Positive electrode material and preparation method thereof, battery and electric equipment

Abstract

The invention relates to a positive electrode material and a preparation method thereof, a battery and electric equipment. The positive electrode material comprises ferric sodium pyrophosphate, and the content a of sulfur impurities in the positive electrode material is more than or equal to 0 and less than or equal to 100ppm.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode material and a preparation method thereof, a battery and an electrical device. Background Art

[0002] In the field of sodium ion battery technology, sodium ferric pyrophosphate (NFPP) is often used as a positive electrode active material due to its high stability. However, due to the contamination of the raw materials of sodium ferric pyrophosphate or the contamination during the production process, sodium ferric pyrophosphate usually contains trace amounts of sulfur impurities, most of which exist in the form of sulfate ions, and a small amount exists in the form of elemental sulfur. This makes it inevitable that batteries made with NFPP as the positive electrode will have sulfur impurities. This substance may cause some side reactions in the battery, thereby affecting the electrochemical performance of the battery, such as capacity decay, decreased cycle performance, and even causing safety hazards. Therefore, it is necessary to provide a positive electrode material with less sulfur impurities so that when the positive electrode material is applied to the battery, the battery has better cycle performance. Summary of the Invention

[0003] In view of this, the present application provides a positive electrode material and a preparation method thereof, a battery and an electrical device. The positive electrode material has a low content of sulfur impurities. When the positive electrode material is applied to a battery, the battery has good cycle performance.

[0004] The present application provides a positive electrode material, which includes sodium ferric pyrophosphate, and the range of the content a of sulfur impurities in the positive electrode material is: 0≤a≤100ppm.

[0005] Furthermore, the range of the median particle size D50 of the positive electrode material is: 3 μm≤D50≤20 μm.

[0006] The present application also provides a method for preparing a positive electrode material, which comprises: providing a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a slurry, adding ammonia water to the slurry so that the pH of the slurry satisfies the range of: 9≤pH≤10, sand-milling and spray-drying the slurry to obtain intermediate particles; and sintering the intermediate particles to obtain the positive electrode material.

[0007] Furthermore, the sintering the intermediate particles includes placing the intermediate particles in a mixed atmosphere of argon gas and reducing gas for sintering.

[0008] Furthermore, in the mixed atmosphere of argon gas and reducing gas, the volume proportion b of argon gas is in the range of: 90%≤b≤98%.

[0009] Furthermore, the sintering of the intermediate particles includes: a temperature T for sintering the intermediate particles satisfies a range of 520° C. ≤ T ≤ 600° C.; and a time t for sintering the intermediate particles satisfies a range of 8 h ≤ t ≤ 14 h.

[0010] Furthermore, the providing of a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a slurry includes: the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium acetate, sodium hydroxide, sodium nitrate, sodium peroxide, sodium citrate, and sodium oxalate; the iron source is selected from at least one of ferric phosphate, ferrous oxalate, ferric nitrate, metallic iron, ferric oxide, ferrous oxide, ferrous acetate, and ferrosoferric oxide; the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and phosphorus pentoxide; and the carbon source is selected from at least one of glucose, citric acid, ascorbic acid, polyethylene glycol, acetylene black, graphene, carbon nanotubes, sucrose, and starch.

[0011] The present application provides a battery, which includes: a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet includes the positive electrode material provided in the present application, or the positive electrode material prepared by the preparation method of the positive electrode material provided in the present application; the separator is arranged on one side of the positive electrode sheet; the negative electrode sheet is arranged on the side of the separator away from the positive electrode sheet; the electrolyte is used to infiltrate at least a portion of the positive electrode sheet, at least a portion of the separator and at least a portion of the negative electrode sheet.

[0012] Furthermore, after the battery has been subjected to 1000 charge and discharge cycles, the content c of sulfur impurities in the electrolyte is in the range of 0≤c≤20ppm.

[0013] The present application provides an electrical device, which includes: a device body and a battery provided in the present application, wherein the battery supplies power to the device body.

[0014] In the present application, the positive electrode material includes sodium ferric phosphate pyrophosphate, the content a of sulfur impurities in the positive electrode material satisfies the range 0≤a≤100ppm, the positive electrode material does not contain sulfur impurities or the content of sulfur impurities is very small, when the positive electrode material is applied to the positive electrode sheet and assembled in the battery, the side reaction of sulfur impurities with the electrolyte can be slowed down to avoid consuming the active ions in the battery, and sulfur impurities can be avoided from reacting with sodium to form a sediment and depositing on the surface of the negative electrode sheet to avoid the solid electrolyte interface film (SEI film, Solid Electrolyte Interface Membrane) The thickness increases the interface impedance of the battery, so that the battery has better cycle electrical performance. In addition, the generation of gases such as carbon dioxide and sulfur dioxide can be slowed down to avoid battery gas production, so that the battery has better safety performance. Furthermore, it is also possible to avoid excessive sulfur impurity content to form sulfuric acid to slow down the decomposition of the electrolyte, so that the electrolyte has a higher ion conduction efficiency, and ultimately the battery has better cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 This is a schematic structural diagram of an energy storage system according to an embodiment of the present application;

[0017] Figure 2 A schematic structural diagram of an energy storage system according to another embodiment of the present application;

[0018] Figure 3 This is a structural diagram of an energy storage system according to another embodiment of the present application;

[0019] Figure 4 This is a schematic structural diagram of a battery according to an embodiment of the present application;

[0020] Figure 5 Schematic diagram of a process for preparing a positive electrode material according to an embodiment of the present application;

[0021] Figure 6 This is a schematic structural diagram of an electrical device according to an embodiment of the present application;

[0022] Figure 7 This is a circuit block diagram of an electrical device according to an embodiment of the present application.

[0023] Description of reference numerals:

[0024] 100-positive electrode material, 200-battery, 210-positive electrode plate, 220-diaphragm, 230-negative electrode plate, 240-electrolyte, 300-electrical equipment, 310-equipment body, 400-energy storage system, 410-first power conversion device, 420-first user load, 430-second user load, 440-energy storage device, 450-high-voltage cable, 460-second power conversion device, 470-energy storage cabinet, 480-photovoltaic storage and charging station, 490-vehicle. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0027] References herein to "embodiments" or "implementations" mean that a particular feature, structure, or characteristic described in connection with the embodiments or implementations may be included in at least one embodiment of the present application. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0028] In the field of sodium-ion batteries, sodium ferric pyrophosphate (NFPP) is often used as the positive electrode active material due to its high stability. However, due to contamination of the raw materials or during the production process, NFPP often contains trace amounts of sulfur impurities, most of which exist in the form of sulfate ions, with a small amount existing in the form of elemental sulfur. This makes the presence of sulfur impurities in batteries made with NFPP as the positive electrode inevitable. This substance may cause some side reactions in the battery, thereby affecting the battery's electrochemical performance, such as capacity fade, reduced cycle performance, and even posing a safety hazard.

[0029] Specifically, sulfur elemental contact with the electrolyte will produce side reactions, thereby consuming the active sodium ions in the sodium ion battery, and sulfur elemental reaction with sodium will generate sodium sulfide and deposit on the surface of the negative electrode plate, thereby causing the solid electrolyte interface film (SEI film, Solid Electrolyte Interface Membrane) between the negative electrode plate and the electrolyte to thicken unevenly, increase the interface impedance and affect the cycle performance of the battery. In addition, sulfur elemental catalyzes the decomposition of the electrolyte to produce gases such as carbon dioxide and sulfur dioxide, causing the battery to produce gas, thereby posing a safety hazard. Among them, some sulfur impurities in the form of sulfate radicals will decompose and be reduced to sulfur elemental sulphur, and the remaining sulfur impurities in the form of sulfate radicals will also combine with the hydrogen ions in the electrolyte and form sulfuric acid, which will enhance the acidity of the electrolyte and aggravate the decomposition of the electrolyte, reduce the ion conduction efficiency of the electrolyte, thereby affecting the cycle performance of the battery. Therefore, it is necessary to provide a positive electrode material with less sulfur impurities so that when the positive electrode material is applied to the battery, the battery has better cycle performance.

