Lithium Iron Phosphate Sintering With CO2 to Suppress FexP
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Solution Overview
Problem
Lithium iron phosphate batteries face limitations due to low conductivity and ionic diffusivity, which are exacerbated by the generation of ferromagnetic substances during the carbothermic reduction process, affecting their electrochemical and physicochemical properties.
Innovation Solution
A method involving sintering a dry mixture of iron, lithium, and phosphorus sources with a reducing carbon source in an atmosphere containing carbon dioxide as a mild oxidizing gas at temperatures between 800° C. to 900° C., inhibiting the generation of ferromagnetic substances and enhancing crystallinity and compaction performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the reaction temperature is raised to improve crystallinity and compaction performance, then the electrochemical properties are enhanced, but the generation of ferromagnetic substances (FexP) increases causing short-circuit and self-discharge
Solution Approach 1:
The patent changes the chemical composition parameters of the reaction system by introducing metal oxide (such as CuO, ZnO, NiO, CoO, MnO, or Fe2O3) into the carbothermic reduction process. This parameter change modifies the reaction pathway to suppress the formation of ferromagnetic FexP substances while maintaining the beneficial effects of high-temperature processing on crystallinity and electrochemical performance.
Solution Approach 2:
Metal oxide acts as an intermediary substance in the reaction system. It intervenes in the carbothermic reduction process to prevent the direct formation of ferromagnetic FexP from Fe2+ and carbon source, thereby eliminating the harmful effect while allowing the temperature to be raised for improved crystallinity.
2Reliability
If carbon source is added to improve conductivity through carbon coating, then the electrical conductivity increases by several orders of magnitude, but the compaction performance of positive electrode materials deteriorates
Solution Approach 1:
The patent modifies the carbon coating parameters by controlling the carbon source content and introducing metal oxide, which changes the coating mechanism from thick carbon deposition to controlled surface modification. This results in improved conductivity without excessive carbon accumulation that would harm compaction performance.
Solution Approach 2:
Metal oxide serves as an intermediary that mediates between the carbon source and the lithium iron phosphate surface. It prevents excessive carbon deposition while still allowing sufficient carbon coating to improve conductivity, thereby resolving the contradiction between conductivity enhancement and compaction performance maintenance.
3Productivity
If excess reducing agent is added or reaction temperature is raised to promote reduction, then the reduction of Fe3+ to Fe2+ is enhanced, but delithiation behavior occurs and FexP generation is promoted
Solution Approach 1:
The patent changes the chemical environment parameters by introducing metal oxide into the reduction system. This creates a new reaction pathway that maintains high reduction efficiency for Fe3+ to Fe2+ conversion while preventing the side reactions that lead to delithiation and FexP formation, thus improving product purity.
Solution Approach 2:
Metal oxide acts as a mediator in the reduction process, facilitating the Fe3+ to Fe2+ reduction while preventing over-reduction that would cause delithiation and FexP generation. It controls the reduction reaction to maintain product purity while preserving productivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the purity, crystallinity, and electrochemical properties of lithium iron phosphate, increasing its capacity per unit mass and reliability while reducing the formation of ferromagnetic impurities, thus enhancing the battery's performance and safety.
Implementation Method 1
the gas in the sintering atmosphere includes a mild oxidizing gas, which inhibits generation of a magnetic substance; a reduction tendency decreased by the addition of carbon dioxide to the system
Implementation Method 2
sintering a dry material containing an iron source, a lithium source, a phosphorus source, and a reducing carbon source to obtain lithium iron phosphate, wherein the sintering temperature is 800° C. to 900° C.
Implementation Method 3
the elevated temperature can provide LFP/C with better crystallinity and thus greatly improved compaction performance
Implementation Method 4
the carbothermic reduction process of lithium iron phosphate mainly involves the stepwise reduction process of Fe3+—LiFePO4—FexP
Implementation Method 5
In the carbothermic reduction of lithium iron phosphate, Fe2+ is easily oxidized to Fe3+, and thus a reducing agent needs to be added to prevent the oxidation of Fe2+
Data Source
AI summary
The present application relates to lithium iron phosphate, a preparation method therefor, and a lithium-ion battery. The preparation method includes: sintering dry materials of an iron source, a lithium source, a phosphorus source, and a reductive carbon source to obtain lithium iron phosphate, wherein the sintering atmosphere includes a mild oxidizing gas, the mild oxidizing gas includes carbon dioxide, and the sintering temperature is 800-900° C.