Lithium cobalt phosphate positive electrode material, preparation method and application thereof
By using cobalt iron phosphate as a precursor and a carbon fast ion conductor double-layer coating, the conductivity and lithium-cobalt misalignment problems of lithium cobalt phosphate cathode materials were solved, significantly improving their capacity and cycle performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG BRUNP RECYCLING TECH CO LTD
- Filing Date
- 2024-03-21
- Publication Date
- 2026-07-10
AI Technical Summary
Existing lithium cobalt phosphate cathode materials have poor conductivity, are prone to lithium-cobalt misalignment during charging and discharging, and are easily reacted with electrolytes at high voltages, resulting in low capacity and poor cycle performance, which limits their commercial application.
Using cobalt iron phosphate as a precursor, the solid solution of cobalt and iron stabilizes the crystal lattice, and the double coating of carbon and fast ion conductors improves the electronic conductivity and ionic conductivity of the material, while reducing lithium-cobalt dislocation.
It significantly improves the capacity and cycle performance of lithium cobalt phosphate cathode material, with a 0.1C discharge capacity of 153.7 mAh/g, a 1C discharge capacity of 140.2 mAh/g, and a capacity retention rate of 94% after 200 cycles at 0.1C.
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Figure CN118221092B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery technology and relates to a lithium cobalt phosphate cathode material, its preparation method and application. Background Technology
[0002] In recent years, energy and environmental pollution have become increasingly serious problems. Lithium-ion rechargeable batteries have gained attention due to their advantages such as high specific energy, high operating voltage, low self-discharge rate, and long cycle life. Currently, the main cathode materials for commercial applications of lithium-ion batteries include lithium iron phosphate, lithium cobalt oxide, and ternary layered oxides. Among them, lithium iron phosphate cathode materials have gained wider commercial application due to their high safety performance, good cycle performance, low cost, and environmental friendliness. With the development of the times and technology, people are paying more attention to the energy density and safety of lithium-ion batteries. The theoretical energy density of lithium iron phosphate is relatively low (587Wh / kg), making it difficult to meet the demand for high energy density. However, lithium cobalt phosphate (LiCoPO4), which also has an olivine structure, has a theoretical discharge specific capacity of 167mAh / g and a relatively high operating voltage platform of 4.8V. This material combines high safety with a high theoretical energy density (802Wh / kg), making it a promising high specific energy density lithium-ion battery cathode material.
[0003] However, problems such as poor conductivity of lithium cobalt phosphate, easy lithium-cobalt dislocation during charging and discharging, and easy reaction between the electrolyte and lithium cobalt phosphate under high voltage conditions leading to material decomposition have not been well solved. The poor electrochemical performance of lithium cobalt phosphate prepared by existing technologies, mainly manifested in low capacity (<140mAh / g) and rapid capacity decay during cycling, limits its further commercial application. Therefore, it is crucial to improve the capacity and cycle performance of lithium cobalt phosphate cathode materials through effective synthesis processes. Summary of the Invention
[0004] The purpose of this invention is to provide a lithium cobalt phosphate cathode material, its preparation method, and its application. The preparation method involves first preparing cobalt iron phosphate, using cobalt iron phosphate as a precursor, which reduces lithium-cobalt misalignment during the charge-discharge process of lithium cobalt phosphate, thereby significantly improving the capacity and cycle performance of the lithium cobalt phosphate cathode material.
[0005] To achieve this objective, the present invention adopts the following technical solution:
[0006] In a first aspect, the present invention provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0007] (1) The divalent cobalt source, ferrous source, phosphorus source, complexing agent and solvent are mixed and heated, and then solid-liquid separation is performed to obtain cobalt iron phosphate precursor;
[0008] (2) The lithium source, the supplementary phosphorus source and the iron cobalt phosphate precursor described in step (1) are mixed and sintered once to obtain the lithium cobalt phosphate cathode material.
[0009] This invention synthesizes cobalt iron phosphate by co-precipitation of divalent cobalt and ferrous sources under the action of a complexing agent. Since the radii of ferrous ions and divalent cobalt ions are similar, the cobalt and iron elements in cobalt iron phosphate can be mixed at the atomic level. Cobalt iron phosphate can serve as an ideal precursor for the synthesis of lithium cobalt phosphate. After mixing with a lithium source and supplementary phosphorus source and sintering, lithium cobalt phosphate cathode material can be obtained. In the lithium cobalt phosphate cathode material of this invention, cobalt and iron are dissolved in solid solution, which can stabilize the crystal lattice and reduce lithium-cobalt dislocation during the charge and discharge process, thereby significantly improving the capacity and cycle performance of lithium cobalt phosphate.
