Insights into the Functional Role of Copper Donors on Phase Transition and NaF-Rich SEI for Fast and Durable Sodium-ion Storage

Abstract

The attractive MoSe₂ anodes face the problems of low conductivity and Se loss. Introducing electron donor has proven effective in enhancing metallic 1T content for improved performance. However, it remains difficult to mitigate the degradation of 1T phase and the loss of active materials, which continues to hinder the cycling stability. Guided by research experience and DFT results, low-valence Cu⁺ atoms were selected as both electron donors and vacancy creators in this work to synergistically address these two challenges. The donated electrons from Cu⁺ to Mo atoms facilitate the phase transition from semi-conducting 2H to metallic 1T in MoSe₂ for accelerated reaction kinetics with a high capacity of 257.0 mAh g^-1 at 50 A g^-1. Meanwhile, the low-valence atoms assisted the formation of accompanying vacancies. The exposed the Cu⁺ donor enhanced the PF₆⁻ adsorption and also catalyze the formation of NaF-rich SEI layer. This effectively mitigated the loss of activity materials and the volume expansion issues, resulting in a high capacity of 364.6 mAh g^-1 (∼124.6% of its original capacity) after 18,000 cycles at 10 A g⁻¹. The insight gained from the doping of low-valence metal atoms offer a promising pathway for the SEI-modulating strategy and also the future development of other type electrode materials.