Multiple redox couples cathode material for Li-ion battery: Lithium chromium phosphate

Carbon coated Li3Cr2(PO4)3/C model materials were synthesized by a sol-gel route and a solid state route with calcination at 800 °C under an inert atmosphere. The model materials were characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD), scanning electron microscopy (SEM), laser diffraction analysis (granulometry) and thermogravimetric analysis (TGA). The electrochemical signatures obtained for the solid state (carbon coated) route synthesized compounds revealed the presence of two redox couples, Cr3+/Cr2+ and Cr4+/Cr3+, between 1.5-2.5 V and 4.0‐4.9 V vs. Li+/Li, respectively. The model materials show an initial specific charge (for lithiation) of 131 mAh g−1 (sol-gel, carbon coated) and 119 mAh g−1 (solid state, carbon coated), which decreases to 90 mAh g−1 and 46 mAh g−1, respectively, after 100 cycles. Operando XRD measurements revealed reversible structural changes in the crystal structure upon cycling, leading to the conclusion of an insertion reaction mechanism.