Preparation method of lithium ferrous fluorosulfate material, positive pole piece and secondary battery

Abstract

The invention provides a preparation method of a lithium ferrous sulfate fluoride material, a positive pole piece and a secondary battery, and belongs to the field of lithium batteries, the preparation method comprises the following steps: mixing ferrous sulfate heptahydrate, a lithium source, a fluorine source and a carbon source to obtain first powder; the first powder is smashed and sieved, and second powder is obtained; carrying out segmented sintering on the second powder to obtain a lithium ferrous fluoride sulfate material; wherein the step-by-step sintering comprises a first step of sintering, a second step of sintering, a third step of sintering and a fourth step of sintering, the temperature of the first step of sintering is 118-122 DEG C, the temperature of the second step of sintering is 145-155 DEG C, the temperature of the third step of sintering is 215-225 DEG C, and the temperature of the fourth step of sintering is 350-400 DEG C. By optimizing the temperature curve in the sintering process, the impure phase in the lithium ferrous fluorosulfate material can be reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a method for preparing lithium iron fluoride sulfate material, a positive electrode sheet, and a secondary battery. Background Technology

[0002] Lithium iron fluoride sulfate (LiFeSO4F) is a novel cathode material for lithium-ion batteries. It has advantages such as low raw material cost, simple preparation process and abundant resources. It also has an energy density comparable to that of traditional lithium iron phosphate (LiFePO4, LFP) materials and has good application prospects.

[0003] Currently, lithium ferrous fluoride materials are typically prepared using a high-temperature solid-state synthesis method, which involves mixing ferrous sulfate and lithium fluoride and then directly calcining the mixture at high temperatures. Products obtained in this way often contain numerous impurities and have low crystal purity, resulting in batteries with poor charge and discharge capacity. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a method for preparing lithium fluorosulfate material, a positive electrode sheet and a secondary battery, aiming to reduce the impurity phase in lithium fluorosulfate material.

[0005] In a first aspect, embodiments of this application provide a method for preparing lithium ferrous fluorosulfate material, the method comprising the following steps: Ferrous sulfate heptahydrate, lithium source, fluorine source, and carbon source are mixed to obtain the first powder; The first powder is pulverized and sieved to obtain the second powder; The second powder was sintered in segments to obtain lithium ferrous fluorosulfate material; The segmented sintering includes a first sintering stage, a second sintering stage, a third sintering stage, and a fourth sintering stage. The temperature of the first sintering stage is 118~122℃, the temperature of the second sintering stage is 145~155℃, the temperature of the third sintering stage is 215~225℃, and the temperature of the fourth sintering stage is 350~400℃.

[0006] In the technical solution of this application embodiment, by constructing a reasonable temperature curve, the water of crystallization in the reaction system can be gradually and fully discharged before high-temperature sintering, thereby helping to reduce impurities in the lithium fluorosulfate material and forming a material with higher phase purity and better performance. Simultaneously, by controlling the release rate of the water of crystallization, the pore distribution in the lithium fluorosulfate material is made more uniform, thus helping to improve the compaction density of the material. Therefore, using this lithium fluorosulfate material to prepare the positive electrode sheet of a lithium-ion battery helps to improve the charge and discharge capacity of the battery. Furthermore, the process flow of the method in this application is simple and can achieve mass production.

[0007] In some embodiments, the sintering time of the first stage is 1-3 hours; and / or, the sintering time of the second stage is 1-3 hours; and / or, the sintering time of the third stage is 0.8-1.2 hours; and / or, the sintering time of the fourth stage is 1-10 hours.

[0008] In this embodiment, controlling the sintering time of the first stage within the above-mentioned range can promote the full conversion of ferrous sulfate heptahydrate to ferrous sulfate tetrahydrate in the reaction system; controlling the sintering time of the second stage within the above-mentioned range can promote the full removal of crystal water from ferrous sulfate tetrahydrate to form ferrous sulfate monohydrate; controlling the sintering time of the third stage within the above-mentioned range can promote the full removal of crystal water in the reaction system, reducing the impurity phases formed due to residual crystal water; controlling the sintering time of the fourth stage within the above-mentioned range can promote the full growth and reconstruction of the crystal form, forming a lithium fluoride iron sulfate material with an excellent crystal structure.

[0009] In some embodiments, the segmented sintering further includes a first transition sintering stage located before the first segmented sintering stage, wherein the temperature of the first transition sintering stage is 88~92°C.

[0010] In this embodiment, a first transition temperature zone is set before the first sintering stage, so that the second powder, which is at room temperature (10~40℃), can be preheated in the first transition temperature zone before entering the first sintering stage. On the one hand, this can make the temperature curve more stable and avoid uneven heating of the material due to rapid heating, thereby preventing the problem of difficulty in timely discharge due to rapid release of crystal water. On the other hand, the free water present in the second powder can also be removed by preheating.

[0011] In some embodiments, the segmented sintering further includes a second transition sintering located between the second segment sintering and the third segment sintering, wherein the temperature of the second transition sintering is 175~185°C.

