Double Donors Tuning Conductivity of LiVPO₄F for Advanced Lithium-Ion Batteries

To fulfill the increasing demand of lithium-ion batteries for realizing high energy density and great cycling stability under high rate, the cathode material capable of efficient electron and Li⁺-ion transportation is necessarily demanded. Herein, we propose a double-donor doping strategy by taking the carbon-coated LiVPO₄F as a model system. The Hall effect confirms that either or both Mg²⁺ substitution of Li⁺ and Nb⁵⁺ substitution of V³⁺ cause the carrier-type transformation from p-type to n-type. The great enhancements of electronic conductivity and ionic conductivity are realized in Li_0.995Mg_0.005V_0.98Nb_0.02PO₄F, which also exhibits a markedly improved Li⁺ diffusion coefficient and reduced electrochemical polarization. The carbon-coating layer can effectively prevent the decomposition reaction of electrolyte, allowing for good structural stability of Li_0.995Mg_0.005V_0.98Nb_0.02PO₄F when suffering fast Li⁺ insertion/extraction. As expected, the Li_0.995Mg_0.005V_0.98Nb_0.02PO₄F cathode exhibited superior electrochemical properties with an initial discharge capacity of 124.5 mA h g^-1 and capacity retention of 97.3% after 600 cycles at 1.6C. Even under a high rate of 8C, the discharge energy density was 392 Wh kg^-1 at the beginning and showed a retention rate of 84.4% after 2000 cycles.