[0030] Specifically, in the preparation process of sodium ferric phosphate pyrophosphate, even if analytically pure raw materials are used, the content of sulfur impurities in the final sodium ferric phosphate pyrophosphate is still as high as 600 ppm due to the generation of side reactions.

[0031] Since the energy people need is highly time- and space-dependent, in order to rationally utilize energy and improve energy utilization, it is necessary to use a medium or device to store one form of energy in the same form or convert it into another form of energy, and then release it in a specific form based on future application needs. Currently, the main way to generate green electricity is to develop green energy such as photovoltaics and wind power to replace fossil energy.

[0032] Currently, the generation of green electricity generally relies on photovoltaics, wind power, and hydropower. However, wind and solar energy are generally intermittent and highly volatile, which can cause grid instability, insufficient electricity during peak hours, and excessive electricity during off-peak hours. Unstable voltage can also damage electricity. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar power curtailment". To solve these problems, we must rely on energy storage. This means converting electrical energy into other forms of energy through physical or chemical means and storing them. When needed, this energy is converted into electrical energy and released. Simply put, energy storage is like a large "power bank", storing electricity when photovoltaic and wind energy are sufficient and releasing the stored electricity when needed.

[0033] Taking electrochemical energy storage as an example, this solution provides an energy storage device 440, which is applied to the energy storage system 400. The energy storage device 440 is equipped with a group of chemical batteries, which mainly use the chemical elements in the battery 200 as energy storage media. The charging and discharging process is accompanied by chemical reactions or changes in the energy storage medium. Simply put, the electricity generated by wind and solar energy is stored in the chemical battery. When the use of external electricity reaches a peak, the stored electricity is released for use, or transferred to places where electricity is scarce for use.

[0034] Currently, energy storage (i.e., energy storage) has a wide range of application scenarios, including power generation side energy storage, grid side energy storage, and power consumption side energy storage. The corresponding types of energy storage devices 440 include:

[0035] (1) Large-scale energy storage power stations used in wind power and photovoltaic power stations can help renewable energy generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power supply on the power supply side, energy storage power stations can achieve load matching of electricity in time and space, enhance the ability to absorb renewable energy, reduce instantaneous power changes, reduce the impact on the power grid, improve the absorption of new energy generation, and are of great significance in grid system backup, alleviating peak load power supply pressure, and peak and frequency regulation.

[0036] (2) The energy storage container used on the grid side mainly functions as peak shaving, frequency regulation, and relief of grid congestion. It can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak period of electricity load, thereby achieving a balance between electricity production and consumption.

[0037] (3) Small energy storage cabinets used on the power consumption side, whose main functions are self-generation and self-use of electricity, peak-valley price arbitrage, capacity cost management, and improving power supply reliability. According to different application scenarios, energy storage on the power consumption side can be divided into industrial and commercial energy storage cabinets, household energy storage devices 440, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the power market that implements peak-valley electricity prices, by charging the energy storage system 400 when the electricity price is low and discharging the energy storage system 400 when the electricity price is high, peak-valley electricity price arbitrage is achieved, thereby reducing electricity costs. In addition, industrial enterprises that are subject to two-part electricity prices can use the energy storage system 400 to store energy during low electricity consumption and discharge it during peak load, thereby reducing peak power and the maximum demand reported, and achieving the purpose of reducing capacity electricity charges. Household photovoltaic storage can improve the level of self-generation and self-use of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installation is driven. Considering that photovoltaic power generation occurs during the day, while user loads are generally higher at night, deploying energy storage can better utilize photovoltaic power, increasing self-generation and self-consumption while reducing electricity costs. Furthermore, energy storage is required for backup power in areas such as communication base stations and data centers.

[0038] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of the present application. Figure 1 The embodiment is described by taking the household energy storage scenario in the user-side energy storage as an example, but the energy storage device 440 of the present application is not limited to the household energy storage scenario.

[0039] The present application provides an energy storage system 400, which includes a first electric energy conversion device 410 (photovoltaic panel), a first user load 420 (household lamps), a second user load 430 (such as air conditioners and other household appliances), and an energy storage device 440. The energy storage device 440 is a small energy storage box that can be mounted on an outdoor wall by wall-mounting. The energy storage device 440 of the present application is not limited to wall-mounting and can also be placed in the user's residence by other means. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices. The energy storage device 440 is used to store the electrical energy and supply it to lamps and household appliances for use during peak electricity prices, or to supply power when the power grid is outage / power outage.

[0040] In some embodiments, see Figure 2 , Figure 2 This is a structural diagram of an energy storage system 400 according to another embodiment of the present application. Figure 2 The embodiment is described using the shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 440 of the present application is not limited to the energy storage scenario on the power generation / distribution side.

[0041] The present application provides an energy storage system 400, which includes: a high-voltage cable 450, a first electric energy conversion device 410, a second electric energy conversion device 460 and an energy storage device 440 provided in the present application. In some embodiments of the power generation side scenario, the second electric energy conversion device 460 can be a wind power conversion device. Since the electric energy generated by wind power conversion is volatile, random and intermittent, the unstable electric energy output by the wind power conversion device can be stored in the energy storage device 440 by connecting to the grid. The energy storage device 440 is connected to the high-voltage cable and outputs smooth electric energy to the power distribution network for use, thereby realizing peak and frequency regulation and stable operation of the power grid; or, wind power The conversion device is always connected to the high-voltage cable. Under normal power generation conditions, the electric energy output by the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 440, reducing the wind and solar power abandonment rates and improving the problem of new energy power generation and consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 440 in conjunction with the high-voltage cable 450 in a grid-connected mode to the power consumption side, providing peak shaving, frequency regulation, standby and other services for the power grid operation, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling of the power grid, and alleviating the power supply pressure of the power grid.

[0042] In some embodiments on the distribution network side, the first power conversion device 410 can be a photovoltaic power conversion device, and the energy storage device 440 is connected to the high-voltage cable 450 and installed between the downstream of the high-voltage cable 450 and the user load. The electric energy output by the photovoltaic power conversion device is stored in the energy storage device 440, which can respond in time and act as a backup power supply when a fault occurs in the power grid / distribution network; or, it can alleviate the line congestion when a line congestion occurs in the high-voltage cable 450 transmission line, and provide power supply support when the power grid is planned to be expanded to delay the economic pressure caused by the expansion of the power grid / distribution network.

[0043] Optionally, the first electric energy conversion device 410 may include but is not limited to a wind power conversion device, and the second electric energy conversion device 460 may include but is not limited to a photovoltaic power conversion device. The first electric energy conversion device 410 and the second electric energy conversion device 460 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0044] Optionally, the battery cell may be a secondary battery. A secondary battery refers to a battery cell that can be recharged to activate the active material after discharge and continue to be used. The battery cell may be a lithium-ion battery, a sodium-ion battery, a sodium-lithium-ion battery, a lithium metal battery, a sodium metal battery, a lithium-sulfur battery, a magnesium-ion battery, a nickel-metal hydride battery, a nickel-cadmium battery, a lead-acid battery, or the like, and this application does not impose specific limitations on this.

[0045] In some embodiments, see Figure 3 , Figure 3 This is a structural diagram of an energy storage system 400 according to another embodiment of the present application. Figure 3 The embodiment is described using the industrial and commercial side energy storage scenario as an example. The energy storage device 440 of the present application is not limited to the generation / distribution side energy storage scenario.

[0046] The present application provides an energy storage system 400, which includes: an energy storage cabinet 470, a high-voltage cable 450, a factory equipped with a first power conversion device 410, a photovoltaic storage and charging station 480 equipped with a second power conversion device 460, and a car 490. In some embodiments of the industrial and commercial side scenario, the first power conversion device 410 can be a photovoltaic panel, which converts solar energy into electricity and stores it in the energy storage cabinet 470 of the factory. In the event of a power outage in the power grid, the energy storage cabinet 470 is used to supply power to ensure safe, stable and continuous operation of the factory. Or when the power load of the factory is high, the power grid issues a command to use the electricity stored in the energy storage cabinet 470 in conjunction with the high-voltage cable 450 in a grid-connected mode to transmit electricity to the factory for use, providing peak / frequency regulation, backup and other services for the operation of the power grid. In addition, the second power conversion device 460 can also be a photovoltaic panel, which converts solar energy into electricity and stores it in the energy storage cabinet 470 of the photovoltaic storage and charging station 480, and directly charges the car 490 through the photovoltaic storage and charging station 480, which is fast and convenient.