[0012] In this embodiment, a second transition temperature zone (175~185℃) is set between the second temperature zone (145~155℃) and the third temperature zone (215~225℃). This makes the temperature change process from the second sintering stage to the third sintering stage smoother, making the temperature curve more reasonable. It also avoids the interference of the high temperature of the third temperature zone with the second temperature zone, which would lead to a decrease in the temperature control accuracy of the second temperature zone.

[0013] In some embodiments, the segmented sintering further includes a third transition sintering located between the third and fourth sintering segments, wherein the temperature of the third transition sintering segment is 295~305°C.

[0014] In this embodiment, a third transition temperature zone (295~305℃) is set between the third temperature zone (215~225℃) and the fourth temperature zone (350~400℃). This makes the temperature change process from the third sintering stage to the fourth sintering stage smoother, resulting in a more reasonable temperature curve. It avoids the impact of sudden temperature rise on crystal arrangement or raw materials, which could lead to the appearance of impurities or affect the phase structure of the product. At the same time, it also avoids the high temperature of the fourth temperature zone interfering with the third temperature zone, thus preventing a decrease in the temperature control accuracy of the third temperature zone.

[0015] In some embodiments, the sintering time of the first transition section is 0.5 to 2 hours; and / or, the sintering time of the second transition section is 1 to 3 hours; and / or, the sintering time of the third transition section is 1 to 3 hours.

[0016] In this embodiment, by controlling the sintering times of the first transition section, the second transition section, and the third transition section within the above range, the time for the material to enter the next temperature zone from the previous temperature zone and the residence time in the transition temperature zone can be adjusted. While ensuring the production rate, the high temperature of the next temperature zone is prevented from affecting the previous temperature zone, and the temperature change experienced by the material is also made more gradual.

[0017] In some embodiments, the lithium source includes at least one water-soluble lithium salt, which includes one or more of lithium acetate, lithium oxalate, lithium carbonate, lithium fluoride, lithium hydroxide, lithium sulfate, and lithium phosphate; and / or, the carbon source includes one or more of nanographite, carbon nanotubes, graphene, and graphene oxide.

[0018] In this embodiment, the lithium salt compound is readily available and water-soluble, allowing it to be well integrated with other materials; the carbon compound has strong electrical conductivity and, as a carbon source, helps to improve the conductivity of the material.

[0019] In some embodiments, the fluorine source includes a first fluorinated compound and a second fluorinated compound, wherein the first fluorinated compound includes one or more of lithium fluoride, ammonium fluoride, and polyvinylidene fluoride, and the second fluorinated compound includes one or more of ammonium fluoride and polyvinylidene fluoride.

[0020] In this embodiment, adding a second fluorinated compound while adding a first fluorinated compound can increase the proportion of fluorine in the material, thereby replenishing the fluorine element and compensating for fluorine loss during sintering. Preferably, the second fluorinated compound can be ammonium fluoride, which not only replenishes the fluorine element but also does not easily introduce other elements, avoiding the generation of impurities or affecting the elemental ratio in the material.

[0021] In some embodiments, the amounts of ferrous sulfate heptahydrate, the lithium source, the fluorine source, and the carbon source fed in are such that the molar ratio of iron, lithium, fluorine, and carbon source is 1:1:(1.05~1.10):(0.02~0.04).

[0022] In this embodiment, by controlling the amount of each raw material to meet the above-mentioned element ratio, the element ratio in the material can be adjusted to obtain a material with better performance. At the same time, it can ensure that the excess of fluorine is within an appropriate range, so as to make up for the loss of fluorine and ensure that the elements in the material are in an appropriate ratio.

[0023] In some embodiments, in the step of pulverizing the first powder and sieving it to obtain the second powder, the D50 particle size of the second powder is 1~3μm and the D100 particle size is 8~15μm.

[0024] In this embodiment, the first powder is pulverized before sintering, and its particle size is controlled within the above-mentioned range, which can achieve near-nanoscale mixing and help shorten the lithium-ion diffusion channel.

[0025] In some embodiments, the step of pulverizing the first powder and sieving it to obtain the second powder is performed by air jet milling.

[0026] In this embodiment, the first powder is pulverized by air jet milling, which not only achieves a relatively uniform particle size distribution but also controls the powder particle size within the range of D50 particle size of 1~3μm and D100 particle size of 8~15μm, resulting in a good pulverization effect.

[0027] In some embodiments, a 400-mesh sieve is used for sieving.

[0028] In this embodiment, large particles in the powder can be removed by sieving.

[0029] Secondly, embodiments of this application provide a positive electrode sheet, which includes lithium fluoride sulfate material prepared by the preparation method described above, or includes the lithium fluoride sulfate material described above.

[0030] In this embodiment, the positive electrode sheet contains the aforementioned lithium fluoride sulfate material, thus having the advantage of high charge and discharge capacity.

[0031] Thirdly, embodiments of this application provide a secondary battery, including the positive electrode sheet described above.

[0032] In this embodiment, the secondary battery includes the aforementioned positive electrode plate, thus having the advantage of high charge and discharge capacity.

[0033] Fourthly, embodiments of this application provide an electrical device, including the secondary battery described above.

[0034] 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

[0035] 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.