[0010] Preferably, in the mixed solution obtained by mixing in step (1), the molar ratio of cobalt, iron and phosphorus is (3-x):x:2, where 0 < x ≤ 1. For example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values. Other unlisted values within the range are also applicable. Preferably, 0.6 ≤ x ≤ 0.8.
[0011] In the preparation of cobalt iron phosphate precursor, the molar ratio of cobalt to iron affects the performance of the cathode material. If the x value is too small, i.e., there is too little iron, the effect of suppressing lithium cobalt dislocation is not good. If the x value is too large, i.e., there is too much iron, the diffraction peak of the synthesized lithium cobalt phosphate will be slightly shifted, and its discharge voltage plateau and capacity will be reduced.
[0012] Preferably, the general chemical formula of the cobalt iron phosphate precursor in step (1) is Co. 3-x Fe x (PO4)2, where 0 < x ≤ 1, for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values. Other unlisted values within the range are also applicable, preferably 0.6 ≤ x ≤ 0.8.
[0013] Preferably, the heating temperature in step (1) is 80℃-120℃, for example, it can be 80℃, 90℃, 100℃, 110℃ or 120℃, and the heating time is 3h-5h, for example, it can be 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0014] Preferably, when the mixed solution obtained in step (1) is heated for reaction, the pH of the reaction system is adjusted to 5-7, for example, it can be 5, 6 or 7, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0015] Preferably, ammonia is used to adjust the pH of the reaction system.
[0016] Preferably, the mixing in step (1) includes mixing a divalent cobalt source, a ferrous source and a solvent to obtain solution A, mixing a phosphorus source, a complexing agent and a solvent to obtain solution B, and then mixing solution A and solution B to obtain a mixed solution.
[0017] Preferably, the concentration of the complexing agent in solution B is 0.1 mol / L to 0.3 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L or 0.3 mol / L, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0018] Preferably, the complexing agent in step (1) includes ethylenediaminetetraacetic acid.
[0019] Preferably, the divalent cobalt source in step (1) includes any one or a combination of at least two of cobalt nitrate, cobalt sulfate, or cobalt chloride, with typical but not limited combinations including a combination of cobalt nitrate and cobalt sulfate.
[0020] Preferably, the divalent iron source in step (1) includes any one or a combination of at least two of ferrous sulfate, ferrous oxalate, ferrous acetate, or ferrous chloride, with a typical but not limited combination including a combination of ferrous sulfate and ferrous oxalate.
[0021] Preferably, the solvent in step (1) includes deionized water.
[0022] Preferably, the lithium source in step (2) includes lithium carbonate and / or lithium hydroxide.
[0023] Preferably, the phosphorus source in step (1) and the supplementary phosphorus source in step (2) each independently include any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate or ammonium monohydrogen phosphate, typically but not limited to a combination of ammonium dihydrogen phosphate and ammonium monohydrogen phosphate.
[0024] Preferably, a carbon source is added during the mixing process in step (2).
[0025] The addition of a carbon source in this invention can achieve a carbon coating layer on the material surface, thereby significantly improving the electronic conductivity of the material, preventing direct contact between lithium cobalt phosphate and the electrolyte, effectively alleviating the decomposition of lithium cobalt phosphate under high voltage conditions, and thus significantly improving the capacity and cycle performance of the material.
[0026] Preferably, the amount of carbon source added is 6wt%-12wt% of the theoretical yield of lithium cobalt phosphate cathode material, for example, it can be 6wt%, 8wt%, 10wt% or 12wt%, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0027] Preferably, the carbon source includes any one or a combination of at least two of glucose, sucrose, polyethylene glycol, citric acid, polyvinyl alcohol, acetylene black, polyacrylic acid, carbon nanotubes, or graphene. Typical but non-limiting combinations include a combination of glucose and sucrose, or a combination of sucrose and polyethylene glycol.
[0028] Preferably, the mixing method in step (2) includes sand milling.
[0029] Preferably, after mixing in step (2), the mixture is first spray-dried and then sintered once.
