Mapping of Transition Metal Redox Energies in Phosphates with NASICON Structure by Lithium Intercalation

Abstract

The position of several transition metal redox energies with respect to the Fermi energy of lithium in phosphates with sodium super ionic conductor (NASICON) framework were determined electrochemically upon lithium intercalation. The materials studied were Li2NaV2(P04)3, LiNa2FeV(P04)3, TiNb(P04)3, LiFeNb(P0j3, and Li2FeTi(P0j3 all having NASICON framework. The positions of the redox couples were found centered at the following energies: V4/V3 at 3.8 eV, Fe37Fe2 at 2.8 eV, Ti4/Ti3 at 2.5 eV, Nb57Nb4 at 2.2 eV, Nb47Nb3 at 1.8 eV, and V3/V2 at 1.7 eV below the Fermi energy of lithium. Several of these redox couples were found to overlap each other. Some of these materials look promising as positive electrode materials for Lit-ion batteries.

Facile Synthesis and Electrochemical Investigation of Li9V3(P2O7)3(PO4)2as High Voltage Cathode for Li-Ion Batteries

“…[2][3][4][5][6] For instance, monoclinic Li 3 V 2 (PO 4 ) 3 can theoretically deliver a capacity of 197 mA h g −1 when all the three Li ions are extracted at an average potential of 4.1 V. 7,8 As suggested by Goodenough and his coworkers, the above described material operates at a higher potential compared to their iron equivalent due to the inductive effect between vanadium and the phosphate groups. 2 This results in increased specific energy. However, monoclinic LVP suffers from sharp drop in electronic conductivity and structural instability with deep de-lithiation at high potentials.…”

A Reitveld quantitative XRD phase-analysis of selected composition of the Sr(0.5+x)Sb(1−x)Fe(1+x)(PO4)3(0 < x < 0.50) system

“…The Nasicon-type family has been the subject of intensive research due to its potential applications as solid electrolyte, electrode material, low thermal expansion ceramics and as storage materials for nuclear waste [1][2][3][4][5][6] The structure of such materials with general formula A x XX (PO 4 ) 3 consists of a three-dimensional network made up of corner-sharing X(X )O 6 octahedra and PO 4 tetrahedra in such a way that each octahedron is surrounded by six tetrahedra and each tetrahedron is connected to four octahedral. Within the Nasicon framework, there are interconnected interstitial sites usually labelled M1 (one per formula unit) and M2 (three per formula unit) through which A cation can diffuse, giving rise to a fast-ion conductivity [1,3,7] ( Fig.…”

Lithium insertion chemistry of some iron vanadates

“…Among these, LiFePO 4 presents the most promising electrochemical performance, with safety, stability and cost advantages over the layered cobalt and nickel oxides [3]. Much attention was also given to Nasicon and anti-Nasicon phosphate [4,5] and sulfate [6,7] structures containing iron and vanadium. The most interesting materials comprise iron(III), titanium(IV), vanadium(V, III), and to a lesser degree, manganese(II, III, IV), niobium(V) and copper(II) [8].…”