Potassium ion battery and overdischarge method

Abstract

The invention relates to a potassium ion battery and an overdischarge method. The overdischarge method comprises the following steps: mixing a Prussian blue analogue K2Mn [Fe (CN) 6], a conductive agent and a binder according to a certain proportion to prepare a positive pole piece; assembling the negative electrode shell, the elastic sheet, the gasket, the potassium sheet or the negative electrode sheet, the electrolyte, the diaphragm, the electrolyte, the positive electrode sheet, the gasket and the positive electrode shell into a potassium ion battery in sequence, and compacting the potassium ion battery; discharging the compacted battery by adopting a certain current density, and stopping discharging when a discharging cut-off condition is met; and dismantling the assembled potassium ion battery and performing exhaust treatment. K2 [MnFe (CN) 6] has the advantages of high specific capacity, low price, simple and convenient synthesis and preparation method and the like. The lithium ion battery is used as a positive electrode of the battery, graphite is used as a negative electrode of the battery, and over-discharge treatment is performed before the battery runs, so that the content of active ions is kept while the durability of the battery is guaranteed. And under the condition of room temperature, the cycle life of 0.1 C current density is more than 300 times, the energy density is 339.9 Wh / kg, and a relatively large application field is provided for the high-performance potassium ion battery.

Description

Technical Field

[0001] The invention belongs to the technical field of potassium ion batteries, and in particular relates to a potassium ion battery and an overdischarge method. Background Art

[0002] The energy storage market has long been dominated by lithium-ion batteries. Although lithium-ion batteries have been widely used in portable electronic devices and new energy vehicles, the price and output of lithium-ion batteries are difficult to meet the growing demand for energy storage applications due to the scarcity and uneven distribution of lithium resources. In contrast, potassium-ion batteries have become a low-cost and sustainable alternative to lithium-ion batteries because they reduce dependence on high-cost elements such as lithium, nickel, cobalt and copper, and are compatible with current commercial graphite. However, during the operation of potassium ions, the loss of active ions caused by irreversible side reactions can lead to more serious battery capacity decay.

[0003] The current method for improving battery energy density and cycle life is mainly to pre-lithiate (pre-sodium, pre-potassium) the electrode materials. These methods mainly include the use of lithium (sodium, potassium) additives, reducing agents or electrochemical devices to introduce additional active ions into the positive or negative electrode of the battery by physical or chemical methods to compensate for the loss of active ions during battery operation, especially during the initial formation of the solid electrolyte interface (SEI). However, these strategies are limited by some practical factors, such as the effect of the weight of the additives on the battery energy density, the effect of the decomposition of the additives on the gas generation, the controllability of the pre-lithiation (pre-sodium, pre-potassium) treatment, the complexity of the operating procedures and the high operating costs. These factors are not conducive to the actual commercial production of batteries.

[0004] As an advanced cathode material for potassium ion batteries at present, K2Mn[Fe(CN)6] has a higher average discharge voltage (3.95V vs. K + / K), a specific capacity of more than 150mAh / g and excellent cycle stability, it is an electrode material with great development prospects. However, in actual use, the full battery cycle stability directly composed of it and graphite is poor, and the graphite generally needs to be pre-potassiumized. In addition, since lithium-ion batteries experience decomposition of electrode materials and dissolution of copper current collectors during over-discharge, the traditional view is that over-discharge is harmful to the operation of the battery. So far, there have been no patents or literature reports on the advantages of over-discharge in battery applications. Summary of the invention

[0005] In order to solve the problem of capacity attenuation and low energy density of the current full battery directly composed of K2Mn[Fe(CN)6] and graphite. The present invention adopts an overdischarge method, which is directly operated in the K2Mn[Fe(CN)6]-graphite full battery formation process to prepare a potassium ion battery capable of maintaining high energy density, high capacity retention rate and long cycle life. To this end, the present invention provides a potassium ion battery and an overdischarge method.

[0006] A potassium ion battery overdischarge method, the method comprising the steps of:

[0007] S1. Prussian blue analog K2Mn[Fe(CN)6], conductive agent and binder are mixed in a certain proportion to prepare a positive electrode sheet;

[0008] S2. Assemble the negative electrode shell, shrapnel, gasket, potassium sheet or negative electrode sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, positive electrode shell in order to form a potassium ion battery and compact it;

[0009] S3. Discharging the compacted battery using a certain current density and stopping when the discharge cutoff condition is reached;

[0010] S4. Dismantle the assembled potassium ion battery and perform exhaust treatment.

