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A systematic study on the structures, magnetic properties, and electrochemical performance of Li x FePO4 was carried out. Interestingly, it was found that the magnetic phase transition temperature is around 295 K in Li x FePO4 (x ≤ 0.12) nanocrystals, which is higher than that of LiFePO4 (T N = 51(1) K) and FePO4 (T N = 114(1) K) phases. The origin of magnetic order around room temperature (RT) in Li x FePO4 (x ≤ 0.12) is proposed to be due to both Fe2+–Fe3+ superexchange and the broken local symmetries induced by Fe2+–Li+ antisite defects. Ab initio calculations were adopted to calculate the total energy change of the ferromagnetic state and antiferromagnetic state (ΔE) to qualitatively estimate T N and proved the existence of the magnetic order around room temperature. Because of the strong Lorentz force in RT magnetic domains, Li ions will be trapped and form sub-10 nm solid solution domains of Li0+δFePO4, which have a direct relationship with electrochemical performance during (de)­lithiation procedures.

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