An Efficient Evaluation of F-doped Polyanion Cathode Materials with Long Cycle Life for Na-Ion Batteries Applications

Abstract

A series of Na3−xV2(PO4−xFx)3 (x = 0, 0.1, 0.15 and 0.3) polyanion cathode materials are synthesized via a sol-gel method. The optimal doping concentration of F in Na3V2(PO4)3 is 0.15 mol %. By neutron powder diffraction data, the chemical composition of as-synthesized material is Na2.85V2(PO3.95F0.05)3. The half-cell of Na2.85V2(PO3.95F0.05)3 cathode exhibits a stable discharge capacity of 103 mAh g−1 and 93% of capacity retention over 250 cycles without decay at 0.1 A g−1, which is higher than that of bare Na3V2(PO4)3 (98 mAh g−1). The high rate capability of Na2.85V2(PO3.95F0.05)3 is also dramatically enhanced via increase the conductivity of host material by F-doping. Moreover, the symmetrical Na-ion full-cell is fabricated using Na2.85V2(PO3.95F0.05)3 as cathode and anode materials. It is achieved that the good reversibility and superior cycling stability about 98% of capacity retention with ~100% of coulombic efficiency at 1.0 A g−1 throughout 1000 cycles. These results demonstrate that the optimal amount of Na2.85V2(PO3.95F0.05)3 is a distinctive potential candidate for excellent long-term cyclic stability with high rate low-cost energy storage applications.

Unfolding the structural features of NASICON materials for sodium‐ion full cells

“…The low‐voltage plateau is due to additional Na + ‐ion insertion leading to the formation of Na 5 V 2 (PO 4 ) 3 142,143 . Besides the advantages, NVP has very low electronic conductivity (1.63 × 10 −6 S cm −1 ), limiting its reversibility and cyclability 38 . The electronic conductivity can be improved using the strategies discussed in the previous section.…”

“…Therefore, NASICON structured materials are considered promising cathode materials for large‐scale grid applications 31–37 . However, practical applications are still limited because of the poor intrinsic electronic conductivity (10 −6 – 10 −8 S cm −1 ) 38,39 . Several methods have been used to improve the electronic conductivity of NASICON materials by combining with carbon‐based materials, 40–42 elemental doping, 43–47 and designing 3D porous architectures 48–51 …”

“…[31][32][33][34][35][36][37] However, practical applications are still limited because of the poor intrinsic electronic conductivity (10 −6 -10 −8 S cm −1 ). 38,39 Several methods have been used to improve the electronic conductivity of NASICON materials by combining with carbon-based materials, [40][41][42] elemental doping, [43][44][45][46][47] and designing 3D porous architectures. [48][49][50][51] In this review, we focus on the recent progress and limitations of NASICON structured electrode materials, which include phosphates (Na x M 2 (PO 4 ) 3 ), fluorophosphate (Na x M 2 (PO 4 ) 2 F), binary transition-metal phosphates (Na x MMʹ(PO 4 ) 2 F), and mixed phosphates (Na x M 2 (PO 4 )(SO 4 ) 2 and Na x M 2 (PO 4 ) 2 P 2 O 7 ) for SIBs.…”

Class of Solid-like Electrolytes for Rechargeable Batteries Based on Metal–Organic Frameworks Infiltrated with Liquid Electrolytes

“…Although NVP holds many advantages, it suffers from the key drawback of inferior intrinsic electronic conductivity ( 1.63 × 10 −6 S cm -1 ) and poor ion diffusivity. 166 To address these problems, researchers have explored many approaches, mainly focus on surface-conducting modification (e.g., carbon coating), elemental doping and downsizing the NVP particles. Here, we choose a simple wet-ball-milling and in-situ carbon-coating process to synthesis NVP/C cathode material.…”

Tailoring Oxygen Site Defects of Vanadium-Based Materials through Bromine Anion Doping for Advanced Energy Storage

“…Differing from the effect of metal element doping, more interesting properties could be triggered by anion doping, such as improved charge/discharge properties and high conductivity, which have been demonstrated in numerous materials systems. For instance, an obvious improvement of properties would be achieved by doping F into Na 3 V 2 (PO 4 ) 3 from 3.72 to 4.26 V, which was conducive to achieving enhanced power density (22%). − Thus, exploring the corresponding anion doping was necessary for the advancement of LiV 3 O 8 .…”