Lithium–sulfur battery
| Specific energy | 500 W·h/kg demonstrated |
|---|---|
| Energy density | 350 W·h/L |
| Charge/discharge efficiency | C/5 nominal |
| Cycle durability | disputed |
| Nominal cell voltage | cell voltage varies nonlinearly in the range 2.5–1.7 V during discharge; batteries often packaged for 3 V |
The lithium–sulfur battery (Li–S battery) is a type of rechargeable battery, notable for its high specific energy. The low atomic weight of lithium and moderate weight of sulfur means that Li–S batteries are relatively light (about the density of water). They were used on the longest and highest-altitude solar-powered aeroplane flight in August 2008.
Lithium–sulfur batteries may succeed lithium-ion cells because of their higher energy density and reduced cost from the use of sulfur. Currently the best Li–S batteries offer specific energies on the order of 500 W·h/kg, significantly better than most lithium-ion batteries which are in the 150 to 200 range. Li–S batteries with up to 1,500 charge and discharge cycles have been demonstrated. As of early 2014, none were commercially available. The key issue of Li–S battery is low electrical conductivity of sulfur cathode needing an extra mass for a conducting agent and the current research focus is to find highly conductive cathodes.
Chemical processes in the Li–S cell include lithium dissolution from the anode surface (and incorporation into alkali metal polysulfide salts) during discharge, and reverse lithium plating to the anode while charging. This contrasts with conventional lithium-ion cells, where the lithium ions are intercalated in the anode and cathodes. Each sulfur atom can host two lithium ions. Typically, lithium-ion batteries accommodate only 0.5–0.7 lithium ions per host atom. Consequently, Li-S allows for a much higher lithium storage density. Polysulfides are reduced on the cathode surface in sequence while the cell is discharging:
Across a porous diffusion separator, sulfur polymers form at the cathode as the cell charges:
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