Improved Structural Reversibility and Cycling Stability of Li 2 MnSiO 4 Cathode Material by the Pillar Effect of [TiO x ] Polyanions

Li 2 MnSiO 4 cathode material suffers from structural distortion caused by irreversible transition of [MnO 4 ] tetrahedron to [MnO 6 ] 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 Li 2 MnSiO 4 as pillars to prevent the structural collapse. The results showed that [TiO 4 ] tetrahedrons and [TiO 6 ] octahedrons coexisted in Mn sites, and the proportion of [TiO 6 ] octahedrons increased with increasing Ti. [TiO x ] pillared Li 2 MnSiO 4 samples presented greatly improved cycling stability, especially [TiO 6 ] enriched Li 2 Mn 0.85 Ti 0.15 SiO 4 , which achieved the highest initial Coulumbic efficiency (86%) and the best capacity retention at C/20 rate. Moreover, Li 2 Mn 0.85 Ti 0.15 SiO 4 exhibited excellent rate performance and retained 93% of initial discharge capacity after 50 th cycles at C/2 rate. Ex‐situ XPS revealed [TiO x ] pillars, especially [TiO 6 ] pillars facilitated the reversible transition of [MnO x ] during cycling. Ex‐situ XRD demonstrated better structure reversibility of [TiO 6 ] enriched sample. The enhanced structural reversibility and cycling stability are ascribed to the pillaring effect of [TiO x ], especially large [TiO 6 ] octahedrons in structure, which ensure the reversible oxidation/reduction of Mn and alleviate the layer exfoliation during cycling.