[0047] Optionally, the first power conversion device 410 and the second power conversion device 460 may include but are not limited to photovoltaic power conversion devices. The first power conversion device 410 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0048] Optionally, the energy storage cabinet 470 may include but is not limited to energy storage application scenarios such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems or temporary power supply systems, and is also used in data centers, military equipment, aerospace, charging piles, electric vehicles and other fields.

[0049] Optionally, energy storage cabinet 470 may include, but is not limited to, battery cells, or integrated battery systems such as battery modules, battery packs, battery clusters, mobile power supplies, energy storage cabinets, and energy storage containers. The energy storage cabinet 470 provided in this embodiment of the present application may be used in, but is not limited to, the products listed above. Other application forms are also possible. This embodiment of the present application does not impose strict limitations on the application form of energy storage cabinet 470. This embodiment of the present application uses energy storage cabinet 470 with a multi-cell battery as an example.

[0050] Optionally, the battery cells constituting the energy storage cabinet 470 may be, but are not limited to, at least one of cylindrical batteries, square batteries, prismatic batteries, or batteries of other shapes.

[0051] Optionally, the energy storage device 440 may include but is not limited to energy storage application scenarios such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems or temporary power supply systems, and is also used in data centers, military equipment, aerospace, charging piles, electric vehicles and other fields.

[0052] Optionally, energy storage device 440 may include, but is not limited to, battery cells, or integrated battery systems such as battery modules, battery packs, battery clusters, mobile power supplies, energy storage cabinets, and energy storage containers. The energy storage device 440 provided in this embodiment of the present application may be, but is not limited to, the products listed above, or may be implemented in other forms. This embodiment of the present application does not impose strict limitations on the application of energy storage device 440. This embodiment of the present application uses a multi-cell battery as an example for explanation.

[0053] Optionally, when the energy storage device 440 is a battery cell, the energy storage device 440 may be, but is not limited to, at least one of a cylindrical battery, a square battery, a prismatic battery, or batteries of other shapes.

[0054] See Figure 4 The present application provides a positive electrode material 100, wherein the positive electrode material 100 includes sodium iron phosphate pyrophosphate, and the content a of sulfur impurities in the positive electrode material 100 is in the range of 0≤a≤100ppm.

[0055] Specifically, the value of the sulfur impurity content a in the positive electrode material 100 can be, but is not limited to, 0, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, 60 ppm, 65 ppm, 70 ppm, 80 ppm, 90 ppm, 95 ppm and 100 ppm, etc.

[0056] It can be understood that when the value of the content a of sulfur impurities in the positive electrode material 100 is 0, it is proved that the positive electrode material 100 does not contain sulfur impurities.

[0057] It can be understood that the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200. The battery 200 is a sodium ion battery, and the active ions in the battery 200 are sodium ions.

[0058] In this embodiment, the positive electrode material 100 includes sodium ferric phosphate pyrophosphate, and the sulfur impurity content a in the positive electrode material 100 satisfies the range of 0≤a≤100ppm. The positive electrode material 100 contains no sulfur impurities or has a very low content of sulfur impurities. When the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200, the side reaction between the sulfur impurities and the electrolyte 240 can be slowed down to avoid consuming active ions in the battery 200. It can also prevent the sulfur impurities from reacting with sodium to form deposits and being deposited on the surface of the negative electrode plate 230, thereby avoiding uneven SEI film thickness and increasing the interfacial impedance of the battery 200, thereby enabling the battery 200 to have better cycle performance. In addition, the generation of gases such as carbon dioxide and sulfur dioxide can be slowed down to avoid gassing of the battery 200, thereby enabling the battery 200 to have better safety performance. Furthermore, it can also prevent excessive sulfur impurity content from forming sulfuric acid, thereby slowing down the decomposition of the electrolyte 240, thereby making the electrolyte 240 have a higher ion conduction efficiency, and ultimately making the battery 200 have better cycle performance.

[0059] It is understandable that the sulfur impurity content in the positive electrode material 100 can be analyzed by ICP-MS quantitative analysis. ICP-MS quantitative analysis is a highly sensitive element quantitative detection technology based on Inductively Coupled Plasma Mass Spectrometry.

[0060] In some embodiments, the median particle size D50 of the positive electrode material 100 is in the range of 3 μm≤D50≤20 μm.

[0061] Specifically, the median particle size D50 of the positive electrode material 100 can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, and 20 μm.

[0062] In this embodiment, when the median particle size D50 of the positive electrode material 100 satisfies the range of 3μm≤D50≤20μm, the median particle size of the positive electrode material 100 is within a reasonable range. When the positive electrode material 100 is applied to the positive electrode sheet 210 and assembled into the battery 200, it is conducive to ion diffusion and can avoid excessive surface active sites of the positive electrode material 100, which reduces the capacity retention rate of the battery 200. The battery 200 has a higher capacity and better cycle performance. When the median particle size of the positive electrode material 100 is too large, the diffusion path of the ions is increased, so that when the positive electrode material 100 is applied to the positive electrode sheet 210 and assembled into the battery 200, the impedance of the battery 200 will be increased. In addition, if the positive electrode material 100 is formed by sintering, its sintering temperature is too high, which may also cause the median particle size of the positive electrode material 100 to be too large, increasing the energy consumption during the preparation process of the positive electrode material 100. When the median particle size of the positive electrode material 100 is too small, the positive electrode material 100 has many surface active sites. When the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200, during the first charge and discharge process of the battery 200, the amount of solid electrolyte interface film formed in the positive electrode plate 210 increases, which may lead to a decrease in the capacity retention rate of the battery 200 and cause the capacity of the battery 200 to decay.

[0063] See Figure 5 The present application also provides a method for preparing a positive electrode material 100, the preparation method comprising:

[0064] S101, providing a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a slurry, adding ammonia water to the slurry so that the pH of the slurry satisfies the range of 9≤pH≤10, and sand-milling and spray-drying the slurry to obtain intermediate particles.

[0065] S102 , sintering the intermediate particles to obtain the positive electrode material 100 .

[0066] Specifically, the pH value of the slurry may be, but is not limited to, 9, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10, and the like.

[0067] It can be understood that the preparation method of the positive electrode material 100 provided in the present application is used to prepare the positive electrode material 100 provided in the present application.

[0068] It can be understood that the intermediate particles include a sodium source, an iron source, a phosphorus source, a carbon source and ammonium sulfate.

[0069] It can be understood that sulfur impurities exist in the sodium source, iron source, phosphorus source and carbon source, some of which exist in the form of sulfate ions and some exist in the form of elemental sulfur.

[0070] It can be understood that a sodium source, an iron source, a phosphorus source, and a carbon source are provided to obtain a slurry, and the sodium source, the iron source, the phosphorus source, and the carbon source are dispersed or dissolved in water to form the slurry.

[0071] This embodiment provides a method for preparing a positive electrode material 100 to prepare the positive electrode material 100 provided in this application. The positive electrode material 100 is subjected to a desulfurization treatment during the preparation process of the positive electrode material 100 so that the positive electrode material 100 has fewer sulfur impurities. When the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200, the side reaction of sulfur impurities with the electrolyte 240 can be slowed down, so that the battery 200 has better electrochemical performance. Specifically, a sodium source, an iron source, a phosphorus source and the carbon source are provided to obtain a slurry, and ammonia water is added to the slurry to promote the reaction of ammonium ions (NH4 + ) and the impurity sulfate ions (SO4 2- ) forms ammonium sulfate ((NH4)2SO4), thereby generating intermediate particles, wherein the intermediate particles include a sodium source, an iron source, a phosphorus source, a carbon source and ammonium sulfate. Furthermore, the intermediate particles are sintered so that the sodium source, the iron source and the phosphorus source react to form sodium ferric pyrophosphate, and the ammonium sulfate is decomposed to form sulfur dioxide and ammonia, which are discharged during the sintering process, so that the positive electrode material 100 contains less sulfur impurities or no sulfur impurities. The preparation method of the positive electrode material 100 provided in this embodiment can effectively remove sulfur impurities, and the process for removing sulfur impurities is simple and efficient, and the positive electrode material 100 has good preparation performance.