[0030] Preferably, in step (2), a solvent (deionized water) is added during mixing, and the slurry is wet-milled using a sand mill until the particle size D50 is 0.4μm-0.6μm, for example, 0.4μm, 0.5μm or 0.6μm. Then, it is spray-dried to obtain spherical dry powder, and then sintered once.
[0031] Preferably, the inlet air temperature of the spray dryer is 210℃-240℃, for example, 210℃, 220℃, 230℃ or 240℃, and the outlet air temperature is 105℃-120℃, for example, 105℃, 110℃, 115℃ or 120℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0032] Preferably, the temperature of the first sintering in step (2) is 750℃-850℃, for example, 750℃, 800℃ or 850℃, the sintering time is 8h-14h, for example, 8h, 10h, 12h or 14h, and the heating rate is 1℃ / min-5℃ / min, for example, 1℃ / min, 3℃ / min or 5℃ / min, but not limited to the listed values. Other unlisted values within the range are also applicable.
[0033] Preferably, after the first sintering in step (2), the process further includes mixing the sintered material obtained from the first sintering with a fast ion conductor and then performing a second sintering.
[0034] In addition to carbon coating, this invention also coats a fast-ion conductor. Specifically, it uses a carbon source and a fast-ion conductor to coat lithium cobalt phosphate. The synthesized lithium cobalt phosphate has an inner coating layer formed by the decomposition of the carbon source, and an outer coating layer formed by the fast-ion conductor. Segmented sintering of the coating layer ensures greater uniformity and tighter bonding between the inner and outer layers. The carbon coating significantly improves the electronic conductivity of the material, while the fast-ion conductor coating exhibits excellent electrochemical stability, does not react with the electrolyte under high voltage, and enables rapid lithium-ion insertion / extraction at the solid-liquid interface. Therefore, this double-layer coating significantly improves both the electronic and ionic conductivity of the material while preventing direct contact between lithium cobalt phosphate and the electrolyte, effectively mitigating the decomposition of lithium cobalt phosphate under high voltage conditions, thereby significantly improving the material's capacity and cycle performance.
[0035] Preferably, the amount of fast ion conductor added is 0.1wt%-0.5wt% of the theoretical amount of lithium cobalt phosphate cathode material, for example, it can be 0.2wt%, 0.4wt% or 0.5wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0036] Preferably, the fast ion conductor comprises any one or a combination of at least two of lithium aluminum titanium phosphate, lithium niobate, lithium titanate, lithium borate, aluminum phosphate, or lithium aluminate. Typical but non-limiting combinations include a combination of lithium aluminum titanium phosphate and lithium niobate, or a combination of lithium niobate and lithium titanate.
[0037] Preferably, the mixing time between the sintered material and the fast ion conductor is 2h-4h, for example, it can be 2h, 3h or 4h, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0038] Preferably, the secondary sintering temperature is 650℃-750℃, for example, 650℃, 700℃ or 750℃, the sintering time is 3h-6h, for example, 3h, 4h, 5h or 6h, and the heating rate is 1℃ / min-5℃ / min, for example, 2℃ / min, 4℃ / min or 5℃ / min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0039] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:
[0040] (1) A solution A is obtained by mixing a divalent cobalt source, a ferrous source, and deionized water. A solution B is obtained by mixing a phosphorus source, a complexing agent, and deionized water. Solutions A and B are then mixed to obtain a mixed solution. The pH of the mixed solution is adjusted to 5-7 using ammonia water, and the reaction is carried out at 80℃-120℃ for 3-5 hours. Solid-liquid separation is then performed to obtain the cobalt iron phosphate precursor, whose general chemical formula is Co. 3-x Fe x (PO4)2, where 0 < x ≤ 1;
[0041] In the mixed solution, the molar ratio of cobalt, iron, and phosphorus is (3-x):x:2, where 0 < x ≤ 1; in solution B, the concentration of the complexing agent is 0.1 mol / L - 0.3 mol / L.
[0042] (2) The lithium source, supplementary phosphorus source, carbon source, deionized water and the iron cobalt phosphate precursor mentioned in step (1) are mixed, and then sand milled and spray dried to obtain spherical dry powder. The powder is then heated to 750℃-850℃ at a heating rate of 1℃ / min-5℃ / min for a first sintering of 8h-14h. The sintered material obtained from the first sintering is mixed with a fast ion conductor, and then heated to 650℃-750℃ at a heating rate of 1℃ / min-5℃ / min for a second sintering of 3h-6h to obtain the lithium cobalt phosphate cathode material.
