Carbons prepared from boron-containing polymers as host materials for lithium insertion

Electrochemical lithium insertion behavior of boron-containing carbons was studied by constant-current potentiometry. The boron-containing carbons were prepared by pyrolyzing a phenolic resin chemically bonded with boron atoms, which was synthesized via an esterification reaction of the phenol hydroxyl groups by boric acid. It was found that the as-prepared boron-containing carbons at pyrolysis temperatures higher than 700 °C could accommodate more lithium species than the corresponding boron-free carbon, yet those prepared at pyrolysis temperatures lower than 700 °C accommodated less lithium than the boron-free control sample. In particular, the boron-containing carbon prepared at 900 °C exhibited a capacity higher than the theoretical value of graphite and reasonable charge/discharge voltage curves. The elemental, X-ray diffractometric and X-ray photoelectron spectroscopic analysis results indicated that at the pyrolysis temperature of 500 °C, the lithium accommodation capacity of the pyrolytic carbon was mainly dependent on its residual hydrogen content, rather than the boron content. However, when pyrolyzed at 900 °C, more boron atoms were bonded with carbon atoms and introduced to the graphene microcrystallite structure. Therefore, boron atoms exerted a considerable effect on the lithium insertion behavior and more lithium species were reversibly inserted into the carbon matrix due to the electron-deficient nature of boron atoms.