Ferroferric lithium sulfate anode material, preparation method and application thereof

Abstract

This application provides a lithium iron fluoride sulfate cathode material, its preparation method, and its application, belonging to the field of lithium-ion battery technology. The preparation method of the lithium iron fluoride sulfate cathode material includes the following steps: providing a FeSO4.H2O@CNT precursor; mixing the FeSO4.H2O@CNT precursor, a lithium source, a fluorine source, a fluorine replenishing agent, and a grinding aid under an inert gas atmosphere, and ball milling to obtain a mixture; drying, sintering, and pulverizing the mixture to obtain the lithium iron fluoride sulfate material. In this invention, by adding a fluorine replenishing agent during ball milling to replenish the fluorine element lost during sintering, the process is simple, the fluorine replenishment effect is significant, and there are few impurities, which can significantly improve the electrochemical performance of the prepared lithium iron fluoride sulfate cathode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a lithium iron fluoride sulfate cathode material, its preparation method, and its application. Background Technology

[0002] With the widespread application of lithium-ion batteries in portable electronic products, energy storage systems, and power batteries for new energy vehicles, research on cathode and anode materials for lithium-ion batteries is becoming increasingly in-depth. Lithium iron fluorosulfate (LiFeSO4F) is a novel polyanionic cathode material with a voltage plateau of 3.9 V and a theoretical capacity of 138 mAh / g. Its ionic conductivity is significantly better than that of lithium iron phosphate (LiFePO4). Furthermore, due to its abundant iron resources and environmental friendliness, it is considered an ideal candidate material for next-generation low-cost power batteries.

[0003] LiFeSO4F exhibits excellent ionic conductivity, but existing technologies often result in poor electronic conductivity due to impurity phases, leading to suboptimal electrochemical performance. Improving the electronic and ionic conductivity of LiFeSO4F to achieve higher specific capacity and superior cycling performance, while simultaneously addressing the challenges of mass production, is a pressing issue. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a lithium iron fluoride sulfate cathode material, its preparation method and application, aiming to solve the problem of poor electrochemical performance of LiFeSO4F obtained by existing preparation methods.

[0005] In a first aspect, the present invention provides a method for preparing lithium iron fluoride sulfate cathode material, comprising the following steps: Provide FeSO4·H2O@CNT precursor; Under an inert gas atmosphere, FeSO4·H2O@CNT precursor was mixed with lithium source, fluorine source, fluorine supplement and grinding aid, and ball milled to obtain a mixture. The mixture is dried, sintered and pulverized to obtain lithium ferrous fluorosulfate material.

[0006] In the technical solution of this application embodiment, a fluorine replenishing agent is added during the ball milling process to replenish the fluorine lost during the sintering process. Compared with replenishing fluorine during the sintering process, the process is simple, can achieve continuous production, and has a significant fluorine replenishment effect with less impurity phase generated, which can significantly improve the electrochemical performance of lithium fluoride sulfate cathode material.

[0007] Furthermore, the FeSO4·H2O@CNT precursor with a core-shell structure allows CNTs to form a continuous conductive network on the FeSO4·H2O surface. Compared to directly using FeSO4·H2O and a carbon source, this enhances the overall electronic conductivity and reduces charge transfer resistance.

[0008] In some embodiments, the molar ratio of iron ions in the FeSO4·H2O@CNT precursor to lithium ions in the lithium source in the mixture is 1:(0.8-1.5); and / or, the molar ratio of lithium in the lithium source to fluorine in the fluorine source in the mixture is 1:(0.8-1.2); and / or, the molar ratio of iron in the FeSO4·H2O@CNT precursor to fluorine in the fluoride supplement in the mixture is 1:(0.1-0.2).

[0009] In the technical solution of this application embodiment, when the molar ratio of each substance falls within the above range, it helps to reduce the occurrence of side reactions, improve the purity of the target product lithium fluoride sulfate, and thus benefit its electrochemical performance as a positive electrode active material for lithium-ion batteries.