[0043] The amount of carbon source added is 6wt%-12wt% of the theoretical amount of lithium cobalt phosphate cathode material produced, and the amount of fast ion conductor added is 0.1wt%-0.5wt% of the theoretical amount of lithium cobalt phosphate cathode material produced.
[0044] In a second aspect, the present invention provides a lithium cobalt phosphate cathode material, which is prepared by the preparation method described in the first aspect.
[0045] Preferably, the lithium cobalt phosphate cathode material includes LiCo. 1-y Fe y PO4, where 0 < y ≤ 1 / 3, for example, it can be 1 / 10, 1 / 8, 1 / 6, 1 / 4 or 1 / 3, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0046] Preferably, the surface of the lithium cobalt phosphate cathode material is further coated with a carbon coating layer and a fast ion conductor coating layer in sequence.
[0047] The lithium cobalt phosphate cathode material of this invention includes a core and a first coating layer and a second coating layer sequentially coated on the surface of the core. The core is LiCo. 1-y Fe yPO4, where 0 < y ≤ 1 / 3. The first coating layer is a carbon coating layer, and the second coating layer is a fast ion conductor coating layer.
[0048] Thirdly, the present invention provides a lithium-ion battery comprising the lithium cobalt phosphate cathode material as described in the second aspect.
[0049] Compared with the prior art, the present invention has the following beneficial effects:
[0050] This invention first synthesizes cobalt iron phosphate, then uses it as a precursor for synthesizing lithium cobalt phosphate. By utilizing the solid solution stabilization of cobalt and iron, the lithium-cobalt dislocation during charge-discharge processes is reduced, significantly improving the capacity and cycle performance of lithium cobalt phosphate. Simultaneously, this invention coats the surface of the lithium cobalt phosphate cathode material with a carbon coating layer and a fast ion conductor coating layer, enhancing the material's electronic and ionic conductivity and preventing direct contact between the material and the electrolyte. This results in lithium-ion batteries using the lithium cobalt phosphate cathode material achieving a discharge capacity of 153.7 mAh / g at 0.1C, a discharge capacity of 140.2 mAh / g at 1C, and a capacity retention rate of 94% after 200 cycles at 0.1C. Attached Figure Description
[0051] Figure 1 This is a SEM image of the lithium cobalt phosphate cathode material obtained in Example 1 of the present invention;
[0052] Figure 2 The XRD patterns of the lithium cobalt phosphate cathode material obtained in Example 1 of this invention and the standard XRD patterns of LiCoPO4 are shown.
[0053] Figure 3 The XRD patterns of the lithium cobalt phosphate cathode material, LiCoPO4, and LiFePO4 obtained in Example 7 of this invention are shown below.
[0054] Figure 4 This is a graph showing the first charge-discharge curve of a lithium-ion battery made using the lithium cobalt phosphate cathode material obtained in Example 1 of this invention.
[0055] Figure 5 The diagram shows the cycle performance of a lithium-ion battery made using the lithium cobalt phosphate cathode material obtained in Example 1 of this invention. Detailed Implementation
[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0057] Example 1
[0058] This embodiment provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0059] (1) Cobalt sulfate and ferrous sulfate are dissolved in deionized water to obtain solution A. Ammonium dihydrogen phosphate and ethylenediaminetetraacetic acid are dissolved in deionized water to obtain solution B. Then, solution A and solution B are mixed to obtain a mixed solution. The mixed solution is heated to 90°C, and ammonia is added to adjust the pH of the mixed solution to 6. After the reaction is completed for 4 hours, the solid and liquid are separated. The obtained solid is washed and dried to obtain the chemical formula Co. 2.4 Fe 0.6 (PO4)2 is a cobalt iron phosphate precursor;
[0060] In the mixed solution, the molar ratio of cobalt, iron, and phosphorus is 2.4:0.6:2; in solution B, the concentration of ethylenediaminetetraacetic acid is 0.2 mol / L.
