CN-121974320-A - Preparation method of lithium iron phosphate anode material

CN121974320ACN 121974320 ACN121974320 ACN 121974320ACN-121974320-A

Abstract

The invention discloses a preparation method of a lithium iron phosphate positive electrode material, which comprises the steps of carrying out secondary sintering on the lithium iron phosphate positive electrode material, introducing a reducing organic acid in the sintering process, firstly creating a uniform and mild reducing atmosphere in a system by virtue of the low-temperature decomposition characteristic and strong reducing property of the reducing organic acid, accurately stabilizing iron in a divalent state, oxidizing and eliminating iron phosphide generated by primary sintering, effectively preventing the generation of elementary iron and phosphorus elementary substances so as to thoroughly cut off the formation path of the iron phosphide, greatly reducing the content of iron phosphide foreign matters in a finished product, supplementing a certain carbon source, purifying and coating the lithium iron phosphate positive electrode material, and cooperatively realizing uniform and compact carbon coating, thereby overcoming the industrial problems that the reduction uniformity and the coating performance are difficult to be considered by a single carbon source, enabling the sintering process to be more stable and controllable, and finally obtaining the lithium iron phosphate material with extremely high phase purity and extremely low magnetic foreign matter content, and having excellent electrochemical performance and safety.

Inventors

Wang Diaohan
SHI YINGFEI
ZHANG MENGNAN
ZHANG JIANHUA
CHEN MAOMAO
ZHU HONGWEI
SHI JUNFENG

Assignees

南京锂源纳米科技有限公司
常州锂源新能源科技有限公司

Dates

Publication Date: 20260505
Application Date: 20260109

Claims (10)

1. The preparation method of the lithium iron phosphate anode material comprises the following steps: (S1) adding a lithium source, an iron source, a phosphorus source and a carbon source into a solvent, and mixing to obtain lithium iron phosphate precursor slurry; (S2) grinding and drying the obtained lithium iron phosphate precursor slurry to obtain lithium iron phosphate precursor powder; (S3) calcining in an inert atmosphere to obtain a primary sintered lithium iron phosphate anode material; The method is characterized by further comprising the following steps: (S4) mixing the reducing organic acid with the primary sintered lithium iron phosphate anode material obtained in the step (S3), and then carrying out secondary calcination in an inert atmosphere to obtain the lithium iron phosphate anode material.
2. The preparation method of the lithium iron phosphate positive electrode material according to claim 1, wherein the step (S4) is characterized in that after the materials are mixed, the temperature is raised to 200-300 ℃, the temperature is kept for 1-2 hours, the temperature is raised to 700-760 ℃ and the calcination is carried out for 4-6 hours, the inert atmosphere is nitrogen, argon or argon-hydrogen mixed gas, and the flow rate of inert shielding gas is 5-10L/min.
3. The method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein the reducing organic acid in the step (S4) is one or more selected from ascorbic acid, citric acid and formic acid.
4. The method for preparing a lithium iron phosphate positive electrode material according to claim 3, wherein the amount of the reducing organic acid used in the step (S4) is 0.8 to 1.2wt% of the lithium iron phosphate positive electrode material prepared in the step (S3).
5. The method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein an organic carbon source is further added in the step (S4), and the organic carbon source is one or more of glucose and sucrose.
6. The method for preparing a lithium iron phosphate positive electrode material according to claim 5, wherein the amount of the organic carbon source used in the step (S4) is 1 to 1.2wt% of the lithium iron phosphate positive electrode material prepared in the step (S3).
7. The method for preparing the lithium iron phosphate positive electrode material according to claim 1, wherein the calcining temperature in the step (S3) is 620-680 ℃, the calcining time is 6-9h, the inert atmosphere is nitrogen, argon or argon-hydrogen mixed gas, and the flow rate of the inert shielding gas is 5-10L/min.
8. The method for preparing the lithium iron phosphate positive electrode material according to claim 1, wherein the lithium source in the step (S1) is at least one of lithium carbonate, lithium oxalate and lithium hydroxide, the iron source and the phosphorus source are ferric phosphate or a ferric phosphate precursor generated by the reaction of a phosphorus-containing compound and an iron-containing compound, the phosphorus-containing compound is at least one of ammonium dihydrogen phosphate, phosphoric acid and ammonium phosphate, the iron-containing compound is at least one of ferrous oxalate, ferrous sulfate and ferrous oxide, and the molar ratio Fe of Fe to P=1 is 0.95-1.05 in the ferric phosphate precursor.
9. The method for producing a lithium iron phosphate positive electrode material according to claim 1, wherein the carbon source in step (S1) is one or more selected from glucose, sucrose, citric acid, ascorbic acid and polyethylene glycol.
10. The method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein in the step (S2), the grinding particle size D50 of the lithium iron phosphate precursor slurry is 0.35 to 0.45 μm.