[0036] Figure 1 This is a schematic flowchart of a method for preparing lithium ferrous fluorosulfate material according to an embodiment of this application; Figure 2 The image shows the XRD pattern of the lithium fluoride sulfate material prepared in Example 1. Figure 3 The image shows the XRD pattern of the lithium fluoride sulfate material prepared in Example 2. Figure 4 The image shows the XRD pattern of the lithium iron fluoride sulfate material prepared in Example 10. Figure 5 The image shows the XRD pattern of the lithium fluoride sulfate material prepared in Example 16. Figure 6 The XRD pattern of lithium fluoride sulfate material prepared in Comparative Example 2 is shown. Figure 7 The image shows the XRD pattern of the lithium fluoride sulfate material prepared in Comparative Example 8. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] In the description of the embodiments of this application, technical terms such as "first" and "second" 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.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0045] Currently, lithium iron fluoride sulfate is typically prepared using a high-temperature solid-state reaction method, which involves mixing ferrous sulfate and lithium fluoride and then directly calcining the mixture at high temperatures. However, this method often results in products containing numerous impurities and having low crystal purity, leading to poor charge / discharge capacity in batteries made from this product.

[0046] To address the technical problem of excessive impurities, this application provides a method for preparing lithium fluorosulfate material, a positive electrode sheet, and a secondary battery. The preparation method proposed in this application, by optimizing the temperature curve of the sintering process, helps to reduce impurities in the lithium fluorosulfate material and improve the charge and discharge capacity of the secondary battery.

[0047] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for preparing lithium ferrous fluorosulfate material, the method comprising the following steps: Step S10: Mix ferrous sulfate heptahydrate, lithium source, fluorine source, and carbon source to obtain the first powder; Step S20: Crush the first powder and sieve it to obtain the second powder; Step S30: The second powder is sintered in segments to obtain lithium ferrous fluorosulfate material; The segmented sintering includes a first-stage sintering, a second-stage sintering, a third-stage sintering, and a fourth-stage sintering. The temperature of the first-stage sintering is 118~122℃, for example, 118℃, 119℃, 120℃, 121℃, 122℃, or any value between two of these values; the temperature of the second-stage sintering is 145~155℃, for example, 145℃, 146℃, 147℃, 148℃, 149℃, 150℃, or any value between two of these values; the temperature of the third-stage sintering is 215~225℃, for example, 21... The temperatures are 5℃, 216℃, 217℃, 218℃, 219℃, 220℃, 221℃, 222℃, 223℃, 224℃, 225℃, and any two of the above values; the sintering temperature of the fourth stage is 350~400℃, for example, it can be 350℃, 355℃, 360℃, 365℃, 370℃, 375℃, 380℃, 385℃, 390℃, 395℃, 400℃, and any two of the above values.

[0048] In this application, the sintering process is optimized and designed to be sintered in at least four temperature zones: the first sintering is carried out in the first temperature zone (118~122℃) to pre-drain water vapor, causing ferrous sulfate heptahydrate to lose its water of crystallization and become ferrous sulfate tetrahydrate; the second sintering is carried out in the second temperature zone (145~155℃) to further release water of crystallization, causing ferrous sulfate tetrahydrate to become ferrous sulfate monohydrate; the third sintering is carried out in the third temperature zone (215~225℃) to remove the remaining water of crystallization while promoting the melting and mutual penetration of the raw materials to gradually form the lithium fluoride sulfate phase; the fourth sintering is carried out in the fourth temperature zone (350~400℃) to promote crystal growth and alignment, thereby obtaining lithium fluoride sulfate material with excellent crystal structure. This application's method, by constructing a reasonable temperature profile, allows the water of crystallization in the reaction system to be gradually and fully discharged before high-temperature sintering. This helps reduce impurities in the lithium fluorosulfate material, resulting in a material with higher phase purity and better performance. Simultaneously, by controlling the release rate of the water of crystallization, the pore distribution in the lithium fluorosulfate material becomes more uniform, thus helping to improve the material's compaction density. When using this lithium fluorosulfate material to prepare the positive electrode sheet for lithium-ion batteries, it helps to improve the battery's charge and discharge capacity. Furthermore, the process flow of this application is simple and can achieve mass production.

[0049] Furthermore, in some embodiments, the sintering temperature of the fourth stage can be 350~380℃. When the fourth stage sintering is carried out in this temperature range, it helps to obtain triclinic lithium fluoride sulfate material, which has a relatively high theoretical capacity. In other embodiments, the sintering temperature of the fourth stage can be controlled in the range of greater than 380℃ and less than or equal to 400℃. When the fourth stage sintering is carried out in this temperature range, it helps to obtain monoclinic lithium fluoride sulfate material. Although the theoretical capacity of this material is reduced, the structure of the material itself is more stable, which helps to form smaller polarization in charge-discharge cycles and thus more fully utilize the capacity.

[0050] Furthermore, in some embodiments, the sintering time of the first stage is 1 to 3 hours; for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any value between the two above.

[0051] In this embodiment, controlling the sintering time of the first stage within the above range can promote the full conversion of ferrous sulfate heptahydrate to ferrous sulfate tetrahydrate in the reaction system.

