# Defect‐Engineered CoSe2 Quantum Dots Exposing Highly Active (111) Facets with Lithiophilic‐Sulfurophilic Functionality for High‐Energy Lithium–Sulfur Batteries

## TL;DR

Defect-engineered CoSe2 quantum dots in carbon microspheres improve lithium-sulfur battery performance by reducing polysulfide shuttle effects and enhancing redox reactions.

## Contribution

A novel sulfur cathode material using defect-engineered CoSe2 quantum dots with lithiophilic-sulfurophilic properties is developed for high-energy Li–S batteries.

## Key findings

- CoSe2@C cathodes show an initial specific capacity of 1397 mAh g−1 at 0.2 C.
- The material exhibits a decay rate of 0.029% per cycle after 1000 cycles at 2 C.
- Defective CoSe2 QDs with (111) facets enhance LiPS adsorption and catalytic conversion.

## Abstract

The shuttle of lithium polysulfides (LiPSs) and sluggish redox kinetics have posed significant barriers to advancing lithium–sulfur batteries. The design of lithiophilic‐sulfiphilic cathode show great promise, however, the integration of these multifunction through precise atomic‐level synergy remains a critical challenge. Herein, defective CoSe2 quantum dots (QDs) confined within carbon microspheres (CoSe2@C) are prepared as sulfur cathode host material. The exposure of the highly active (111) facets provides more active sites and accelerates the catalytic conversion kinetics of LiPSs. Additionally, the abundant selenium vacancies exhibit dual‐bonding capability with Li and S atoms, thereby improving the adsorption of LiPSs and lowering the reaction energy barrier. Moreover, the carbon microspheres matrix effectively alleviates the aggregation of CoSe2 QDs and increases the specific surface area. Benefiting from the above merits, the titled cathode exhibits enhanced conductivity and charge transfer, which effectively enhances the dynamics and alleviates shuttle effects. Consequently, the Li–S batteries assembled with CoSe2@C cathodes show extraordinary performance with an initial specific capacity of 1397 mAh g−1 at 0.2 C, a decay rate of 0.029% per cycle after 1000 cycles at 2 C. This work offers viewpoint for designing highly efficient catalysts for Li–S batteries.

Defective CoSe2 QDs confined within carbon microspheres (CoSe2@C) are prepared as an advanced sulfur cathode host material. The exposure of highly active (111) facets and the abundant selenium vacancies not only provides more active sites but also accelerates the catalytic conversion dynamics and lowers the reaction energy barrier of Li–S batteries.