Flame Spray Pyrolysis Engineering of Highly Spherical LiMn 0.5 Fe 0.5 PO ₄ Nanoparticles With Boosted Volumetric Energy Density for Lithium‐Ion Batteries

LiMn x Fe 1‐x PO 4 (LMFP) olivine cathodes are promising for high‐energy‐density lithium‐ion batteries. Nanosizing particles effectively shortens the Li + diffusion pathways and sluggish Mn 2+ /Mn 3+ kinetics severely, but compromises electrode tap density and volumetric performance. We present a materials design strategy that integrates precursor engineering, solvent mediation, and homogeneous doping via flame spray pyrolysis (FSP) to simultaneously overcome these constraints. An organic phosphate ester precursor is employed to induce the formation of a transient molten intermediate phase, enabling surface tension‐driven spheroidization of particles. Concurrently, solvent engineering modulates droplet evaporation kinetics, prolonging high‐temperature residence time to ensure complete crystallization. The inherent rapid mixing and quenching of FSP ensure atomic‐scale homogeneity, which we leverage to implement element co‐doping that enhances bulk ion/electron transport. The synergistic effects of these properties enable the optimized LMFP cathode to achieve an exceptional electrode‐level volumetric energy density of 1145–1317 Wh L −1 . It also delivers a high initial capacity of 155.4 mAh g −1 at 0.1 C and 135 mAh g −1 at 5 C, retaining 97.6% capacity after 1000 cycles at 1 C. This work demonstrates that FSP is a versatile platform for designing electrode materials, simultaneously tackling the intertwined challenges of kinetics and density, and provides a viable pathway toward practical high‐energy batteries.