S‐Decorated Porous Ti 3 C 2 MXene Combined with In Situ Forming Cu 2 Se as Effective Shuttling Interrupter in Na–Se Batteries

Given natural abundance of Na and superior kinetics of Se, Na–Se batteries have attracted much attention but still face the problem of shuttling effect of soluble intermediates. The first‐principle calculations reveal the S‐decorated Ti 3 C 2 exhibits increased binding energy to sodium polyselenides, suggesting a better capture and restriction on intermediates. The obtained Se@S‐decorated porous Ti 3 C 2 (Se@S‐P‐Ti 3 C 2 ) exhibits a high reversible capacity of 765 mAh g −1 at 0.1 A g −1 (calculated based on Se), ≈1.2, 1.3, and 1.7 times of Se@porous Ti 3 C 2 (Se@P‐Ti 3 C 2 ), Se@Ti 3 C 2 , 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 Ti 3 C 2 , which provides effective immobilization toward polyselenides, makes full use of nanosized Se, and alleviates volume expansion during sodiation/desodiation. Additionally, in situ forming Cu 2 Se can generate Cu nanoparticles through discharge process and then transform polyselenides into solid‐phase Cu 2 Se, further suppressing the shuttling effect. This work provides a practical strategy to immobilize and transform sodium polyselenides for high‐capacity and long‐life Na–Se batteries.