Co-substitution of Mg2+ and Ti4+ in Na3V2(PO4)3 nanoparticles coated with highly conductive carbon nanotubes for superior sodium storage

Benefiting from the stable structure, high theoretical specific capacities and long voltage plateau, Na3V2(PO4)3 has been considered as a promising cathode material for sodium-ion batteries (SIBs). Nevertheless, the poor intrinsic conductivity has seriously impeded its deeper development. Herein, unlike previous researchers who doped Mg2+ and Ti4+ separately, a simultaneously modified strategy combining Mg2+/Ti4+ co-substitution and coating carbon nano-tube is proposed. The replacement of V3+ by Mg2+ and Ti4+ can generate the beneficial p- and n-type doping effect. The introduction of Mg2+ produces the extra acceptor level, obtaining another hole carrier to increase the electronic conduction. Ti4+ is utilized to meet the charge compensation. Meanwhile, it can bring excess electrons due to the n-type substitution when Ti4+ replaces V3+. Moreover, carbon nano-tube (CNT) can construct a conductive network between the particles to facilitate the transport of electrons. Consequently, the optimized Na3V1.93Mg0.07Ti0.07(PO4)3 @CNT (MgTi0.07 @CNT) has superior electrochemical performance. Therefore, MgTi0.07 @CNT sample can be a promising cathode with excellent sodium storage properties and accelerated kinetic characteristics.