Fluorine-coated positive electrode material and preparation method thereof

Abstract

The application provides a fluorine-coated positive electrode material and a preparation method thereof, and relates to the technical field of lithium batteries. The fluorine-coated positive electrode material is obtained by in-situ sintering of a positive electrode material and a fluorine-containing compound. The fluorine content of the fluorine-coated positive electrode material after first pretreatment is F1, and the fluorine content of the fluorine-coated positive electrode material after second pretreatment is F2, wherein the first pretreatment is acid treatment, and the second pretreatment is alkali treatment. F1 and F2 satisfy: 300ppm<=|F1-F2|<=700ppm, and 400ppm<=F1<=2000ppm. The effective fluorine content of the positive electrode material is moderate, a relatively thin coating layer can ensure that the capacity and impedance of the positive electrode material are not affected, and in long-term cycle tests, the positive electrode material can resist electrolyte corrosion and has relatively excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a fluorine-coated cathode material and its preparation method. Background Technology

[0002] In recent years, with the rapid development of new energy technologies and markets, the market's performance requirements for lithium batteries have been continuously increasing. As an important component of lithium batteries, cathode materials are facing even more severe challenges. Coating is a commonly used modification method in the preparation of lithium battery cathode materials. By forming a coating layer on the surface of the cathode material, the surface of the cathode material can be protected during cycling, reducing Li loss caused by SEI film formation.

[0003] However, the choice of coating components and the high temperature and ventilation conditions during the sintering of lithium battery cathode materials can greatly affect the coating effect. For example, simply mixing the coating components with the cathode material and then sintering may result in adverse situations such as decomposition and volatilization of the coating components, making it difficult to give full play to the advantages of coating modification.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a fluorine-coated cathode material and its preparation method. By in-situ coating the cathode material with an appropriate amount of fluoride, the surface of the cathode material can be effectively protected during cycling, ensuring the material's cycle performance.

[0006] This invention provides a fluorine-coated cathode material, which is obtained by in-situ sintering of a cathode material and a fluorine-containing compound. The fluorine content of the fluorine-coated cathode material after a first pretreatment is F1, and the fluorine content of the fluorine-coated cathode material after a second pretreatment is F2. The first pretreatment is an acid treatment, the second pretreatment is an alkaline treatment, and the fluorine content is 300ppm≤|F1-F2|≤700ppm, 400ppm≤F1≤2000ppm.

[0007] In an exemplary embodiment of the present invention, the first pretreatment step includes: adding an acid solution to a fluorine-coated positive electrode material, shaking to dissolve, and obtaining a first pretreatment solution; wherein the acid solution is selected from one or more of sulfuric acid solution, hydrochloric acid solution, and nitric acid solution.

[0008] In an exemplary embodiment of the present invention, the second pretreatment step includes: adding an alkali to the fluorine-coated positive electrode material, performing a melt treatment, and then leaching with water to obtain a second treatment solution; the alkali is selected from one or both of sodium hydroxide and potassium hydroxide.

[0009] In an exemplary embodiment of the present invention, the fluorine-coated cathode material is selected from one or more of fluorine-coated lithium cobalt oxide cathode materials, fluorine-coated ternary cathode materials, and fluorine-coated lithium iron phosphate cathode materials, wherein the general formula of the fluorine-coated ternary cathode material is Li. x Co i Ni j Mn k M m O2-F b Where 0.9≤x≤1, i+j+k+m=1, 0.0004≤b≤0.002; M is selected from one or more of B, Mg, K, Ca, CO, V, Cr, Cu, Zn, Zr, Nb and Sn.

[0010] The present invention also provides a method for preparing the fluorine-coated cathode material as described in any one of the above claims, comprising:

[0011] S1, Obtain the cathode material;

[0012] S2, the positive electrode material is mixed with a fluorine-containing compound and a porous additive to obtain a mixture;

[0013] S3, the mixture is subjected to a first sintering treatment to remove the porous additive, and a first sintered material is obtained;

[0014] S4, the first sintering material is subjected to a second sintering treatment to obtain the fluorine-coated cathode material.

[0015] In an exemplary embodiment of the present invention, in step S2, the fluorine-containing compound is selected from one or more of MgF2, AlF3 and LiF.

[0016] In an exemplary embodiment of the present invention, in step S2, the porous additive is a porous molecular sieve.

[0017] In an exemplary embodiment of the present invention, the particle size of the porous molecular sieve is 100–220 μm.

