 A / g after 2000 cycles, Ra, Rb, and Rc of the potassium-ion batteries were all low. This indicates that the electrolytes of Comparative Examples 1 to 4 have narrow electrochemical stability windows, and the potassium-ion batteries have low energy density, poor cycle performance, poor wide temperature range adaptability, and poor structural reversibility. In Comparative Example 5, the molar ratio of organic solvent to water in the electrolyte was higher than 5:1, indicating a high content of organic solvent in the electrolyte solvent. Although the resulting electrolyte had a high electrochemical stability window, the excessive organic solvent content led to high electrolyte viscosity and low ionic conductivity. Consequently, the energy density, cycle capacity retention rate (1 A / g after 2000 cycles), Ra, Rb, and Rc of the resulting potassium-ion battery were all low. This indicates that potassium-ion batteries have low energy density, poor cycle performance, poor wide-temperature adaptability, and poor structural reversibility.

[0091] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0092] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises potassium salt, water, and organic solvent; The concentration of the potassium salt is 1 mol / kg to 8 mol / kg; The number of donors for the organic solvent is from 10 kcal / mol to 30 kcal / mol; The molar ratio of the organic solvent to the water is 1:5 to 5:

1.

2. The electrolyte according to claim 1, characterized in that, The organic solvent includes at least one of sulfolane, sulfolane, succinate, hexanetrionitrile, and acetamide.

3. The electrolyte according to claim 1, characterized in that, The potassium salt includes at least one of potassium trifluoromethanesulfonate, potassium hexafluorophosphate, potassium bis(fluorosulfonyl)imide, and potassium bis(trifluoromethanesulfonyl)imide.

4. The electrolyte according to claim 1, characterized in that, In the electrolyte, the concentration of the potassium salt is 1 mol / kg to 5 mol / kg; preferably, the concentration of the potassium salt is 2.45 mol / kg to 5 mol / kg.

5. The electrolyte according to any one of claims 1 to 4, characterized in that, The molar ratio of the organic solvent to the water is 1:3 to 3:

1.

6. The electrolyte according to any one of claims 1 to 4, characterized in that, The molar ratio of the potassium salt to the organic solvent is from 1:7.34 to 1:0.92; preferably, the molar ratio of the potassium salt to the organic solvent is from 1:3 to 1:

1.

7. The electrolyte according to any one of claims 1 to 4, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The electrochemical stability window of the electrolyte is 3V~4V; (2) The electrolyte is liquid under the condition of temperature ranging from -20℃ to 60℃.

8. A method for preparing the electrolyte according to any one of claims 1 to 7, characterized in that, include: The potassium salt and the organic solvent are subjected to a first mixing treatment to obtain a first mixed solution. The temperature of the first mixing treatment is 50℃~80℃, and the time of the first mixing treatment is 0.5h~2h. The first mixed solution is subjected to a second mixing treatment with the water to obtain a second mixed solution. The temperature of the second mixing treatment is 40℃~60℃, and the time of the second mixing treatment is 0.5h~1h. The second mixed solution is bubbled with an inert gas to obtain the electrolyte.

9. The method according to claim 8, characterized in that, At least one of the following conditions must be met: (1) In the first mixed solution, the molar ratio of the potassium salt to the organic solvent is 1:7.34 to 1:0.92; preferably, the molar ratio of the potassium salt to the organic solvent is 1:3 to 1:1; (2) In the second mixed solution, the molar ratio of the organic solvent to the water is 1:5 to 5:

1.

10. A potassium-ion battery, characterized in that, The electrolyte includes any one of claims 1 to 7 or an electrolyte prepared by the method described in any one of claims 8 to 9.

11. The potassium-ion battery according to claim 10, characterized in that, The potassium ion battery includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes at least one of a Prussian blue analogue, KVPO4F, and K z V2O5; wherein, the chemical formula of the Prussian blue analogue is K x M[Fe(CN)6] 1-y ·nH2O, where M includes at least one of Mn, Fe, Cu, Ni, Co, and Zn, 0 < x ≤ 2, 0 < y ≤ 1, 0 < n ≤ 1, 0 < z ≤ 1; the negative electrode plate includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes at least one of an organic material and a polyanion compound.

12. The potassium-ion battery according to claim 11, characterized in that, The organic material includes at least one of 3,4,9,10-perylenetetracarboxylic diimide and 1,4,5,8-naphthalenetetracarboxylic anhydride, and the polyanionic compound includes potassium titanium phosphate.

13. The potassium-ion battery according to claim 11, characterized in that, The positive electrode current collector includes at least one of titanium mesh, carbon cloth, carbon felt, and graphite paper; the negative electrode current collector includes at least one of carbon-coated aluminum foil, carbon felt, graphite paper, and carbon-coated copper foil.

14. The application of the potassium-ion battery according to any one of claims 10-13 in an energy storage system.

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