High-voltage structural evolution and its kinetic consequences for the Na4MnV(PO4)3 sodium-ion battery cathode material

Reversible Multi‐Electron Reaction Mechanism of Sodium Vanadium/Manganese Phosphate Cathode for Enhanced Na‐Storage Capability

“…The capacity fading is attributed to the overly activation of V 4 + ions in phosphates that causes structural instability and electrochemical irreversibility of the material. [32] Obviously differing from Mn-free Na 3 V 2 (PO 4 ) 3 /C and Mn-rich Na 4 VMn(PO 4 ) 3 /C samples, the NVMP/C sample delivers an impressive electrochemical performance with enhanced electrochemical reversibility and improved cycling stability. As seen from Figure 3a, NVMP/C sample exhibits symmetric charge/ discharge profiles consisting of two stable potential plateaus located at 3.4 V and 3.8 V, reaching a practical capacity of 126.1 mAh g À 1 , and an average working potential of 3.42 (vs Na + /Na) at 10 mA g À 1 .…”

“…In addition, the reversible capacity rapidly decreases from 108.2 mAh g −1 to 48.0 mAh g −1 after 40 cycles at 20 mA g −1 . The capacity fading is attributed to the overly activation of V 4+ ions in phosphates that causes structural instability and electrochemical irreversibility of the material [32] . Obviously differing from Mn‐free Na 3 V 2 (PO 4 ) 3 /C and Mn‐rich Na 4 VMn(PO 4 ) 3 /C samples, the NVMP/C sample delivers an impressive electrochemical performance with enhanced electrochemical reversibility and improved cycling stability.…”

“…More badly, rapid capacity degradation occurs upon extended cycling due to formation of distorted phases and progressive amorphization. [32] As claimed by Ghosh et al, [33] Na 3.75 V 1.25 Mn 0.75 (PO 4 ) 3 composition with relatively low Mn substitution could be charged/discharged with improved cycling stability. Afterwards, Zhang et al [34] reported superior Nastorage performance of Na 3.5 V 1.5 Mn 0.5 (PO 4 ) 3 composition based on electrochemical reactions of V 4 + /V 3 + and Mn 3 + /Mn 2 + redox couples, with a reversible capacity of about 110.0 mAh g À 1 and a capacity retention of 87.2 % after 4000 cycles.…”

“…The additional capacity is attributed to the Mn substitution‐induced activation of V 4+ into V 5+ in the high‐potential region of 3.8–4.0 V. However, the activation caused structural destruction and irreversible electrochemical process, therefore resulting in a large irreversible capacity loss at the first discharge. More badly, rapid capacity degradation occurs upon extended cycling due to formation of distorted phases and progressive amorphization [32] . As claimed by Ghosh et al., [33] Na 3.75 V 1.25 Mn 0.75 (PO 4 ) 3 composition with relatively low Mn substitution could be charged/discharged with improved cycling stability.…”

The advent of manganese-substituted sodium vanadium phosphate-based cathodes for sodium-ion batteries and their current progress: a focused review

“…authenticated that extending the sodium extraction potential above 3.8 V in Na 4 MnV(PO 4 ) 3 could induce the development of distorted NASICON-type phases and gradual amorphization. 88 More importantly, it was debated that the thermodynamic instability of the exclusively desodiated Na 4 MnV(PO 4 ) 3 phase is the primary reason behind its structural and electrochemical downfall rather than the kinetic limitations associated with the reversible structural changes. Interestingly, the authors further recognized that the unfavorable phase transitions were mainly associated with the local environment changes in the vanadium sites rather than the manganese sites.…”