[0018] In an exemplary embodiment of the present invention, in step S3, the temperature of the first sintering treatment is 840-1000°C, the time is 2-12 hours, and the oxygen concentration of the sintering atmosphere is greater than or equal to 40%.

[0019] In an exemplary embodiment of the present invention, in step S4, the temperature of the second sintering treatment is 400-600°C, the time is 2-12 hours, and the oxygen concentration of the sintering atmosphere is less than or equal to 10%.

[0020] The beneficial effects of the fluorine-coated cathode material and its preparation method in the embodiments of the present invention are as follows:

[0021] The fluorine-coated cathode material of this invention is formed by in-situ coating of cathode material and fluoride. The preparation method is simple and can form a stable coating on the surface of the cathode material, avoiding adverse consequences such as high surface impedance and excessive capacity loss. Simultaneously, the fluorine content of this fluorine-coated cathode material remains within a certain range under different pretreatment methods, thus characterizing the effective fluorine content on the cathode material surface. At this content level, the fluorine-coated cathode material exhibits a moderate coating thickness and an appropriate effective fluorine content on the surface. The relatively thin coating layer ensures that its capacity and impedance are not affected, and it resists electrolyte corrosion during long-cycle testing, demonstrating superior electrical performance.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows a scanning electron microscope (SEM) image of the fluorine-coated cathode material provided in Embodiment 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope image of the fluorine-coated cathode material provided in Comparative Example 3 of the present invention.

[0026] Figure 3 This is a scanning electron microscope image of the fluorine-coated cathode material provided in Comparative Example 7 of the present invention.

[0027] Figure 4 This is a graph showing the relationship between the values ​​of |F1-F2| and the capacity of 0.1C.

[0028] Figure 5 This is a graph showing the relationship between the values ​​of |F1-F2| and the capacity retention rate over 50 cycles.

[0029] Figure 6 The results are EIS test results at 4.5V SOC 100% corresponding to Example 1 and Comparative Examples 1-3. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0031] The following is a detailed description of the fluorine-coated cathode material and its preparation method according to embodiments of the present invention.

[0032] The present invention provides a fluorine-coated positive electrode, wherein the fluorine-coated positive electrode material is obtained by in-situ sintering of a positive electrode material and a fluorine-containing compound.

[0033] Specifically, the fluorine-coated cathode material can be selected from one or more of fluorine-coated lithium cobalt oxide cathode materials, fluorine-coated ternary cathode materials, and fluorine-coated lithium iron phosphate cathode materials. For example, in one embodiment, the fluorine-coated cathode material is a fluorine-coated ternary cathode material with the general formula Li. x Co i Ni j Mn k M m O2-F b Where 0.9≤x≤1, i+j+k+m=1, 0.0004≤b≤0.002; M is selected from one or more of B, Mg, K, Ca, Co, V, Cr, Cu, Zn, Zr, Nb, and Sn. Specifically, the valence states of M are as follows: B 3+ Mg 2+ K + Ca 2+ Co 3+ V 3+ V 4+ Cr 3+ Cu 2+ Zn 2+ Zr 4+ 、Nb 5+ Sn 4+ .

[0034] Furthermore, in one embodiment, 0 ≤ m ≤ 0.2.

[0035] In one embodiment, the method for preparing the fluorine-coated cathode material includes the following steps:

[0036] S1, Obtain the cathode material;

[0037] S2, the positive electrode material is mixed with a fluorine-containing compound and a porous additive to obtain a mixture;

[0038] S3, the mixture is subjected to a first sintering treatment to remove the porous additive, and a first sintered material is obtained;

[0039] S4, the first sintering material is subjected to a second sintering treatment to obtain the fluorine-coated cathode material.

[0040] Specifically, in step S1, the cathode material precursor can be lithium cobalt oxide cathode material, multi-element cathode material, lithium iron phosphate, etc. The cathode material can be obtained through existing preparation methods such as co-precipitation, high-temperature solid-state method, and hydrothermal method. For example, a transition metal salt solution (e.g., containing Ni) can be used. 2+ Co 2+ Mn 2+ Mg 2+ Soluble salts, precipitants, and complexing agents are added to the reactor, and parameters such as pH and temperature of the reaction solution are controlled to obtain a precursor. The precursor is then mixed with lithium salt and calcined to obtain a multi-element cathode material.