[0072] Specifically, ammonia water is added to the slurry so that the pH of the slurry satisfies the range of 9≤pH≤10. If the pH of the slurry is within a reasonable range, the amount of ammonia water added is within a reasonable range. On the one hand, ammonia water provides sufficient and appropriate ammonium ions to combine with sulfate ions in the sodium source, iron source, phosphorus source, and carbon source to form ammonium sulfate, and decomposes and discharges in the form of gas during further sintering, so that the content of sulfur impurities in the positive electrode material 100 prepared by the preparation method is small or almost non-existent. On the other hand, it is possible to avoid excessive ammonia water causing the positive electrode material 100 to have an excessive amount of residual alkali after further sintering, so as to avoid the loss of part of the adhesive, so that the positive electrode plate 210 has better bonding performance and performance. When the pH of the slurry is too high, the amount of ammonia water added is too great, which, on the one hand, results in a waste of ammonia water, and, on the other hand, may increase the residual alkali content of the positive electrode material 100 after further sintering. When the positive electrode material 100 is applied to the positive electrode plate 210, the binder in the positive electrode material 100 reacts under alkaline conditions, thereby partially losing the binder and subsequently causing a decrease in the bonding performance of the positive electrode plate 210. When the pH of the slurry is too low, the amount of ammonia water added is too small, and the ammonium ions provided by the ammonia water are too few, making it difficult to convert the sulfur impurities in the sodium source, iron source, phosphorus source, and carbon source into ammonium sulfate. As a result, during further sintering, the sulfur impurities in the sodium source, iron source, phosphorus source, and carbon source remain in the form of sodium sulfate and cannot be decomposed, resulting in the positive electrode material 100 obtained by the preparation method still containing a large amount of sulfur impurities.

[0073] It is understood that the carbon source is mixed with the slurry and then sand-milled to fully mix the carbon source with the sodium source, iron source, and phosphorus source. During further sintering, the sodium source, iron source, and phosphorus source form the sodium ferric phosphate pyrophosphate. The carbon source is coated on the periphery of the sodium ferric phosphate pyrophosphate to form a carbon coating layer, thereby improving the conductivity of the positive electrode material 100. When the positive electrode material 100 is applied to the positive electrode sheet 210 and assembled in the battery 200, the impedance of active ions entering or leaving the positive electrode material 100 can be reduced, thereby improving the ion transmission efficiency of the battery 200 and making the battery 200 have higher energy efficiency.

[0074] It is understandable that ammonia is added to the slurry to react sulfur impurities in the sodium source, iron source, phosphorus source, and carbon source with ammonium ions to form ammonium sulfate. Ammonium sulfate has a lower decomposition temperature, which facilitates the decomposition of ammonium sulfate during the further sintering process. Compared to the solution of adding other alkaline solutions such as sodium hydroxide and sodium carbonate to the slurry, sodium sulfate reacts with sulfur impurities in the sodium source, iron source, phosphorus source, and carbon source to form sodium sulfate. The decomposition temperature of sodium sulfate is too high, which is not conducive to the removal of sulfate ions during the further sintering process, making it difficult to reduce the content of sulfur impurities in the prepared positive electrode material 100.

[0075] Optionally, the particle size of the slurry after sand grinding is less than 1 μm, and then spray drying is performed to obtain the intermediate particles, which facilitates further sintering of the intermediate particles.

[0076] Optionally, in a specific embodiment, the molar ratio of the sodium source, the iron source, and the phosphorus source is in the range of (3.5-4.5): (2.5-3.5): 4. Specifically, when the amount of the phosphorus source is 4 mol, the amount of the sodium source is 3.5 mol-4.5 mol, and the amount of the iron source is 2.5 mol-3.5 mol.

[0077] In some embodiments, sintering the intermediate particles includes placing the intermediate particles in a mixed atmosphere of argon gas and reducing gas for sintering.

[0078] It can be understood that the hydrogen gas is mixed with the reducing gas and then introduced into the intermediate particles at the same time.

[0079] In this embodiment, argon is an inert gas and serves as a shielding gas to isolate oxygen, preventing it from entering during the sintering process and affecting the reaction. Furthermore, some sulfur impurities in the sodium, iron, and phosphorus sources exist as elemental sulfur. The reducing gas reacts with the elemental sulfur during the sintering process to form a gas, which is then reduced by the reducing gas. The resulting gas is then discharged with the sintering atmosphere, thereby removing the sulfur impurities in the sodium, iron, and phosphorus sources that exist as elemental sulfur, thereby reducing the content of sulfur impurities in the prepared positive electrode material 100. When these sulfur impurities are applied to the positive electrode sheet 210 and assembled into the battery 200, the battery 200 exhibits improved performance.

[0080] Optionally, the reducing gas includes one of hydrogen and carbon monoxide. When the reducing gas is hydrogen, the hydrogen reacts with elemental sulfur during the sintering process to form hydrogen sulfide; when the reducing gas is carbon monoxide, the carbon monoxide reacts with elemental sulfur during the sintering process to form carbonyl sulfide (COS) gas.

[0081] In some embodiments, in the mixed atmosphere of argon gas and reducing gas, the volume proportion b of argon gas is in the range of: 90%≤b≤98%.

[0082] Specifically, the volume percentage b of argon gas may be, but is not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc.

[0083] In the mixed atmosphere of argon and reducing gas provided in this embodiment, when the volume fraction b of the argon satisfies the range of 90% ≤ b ≤ 98%, the volume fraction of argon is within a reasonable range, and accordingly, the volume fraction of the reducing gas is also within a reasonable range. The argon is mixed with the reducing gas to remove sulfur impurities present in the form of elemental sulfur in the sodium source, iron source, phosphorus source, and carbon source. The reducing gas can reduce the elemental sulfur, so that the elemental sulfur is converted into gas and discharged with the mixed atmosphere, thereby reducing the sulfur impurities in the prepared positive electrode material 100. When the sulfur impurities are applied to the positive electrode plate 210 and assembled in the battery 200, the battery 200 has better performance. When the volume fraction of argon is too large, the volume fraction of hydrogen is too small, making it difficult to fully remove the sulfur impurities present in the form of elemental sulfur in the sodium source, iron source, phosphorus source, and carbon source. When the volume fraction of argon is too small, the volume fraction of hydrogen is too large, posing a safety hazard.

[0084] Preferably, in some embodiments, in the mixed atmosphere of argon gas and reducing gas, the volume proportion of argon gas is 95%, and the volume proportion of hydrogen gas is 5%.

[0085] In some embodiments, the sintering the intermediate particles includes: a temperature T for sintering the intermediate particles satisfies a range of 520° C. ≤ T ≤ 600° C.; and a time t for sintering the intermediate particles satisfies a range of 8 h ≤ t ≤ 14 h.

[0086] Specifically, the temperature T for sintering the intermediate particles may be, but is not limited to, 520°C, 525°C, 530°C, 540°C, 550°C, 555°C, 560°C, 570°C, 575°C, 580°C, 585°C, 590°C, 595°C and 600°C, etc.

[0087] Specifically, the time t for sintering the intermediate particles may be, but is not limited to, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, and 14 h.