[0052] Furthermore, in some embodiments, the sintering time of the second stage is 1 to 3 hours; for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any value between any two of the above.

[0053] In this embodiment, controlling the sintering time of the second stage within the above range can promote the complete removal of crystal water from ferrous sulfate tetrahydrate to form ferrous sulfate monohydrate.

[0054] Furthermore, in some embodiments, the sintering time of the third stage is 0.8 to 1.2 hours; for example, it can be 0.8 hours, 0.9 hours, 1 hour, 1.1 hours, 1.2 hours, or any value between any two of the above.

[0055] In this embodiment, controlling the sintering time of the third stage within the above range can promote the complete removal of water of crystallization in the reaction system and reduce the impurity phases formed due to residual water of crystallization.

[0056] Furthermore, in some embodiments, the sintering time of the fourth stage is 1 to 10 hours; for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or any value between any two of the above.

[0057] In this embodiment, controlling the sintering time of the fourth stage within the above range can promote the full growth and reconstruction of the crystal form, forming a lithium fluoride sulfate material with an excellent crystal structure.

[0058] Furthermore, in some embodiments, the segmented sintering further includes a first transition sintering stage located before the first segmented sintering stage, wherein the temperature of the first transition sintering stage is 88~92℃; for example, it can be 88℃, 89℃, 90℃, 91℃, 92℃, or any value between any two of the above.

[0059] In this embodiment, a first transition temperature zone is set before the first sintering stage, so that the second powder, which is at room temperature (10~40℃), can be preheated in the first transition temperature zone before entering the first sintering stage. On the one hand, this can make the temperature curve more stable and avoid uneven heating of the material due to rapid heating, thereby preventing the problem of difficulty in timely discharge due to rapid release of crystal water. On the other hand, the free water present in the second powder can also be removed by preheating.

[0060] Furthermore, in some embodiments, the segmented sintering further includes a second transition sintering located between the second segment sintering and the third segment sintering, wherein the temperature of the second transition sintering is 175~185℃; for example, it can be 175℃, 176℃, 177℃, 178℃, 179℃, 180℃, 181℃, 182℃, 183℃, 184℃, 185℃, and any value between any two of the above.

[0061] In this embodiment, a second transition temperature zone (175~185℃) is set between the second temperature zone (145~155℃) and the third temperature zone (215~225℃). This makes the temperature change process from the second sintering stage to the third sintering stage smoother, making the temperature curve more reasonable. It also avoids the interference of the high temperature of the third temperature zone with the second temperature zone, which would lead to a decrease in the temperature control accuracy of the second temperature zone.

[0062] Furthermore, in some embodiments, the segmented sintering further includes a third transition sintering section located between the third and fourth sintering sections, wherein the temperature of the third transition sintering section is 295~305℃; for example, it can be 295℃, 296℃, 297℃, 298℃, 299℃, 300℃, 301℃, 302℃, 303℃, 304℃, 305℃, or any value between any two of the above.

[0063] In this embodiment, a third transition temperature zone (295~305℃) is set between the third temperature zone (215~225℃) and the fourth temperature zone (350~400℃). This makes the temperature change process from the third sintering stage to the fourth sintering stage smoother, resulting in a more reasonable temperature curve. It avoids the impact of sudden temperature rise on crystal arrangement or raw materials, which could lead to the appearance of impurities or affect the phase structure of the product. At the same time, it also avoids the high temperature of the fourth temperature zone interfering with the third temperature zone, thus preventing a decrease in the temperature control accuracy of the third temperature zone.

[0064] As a preferred embodiment, the temperature range for controlling the sintering process can be set according to the following temperature curve: 88~92℃→118~122℃→145~155℃→175~185℃→215~225℃→295~305℃→350~400℃. In this way, the temperature curve can be set more reasonably, which can not only fully remove water vapor, but also form a better phase structure, resulting in materials with higher phase purity and better performance.

[0065] Further, in some embodiments, the sintering time of the first transition section is 0.5 to 2 hours; for example, it can be 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, 1.2 hours, 1.5 hours, 1.7 hours, 1.9 hours, 2 hours, or any value between any two of the above. The sintering time of the second transition section is 1 to 3 hours; for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any value between any two of the above. The sintering time of the third transition section is 1 to 3 hours; for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any value between any two of the above.

[0066] In this embodiment, in actual production, the material is conveyed from the previous temperature zone to the next temperature zone at a certain conveying rate. By controlling the sintering time of the first transition section, the second transition section, and the third transition section within the above range, the time for the material to enter the next temperature zone from the previous temperature zone and the residence time in the transition temperature zone can be adjusted. While ensuring the production rate, the high temperature of the next temperature zone is avoided from affecting the previous temperature zone. At the same time, the temperature change experienced by the material is also made more gradual.

[0067] Furthermore, in some embodiments, step S30 can be performed in a protective atmosphere. The protective atmosphere may include, but is not limited to, nitrogen, argon, etc.

[0068] Furthermore, in some embodiments, the lithium source includes at least one water-soluble lithium salt, which includes one or more of lithium acetate, lithium oxalate, lithium carbonate, lithium fluoride, lithium hydroxide, lithium sulfate, and lithium phosphate; the carbon source includes one or more of nanographite, carbon nanotubes (CNTs), graphene, and graphene oxide (GO).

