Rational Design of Li₃V₂(PO₄)₃/C for Phosphate-Based Symmetric Full-Cell Li-Ion Batteries

To further increase the energy density of lithium-ion batteries (LIBs), various researches have been conducted on high-voltage and high-capacity cathode materials. In this perspective, monoclinic Li₃V₂(PO₄)₃ is a promising candidate due to its promising theoretical discharge capacity of 197 mAh/g with complex phase transition in the voltage range of 3.0 to 4.8 V. However, such asymmetric phase transition behavior with 3 Li⁺ ion extraction/insertion is highly irreversible, resulting in an initial discharge capacity of 163 mAh/g with deteriorated capacity retention. We suggest that cycling Li₃V₂(PO₄)₃ in the voltage range of 3.0 to 4.5 V suppresses the irreversible phase transition and elution of transition metal. Hence, Li₃V₂(PO₄)₃ in the voltage range of 3.0 to 4.5 V delivers an initial discharge capacity of about 142 mAh/g and exhibits extremely long cycle retention (78.70% 2,000 cycles), as when cycling in the voltage range of 3.0 to 4.3 V (81.67% 2,000 cycles). Furthermore, we present the possibility of a Li₃V₂(PO₄)₃||Li₃V₂(PO₄)₃ symmetric all-solid-state battery based on an N/P ratio and a cutoff voltage design, which is demonstrated in liquid electrolyte half-cells and symmetric full cells.