S-Decorated Porous Ti3C2 MXene Combined with In Situ Forming Cu2Se as Effective Shuttling Interrupter in NaSe Batteries

Given natural abundance of Na and superior kinetics of Se, NaSe batteries have attracted much attention but still face the problem of shuttling effect of soluble intermediates. The first-principle calculations reveal the S-decorated Ti3C2 exhibits increased binding energy to sodium polyselenides, suggesting a better capture and restriction on intermediates. The obtained Se@S-decorated porous Ti3C2 (Se@SPTi3C2) exhibits a high reversible capacity of 765 mAh g(-1) at 0.1 A g(-1) (calculated based on Se), approximate to 1.2, 1.3, and 1.7 times of Se@porous Ti3C2 (Se@PTi3C2), Se@Ti3C2, and Se, respectively. It gives considerable capacity of 664 mAh g(-1) at 20 A g(-1) and impressive cycling stability over 2300 cycles with an ultralow capacity decay of 0.003% per cycle. The excellent electrochemical performance can be ascribed to the S-modified porous Ti3C2, which provides effective immobilization toward polyselenides, makes full use of nanosized Se, and alleviates volume expansion during sodiation/desodiation. Additionally, in situ forming Cu2Se can generate Cu nanoparticles through discharge process and then transform polyselenides into solid-phase Cu2Se, further suppressing the shuttling effect. This work provides a practical strategy to immobilize and transform sodium polyselenides for high-capacity and long-life NaSe batteries.

Automated summary

This study successfully immobilized selenium polyselenides using sulfur-modified Ti3C2, resulting in excellent electrochemical performance of Se@S-decorated porous Ti3C2 with high reversible capacity, impressive cycling stability, and ultra-low capacity decay.