[0088] In this embodiment, when the temperature T for sintering the intermediate particles satisfies the range of 520°C ≤ T ≤ 600°C, and the time t for sintering the intermediate particles satisfies the range of 8h ≤ t ≤ 14h, the temperature and time for sintering the intermediate particles are both within a reasonable range. On the one hand, the sintering temperature and time facilitate the decomposition of ammonium sulfate, allowing the ammonium sulfate in the intermediate particles to fully decompose into sulfur dioxide and ammonia, which are then discharged with the mixed atmosphere, thereby resulting in a low content of or no sulfur impurities in the generated positive electrode material 100. On the other hand, the sintering temperature and time facilitate the formation of sodium ferric pyrophosphate from the sodium source, iron source, and phosphorus source, thereby preventing the sodium source, iron source, and phosphorus source from forming other impurity phases such as sodium ferric phosphate and sodium ferric pyrophosphate, thereby ensuring that the positive electrode material 100 has good uniformity. When the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200, the positive electrode material 100 and the electrolyte 240 have fewer side reactions, which can slow down the capacity decay of the battery 200, thereby making the battery 200 have better cycle performance. On the other hand, the sintering temperature and the sintering time are conducive to forming a positive electrode material 100 with a median particle size that satisfies the range of 3μm≤D50≤20μm, thereby making the positive electrode material 100 have better performance. When the temperature for sintering the intermediate particles is too high and / or the time for sintering the intermediate particles is too long, the sodium iron phosphate pyrophosphate formed by the sodium source, iron source, and phosphorus source may decompose into mixed phases of sodium iron phosphate, sodium iron pyrophosphate, etc., reducing the uniformity of the positive electrode material 100, thereby reducing the material specific capacity of the positive electrode plate 210 and reducing the capacity of the battery 200 when the positive electrode material 100 is applied to the battery 200. On the other hand, it will also cause a waste of energy and increase the preparation cost of the positive electrode material 100. On the other hand, it may cause the median particle size of the positive electrode material 100 to be too large, increase the diffusion path of ions, so that when the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200, it will increase the impedance of the battery 200. When the temperature for sintering the intermediate particles is too low and / or the time for sintering the intermediate particles is too short, it is difficult for the ammonium sulfate in the intermediate particles to fully decompose into sulfur dioxide and ammonia and be discharged with the mixed atmosphere, so that the generated positive electrode material 100 still contains a large amount of sulfur impurities. In addition, if the sintering temperature is too low, it is difficult for the sodium source, iron source, and phosphorus source to form sodium iron pyrophosphate. When the positive electrode material 100 is applied to the positive electrode plate 210 and assembled in the battery 200, the positive electrode material 100 may react with the electrolyte 240 and consume active ions, and the by-products generated may cause problems such as uneven SEI thickness and gas production in the battery 200, thereby causing the capacity of the battery 200 to decay and poor cycle performance.

[0089] In some embodiments, the providing of a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a slurry includes: the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium acetate, sodium hydroxide, sodium nitrate, sodium peroxide, sodium citrate, and sodium oxalate; the iron source is selected from at least one of ferric phosphate, ferrous oxalate, ferric nitrate, metallic iron, ferric oxide, ferrous oxide, ferrous acetate, and ferrosoferric oxide; the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and phosphorus pentoxide; and the carbon source is selected from at least one of glucose, citric acid, ascorbic acid, polyethylene glycol, acetylene black, graphene, carbon nanotubes, sucrose, and starch.

[0090] In this embodiment, the sodium source, the iron source and the phosphorus source are mixed to obtain the slurry, and the sodium source, the iron source and the phosphorus source are evenly dispersed so that during further sintering, the sodium source, the iron source and the phosphorus source generate the sodium iron pyrophosphate.

[0091] See Figure 4 The present application provides a battery 200, which includes: a positive electrode sheet 210, a separator 220, a negative electrode sheet 230 and an electrolyte 240. The positive electrode sheet 210 includes the positive electrode material 100 provided in the present application, or the positive electrode material 100 prepared by the preparation method of the positive electrode material 100 provided in the present application; the separator 220 is arranged on one side of the positive electrode sheet 210; the negative electrode sheet 230 is arranged on the side of the separator 220 away from the positive electrode sheet 210; the electrolyte 240 is used to infiltrate at least a portion of the positive electrode sheet 210, at least a portion of the separator 220 and at least a portion of the negative electrode sheet 230.

[0092] Optionally, in some embodiments, the battery 200 is a sodium ion battery.

[0093] It is understandable that the electrolyte 240 includes active ions such as sodium ions. During the charge and discharge cycle of the battery 200 , the active ions are transferred between the positive electrode plate 210 and the negative electrode plate 230 .

[0094] In this embodiment, the positive electrode plate 210 of the battery 200 includes the positive electrode material 100 provided in this application. During the preparation process of the positive electrode material 100, the positive electrode material 100 is subjected to a desulfurization treatment so that the sulfur impurity content a of the positive electrode material 100 satisfies the range of 0≤a≤100ppm. In other words, the positive electrode material 100 has no sulfur impurities or contains very little sulfur impurities. This can slow down the side reaction of sulfur impurities with the electrolyte 240 to avoid consuming active ions in the battery 200. It can also prevent sulfur impurities from reacting with sodium to form deposits and depositing on the surface of the negative electrode plate 230, thereby avoiding uneven SEI film thickness and increasing the interfacial impedance of the battery 200, thereby enabling the battery 200 to have better cycle performance. In addition, it can also slow down the generation of gases such as carbon dioxide and sulfur dioxide to avoid gas production in the battery 200, thereby enabling the battery 200 to have better safety performance. Furthermore, it can also prevent excessive sulfur impurity content from forming sulfuric acid, thereby slowing down the decomposition of the electrolyte 240, thereby making the electrolyte 240 have a higher ion conduction efficiency, and ultimately making the battery 200 have better cycle performance.

[0095] In some embodiments, after the battery 200 undergoes 1000 charge and discharge cycles, the content c of sulfur impurities in the electrolyte 240 is in the range of 0≤c≤20 ppm.

[0096] Specifically, the value of the sulfur impurity content c in the electrolyte 240 can be, but is not limited to, 0, 2 ppm, 3 ppm, 5 ppm, 6 ppm, 8 ppm, 10 ppm, 12 ppm, 14 ppm, 16 ppm, 18 ppm, and 20 ppm.

[0097] In this embodiment, after the battery 200 has undergone 1000 charge and discharge cycles, the content c of sulfur impurities in the electrolyte 240 satisfies the range of 0≤c≤20ppm. The content of sulfur impurities in the electrolyte 240 is extremely small, which can avoid the consumption of the electrolyte 240 and the increase in the impedance of the battery 200, so that the battery 200 has a higher capacity retention rate and energy retention rate.

[0098] It can be understood that the capacity retention rate of the battery 200 after 1000 cycles is greater than or equal to 97%, and the energy retention rate after 1000 cycles is greater than or equal to 94%.

[0099] It is understandable that the content of sulfur impurities in the electrolyte 240 can be analyzed by ICP-MS quantitative analysis. ICP-MS quantitative analysis is a highly sensitive element quantitative detection technology based on Inductively Coupled Plasma Mass Spectrometry.

[0100] The following is a further introduction to the technical solution of this application in multiple embodiments:

[0101] Examples 1 to 7, Comparative Examples 1 to 8:

[0102] 1. Preparation of positive electrode material 100:

[0103] A sodium source, an iron source, and a phosphorus source were mixed in a ratio of Na:Fe:P = 4:3:4, and a carbon source was added to obtain a slurry. Ammonia was added to adjust the pH of the slurry. The slurry was sand-milled to a particle size D50 < 1 μm. The slurry was then spray-dried to obtain intermediate particles. The intermediate particles were sintered in a mixed gas atmosphere to obtain the positive electrode materials 100 of Examples 1 to 7 and Comparative Examples 1 to 8.

[0104] Among them, the amount of added carbon source is 5% to 30% of the total mass to ensure that the mass content of carbon material in the sintered positive electrode material 100 is 1% to 10%. In Examples 1 to 7 and Comparative Examples 1 to 8, the mass content of carbon material is 3% as an example, which does not represent a limitation on the mass content of carbon material.

[0105] Table 1 shows the type of mixed atmosphere for sintering the intermediate particles, the temperature T for sintering the intermediate particles, the time t for sintering the intermediate particles, and the pH value of the slurry.

