Lithium iron fluorosulfate positive electrode material, preparation method therefor, and use thereof

Abstract

Provided are a lithium iron fluorosulfate positive electrode material, a preparation method therefor, and a use thereof. The positive electrode material comprises lithium iron fluorosulfate, and carbon nanotubes coated on the lithium iron fluorosulfate. The positive electrode material is secondary particles, and the particle size of the secondary particles is 2-10 μm. The secondary particles are composed of nanoscale primary particles, and the particle size of the primary particles is 20-200 nm. The preparation method comprises the following steps: 1) grinding lithium fluoride to a particle size of 10 μm or less; 2) ball milling and mixing the ground lithium fluoride with ferrous sulfate and carbon nanotubes, to obtain a mixture; and 3) performing calcining on the mixture, to obtain a lithium iron fluorosulfate positive electrode material. The positive electrode material has better electronic conductivity and ionic conductivity, a higher specific capacity, and better cycle performance, as well as excellent high-temperature performance and low-temperature performance.

Description

A lithium iron fluoride sulfate cathode material, its preparation method and application Technical Field

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

[0002] With the rapid development of the world economy, the demand for energy in various countries is increasing day by day, and the global energy shortage has become a topic of concern. Finding renewable, clean, and green energy has become the most urgent task at present. As a type of green and environmentally friendly renewable resource, lithium-ion batteries have the advantages of large capacity and high energy density, and are considered to be the most promising rechargeable batteries.

[0003] Among lithium-ion battery cathode materials, polyanionic lithium-ion battery cathode materials have an open three-dimensional framework structure, resulting in small volume changes during lithium-ion extraction / insertion, thus exhibiting good cycle stability. Lithium iron fluoride sulfate (LiFeSO4F), as a novel polyanionic lithium-ion battery cathode material, has two major advantages over traditional LiFePO4 (LFP): (1) it has a higher operating voltage (3.6V); and (2) it has higher ionic conductivity. Lithium iron fluoride sulfate has two crystal forms: tavorite monoclinic and triplite triclinic. The monoclinic form has a lower operating voltage of 3.6V but higher ionic conductivity and discharge specific capacity. The triclinic form has a higher operating voltage of 3.9V and higher energy density but lower discharge specific capacity.

[0004] For lithium iron fluoride sulfate cathode materials, the most commonly used synthesis method is the solvothermal method. US patent US 9,216,912B2, Korean patent KR20160112340A, and Chinese patent CN105668643A all mention the solvothermal preparation method of LiFeSO4F material with tavorite monoclinic crystal structure. However, this method is complicated and costly, and the prepared material has poor electronic conductivity, which prevents further improvement in the specific capacity and cycle performance of the material, seriously restricting the application of LiFeSO4F as an electrode material.

[0005] The challenge in the field of LiFeSO4F is to further improve its electronic and ionic conductivity to achieve higher specific capacity and better cycle performance, while keeping production costs low. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the prior art, the present invention provides an improved lithium iron fluoride sulfate cathode material, which has better electronic conductivity and ionic conductivity, higher specific capacity and better cycle performance, and excellent high-temperature performance and low-temperature performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A lithium iron fluorosulfate cathode material, the cathode material comprising lithium iron fluorosulfate and carbon nanotubes coated on the lithium iron fluorosulfate, wherein the cathode material is a secondary particle with a particle size of 2-10 μm; the secondary particle is composed of nanoscale primary particles with a particle size of 20-200 nm.

[0009] In existing technologies, the specific capacity and cycle performance of lithium iron fluoride sulfate cathode materials are insufficient, and their preparation methods, such as solvothermal processes, are typically complex and costly. This invention, by coating lithium iron fluoride sulfate with carbon nanotubes and controlling the primary and secondary particle sizes of the cathode material, significantly improves its electronic and ionic conductivity, resulting in a cathode material with higher specific capacity and superior cycle performance, exhibiting excellent high-temperature and low-temperature performance. Surface coating with carbon nanotubes enhances the material's electronic conductivity and simultaneously constructs lithium-ion channels, further improving its ionic conductivity. This, in turn, enhances both the ionic and electronic conductivity of the lithium iron fluoride sulfate material. When used in lithium-ion batteries, it can block side reactions in the electrolyte, ensuring the cycle stability of the cathode material in lithium-ion batteries.

