Manganese pyrosilicates as novel positive electrode materials for Na-ion batteries

Abstract

Desodiation of the Na2Mn2Si2O7–carbon nanocomposite exhibits unique rearrangements in a Mn-coordination environment.

Manganese‐based polyanionic cathodes for sodium‐ion batteries

“…Silicate polyanionic materials having the advantages of low cost and high elemental abundance play a delightful role in lithium-ion batteries (LIBs). In SIBs, two types of Mn-based silicates have been reported, one is Na 2 Mn 2 Si 2 O 7 [69,127] . Unlike edge-sharing connectivity of Mn-O polyhedra in Li 2 Mn 2 Si 2 O 7 , corner-sharing in Na 2 Mn 2 Si 2 O 7 is apparent, and this structure theoretically enables the strain introduced by the Jahn-Teller distortion of Mn 3+ to be relieved by taking only smaller atomic rearrangements.…”

“…(d) Schematic illustration of the structural evolution of Na 2 Mn 2 Si 2 O 7 at different voltages. Reproduced with permission: Copyright 2018, Royal Society of Chemistry [ 127 ] . (e) Galvanostatic charge–discharge profiles of Na 2 MnSiO 4 at 0.1 C using NaPF 6 electrolyte in EC:PC v/v 1:1 with 5 vol% VC.…”

“…Unlike edge‐sharing connectivity of Mn–O polyhedra in Li 2 Mn 2 Si 2 O 7 , corner‐sharing in Na 2 Mn 2 Si 2 O 7 is apparent, and this structure theoretically enables the strain introduced by the Jahn–Teller distortion of Mn 3+ to be relieved by taking only smaller atomic rearrangements. It can deliver a theoretical capacity of 165 mAh g −1 , but even after carbon coating, only about 25% is actually released with an average discharge voltage of only 2.2 V [ 127 ] . Such sluggish kinetics may be related to the rearrangement of the Mn coordination accompanied by a substantial volume contraction (Figure 6d) [ 127 ] or possibly to the huge migration coefficient change of the sodium ions during cycling [ 69 ] .…”

“…It can deliver a theoretical capacity of 165 mAh g −1 , but even after carbon coating, only about 25% is actually released with an average discharge voltage of only 2.2 V [ 127 ] . Such sluggish kinetics may be related to the rearrangement of the Mn coordination accompanied by a substantial volume contraction (Figure 6d) [ 127 ] or possibly to the huge migration coefficient change of the sodium ions during cycling [ 69 ] .…”