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CN-122000334-A - Modified positive electrode material, preparation method thereof, positive electrode and lithium ion battery

CN122000334ACN 122000334 ACN122000334 ACN 122000334ACN-122000334-A

Abstract

The application provides a modified anode material, a preparation method thereof, an anode and a lithium ion battery. The modified anode material comprises an inner core and a porous carbon coating layer arranged on the surface of the inner core, wherein the inner core is provided with a general formula LiMn x Fe 1‑x‑y Co y PO 4 , x is more than or equal to 0.3 and less than or equal to 0.8,0.01 and y is more than or equal to 0.03, and the material of the porous carbon coating layer comprises porous carbon doped with nitrogen element and reduced graphene oxide. The porous carbon and the reduced graphene oxide are combined, so that the three-dimensional conductive framework and the two-dimensional conductive sheet layer are linked to form a three-dimensional conductive network, the conductivity of the modified cathode material is remarkably improved, the volume expansion of the modified cathode material in the charge-discharge cycle process is relieved, the doping of Co ions can shorten M-P bonds (M=Mn and/or Fe, and P is phosphorus in phosphate groups), the unit cell volume is reduced, the lithium ion transmission path is widened, and the rate performance and the cycle performance of the lithium ion battery are improved.

Inventors

  • HUANG ZIXUAN
  • YANG HANG
  • ZHANG YA
  • CHEN YIHONG
  • CHENG JIAN
  • HU CHENG
  • ZHANG ERDONG
  • HUANG XING
  • LIN JIANQUAN
  • LIN MENGYAN
  • Wang Zhuangzhou
  • HE JIAYI
  • LI HAOYUE

Assignees

  • 上海轩邑新能源发展有限公司

Dates

Publication Date
20260508
Application Date
20260228

Claims (10)

  1. 1. The modified positive electrode material is characterized by comprising a core and a porous carbon coating layer arranged on the surface of the core, wherein the core is of a general formula LiMn x Fe 1-x-y Co y PO 4 , x is more than or equal to 0.3 and less than or equal to 0.8,0.01 and y is more than or equal to 0.03, and the porous carbon coating layer comprises porous carbon doped with nitrogen element and reduced graphene oxide.
  2. 2. The modified cathode material according to claim 1, wherein the modified cathode material has a specific surface area of 16.5-24 m 2 /g, preferably 20-23 m 2 /g, and a compaction density of 2.15-2.35 g/cm 3 ; preferably, the carbon content in the porous carbon coating layer is 1.2-2.5wt% based on the weight percentage of the modified cathode material.
  3. 3. The modified cathode material according to claim 1 or 2, wherein the weight ratio of the porous carbon to the reduced graphene oxide is (1-5): 5-9, preferably (1-3): 7-9; preferably, the content of oxygen-containing functional groups in the reduced graphene oxide is less than or equal to 30wt% based on the weight percentage of the reduced graphene oxide.
  4. 4. A method of preparing the modified cathode material of any one of claims 1 to 3, comprising: Step S1, mixing a manganese source, an iron source, a phosphorus source, a cobalt source and 2-methylimidazole with a solvent, and sequentially carrying out solvothermal reaction and first drying to obtain a composite precursor containing a metal organic framework material; Step S2, mixing a lithium source, the composite precursor and graphene oxide suspension, and sequentially grinding and drying for the second time to obtain a material to be calcined, wherein the graphene oxide suspension is a mixture of graphene oxide and water; And step S3, calcining the material to be calcined in the atmosphere of protective gas, and cooling to obtain the modified anode material.
  5. 5. The method according to claim 4, wherein in the step S1, a molar ratio of manganese element in the manganese source, iron element in the iron source, cobalt element in the cobalt source to phosphorus element in the phosphorus source is (0.3 to 0.8): (0.17 to 0.69): (0.01 to 0.03): 1; preferably, the molar ratio of cobalt element in the cobalt source to the 2-methylimidazole is 1 (2-4); preferably, the manganese source, the iron source, the phosphorus source, the cobalt source, the 2-methylimidazole and the solvent are mixed to obtain a mixed solution, and more preferably, the molar concentration of the 2-methylimidazole in the mixed solution is 0.2-0.4 mol/L; Preferably, the manganese source is selected from one or more of the group consisting of manganese acetate, manganese carbonate and manganese dioxide, and/or the iron source is selected from one or more of the group consisting of iron phosphate, iron acetate tetrahydrate, iron nitrate nonahydrate and ferrous sulfate heptahydrate, and/or the phosphorus source is selected from one or more of the group consisting of phosphoric acid, lithium dihydrogen phosphate and ammonium dihydrogen phosphate, and/or the cobalt source is selected from cobalt nitrate hexahydrate and/or cobalt chloride, and/or the solvent is selected from a mixture of water and an organic solvent, or an organic solvent, wherein the organic solvent is selected from one or more of the group consisting of methanol, ethanol, ethylene glycol and N, N-dimethylformamide; preferably, the temperature of the solvothermal reaction is 150-250 ℃ and the time is 12-72 h; preferably, the temperature of the first drying is 60-90 ℃ and the time is 8-24 hours.
  6. 6. The method for preparing the modified cathode material according to claim 4, wherein in the step S2, the method for preparing the graphene oxide suspension comprises the steps of mixing the graphene oxide with water, and performing ultrasonic treatment to obtain the graphene oxide suspension; preferably, the ultrasonic treatment is carried out for 1-3 hours at a frequency of 30-50 kHz; Preferably, the solid content of the graphene oxide suspension is 0.5-2wt%.
  7. 7. The method for preparing a modified cathode material according to claim 6, wherein in the step S2, a weight ratio of the graphene oxide to the cobalt source in the graphene oxide suspension is 1 (0.1-0.35); Preferably, the molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is 1 (0.9-1.1); Preferably, the lithium source is selected from one or more of the group consisting of lithium carbonate, lithium hydroxide and lithium dihydrogen phosphate; Preferably, stirring is performed during the mixing in the step S2, more preferably, the stirring speed is 200-400 rpm, and the time is 1-3 hours; Preferably, the grinding speed is 1500-2200 rpm, and the time is 0.5-2.5 h; preferably, the temperature of the second drying is 100-110 ℃ and the time is 0.5-1.5 h, and more preferably, the second drying is performed by spray drying.
  8. 8. The method for producing a modified cathode material according to any one of claims 4 to 7, wherein in the step S3, the calcination process includes a temperature raising stage and a temperature maintaining stage; preferably, the temperature rising rate of the temperature rising stage is 2-5 ℃ per minute; Preferably, the temperature of the heat preservation stage is 500-750 ℃ and the time is 6-12 hours; Preferably, the introducing rate of the shielding gas is 0.5-1L/min, and more preferably, the shielding gas is selected from nitrogen and/or inert gas.
  9. 9. A positive electrode comprising a positive electrode current collector and a positive electrode active material layer arranged in a stack, characterized in that the positive electrode active material layer comprises the modified positive electrode material according to any one of claims 1 to 3.
  10. 10. A lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode of claim 9.