[0010] Understandably, in the preparation of lithium iron fluoride sulfate cathode materials, the molar ratio of iron ions to lithium ions is a key factor determining the product structure, purity, and electrochemical performance. An imbalance in the ratio will not only lead to impurity phase problems, but also affect the electrochemical performance of the final product. For example, if the iron ion ratio is too high, excess iron ions may occupy the lattice sites of lithium ions, hindering lithium ion diffusion and resulting in a decrease in ionic conductivity; while if the lithium ion ratio is too high, it may accelerate capacity decay.

[0011] Understandably, the main function of the fluorine replenishing agent is to replenish the fluorine lost through high-temperature volatilization. When the fluorine replenishing agent is added in excess, it may decompose and generate a large amount of HF gas, which will corrode the equipment and exacerbate the loss of other components in the system (such as lithium source). If the fluorine replenishing agent is added in insufficient amounts, it will lead to defects in the main structure and impurities, which will in turn cause the electrochemical performance of the prepared lithium fluoride sulfate cathode material to deteriorate.

[0012] In some embodiments, the sintering temperature is 380℃-400℃ and the holding time is 6-8h; and / or, the drying temperature is 60-100℃ and the drying time is 6-24h.

[0013] In the technical solution of this application embodiment, when the sintering temperature is within the above range, the technical problem of many impurity phases caused by the existing high-temperature calcination can be avoided because the sintering temperature is set relatively low.

[0014] In some embodiments, the ratio of iron ions to CNTs in the FeSO4·H2O@CNT precursor is 1 mol: (5-6) g.

[0015] In the technical solution of this application embodiment, iron ions and CNTs can achieve a better coating effect within the above-mentioned ratio range, which is beneficial to improving the electronic conductivity and ion transport efficiency of the prepared ferrous fluorosulfate sodium.

[0016] In some embodiments, the lithium source is selected from one or more of LiF, lithium acetate, lithium nitrate or lithium acetate; and / or, the fluorine source is selected from one or more of LiF, NH4F, PVDF or fluoroethylene carbonate.

[0017] In the technical solutions of this application embodiment, when a lithium-containing fluorine source such as LiF is selected, it can be used as both a fluorine source and a lithium source to avoid introducing impurities.

[0018] Furthermore, the grinding aid is selected from one or more of anhydrous ethanol, isopropanol, ethylene glycol, or water.

[0019] In the technical solution of this application embodiment, the grinding aid helps to fully and uniformly mix inorganic powder raw materials. Solvents such as anhydrous ethanol, isopropanol, ethylene glycol, and water have low toxicity and volatility, have little impact on the environment and operators, conform to the principles of green chemistry, and at the same time, the preparation cost is also reduced.

[0020] In some embodiments, the fluoride supplement is one or more of NH4F, polyvinylidene fluoride, or fluoroethylene carbonate.

[0021] In the technical solution of this application embodiment, NH4F, polyvinylidene fluoride, or fluoroethylene carbonate is used as a fluorine supplementing agent. While providing fluorine supplementation, it does not introduce impurities into the system, which is beneficial for improving the structural stability and purity of the obtained lithium fluoride sulfate material. Furthermore, the raw materials are widely available, which is beneficial for industrial production. Specifically, the fluorine source and the fluorine supplementing agent can be the same or different. When they are the same, a sufficient dosage of both should be used.

[0022] In some embodiments, FeSO4·H2O@CNT is prepared by the following method: A mixed solution containing a soluble organic polymer, CNTs, and FeSO4·7H2O is provided; The mixed solution is subjected to a first drying process to obtain a dried material; The dried material underwent a second drying process to obtain the FeSO4·H2O@CNT precursor; In the mixed solution, the mass ratio of soluble organic polymer to CNT is 1:(5-15).

[0023] In the technical solution of this application embodiment, the addition of soluble organic polymers (e.g., PVP) can improve the dispersion of CNTs in the mixed solution, and they will decompose during the subsequent sintering process without affecting the purity of the product lithium fluoride sulfate material.

[0024] In some embodiments, the first drying process is spray drying, wherein the inlet air temperature of the spray drying is 150-250°C and the outlet air temperature of the spray drying is 80-100°C; the temperature of the second drying process is 170-190°C and the time of the second drying process is 5-7 hours.

