Identifying the tri-roles of anion vacancy on improving K-ion storage

Abstract

Anion vacancy engineering (AVE) is an emerging strategy to improve K-ion storage of conversion-type anode materials, despite its intensive application in Li/Na-ion batteries. The existing mechanisms of AVE's effects mainly focus on charge transfer but fail to clarify other critical issues. Here, we propose a new insight into AVE's effect on K-ion storage by introducing Te vacancies into a representative conversion-type NiTe. In addition to existing mechanisms, we demonstrate Te vacancies play three other unprecedented roles. (1) Te vacancies minimize the intrinsic volume strain from 15% to 6%, significantly suppressing anode pulverization and element dissolution. (2) Te vacancies induce the in-situ formation of a thin yet robust KF-based inorganic-rich solid electrolyte interphase, further accommodating volume strain and element dissolution. (3) Te vacancies reduce Ni-Te bond lengths and promote K-ion diffusion by modulating local atomic structure. Therefore, NiTe_1−x delivers an outstanding cycling performance (229.5 mAh g⁻¹ at 3.0 A g⁻¹ for 1350 cycles) and rate capability (171.7 mAh g⁻¹ at 5.0 A g⁻¹). Furthermore, NiTe_1−x-based full cells showcase a remarkable energy density of 200.4 Wh kg⁻¹. This work comprehensively elucidates the AVE's effects on alkali-ion storage, promoting the development of advanced conversion-type anode materials for practical applications.