[0010] In this invention, the particle size of the secondary particles is obtained by SEM testing; the particle size of the primary particles is obtained by SEM testing.

[0011] In some embodiments, the carbon nanotubes account for 2% to 12% of the mass of the cathode material.

[0012] In some embodiments, the carbon nanotubes are selected from single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0013] In some embodiments, the carbon nanotubes have an outer diameter of 10–90 nm, an inner diameter of 1–5 nm, a layer spacing of 0.3–0.4 nm, and a length of 10–100 μm.

[0014] In some embodiments, the general chemical formula of the lithium iron fluoride sulfate is Li. x FeSO4F x Where x is 1.02 to 1.10, and x is preferably 1.02 to 1.06.

[0015] In some embodiments, the lithium iron fluoride sulfate includes tavorite monoclinic and triplite triclinic crystal forms, wherein the molar ratio of the monoclinic to the triclinic crystal form is 25:1 to 65:1.

[0016] In this invention, the molar ratio of monoclinic to triclinic crystal forms is calculated by the following method: the ratio of the specific capacity corresponding to the 3.6V working voltage platform to the specific capacity corresponding to the 3.9V working voltage platform in the first charge-discharge curve of the cathode material at 25℃ and 0.1C.

[0017] In some embodiments, the cathode material is prepared by a method comprising the following steps: 1) grinding lithium fluoride to a particle size of less than 10 μm; 2) ball milling and mixing the ground lithium fluoride, ferrous sulfate, and carbon nanotubes to obtain a mixture; 3) calcining the mixture to obtain the lithium iron fluoride sulfate cathode material.

[0018] This invention first grinds lithium fluoride to a specific small particle size, then ball-mills it with other precursors such as ferrous sulfate and modifier carbon nanotubes to ensure thorough mixing, followed by calcination and solid-phase reaction. This process yields a cathode material with controllable particle size and improves the charge-discharge performance and cycle performance of the cathode material.

[0019] In some embodiments, the cathode material has a discharge specific capacity of 120 mAh at 25°C and 0.1C. · g -1 The above parameters show that after 200 cycles at 25℃ and 1C, the capacity retention rate is over 75%, and the discharge specific capacity at 0℃ and 0.1C is 120mAh. · g -1 The above describes the cathode material of this invention, which exhibits better electronic and ionic conductivity, higher specific capacity, superior cycle performance, and excellent low-temperature performance.

[0020] In some embodiments, the cathode material has a discharge specific capacity of 135 mAh at 25°C and 0.1C. · g -1 The above parameters show that after 200 cycles at 25℃ and 1C, the capacity retention rate is over 95%, and the discharge specific capacity at 0℃ and 0.1C is 135mAh. · g -1 The above describes the cathode material of this invention, which exhibits better electronic and ionic conductivity, higher specific capacity, superior cycle performance, and excellent low-temperature performance.

[0021] The present invention also provides a method for preparing the aforementioned lithium iron fluoride cathode material, the method comprising the following steps: 1) grinding lithium fluoride to a particle size of less than 10 μm; 2) ball milling and mixing the ground lithium fluoride, ferrous sulfate, and carbon nanotubes to obtain a mixture; 3) calcining the mixture to obtain the lithium iron fluoride cathode material.

[0022] In some embodiments, in step 1), lithium fluoride is ground to a particle size of 5-10 μm.

[0023] In some embodiments, in step 1), lithium fluoride is ground by ball milling.

[0024] Preferably, the rotational speed of the ball mill is 300-500 r / min.

[0025] Preferably, the ball milling time is 12 to 24 hours.

[0026] In some embodiments, the ferrous sulfate is ferrous sulfate monohydrate.

[0027] In some embodiments, the molar ratio of the ground lithium fluoride to ferrous sulfate is 1.05 to 1.15:1.

[0028] In some embodiments, in step 2), the ball milling is performed in a planetary ball mill.

[0029] In some embodiments, in step 2), the rotational speed of the ball mill is 300-500 r / min.

