Lithium–sulfur Battery - Chemistry

Chemistry

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. 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:

S
8 → Li
2S
8 → Li
2S
6 → Li
2S
4 → Li
2S
3

Across a porous diffusion separator, sulfur polymers form at the cathode as the cell charges:

Li
2S → Li
2S
2 → Li
2S
3 → Li
2S
4 → Li
2S
6 → Li
2S
8 → S
8

These reactions are analogous to those in the sodium–sulfur battery.

Most use a carbon/sulfur cathode and a lithium anode. Sulfur is very cheap, but lacks electroconductivity. Sulfur alone is 5*10−30 S cm−1 at 25°C. A carbon coating provides the missing electroconductivity. Carbon nanofibers provide an effective electron conduction path and structural integrity, at the disadvantage of higher cost.

Each sulfur atom can host two lithium ions. Typically, lithium-ion batteries accommodate only 0.5–0.7 lithium ions per host atom.

Read more about this topic:  Lithium–sulfur Battery

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