Bismuth telluride anode boosting highly reversible electrochemical activity for potassium storage

Abstract

To ensure high capacity with reasonable cycling stability using the conversion or K-alloy reaction, the anode should minimize or embrace the volume expansion during the discharge (potassiation) and charge (depotassiation) processes. Herein, we report on a Bi2Te3 composite modified by nanosized carbon that boosts the highly reversible capacity with long cycling stability. The as-synthesized Bi2Te3 powders and acetylene black carbon were compositized via high-energy ball-milling, resulting in improvement of the electrical conductivity to ∼10−4 S cm−1 from ∼10−7 S cm−1. Electrochemical investigation revealed that the proposed Bi2Te3@C retained over 79.8% of its initial capacity (311 mAh g− 1) for 500 cycles at a current of 1000 mA g− 1. We unveil the reaction chemistry behind the acceptable performance using operando X-ray diffraction, X-ray absorption near edge structure spectroscopy, and time-of-flight secondary-ion mass spectrometry. The Bi2Te3 undergoes a conversion reaction to form Bi0 metal and K2Te as a conversion byproduct, after which Bi is further potassiated to K3Bi. The highly reversible behavior is attributed to the enlargement of the active area along with the filling of voids among Bi2Te3 particles by nanosized carbons in the composite electrode, enabling not only facile electron transport but also preservation of the electrode shape even after long-term cycling. Our approach highlights the feasibility of applying Bi2Te3@C as a sustainable anode material for potassium-ion batteries.