Dual-functionality of CZTS nanoflakes: as an anode material for lithium-ion batteries and as a counter electrode in DSSCs – a DFT and experimental investigation†

This research work aims to develop a new dual-functional electrode material suitable for both lithium-ion batteries (LIBs) and dye-sensitized solar cells (DSSCs). Nanostructured Cu₂ZnSnS₄ (CZTS) was synthesized through the solvothermal method. Structural properties analysed through the X-ray diffraction pattern (XRD) and Raman spectra reveal the formation of the CZTS with kesterite structure . The stoichiometry and the oxidation states of CZTS have been analyzed using X-ray photoelectron spectroscopy (XPS). The core level XPS spectra of Cu 2p, Zn 2p, Sn 3d, and S 2p confirm the presence of the constituent elements in the required oxidation states (Cu⁺, Zn²⁺, Sn⁴⁺, S²⁻). The surface morphology of the CZTS nanoparticles showed a nanoflake-like structure with a surface area of 34.20 m² g⁻¹. The geometrical optimization, electronic, and optical properties were calculated using DFT calculations. The semiconducting material CZTS is electrochemically active toward Li, which can be used as an alternative anode material for lithium-ion batteries offering potential improvements in cycling stability and specific capacity. The electrochemical studies of the CZTS nanoflakes exhibited a specific capacity of 1141.08 mA h g⁻¹ and 350 mA h g⁻¹ at 0.1C and 1C rates respectively. The cycling stability of CZTS at a high scan rate of 1C, and the specific capacity of 220 mA h g⁻¹ over 70 cycles with 73% coulombic efficiency, suggest it to be a promising alternative anode material in the next-generation lithium-ion batteries. The performance of CZTS as a counter electrode in dye-sensitized solar cells was also explored. The DSSC constructed with CZTS as the counter electrode showed an efficiency of 5.9%.