[0069] In this embodiment, the lithium salt compound is readily available and water-soluble, allowing it to be well integrated with other materials; the carbon compound has strong electrical conductivity and, as a carbon source, helps to improve the conductivity of the material.

[0070] In step S10, the fluorine source can be any fluorine-containing compound commonly used in the art. Further, in some embodiments, the fluorine source includes a first fluorine-containing compound and a second fluorine-containing compound, wherein the first fluorine-containing compound includes one or more of lithium fluoride, ammonium fluoride, and polyvinylidene fluoride (PVDF), and the second fluorine-containing compound includes one or more of ammonium fluoride and PVDF.

[0071] In this embodiment, adding a second fluorinated compound while adding a first fluorinated compound can increase the proportion of fluorine in the material, thereby replenishing the fluorine element and compensating for fluorine loss during sintering. Preferably, the second fluorinated compound can be ammonium fluoride, which not only replenishes the fluorine element but also does not easily introduce other elements, avoiding the generation of impurities or affecting the elemental ratio in the material.

[0072] Furthermore, in some embodiments, in step S10, the amounts of ferrous sulfate heptahydrate, the lithium source, the fluorine source, and the carbon source fed satisfy the following: the molar ratio of iron, lithium, fluorine, and carbon source is 1:1:(1.05~1.10):(0.02~0.04); for example, it can be 1:1:1.05:0.02, 1:1:1.06:0.02, or 1:1:1 .07:0.02, 1:1:1.08:0.02, 1:1:1.10:0.02, 1:1:1.05:0.03, 1:1:1.07:0.03, 1:1:1.10:0.03, 1:1:1.05:0.04, 1:1:1.07:0.04, 1:1:1.08:0.04, 1:1:1.10:0.04, etc.

[0073] In this embodiment, by controlling the amount of each raw material to meet the above-mentioned element ratio, the element ratio in the material can be adjusted to obtain a material with better performance. At the same time, it can ensure that the excess of fluorine is within an appropriate range, so as to make up for the loss of fluorine and ensure that the elements in the material are in an appropriate ratio.

[0074] Furthermore, in some embodiments, in step S20, the D50 particle size of the second powder is 1~3μm, for example, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm and any value between any two of the above; the D100 particle size is 8~15μm, for example, it can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm and any value between any two of the above.

[0075] In this embodiment, the first powder is pulverized before sintering, and its particle size is controlled within the above-mentioned range, which can achieve near-nanoscale mixing and help shorten the lithium-ion diffusion channel.

[0076] Furthermore, in some embodiments, in step S20, pulverization is performed by airflow pulverization.

[0077] In this embodiment, the first powder is pulverized by air jet milling, which not only achieves a relatively uniform particle size distribution but also controls the powder particle size within the range of D50 particle size of 1~3μm and D100 particle size of 8~15μm, resulting in a good pulverization effect.

[0078] Furthermore, in some embodiments, in step S20, a 400-mesh sieve is used for sieving.

[0079] In this embodiment, large particles in the powder can be removed by sieving. The specifications of the sieve can be referenced in GB / T 5330.1-2012 Industrial metal wire mesh and metal wire woven mesh mesh aperture size and metal wire diameter combination.

[0080] Secondly, this application provides a positive electrode sheet comprising lithium ferrous fluorosulfate material prepared by the method described above. The specific characteristics and preparation method of the lithium ferrous fluorosulfate material can be referred to the above embodiments. Since this positive electrode sheet uses the aforementioned lithium ferrous fluorosulfate material as the main active material and adopts all the technical solutions of all the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated further here. In summary, because lithium ferrous fluorosulfate material has advantages such as fewer impurities and higher purity, the positive electrode sheet based on lithium ferrous fluorosulfate material has the advantage of high charge / discharge capacity.

[0081] Thirdly, embodiments of this application provide a secondary battery, including the positive electrode sheet described above. The secondary battery proposed in this application has the aforementioned positive electrode sheet, and therefore has the advantage of high charge / discharge capacity.

[0082] Fourthly, embodiments of this application provide an electrical device, including a secondary battery as described in the above embodiments.

[0083] The electrical devices provided in this application embodiment can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0084] 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.

[0085] I. Preparation Method Example 1 (1) According to the molar ratio of iron, lithium, fluorine and carbon source of 1:1:1.1:0.02, ferrous sulfate heptahydrate, lithium fluoride, PVDF and carbon nanotubes were weighed and mixed at high speed for 1 hour to obtain the first powder.

[0086] (2) The first powder is pulverized by airflow and then passed through a 400-mesh sieve to obtain the second powder. The D50 particle size of the second powder is 2 μm and the D100 particle size is 10 μm.

[0087] (3) The second powder is sintered in stages to obtain lithium fluoride sulfate material. The staged sintering steps are as follows: sintering the first transition stage at 90℃ for 1 h; sintering the first stage at 120℃ for 2 h; sintering the second stage at 150℃ for 2 h; sintering the second transition stage at 180℃ for 2 h; sintering the third stage at 220℃ for 1 h; sintering the third transition stage at 300℃ for 2 h; and sintering the fourth stage at 390℃ for 3 h.