[0106] 2. Preparation of positive electrode sheet 210:

[0107] The positive electrode material 100, conductive carbon black (SP), and adhesive polyvinylidene fluoride (PVDF) are dispersed in a solvent N-methylpyrrolidone (NMP) and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector (aluminum foil); after drying, cold pressing, slitting, and cutting, the positive electrode sheets 210 of Examples 1 to 7 and Comparative Examples 1 to 8 are obtained.

[0108] Among them, the positive electrode material 100 of Example 1 is applied to the positive electrode sheet 210 of Example 1, the positive electrode material 100 of Example 2 is applied to the positive electrode sheet 210 of Example 2; the positive electrode material 100 of Comparative Example 1 is applied to the positive electrode sheet 210 of Comparative Example 1, and so on.

[0109] 3. Preparation of negative electrode sheet 230:

[0110] Hard carbon, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are dispersed in deionized water and mixed to form a conductive slurry. The conductive slurry is coated on the negative electrode collector (copper foil). After drying, cold pressing, slitting, and cutting, the negative electrode sheet 230 is obtained.

[0111] 4. Preparation of electrolyte 240:

[0112] The ester solvent is fully mixed in an argon atmosphere glove box with a moisture content of ≤0.01ppm, and then the sodium salt (sodium hexafluorophosphate) is dissolved in the mixed solvent and stirred until completely and evenly dissolved. Finally, the sodium salt additive and the film-forming additive are added and mixed evenly to obtain the electrolyte 240.

[0113] 5. Preparation of diaphragm 220:

[0114] The separator 220 is made of a polyethylene film.

[0115] 6. Preparation of Battery 200:

[0116] A lamination process is adopted to make the prepared positive electrode sheet 210, separator 220, and negative electrode sheet 230 into a laminated bare cell in order. After welding the tabs, the bare cell is assembled in an aluminum-plastic film. After vacuum baking, the prepared electrolyte 240 is injected and the cell is packaged to finally obtain implementation batteries 1 to implementation batteries 7 and comparison batteries 1 to comparison batteries 8, wherein implementation battery 1 adopts the positive electrode sheet 210 of embodiment 1, implementation battery 2 adopts the positive electrode sheet 210 of embodiment 2, comparison battery 1 adopts the positive electrode sheet 210 of comparison example 1, comparison battery 2 adopts the positive electrode sheet 210 of comparison example 2, and so on.

[0117] Table 1: Preparation parameter table of the positive electrode materials 100 of Examples 1 to 7 and Comparative Examples 1 to 8.

[0118]

[0119]

[0120] It is understood that in Table 1, when the type of mixed atmosphere is Ar+H2, it means that the mixed atmosphere is formed by mixing argon and hydrogen. In Comparative Example 7, it means that during the preparation process of the positive electrode material 100, no ammonia water is added to the slurry.

[0121] It can be understood that in Examples 1 to 7, Comparative Examples 2 and 3, and Comparative Examples 5 to 7, in the mixed atmosphere of argon and hydrogen, the volume proportion of argon is 95%, and the volume proportion of hydrogen is 5%. In Comparative Example 8, in the mixed atmosphere of argon and hydrogen, the volume proportion of argon is 99%, and the volume proportion of hydrogen is 1%.

[0122] Performance test of battery 200:

[0123] 1. Test of the sulfur impurity content a in the positive electrode material 100:

[0124] The sulfur impurity content of the positive electrode material 100 is measured using ICP-MS. Specifically, a small amount of the positive electrode material 100 is dissolved in aqua regia. A plasma-excited light source is then used to vaporize the sample, dissociating it into atoms. The atoms are excited and emit light in the light source. A spectrometer decomposes the light emitted by the light source into a spectrum arranged by wavelength, which is detected using a photoelectric device. The sample is qualitatively analyzed based on the measured spectral wavelengths and quantitatively analyzed based on the intensity of the emitted light to determine the sulfur impurity content a in the positive electrode material 100.

[0125] The values ​​of the sulfur impurity content a in the positive electrode material 100 in the embodiment batteries 1 to the embodiment batteries 7 and the comparison batteries 1 to the comparison batteries 8 are shown in Table 2.

[0126] 2. Test of the sulfur impurity content c in the electrolyte 240 after the battery 200 has undergone 1000 charge and discharge cycles:

[0127] The sulfur impurity content in the electrolyte 240 is also tested using the ICP-MES method. First, the electrolyte 240 needs to be diluted, and then the sulfur impurity content in the positive electrode material 100 is tested using the same method as described above.

[0128] Among them, after 1000 charge-discharge cycles of the embodiment batteries 1 to 7 and the comparison batteries 1 to 8, the content c of sulfur impurities in the electrolyte 240 is as shown in Table 2.

[0129] 3. Capacity test after power-off discharge:

[0130] A positive electrode slurry was prepared with a mass ratio of 100:PVDF:acetylene black = 8:1:1. The slurry was then rolled and cut into sheets, which became the positive electrode sheet 210. The negative electrode sheet was a sodium sheet, and a buckle battery was assembled. The buckle battery charge and discharge voltage was 1.5-4V, and the 0.1C discharge capacity was recorded.

[0131] The values ​​of the charge-discharge capacity in grams of implementation batteries 1 to implementation batteries 7 and comparison batteries 1 to comparison batteries 8 are shown in Table 2.

[0132] 4. Test of the capacity retention rate of battery 200 after 1000 cycles:

[0133] The implementation batteries 1 to implementation batteries 7 and the comparison batteries 1 to comparison batteries 8 were subjected to constant current charge and discharge cycle tests on a charge and discharge instrument. The test temperature was 25°C, the charge and discharge rate was 1C (the magnitude of the charge and discharge current is usually expressed in terms of the charge and discharge rate, and the charge and discharge current is calculated as follows: charge and discharge current = charge and discharge rate × rated capacity of the battery), and the charge and discharge voltage window was 1.5V-4V (i.e., the charge cut-off voltage of battery 200 is 4V, and the discharge cut-off voltage of battery 200 is 1.5V; it is generally believed that when the charge cut-off voltage is ≥3.65V, the charge cut-off voltage of battery 200 is higher). The capacity retention rate after 1000 cycles was calculated using the following calculation formula: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0134] A complete charge and discharge cycle is generally referred to as a charge-discharge cycle. For example, the battery 200 is first charged from 1.5V to 4V, and then discharged from 4V to 1.5V, thus forming a charge-discharge cycle. A cycle of N turns means repeating the above process N times.

[0135] The capacity retention rates of Example Batteries 1 to 7 and Comparative Batteries 1 to 8 after 1000 cycles are shown in Table 2.

[0136] 5. Test of the energy retention rate of the battery 200 after 1000 cycles:

[0137] The implementation batteries 1 to implementation batteries 7 and the comparison batteries 1 to comparison batteries 8 were subjected to constant current charge and discharge cycle tests on a charge and discharge instrument. The test temperature was 25°C, the charge and discharge rate was 1C, and the charge and discharge voltage window was 1.5V-4V. The energy retention rate after 1000 cycles was calculated using the following formula: Energy retention rate after the nth cycle = (discharge energy of the nth cycle / discharge capacity of the first cycle) × 100%.

[0138] The energy retention rates of Example Batteries 1 to 7 and Comparative Batteries 1 to 8 after 1000 cycles are shown in Table 2.

[0139] Table 2: Performance parameters of implementation batteries 1 to implementation batteries 7 and comparison batteries 1 to comparison batteries 8.