[0025] In the technical solution of this application embodiment, spray drying can be used to obtain a gray-black powdery FeSO4·H2O@CNT precursor with uniform particle size distribution, which is beneficial to improving the uniformity of the mixture obtained by subsequent ball milling.

[0026] Secondly, embodiments of this application provide a lithium ferrous fluorosulfate cathode material, which is prepared by the method described in the first aspect.

[0027] In the technical solution of this application embodiment, the obtained lithium ferrous fluorosulfate has good purity and structural stability, as well as good electronic conductivity and ionic conductivity, making it suitable as a positive electrode active material.

[0028] Thirdly, embodiments of this application provide a positive electrode sheet, comprising the lithium ferrous fluorosulfate positive electrode material described in the second aspect.

[0029] In the technical solution of this application embodiment, the above-mentioned lithium ferrous fluorosulfate is used as the active material of the positive electrode sheet. The specific capacity at 0.1C charging can reach 136mAh / g, the specific capacity at 0.1C discharging can reach 123mAh / g, and the cycle efficiency can reach 90%, showing good electrochemical performance.

[0030] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0032] Figure 1This is a 0.1C charge-discharge curve of the lithium iron fluoride cathode material obtained in Example 1 of this application; Figure 2 This is a SEM image of the lithium iron fluoride cathode material obtained in Example 1 of this application; Figure 3 The image shows the XRD pattern of the lithium iron fluoride cathode material obtained in Example 1 of this application. Specific Implementation The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In the description of the embodiments of this application, technical terms such as "solution 1" and "solution 2" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0036] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0037] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0038] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0039] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0040] During the sintering process, lithium ferrous fluorosulfate undergoes fluorine decomposition, often resulting in insufficient fluorine content in the final product, which affects the electrochemical performance of the product. The reported fluorine replenishment process is carried out during sintering, which not only requires harsh preparation conditions and is difficult to scale up for continuous production, but also easily introduces impurity phases such as FeSO4 and Fe2O3, leading to poor electrical performance of the finished product.

[0041] To address the aforementioned issues, this application provides a lithium iron fluoride sulfate cathode material, its preparation method, and its application. The in-situ fluorination method effectively solves the problems of impurity phases and continuous production difficulties caused by existing fluorination processes.

[0042] In a first aspect, the present invention provides a method for preparing lithium iron fluoride sulfate cathode material, comprising the following steps: S10 provides FeSO4·H2O@CNT precursor; S20. Under an inert gas atmosphere, FeSO4·H2O@CNT precursor, lithium source, fluorine source, fluorine supplement and grinding aid are mixed and ball-milled to obtain a mixture. S30. The mixture is dried, sintered and pulverized to obtain lithium ferrous fluorosulfate material.

[0043] In this application, a fluorine replenishing agent is added during ball milling to compensate for the fluorine lost during sintering. Compared to replenishing fluorine during the sintering process, this method is simpler, allows for continuous production, and provides a significant fluorine replenishment effect with fewer impurity phases, thus significantly improving the electrochemical performance of the lithium iron fluoride sulfate cathode material. Simultaneously, the core-shell structure of the FeSO4·H2O@CNT precursor allows CNTs to form a continuous conductive network on the FeSO4·H2O surface. Compared to processes that directly use FeSO4·H2O and a carbon source, this enhances overall electronic conductivity and reduces charge transfer impedance.

[0044] Specifically, in the mixture, the molar ratio of iron in the FeSO4·H2O@CNT precursor to lithium in the lithium source is 1:(0.8-1.5). For example, the molar ratio of iron to lithium can be any value within the range of 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or 1:(0.8-1.5).

[0045] Understandably, in the preparation of lithium iron fluoride sulfate cathode materials, the molar ratio of iron ions to lithium ions is a key factor determining the product structure, purity, and electrochemical performance. An imbalance in the ratio not only leads to impurity phase problems but also affects the electrochemical performance of the final product. If the iron ion ratio is too high, excess iron ions may occupy the lattice sites of lithium ions, hindering lithium ion diffusion and resulting in a decrease in ionic conductivity. On the other hand, if the lithium ion ratio is too high, it may accelerate capacity decay.

