Sodium-ion batteries have garnered significant attention as a cost-effective alternative to lithium-ion batteries due to the abundance and affordability of sodium precursors. However, the lack of suitable electrode materials with both high capacity and excellent stability continues to hinder their practical viability. Herein, we couple lattice strain and sulfur deficiency effects in a tin monosulfide/reduced graphene oxide composite to enhance sodium storage performance. Experimental results and theoretical calculations reveal that the synergistic effects of lattice strain and sulfur vacancies in tin monosulfide promote rapid (de)intercalation near the surface/edge of the material, thereby enhancing its pseudocapacitive sodium storage properties. Consequently, the strained and defective tin monosulfide/reduced graphene oxide composite demonstrates a high reversible capacity of 511.82 mAh g⁻¹ at 1 A g⁻¹ and an outstanding rate capability of 450.60 mAh g⁻¹ at 3 A g⁻¹. This study offers an effective strategy for improving sodium storage performance through lattice strain and defect engineering.

The increasing demand for new energy sources has promoted the improvement of the energy storage capacity of lithium-ion batteries (LIBs) that urged the development of higher energy density cathode materials. The enhancement of the classical cathode in the last 30 years has reached a bottleneck, and then the discovery of the lithium-excess disordered materials has greatly expanded the research space of the cathode materials. Compared with the conventional layered oxides, the lithium-excess disordered rock-salt oxides (LEDRXs) with a more stable structure has higher extractable Li⁺ content, even though the inactive high-valent transition metals (TMs) were needed to compensate for the excess Li, which would reduce the total TM redox content. In addition, oxygen redox provides additional electron capacity for the materials, which also causes O loss and results in the subsequent poor cycle performance. Herein, a series of studies about LEDRXs and their targeted modification measures are summarized, including the prospect of the materials, in order to provide ideas for the design of high-performance LEDRXs. Finally, the new discoveries and outlook on future research directions of LEDRX cathode materials for LIBs with higher energy density are given.