As a well-known graphite-like material in superconductivity, lithium borocarbide (LiBC) can also be utilized as an electrode material in Li-ion batteries with a high specific capacity, which is assigned to the B–B bond produced through the aqueous reaction or the initial charge process. In this work, a rod-like LiBC sample (Ti-LiBC) is synthesized with the precursors of LiH + B + graphite in a sealed Ti tube through high-temperature sintering. Compared with the normal SUS-LiBC sintered in a sealed SUS304 tube, the Ti-LiBC possesses a lot of B–B bonds and a strong EPR signal, and it delivers a higher specific capacity (ca. 500 mAh g–1 at a mean discharge and charge potentials of 0.85 and 1.89 V, respectively) with excellent rate and cycle performances. Actually, the Ti metal can react with the H2 gas to produce the TiH2 phase at a high temperature, of which the extent determines the morphology of LiBC product, and the substitution of Li metal for LiH as the precursor can also result in the rod-like structure and the high specific capacity. Therefore, a hydrogen-free atmosphere is the key to synthesizing rodlike LiBC with excellent electrochemical properties, and this strategy might be extended to other graphite-like materials.
As a graphite-like material, the LiBC can deliver a high capacity up to 500 mA h g–1 in Li-ion batteries, which is dependent on the carbon precursor, the high-temperature treatment, and the lithium insufficiency. However, the underlying mechanism is still not clear for the electrochemical reactions of LiBC. In this work, the pristine LiBC was reacted with aqueous solutions of different alkalinity, which was delithiated chemically and retained the layered structure. According to the XPS and NMR results, the B–B bond might be produced through the aqueous reaction or the initial charge process, which can be oxidized (charged) and reduced (discharged) in the electrochemical measurements. In the Li-ion battery, the reversible capacity of LiBC increases evidently with the alkalinity of aqueous solution and significantly rises to a similar value of ca. 285 mA h g–1 under 200 cycles. Therefore, the specific capacity of LiBC should be contributed by the active sites of B–B bonds, which can be significantly increased through the reaction with the hydroxyl ions, and this strategy might be adopted to activate more graphite-like materials.
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