Sulfur electrodes have become cathode materials for lithium batteries with great application potential

In recent years, due to the rise of electric vehicles and smart grids, the energy density of traditional lithium batteries can no longer meet people's needs
.
More and more researchers are beginning to find and study electrode materials
with high energy density.
Among them, sulfur, as the cathode material of lithium battery with the highest specific capacity, has the advantages of low production cost, low toxicity, high capacity and high energy density, which has aroused great research
interest among lithium battery workers.

However, lithium-sulfur batteries also face three unavoidable challenges: (1) the conductivity of sulfur is very low, which greatly reduces the power density and sulfur utilization rate of lithium-sulfur batteries; (2) The dissolution and irreversible reaction of polysulfide intermediates led to the capacity decay of lithium-sulfur batteries; (3) The large volume change caused by sulfur during lithium insertion and delithiumization will destroy the integrity of the sulfur electrode structure and lead to capacity attenuation
.
In response to these three challenges, Professor Wang Chunsheng's research group at the University of Maryland conducted in-depth and meticulous research, which significantly improved the cycle stability and rate performance
of sulfur electrodes.

Among the various methods currently used to improve the electrochemical performance of sulfur electrodes, carbon coating is considered to be one of the
most effective.
At the same time, carbon materials have low production cost, high conductivity, and can inhibit the dissolution of polysulfides and overcome structural damage
caused by volume expansion.
However, it is difficult to avoid the dissolution of polysulfides and achieve long cycle stability
by relying on physical coating alone.
To further address these issues, oxygenated carbon materials were used for the first time to inhibit the dissolution and side reactions
of polysulfides.
Oxygen-containing groups in carbon materials can form chemical bonds with sulfur, thereby stabilizing sulfur electrodes
.
The oxygen-containing carbon-sulfur compound can be stably cycled 2000 times in lithium batteries, and the average weekly charge-discharge cycle capacity loss is only 0.
0045%.

This represents one of
the most stable carbon-sulfur composite cathode materials available.

Over the course of the study, the team found that inserting the carbon-sulfur complex to 0.
6 volts during the first few cycles significantly increased the reversible capacity
of the battery.
This is because deep lithium intercalation can activate sulfur that is originally not electrochemically active, so that sulfur stabilized by sulfur-oxygen bonds produces electrochemical activity
.
This oxygen-containing carbon-sulfur complex also exhibits excellent electrochemical performance
in sodium-sulfur batteries.
Therefore, the results show that carbon-sulfur composites with stable oxygen groups are very promising cathode materials
for lithium batteries and sodium batteries.