[0061] (2) The iron cobalt phosphate precursor mentioned in step (1) is mixed with lithium carbonate and phosphoric acid in the ratio of Li:M:P = 1:1:1 (M = Co, Fe). Then, carbon source and deionized water are added for dispersion. The particle size of the mixed slurry is ground to D50 of 0.5 μm using a sand mill. Then, spray drying is carried out under the conditions of inlet air temperature of 220℃ and outlet air temperature of 110℃.
[0062] The spray-dried powder was placed in a nitrogen tube furnace and heated from room temperature to 800°C at a rate of 3°C / min for a first sintering of 10 hours. After cooling, the sintered material was ball-milled with a fast ion conductor using a planetary ball mill at 400 rpm / min for 3 hours. Then, the temperature was increased to 700°C at a rate of 3°C / min for a second sintering of 4 hours. Finally, the cooled material was pulverized to obtain lithium cobalt phosphate (LiCo) core material. 0.8 Fe 0.2 Lithium cobalt phosphate cathode material, whose coating consists of an inner carbon coating layer generated by the decomposition of carbon source and an outer coating layer generated by fast ion conductor;
[0063] The carbon source is polyethylene glycol, and the amount of carbon source added is 8 wt% of the theoretical amount of lithium cobalt phosphate cathode material. The fast ion conductor is nano-lithium titanium aluminum phosphate, and the amount of fast ion conductor added is 0.3 wt% of the theoretical amount of lithium cobalt phosphate cathode material.
[0064] The SEM image of the lithium cobalt phosphate cathode material obtained in this embodiment is as follows: Figure 1 As shown, it can be clearly seen that the lithium cobalt phosphate grains are basically spherical, with a uniform distribution of particle size, and the carbon coating effect is good; the XRD pattern (curve near the top) of the lithium cobalt phosphate cathode material prepared in this embodiment and the standard XRD pattern of LiCoPO4 are shown below. Figure 2 As shown, from Figure 2 As can be seen, lithium cobalt phosphate has high crystallinity and no impurity peaks, and the solid solution of iron did not damage its crystal structure; the first charge-discharge curve of the lithium-ion battery made from the lithium cobalt phosphate cathode material obtained in this embodiment is shown in the figure. Figure 4 As shown, the 0.1C discharge capacity is 153.7 mAh / g, and the 1C discharge capacity is 140.2 mAh / g; the cycle performance of the lithium-ion battery made from the lithium cobalt phosphate cathode material obtained in this embodiment is shown in the figure. Figure 5 As shown, the discharge capacity after 200 cycles at 0.1C is 144.5mAh / g, with a capacity retention rate as high as 94%.
[0065] Example 2
[0066] This embodiment provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0067] (1) Cobalt sulfate and ferrous sulfate are dissolved in deionized water to obtain solution A. Ammonium dihydrogen phosphate and ethylenediaminetetraacetic acid are dissolved in deionized water to obtain solution B. Then, solution A and solution B are mixed to obtain a mixed solution. The mixed solution is heated to 100°C, and ammonia is added to adjust the pH of the mixed solution to 5. After the reaction is completed for 3 hours, the solid and liquid are separated. The obtained solid is washed and dried to obtain the chemical formula Co. 2.4 Fe 0.6 (PO4)2 is a cobalt iron phosphate precursor;
[0068] In the mixed solution, the molar ratio of cobalt, iron, and phosphorus is 2.4:0.6:2, where 0 < x ≤ 1; in solution B, the concentration of ethylenediaminetetraacetic acid is 0.15 mol / L.
[0069] (2) The iron cobalt phosphate precursor mentioned in step (1) is mixed with lithium hydroxide and phosphoric acid in the ratio of Li:M:P = 1:1:1 (M = Co, Fe). Then, carbon source and deionized water are added for dispersion. The particle size of the mixed slurry is ground to D50 of 0.4 μm using a sand mill. Then, spray drying is carried out under the conditions of inlet air temperature of 230℃ and outlet air temperature of 115℃.
[0070] The spray-dried powder was placed in a nitrogen tube atmosphere furnace and heated from room temperature to 750°C at a rate of 3°C / min for a first sintering of 12 hours. After cooling, the sintered material was ball-milled with a fast ion conductor using a planetary ball mill at 400 rpm / min for 4 hours. Then, the temperature was increased to 700°C at a rate of 4°C / min for a second sintering of 3 hours. Finally, the cooled material was pulverized to obtain lithium cobalt phosphate (LiCo) core material. 0.8 Fe 0.2Lithium cobalt phosphate cathode material, whose coating consists of an inner carbon layer generated by the decomposition of carbon source and an outer coating layer generated by fast ion conductor;
[0071] The carbon source is citric acid, and the amount of carbon source added is 10 wt% of the theoretical amount of lithium cobalt phosphate cathode material. The fast ion conductor is nano-lithium titanium aluminum phosphate, and the amount of fast ion conductor added is 0.4 wt% of the theoretical amount of lithium cobalt phosphate cathode material.
