A basic Li-O2 battery consists of a metal lithium anode, a separator, an electrolyte, and a cathode.
The benefit of Li-Air battery is potentially high energy density
For EV market, some basic data:
- A maximum volume of 300 L (family car) for the battery and its auxiliary systems.
- A driving range of 500 miles (800 km) requires 125 kWh capacity (at 250 Wh/mile) (reference: DOI: 10.1021/jz1005384 |J. Phys. Chem. Lett. 2010, 1, 2193–2203)
Li-air battery challenges:
- power density, measured in W per kg of battery mass, is currently very low. Discharge current densities is in the order of 1 mA/cm; Higher power needs larger surface area of cathode.
- Clog of cathode pores
- Large overvoltages
- Cyclability
- O2 contaminated by N2 and H2O
- Safety issue: Li metal anode may cause dendrite and shorts. The reaction product of aprotic cells is Li2O2, a strong oxidizer, which can react with organic electrolyte, leading to safety risks
Typical Li-Air battery structures
Anode
Lithium foil is used as an anode
Separator
A 25oum thick glass mat fiber is used as a seperator
Cathode
The cathode needs to be both porous, to allow for oxygen and lithium-ion diffusion, and still electrically conductive. An exemplary composition of the active cathode materials by weight percent were carbon:R-MnO2:PVDF = 54:10:36. A porous cathode constructed from high surface area Super P carbon particles mixed with R-MnO2 nanorods serving as a catalyst. Both are uniformly distributed in PVDF binder and bound to a 1.6 mm-thick metallic nickel foam current collector.
Electrolyte
4 different electrolytes are used in Li-Air batteries with different working principles:
In aprotic electrolyte, the fundamental cathode discharge reactions might be as the following:
or
For aqueous cathode electrolytes, there are two options: acidic or alkaline media. The the reactions are as the following:
Overpotentials
