Hydrothermal synthesis of high-performance carbon-free LiFePO4 cathodes for lithium-ion batteries under temperature-controlled conditions

Achieving high electrochemical performance in lithium iron phosphate (LiFePO 4 , LFP) without carbon coating remains a critical challenge because of its intrinsically low electronic conductivity. In this study, we demonstrate that carbon-coating-free LFP with competitive electrochemical performance can be obtained through a one-pot hydrothermal route by directly controlling the synthesis temperature, thereby isolating the intrinsic effect of temperature on the structure–property relationship. Pristine LFP powders were synthesized at 190–220 °C, and all samples exhibited a phase-pure olivine structure. Among them, the sample prepared at 200 °C showed smallest FWHM of the (121) reflection, the largest Scherrer crystallite size (~82 nm), and the lowest microstrain, indicating the most favorable crystallographic development. SEM and TEM analyses revealed that 200 °C consisted of uniformly dispersed sub-micron rod-/plate-like particles, whereas 190 °C sample showed incomplete crystallization and the samples synthesized at higher temperatures exhibited thermally driven coarsening. XPS confirmed that the 200 °C sample had near-stoichiometric composition, Fe 2+ -dominant surface chemistry and a more uniform oxygen environment. Electrochemically, the 200 °C sample delivered the highest discharge capacity (130.4 mAh g -1 at 0.1 C), retained stable short-term cycling behavior over 30 cycles, maintained superior rate capability (~90 mAh g -1 at 1 C), and exhibited the lowest charge-transfer resistance (R ct ≈ 405 Ω), while the corresponding Coulombic-efficiency profiles supporting initial reversibility. These results identify 200 °C as the optimal hydrothermal condition and demonstrate that temperature-driven control of crystallographic development and morphology can enable competitive electrochemical performance in LFP without carbon coating. • One-pot hydrothermal synthesis produces carbon-free LiFePO 4 without post-treatment. • Hydrothermal temperature governs crystallinity, morphology, and surface chemistry of LiFePO 4 . • An optimal temperature of 200 °C yields the highest crystallinity and uniform sub-micron particles. • LiFePO 4 synthesized at 200 °C delivers high reversible capacity and excellent cycling stability. • Reduced charge-transfer resistance at 200 °C enables superior rate performance.