[0072] Example 3
[0073] This embodiment provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0074] (1) Cobalt sulfate and ferrous sulfate are dissolved in deionized water to obtain solution A. Ammonium dihydrogen phosphate and ethylenediaminetetraacetic acid are dissolved in deionized water to obtain solution B. Then, solution A and solution B are mixed to obtain a mixed solution. The mixed solution is heated to 120°C, and ammonia is added to adjust the pH of the mixed solution to 7. After the reaction is completed for 5 hours, the solid and liquid are separated. The obtained solid is washed and dried to obtain the chemical formula Co. 2.4 Fe 0.6 (PO4)2 is a cobalt iron phosphate precursor;
[0075] In the mixed solution, the molar ratio of cobalt, iron, and phosphorus is 2.4:0.6:2; in solution B, the concentration of ethylenediaminetetraacetic acid is 0.2 mol / L.
[0076] (2) The iron cobalt phosphate precursor mentioned in step (1) is mixed with lithium carbonate and ammonium monohydrogen phosphate in the ratio of Li:M:P = 1:1:1 (M = Co, Fe). Then, carbon source and deionized water are added for dispersion. The particle size of the mixed slurry is ground to D50 of 0.6 μm using a sand mill. Then, spray drying is carried out under the conditions of inlet air temperature of 240℃ and outlet air temperature of 110℃.
[0077] The spray-dried powder was placed in a nitrogen tube furnace and heated from room temperature to 850°C at a rate of 3°C / min for a first sintering of 10 hours. After cooling, the sintered material was ball-milled with a fast ion conductor using a planetary ball mill at 400 rpm / min for 2 hours. Then, it was sintered again at a rate of 4°C / min to 750°C for a second sintering of 5 hours. Finally, the cooled material was pulverized to obtain lithium cobalt phosphate (LiCo) core material. 0.8 Fe 0.2 Lithium cobalt phosphate cathode material, whose coating consists of an inner carbon layer generated by the decomposition of carbon source and an outer coating layer generated by fast ion conductor;
[0078] The carbon source is polyvinyl alcohol, and the amount of carbon source added is 12 wt% of the theoretical amount of lithium cobalt phosphate cathode material. The fast ion conductor is nano-lithium niobate, and the amount of fast ion conductor added is 0.5 wt% of the theoretical amount of lithium cobalt phosphate cathode material.
[0079] Example 4
[0080] This embodiment provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0081] (1) Cobalt nitrate and ferrous sulfate were dissolved in deionized water to obtain solution A. Ammonium dihydrogen phosphate and ethylenediaminetetraacetic acid were dissolved in deionized water to obtain solution B. Solution A and solution B were then mixed to obtain a mixed solution. The mixed solution was heated to 110°C, and ammonia was added to adjust the pH of the mixed solution to 6. After the reaction was completed for 4 hours, the solid and liquid were separated. The obtained solid was washed and dried to obtain the chemical formula Co. 2.4 Fe 0.6 (PO4)2 is a cobalt iron phosphate precursor;
[0082] In the mixed solution, the molar ratio of cobalt, iron, and phosphorus is 2.4:0.6:2; in solution B, the concentration of ethylenediaminetetraacetic acid is 0.3 mol / L.
[0083] (2) The iron cobalt phosphate precursor mentioned in step (1) is mixed with lithium hydroxide and phosphoric acid in the ratio of Li:M:P = 1:1:1 (M = Co, Fe). Then, carbon source and deionized water are added for dispersion. The particle size of the mixed slurry is ground to D50 of 0.5 μm using a sand mill. Then, spray drying is carried out under the conditions of inlet air temperature of 225℃ and outlet air temperature of 110℃.
