Layered Na–Ni–B with Low Volume Expansion for Sodium-Ion Batteries

With the shortage of lithium and growing demand for electrochemical energy storage, finding substitute high-abundance elements to replace lithium has become a vital issue. In our research, a structural search on the Na–Ni–B system has been conducted and two new metastable phases possess the same composition NaNiB2, as well as low-energy phases NaNiB and NiB2 have been found. Notably, C2221-NaNiB2 possesses the lowest formation energy (0.032 eV/atom) above the convex hull and maintains thermodynamic stability with the range of 6–16 GPa, indicating potential synthesis under high pressure. During the desodiation process, C2221-NaNiB2 exhibits a volume change of less than 6%, showing advantages for stability and rate performance. Combined with our previous research on the Li–Ni/Co–B system, the alkali metal-transition metal boride systems appear to offer a facile route toward obtaining stable layered structures. Therefore, C2221-NaNiB2 with high electrical conductivity demonstrates substantial potential for electrode material applications and provides a theoretical basis for experimental synthesis to some extent.