Sodium ferric pyrophosphate coated ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of battery electrodes, and discloses a sodium ferric pyrophosphate coated ternary positive electrode material, a preparation method thereof and a lithium ion battery. The invention provides a preparation method of a sodium ferric pyrophosphate coated ternary positive electrode material. The preparation method comprises the following steps: S1, obtaining a ternary positive electrode material; and S2, mixing the ternary positive electrode material, a ferric pyrophosphate precursor and a sodium source to obtain a mixed material, and sintering the mixed material to obtain the sodium ferric pyrophosphate coated ternary positive electrode material. According to the preparation method of the sodium ferric pyrophosphate coated ternary positive electrode material provided by the invention, one-step synergistic modification of bulk phase doping and surface coating is realized, and meanwhile, the bulk phase structure and the interface stability are improved, so that the electrochemical performance of the material is improved. The method also has the following advantages that the binding force of the coating layer is strong, the process is simple, the operation steps are few, doping and in-situ coating are synergistically realized, and industrial amplification is easy.

Description

Technical Field

[0001] This invention relates to the field of battery electrode technology, specifically to a sodium iron pyrophosphate coated ternary cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the widespread adoption of new energy vehicles, the scale of power batteries is continuously expanding, and the demand for high-energy-density cathode materials is also increasing. LiNi 0.80 Co 0.10 Mn 0.10 Layered high-nickel cathodes, represented by O2, exhibit the most outstanding performance and have attracted widespread attention from researchers. High-nickel ternary materials have poor air stability, readily reacting with water and carbon dioxide in the air to form residual lithium hydroxide and lithium carbonate alkalis on their surface. During electrode material preparation, these residual alkalis react with PVDF, causing the slurry to become gel-like, reducing the material's processing performance and electrochemical performance. Enhancing the air stability of high-nickel ternary materials is crucial for their large-scale application in power batteries. Currently, most high-nickel ternary materials employ surface coating with metal oxides, metal phosphates, etc., to improve air stability and electrochemical performance. Traditional coating methods, such as deposition and wet chemical methods, are too costly and difficult to scale up for mass production.

[0003] At present, the secondary sintering of high-nickel ternary materials mainly adopts deposition and wet chemical methods, which are too costly and difficult to scale up. The dry chemical method has the following advantages over wet and deposition methods: (1) simple process, short process, low cost, no solvent required, and less equipment investment; (2) no wastewater discharge, which is more environmentally friendly; (3) avoids the substrate material from contacting water, protecting the layered structure of the cathode material; (4) the cathode material is mixed with micron or nano coating material by physical mechanical force, which makes it easy to control the thickness of the coating layer; (5) during the dry mixing process, dopants and coating agents can be added at the same time, thereby achieving bulk doping and coating synergistic modification. Dry coating is a solvent-free coating process in which the coating material is mechanically mixed with the cathode material, and the coating agent is cured or reacted with the substrate surface at a lower temperature to form a coating layer.

[0004] However, most dry coating processes currently employ non-in-situ coating, which involves first synthesizing the coating material and then mixing it with a high-nickel ternary material before sintering it again, resulting in poor cycle performance. Summary of the Invention

[0005] This invention provides a sodium iron pyrophosphate coated ternary cathode material, its preparation method, and a lithium-ion battery, achieving the effect of improving the cycle performance of lithium-ion batteries.

[0006] In a first aspect, the present invention provides a method for preparing a sodium iron pyrophosphate-coated ternary cathode material, comprising the following steps: S1. Obtain ternary cathode material; S2. The ternary cathode material, iron pyrophosphate precursor and sodium source are mixed to obtain a mixed material, and the mixed material is sintered to obtain sodium iron pyrophosphate coated ternary cathode material.

[0007] In one alternative implementation, S2 satisfies at least one of the following conditions: (1) The molar ratio of phosphorus in the iron pyrophosphate precursor to sodium in the sodium source is (0.6-1.1):1; (2) The mass ratio of the ternary cathode material to the iron pyrophosphate precursor is (20-200):1; (3) The sintering atmosphere is air or oxygen; (4) The sintering temperature is 500-700℃ and the sintering time is 6-15h; (5) The heating rate of the sintering is 1-5℃ / min; (6) The sintering atmosphere flow rate is 1-2 L / min; (7) The amount of sodium pyrophosphate coating in the sodium pyrophosphate coated ternary cathode material is 1-3 wt%.