[0030] In some embodiments, in step 2), the ball milling time is 15 to 60 minutes.

[0031] In some embodiments, the calcination temperature is 290–340°C; preferably 290–310°C. If the calcination temperature is too high, the monoclinic crystal form in lithium iron fluoride sulfate will transform into the triclinic crystal form, which will reduce the discharge specific capacity of the cathode material.

[0032] In some embodiments, the calcination is carried out in an inert gas atmosphere; the calcination time is 20 to 28 hours.

[0033] In some embodiments, the preparation method further includes a step of sieving after calcination.

[0034] In some embodiments, the sieve used for sieving has a mesh size of 200 to 600; preferably 300 to 500, and more preferably 400.

[0035] The present invention also provides an application of the aforementioned lithium iron fluoride sulfate cathode material in lithium-ion batteries.

[0036] The present invention also provides a lithium-ion battery comprising a positive electrode material, a negative electrode material and a separator, wherein the positive electrode material comprises the aforementioned lithium iron fluoride sulfate positive electrode material.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] The cathode material of this invention is a polyanionic cathode material. The surface of the lithium iron fluoride sulfate material is coated with carbon nanotubes, which are uniformly distributed and interspersed on the lithium iron fluoride sulfate. After coating the surface with carbon nanotubes, the ionic conductivity and electronic conductivity of the lithium iron fluoride sulfate material can be further improved. When used in lithium-ion batteries, it can block the side reactions of the electrolyte and ensure the cycle stability of the cathode material when used in lithium-ion batteries. The cycle stability of the cathode material of this invention is greatly improved compared with the prior art.

[0039] The lithium-ion battery cathode material of the present invention has excellent specific capacity and cycle performance, as well as excellent low-temperature performance. Moreover, its preparation method is simple, low-cost, and highly reproducible. Attached Figure Description

[0040] Figure 1 is a SEM image of the cathode material obtained in Example 1.

[0041] Figure 2 shows the SEM image of the cathode material obtained in Comparative Example 1.

[0042] Figure 3 is the XRD pattern of the cathode material obtained in Example 1.

[0043] Figure 4 shows the XRD pattern of the cathode material obtained in Comparative Example 1.

[0044] Figure 5 shows the first charge-discharge curves of the lithium-ion battery cathode materials assembled in the corresponding embodiments and comparative examples at 25°C and 0.1C.

[0045] Figure 6 shows the cycle test curves of the lithium-ion battery cathode materials assembled in the corresponding embodiments and comparative examples at 25°C and 1C.

[0046] Figure 7 shows the cycle test curves of the lithium-ion battery cathode material assembled in Example 1 at 25°C, 1C, and 5C.

[0047] Figure 8 shows the first charge-discharge curves at 0.1C for the lithium-ion battery cathode material assembled in Example 1 at different temperatures, where room temperature is 25°C.

[0048] Figure 9 shows the first charge-discharge curves at 0.1C for the lithium-ion battery cathode material (LFSF) assembled in Example 1 and the commercial lithium iron phosphate (LFP) cathode material at 0°C.

[0049] Figure 10 shows the 1C cycle test curves of the lithium-ion battery cathode material (LFSF) assembled in Example 1 and the commercial lithium iron phosphate (LFP) cathode material under 0°C conditions. Detailed Implementation

[0050] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described.

[0051] Example 1

[0052] This embodiment provides a lithium iron fluoride sulfate cathode material, the preparation method of which is as follows:

[0053] 1) Weigh a certain amount of lithium fluoride, pour it into a ball mill jar, tighten the ball mill jar lid, seal the jar, clamp it on a planetary ball mill, and mill at a speed of 400 r / min for 16 hours to obtain lithium fluoride with a particle size of 5 μm, which is then ready for use.

[0054] 2) Weigh ferrous sulfate monohydrate and the ball-milled lithium fluoride as described above, making their molar ratio 1:1.1. Then add multi-walled carbon nanotubes (outer diameter 20 nm, inner diameter 2 nm, interlayer spacing 0.3 nm, length 25 μm) to obtain a mixture. The mass fraction of multi-walled carbon nanotubes in the mixture is 5%. Pour the mixture into a ball mill jar, mix briefly, tighten the jar lid, seal it, clamp it on a planetary ball mill, and mill at 450 r / min for 30 minutes.

