Improved Structural Reversibility and Cycling Stability of Li₂MnSiO₄ Cathode Material by the Pillar Effect of [TiO_x] Polyanions

Abstract

Li2MnSiO4 cathode material suffers from structural distortion caused by irreversible transition of [MnO4] tetrahedron to [MnO6] octahedron and layer exfoliation upon full delithiation, thus resulting in rapid capacity decay during cycling. In this study, Ti was introduced into the Mn site in Li2MnSiO4 as pillars to prevent the structural collapse. The results showed that [TiO4] tetrahedrons and [TiO6] octahedrons coexisted in Mn sites, and the proportion of [TiO6] octahedrons increased with increasing Ti. [TiOx] pillared Li2MnSiO4 samples presented greatly improved cycling stability, especially [TiO6] enriched Li2Mn0.85Ti0.15SiO4, which achieved the highest initial Coulumbic efficiency (86%) and the best capacity retention at C/20 rate. Moreover, Li2Mn0.85Ti0.15SiO4 exhibited excellent rate performance and retained 93% of initial discharge capacity after 50th cycles at C/2 rate. Ex‐situ XPS revealed [TiOx] pillars, especially [TiO6] pillars facilitated the reversible transition of [MnOx] during cycling. Ex‐situ XRD demonstrated better structure reversibility of [TiO6] enriched sample. The enhanced structural reversibility and cycling stability are ascribed to the pillaring effect of [TiOx], especially large [TiO6] octahedrons in structure, which ensure the reversible oxidation/reduction of Mn and alleviate the layer exfoliation during cycling.

Insight into cations substitution on structural and electrochemical properties of nanostructured Li2FeSiO4/C cathodes

“…38 Since there is no other oxidation or reduction hike observed in the CV curve, it is clear that the dopant ions are not participating directly in the redox activity of LFSO/C. 14,39 However, Ag containing sample exhibits higher potential difference at a low scan rate and lower peak current than that of the other samples, which demonstrates its poor electrochemical performance.…”