Structural and Morphological Tuning of LiCoPO₄ Materials Synthesized by Solvo-Thermal Methods for Li-Cell...

Olivine-type lithium metal phosphates (LiMPO₄) are promising cathode materials for lithium-ion batteries. LiFePO₄ (LFP) is commonly used in commercial Li-ion cells but the Fe³⁺/Fe²⁺ couple can be usefully substituted with Mn³⁺/Mn²⁺, Co³⁺/Co²⁺, or Ni³⁺/Ni²⁺, in order to obtain higher redox potentials. In this communication we report a systematic analysis of the synthesis condition of LiCoPO₄ (LCP) using a solvo-thermal route at low temperature, the latter being a valuable candidate to overcome the theoretical performances of LFP. In fact, LCP shows higher working potential (4.8 V vs. 3.6 V) compared to LFP and similar theoretical capacity (167 mAh·g^-1). Our goal is to show the effect of the synthesis condition of the ability of LCP to reversibly cycle lithium in electrochemical cells. LCP samples have been prepared through a solvo-thermal method in aqueous-non aqueous solvent blends. Different Co²⁺ salts have been used to study the effect of the anion on the crystal growth as well as the effect of solution acidity, temperature and reaction time. Materials properties have been characterized by Fast-Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopies. The correlation between structure/morphology and electrochemical performances has been investigated by galvanostatic charge-discharge cycles.