Constructing hierarchical heterojunction structure for K/Co co-substituted Na3V2(PO4)3 by integrating carbon quantum dots.

[Display omitted] Na 3 V 2 (PO 4) 3 (NVP) has been widely adopted as cathode in sodium ion battery devices. Nevertheless, the weak intrinsic conductivity and serious structural collapse limit the further development. Herein, a simultaneous modified strategy of doping K/Co and integrating carbon quantum dots (CQD) is proposed. Substituting K+ is beneficial to afford amount of Na+ transport within the stabled and expanded lattice. The introduction of Co2+ generates beneficial hole carriers to improve conductivity. Furthermore, the bonding of conductive CQD guides to obtain nano-sized NVP grains, reducing the pathway for ionic migration to accelerate the diffusion capability. Importantly, a unique p-n type heterojunction construction is established in the interface between CQD (n -type) and NVP (p-type). This heterojunction structure enhances the mobility of electrons owing to the free pathways, in which the electrons transport in a relatively lower energy level without the scatter and collision of anions dopants. Ultimately, K 0.1 Na 2.95 V 1.95 Co 0.05 (PO 4) 3 @CQD exhibits with the best energy output level. It's initial capacity under 5C is 109.8 mA h g−1 and the retention is 87.6% after cycle 400 cycles. Even at 20 and 50C, its output is 93.5 and 82.6 mA h g−1 for 1st and 66.6 and 52.1 mA h g−1 for 1000th cycle, respectively. Finally, an asymmetric full cell test confirms its application practically. [ABSTRACT FROM AUTHOR]