[0088] Example 2 (1) According to the molar ratio of iron, lithium, fluorine and carbon source of 1:1:1.1:0.02, ferrous sulfate heptahydrate, lithium fluoride, PVDF and graphene are weighed and mixed at high speed for 1 hour to obtain the first powder.

[0089] (2) The first powder is pulverized by airflow and then passed through a 400-mesh sieve to obtain the second powder. The D50 particle size of the second powder is 1 μm and the D100 particle size is 9 μm.

[0090] (3) The second powder is sintered in stages to obtain lithium fluoride sulfate material. The staged sintering steps are as follows: sintering the first transition stage at 90℃ for 1 h; sintering the first stage at 120℃ for 2 h; sintering the second stage at 150℃ for 2 h; sintering the second transition stage at 180℃ for 2 h; sintering the third stage at 220℃ for 1 h; sintering the third transition stage at 300℃ for 2 h; and sintering the fourth stage at 390℃ for 3 h.

[0091] Example 3 (1) According to the molar ratio of iron, lithium, fluorine and carbon source of 1:1:1.05:0.03, ferrous sulfate heptahydrate, lithium carbonate, PVDF and graphene oxide were weighed and mixed at high speed for 1 hour to obtain the first powder.

[0092] (2) The first powder is pulverized by airflow and then passed through a 400-mesh sieve to obtain the second powder. The D50 particle size of the second powder is 1 μm and the D100 particle size is 8 μm.

[0093] (3) The second powder is sintered in stages to obtain lithium fluoride sulfate material. The staged sintering steps are as follows: sintering the first transition stage at 90℃ for 1 h; sintering the first stage at 120℃ for 2 h; sintering the second stage at 150℃ for 2 h; sintering the second transition stage at 180℃ for 2 h; sintering the third stage at 220℃ for 1 h; sintering the third transition stage at 300℃ for 2 h; and sintering the fourth stage at 390℃ for 3 h.

[0094] Example 4 (1) According to the molar ratio of iron, lithium, fluorine and carbon source of 1:1:1.08:0.04, ferrous sulfate heptahydrate, PVDF, ammonium fluoride and nano-graphite were weighed and mixed at high speed for 1 hour to obtain the first powder.

[0095] (2) The first powder is pulverized by airflow and then passed through a 400-mesh sieve to obtain the second powder. The D50 particle size of the second powder is 3 μm and the D100 particle size is 15 μm.

[0096] (3) The second powder is sintered in stages to obtain lithium fluoride sulfate material. The staged sintering steps are as follows: sintering the first transition stage at 90℃ for 1 h; sintering the first stage at 120℃ for 2 h; sintering the second stage at 150℃ for 2 h; sintering the second transition stage at 180℃ for 2 h; sintering the third stage at 220℃ for 1 h; sintering the third transition stage at 300℃ for 2 h; and sintering the fourth stage at 390℃ for 3 h.

[0097] Example 5 (1) According to the molar ratio of iron, lithium, fluorine and carbon source of 1:1:1.1:0.02, ferrous sulfate heptahydrate, lithium fluoride, PVDF and carbon nanotubes were weighed and mixed at high speed for 1 hour to obtain the first powder.

[0098] (2) The first powder is pulverized by airflow and then passed through a 400-mesh sieve to obtain the second powder. The D50 particle size of the second powder is 2 μm and the D100 particle size is 10 μm.

[0099] (3) The second powder is sintered in stages to obtain lithium iron fluoride sulfate material. The staged sintering steps are as follows: sintering the first transition stage at 88℃ for 2 hours; sintering the first stage at 118℃ for 3 hours; sintering the second stage at 145℃ for 3 hours; sintering the second transition stage at 185℃ for 1 hour; sintering the third stage at 225℃ for 0.8 hours; sintering the third transition stage at 295℃ for 3 hours; and sintering the fourth stage at 390℃ for 10 hours.

[0100] Example 6 (1) According to the molar ratio of iron, lithium, fluorine and carbon source of 1:1:1.1:0.02, ferrous sulfate heptahydrate, lithium fluoride, PVDF and carbon nanotubes were weighed and mixed at high speed for 1 hour to obtain the first powder.

[0101] (2) The first powder is pulverized by airflow and then passed through a 400-mesh sieve to obtain the second powder. The D50 particle size of the second powder is 2 μm and the D100 particle size is 10 μm.

[0102] (3) The second powder is sintered in stages to obtain lithium iron fluoride sulfate material. The staged sintering steps are as follows: sintering the first transition stage at 92℃ for 0.5h; sintering the first stage at 122℃ for 1h; sintering the second stage at 155℃ for 1h; sintering the second transition stage at 175℃ for 3h; sintering the third stage at 215℃ for 1.2h; sintering the third transition stage at 305℃ for 1h; and sintering the fourth stage at 390℃ for 1h.

[0103] Example 7 The scheme in this embodiment is basically the same as that in Embodiment 1, except that the sintering temperature of the fourth stage is changed to 381℃. All other steps and conditions remain unchanged.

