New Insights into the Chemistry of the Hydrothermal Synthesis of Olivine Lithium Metal Phosphates

Abstract The effect of alkali ions (Na + and K + ) on the hydrothermal synthesis of olivine lithium metal phosphates in the P excess system was investigated by taking the synthesis of LiMn 0.8 Fe 0.19 Mg 0.01 PO 4 as a case study. It is found that the coexisting Na + can compete with Li + to partly form NaMnPO 4 as an impurity when the Na + /Li + ratio exceeds the critical value, and this is not the case for the coexisting K + . These behaviors should be related to the difference in the ionic size of the alkali ions which also leads to a very different process of LiMn 0.8 Fe 0.19 Mg 0.01 PO 4 formation. The samples derived from the K + ‐coexisting reaction system can deliver much higher reversible capacities as compared with the sample derived from the Na + ‐coexisting reaction system. This study provides new insights into the chemistry of the hydrothermal synthesis of olivine lithium metal phosphates, with an important implication for controllable synthesis and property manipulation.