[0008] In one optional embodiment, the method for preparing the sodium iron pyrophosphate-coated ternary cathode material satisfies at least one of the following conditions: (1) The chemical formula of the iron pyrophosphate precursor is H y Fe 3-x M x (PO4)4, wherein M includes one or more of Ni, Mg, Ca, Ti, Zr, and Cu, and 0 <x≤1.2,0<y≤4; Preferably, the chemical formula of the iron pyrophosphate precursor is H4Fe. 2.5 Cu 0.5 (PO4)4; (2) The sodium source includes one or more of sodium carbonate, sodium hydroxide, and sodium bicarbonate; (3) The specific surface area of ​​the iron pyrophosphate precursor is 1-10 m². 2 / g; (4) The median particle size D50 of the iron pyrophosphate precursor is 5~10 μm; (5) The chemical formula of the ternary cathode material is Li 1+c Ni a Co b Mn 1-a-b O2, where 0.8≤a≤1, 0 <b≤0.1,0<c≤0.5; Preferably, the chemical formula of the ternary cathode material is Li. 1.05Ni 0.8 Co 0.1 Mn 0.1 O2; Preferably, the value of c in the chemical formula of the ternary cathode material is in the range of 0. <c≤0.05。

[0009] In one optional implementation, step S1 includes the following steps: S1-1. Mix the nickel-cobalt-manganese hydroxide precursor with a lithium source to obtain a mixture; S1-2. Sinter the mixture in S1-1, cool it, and then crush it to obtain a ternary cathode material sintered material; S1-3. Wash the ternary cathode material, then separate the solid and liquid components and dry it to obtain the ternary cathode material.

[0010] In an optional embodiment, the chemical formula of the nickel-cobalt-manganese hydroxide precursor in S1-1 is Ni x Co y Mn 1-x-y (OH)₂, 0.8≤x≤1, 0 <y≤0.1; Preferably, the chemical formula of the nickel-cobalt-manganese hydroxide precursor in S1-1 is Ni 0.8 Co 0.1 Mn 0.1 (OH)2; Optionally, the specific surface area of ​​the nickel-cobalt-manganese hydroxide precursor ranges from 5 to 20 m². 2 / g, tap density ranges from 1.0 to 4.0 g / cm³. 3 ; And / or, the median particle size D50 of the nickel-cobalt-manganese hydroxide precursor is in the range of 12-18 μm.

[0011] In an optional embodiment, the molar ratio of lithium in the lithium source in S1-1 to the sum of nickel, cobalt and manganese metal elements in the nickel-cobalt-manganese hydroxide precursor is (0.8-1.1):1. And / or, the lithium source includes one or more of lithium carbonate and lithium hydroxide.

[0012] In one optional embodiment, the sintering atmosphere in S1-2 is air or oxygen, and the sintering heating rate is 2-8℃ / min. And / or, the sintering temperature in S1-2 is 400-700℃, and the sintering time is 14-19h; Optionally, the sintering step in S1-2 includes heating the mixture in S1-1 to 300-500℃ at a heating rate of 2-4℃ / min and holding it at that temperature for 1-3h, and then heating it to 500-700℃ at a heating rate of 1-3℃ / min and holding it at that temperature for 10-12h. Preferably, the sintering step in S1-2 includes heating the mixture in S1-1 to 400°C at a heating rate of 3°C / min and holding it at that temperature for 2 hours, and then heating it to 700°C at a heating rate of 2°C / min and holding it at that temperature for 12 hours.

[0013] In one optional embodiment, the washing speed in S1-3 is 200-400 rpm; And / or, the solid-liquid separation method includes vacuum filtration or pressure filtration; And / or, the drying temperature is 80-190℃, and the drying time is 2-12 h.

[0014] Secondly, the present invention provides a sodium iron pyrophosphate coated ternary cathode material, which is prepared by the aforementioned preparation method.