[0055] 3) The ball-milled mixture was placed in a tube furnace for calcination at a heating rate of 5℃ / min, a calcination temperature of 300℃, an argon atmosphere, and a calcination time of 24 hours.

[0056] 4) After calcination, allow it to cool naturally to room temperature, then pass it through a 400-mesh sieve to obtain the positive electrode material, whose general formula is Li. 1.019 FeSO4F 1.019 Figure 1 shows the SEM image of the obtained cathode material. The secondary particles are 5 μm in size and consist of nanoscale primary particles; the primary particles have a diameter of 60 nm. The particle size of the secondary particles was obtained by SEM testing; the particle size of the primary particles was also obtained by SEM testing. Figure 3 shows the XRD pattern of the obtained cathode material. In this material, lithium iron fluoride sulfate includes tavorite monoclinic and triplite triclinic crystal forms, with a molar ratio of 65:1 between the monoclinic and triclinic crystal forms. The molar ratio of the monoclinic to triclinic crystal forms was calculated as follows: the ratio of the specific capacity corresponding to the 3.6V operating voltage plateau to the specific capacity corresponding to the 3.9V operating voltage plateau in the first charge-discharge curve of the cathode material at 25℃ and 0.1C. The test method for the charge-discharge curve is described in the performance test section below.

[0057] Example 2

[0058] This embodiment provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that the calcination temperature is replaced with 320℃. The general formula and molar ratio of the obtained cathode material are shown in Table 1 below.

[0059] Example 3

[0060] This embodiment provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as that in Example 1, except that multi-walled carbon nanotubes are replaced with single-walled carbon nanotubes (outer diameter 40 nm, inner diameter 4 nm, interlayer spacing 0.3 nm, length 40 μm). The general formula and molar ratio of the obtained cathode material are shown in Table 1 below.

[0061] Example 4

[0062] This embodiment provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that the mass fraction of multi-walled carbon nanotubes is replaced with 10%. The general formula and molar ratio of the obtained cathode material are shown in Table 1 below.

[0063] Example 5

[0064] This embodiment provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that the particle size of the ground lithium fluoride is adjusted to 10 μm. The general formula and molar ratio of the obtained cathode material are shown in Table 1 below.

[0065] Example 6

[0066] This embodiment provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that the molar ratio of ferrous sulfate monohydrate and ball-milled lithium fluoride is adjusted to 1:1.05. The general formula and crystal form molar ratio of the obtained cathode material are shown in Table 1 below.

[0067] Comparative Example 1

[0068] This comparative example provides a lithium iron fluorosulfate cathode material, the preparation method of which is basically the same as that of Example 1, the only difference being that multi-walled carbon nanotubes were not added to the mixture. Figure 2 is the SEM image of the obtained cathode material, and Figure 4 is the XRD pattern of the obtained cathode material. Comparing with the SEM image of Example 1, it can be found that the cathode material of Example 1 has a uniform carbon coating layer of multi-walled carbon nanotubes. Comparing with the XRD pattern of Example 1, it can be seen that the carbon coating layer of multi-walled carbon nanotubes in Example 1 did not change the actual material composition of lithium iron fluorosulfate.

[0069] Comparative Example 2

[0070] This comparative example provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that step 1) is not performed, i.e., the lithium fluoride is not ball-milled beforehand. The results showed that the obtained cathode material was prone to agglomeration when dispersed in N,N'-methylpyrrolidone, leading to a decrease in the specific capacity and cycle performance of the assembled button cell.

[0071] Comparative Example 3

[0072] This comparative example provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that ball milling in step 2) is replaced with manual grinding. The results showed that the ferrous sulfate monohydrate and lithium fluoride were not mixed evenly enough, resulting in a significant decrease in the specific capacity of the assembled button cell.

