Exploring hybrid hard carbon/Bi2S3-based negative electrodes for Na-ion batteries

Exploring hybrid hard carbon/Bi2S3-based negative electrodes for Na-ion batteries. Blaž Tratnik, Sergio Aina, Elena Tchernychova, Matej Gabrijelčič, Gregor Mali, Maria Pilar Lobera, Maria Bernechea, Mathieu Morcrette, Alen Vizintin, Robert Dominko. Green Chem., 2024,26, 6089-6099

The study presents a hybrid hard-carbon/nanocrystalline-Bi2S3 material applicable for negative electrodes in sodium-ion batteries. Through a series of comprehensive analyzes, including electrochemical measurements, operando XRD, ex situ solid-state NMR, and high-resolution STEM imaging, the effectiveness of the HC/Bi2S3 hybrid configuration in the negative electrode function is elucidated with a focus on the underlying charge storage mechanism. Electrochemical analysis demonstrates the improved performance of the hybrid materials over the pristine HC negative electrode and highlights the robustness and stability of the HC/Bi2S3 hybrids over prolonged cycling even under high current densities. Here, the final capacities observed after 100 cycles reached a value of 252 mA h g−1, compared to 216 mA h g−1 of pristine HC. Cyclic voltammetry measurements demonstrate a complex charge storage behavior that integrates both surface and diffusion-driven processes at different potentials during reduction and oxidation. A series of phase transformations during cycling observed in operando XRD expose irreversible reactions during the initial cycle between Bi2S3 and sodium ions, such as the breakdown of the Bi2S3 nanocrystal structure. This phenomenon is further confirmed by the detection of Na2S species using ex situ solid-state NMR. High-resolution STEM imaging reveals morphological changes in Bi2S3 nanocrystals and highlights their resistance to pulverization due to their nanoscale dimensions. This work provides comprehensive insights into the electrochemical performance of the HC/Bi2S3 and sheds light on specific mechanisms and reactions occurring during cycling.