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 Li0.995Mg0.005V0.98Nb0.02PO4F, 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 Li0.995Mg0.005V0.98Nb0.02PO4F when suffering fast Li+ insertion/extraction. As expected, the Li0.995Mg0.005V0.98Nb0.02PO4F 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.