[0041] Specifically, in step S2, the fluorine-containing compound is selected from one or more of MgF2, AlF3, and LiF. These fluorine-containing compounds have strong corrosion resistance, and after coating, they provide better protection for the cathode material during cycling, effectively improving the electrochemical performance of the cathode material.

[0042] Specifically, in step S2, the particle size of the porous additive is 100–220 μm, more preferably 150–200 μm. This particle size allows the porous additive to both improve coating uniformity and ensure effective separation from the coated product.

[0043] The porous agent can be selected from porous molecular sieves and / or porous alumina. More preferably, porous alumina is selected as the porous agent. During the coating process, the addition of the porous agent, with its loose and porous state, can prevent the generated lithium fluoride from volatilizing and dripping to the bottom layer, providing a synthesis atmosphere for the formation of the fluoride coating layer and improving the uniformity of the coating.

[0044] Further, in step S2, the mixing process is as follows: the cathode material and the fluorinated compound are mixed and ball-milled for a certain time to obtain a premix. The premix and the porous additive are then mixed by shaking or manual mixing to obtain a mixture. Preferably, the ball milling parameters are 200–400 r / min and the ball milling time is 1–60 min. First, the cathode material and the fluorinated compound are ball-milled and mixed, and then mixed with the porous additive, which can improve the coating effect of the cathode material and the porous additive.

[0045] Specifically, in steps S3 and S4, the temperature of the first sintering treatment is 840–1000℃, the time is 2–12 h, and the oxygen concentration of the sintering atmosphere is greater than or equal to 40%. The temperature of the second sintering treatment is 400–600℃, the time is 2–12 h, and the oxygen concentration of the sintering atmosphere is less than or equal to 10%.

[0046] More preferably, the temperature of the first sintering treatment is 860–960°C, the time is 6–10 h, and the oxygen concentration of the sintering atmosphere is 60–100%. The temperature of the second sintering treatment is 400–500°C, the time is 2–5 h, and the oxygen concentration of the sintering atmosphere is 1–10%.

[0047] In the aforementioned sintering process, a first sintering is performed under high temperature and high oxygen conditions, followed by a second sintering under lower temperature and low oxygen concentration conditions. This provides conditions for the formation of an effective fluorine coating compound on the surface of the cathode material, reducing ineffective coating caused by side reactions between fluorine and other materials. Furthermore, the coating layer formed in this manner exhibits better stability, effectively improving the electrochemical performance of the product.

[0048] Furthermore, in step S3, the porous additive is removed by sieving. For example, if the particle size of the porous additive is 220 μm, a sieve with a mesh diameter of less than 220 μm is used for sieving to remove the porous additive.

[0049] Furthermore, in step S4, after sintering is completed, the material is further sieved to remove impurities and obtain fluorine-coated cathode material.

[0050] In this embodiment, the fluorine content of the fluorine-coated cathode material after the first pretreatment is F1; and the fluorine content of the fluorine-coated cathode material after the second pretreatment is F2. Specifically, the fluorine contents F1 and F2 satisfy the following conditions: 300ppm≤|F1-F2|≤700ppm, 400ppm≤F1≤2000ppm. More preferably, the fluorine contents F1 and F2 satisfy: 350ppm≤|F1-F2|≤650ppm, 900ppm≤F1≤1700ppm.

[0051] The effective coating amount on the cathode material surface was characterized by the fluorine content measured using two pretreatment methods. The fluorine content (F1) obtained after the first pretreatment remained between 900 ppm and 1700 ppm, while the difference in fluorine content (F2) obtained after the second pretreatment remained between 350 ppm and 650 ppm. The first pretreatment was acid treatment, and the second was alkaline treatment. Acid and alkaline treatments effectively eliminated interference from impurity ions. The fluorine content obtained by the two pretreatment methods, within specific ranges, indicated the effective fluorine coating amount on the cathode material surface, ensuring the protective effect of the coating layer on the cathode material surface.

[0052] It is understood that in this embodiment, ppm is used to characterize the mass concentration of fluoride ions. For example, maintaining the fluoride content F1 at 900ppm means that the mass fraction of fluoride ions in the cathode material is 0.09%.