[0011] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the binder is one of polyvinylidene fluoride PVDF and polytetrafluoroethylene PTFE.

[0012] According to the aspects and any possible implementation methods described above, an implementation method is further provided, S1 specifically comprising: using K2Mn[Fe(CN)6] as the positive electrode active material, mixing the positive electrode active material, conductive agent, and binder in a mass ratio of 7:2:1, adding N-methylpyrrolidone and stirring evenly, uniformly coating on an aluminum foil current collector, and vacuum drying at 80°C to obtain a positive electrode sheet.

[0013] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the material for preparing the negative electrode plate includes graphite, a conductive agent and a binder.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein the binder is one of polyvinylidene fluoride PVDF, polytetrafluoroethylene PTFE, polyvinyl alcohol PVA, sodium hydroxymethyl cellulose CMC, potassium alginate or sodium alginate.

[0015] According to the above aspects and any possible implementation manner, an implementation manner is further provided, wherein the conductive agent is a combination of one or more of acetylene black, Ketjen black, carbon nanotubes and graphene.

[0016] According to the above aspects and any possible implementation, an implementation is further provided, wherein the separator is a polyolefin such as polyethylene PE, polypropylene PP, polyvinylidene fluoride PVDF, polyimide PI, and glass fiber paper.

[0017] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the discharge cut-off condition is that the loading amount of the positive electrode K2Mn[Fe(CN)6] active material in the battery is 50 mAh / g.

[0018] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the electrolyte includes a potassium salt, a solvent and a diluent, the electrolyte solvent is triethyl phosphate TEP, the diluent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether HFE, and the potassium salt is potassium bis(fluorosulfonyl)imide KFSI or potassium bis(trifluoromethanesulfonyl)imide KTFSI.

[0019] The present invention also provides a potassium ion battery, which is obtained by being treated by the overdischarge method.

[0020] Beneficial effects of the present invention

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention provides an overdischarge method for a potassium ion battery, wherein a Prussian blue analog K2Mn[Fe(CN)6], a conductive agent and a binder are mixed in a certain proportion to prepare a positive electrode sheet; a negative electrode shell, a spring sheet, a gasket, a potassium sheet or a negative electrode sheet, an electrolyte, a diaphragm, an electrolyte, a positive electrode sheet, a gasket and a positive electrode shell are assembled into a potassium ion battery in this order and compacted; the compacted battery is discharged using a certain current density and the discharge is stopped when a discharge cut-off condition is reached; the assembled potassium ion battery is dismantled and exhaust gas is treated. K2[MnFe(CN)6] has the advantages of high specific capacity, low price and simple synthesis and preparation method. It is used as the positive electrode of the battery and graphite is used as the negative electrode of the battery. An overdischarge treatment is performed before the battery is operated, thereby maintaining the active ion content and ensuring the durability of the battery. Under room temperature conditions, the cycle life of 0.1C current density is greater than 300 times, and the energy density is 339.9Wh / kg, which provides a large application field for high-performance potassium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The charge-discharge curve of the K2Mn[Fe(CN)6] material in Example 1 after discharge at a current density of 15 mA / g;

[0024] Figure 2This is a cycle stability diagram of the K2Mn[Fe(CN)6] material in Example 1 of the present invention after discharge at a current density of 15 mA / g;

[0025] Figure 3 This is a cycle stability diagram of the K2Mn[Fe(CN)6] material in Example 1 of the present invention at a current density of 15 mA / g without undergoing discharge;

[0026] Figure 4 The charge-discharge curve of the potassium ion battery in Example 2 of the present invention after discharge at a current density of 15 mA / g;

[0027] Figure 5 This is a cycle stability diagram of the potassium ion battery in Example 2 of the present invention at a current density of 15 mA / g, with and without discharge. DETAILED DESCRIPTION

[0028] In order to better understand the technical solution of the present invention, the content of the present invention includes but is not limited to the specific implementation methods described below, and similar technologies and methods should be considered to be within the scope of protection of the present invention. In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] It should be clear that the embodiments described in the present invention are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0031] The present invention provides an overdischarge method for a potassium ion battery, the method comprising the steps of:

