A team at the University of Manchester (UK) has developed a doped graphene cathode for highly stable lithium-sulfur batteries. In an open access paper in the Nature journal Communications Chemistry, they report 100% charge capacity of Li-S batteries using the cathode material with 500 charge/discharge cycles at 0.5 C, 1 C, 2 C and 3 C charge rates.

The cathode combines laser-synthesized sulfur (S) and nitrogen- (N-) doped graphene electrodes (without a binder) with molybdenum sulfide (MoS₂) nanoparticle loading.

The N/S doped porous graphene structure enhanced interface adsorption by the production of –SO₂, which suppressed diffusion of polysulfide into the electrolyte through promoting oxygen-containing functional groups chemically bonding with sulfur.

Low electrolyte resistance, interphase contact resistance and charge-transfer resistance accelerate electrons and Li⁺ transport by laser-induced N/S doped graphene.

Lithium sulfur (Li–S) batteries have a very high theoretical specific capacity of 1675 mAh/g and a relatively higher theoretical energy density of 2600 Wh/kg, which offer a potential candidate among various alternatives for the battery of the future. Although energy density of 550–600 Wh/kg is a target for practical Li–S batteries, which is 20% of the theoretical energy density based on mass calculation, this level of energy density has been achieved in commercial Li-ion battery with a LiCoO₂ cathode. Therefore achieving high volumetric energy density of Li–S battery is one of the primary challenges. Low cycle stability is also hindering practical application of Li–S battery. The soluble lithium polysulfide is the key factor of the “shuttle” effect in electrochemical reaction on the sulfur cathode. It induced low cycle stability from the loss of sulfur to electrolyte.

… Here, we show a pulsed UV laser direct writing technique to form S and N doped graphene electrodes with various nanoparticles loading, such as silver, platinum, silicon, and molybdenum sulfide from a specially formulated organic ink with various microparticles. This technique is a one-step fabrication process without a binder to form a current collector for lithium sulfur battery cathodes. The process enables long-term cycles with almost no fading in charge capacities.

—Huang et al.

Resources

• Yihe Huang, Richard Field, Qian Chen, Yudong Peng, Monika S. Walczak, Hu Zhao, Guangyu Zhu, Zhu Liu & Lin Li (2019) “Laser induced molybdenum sulphide loading on doped graphene cathode for highly stable lithium sulphur battery” Communications Chemistry volume 2, Article number: 138 doi: 10.1038/s42004-019-0240-2