[0046] Furthermore, in the mixture, the molar ratio of lithium in the lithium source to fluorine in the fluorine source is 1:(0.8-1.2). For example, the molar ratio of lithium in the lithium source to fluorine in the fluorine source can be any value within the range of 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2 or 1:(0.8-1.2).

[0047] In this application, when the molar ratio of lithium in the lithium source to fluorine in the fluorine source falls within the above-mentioned range, the prepared lithium fluoride sulfate has stable performance.

[0048] Furthermore, in the mixture, the molar ratio of iron in the FeSO4·H2O@CNT precursor to fluorine in the fluorine supplement is 1:(0.1-0.2). For example, the molar ratio of iron in the FeSO4·H2O@CNT precursor to fluorine in the fluorine supplement can be any value within the range of 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19, 1:0.2, or 1:(0.1-0.2).

[0049] In this application, the main function of the fluorine replenishing agent is to replenish the fluorine lost through high-temperature volatilization. If the fluorine replenishing agent is added in excess, it may decompose and generate a large amount of HF gas, which may corrode the equipment and exacerbate the loss of other components (such as lithium source) in the system. If the fluorine replenishing agent is added in insufficient amounts, it will lead to defects in the main structure and impurities, thereby causing the electrochemical properties to deviate from the expected values.

[0050] Specifically, the fluoride supplement is one or more of NH4F, polyvinylidene fluoride, or fluoroethylene carbonate.

[0051] In this application, NH4F, polyvinylidene fluoride (PVDF), or fluoroethylene carbonate (FEC) are used as fluorine replenishing agents. These agents not only replenish fluorine but also do not introduce byproducts into the system, which is beneficial for improving the structural stability and purity of the obtained lithium fluorosulfate material. Furthermore, the raw materials are widely available, which is advantageous for industrial production. Specifically, the fluorine source and the fluorine replenishing agent can be the same or different. When they are the same, a sufficient dosage of both should be used.

[0052] Specifically, the lithium source is selected from one or more of LiF, lithium acetate, lithium nitrate, and lithium acetate.

[0053] In this application, the selection of lithium source has a certain impact on the phase purity, morphology, electrochemical performance and synthesis process of the product. An ideal lithium source should be able to achieve rapid and uniform chemical reaction at low temperature and minimize by-products. Therefore, the lithium source selected in this application has a wide range of material sources and can achieve rapid and uniform reaction.

[0054] Specifically, the fluorine source is selected from one or more of LiF, NH4F, polyvinylidene fluoride, or fluoroethylene carbonate.

[0055] In this application, the choice of fluorine source directly affects the integrity of the material's crystal structure. When a lithium-containing fluorine source such as LiF is selected, it can be used as both a fluorine source and a lithium source.

[0056] Furthermore, the grinding aid is selected from one or more of anhydrous ethanol, isopropanol, ethylene glycol, and water.

[0057] In this application, the grinding aid helps to thoroughly and uniformly mix inorganic powder raw materials. Solvents such as anhydrous ethanol, isopropanol, and ethylene glycol have low toxicity and volatility, resulting in minimal impact on the environment and operators, thus conforming to the principles of green chemistry. Water, and mixtures of water with other grinding aids, also offer lower cost-effectiveness while adhering to green chemistry principles. Specifically, the ball mill jar is designed to rotate at 300-500 r / min, with a grinding time of 5-8 h.

[0058] In this application, the ball milling speed and time jointly determine the energy input for precursor mixing, which directly affects the mixing uniformity, particle refinement and reactivity of the raw materials. Appropriate speed and ball milling time can obtain highly uniform and highly pure active materials, while excessive speed or time may lead to over-grinding, introduction of impurities and destruction of structure, thereby impairing electrochemical performance.

[0059] Furthermore, the mixture is dried using vacuum drying at a temperature of 60-100℃ for 10-20 hours.

[0060] In this application, if the vacuum drying temperature is too low or the vacuum drying time is insufficient, the water of crystallization and adsorbed water in the FeSO4·H2O@CNT precursor cannot be completely removed, resulting in a large amount of water vapor during subsequent high-temperature sintering, leading to fluorine loss, material oxidation, or even structural damage. On the other hand, if the temperature is too high or the time is too long, it may cause partial decomposition or crystal transformation of the FeSO4·H2O@CNT precursor, destroying the intended uniform structure and ultimately damaging the purity and electrochemical performance of the product.