[0104] Example 8 The scheme in this embodiment is basically the same as that in Embodiment 1, except that the sintering temperature of the fourth stage is changed to 400℃. All other steps and conditions remain unchanged.

[0105] Example 9 The scheme in this embodiment is basically the same as that in Embodiment 1, except that the sintering temperature of the fourth stage is changed to 350℃. All other steps and conditions remain unchanged.

[0106] Example 10 The scheme in this embodiment is basically the same as that in Embodiment 1, except that the sintering temperature of the fourth stage is changed to 360℃. All other steps and conditions remain unchanged.

[0107] Example 11 The scheme in this embodiment is basically the same as that in Embodiment 1, except that the sintering temperature of the fourth stage is changed to 380℃. All other steps and conditions remain unchanged.

[0108] Example 12 The scheme in this embodiment is basically the same as that in Embodiment 1, except that there is no third transition sintering in this embodiment, that is, the temperature curve becomes 90℃→120℃→150℃→180℃→220℃→390℃. Apart from this, all other steps and conditions remain unchanged.

[0109] Example 13 The scheme in this embodiment is basically the same as that in Embodiment 1, except that there is no second transition sintering in this embodiment, that is, the temperature curve becomes 90℃→120℃→150℃→220℃→300℃→390℃. Apart from this, all other steps and conditions remain unchanged.

[0110] Example 14 The scheme in this embodiment is basically the same as that in Embodiment 1, except that there is no first transition sintering, second transition sintering, or third transition sintering in this embodiment; that is, the temperature curve becomes 120℃→150℃→220℃→390℃. Apart from this, all other steps and conditions remain unchanged.

[0111] Example 15 The scheme in this embodiment is basically the same as that in Embodiment 1, except that PVDF is replaced with ammonium fluoride. All other steps and conditions remain unchanged.

[0112] Example 16 The scheme in this embodiment is basically the same as that in Embodiment 1, except that PVDF is not added in this embodiment, and the molar ratio of iron, lithium, fluorine and carbon source is 1:1:1:0.02. All other steps and conditions remain unchanged.

[0113] Comparative Example 1 This comparative example is basically the same as Example 1, except that: Without adding PVDF, the molar ratio of iron, lithium, fluorine, and carbon source is 1:1:1:0.02; and, Step (3) is changed to: sintering the second powder at 390℃ for 3h to obtain lithium ferrous fluorosulfate material.

[0114] Apart from that, all other steps and conditions remain unchanged.

[0115] Comparative Example 2 This comparative example is basically the same as Example 1, except that step (3) is changed to: sintering the second powder at 390°C for 3 hours to obtain lithium ferrous fluorosulfate material. Other than that, all other steps and conditions remain unchanged.

[0116] Comparative Example 3 This comparative example is basically the same as Example 1, except that step (3) is changed to: sintering the second powder at 150°C for 2 hours and then at 390°C for 3 hours to obtain lithium ferrous fluorosulfate material. Other than that, all other steps and conditions remain unchanged.

[0117] Comparative Example 4 This comparative example is basically the same as Example 1, except that in step (3) of this comparative example, the sintering temperature of the first stage is changed to 115°C. Apart from this, all other steps and conditions remain unchanged.

[0118] Comparative Example 5 This comparative example is basically the same as Example 1, except that in step (3) of this comparative example, the sintering temperature of the first stage is changed to 125°C. Apart from this, all other steps and conditions remain unchanged.

[0119] Comparative Example 6 This comparative example is basically the same as Example 1, except that in step (3) of this comparative example, the sintering temperature of the second stage is changed to 140°C. Apart from this, all other steps and conditions remain unchanged.

[0120] Comparative Example 7 This comparative example is basically the same as Example 1, except that in step (3) of this comparative example, the sintering temperature of the second stage is changed to 160°C. Apart from this, all other steps and conditions remain unchanged.

[0121] Comparative Example 8 This comparative example is basically the same as Example 10, except that: Without adding PVDF, the molar ratio of iron, lithium, fluorine, and carbon source is 1:1:1:0.02; and, Step (3) is changed to: sintering the second powder at 360°C for 3 hours to obtain lithium fluoride sulfate material.

[0122] Apart from that, all other steps and conditions remain unchanged.

[0123] II. Testing Methods (1) Performance testing of lithium ferrous fluorosulfate materials 1. Impurity phase content and fluorine content detection: The lithium iron fluoride sulfate material was detected using a Rigaku X-ray diffractometer (XRD) from Japan. The test results are shown in [Figure number missing]. Figures 2 to 7 In the figure, the horizontal axis 2Theta represents the diffraction angle 2θ, and the vertical axis Intensity represents the diffraction intensity.

[0124] 2. Compacted density (PD): The compacted density was tested using a UTM7305 battery powder compaction density tester provided by Shenzhen Sansi Zongheng Technology Co., Ltd. The test pressure was 3T and the pressing time was 30s. The test results are shown in Table 1.

[0125] 3. Specific surface area (BET) test: The specific surface area was tested using a BELSORP MaxII specific surface area analyzer manufactured by Mickey Bayer of Japan. The test results are shown in Table 1.

