工业制备磷酸铁之pH与磷铁计量比协同调控

　　

摘要：磷酸铁（FePO₄·xH₂O）是制备磷酸铁锂正极材料的关键前驱体，其化学纯度、物相结构、粒度分布与振实密度等指标直接决定正极材料的电化学性能。液相沉淀法是当前主流的磷酸铁制备工艺，其中pH值与P/Fe摩尔比是贯穿反应全程、对产品质量影响最为显著的两个核心控制变量。本文从铁离子水解形态的热力学分析出发，系统解释了铁源氧化、沉淀、陈化与洗涤各工艺阶段pH控制窗口的化学机理，并把P/Fe摩尔比作为与pH相互耦合的参数纳入统一框架，建立了"pH—P/Fe配比"双变量与各阶段产品关键指标（杂质含量、物相纯度、振实密度、粒度分布、收率及电化学性能）之间的关联。阐述了：沉淀阶段应严格将pH控制在1.8~2.2区间以获得纯相二水磷酸铁，同时将P/Fe摩尔比控制在1.00~1.02的轻微富磷区间；P/Fe偏低（铁过量）会以Fe(OH)₃杂相形式严重劣化克容量，P/Fe偏高（磷过量）则造成磷残留并影响浆料稳定性。在此基础上提出了覆盖全流程、兼顾pH动态轨迹与计量配比的协同调控策略，为电池级磷酸铁的稳定化、规模化生产提供了理论指导。

关键词：磷酸铁；pH控制；P/Fe摩尔比；沉淀反应；振实密度；磷酸铁锂

Abstract：Iron phosphate (FePO₄·xH₂O) is a key precursor for lithium iron phosphate (LiFePO₄) cathode materials, and its chemical purity, phase structure, particle size distribution, and tap density directly determine the electrochemical performance of the final cathode material. Liquid-phase precipitation is currently the mainstream process for iron phosphate production, in which pH and the P/Fe molar ratio are the two core control variables that run through the entire reaction and most significantly affect product quality. Starting from a thermodynamic analysis of iron hydrolysis speciation, this paper systematically elucidates the chemical mechanisms underlying the pH control windows in the stages of iron-source oxidation, precipitation, aging, and washing. It further incorporates the P/Fe molar ratio, as a parameter coupled with pH, into a unified framework and establishes the relationship between the dual variables of pH and P/Fe ratio and the key product indicators at each stage, including impurity content, phase purity, tap density, particle size distribution, yield, and electrochemical performance. The results indicate that the pH in the precipitation stage should be strictly controlled within 1.8–2.2 to obtain phase-pure iron phosphate dihydrate, while the P/Fe molar ratio should be maintained in the slightly phosphorus-rich range of 1.00–1.02. A low P/Fe ratio (iron excess) severely degrades specific capacity through the formation of Fe(OH)₃ impurity phases, whereas a high P/Fe ratio (phosphorus excess) leads to residual phosphorus and compromises slurry stability. On this basis, a coordinated control strategy covering the entire process and balancing the dynamic pH trajectory and stoichiometric ratio is proposed, providing theoretical guidance for the stable, large-scale production of battery-grade iron phosphate.

Keyword: iron phosphate; pH control; P/Fe molar ratio; precipitation; tap density; lithium iron phosphate

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