[0073] Comparative Example 4

[0074] This comparative example provides a lithium iron fluorosulfate cathode material, the preparation method of which is basically the same as in Example 1, except that the calcination temperature is replaced with 350℃. The results showed that a larger amount of triclinic lithium iron fluorosulfate was generated during the calcination process, leading to a decrease in the discharge specific capacity of the assembled button cell.

[0075] Comparative Example 5

[0076] This comparative example provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as in Example 1, except that the molar ratio of ferrous sulfate monohydrate and ball-milled lithium fluoride is adjusted to 1:1. The results showed that due to the loss of lithium fluoride during the ball milling and calcination processes, the solid-phase reaction was not fully carried out under this feeding condition, ultimately leading to a decrease in the specific capacity and poorer cycle performance of the assembled button cell.

[0077] Comparative Example 6

[0078] This comparative example provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as that of Example 1, except that multi-walled carbon nanotubes are replaced with SP conductive carbon black.

[0079] Comparative Example 7

[0080] This comparative example provides a lithium iron fluoride sulfate cathode material, the preparation method of which is basically the same as that of Example 1, except that multi-walled carbon nanotubes are replaced with KB Ketjen Black.

[0081] Performance Testing: At the test temperature, 0.27g of the positive electrode material from each example and comparative example was weighed, and 0.015g of conductive carbon black and 0.015g of polyvinylidene fluoride were added. The mixture was then uniformly dispersed in N,N'-methylpyrrolidone. After thorough mixing, the mixture was coated onto aluminum foil to form an electrode sheet. In an argon atmosphere glove box, a coin cell was assembled using a lithium metal sheet as the counter electrode, a 16μm polyethylene separator, and a 1M LiPF6EMC:FEC (3:1V) + 0.05M LiDFOB electrolyte. Charge-discharge tests were performed on the battery within a voltage range of 2.5-4.5V. The results are shown in Table 1 below. (Composition: General chemical formula Li...) x FeSO4F x The testing method for Li and Fe is as follows: Inductively Coupled Plasma (ICP) is used for testing. High-temperature plasma ionizes the atoms in the final product, and the content of Li and Fe is quantitatively analyzed by measuring the specific spectral lines emitted or absorbed by these ions. After the final product is ionized in the plasma, the atoms or ions emit characteristic spectra. Qualitative and quantitative analysis is then performed based on the characteristic spectral lines of Li and Fe.

[0082] Table 1

[0083] As can be seen from the comparison between Example 1 and Comparative Example 1, the button battery assembled with pure-phase lithium iron fluoride sulfate cathode material (without carbon nanotube coating) has poor electrochemical performance, extremely low specific capacity, and extremely poor cycle performance. However, after coating with carbon nanotubes in Example 1, both the specific capacity and cycle performance are significantly improved.

[0084] The comparison between Example 1 and Comparative Example 2 shows that if lithium fluoride is not ball-milled beforehand, the electrochemical performance of the coin cells assembled from the final product decreases, and the cycle performance deteriorates. However, in Example 1, after ball-milling the lithium fluoride beforehand, both the specific capacity and cycle performance are significantly improved.

[0085] The comparison between Example 1 and Comparative Example 3 shows that if ball milling is replaced with hand milling, the final product assembled into button batteries has extremely poor cycle performance. However, after ball milling, the cycle performance of Example 1 is significantly improved.

[0086] As can be seen from the comparison between Example 1 and Comparative Example 4, if the calcination temperature is too high, a large amount of tripletite phase will be generated, resulting in a decrease in the specific capacity and cycle performance of the coin cell assembled from the final product. Using the calcination temperature of the present invention, a very small amount of tripletite phase will be generated, significantly improving the specific capacity and cycle performance.

[0087] The comparison between Example 1 and Comparative Example 6 shows that if the carbon nanotubes are replaced with conductive carbon black, the specific capacity and rate performance of the coin cells assembled from the final product are extremely poor. However, after being coated with carbon nanotubes in Example 1, both the specific capacity and rate performance are significantly improved.

[0088] The comparison between Example 1 and Comparative Example 7 shows that if carbon nanotubes are replaced with Ketjen Black, the specific capacity and cycle performance of the coin cells assembled from the final product decrease. However, in Example 1, after being coated with carbon nanotubes, both the specific capacity and cycle performance are significantly improved.