[0084] The spray-dried powder was placed in a nitrogen tube furnace and heated from room temperature to 800℃ at a rate of 5℃ / min for a first sintering of 10 hours. After cooling, the sintered material was ball-milled with a fast ion conductor using a planetary ball mill at 400 rpm / min for 4 hours. Then, the temperature was increased to 730℃ at a rate of 4℃ / min for a second sintering of 6 hours. Finally, the cooled material was pulverized to obtain lithium cobalt phosphate (LiCo) core material. 0.8 Fe 0.2 Lithium cobalt phosphate cathode material, whose coating consists of an inner carbon layer generated by the decomposition of carbon source and an outer coating layer generated by fast ion conductor;
[0085] The carbon source is polyvinyl alcohol, and the amount of carbon source added is 10 wt% of the theoretical amount of lithium cobalt phosphate cathode material. The fast ion conductor is nano-aluminum phosphate, and the amount of fast ion conductor added is 0.35 wt% of the theoretical amount of lithium cobalt phosphate cathode material.
[0086] Example 5
[0087] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. Except for the molar ratio of cobalt, iron and phosphorus in the mixed solution in step (1) being 2.2:0.8:2, the preparation method is the same as in Example 1.
[0088] Example 6
[0089] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. Except for the molar ratio of cobalt, iron and phosphorus in the mixed solution in step (1) being 2.6:0.4:2, the preparation method is the same as in Example 1.
[0090] Example 7
[0091] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. Except for the molar ratio of cobalt, iron and phosphorus in the mixed solution in step (1) being 2:1:2, the preparation method is the same as in Example 1.
[0092] The XRD patterns (curve near the top) of the lithium cobalt phosphate cathode material obtained in this embodiment, as well as the standard XRD patterns of LiCoPO4 and LiFePO4, are shown below. Figure 3 As shown, from Figure 3 It can be seen from this that when there is a large amount of iron in the solid solution, the resulting LiCo... 2 / 3 Fe 1 / 3 The diffraction peaks of the PO4 composite cathode material are located between those of the standard LiCoPO4 and LiFePO4.
[0093] Example 8
[0094] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. Except for step (2), which does not involve adding a carbon source, the preparation method is the same as in Example 1.
[0095] Example 9
[0096] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. Except for step (2), in which fast ion conductors are not added and secondary sintering is not performed, the preparation method is the same as in embodiment 1.
[0097] Example 10
[0098] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. Except for step (2), in which the fast ion conductor and carbon source are added together for a first sintering and no second sintering is performed, the preparation method is the same as in embodiment 1.
[0099] Example 11
[0100] This embodiment provides a method for preparing lithium cobalt phosphate cathode material. The preparation method is the same as in Example 1 except that the order of adding carbon source and fast ion conductor is changed in step (2), fast ion conductor is coated during the first sintering and carbon is coated during the second sintering.
[0101] Comparative Example 1
[0102] This comparative example provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0103] Cobalt phosphate, lithium carbonate, and phosphoric acid were mixed in a ratio of Li:Co:P = 1:1:1. Then, polyethylene glycol (8 wt% of the theoretical mass of lithium cobalt phosphate) was added. The mixture was then dispersed with deionized water. The slurry was ground to a particle size of 0.5 μm using a sand mill and then dried to obtain spherical dry powder using a centrifugal spray dryer (inlet air temperature 220℃, outlet air temperature 110℃). The spherical dry powder was placed in a nitrogen tube furnace and heated from room temperature to 800℃ at a heating rate of 3℃ / min, and held for 10 hours. The cooled material was then pulverized to obtain the LiCoPO4 / C composite material.
[0104] Comparative Example 2
[0105] This comparative example provides a method for preparing a lithium cobalt phosphate cathode material, the method comprising the following steps:
[0106] (1) Cobalt phosphate, lithium carbonate and phosphoric acid are mixed in the ratio of Li:Co:P = 1:1:1, and then polyethylene glycol of 8 wt% of the theoretical mass of lithium cobalt phosphate is added. The mixed raw materials are then dispersed with deionized water, and the particle size of the mixed slurry is ground to D50 of 0.5 μm using a sand mill. The spherical dry powder is obtained by centrifugal spray drying equipment (inlet air temperature 220℃, outlet air temperature 110℃).
