Benefits of Chromium Substitution in Na₃V₂(PO₄)₃ as a Potential Candidate for Sodium‐Ion Batteries

Abstract

The effect of low‐level chromium substitution in Na3V2‐xCrx(PO4)3 (0≤x≤0.4), a potential cathode material in Na‐ion cells, has been examined. A suitable synthesis procedure is developed to obtain composites of crystalline NASICON phosphate and an amorphous carbon phase to enhance the electrical conductivity of the electrode. The optimized cathode materials were characterized by using X‐ray diffraction and spectroscopic techniques. The electrochemical evaluation was carried out by using galvanostatic and potentiostatic methods. The activity of the V5+/V4+ redox couple at approximately 4 V is remarkable for the samples containing chromium. A reversible capacity of 107 mAh g−1 with a coulombic efficiency of 99 % was determined for Na3V1.9Cr0.1(PO4)3 after 40 cycles. The observed performance correlates with a good kinetic response, resulting from low charge‐transfer resistance and high diffusion coefficient.

Induced Rate Performance Enhancement in Off‐Stoichiometric Na3+3xV2−x(PO4)3 with Potential Applicability as the Cathode for Sodium‐Ion Batteries

“…[30,31] It is commonly reported that the I G /I D1 ratio is am easureo ft he level of graphitization of the carbon material. [16,37,38] On increasing the Cr ate from C/2 to 40 C, ad ecrease in capacity is clearlyo bserved as expected from the fast kinetics which are imposed at the highest rate. Figure 6d isplays the charge and dischargec urves recorded on sodium half-cells assembled witht he studied samples as workinge lectrodes.…”

“…The quantitative analysis showed ag ood agreement between the actual composition and their theoretical values (Table S2). [16] For NVP-0.1, small and dark nanosized particlesa ppear neart he Na 3 V 2 (PO 4 ) 3 surface (marked with arrows). These values are close to the stoichiometric ones.…”

“…According to this assumption, the research of electrode materials for sodium-ion batteries is resurging after many years of reluctance. [14,15] Thiss patial atom distribution intrinsically avoids ad irect M-O-M concatenation which hinderse lectron delocalization and hence leads to ap oor electronic conductivity.T oo vercome this drawback, different solutions have been envisaged such as metal doping [16,17] or carbon coating. [8][9][10] Concerning the research of cathode materials, theoretical calculations have demonstrated that the open framework of layered oxidesa nd polyanionic compounds with the NASICON structurea re better to host large sodium ions, and hence pro-vide phase stability on cycling.…”

Rational Architecture Design Enables Superior Na Storage in Greener NASICON‐Na4MnV(PO4)3 Cathode

“…[5][6][7] On the other hand, the applications of PBAs are limited by their low volume density, inferior thermal stability, and toxicity of cyanide. Lavela and co-workers used Cr to replace 10% of V and the as-synthesized Na 3 V 1.8 Cr 0.2 (PO 4 ) 3 showed a short plateau above 3.8 V. [24] This high-potential plateau can be prolonged by increasing the amount of Cr to 50%, forming a new material Na 3 VCr(PO 4 ) 3 , which has been reported by Yang and co-workers. [11][12][13] Recently, the Na superionic conductor (NASICON)-structured polyanion-type materials are of significant interest because of their unique crystal framework that is constructed by units of MO 6 octahedrons (M represents transition metals) and XO 4 tetrahedrons (X = P, S, Si, As), building 3D ion channels for fast Na + migration.…”

Towards High‐Performance Aqueous Sodium‐Ion Batteries: Stabilizing the Solid/Liquid Interface for NASICON‐Type Na2VTi(PO4)3 using Concentrated Electrolytes

“…[15,16] The V 4 + /V 3 + and Ti 4 + /Ti 3 + redox processes in vanadium-and titanium-based insertion hosts with the NASI-CON structure occur within the electrochemical stability window of water. [20][21][22][23][24][25] In consequence,a mphoteric insertion hosts that can be used as cathode and anode materials are being developed. Specifically,N aTi 2 (PO 4 ) 3 is of high interest because it is redox active at the lower end of the aqueous electrolyte stabilityw indow,w hicht hus enables enhanced energy densities.…”