[0032] S1. Prussian blue analog K2Mn[Fe(CN)6], conductive agent and binder are mixed in a certain proportion to prepare a positive electrode sheet;

[0033] S2. Assemble the negative electrode shell, shrapnel, gasket, potassium sheet or negative electrode sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, positive electrode shell in order to form a potassium ion battery and compact it;

[0034] S3. Discharging the compacted battery using a certain current density and stopping when the discharge cutoff condition is reached;

[0035] S4. Dismantle the assembled potassium ion battery and perform exhaust treatment.

[0036] The positive electrode material of the battery is K2Mn[Fe(CN)6], a Prussian blue analogue.

[0037] The negative electrode material of the battery is graphite.

[0038] The potassium-containing electrolyte includes potassium salt, solvent and diluent, and the separator separates the positive and negative electrodes to prevent the positive and negative electrodes from direct contact and short circuit.

[0039] The battery material K2Mn[Fe(CN)6] and graphite are mixed with a conductive agent and a binder to form a slurry, which is then coated on a current collector and vacuum dried to obtain a battery electrode.

[0040] The total proportion of the conductive agent and the binder in the positive and negative electrode sheets is 30wt.% to 5wt.%. Under this proportion, the positive and negative electrode sheets have the best conductivity and stability, and the electrode sheets will not crack during the cycle process.

[0041] The loading amount of the positive electrode material K2Mn[Fe(CN)6] is 2 mg / cm 2 ~10mg / cm 2 , 0.3mAh~15mAh (calculated based on the mass of the positive electrode active material in the battery) potassium ion batteries can be assembled.

[0042] The loading amount of graphite of the negative electrode plate material is 1 mg / cm 2 ~5mg / cm 2 , which can correspond to the above-mentioned positive electrode sheet to form a 0.3mAh to 15mAh (calculated based on the mass of the positive electrode active material in the battery) potassium ion battery.

[0043] The conductive agent used in the positive and negative electrode sheets is one or more of acetylene black, Ketjen black, carbon nanotubes and graphene.

[0044] The binder used in the positive electrode plate is one of polyvinylidene fluoride PVDF and polytetrafluoroethylene PTFE.

[0045] The binder used in the negative electrode plate is one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), sodium hydroxymethyl cellulose (CMC), potassium alginate and sodium alginate.

[0046] Aluminum foil is used as the positive electrode and negative electrode current collectors.

[0047] The electrolyte potassium salt is potassium bis(fluorosulfonyl)imide (KFSI) or potassium bis(trifluoromethanesulfonyl)imide (KTFSI). Preferably, the potassium salt concentration is 0.5 mol / L KFSI and 0.5 mol / L KTFSI.

[0048] The electrolyte solvent is triethyl phosphate TEP, and the diluent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether HFE. Preferably, the volume ratio of the solvent to the diluent is 1:1, and under this ratio, the electrolyte solution has the lowest viscosity (room temperature viscosity is 6.9mPa·s) and the highest conductivity (2.448mS / cm).

[0049] The membrane material includes but is not limited to: polyethylene PE, polypropylene PP, polyvinylidene fluoride PVDF, polyimide PI, glass fiber paper, etc.

[0050] The over-discharge method is directly performed after the battery is assembled and before the battery is operated. The over-discharge method uses the specific capacity of the positive active material of the battery as the cut-off condition. Specifically, the button battery is assembled in the order of negative electrode shell, spring, gasket, negative electrode sheet (graphite or potassium metal), electrolyte, diaphragm, electrolyte, positive electrode sheet, gasket, and positive electrode shell from top to bottom. After assembly, the button battery sealing machine is used to compact the battery for subsequent testing. After the battery is assembled, it is allowed to stand for 12 hours to ensure that the electrode sheet and diaphragm are completely wetted by the electrolyte. First, an over-discharge treatment is performed. The program is set in the battery test system to discharge at a current density of 0.1C. The discharge cut-off condition is 30mAh / g to 150mAh / g based on the mass of the positive electrode K2Mn[Fe(CN)6] in the battery. When this is used as the over-discharge cut-off condition, it can be ensured that the crystal structure of the positive electrode K2Mn[Fe(CN)6] is not destroyed, and 0.4 to 2 K are embedded in K2Mn[Fe(CN)6]. + , used to supplement the K in the formation process of the negative electrode graphite solid electrolyte interface (SEI) + consumption.

