The Role of Al₂O₃ ALD Coating on Sn‐Based Intermetallic Anodes for Rate Capability and Long‐Term Cycling in Lithium‐Ion Batteries

Abstract The electrochemical performances of CoSn₂ and Ni₃Sn₄ as potential anode materials in lithium‐ion batteries (LIBs) are investigated using varying thicknesses of an alumina layer deposited by the atomic layer deposition (ALD) technique. Rate capability results showed that at high current densities, Al₂O₃‐coated CoSn₂ and Ni₃Sn₄ electrodes after 10‐ALD cycles outperformed uncoated materials. The charge capacities of coated CoSn₂ and Ni₃Sn₄ electrodes are 571 and 134 mAh g⁻¹, respectively, at a high current density of 5 A g⁻¹, while the capacities of uncoated electrodes are 363 and 11 mAh g⁻¹. When the current density is reduced to 1 A g⁻¹, however, the cycling performances of Al₂O₃‐coated CoSn₂ and Ni₃Sn₄ electrodes fade faster after almost 40 cycles than uncoated electrodes. The explanation is found in the composition of the solid‐electrolyte interface (SEI), which strongly depends on the current rate. Thus, X‐ray photoelectron spectroscopy analysis of SEI layers on coated samples cycles at a low current density of 0.1 Ag⁻¹, revealed organic carbonates as major products, which probably have a low ionic conductivity. In contrast, the SEI of coated materials cycled at 5 Ag⁻¹ consists mostly of mixed inorganic/organic fluorine‐rich Al‐F and C‐F species facilitating a higher ionic transport, which improves electrochemical performance.