Understanding the superior sodium-ion storage in a novel Na3.5Mn0.5V1.5(PO4)3 cathode

A Novel NASICON‐Type Na4MnCr(PO4)3 Demonstrating the Energy Density Record of Phosphate Cathodes for Sodium‐Ion Batteries

“…[4][5][6] Especially, designing high-energy-density cathode materials is of great significance to meet the practical requirements. [7] Currently, various interesting cathode materials have been reported for SIBs, such as layered/tunnel-type transition-metal oxides, [8][9][10] polyanionic compounds, [11][12][13][14][15][16][17] Prussian blue analogues, [18,19] and organic salts. [20,21] Among them, the polyanion-type phosphates have always been a research hotspot by virtue of the strong binding energy of PO bonds, the 3D open frameworks, and the structural diversity.…”

“…The corresponding migration barrier (0.38 eV) is comparable to that of Na 3 V 2 (PO 4 ) 3 , and is much smaller than those of most reported SIB cathode materials. [14,16,46] In addition, the projected density of states (DOS) of NMCP exhibit some metallic properties especially for the spin up electrons (Figure 5c, the band structure is provided in Figure S19, Supporting Information). The excellent reaction kinetics and desirable rate performance of NMCP are ascribed to the low ionicmigration energy barrier and decent electronic conductivity.…”

Impact of Mg2+ and Al3+ Substitutions on the Structural and Electrochemical Properties of NASICON‐NaxVMn0.75M0.25(PO4)3 (M = Mg and Al) Cathodes for Sodium‐Ion Batteries

“…At the end of the charge at 3.8 V versus Na + /Na 0 , only the reflections corresponding to the new phase are noticed whose composition is estimated as “Na 2.0 VMn 0.75 Al 0.25 (PO 4 ) 3 .” Overall, the removal of 1.75 moles of sodium ions from the Al‐NVMP structure decreases the unit cell volume by 8.2%, which is comparable with values reported for other NASICON cathodes. [ 22,23,24 ] On the subsequent discharge to 2.75 V, the abovementioned processes are reversed and the structure of Al‐NVMP cathode is fully restored. The normalized XANES of the Al‐NMVP cathodes with different state of charges are shown in Figure 4b,c.…”

“…Further, when the charging window is extended to 4.3 V versus Na + /Na 0 , higher first charge capacity has been obtained (≈150 mA h g −1 , which is equivalent to removal of three moles of sodium per formula unit), thanks to the activity of V 5+ /V 4+ /V 3+ and Mn 3+ /Mn 2+ redox couples. [ 23–26 ]…”

Dually Decorated Na3V2(PO4)2F3 by Carbon and 3D Graphene as Cathode Material for Sodium‐Ion Batteries with High Energy and Power Densities

“…As for cathode materials, the polyanionic compounds have recently been intensively attractive for SIBs because of their advantages such as high working voltage, excellent thermal stability and large channel for Na + transport, which result from stable frame structure of polyanionic compounds and inductive effects of polyanionic groups. [8] Recently the investigated polyanion cathode materials mainly include NaVPO 4 F, [9] NaFePO 4 , [10,11] Na 3 V 2 (PO 4 ) 3 , [12][13][14][15][16][17] Na 2 FePO 4 F, [18] Na 3 Cr 2 (PO 4 ) 3 [19] Na 3.5 Mn 0.5 V 1.5 (PO 4 ) 3 , [20] Na 2 MnPO 4 F, [21] Na 3 V 2 O 2 (PO 4 ) 2 F, [22][23][24][25][26][27] Na 4 MnV(PO 4 ) 3 , [28] Na 3 V 2 (PO 4 ) 2 F 3 , [29][30][31][32][33][34][35][36][37][38][39][40][41][42] Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 , [43,44] and Na 2 Fe 2 (SO 4 ) 3 , [45,46] which all display higher working voltage than their oxide counterparts. Among the above-mentioned polyanion compounds for SIBs, Na 3 V 2 (PO 4 ) 2 F 3 with NASICON (sodium superionic conductor) structure has been considered as one of the most promising candidates because of its higher working voltage, higher mobility of Na + , better cyclability, larger capacity, and hence larger energy density.…”