[0015] Thirdly, the present invention provides a lithium-ion battery comprising the aforementioned sodium iron pyrophosphate-coated ternary cathode material.

[0016] The technical solution of this invention has the following advantages: 1. The preparation method of sodium iron pyrophosphate coated ternary cathode material provided by the present invention includes the following steps: S1, obtaining ternary cathode material; S2, mixing the ternary cathode material, iron pyrophosphate precursor and sodium source to obtain a mixed material, and sintering the mixed material to obtain sodium iron pyrophosphate coated ternary cathode material.

[0017] During the in-situ coating process of sodium iron pyrophosphate, the reaction between iron pyrophosphate and residual alkali on the surface of the ternary cathode material (referring to the side reaction between residual lithium source on the cathode material surface and iron pyrophosphate) generates lithium iron pyrophosphate, reducing the residual alkali in the material. Simultaneously, lithium iron pyrophosphate is also a good fast ion conductor, effectively reducing the interfacial impedance of the material. Meanwhile, the sodium iron pyrophosphate (NaFeP2O7) generated on the surface is a stable phosphate that effectively isolates the electrolyte and suppresses side reactions. During the in-situ coating process, some Na is embedded in the surface lattice of the cathode material, acting as a pillar and suppressing lattice collapse and phase transition during deep delithiation of the ternary cathode material, thus significantly improving the material's stability. The in-situ coating process, with the formation of NaFeP2O7 and LiFeP2O7 coatings and Na doping, achieves a one-step synergistic modification of bulk doping and surface coating, simultaneously improving the bulk structure and interfacial stability, thereby enhancing the electrochemical performance of the material.

[0018] In the in-situ coating process, sodium iron pyrophosphate and lithium iron pyrophosphate react at the atomic / molecular level during the sintering of the matrix material, achieving uniform distribution at the nanoscale or even atomic scale, forming a continuous, dense, and defect-free coating layer. In-situ coating is the final sintering process that integrates the coating into the material, reducing production steps and minimizing product consistency risks.

[0019] The method for coating ternary cathode materials with sodium iron pyrophosphate provided by this invention has strong coating adhesion, simple process, few operation steps, synergistic achievement of doping and in-situ coating, and is easy to scale up industrially. Detailed Implementation

[0020] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0021] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0022] Example 1 This embodiment provides a method for preparing a ternary cathode material coated with sodium iron pyrophosphate, including the following steps: S1. Based on the molar ratio of lithium: the total molar ratio of nickel, cobalt, and manganese in the precursor is 1.05:1, weigh out Ni... 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor, lithium hydroxide. Ni 0.8 Co 0.1 Mn 0.1 The specific surface area of ​​the (OH)₂ precursor is 6.22 m². 2 / g, tap density is 2.51 g / cm³ 3 The median particle size D50 is 15.20 μm, and the purity of lithium hydroxide is 57.45%. The above raw materials are mixed evenly using a high-speed mixer to obtain a mixture. S2. The mixture in S1 is heated to 400℃ in a box furnace at a heating rate of 3℃ / min, held at 400℃ for 2h, then heated to 700℃ at a heating rate of 2℃ / min, held at 700℃ for 12h, with oxygen in the sintering atmosphere and an oxygen flow rate of 1.5L / min, and then cooled to room temperature naturally and pulverized to obtain a ternary cathode material sintered material.

[0023] S3. The pulverized ternary cathode material sintered material is sieved through a 44μm pore size filter screen. 500g of the sintered material is weighed and washed with water at a water-to-material ratio of 2:1, a washing speed of 200rpm, and a stirring time of 5min. The mixture is then filtered using a vacuum filter to separate the solid. The solid is dried in a box furnace at 120℃ for 10h to obtain the ternary cathode material with the chemical formula Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0024] S4. Mix 100g of ternary cathode material with 1.12g of ferric pyrophosphate precursor H4Fe 2.5 Cu 0.5 (PO4)4 and 0.69 g of sodium carbonate were placed in a dry mixer and dispersed at high speed to obtain a uniform mixture. The specific surface area of ​​the ferric pyrophosphate precursor was 6 m². 2 / g, the median particle size D50 of the iron pyrophosphate precursor is 7 μm, and the molar ratio of phosphorus in the iron pyrophosphate precursor to sodium in the sodium source is 0.619:1.