[0089] At 0°C, the electrical performance of the cathode material of Example 1 and commercial lithium iron phosphate (LFP) was tested using the above method. As shown in Table 2 below, it can be seen that the electrochemical performance of the material of Example 1 at low temperature is significantly better than that of conventional LFP.

[0090] Table 2

[0091] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0092] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A lithium iron fluoride sulfate cathode material, characterized in that: The cathode material includes lithium iron fluorosulfate and carbon nanotubes coated on the lithium iron fluorosulfate, and the cathode material is a secondary particle with a particle size of 2 to 10 μm; the secondary particle is composed of nanoscale primary particles with a particle size of 20 to 200 nm.

2. The lithium iron fluoride cathode material according to claim 1, characterized in that: The carbon nanotubes account for 2% to 12% of the mass of the cathode material; and / or, the carbon nanotubes are selected from single-walled carbon nanotubes or multi-walled carbon nanotubes; and / or, the carbon nanotubes have an outer diameter of 10 to 90 nm, an inner diameter of 1 to 5 nm, a layer spacing of 0.3 to 0.4 nm, and a length of 10 to 100 μm.

3. The lithium iron fluoride sulfate cathode material according to claim 1, characterized in that: The general chemical formula of the lithium fluorosulfate is Li. x FeSO4F x Where x is 1.02 to 1.10; and / or, the lithium iron fluoride sulfate includes tavorite monoclinic and triplite triclinic crystal forms, wherein the molar ratio of the monoclinic to the triclinic crystal form is 25:1 to 65:

1.

4. The lithium iron fluoride sulfate cathode material according to claim 1, characterized in that: The cathode material is prepared by a method comprising the following steps: 1) grinding lithium fluoride to a particle size of less than 10 μm; 2) ball milling and mixing the ground lithium fluoride, ferrous sulfate, and carbon nanotubes to obtain a mixture; 3) calcining the mixture to obtain the lithium iron fluoride sulfate cathode material.

5. The lithium iron fluoride sulfate cathode material according to claim 1, characterized in that: The cathode material has a discharge specific capacity of 120mAh at 25℃ and 0.1C. · g -1 The above parameters show that after 200 cycles at 25℃ and 1C, the capacity retention rate is over 75%, and the discharge specific capacity at 0℃ and 0.1C is 120mAh. · g -1 above.

6. A method for preparing the lithium iron fluoride sulfate cathode material according to any one of claims 1-5, characterized in that: The preparation method includes the following steps: 1) grinding lithium fluoride to a particle size of less than 10 μm; 2) ball milling and mixing the ground lithium fluoride, ferrous sulfate, and carbon nanotubes to obtain a mixture; 3) calcining the mixture to obtain the lithium iron fluoride cathode material.

7. The method for preparing lithium iron fluoride sulfate cathode material according to claim 6, characterized in that: In step 1), lithium fluoride is ground to a particle size of 5-10 μm; and / or, in step 1), lithium fluoride is ground by ball milling; preferably, the ball milling speed is 300-500 r / min; and / or, the ball milling time is 12-24 h.

8. The method for preparing lithium iron fluoride sulfate cathode material according to claim 6, characterized in that: The ferrous sulfate is ferrous sulfate monohydrate; and / or, the molar ratio of the ground lithium fluoride to ferrous sulfate is 1.05 to 1.15:

1.

9. The method for preparing lithium iron fluoride sulfate cathode material according to claim 6, characterized in that: In step 2), the ball milling is carried out in a planetary ball mill; and / or, in step 2), the rotational speed of the ball mill is 300-500 r / min; and / or, in step 2), the ball milling time is 15-60 min.

10. The method for preparing lithium iron fluoride sulfate cathode material according to claim 6, characterized in that: The calcination temperature is 290–340°C; preferably 290–310°C; and / or the calcination is carried out in an inert gas atmosphere; the calcination time is 20–28 h; and / or the preparation method further includes a step of sieving after calcination.

11. Use of the lithium iron fluoride sulfate cathode material according to any one of claims 1-5 in a lithium-ion battery.

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