[0061] Specifically, the sintering temperature is 380℃-400℃, the holding time is 6-8h, and the heating rate is 1-3℃ / min.

[0062] Understandably, sintering temperature is crucial for the formation and decomposition of the pure phase in lithium iron fluoride sulfate materials. Too low a temperature leads to incomplete reaction and residual impurities, while too high a temperature causes fluorine loss and decomposition of active materials. Holding time and heating rate jointly regulate grain size and structural integrity. Too short a time or too rapid a temperature rise can cause lattice defects and uneven reaction, while too long a time or too slow a temperature rise can lead to excessive grain growth and a decrease in specific surface area, ultimately affecting the material's capacity and cycle stability.

[0063] The mixture obtained after ball milling is dried and then further includes a step of sieving the dried material with a sieve. Preferably, a 400-mesh sieve is used to sieve the dried material and the zirconium balls added during the ball milling process to obtain a dried material with a D50 particle size of 1-2 μm. Then, the dried material with a D50 particle size of 1-2 μm is sintered.

[0064] In this application, controlling the particle size of the material before sintering helps to obtain lithium fluoride sulfate material with uniform particle distribution and good electrochemical performance.

[0065] Furthermore, in the FeSO4·H2O@CNT precursor, the ratio of iron ions to CNTs is 1 mol: (5-6) g.

[0066] Understandably, iron ions and CNTs in the aforementioned ratio range can achieve a better coating effect, further improving the electronic conductivity and ion transport efficiency of the product.

[0067] Furthermore, the D50 particle size of the lithium ferrous fluorosulfate obtained after pulverization is 3-5 μm.

[0068] Furthermore, in this application, FeSO4·H2O@CNT is prepared using the following method: S101, Provide a mixed solution containing a soluble organic polymer, CNTs and FeSO4·7H2O; S102. The mixed solution is subjected to a first drying treatment to obtain a dried material; S103. The dried material is subjected to a second drying treatment under inert gas to obtain FeSO4·H2O@CNT precursor.

[0069] In this application, a first drying process is performed to ensure close contact between FeSO4·H2O and CNTs at this stage. Subsequently, a second drying process is performed under an inert gas atmosphere to obtain a FeSO4·H2O@CNT precursor with uniform composition distribution.

[0070] Specifically, the first drying process is spray drying, wherein the inlet air temperature is 150-250℃ and the outlet air temperature is 80-100℃. In this application, spray drying is used in the first drying process to ensure uniform mixing of FeSO4·H2O and CNTs. The second drying process is performed at a temperature of 170-190℃ for 5-7 hours.

[0071] Furthermore, in the mixed solution, the mass ratio of the soluble organic polymer to CNTs is 1:(5~15). For example, the mass ratio of the soluble organic polymer to CNTs can be any value within the range of 1:5, 1:8, 1:10, 1:12, 1:15, or 1:(5~15). Understandably, in this application, if too much CNT is added, the dispersibility of the mixed solution will deteriorate, which will affect the uniform distribution of the components in the prepared FeSO4·H2O@CNT precursor. Conversely, if too little CNT is added, the electrochemical performance of the prepared FeSO4·H2O@CNT precursor will decrease.

[0072] Secondly, embodiments of this application provide a lithium ferrous fluoride sulfate cathode material, which is prepared by the aforementioned method for preparing lithium ferrous fluoride sulfate cathode materials.

[0073] The lithium iron fluoride sulfate cathode material prepared in this application has better electrochemical performance.

[0074] Thirdly, embodiments of this application provide a positive electrode sheet, including the aforementioned lithium ferrous fluorosulfate positive electrode material.

[0075] In this application, because the prepared lithium ferrous fluorosulfate cathode material has better electrochemical performance, when the cathode material is used to prepare the cathode sheet, the prepared cathode sheet also has better electrochemical performance.

