Intercalation of hexagonal boron nitride and graphite with lithium by sequential process of ball milling and heat treatment

Recently, intercalation compounds with various intercalants between hexagonal boron nitride (h-BN) layers have been studied, where lithium BN intercalation compound (Li-BNIC) is one of such compounds successfully synthesized. They are expected to exhibit similar properties to lithium graphite intercalation compounds (Li-GICs) that are known as the anode material for lithium ion batteries. It is difficult, however, to apply Li-BNIC for the batteries due to its returning to an insulator when Li is deintercalated. In this study a Li-BN-graphite ternary system has been focused because it is reported that graphite-like BC2N is a promising material for rechargeable Li batteries. The primary purpose of this study is thus to investigate combined reactivity of BN and graphite with Li through milling and heating processes, and possible intercalation of Li into the matrix: h-BN, graphite or BCN. The pieces of lithium metal, h-BN and graphite powders were ball-milled using a vibratory ball-mill machine and heat-treated at 700 °C for 2 h under argon atmosphere. The samples were then characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, 7Li nuclear magnetic resonance and Differential thermal analysis study. Li-GICs were mainly produced by milling, while post-annealing caused their eliminations and instead produced Li-BNICs with small amount of other lithium compounds. In terms of thermal stability, Li-BNIC is more stable than Li-GICs. In a Li-BN-graphite system, an activation energy of Li-BNIC was estimated to be 119.6 kJ/mol, which is higher than reported activation energies for Li-GICs.