[0025] S5. The obtained mixed material is heated to 500℃ at a heating rate of 1℃ / min and held at that temperature for 5h. The sintering atmosphere is oxygen with an oxygen flow rate of 1.5L / min. After natural cooling to room temperature and pulverization, sodium iron pyrophosphate coated ternary cathode material is obtained, wherein the coating amount of sodium iron pyrophosphate is 1.5wt%, denoted as 1.5wt% NFPP in-situ-NCM.

[0026] Example 2 This embodiment provides a method for preparing a ternary cathode material coated with sodium iron pyrophosphate, including the following steps: S1. Based on the molar ratio of lithium: the total molar ratio of nickel, cobalt, and manganese in the precursor is 1.05:1, weigh out Ni... 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor, lithium hydroxide. Ni 0.8 Co 0.1 Mn 0.1 The specific surface area of ​​the (OH)₂ precursor is 6.22 m². 2 / g, tap density is 2.51 g / cm³ 3 The median particle size D50 is 15.20 μm, and the purity of lithium hydroxide is 57.45%. The above raw materials are mixed evenly using a high-speed mixer to obtain a mixture. S2. The mixture in S1 is heated to 400℃ in a box furnace at a heating rate of 3℃ / min, held at 400℃ for 2h, then heated to 700℃ at a heating rate of 2℃ / min, held at 700℃ for 12h, with oxygen in the sintering atmosphere and an oxygen flow rate of 1.5L / min, and then cooled to room temperature naturally and pulverized to obtain a ternary cathode material sintered material.

[0027] S3. The pulverized ternary cathode material sintered material is sieved through a 44μm pore size filter screen. 500g of the sintered material is weighed and washed with water at a water-to-material ratio of 2:1, a washing speed of 200rpm, and a stirring time of 5min. The mixture is then filtered using a vacuum filter to separate the solid. The solid is dried in a box furnace at 120℃ for 10h to obtain the ternary cathode material with the chemical formula Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0028] S4. Mix 100g of ternary cathode material with 0.75g of iron pyrophosphate precursor H4Fe 2.5 Cu 0.5 (PO4)4 and 0.46 g of sodium carbonate were placed in a dry mixer and dispersed at high speed to obtain a uniform mixture. The specific surface area of ​​the iron pyrophosphate precursor was 6 m². 2 / g, the median particle size D50 of the iron pyrophosphate precursor is 7 μm, and the molar ratio of phosphorus in the iron pyrophosphate precursor to sodium in the sodium source is 0.622:1.

[0029] S5. The obtained mixed material is heated to 500℃ at a heating rate of 1℃ / min and held at that temperature for 5h. The sintering atmosphere is oxygen with an oxygen flow rate of 1.5L / min. After natural cooling to room temperature and pulverization, sodium iron pyrophosphate coated ternary cathode material is obtained, wherein the coating amount of sodium iron pyrophosphate is 1wt%, denoted as 1wt% NFPP in-situ-NCM.

[0030] Example 3 This embodiment provides a method for preparing a ternary cathode material coated with sodium iron pyrophosphate, including the following steps: S1. Based on the molar ratio of lithium: the total molar ratio of nickel, cobalt, and manganese in the precursor is 1.05:1, weigh out Ni... 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor, lithium hydroxide. Ni 0.8 Co 0.1 Mn 0.1 The specific surface area of ​​the (OH)₂ precursor is 6.22 m². 2 / g, tap density is 2.51 g / cm³3 The median particle size D50 is 15.20 μm, and the purity of lithium hydroxide is 57.45%. The above raw materials are mixed evenly using a high-speed mixer to obtain a mixture. S2. The mixture in S1 is heated to 400℃ in a box furnace at a heating rate of 3℃ / min, held at 400℃ for 2h, then heated to 700℃ at a heating rate of 2℃ / min, held at 700℃ for 12h, with oxygen in the sintering atmosphere and an oxygen flow rate of 1.5L / min, and then cooled to room temperature naturally and pulverized to obtain a ternary cathode material sintered material.