[0076] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0077] I. Preparation Method Example 1 S10. Weigh 0.556g of polyvinylpyrrolidone and dissolve it in 200g of deionized water. Stir until completely dissolved to obtain the first solution. Then, weigh 5.56g of CNT powder and 278g (1mol) of FeSO4·7H2O and disperse them in the first solution. Stir until completely dissolved to obtain the mixed solution.

[0078] Then, the above mixed solution is subjected to a first drying treatment in a centrifugal spray dryer, wherein the inlet air temperature is 220°C and the outlet air temperature is 90°C, to obtain a dried material; finally, the dried material is subjected to a second drying treatment under an inert gas, wherein the drying temperature is 180°C and the drying time is 6 hours, to obtain the FeSO4·H2O@CNT precursor.

[0079] S20. The obtained FeSO4·H2O@CNT precursor, 26g LiF, 5.2g NH4F and anhydrous ethanol were added to a ball mill jar; ball milling was carried out under nitrogen protection, wherein the ball mill jar speed was 400 r / min and the grinding time was 6h to obtain a mixture.

[0080] S30. The above mixture is removed and dried in a vacuum oven at 80°C for 12 hours to obtain a dried material. Then, the dried material is sieved through a 400-mesh sieve to obtain a sieved material with a D50 particle size of 1.65 μm. Further, the sieved material is sintered in a tube furnace under nitrogen protection at 390°C for 7 hours at a heating rate of 2°C / min. After sintering, the sintered product is removed and pulverized in a pulverizer to obtain lithium iron fluoride sulfate cathode material with a D50 particle size of 3.25 μm.

[0081] Example 2 The only difference between Example 1 and Example 2 is that the sintering temperature in step S30 is 400°C, while all other aspects are the same as in Example 1.

[0082] Example 3 The only difference between Example 1 and Example 2 is that the sintering temperature in step S30 is 380°C, while all other aspects are the same as in Example 1.

[0083] Example 4 The only difference from Example 1 is that the amount of NH4F added in step S20 is 3.7g, and everything else is the same as Example 1.

[0084] Example 5 The only difference from Example 1 is that the amount of NH4F added in step S20 is 7.4g, and everything else is the same as Example 1.

[0085] Example 6 The only difference from Example 1 is that the amount of polyvinylpyrrolidone added in step S10 is 1g and the amount of CNT powder added is 5g. Everything else is the same as in Example 1.

[0086] Example 7 The only difference from Example 1 is that the amount of polyvinylpyrrolidone added in step S10 is 0.33g and the amount of CNT powder added is 5g. Everything else is the same as in Example 1.

[0087] Example 8 The only difference from Example 1 is that the amount of polyvinylpyrrolidone added in step S10 is 1.2g and the amount of CNT powder added is 6g. Everything else is the same as in Example 1.

[0088] Example 9 The only difference from Example 1 is that the amount of polyvinylpyrrolidone added in step S10 is 0.4g and the amount of CNT powder added is 6g. Everything else is the same as in Example 1.

[0089] Comparative Example 1 Compared to Example 1, the only difference is that the sintering temperature in step S30 is 450°C, while everything else is the same as in Example 1.

[0090] Comparative Example 2 Compared to Example 1, the only difference is that the sintering temperature in step S30 is 350°C, while everything else is the same as in Example 1.

[0091] Comparative Example 3 Compared to Example 1, the only difference is that NH4F is not added in step S20.

[0092] Comparative Example 4 Compared to Example 1, the only difference is that the amount of NH4F added in step S20 is 2.5g.

[0093] Comparative Example 5 Compared to Example 1, the only difference is that the amount of NH4F added in step S20 is 8.5g.

[0094] Comparative Example 6 The only difference from Example 1 is that the amount of polyvinylpyrrolidone added in step S10 is 0.2g and the amount of CNT powder added is 4.5g. Everything else is the same as in Example 1.

[0095] Comparative Example 7 The only difference from Example 1 is that the amount of polyvinylpyrrolidone added in step S10 is 1.5g and the amount of CNT powder added is 6.5g. Everything else is the same as in Example 1.

[0096] Comparative Example 8 Compared to Example 1, the only difference is that the drying temperature of the second drying process in step S20 is 250°C.

