This protocol synthesizes FePO₄·2H₂O as a LiFePO₄ precursor using a controlled oxidation–precipitation route: Fe²⁺ (from FeSO₄) is oxidized to Fe³⁺ in dilute H₃PO₄ using H₂O₂, followed by tight pH control (~2.16) and aging at 90 °C to crystallize FePO₄·2H₂O.
General Protocol
Ferric phosphate dihydrate (FePO₄·2H₂O) is a critical precursor for LiFePO₄ cathode production, where phase purity and impurity control (e.g., sulfate carryover) directly affect downstream electrochemical performance. This protocol prepares FePO₄·2H₂O via an oxidation–precipitation method in which FeSO₄ is dissolved in diluted phosphoric acid, oxidized using hydrogen peroxide, and precipitated at a tightly controlled pH setpoint (2.15–2.18) followed by thermal aging at 90 °C to promote uniform crystallization.
The workflow is designed for modular lab automation: steps are defined with explicit parameters (dosing order/rate, temperature ramps, stirring rate, pH checkpoints, aging time) so the recipe can be optimized and reproducibly rerun. Manual fallback steps are included for filtration/washing/drying if automation modules are not available. Quality checkpoints include pH stability at setpoint, visual color/texture transitions, and wash validation (optional sulfate test), enabling consistent “battery-grade” precursor batches with full run traceability.
Ferric phosphate dihydrate (FePO₄·2H₂O) is an industry-relevant battery precursor used to produce LiFePO₄ (LFP) cathode materials for energy storage applications. This protocol is written to leverage a modular, programmable synthesis protocol where the full recipe—dosing order, dosing rate, mixing, temperature profile, and pH setpoint—can be optimized and then rerun identically. The key advantage is reproducibility: each run generates structured logs (time/temperature/stirring/dosing checkpoints and operator-entered pH/observations), enabling consistent “battery-grade” precursor quality across batches and accelerating development cycles.
The synthesis follows a controlled oxidation–precipitation route: Fe²⁺ (from FeSO₄·7H₂O) is dissolved in diluted phosphoric acid, oxidized to Fe³⁺ using H₂O₂, then precipitated under tightly controlled acidity (pH 2.15–2.18) and aged at 90 °C to crystallize FePO₄·2H₂O. Downstream steps focus on impurity removal (especially sulfate carryover) via repeated washing and controlled drying to obtain a free-flowing powder suitable for subsequent conversion to LiFePO₄/C.
Dissolve 14.9 g Ferrous Sulfate Heptahydrate in 60.0 mL DI water (fresh) until fully clear.(Optional stabilizer) Add 0.2 mL Phosphoric Acid (85%) to the stock to reduce air-oxidation during handling.Load the full 60.0 mL stock into the dispenser.
Sterlization Module module step
Reservoir Dispensing Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Stirring and Heating Module module step
Add 10% Sodium Hydroxide slowly until pH 2.15–2.18. Note: pH stays within range for ≥3 minutes.
Aging/crystal growth
Wait module step
Vacuum filter (or centrifuge) and collect cake.
Wash with DI water 3–6 cycles (log cycle count).Optional QC: sulfate check in final wash.
70–90°C overnight to constant mass.Airtight container + batch ID.
Aging/crystal growth
The authors declare no conflict of interest.