Progress towards efficient phosphate-based materials for sodium-ion batteries in electrochemical energy storage

A Comprehensive Review on Strategies for Enhancing the Performance of Polyanionic-Based Sodium-Ion Battery Cathodes

“…Phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage are called pyrophosphates. The general formula of pyrophosphate for SIBs is Na x M y (P 2 O 7 ) z where M = transition metal (V, Mn, Fe, Co, Ni, or Mo); x , y , and z are integers, and x > 1 . Depending upon the transition metal choice and synthesis process pyrophosphates can crystallize in numerous structures like tetragonal, triclinic, and orthorhombic.…”

“…Zhero et al also denoted improvement in monoclinic NVPF after doping Cr 3+ into V positions. Additionally, Al doping also improved the performance compared to Al-free NVPF . Jin and his colleagues used electrospinning to create NaVPO 4 F/C nanofibers that had a high capacity (about 126 mA h g –1 C), good rate efficiency (about 61 mA h g –1 at 50C), and a long-life cycle.…”

“…Although the maricite phase is thermodynamically stable as compared to olivine it is electrochemically inactive as it lacks Na + ion diffusion channels due to the structural arrangement. In the maricite phase the adjacent octahedral units are shared on the edges, which are further connected with tetrahedral units to share the corners, whereas in the olivine phase the corner-shared octahedral units are connected with tetrahedral units. , The olivine phase of NaFePO 4 shows 80% theoretical capacity that is of 125 mA h g –1 …”

“…The general formula of pyrophosphate for SIBs is Na x M y (P 2 O 7 ) z where M = transition metal (V, Mn, Fe, Co, Ni, or Mo); x , y , and z are integers, and x > 1. 84 Depending upon the transition metal choice and synthesis process pyrophosphates can crystallize in numerous structures like tetragonal, triclinic, and orthorhombic. Among them pyrophosphates of Fe, V, and Mn exhibit good electrochemical activity relative to phosphates because of the greater stability of the P 2 O 7 4– group, but their rate capabilities, crystallinity, and theoretical specific capacities are comparatively poor.…”

“…In the maricite phase the adjacent octahedral units are shared on the edges, which are further connected with tetrahedral units to share the corners, whereas in the olivine phase the corner-shared octahedral units are connected with tetrahedral units. 84 , 85 The olivine phase of NaFePO 4 shows 80% theoretical capacity that is of 125 mA h g –1 . 68 …”