Lithium Iron Phosphate Synthesis with Low-Titanium Ferrous Sulfate
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Solution Overview
Problem
Existing methods for preparing lithium iron phosphate from ferrous sulfate by-products from titanium dioxide face challenges in effectively removing impurities, particularly titanium, and generate environmental hazards due to the use of sodium sulfide and hydrogen sulfide gas.
Innovation Solution
A method involving pH adjustment of the ferrous sulfate solution with sulfuric acid, addition of iron powder for reduction, and subsequent use of iron phosphate or lithium iron phosphate waste to facilitate purification, followed by a hydrothermal reaction with lithium hydroxide and phosphoric acid to achieve low titanium content and produce high-purity lithium iron phosphate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sodium sulfide is used to purify ferrous sulfate by removing metal impurities through sulfide precipitation, then impurity removal effectiveness is improved, but hydrogen sulfide gas is generated causing safety risks and environmental pollution
Solution Approach 1:
The patent changes the chemical parameters of the purification system by replacing sulfide-based reagents with ammonia-based reagents. Specifically, it uses ammonia water to adjust pH to 8-9, creating alkaline conditions that precipitate metal impurities as hydroxides rather than sulfides, thereby eliminating hydrogen sulfide gas generation while maintaining effective impurity removal
Solution Approach 2:
The patent converts the harmful hydrogen sulfide gas generation into a beneficial process by using ammonia water instead. The ammonia not only adjusts pH to precipitate impurities but also forms soluble ammonium sulfite/sulfate complexes that can be easily removed in wastewater treatment, turning a potentially harmful chemical process into an environmentally friendly one
2Manufacturing precision
If phosphoric acid and flocculant are added to ferrous sulfate solution for impurity removal, then purification is achieved, but excess alkaline cations and organic compounds are introduced increasing wastewater treatment difficulty
Solution Approach 1:
The patent extracts and removes the problematic components from the purification process. Instead of adding phosphoric acid and flocculant that leave residual cations and organic compounds, it uses a minimal addition approach with ammonia water and air oxidation, extracting only the necessary purification function while leaving the solution free of excessive additives that would complicate wastewater treatment
Solution Approach 2:
The patent achieves homogeneous purification using ammonia water and air oxidation throughout the solution. The ammonia distributes uniformly, raising pH consistently to precipitate impurities, and the air oxidation uniformly converts Fe2+ to Fe3+ for complete precipitation as Fe(OH)3, eliminating the need for localized or staged addition of multiple different chemicals
3Manufacturing precision
If conventional purification methods are used to remove titanium impurities from ferrous sulfate, then some titanium removal is achieved, but extremely low control values for titanium content cannot be reached
Solution Approach 1:
The patent performs preliminary oxidation of Fe2+ to Fe3+ using air oxidation before precipitation. This preliminary action ensures that all iron is in the +3 state, which forms more complete and finer Fe(OH)3 precipitates that can adsorb titanium impurities more effectively, thereby achieving extremely low titanium content control values
Solution Approach 2:
The patent creates a composite precipitate system where Fe(OH)3 forms a gel-like network structure that adsorbs titanium impurities. The combination of Fe(OH)3 precipitate and adsorbed titanium creates a composite removal mechanism that achieves much lower titanium content than conventional single-method approaches
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
The method achieves deep purification of ferrous sulfate, reducing titanium content to less than 10 ppm, resulting in high-performance lithium iron phosphate with improved safety and environmental sustainability for lithium-ion batteries.
Implementation Method 1
add iron powder, and stir the mixture to react at a temperature of 80-90° C. for 2-3 hours
Implementation Method 2
add phosphoric acid and the lithium hydroxide solution in a co-current manner in an autoclave for neutralization
Implementation Method 3
heat the mixture under stirring, then filter, wash, and dry the mixture to obtain lithium iron phosphate powder
Data Source
AI summary
The present invention relates to the field of lithium battery material preparation technologies, particularly to a method for preparing lithium iron phosphate using the by-product ferrous sulfate from titanium dioxide. The method comprises the following steps: dissolving by-product ferrous sulfate from titanium dioxide in acidic aqueous solution, stirring with iron powder for reaction; adding iron phosphate or lithium iron phosphate waste powder to the solution, heating and stirring the mixture, allowing the mixture to settle and cool, and filtering the cooled mixture to obtain a purified ferrous sulfate solution; and adding phosphoric acid and a lithium hydroxide solution in an autoclave, and finally adding the purified ferrous sulfate solution, heating the mixture under stirring, then filtering, washing, and drying the mixture to obtain lithium iron phosphate powder; Using it as an iron source to prepare positive electrode materials for lithium-ion batteries has excellent electrochemical performance.