Description

Modified positive electrode material, preparation method thereof, positive electrode and lithium ion battery Technical Field The application relates to the technical field of lithium ion batteries, in particular to a modified positive electrode material, a preparation method thereof, a positive electrode and a lithium ion battery. Background Lithium ion batteries have become the core of current new energy technology research due to their environmental protection characteristics, wide range of use, and efficient energy storage capability. Among the numerous positive electrode materials, lithium iron phosphate (LiFePO 4) has become the first choice for commercial applications due to its excellent structural stability, higher energy density, excellent environmental compatibility and safety properties, and longer cycle life. Lithium iron manganese phosphate (LiMnFePO 4), which also has an olivine structure, has a higher discharge voltage plateau (the discharge voltage plateau of lithium iron phosphate is about 3.4V, and lithium iron manganese phosphate is about 4.1V) and a higher theoretical specific capacity (up to 170 mAh/g) than lithium iron phosphate, and thus, lithium iron manganese phosphate materials are also attracting attention of researchers. However, the lithium iron manganese phosphate material has a certain negative influence on the performance of the lithium iron manganese phosphate material due to the inherent defects of the olivine structure, namely low electron conductivity and limited lithium ion diffusion path, and limits the exertion of the performance of the finished product. In the olivine structure, electrons can only be transported in a "point-to-point" fashion, while lithium ions have only one-dimensional curved channels that travel along the (010) direction. Therefore, in practical application, in order to improve the electron conductivity and the lithium ion diffusion kinetics of the lithium iron manganese phosphate material, researchers generally adopt the following strategies that firstly, a material with high conductivity such as a carbon material or a lithium salt is adopted for coating, so as to improve the electron conductivity of the lithium iron manganese phosphate material, secondly, the diffusion of lithium ions is promoted through element doping such as cobalt element, nickel element and the like, and thirdly, the primary particle size and the morphology of the lithium iron manganese phosphate material are adjusted so as to shorten the transmission distance of the lithium ions, so that the transmission efficiency of the lithium ions is improved. The prior document (publication No. CN 115893363A) discloses a composite positive electrode material, a preparation method and application thereof, wherein the preparation method comprises the following steps of (1) mixing a first lithium source, a manganese source, an iron source and a phosphorus source with a solvent to obtain a lithium iron manganese phosphate precursor, carrying out heat treatment on the lithium iron manganese phosphate to obtain a lithium iron manganese phosphate powder, mixing nickel cobalt manganese hydroxide with a second lithium source, carrying out sintering treatment to obtain a lithium nickel cobalt manganese oxide positive electrode material, (2) mixing the lithium iron manganese phosphate powder obtained in the step (1), the lithium nickel cobalt manganese oxide positive electrode material with an MOF material, stirring to obtain a mixed powder, and (3) calcining the mixed powder obtained in the step (2) to obtain the composite positive electrode material coated with LMFP and NCM by the MOF. The prior document (publication No. CN 116344762A) discloses a preparation method of a MOF-derived porous carbon thin layer coated lithium iron manganese phosphate material, which is characterized in that a nitrogen-doped metal organic framework material and a lithium iron manganese phosphate material are respectively prepared, the two materials are subjected to low-temperature ultrasonic mixing in a phosphate buffer solution to obtain homogeneous slurry, and sanding, spray drying and sintering are carried out in an inert atmosphere to obtain the MOF-derived porous carbon thin layer coated carbon-nitrogen co-doped lithium iron manganese phosphate material. The prior document (CN 117038936A) discloses a modified lithium iron manganese phosphate material, a preparation method thereof, a positive electrode and a lithium battery. The preparation method comprises the steps of S1, carrying out hydrothermal reaction on raw materials comprising a ZIF-67 matrix, a lithium source, an iron source, a manganese source, a phosphorus source and an iridium source, and then cooling to obtain a precursor precipitate, and S2, sintering the precursor precipitate in an inert atmosphere to obtain the modified manganese ferric lithium phosphate material. The prior document (CN 118173765A) discloses a composite lithium iron manganese phos