[0107] (2) Place the spherical dry powder into a nitrogen tube furnace and heat it from room temperature to 800℃ at a heating rate of 3℃ / min and hold it for 10h. After cooling, add nano-lithium titanium aluminum phosphate with a theoretical mass of 0.3wt% of lithium cobalt phosphate. Then, use a planetary ball mill at a speed of 400rpm / min to ball mill for 3h to mix evenly. Then, heat it to 700℃ at a heating rate of 3℃ / min for secondary sintering and hold it for 4h. Finally, crush the cooled material to obtain a lithium cobalt phosphate cathode material with a core of lithium cobalt phosphate (LiCoPO4) and a coating layer consisting of an inner coating carbon layer generated by the decomposition of carbon source and an outer coating layer generated by fast ion conductor.
[0108] The prepared lithium cobalt phosphate cathode material, prepared in the above examples and comparative examples, was dispersed in NMP with acetylene black and polyvinylidene fluoride at a mass ratio of 8:1:1. The mixture was then stirred into a slurry, coated onto aluminum foil, and dried and pressed to form a cathode sheet. Using lithium metal as the counter electrode, 1 mol / L LiPF6 / (EC+DMC+EMC) as the electrolyte, and Cellgard 2035 as the separator, a button cell was assembled in a glove box. The cell model was CR2016. The assembled cell was electrochemically tested using a Land battery tester, and the tested charge / discharge voltage ranged from 2.0 to 4.95 V.
[0109] The test results are shown in Table 1:
[0110] Table 1
[0111]
[0112]
[0113] As can be seen from Table 1:
[0114] This invention uses cobalt iron phosphate as a precursor. The molar ratio of cobalt to iron in the precursor, carbon coating, and double coating with a fast ion nanoparticle conductor all affect the product performance. Specifically, a carbon coating layer is first formed through a single sintering process, followed by a second sintering process to form a fast ion nanoparticle coating layer. The test results show that, even though Comparative Example 1 uses cobalt phosphate as a precursor and Comparative Example 2 is coated with carbon and fast ion conductor, the resulting lithium cobalt phosphate cathode materials still suffer from lithium-cobalt misalignment. The performance of Comparative Example 1 and Comparative Example 2 is poor. Therefore, the lithium cobalt phosphate cathode material prepared by the method described in this invention can significantly improve the battery discharge capacity, and the capacity retention rate of the examples is maintained at a very high level.
[0115] In summary, this invention provides a lithium cobalt phosphate cathode material, its preparation method, and its application. The preparation method involves first preparing cobalt iron phosphate, and then using cobalt iron phosphate as a precursor to prepare the lithium cobalt phosphate cathode material. This method can reduce lithium-cobalt misalignment during the charging and discharging process of lithium cobalt phosphate, thereby significantly improving the capacity and cycle performance of the lithium cobalt phosphate cathode material.
[0116] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A method for preparing a lithium cobalt phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) A solution A is obtained by mixing a divalent cobalt source, a ferrous source, and deionized water. A solution B is obtained by mixing a phosphorus source, a complexing agent, and deionized water. Then, solutions A and B are mixed to obtain a mixed solution. The pH of the mixed solution is adjusted to 5-7 using ammonia water, and the reaction is carried out at 80℃-120℃ for 3-5 hours. Then, solid-liquid separation is performed to obtain the cobalt iron phosphate precursor. The chemical formula of the cobalt iron phosphate precursor is Co. 3-x Fe x (PO4)2, where 0.4 ≤ x ≤ 0.8; In the mixed solution, the molar ratio of cobalt, iron, and phosphorus is (3-x):x:2, where 0.4 ≤ x ≤ 0.8; in solution B, the concentration of the complexing agent is 0.1 mol / L - 0.3 mol / L. (2) The lithium source, supplementary phosphorus source, carbon source, deionized water and the iron cobalt phosphate precursor mentioned in step (1) are mixed, and then sand milled and spray dried to obtain spherical dry powder. The powder is then heated to 750℃-850℃ at a heating rate of 1℃ / min-5℃ / min for a first sintering of 8h-14h. The sintered material obtained from the first sintering is mixed with a fast ion conductor, and then heated to 650℃-750℃ at a heating rate of 1℃ / min-5℃ / min for a second sintering of 3h-6h to obtain the lithium cobalt phosphate cathode material. The amount of carbon source added is 6wt%-12wt% of the theoretical amount of lithium cobalt phosphate cathode material generated, and the amount of fast ion conductor added is 0.1wt%-0.5wt% of the theoretical amount of lithium cobalt phosphate cathode material generated.