[0097] Comparative Example 9 Compared to Example 1, the only difference is that the drying temperature of the second drying process in step S10 is 150°C.

[0098] Comparative Example 10 Compared to Example 1, the only difference is that a second drying process is not performed after spray drying in step S10.

[0099] Comparative Example 11 Compared to Example 1, the only difference is that CNT is not added in step S10, that is, FeSO4·H2O is used instead of FeSO4·H2O@CNT in the same molar amount.

[0100] Comparative Example 12 Compared to Example 1, the only difference is that NH4F is not added during the ball milling process in step S20, but a fluorine supplement is added during the sintering process. During sintering, a separate crucible is used to hold NH4F on the side of the sintered material, and fluorine is added through diffusion by the volatilization of NH4F during the sintering process.

[0101] II. Test Methods and Test Results Specifically, in this application, the lithium ferrous fluorosulfate product prepared in Example 1 was characterized using a Rigaku X-ray powder diffractometer (XRD) from Japan, and the results are as follows: Figure 3 As shown, the XRD pattern reveals the characteristic diffraction peaks of lithium iron fluoride sulfate cathode material, and there are no impurity peaks of FeSO4 or Fe2O3.

[0102] Specifically, in this application, the lithium iron fluoride sulfate cathode material prepared in Example 1 was characterized using a Zeiss Sigma 500 field emission scanning electron microscope (SEM), and the results are as follows: Figure 2 As shown, the microstructure of the prepared cathode material is uniformly granular.

[0103] Further, the lithium iron fluoride sulfate positive electrode material prepared in Example 1 was mixed with conductive carbon powder and PVDF binder at a mass ratio of 85:10:5, homogenized, coated onto aluminum foil, dried at 100°C, and then rolled using a roller mill. Subsequently, electrode sheets with a diameter of 14 mm were obtained using a stamping machine. The mass of the active material was obtained by weighing and deducting the mass of the aluminum foil. After the positive electrode sheets were dried, CR2032 coin cell half-cells were assembled in a UNlab type inert gas glove box from Braun GmbH, Germany. The assembly sequence was: negative electrode shell, lithium sheet, electrolyte, separator, electrolyte, electrode sheet, gasket, spring sheet, and positive electrode shell. In this application, the electrochemical performance of the CR2032 coin cell half-cell was tested using the Wuhan Landian CT2001A battery testing system, with a voltage range of 2.0V to 4.5V. The test results are as follows: Figure 1 And as shown in Table 1: Table 1 Electrochemical performance data of the cathode materials obtained in Examples 1-9 and Comparative Examples 1-12 The comparison of electrochemical performance data of the cathode materials obtained in Examples 1-3 and Comparative Examples 1 and 2 shows that excessively high or low sintering temperatures lead to a decrease in the electrochemical performance of the materials, particularly the 0.1C charging specific capacity and 0.1C discharging specific capacity, which are significantly affected. The comparison of Examples 1, 4, 5 and Comparative Examples 3-5 shows that adding a fluorine supplement significantly improves the electrochemical performance of the cathode materials compared to not adding one. When the fluorine supplement is within a certain addition range, the overall electrochemical performance of the cathode materials is excellent, demonstrating a good fluorine supplementation effect. The comparison of Examples 1, 6-9 and Comparative Examples 6 and 7 shows that during the preparation of the FeSO4·H2O@CNT precursor, the amount of soluble organic polymer relative to CNTs has a certain impact on the final electrochemical performance of the cathode material. Too little organic polymer and CNTs result in poor conductivity and low capacity, while too much organic polymer leads to cost issues.

[0104] Furthermore, a comparison of Example 1 and Comparative Examples 8-10 shows that the second drying treatment in step S10 has a significant positive impact on the electrochemical performance of the obtained lithium fluoride sulfate cathode material, and the drying temperature of the second drying treatment needs to be controlled. In this application, FeSO4·H2O and CNTs can achieve close contact during the first drying treatment (i.e., spray drying). The presence of moisture and the drying temperature both affect the core-shell structure of the obtained FeSO4·H2O@CNT precursor, thereby affecting subsequent preparation processes. By performing a second drying treatment under inert gas conditions after the first drying treatment, and setting the drying temperature to 170-190℃, it is beneficial to fully remove moisture and optimize the electrochemical performance of the prepared lithium fluoride sulfate cathode material.