[0053] Further, in one embodiment, the first pretreatment step includes: adding an acid solution to the fluorine-coated positive electrode material, shaking to dissolve it, and obtaining a first pretreatment solution; wherein the acid solution is selected from one or more of sulfuric acid solution, hydrochloric acid solution, and nitric acid solution. Preferably, the acid solution is aqua regia, i.e., a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1. For example, in one embodiment, the specific process of the first pretreatment is as follows: weighing an appropriate amount of dried fluorine-coated positive electrode material into a beaker, adding a certain amount of aqua regia, gently shaking the beaker during the addition process to ensure the full dissolution of the positive electrode material, and then transferring it to a volumetric flask and making up to volume to obtain the first pretreatment solution.

[0054] Further, in one embodiment, the second pretreatment step includes: adding an alkali to the fluorine-coated positive electrode material, melting it, and then leaching it with water to obtain a second treatment solution. The alkali is selected from one or both of sodium hydroxide and potassium hydroxide. More preferably, potassium hydroxide is selected as the alkali. For example, in one specific embodiment, potassium hydroxide is used for the second pretreatment. The specific process is as follows: a certain amount of potassium hydroxide is placed at the bottom of a nickel crucible, an appropriate amount of dried fluorine-coated positive electrode material is weighed and spread evenly on top of the potassium hydroxide, and then an equal amount of potassium hydroxide is added. After sealing the crucible, it is placed in a muffle furnace, heated to 500–700°C, melted for 10–30 minutes, cooled, and removed. The sample is then dissolved by heating the crucible with boiling water, washed multiple times with water, transferred to a volumetric flask, and diluted to volume to obtain the second treatment solution.

[0055] In one embodiment, the fluorine content of the first and second treated solutions was determined according to the method in GB / T 21057-2007 "General Method for Determination of Fluorine Content in Inorganic Fluorine Chemical Products" to obtain fluorine contents F1 and F2. Specifically, a working curve was plotted according to the method in the above standard. The first and second treated solutions were used as test solutions, and corresponding blank test solutions were prepared. The corresponding potential values ​​were measured according to the method in the above standard (2 drops of bromomethyl green indicator solution were added, and the solution was adjusted to a bright yellow color with sodium hydroxide solution or nitric acid solution. 10 mL of total ionic strength agent was added, diluted to the mark with water, and shaken well. The solution was then poured into a beaker, and under electromagnetic stirring, a fluoride ion selective electrode and a saturated calomel electrode were inserted, a potentiometer was connected, and the solution was continuously stirred until zero. When the potential value reached equilibrium, stirring was stopped, and the potential value was recorded after 15 seconds). The fluoride ion mass concentration of the test solution and the blank test solution was found from the working curve, and the corresponding fluorine contents F1 and F2 were obtained.

[0056] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0057] Example 1

[0058] This embodiment provides a method for preparing a fluorine-coated cathode material, including the following steps:

[0059] (1) Add 0.2wt% LiF to LiCoO2, and ball mill for 4 hours. Set the ball mill jar to 300r / min to obtain mixture 1.

[0060] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0061] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0062] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0063] Example 2

[0064] This embodiment provides a method for preparing a fluorine-coated cathode material, including the following steps:

[0065] (1) Add 0.2wt% LiF to LiCoO2, and ball mill for 4 hours. Set the ball mill jar to 300r / min to obtain mixture 1.

[0066] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0067] (3) The mixture 2 was sintered at 950°C for 8 hours in an atmosphere with an oxygen content of 80%v, and the porous alumina was removed by sieving to obtain sintered material 1.

[0068] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0069] Example 3

[0070] This embodiment provides a method for preparing a fluorine-coated cathode material, including the following steps:

[0071] (1) Add 0.2wt% LiF to LiCoO2, and ball mill for 4 hours. Set the ball mill jar to 300r / min to obtain mixture 1.

[0072] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0073] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0074] (4) Sintering material 1 at 550°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0075] Example 4

[0076] This embodiment provides a method for preparing a fluorine-coated cathode material, including the following steps:

[0077] (1) Add 0.3wt% MgF2 to LiCoO2, and ball mill the mixture for 4 hours. Set the ball mill jar to 300r / min to obtain mixture 1.

[0078] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0079] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0080] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0081] Comparative Example 1

[0082] This comparative example provides a method for preparing a fluorine-coated cathode material, comprising the following steps:

[0083] (1) Add 0.1wt% LiF to LiCoO2, and ball mill for 4 hours. Set the ball mill jar to 300r / min to obtain mixture 1.