[0031] S3. The pulverized ternary cathode material sintered material is sieved through a 44μm pore size filter screen. 500g of the sintered material is weighed and washed with water at a water-to-material ratio of 2:1, a washing speed of 200rpm, and a stirring time of 5min. The mixture is then filtered using a vacuum filter to separate the solid. The solid is dried in a box furnace at 120℃ for 10h to obtain the ternary cathode material with the chemical formula Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0032] S4. Mix 100g of ternary cathode material with 2.24g of iron pyrophosphate precursor H4Fe 2.5 Cu 0.5 (PO4)4 and 1.38 g of sodium carbonate were placed in a dry mixer and dispersed at high speed to obtain a uniform mixture. The specific surface area of ​​the ferric pyrophosphate precursor was 6 m². 2 / g, the median particle size D50 of the iron pyrophosphate precursor is 7 μm, and the molar ratio of phosphorus in the iron pyrophosphate precursor to sodium in the sodium source is 0.619:1.

[0033] S5. The obtained mixed material is heated to 500℃ at a heating rate of 1℃ / min and held at that temperature for 5h. The sintering atmosphere is oxygen with an oxygen flow rate of 1.5L / min. After natural cooling to room temperature and pulverization, sodium iron pyrophosphate coated ternary cathode material is obtained, wherein the coating amount of sodium iron pyrophosphate is 3wt%, denoted as 3wt% NFPP in-situ-NCM.

[0034] Comparative Example 1: This comparative example provides a method for preparing a ternary cathode material coated with sodium iron pyrophosphate, including the following steps: S1. Based on the molar ratio of lithium: the total molar ratio of nickel, cobalt, and manganese in the precursor is 1.05:1, weigh out Ni... 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor, lithium hydroxide. Ni 0.8 Co0.1 Mn 0.1 The specific surface area of ​​the (OH)₂ precursor is 6.22 m². 2 / g, tap density is 2.51 g / cm³ 3 The median particle size D50 is 15.20 μm, and the purity of lithium hydroxide is 57.45%. The above raw materials are mixed evenly using a high-speed mixer to obtain a mixture. S2. The mixture in S1 is heated to 400℃ in a box furnace at a heating rate of 3℃ / min, held at 400℃ for 2h, then heated to 700℃ at a heating rate of 2℃ / min, held at 700℃ for 12h, with oxygen in the sintering atmosphere and an oxygen flow rate of 1.5L / min, and then cooled to room temperature naturally and pulverized to obtain a ternary cathode material sintered material.

[0035] S3. The pulverized ternary cathode material was sieved through a 44μm pore size filter. 500g of the sieved material was weighed and washed with water at a water-to-material ratio of 2:1, a washing speed of 200 rpm, and a stirring time of 5 min. The mixture was then filtered using a vacuum filter and dried in a box furnace at 120℃ for 10 h to obtain the ternary cathode material with the chemical formula Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0036] S4. Take 1.12 g of H4Fe 2.5 Cu 0.5 (PO4)4 and 0.69 g of sodium carbonate were placed in a dry mixer and dispersed at high speed to obtain a uniform mixture.

[0037] S5. The mixed material obtained in S4 is heated to 600℃ at a heating rate of 1℃ / min and held at that temperature for 15h. The sintering atmosphere is oxygen with an oxygen flow rate of 1.5L / min. After natural cooling to room temperature, it is pulverized to obtain sodium iron pyrophosphate.

[0038] S6. Take 1g of sodium pyrophosphate from S4 and 100g of the water-washed cathode material from S3 (coating amount of 1%), and mix them using a dry mixer to obtain a second mixed material. The obtained second mixed material is heated to 500℃ at a heating rate of 1℃ / min and held at that temperature for 5h. The sintering atmosphere is oxygen with an oxygen flow rate of 1.5L / min. After natural cooling to room temperature and pulverization, the sodium pyrophosphate-coated ternary cathode material is obtained, denoted as NFPP non-in-situ-NCM.