[0051] As an embodiment disclosed in the present invention, the present invention also provides a potassium ion battery, which is obtained after being treated by the over-discharge method of the present invention. After obtaining the battery that has been treated by discharge, a normal charge and discharge cycle is subsequently performed. The specific operation process is as follows: after the over-discharge is cut off, the battery is disassembled in the glove box, and after exhausting, the positive and negative electrode sheets and diaphragms in the battery are assembled into button batteries in the order of negative electrode shell, spring, gasket, negative electrode sheet (graphite or potassium metal), electrolyte, diaphragm, electrolyte, positive electrode sheet, gasket, positive electrode shell from top to bottom to obtain an assembled battery after discharge treatment; after assembly, a button battery sealing machine is used to compact the battery for subsequent testing. After the battery is assembled, it is allowed to stand for 12 hours, and a battery testing system is used at room temperature with a current density of 0.1C to cycle according to the process of charging first and then discharging. The cycle voltage range of the half-battery is 2.7V-4.4V vs.K + / K, cycling within this voltage range can ensure that the two K + All of them are deintercalated during charging and embedded in the lattice during discharging. The full battery voltage is 1.5V-4.3V. Cycling within this voltage range can ensure that the two K + During the charging process, all of it is deintercalated from the positive electrode K2Mn[Fe(CN)6] into the negative electrode graphite, and during the discharging process, all of it is deintercalated from the negative electrode graphite into the positive electrode K2Mn[Fe(CN)6]. Preferably, the over-discharge cut-off condition of the battery is 50mAh / g.

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only for illustration and are not intended to limit the present application.

[0053] The present invention includes a positive electrode material, a negative electrode material, an electrolyte, a diaphragm and an overdischarge method. The positive electrode material of the battery is a Prussian blue analog K2Mn[Fe(CN)6], the negative electrode material of the battery is graphite, the potassium-containing electrolyte includes its potassium salt, a solvent and a diluent, and the diaphragm separates the positive and negative electrodes to prevent the positive and negative electrodes from directly contacting and short-circuiting. The overdischarge method is performed directly after the battery is assembled and before the battery is operated.

[0054] In specific implementation, the overdischarge method is first performed after the battery is assembled, with a cutoff condition of 30mAh / g to 150mAh / g. After the battery is overdischarged, it is disassembled in a glove box, vented and reassembled, and a subsequent cycle stability test is performed after assembly. Preferably, the overdischarge cutoff condition is 50mAh / g.

[0055] In the specific implementation, preferably, the positive electrode active material in the positive electrode plate is K2Mn[Fe(CN)6], and the mass ratio is 70wt.% to 90wt.%, at which the positive electrode has a higher active material loading. The total proportion (mass ratio) of conductive carbon and binder in the positive electrode plate is 30wt.% to 10wt.%, at which the positive electrode plate has the best conductivity and stability, and the plate will not crack during the cycle. Ensure that the sum of the mass ratios of conductive carbon, binder and positive electrode active material is 100%. The loading amount of positive electrode active material can be controlled at 2mg / cm 2 ~10mg / cm 2 This ratio can meet the needs of assembling 0.3mAh to 15mAh (calculated based on the mass of the positive electrode active material in the battery) potassium ion batteries.

[0056] In the specific implementation, preferably, the negative electrode active material in the negative electrode plate is graphite, and the mass ratio is 80wt.% to 95wt.%. At this ratio, the negative electrode has a higher coulombic efficiency. The total proportion (mass ratio) of conductive carbon and binder in the negative electrode plate is 20wt.% to 5wt.%. At this ratio, the negative electrode plate has the best conductivity and stability, and the plate will not crack during the cycle. Ensure that the sum of the mass ratios of conductive carbon, binder and negative electrode active material is 100%. The loading amount of negative electrode active material can be controlled at 1mg / cm 2 ~5mg / cm 2 This ratio can correspond to the above-mentioned positive electrode sheet and meet the needs of assembling 0.3mAh to 15mAh (calculated based on the mass of the positive electrode active material in the battery) potassium ion batteries.

