Theoretical search for possible Li-Ni-B crystal structures using an adaptive genetic algorithm

The structural diversity of rare-earth and transition metal borides indicates that alkali-transition metal borides (A-T-B) show tremendous promise in exhibiting a variety of crystal structures with different dimensionalities of T-B frameworks. On the other hand, the A-T-B ternary systems are severely underexplored because of the synthetic challenges associated with their preparation. Accurate and efficient computational predictions of low-energy stable and metastable phases can identify the optimal compositions of the hypothetical compounds in the A-T-B systems to guide the synthesis. In this work, we have computationally discovered several new phases in the Li-Ni-B ternary system. The newly discovered LiNiB, Li2Ni3B, and Li2NiB phases expand the existing theoretical database, and the convex-hull surface of Li-Ni-B has been re-constructed. The lowest energy structure of the LiNiB compound has been found by an adaptive genetic algorithm with layered motif, which matches with the experimentally determined structure. According to our electrochemical calculations, LiNiB and another predicted layered Li2NiB compounds have great potential as anode materials for lithium batteries. The Li2Ni3B compound with the space group P4(3)32 was predicted to crystallize in a cubic structure composed of distorted octahedral units of BNi6, which is isostructural to two noncentrosymmetric superconductors Li2Pd3B and Li2Pt3B. While we were unable to experimentally confirm the Li2Ni3B compound utilizing the hydride synthetic route, attempts to synthesize this compound by alternate methods remain highly desirable, considering its potential superconducting properties.