[0039] Comparative Example 2: This comparative example provides a method for preparing a ternary cathode material, including the following steps: S1. Based on the molar amount of lithium: the total molar amount of nickel, cobalt, and manganese in the precursor is 1.05. Weigh out Ni... 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor, lithium hydroxide. Ni 0.8 Co 0.1 Mn 0.1 The specific surface area of ​​the (OH)₂ precursor is 6.22 m². 2 / g, tap density is 2.51 g / cm³ 3 The median particle size D50 is 15.20 μm, and the purity of lithium hydroxide is 57.45%. The above raw materials are mixed evenly using a high-speed mixer to obtain a mixture. S2. The mixture in S1 is heated to 400℃ in a box furnace at a heating rate of 3℃ / min, held at 400℃ for 2h, then heated to 700℃ at a heating rate of 2℃ / min, held at 700℃ for 12h, with oxygen in the sintering atmosphere and an oxygen flow rate of 1.5L / min, and then cooled to room temperature naturally and pulverized to obtain a ternary cathode material sintered material.

[0040] S3. The pulverized ternary cathode material is sieved through a 44μm pore size filter screen. 500g of the pulverized ternary cathode material is weighed and washed with water at a water-to-material ratio of 2:1, a stirring time of 5 min, and a washing speed of 200 rpm. The mixture is then filtered using a vacuum filter and dried in a box furnace at 120℃ for 10 h to obtain the ternary cathode material with the chemical formula Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0041] S4. Take 100g of ternary cathode material, heat it to 500℃ at a heating rate of 1℃ / min and hold it at that temperature for 5h. The sintering atmosphere is oxygen with an oxygen flow rate of 1.5L / min. After naturally cooling to room temperature and pulverizing, the ternary cathode material is obtained and is denoted as -uncoated-NCM.

[0042] Test Example 1 Electrical performance testing: The ternary cathode materials prepared in Examples 1-3 and Comparative Examples 1-2, polyvinylidene fluoride (PVDF), and conductive agent (Super P) were homogenized at a mass ratio of 90 (cathode material): 3 (PVDF): 7 (Super P). Aluminum foil was then laid flat on a coating machine for coating (area density 9.6-9.8 mg / cm³). 2The cells were dried in an 80℃ forced-air drying oven for 3 hours. Then, they were drilled, weighed, and the electrodes were baked to form button cells. Finally, the cells were placed in the Blue Electric Testing System for electrical performance testing. The electrical performance testing parameters were set as follows: voltage range 2.5V-4.25V, 50 cycles of 0.2C / 0.2C→1C / 1C. The test results are shown in Table 1.

[0043] Table 1. Cyclic and capacity data for Examples 1-3 and Comparative Examples 1-2

[0044] Table 1 clearly shows that the capacity decreased after cycling. Comparing Comparative Examples 1 and 2, the cycle retention rate of the ternary cathode materials in Examples 1-3 was higher than that in Comparative Examples 1-2, indicating that the cycle performance of the sodium iron pyrophosphate coated ternary cathode materials provided in Examples 1-3 of this invention is significantly improved. This may be attributed to the fact that during the in-situ coating process of sodium iron pyrophosphate, some of the iron pyrophosphate reacts with the residual alkali on the surface to form lithium iron pyrophosphate, which improves the electronic conductivity of the material. Simultaneously, the sodium iron pyrophosphate generated on the surface acts as a protective layer, effectively isolating the material from side reactions with the electrolyte. Partial Na doping on the surface enters the material lattice, acting as a pillar and improving the structural stability of the material. The synergistic effect of the one-step in-situ surface coating of lithium iron pyrophosphate and Na bulk doping stabilizes the material interface, which is beneficial to improving cycle performance. Considering both capacity and cycle performance, the optimal coating amount is 1 wt%.

[0045] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a ternary cathode material coated with sodium iron pyrophosphate, characterized in that, Includes the following steps: S1. Obtain ternary cathode material; S2. The ternary cathode material, iron pyrophosphate precursor and sodium source are mixed to obtain a mixed material, and the mixed material is sintered to obtain sodium iron pyrophosphate coated ternary cathode material.

2. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 1, characterized in that, S2 satisfies at least one of the following conditions: (1) The molar ratio of phosphorus in the iron pyrophosphate precursor to sodium in the sodium source is (0.6-1.1):1; (2) The mass ratio of the ternary cathode material to the iron pyrophosphate precursor is (20-200):1; (3) The sintering atmosphere is air or oxygen; (4) The sintering temperature is 500-700℃ and the sintering time is 6-15h; (5) The heating rate of the sintering is 1-5℃ / min; (6) The sintering atmosphere flow rate is 1-2 L / min; (7) The amount of sodium pyrophosphate coating in the sodium pyrophosphate coated ternary cathode material is 1-3 wt%.

3. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The chemical formula of the iron pyrophosphate precursor is H y Fe 3-x M x (PO4)4, wherein M includes one or more of Ni, Mg, Ca, Ti, Zr, and Cu, and 0 <x≤1.2,0<y≤4; Preferably, the chemical formula of the iron pyrophosphate precursor is H4Fe. 2.5 Cu 0.5 (PO4)4; (2) The sodium source includes one or more of sodium carbonate, sodium hydroxide, and sodium bicarbonate; (3) The specific surface area of ​​the iron pyrophosphate precursor is 1-10 m². 2 / g; (4) The median particle size D50 of the iron pyrophosphate precursor is 5~10 μm; (5) The chemical formula of the ternary cathode material is Li 1+c Ni a Co b Mn 1-a-b O2, where 0.8≤a≤1, 0 <b≤0.1,0<c≤0.5; Preferably, the chemical formula of the ternary cathode material is Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2; Preferably, the value of c in the chemical formula of the ternary cathode material is in the range of 0. <c≤0.05。 4. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 1, characterized in that, S1 includes the following steps: S1-1. Mix the nickel-cobalt-manganese hydroxide precursor with a lithium source to obtain a mixture; S1-2. Sinter the mixture in S1-1, cool it, and then crush it to obtain a ternary cathode material sintered material; S1-3. Wash the ternary cathode material, then separate the solid and liquid components and dry it to obtain the ternary cathode material.

5. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 4, characterized in that, The chemical formula of the nickel-cobalt-manganese hydroxide precursor in S1-1 is Ni x Co y Mn 1-x-y (OH)₂, 0.8≤x≤1, 0 <y≤0.1; Preferably, the chemical formula of the nickel-cobalt-manganese hydroxide precursor in S1-1 is Ni 0.8 Co 0.1 Mn 0.1 (OH)2; Optionally, the specific surface area of ​​the nickel-cobalt-manganese hydroxide precursor ranges from 5 to 20 m². 2 / g, tap density ranges from 1.0 to 4.0 g / cm³. 3 ; And / or, the median particle size D50 of the nickel-cobalt-manganese hydroxide precursor is in the range of 12-18 μm.

6. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 4 or 5, characterized in that, The molar ratio of lithium in the lithium source in S1-1 to the sum of nickel, cobalt, and manganese in the nickel-cobalt-manganese hydroxide precursor is (0.8-1.1):

1. And / or, the lithium source includes one or more of lithium carbonate and lithium hydroxide.

7. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 4, characterized in that, The sintering atmosphere in S1-2 is air or oxygen; And / or, the sintering heating rate in S1-2 is 2-8℃ / min, the sintering temperature is 400-700℃, and the sintering time is 14-19h; Optionally, the sintering step in S1-2 includes heating the mixture in S1-1 to 300-500℃ at a heating rate of 2-4℃ / min and holding it at that temperature for 1-3h, and then heating it to 500-700℃ at a heating rate of 1-3℃ / min and holding it at that temperature for 10-12h. Preferably, the sintering step in S1-2 includes heating the mixture in S1-1 to 400°C at a heating rate of 3°C / min and holding it at that temperature for 2 hours, and then heating it to 700°C at a heating rate of 2°C / min and holding it at that temperature for 12 hours.

8. The method for preparing sodium iron pyrophosphate-coated ternary cathode material according to claim 4, characterized in that, The washing speed in S1-3 is 200-400 rpm; And / or, the solid-liquid separation method includes vacuum filtration or pressure filtration; And / or, the drying temperature is 80-190℃, and the drying time is 2-12 h.

9. A ternary cathode material coated with sodium iron pyrophosphate, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that, It includes the sodium iron pyrophosphate-coated ternary cathode material as described in claim 9.

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