[0084] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0085] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0086] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0087] Comparative Example 2

[0088] This comparative example provides a method for preparing a fluorine-coated cathode material, comprising the following steps:

[0089] (1) Add 0.25wt% LiF to LiCoO2, and ball mill for 4h. Set the ball mill jar to 300r / min to obtain mixture 1.

[0090] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0091] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0092] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0093] Comparative Example 3

[0094] This comparative example provides a method for preparing a fluorine-coated cathode material, comprising the following steps:

[0095] (1) Add 0.3wt% LiF to LiCoO2, and ball mill for 4 hours. Set the ball mill jar to 300r / min to obtain mixture 1.

[0096] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0097] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0098] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0099] Comparative Example 4

[0100] This comparative example provides a method for preparing a fluorine-coated cathode material, comprising the following steps:

[0101] (1) Add 0.25wt% LiF to LiCoO2, and ball mill for 4h. Set the ball mill jar to 300r / min to obtain mixture 1.

[0102] (2) The mixture 1 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0103] (3) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0104] Comparative Example 5

[0105] This comparative example provides a method for preparing a fluorine-coated cathode material, comprising the following steps:

[0106] (1) Add 0.15wt% MgF2 to LiCoO2, and ball mill for 4h. Set the ball mill jar to 300r / min to obtain mixture 1.

[0107] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0108] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0109] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0110] Comparative Example 6

[0111] (1) Add 0.15wt% AlF3 to LiCoO2, and ball mill for 4h. Set the ball mill jar to 300r / min to obtain mixture 1.

[0112] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0113] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0114] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0115] Comparative Example 7

[0116] (1) Add 0.3wt% AlF3 to LiCoO2, ball mill and mix for 4h, set the ball mill jar to 300r / min, and obtain mixture 1.

[0117] (2) Mix 1 with 30 wt% porous alumina (particle size 200 μm), shake well by hand to obtain 2;

[0118] (3) The mixture 2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80% and porous alumina was removed by sieving to obtain sintered material 1.

[0119] (4) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain fluorine-coated cathode material.

[0120] Comparative Example 8

[0121] This comparative example provides a method for preparing a cathode material, including the following steps:

[0122] (1) LiCoO2 was sintered at 875°C for 8 hours in an atmosphere with an oxygen content of 80v% to obtain sintered material 1;

[0123] (2) Sintering material 1 at 450°C for 2 hours in an atmosphere with an oxygen content of 5v%, and then sieve to obtain the positive electrode material.

[0124] The cathode materials obtained in Examples 1-4 and Comparative Examples 1-8 were subjected to a first pretreatment and a second pretreatment, respectively, to obtain corresponding first pretreatment solutions and second pretreatment solutions.

[0125] The preparation process of the first pretreatment solution is as follows: Weigh 0.2g of the dried sample into a beaker, add 10mL of aqua regia, gently shake the beaker during the addition process, and then transfer it to a 50mL volumetric flask and make up to volume to obtain the first pretreatment solution.

[0126] The preparation process of the second pretreatment is as follows: 0.8g of potassium hydroxide is placed at the bottom of a nickel crucible, 0.2g of dried fluorine-coated positive electrode material is weighed and spread on top of the potassium hydroxide, and then another 0.8g of potassium hydroxide is added. After covering the crucible, it is placed in a muffle furnace, heated to 650℃, melted for 15min, cooled and removed, and the sample is dissolved by heating the crucible with boiling water. After washing the sample with water several times, it is transferred to a 50mL volumetric flask and diluted to volume to obtain the second treatment solution.

[0127] The fluorine content F1 of the first pretreatment solution and the fluorine content F2 of the second pretreatment solution for Examples 1-4 and Comparative Examples 1-8 were measured according to the method of GB / T 21057-2007. The capacity of the cathode materials obtained in Examples 1-4 and Comparative Examples 1-8 at 0.1C and the capacity retention rate after 50 cycles were also determined. The results are shown in Table 1 below. Figures 1-6 As shown:

[0128] Table 1

[0129]

[0130] in, Figure 1 The scanning electron microscope (SEM) image of the fluorine-coated cathode material provided in Example 1 is shown below. Figure 1 It can be seen that a smooth material surface can be obtained when the fluorine coating amount is 300ppm≤|F1-F2|≤700ppm, that is, within the required range.

[0131] Figure 2 The scanning electron microscope (SEM) image of the fluorine-coated cathode material provided in Comparative Example 3 is from... Figure 2It can be seen that excessive fluoride coating leads to a rough sample surface and obvious additive clumping.

