One-Step Low-Temperature Route for the Preparation of Electrochemically Active LiMnPO₄ Powders

Abstract

Pure and well-crystallized LiMnPO4 powders were obtained by a direct precipitation route in an aqueous medium at 373 K. A thermodynamic study of the system Li+/Mn(II)/phosphate/H2O identified a pH range in which LiMnPO4 precipitation was the most probable. From these theoretical considerations, the olivine-type compound precipitation turned out to be straightforward, i.e., no further thermal treatment was needed. A systematic study of the influence of synthesis parameters enabled tailoring of the size of the as-obtained particles. The smallest precipitated particles (∼100 nm) led to a global improvement of the electrochemical behavior when used in lithium batteries, consisting in lowering the polarization and enhancement of the reversible capacities (∼70 mAh/g at C/20). A two-phase Li extraction/insertion mechanism was identified, using the potential intermittent titration technique (PITT) and in situ X-ray diffraction, between LiMnPO4 and the delithiated phase MnPO4, indexed in the space group Pmnb with unit cell parameters a = 5.93(2) Å, b = 9.69(6) Å, and c = 4.78(1) Å.