[0140]

[0141] Please refer to Table 1 and Table 2. From the data of Examples 1 to 7 and Comparative Example 7, it can be seen that during the preparation process of the positive electrode materials 100 of Examples 1 to 7, ammonia water is added to the slurry to make the pH of the slurry meet the range of 9≤pH≤10, and the positive electrode material 100 is obtained by further sintering the intermediate particles. In the preparation process of the positive electrode material 100 of Comparative Example 7, no ammonia was added to the slurry. As a result, the sulfur impurity content of the positive electrode material 100 in Example 1 to Example 7 was lower than that of the positive electrode material 100 in Comparative Example 7. The sulfur impurity content of the electrolyte 240 in Example 1 to Example 7 was lower than that of the electrolyte 240 in Comparative Example 7. This is because: in Examples 1 to 7, ammonia was added to the slurry, which separated ammonium ions from the slurry. The ammonium ions reacted with sulfate ions, an impurity in the sodium source, iron source, and phosphorus source, to form ammonium sulfate, thereby generating intermediate particles. The intermediate particles included a sodium source, an iron source, a phosphorus source, and ammonium sulfate. Furthermore, the intermediate particles were sintered to cause the sodium source, iron source, and phosphorus source to react and form sodium ferric pyrophosphate, and the ammonium sulfate to decompose to form sulfur dioxide and ammonia gas, which were discharged during the sintering process. As a result, the positive electrode material 100 contained less sulfur impurities or no sulfur impurities. In Comparative Example 7, however, no ammonia was added to the slurry. Consequently, the sulfur impurities in the intermediate particles existed as sodium sulfate, which could not be effectively decomposed during further sintering. Consequently, the prepared sulfur impurity content was relatively high. After charge and discharge cycling, Comparative Battery 7 still contained a high level of sulfur impurities, resulting in lower capacity retention and energy retention after 1000 cycles. In contrast, Example Batteries 1 through 7 exhibited higher capacity and energy retention after 1000 cycles. In other words, Example Batteries 1 through 7 exhibited higher capacity and better cycle performance.

[0142] Furthermore, from the data of Examples 5 to 7, Comparative Examples 5 and 6, it can be seen that, under the same other conditions, in the preparation process of the positive electrode material 100, ammonia water is added to the slurry in Examples 5 to 7, and the pH of the ammonia water is adjusted to 9≤pH≤10, while the pH of the slurry in Comparative Example 5 is too high and the pH of the slurry in Comparative Example 6 is too low, which results in: the content of sulfur impurities in the positive electrode material 100 in the implementation battery 5 to the implementation battery 7 is lower than the content of sulfur impurities in the positive electrode material 100 in the comparative battery 6, the content of sulfur impurities in the electrolyte 240 in the implementation battery 5 to the implementation battery 7 is lower than the content of sulfur impurities in the electrolyte 240 in the comparative battery 6, the capacity retention rate of the implementation battery 5 to the implementation battery 7 is higher than the capacity retention rate of the comparative battery 6 and the comparative battery 7, and the energy retention rate of the implementation battery 5 to the implementation battery 7 is higher than the energy retention rate of the comparative battery 6 and the comparative battery 7. This is because: in Examples 5 to 7, the pH of the slurry is within a reasonable range and the amount of ammonia water added is within a reasonable range. On the one hand, the ammonia water provides sufficient and appropriate ammonium ions to combine with the sulfate ions in the sodium source, iron source, and phosphorus source to form ammonium sulfate, which decomposes during further sintering and is discharged as a gas. As a result, the sulfur impurity content in the positive electrode material 100 prepared by the preparation method is low or almost absent. On the other hand, excessive ammonia water can be avoided, which can lead to excessive residual alkali in the positive electrode material 100 after further sintering, thereby avoiding partial loss of the binder. This ensures that the positive electrode sheet 210 has good bonding and performance, and ultimately, the capacity retention rate and energy retention rate of the embodiment batteries 5 to 7 after 1000 cycles are high. In Comparative Example 5, the pH of the slurry was too high, and the amount of ammonia added was too high, which may increase the residual alkali content of the positive electrode material 100 after further sintering. When the positive electrode material 100 is applied to the positive electrode sheet 210, the binder in the positive electrode material 100 will react under alkaline conditions, thereby losing some of the binder, which in turn leads to a decrease in the bonding performance of the positive electrode sheet 210, thereby affecting the performance of the positive electrode sheet 210 and causing the cycle performance of the comparative battery 5 to decline. In Comparative Example 6, the pH of the slurry was too low, and the amount of ammonia added was too small. The ammonium ions provided by the ammonia were too few, making it difficult to convert the sulfur impurities in the sodium source, iron source, and phosphorus source into ammonium sulfate. As a result, during further sintering, the sulfur impurities in the sodium source, iron source, and phosphorus source still exist in the form of sodium sulfate and cannot be decomposed. As a result, the capacity retention rate and energy retention rate of the comparative battery 6 after 1000 cycles are both low.

[0143] Furthermore, it can be seen from the data of Examples 1 to 3 and Comparative Example 2 that, when other parameters remain unchanged, the temperature T for sintering the intermediate particles in Examples 1 to 3 satisfies the range of 520°C ≤ T ≤ 600°C, while the temperature T for sintering the intermediate particles in Comparative Example 2 is too low, which results in: the content of sulfur impurities in the positive electrode material 100 in the implementation batteries 1 to 3 is lower than the content of sulfur impurities in the positive electrode material 100 in the comparative battery 2, the content of sulfur impurities in the electrolyte 240 in the implementation batteries 1 to 3 is lower than the content of sulfur impurities in the electrolyte 240 in the comparative battery 2, and the implementation batteries 1 to 3 are lower than the content of sulfur impurities in the electrolyte 240 in the comparative battery 2. The capacity retention rates of Example 1 to Example 3 after 1000 cycles were higher than those of Comparative Cell 2 after 1000 cycles, and the energy retention rates of Example 1 to Example 3 after 1000 cycles were higher than those of Comparative Cell 2 after 1000 cycles. This is because: in Examples 1 to 3, the temperature for sintering the intermediate particles was within a reasonable range, which facilitated the decomposition of ammonium sulfate, allowing the ammonium sulfate in the intermediate particles to fully decompose into sulfur dioxide and ammonia, which were then discharged with the mixed atmosphere, thereby resulting in a low content of or no sulfur impurities in the generated positive electrode material 100. Furthermore, the sintering temperature was conducive to the formation of sodium ferric pyrophosphate from the sodium source, iron source, and phosphorus source, preventing the sodium source, iron source, and phosphorus source from forming other impurities such as sodium ferric phosphate and sodium ferric pyrophosphate, thereby ensuring that the positive electrode material 100 had better uniformity and ultimately resulted in Example 1 to Example 3 having higher capacity and better cycle performance. In Comparative Example 2, the temperature for sintering the intermediate particles is too low, and the ammonium sulfate in the intermediate particles is difficult to fully decompose into sulfur dioxide and ammonia and be discharged with the mixed atmosphere, so that the generated positive electrode material 100 still contains a large amount of sulfur impurities, and ultimately the cycle performance of the comparative battery 2 is poor.

[0144] Furthermore, it can be seen from the data of Example 1, Example 4, Example 5 and Comparative Example 3 that, during the preparation process of the positive electrode materials 100 of Example 1, Example 4 and Example 5, the time t for sintering the intermediate particles satisfies the range of 8h≤t≤14h, and the time t for sintering the intermediate particles in Comparative Example 3 is too short, so that the content of sulfur impurities in the positive electrode materials 100 in the implementation battery 1, the implementation battery 4 and the implementation battery 5 is lower than the content of sulfur impurities in the positive electrode material 100 in the comparative battery 3, the content of sulfur impurities in the electrolyte 240 in the implementation battery 1, the implementation battery 4 and the implementation battery 5 is lower than the content of sulfur impurities in the electrolyte 240 in the comparative battery 3, and the implementation battery 1, the implementation battery 4 and the implementation battery 5 are lower than the content of sulfur impurities in the electrolyte 240 in the comparative battery 3. The capacity retention rate after 1000 cycles was higher than that of Comparative Cell 3 after 1000 cycles. The energy retention rate of Example 1, Example 4, and Example 5 after 1000 cycles was higher than that of Comparative Cell 3 after 1000 cycles. This is because: in Examples 1, 4, and 5, the sintering time of the intermediate particles was within a reasonable range, which facilitated the decomposition of ammonium sulfate, allowing the ammonium sulfate in the intermediate particles to fully decompose into sulfur dioxide and ammonia, which were discharged with the mixed atmosphere. As a result, the content of sulfur impurities in the resulting positive electrode material 100 was low or absent, and ultimately, Example 1 to Example 3 had higher capacity and better cycle performance. In Comparative Example 3, the sintering time of the intermediate particles was too low, and the ammonium sulfate in the intermediate particles had not yet fully decomposed into sulfur dioxide and ammonia and been discharged with the mixed atmosphere. As a result, the resulting positive electrode material 100 still contained a large amount of sulfur impurities, and ultimately, the cycle performance of Comparative Cell 3 was poor.

