The use of lithium metal as an anode in the rechargeable Li-ion battery is a promising development. It offers a high theoretical specific capacity, long cycle life and excellent energy density. However, it is limited in its reactivity. Various solutions have been developed to mitigate the reactivity of lithium metal anodes including: pyrophoric coating with CO2, polymer solid electrolyte interphase (SEI), and alkali metal ions.
The reactivity of lithium metal anodes in the current Li-ion battery design is an important concern in the development of portable electronic devices. The reactivity of lithium anodes leads to unstable solid electrolyte interphases (SEIs), runaway reactions, and instabilities in the electrode film resulting in poor performance.
One approach to stabilize the reactivity of lithium metal is to coat the metal powder with a wax layer that provides a continuous protective barrier against the reactivity of lithium metal. A wax-coated lithium powder with a thin and dense LiF passivation layer has been described as a possible solution to this problem.
A wax-coated lithium powder may be coated by dispersing the lithium metal powder in a solvent, then contacting the dispersed lithium metal powder with a wax at a temperature above the melting point of the lithium. Suitable waxes include natural waxes such as 12-hydroxystearic acid, synthetic waxes such as low molecular weight polyethylene, petroleum waxes such as paraffin oil, microcrystalline waxes and the like.
Wax-coated lithium powder is stable in solvents such as N-methyl-2-pyrrolidone and gamma-butyrolactone commonly used as the electrolyte solvents in the rechargeable Li-ion battery industry. The wax-coated lithium powder also has an improved storage life in these solvents as compared to CO2-passivated lithium metal powder.