Description

Preparation method of lithium iron phosphate anode material Technical Field The invention relates to the technical field of lithium ion battery positive electrode materials, in particular to a preparation method of a lithium iron phosphate positive electrode material capable of remarkably improving the safety performance and electrochemical performance of the material by inhibiting the generation of ferric phosphide. Background Lithium iron phosphate (LiFePO 4) has become a key material in the fields of power batteries and energy storage systems by virtue of its excellent safety properties and cycle stability. However, the industrial preparation process has long faced a serious technical challenge that iron phosphide (Fe 2 P) impurities are easily generated in the high-temperature sintering stage. The existence of iron phosphide impurity seriously jeopardizes the battery constitution in various aspects, namely 1, the capacity and efficiency loss is that Fe 2 P does not have electrochemical activity, the generation of the Fe 2 P irreversibly consumes active iron and phosphorus elements in the system, the gram capacity of the material and the energy density of the battery are reduced, 2, the magnetic foreign matter is introduced, namely, the Fe 2 P is used as a ferromagnetic substance, and the magnetic foreign matter content of the material is obviously improved. The Fe 2 P has good electronic conductivity and catalytic activity, can continuously catalyze the oxidative decomposition of electrolyte in the battery cycle, and leads to unstable gas production and CEI film, and becomes a local current priority channel and catalytic hot spot under the abuse conditions of overcharging and the like, so as to induce severe concentrated heat release, obviously reduce the trigger temperature of thermal runaway and seriously threaten the safety of the battery. The existence of the impurity phase obviously restricts the electrochemical performance and the safety performance of the material, and becomes one of the main bottlenecks restricting the development of the high-end lithium iron phosphate material. The formation of Fe 2 P essentially results from the "local stoichiometric imbalance" and "local over-reduction" during the high temperature solid phase reaction. In the currently prevailing carbothermal reduction process, the organic carbon source used (e.g. glucose, sucrose, etc.) generates a strong reducing atmosphere at high temperature cracking, aiming at reducing Fe 3+ in the feedstock to Fe 2+ required for synthesis. However, due to uneven mixing of the carbon source and the raw materials or inaccurate control of sintering process parameters, micro-regions with too strong reducibility are extremely easily formed locally. The type of carbon source and its heating behavior are important factors that affect the uniformity of mixing and ultimately induce the formation of iron phosphide. In carbothermal reduction synthesis of lithium iron phosphate, a small molecular carbon source generates highly disordered amorphous carbon after primary calcination and decomposition, is rich in defects and active sites, and is beneficial to improving ion and electron conductivity. However, the physicochemical properties of the small molecular carbon source itself also tend to cause uneven mixing with other components, and may induce the formation of by-products such as iron phosphide. The small molecular saccharides are solid crystals during initial mixing, and are difficult to realize uniform dispersion of molecular level or nano level with raw material powder, and are mainly physically attached to the surface of particles. During subsequent warm-up (about 150-250 ℃) they melt rapidly and undergo a caramelization reaction, forming a high viscosity liquid intermediate, causing a large number of feedstock particles to become cohesively entrapped, forming an internally carbon-rich, externally carbon-depleted hard agglomerate. More importantly, these carbon sources do not simply evaporate during subsequent pyrolysis, but rather undergo complex pyrolysis and gasification processes, resulting in the dynamic migration and redistribution of strongly reducing gases (e.g., CO) between the pores and particles of the material. This results in a severely non-uniform reducing atmosphere on a microscopic scale, forming localized micro-regions of excess reducibility within the initial carbon-enriched agglomerates or in the "hot spot" regions of gas retention. Within this micro-region, part of the Fe 2+ is further reduced to elemental iron (Fe) while part of the phosphate (PO 43-) may also be reduced to elemental phosphorus (P). The two react to form stable and good-conductivity Fe 2 P, which simplifies the reaction to be 2Fe+P- & gtFe 2 P. The occurrence of the side reaction damages the stoichiometric accuracy of the target product and causes systematic damage to the material performance. The generation of the ferric phosphide is a key tech