[0126] (2) Performance testing of secondary batteries The lithium ferrous fluorosulfate materials prepared in the various examples and comparative examples were mixed with conductive carbon black and a binder (PVDF) at a mass ratio of 7:2:1, respectively. The PVDF was dissolved in N-methylpyrrolidone (NMP) to form a slurry. The slurry was coated onto aluminum foil and then dried in a vacuum oven at 100°C to obtain the positive electrode sheet. Using lithium hexafluorophosphate (LiPF6) as the lithium salt and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 as organic solvents, a 1 mol / L electrolyte was prepared. A button cell was fabricated using the lithium sheet as the negative electrode, the above electrolyte, and the positive electrode sheet.

[0127] The battery performance testing system (model: CT3002A) of Wuhan Landian Electronics Technology Co., Ltd. was used to test the battery. The test temperature was 25±1℃, the voltage range was 2.0-4.4V, and the rate range was 0.1C-10C. The test results are shown in Table 1.

[0128] Table 1

[0129] The data analysis is as follows: like Figures 2 to 7 As shown, the lithium fluoride sulfate materials prepared in Examples 1, 2, and 16 and Comparative Example 2 are monoclinic crystals, and each example exhibits higher phase purity than Comparative Example 2; the lithium fluoride sulfate materials prepared in Example 10 and Comparative Example 8 are triclinic crystals, and Example 10 exhibits higher phase purity than Comparative Example 8. This indicates that the method of this application, by optimizing the temperature profile, helps to reduce impurities and improve the phase purity of the material.

[0130] Furthermore, as can be seen from the data in Table 1, each embodiment exhibits high compaction density, 0.1C initial charge capacity, and 0.1C initial discharge capacity. Moreover, Embodiment 1 has higher compaction density and charge / discharge capacity than Comparative Examples 1 to 7, and Embodiment 10 has higher compaction density and charge / discharge capacity than Comparative Example 8. This indicates that optimizing the temperature curve helps to improve compaction density and increase battery capacity.

[0131] 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 lithium iron fluoride sulfate material, characterized in that, Includes the following steps: Ferrous sulfate heptahydrate, lithium source, fluorine source, and carbon source are mixed to obtain the first powder; The first powder is pulverized and sieved to obtain the second powder; The second powder was sintered in segments to obtain lithium ferrous fluorosulfate material; The segmented sintering includes a first sintering stage, a second sintering stage, a third sintering stage, and a fourth sintering stage. The temperature of the first sintering stage is 118~122℃, the temperature of the second sintering stage is 145~155℃, the temperature of the third sintering stage is 215~225℃, and the temperature of the fourth sintering stage is 350~400℃.

2. The preparation method according to claim 1, characterized in that, The sintering time for the first stage is 1-3 hours; and / or, The second sintering time is 1-3 hours; and / or, The sintering time for the third stage is 0.8~1.2h; and / or, The sintering time for the fourth stage is 1 to 10 hours.

3. The preparation method according to claim 1, characterized in that, The segmented sintering further includes a first transition sintering stage located before the first segmented sintering, wherein the temperature of the first transition sintering stage is 88~92℃; and / or, The segmented sintering further includes a second transition sintering section located between the second and third segmented sintering sections, wherein the temperature of the second transition sintering section is 175~185℃; and / or, The segmented sintering also includes a third transition sintering section located between the third and fourth sintering sections, wherein the temperature of the third transition sintering section is 295~305℃.

4. The preparation method according to claim 3, characterized in that, The sintering time for the first transition section is 0.5~2 hours; and / or, The sintering time for the second transition section is 1-3 hours; and / or, The sintering time for the third transition section is 1 to 3 hours.

5. The preparation method according to claim 4, characterized in that, The lithium source includes at least one water-soluble lithium salt, which includes one or more of lithium acetate, lithium oxalate, lithium carbonate, lithium fluoride, lithium hydroxide, lithium sulfate, and lithium phosphate; and / or, The carbon source includes one or more of the following: nano-graphite, carbon nanotubes, graphene, and graphene oxide; and / or, The fluorine source includes a first fluorine-containing compound and a second fluorine-containing compound. The first fluorine-containing compound includes one or more of lithium fluoride, ammonium fluoride, and polyvinylidene fluoride. The second fluorine-containing compound includes one or more of ammonium fluoride and polyvinylidene fluoride.

6. The preparation method according to claim 1, characterized in that, The amounts of the ferrous sulfate heptahydrate, the lithium source, the fluorine source, and the carbon source fed in are such that the molar ratio of iron, lithium, fluorine, and carbon source is 1:1:(1.05~1.10):(0.02~0.04).

7. The preparation method according to claim 1, characterized in that, In the step of pulverizing the first powder and sieving it to obtain the second powder, the D50 particle size of the second powder is 1~3μm and the D100 particle size is 8~15μm.

8. The preparation method according to claim 1, characterized in that, In the step of pulverizing the first powder and sieving it to obtain the second powder, the pulverization is performed by air jet milling; and / or, The sieve used during sieving is a 400-mesh sieve.

9. A positive electrode sheet, characterized in that, This includes lithium ferrous fluorosulfate materials prepared by the preparation method according to any one of claims 1 to 8.

10. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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