[0057] In a specific implementation, in the potassium ion battery provided by the present invention, the capacity ratio of the negative electrode plate and the positive electrode plate can be controlled to be 1.1:1 to 1.2:1, which can ensure that K in the positive electrode K2Mn[Fe(CN)6] + During the charge and discharge process, the battery is completely deintercalated / intercalated, which makes the battery have a higher capacity and prevents the negative electrode from lacking K + The receiving position of the potassium precipitate may cause safety hazards.

[0058] In a specific implementation, the conductive carbon used in the positive electrode sheet and the negative electrode sheet can be one or more of acetylene black, Ketjen black, carbon nanotubes and graphene. The positive electrode sheet and the negative electrode sheet can use the same conductive carbon, or the positive electrode sheet and the negative electrode sheet can also use two different conductive carbons, which is not limited here.

[0059] In a specific implementation, the binder used in the positive electrode plate is one of polyvinylidene fluoride PVDF and polytetrafluoroethylene PTFE, and the current collector is aluminum foil.

[0060] In a specific implementation, the binder used in the negative electrode plate is one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene PTFE, polyvinyl alcohol PVA, sodium hydroxymethyl cellulose CMC, potassium alginate, and sodium alginate, and the current collector is aluminum foil.

[0061] In a specific implementation, the potassium ion battery electrolyte includes a potassium salt, a solvent and a diluent, the electrolyte solvent is triethyl phosphate TEP, and the diluent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether HFE. Preferably, the volume ratio of the solvent to the diluent is 1:1. The electrolyte potassium salt is potassium bis(fluorosulfonyl)imide KFSI and potassium bis(trifluoromethanesulfonyl)imide (KTFSI). Preferably, the potassium salt concentration is 0.5 mol / L KFSI and 0.5 mol / L KTFSI. At this ratio, the electrolyte solution has the lowest viscosity (room temperature viscosity is 6.9 mPa·s) and the highest conductivity (2.448 mS / cm).

[0062] In a specific implementation, the potassium ion battery separator can be selected from polyolefins such as polyethylene (PE) and polypropylene (PP), polyvinylidene fluoride PVDF, polyimide PI, and glass fiber paper.

[0063] It should be noted that the potassium ion battery provided by the present invention may be a button-type potassium ion battery, or may be a soft-pack potassium ion battery, which is not limited herein.

[0064] In specific implementation, when the binder used in the battery pole piece is polyvinylidene fluoride PVDF, the solvent used to prepare the slurry is N-methylpyrrolidone NMP; when the binder used in the electrode pole piece is polytetrafluoroethylene PTFE, the solvent used to prepare the slurry is isopropyl alcohol; when the binder used in the electrode pole piece is sodium carboxymethyl cellulose CMC, the solvent used to prepare the slurry is water; when the binder used in the electrode pole piece is sodium alginate or sodium alginate, the solvent used to prepare the slurry is water.

[0065] It should be noted that in the process of preparing the electrode slurry, there is no fixed ratio for the mixture of the solvent, the electrode material, the binder, and the conductive agent, as long as they are stirred evenly to form a slurry.

[0066] The following is a specific example of preparing a button-type potassium ion battery, which mainly relies on the movement of potassium ions between the positive electrode and the negative electrode to work, and the specific implementation process of the present invention is described in detail.

[0067] Example 1

[0068] (1) Preparation of positive electrode sheet: K2Mn[Fe(CN)6] is used as the positive electrode active material. The positive electrode active material, conductive carbon Ketjen black, and binder PVDF are mixed in a mass ratio of 7:2:1. At this ratio, the positive electrode sheet has the best conductivity and stability, and the sheet will not crack during the cycle. After adding N-methylpyrrolidone and stirring evenly, it is evenly coated on the aluminum foil current collector and vacuum dried at 80°C to obtain the positive electrode sheet. The loading amount of the positive electrode active material is 2 mg / cm 2 .