[0145] Furthermore, from the data of Example 1 and Comparative Example 1 and Comparative Example 4, it can be seen that the positive electrode material 100 of Example 1 adopts a mixed atmosphere of argon and hydrogen during the sintering process, while the positive electrode material 100 of Comparative Example 1 and Comparative Example 4 adopts a nitrogen atmosphere during the sintering process. From the data in Table 2, it can be seen that the content of sulfur impurities in the positive electrode material 100 in the embodiment battery 1 is lower than the content of sulfur impurities in the positive electrode material 100 in the comparative battery 1 and the comparative battery 4. The content of sulfur impurities in the electrolyte 240 in the embodiment battery 1 is The sulfur impurity content in the electrolyte 240 of Example 1 is lower than that in Comparative Cell 1 and Comparative Cell 4. This is because, in Example 1, during the sintering process of the positive electrode material 100, argon is used as a protective gas, and hydrogen is used as a reducing gas. These gases can reduce sulfur impurities present in the sodium, iron, and phosphorus sources in the form of elemental sulfur. The hydrogen reacts with the elemental sulfur to form hydrogen sulfide, which is discharged with the mixed atmosphere. As a result, the sulfur impurity content in the positive electrode material 100 of Example 1 and the sulfur impurity content in the electrolyte 240 are both lower. In contrast, in Comparative Examples 1 and 4, nitrogen is unable to reduce sulfur impurities present in the form of elemental sulfur in the sodium, iron, and phosphorus sources. Even though sulfur impurities present in the form of sulfate ions are removed during the sintering process, sulfur impurities present in the form of elemental sulfur cannot be removed. Consequently, the sulfur impurity content in the positive electrode material 100 and the sulfur impurity content in the electrolyte 240 of Comparative Cell 1 and Comparative Cell 4 are both higher. Furthermore, the experimental data of comparative battery 1 is better than the experimental data of comparative battery 4. This is because the temperature for sintering the intermediate particles in comparative example 4 is too low, making it difficult to decompose all the ammonium sulfate into gas and discharge it during the sintering stage. Therefore, in the positive electrode material 100 of comparative example 4, there are sulfur impurities in the form of sulfate ions and sulfur impurities in the form of elemental sulfur.

[0146] Furthermore, from the data of Example 7 and Comparative Example 8, it can be seen that, under the same other conditions, in the mixed atmosphere of argon and hydrogen in Example 7, the volume proportion of argon is 95% and the volume proportion of hydrogen is 5%; in Comparative Example 8, the volume proportion of argon is 99% and the volume proportion of hydrogen is 1%. This results in the sulfur impurity content in the positive electrode material 100 in Comparative Example 8 being significantly higher than the sulfur impurity content in the positive electrode material 100 in Example 7, the sulfur impurity content in the electrolyte 240 in the comparative cell 8 being significantly higher than the sulfur impurity content in the electrolyte 240 in the exemplary cell 8, and the cycle performance of the comparative cell 8 being significantly worse than the cycle performance of the exemplary cell 7. This is because: in the mixed atmosphere of argon and hydrogen, if the volume proportion of hydrogen is too small, it is difficult for the hydrogen to fully remove the sulfur impurities present in the form of elemental sulfur in the sodium source, iron source, phosphorus source, and carbon source, resulting in excessive sulfur content in the resulting positive electrode material 100.

[0147] See Figure 6 and Figure 7The present application provides an electrical device 300 , which includes: a device body 310 and a battery 200 provided in the present application, wherein the battery 200 supplies power to the device body 310 .

[0148] It can be understood that the battery 200 is electrically connected to the electrical device 300 .

[0149] In this embodiment, the positive electrode plate 210 of the battery 200 includes the positive electrode material 100 of the present application. The battery 200 has a higher capacity and better cycle performance, so that the battery 200 has better performance and a longer service life. When the battery 200 is applied to the electrical device 300, the battery 200 can provide stable power to the device body 310, which is beneficial to improving user experience.

[0150] Optionally, the power-consuming device 300 of the embodiment of the present application may be, but is not limited to, a mobile phone, tablet computer, laptop computer, desktop computer, smart bracelet, smart watch, e-reader, game console and other portable electronic devices. It may also be a vehicle such as a car, truck, car, van, truck, motor vehicle, high-speed rail, electric automatic vehicle and other vehicles. In addition, it may also be various household appliances, etc. Figure 6 The electrical equipment 300 in the embodiment is an energy storage battery cabinet.

[0151] It can be understood that the electrical device 300 described in this embodiment is merely a form of the electrical device 300 used by the battery 200, and should not be understood as a limitation on the electrical device 300 provided in this application, nor should it be understood as a limitation on the electrical device 300 provided in each embodiment of this application.

[0152] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of the present application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application, unless there is a contradiction between them.

[0153] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A positive electrode material, characterized in that The positive electrode material includes sodium iron phosphate pyrophosphate, and the content a of sulfur impurities in the positive electrode material is in the range of 0≤a≤100 ppm.

2. The positive electrode material according to claim 1, characterized in that The range of the median particle size D50 of the positive electrode material is: 3μm≤D50≤20μm.

3. A method for preparing a positive electrode material, characterized in that: The preparation method comprises: Providing a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a slurry, adding ammonia water to the slurry so that the pH of the slurry satisfies the range of 9≤pH≤10, and sand-milling and spray-drying the slurry to obtain intermediate particles; The intermediate particles are sintered to obtain the positive electrode material.

4. The preparation method according to claim 3, characterized in that The sintering of the intermediate particles includes placing the intermediate particles in a mixed atmosphere of argon gas and reducing gas for sintering.

5. The preparation method according to claim 4, characterized in that In the mixed atmosphere of argon gas and reducing gas, the volume proportion b of argon gas is in the range of: 90%≤b≤98%.

6. The preparation method according to claim 3, characterized in that The sintering of the intermediate particles includes: a temperature T for sintering the intermediate particles satisfies a range of 520° C. ≤ T ≤ 600° C.; and a time t for sintering the intermediate particles satisfies a range of 8 h ≤ t ≤ 14 h.

7. The preparation method according to claim 3, characterized in that The providing of a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a slurry comprises: The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium acetate, sodium hydroxide, sodium nitrate, sodium peroxide, sodium citrate, and sodium oxalate; The iron source is selected from at least one of ferric phosphate, ferrous oxalate, ferric nitrate, metallic iron, ferric oxide, ferrous oxide, ferrous acetate, and ferrosoferric oxide; The phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and phosphorus pentoxide; The carbon source is selected from at least one of glucose, citric acid, ascorbic acid, polyethylene glycol, acetylene black, graphene, carbon nanotubes, sucrose, and starch.

8. A battery, characterized in that: The battery comprises: A positive electrode sheet, comprising the positive electrode material according to claim 1 or 2, or a positive electrode material prepared by the method for preparing the positive electrode material according to any one of claims 3 to 7; A diaphragm, the diaphragm being provided on one side of the positive electrode plate; a negative electrode plate, the negative electrode plate being disposed on a side of the diaphragm away from the positive electrode plate; and An electrolyte is used to soak at least a portion of the positive electrode sheet, at least a portion of the separator, and at least a portion of the negative electrode sheet.

9. The battery according to claim 8, characterized in that After the battery has been subjected to 1000 charge and discharge cycles, the content c of sulfur impurities in the electrolyte is in the range of 0≤c≤20ppm.

10. An electrical device, characterized in that: The electrical equipment includes: the device itself; and The battery according to claim 8 or 9, wherein the battery supplies power to the device body.

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