[0105] Furthermore, Comparative Example 11 is the case where the precursor does not contain CNTs. It can be seen that compared with the example using FeSO4·H2O@CNT precursor, the 0.1C charge specific capacity and 0.1C discharge specific capacity of the cathode material obtained in Comparative Example 11 are significantly reduced.

[0106] Furthermore, Comparative Example 12 employed a fluorine replenishment process during sintering. In this application, the embodiment employs a ball milling process to replenish the fluorine lost during sintering. Compared to replenishing fluorine during the sintering process, this method is simpler, enables continuous production, and improves the electrochemical performance of the resulting lithium ferrous fluoride cathode material, demonstrating a better fluorine replenishment effect.

[0107] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a lithium ferrous fluorosulfate cathode material, characterized in that, Includes the following steps: Provide FeSO4·H2O@CNT precursor; Under an inert gas atmosphere, the FeSO4·H2O@CNT precursor was mixed with a lithium source, a fluorine source, a fluorine supplement, and a grinding aid, and then ball-milled to obtain a mixture. The mixture is dried, sintered, and pulverized to obtain the lithium ferrous fluorosulfate material.

2. The method for preparing lithium iron fluoride sulfate cathode material according to claim 1, characterized in that, In the mixture, the molar ratio of iron in the FeSO4·H2O@CNT precursor to lithium in the lithium source is 1:(0.8-1.5); and / or In the mixture, the molar ratio of lithium in the lithium source to fluorine in the fluorine source is 1:(0.8-1.2); and / or In the mixture, the molar ratio of iron in the FeSO4·H2O@CNT precursor to fluorine in the fluorine supplement is 1:(0.1-0.2).

3. The method for preparing lithium iron fluoride sulfate cathode material according to claim 1, characterized in that, The sintering temperature is 380℃-400℃, and the holding time is 6-8 hours; and / or The drying temperature is 60-100℃, and the drying time is 6-24h.

4. The method for preparing lithium iron fluoride sulfate cathode material according to claim 1, characterized in that, In the FeSO4·H2O@CNT precursor, the ratio of iron ions to CNTs is 1 mol: (5-6) g.

5. The method for preparing lithium iron fluoride sulfate cathode material according to claim 1, characterized in that, The fluoride replenishing agent is one or more of NH4F, polyvinylidene fluoride, or fluoroethylene carbonate; and / or The fluorine source is selected from one or more of LiF, NH4F, polyvinylidene fluoride, or fluoroethylene carbonate; and / or The lithium source is selected from one or more of LiF, lithium acetate, lithium nitrate, or lithium acetate; and / or The grinding aid is selected from one or more of anhydrous ethanol, isopropanol, ethylene glycol, or water.

6. The method for preparing lithium iron fluoride sulfate cathode material according to claim 1, characterized in that, The FeSO4·H2O@CNT was prepared by the following method: A mixed solution containing a soluble organic polymer, CNTs, and FeSO4·7H2O is provided; The mixed solution is subjected to a first drying treatment to obtain a dried material; The dried material was subjected to a second drying treatment to obtain the FeSO4·H2O@CNT precursor; The mass ratio of the soluble organic polymer to CNT in the mixed solution is 1:(5-15).

7. The method for preparing lithium iron fluoride sulfate cathode material according to claim 6, characterized in that, The first drying process is spray drying, wherein the inlet air temperature of the spray drying is 150-250℃, and the outlet air temperature of the spray drying is 80-100℃; and / or The temperature of the second drying process is 170-190℃, and the time of the second drying process is 5-7 hours.

8. A lithium iron fluoride sulfate cathode material, characterized in that, It is prepared by the method described in any one of claims 1-7.

9. A positive electrode sheet, characterized in that, Including the lithium iron fluoride sulfate cathode material as described in claim 8.

10. A secondary battery, characterized in that, It includes the lithium iron fluoride sulfate cathode material as described in claim 8 or the cathode sheet as described in claim 9.

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