[0069] (2) Preparation of half-cell: A metal potassium sheet was used as the counter electrode and reference electrode, a glass fiber was used as a separator, and the electrolyte was selected to be 0.5 mol / L potassium bis(fluorosulfonyl)imide KFSI and 0.5 mol / L potassium bis(trifluoromethanesulfonyl)imide KTFSI dissolved in a mixed solution of triethyl phosphate TEP and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether HFE (TEP:HFE=1:1 Vol%). In a glove box with a water and oxygen content of less than 0.1 ppm, a button cell was assembled in the order of negative electrode shell, spring sheet, gasket, potassium sheet (also used as reference electrode and counter electrode), electrolyte, separator, electrolyte, positive electrode sheet, gasket, and positive electrode shell. After assembly, the cell was compacted using a button cell sealing machine for subsequent testing.

[0070] (3) Implementation of over-discharge method: After the battery is assembled, it is allowed to stand for 12 hours, and a constant current charge and discharge test is performed at room temperature using a battery testing system. The first cycle is over-discharged, and the over-discharge cut-off condition is 50 mAh / g based on the mass of the positive electrode K2Mn[Fe(CN)6] in the battery.

[0071] After the over-discharge is cut off, the battery is disassembled in the glove box. After exhausting, the positive electrode sheet, potassium sheet and diaphragm in the battery are assembled into a button battery in the order of negative electrode shell, spring sheet, gasket, potassium sheet, electrolyte, diaphragm, electrolyte, positive electrode sheet, gasket and positive electrode shell from top to bottom; after assembly, the battery is compacted using a button battery sealing machine for subsequent testing, that is, the components obtained after discharge are reassembled to form an assembled battery for testing. The specific process is as follows: After the battery is assembled, it is left to stand for 12 hours, and a battery test system is used at room temperature with a current density of 0.1C, and the battery is first charged to 4.4V vs.K + / K, after discharge to 2.7V vs.K + / K process is cycled. Figure 1 The battery's charge and discharge curves are shown after overdischarge to 50 mAh / g (based on the amount of positive electrode active material loaded in the battery). After discharge treatment, the battery can still maintain a maximum discharge specific capacity of 153.9 mAh / g. Figure 2The battery showed good cycle stability after discharge. After 500 cycles, the discharge capacity remained at 130.5 mAh / g, with a capacity retention rate of 85.29%. Figure 3 The half-cell cycle stability after overdischarge was studied, and the capacity retention rate was 83.77% after 300 cycles. The overdischarge treatment significantly improved the cycle stability of the K2Mn[Fe(CN)6] half-cell.

[0072] Example 2

[0073] (1) Preparation of positive electrode sheet: The positive electrode sheet was prepared by the method of step (1) of Example 1.

[0074] (2) Preparation of negative electrode sheet: Commercial graphite was used as the negative electrode active material. The negative electrode active material, conductive carbon Ketjen black, and binder CMC were mixed in a mass ratio of 8:1:1. After adding water and stirring evenly, the mixture was evenly coated on the aluminum foil current collector. After vacuum drying at 80°C, the negative electrode sheet was obtained. The loading amount of the negative electrode active material was 1 mg / cm 2 .

[0075] (3) Preparation of potassium ion battery: glass fiber was used as a separator, and the electrolyte was selected as 0.5 mol / L potassium bis(fluorosulfonyl)imide KFSI and 0.5 mol / L potassium bis(trifluoromethanesulfonyl)imide KTFSI dissolved in a mixed solution of triethyl phosphate (TEP) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (HFE) (TEP:HFE=1:1 Vol%). In a glove box with a water and oxygen content of less than 0.1 ppm, button cells were assembled in the order of negative electrode shell, spring sheet, gasket, negative electrode sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, and positive electrode shell. After assembly, the battery was compacted using a button battery sealing machine for subsequent testing.

[0076] (4) Overdischarge: After the battery is assembled, it is left to stand for 12 hours. The battery test system is used to perform constant current charge and discharge tests at room temperature. The first cycle is overdischarged. The overdischarge cutoff condition is 50mAh / g based on the mass of the positive electrode K2Mn[Fe(CN)6] in the battery. After overdischarge, an additional 0.67 K + , the additional potassium ions K + It can just make up for the consumption of K+ in the formation process of negative electrode graphite SEI, ensure that K+ in K2Mn[Fe(CN)6] will not be lost, improve battery specific capacity, and further improve battery energy density. At the same time, due to over-discharge, K+ in K2Mn[Fe(CN)6] is guaranteed to be +There will be no loss, and K2Mn[Fe(CN)6] can still maintain full charge and discharge during subsequent cycles, so the cycle stability of the whole battery is improved, solving the previous problem of full battery capacity attenuation.