[0132] Figure 3 The image shows a scanning electron microscope (SEM) pattern of the fluorine-coated cathode material provided in Comparative Example 7. Figure 3 It can be seen that using AlF3 as a coating agent makes it difficult for the additive to integrate with the matrix, and it is easy to fall off during the preparation process, resulting in a low F content and poor performance in the finished material.

[0133] From Table 1 and Figure 4 , Figure 5 It can be seen that when the fluorine content F1 after acid treatment and the fluorine content F2 after alkali treatment meet the requirements of 300ppm≤|F1-F2|≤700ppm and 400ppm≤F1≤2000ppm, the effective fluorine coating of the obtained cathode material is appropriate, and the product obtains higher capacity and better cycle performance. Referring to the parameters of Comparative Example 4 and Example 1, the capacity and cycle performance of the obtained cathode material are poor when porous alumina is not added.

[0134] In addition, from Figure 6 It can be seen that when the fluorine coating amount is appropriate, the material has a lower impedance.

[0135] The embodiments described above are some, but not all, of the embodiments of this disclosure. The detailed description of the embodiments of this disclosure is not intended to limit the scope of the claimed disclosure, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

Claims

1. A fluorine-coated cathode material, characterized in that, The fluorine-coated cathode material is obtained by in-situ sintering of cathode material and fluorine-containing compound. The fluorine-coated cathode material undergoes a first pretreatment, which includes adding an acid solution to the fluorine-coated cathode material, shaking to dissolve it, and obtaining a first pretreatment solution. The fluorine content of the first pretreatment solution is F1. The fluorine-coated cathode material undergoes a second pretreatment, which includes adding an alkali to the fluorine-coated cathode material, melting it, and then leaching it with water to obtain a second treatment solution. The fluorine content of the second treatment solution is F2. The first pretreatment is an acid treatment, the second pretreatment is an alkali treatment, and the fluorine content is 300 ppm ≤ |F1-F2| ≤ 700 ppm, 400 ppm ≤ F1 ≤ 2000 ppm.

2. The fluorine-coated cathode material according to claim 1, characterized in that, The acid solution is selected from one or more of sulfuric acid solution, hydrochloric acid solution and nitric acid solution.

3. The fluorine-coated cathode material according to claim 1, characterized in that, The alkali is selected from one or both of sodium hydroxide and potassium hydroxide.

4. The fluorine-coated cathode material according to claim 1, characterized in that, The fluorine-coated cathode material is selected from one or more of fluorine-coated lithium cobalt oxide cathode materials, fluorine-coated multi-element cathode materials, and fluorine-coated lithium iron phosphate cathode materials, wherein the general formula of the fluorine-coated multi-element cathode material is Li. x Co i Ni j Mn k M m O2-F b Where 0.9≤x≤1, i+j+k+m=1, 0.0004≤b≤0.002; M is selected from one or more of B, Mg, K, Ca, CO, V, Cr, Cu, Zn, Zr, Nb and Sn.

5. A method for preparing a fluorine-coated cathode material as described in any one of claims 1 to 4, characterized in that, include: S1, Obtain the cathode material; S2, the positive electrode material is mixed with a fluorine-containing compound and a porous additive to obtain a mixture; S3, the mixture is subjected to a first sintering treatment to remove the porous additive, and a first sintered material is obtained; S4, the first sintering material is subjected to a second sintering treatment to obtain the fluorine-coated cathode material.

6. The method for preparing the fluorine-coated cathode material according to claim 5, characterized in that, In step S2, the fluorine-containing compound is selected from one or more of MgF2, AlF3 and LiF.

7. The method for preparing the fluorine-coated cathode material according to claim 5, characterized in that, In step S2, the porous additive is a porous molecular sieve.

8. The method for preparing the fluorine-coated cathode material according to claim 7, characterized in that, The porous molecular sieve has a particle size of 100~220 μm.

9. The method for preparing the fluorine-coated cathode material according to claim 5, characterized in that, In step S3, the temperature of the first sintering treatment is 840~1000 ℃, the time is 2~12 h, and the oxygen concentration of the sintering atmosphere is greater than or equal to 40%.

10. The method for preparing the fluorine-coated cathode material according to claim 5, characterized in that, In step S4, the temperature of the second sintering treatment is 400~600℃, the time is 2~12 h, and the oxygen concentration of the sintering atmosphere is less than or equal to 10%.

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