Lithium–air battery

The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.

Pairing lithium and ambient oxygen can theoretically lead to electrochemical cells with the highest possible specific energy. Indeed, the theoretical specific energy of a non-aqueous Li–air battery, in the charged state with Li₂O₂ product and excluding the oxygen mass, is ~40.1 MJ/kg = 11.14 kWh/kg of lithium. This is comparable to the theoretical specific energy of gasoline, ~46.8 MJ/kg. In practice, Li–air batteries with a specific energy of ~6.12 MJ/kg = 1.7 kWh/kg of lithium at the cell level have been demonstrated. This is about 5 times greater than that of a commercial lithium-ion battery, and is sufficient to run a 2,000 kg electric vehicle for ~500 km (310 miles) on a single charge using 60 kg of lithium (i.e. 20.4 kWh/100 km). However, the practical power and cycle life of Li–air batteries need significant improvements before they can find a market niche.

Significant electrolyte advances are needed to develop a commercial implementation. Four approaches are being considered: aprotic, aqueous, solid-state and mixed aqueous–aprotic.

A major market driver for batteries is the automotive sector. The energy density of gasoline is approximately 13 kW·h/kg, which corresponds to 1.7 kW·h/kg of energy provided to the wheels after losses. Theoretically, lithium–air can achieve 12 kW·h/kg (43.2 MJ/kg) excluding the oxygen mass. Accounting for the weight of the full battery pack (casing, air channels, lithium substrate), while lithium alone is very light, the energy density is considerably lower.