[0077] As an embodiment disclosed by the present invention, the present invention also provides a potassium ion battery, which is obtained by being treated by the over-discharging method.

[0078] Specifically, after the over-discharge is cut off, the assembled battery that has undergone the above-mentioned over-discharge treatment is disassembled in the glove box, and after exhausting, the positive electrode sheet, negative electrode sheet and diaphragm in the battery are reassembled into a button battery in the order of negative electrode shell, spring, gasket, negative electrode sheet, electrolyte, diaphragm, electrolyte, positive electrode sheet, gasket, positive electrode shell from top to bottom; after assembly, the battery is compacted using a button battery sealing machine for subsequent testing, that is, the battery that has undergone the discharge treatment is assembled and tested again, and the process is as follows: after the battery is assembled, it is allowed to stand for 12 hours, and a battery testing system is used at room temperature with a current density of 0.1C, and the battery is cycled according to the process of first charging to 4.3V and then discharging to 1.5V. Figure 4 The battery's charge and discharge curves are shown after overdischarge to 50mAh / g (based on the loading amount of the positive electrode active material in the battery). After discharge treatment, the battery can still maintain a maximum discharge specific capacity of 146.3mAh / g, and the battery energy density is 339.9Wh / kg. Figure 5 The battery showed cycle stability after discharge. After 300 cycles, the charge-discharge capacity remained at 128.7 mAh / g, with a capacity retention rate of 87.97%. The capacity retention rate of the battery that had not undergone discharge was only 30.79% after 100 cycles. Therefore, by comparison, it can be seen that over-discharge treatment significantly improved the cycle stability and energy density of the K2Mn[Fe(CN)6]-graphite full battery.

[0079] The above description shows and describes several preferred embodiments of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not depart from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for overdischarging a potassium ion battery, It is characterized in that The method comprises the steps of: S1. Prussian blue analog K 2 Mn[Fe(CN) 6 ], the conductive agent and the binder are mixed in a certain proportion to prepare the positive electrode sheet; S2. Assemble the negative electrode shell, shrapnel, gasket, potassium sheet or negative electrode sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, positive electrode shell in order to form a potassium ion battery and compact it; S3. Discharging the compacted battery using a certain current density and stopping when the discharge cutoff condition is reached; S4. Dismantle the assembled potassium ion battery and perform exhaust treatment.

2. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that The binder is one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

3. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that S1 specifically includes: Use K 2 Mn[Fe(CN) 6 ] As the positive electrode active material, the positive electrode active material, the conductive agent and the binder are mixed in a mass ratio of 7:2:1, N-methylpyrrolidone is added and stirred evenly, and then evenly coated on the aluminum foil current collector, and vacuum dried at 80°C to obtain the positive electrode sheet.

4. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that The materials used to prepare the negative electrode plate include graphite, a conductive agent and a binder.

5. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that The binder is one of polyvinylidene fluoride PVDF, polytetrafluoroethylene PTFE, polyvinyl alcohol PVA, sodium hydroxymethyl cellulose CMC, potassium alginate or sodium alginate.

6. The overdischarge method of a potassium ion battery according to claim 1 or 4, It is characterized in that The conductive agent is a combination of one or more of acetylene black, Ketjen black, carbon nanotubes and graphene.

7. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that The separator is a polyolefin such as polyethylene PE, polypropylene PP, polyvinylidene fluoride PVDF, polyimide PI, and glass fiber paper.

8. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that The discharge cut-off condition is that the positive electrode K 2 Mn[Fe(CN) 6 ]The loading capacity of active material is 30mAh / g~150mAh / g.

9. The overdischarge method of a potassium ion battery according to claim 1, It is characterized in that The electrolyte comprises potassium salt, solvent and diluent, the electrolyte solvent is triethyl phosphate TEP, the diluent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether HFE, and the potassium salt is potassium bis(fluorosulfonyl)imide KFSI or potassium bis(trifluoromethanesulfonyl)imide KTFSI.

10. A potassium ion battery, It is characterized in that The battery is obtained by being treated by the overdischarge method according to any one of claims 1 to 9.

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