Li-S Cells

Owned by Eric Zhao
Last updated: Nov 27, 2021
3 min read

Fundamental Difference in in the Cathodes:



Li-ion batteries use lithium-doped cobalt oxide in the cathode to store lithium ions [2].

Li-S batteries use Sulfur in the cathode to store lithium ions [3].

*Left to right for discharging, right to left for charging*

 

Lithium-sulfur

Previously:

  • Lithium-Sulfur (Li-S) batteries were sought after because of their theoretically higher energy densities when compared to Li-ion.

  • Lifetime:

    • Less than Li-ion due to dendrite formation in normal use conditions. Lithium does not re-deposit smoothly upon anode, but forms dendrites instead [1].

      • Can cause fires from short-circuiting, then having the electrolyte catch fire

    • Projected # of Cycles:

      • ~50 cycles [1].

      • Small electric vehicles need at least 1000 cycles to be viable [1].

  • Specific Energy: 450 Wh/kg

  • Energy Density: 550 Wh/L

  • Key Issues

Key Issue = Polysulfide "shuttle" effect = Lithium polysulfide Li2Sx is highly soluble in the common electrolytes used for Li–S batteries, resulting in the leakage of sulphur into the anode, forming polysulfides, which grow in chain sizes and shuffle back and forth during cycles. It is possible for this issue to be solved in the future (maybe by 2030) but for current cars, 50 cycles is not enough.

New Findings:

Overview: New advancements in research and industry are making Li-S more competitive, yet they are still not technologically or economically ready.

  • Boron Nitride Nanotubes (BNNTs)

BNNTs are used as nano-insulars in the battery’s cathode to stabilize it and protect it during charge and discharge [2]. BNNTs are advanced nano-materials that have special properties like:

  1. being an electric insulator

  2. withstands temperatures over 900 degrees Celsius

  3. 7X more thermally conductive than copper

Li-S Energy Ltd, a growing Australian company, made Li-S pouch cells that reached 900 charge/discharge cycles at over 60% retained capacity [2]. However, this test was conducted on a single layer of BNNT material. So, more research and development is needed to scale up these cells to use multilayer BNNTs.

  • Li-Nanomesh

The nano-composite mitigates dendrite formation in the battery’s anode. The company’s initial tests have shown that by applying the nanomesh, the cells' cycle count went from only 45 to 1000 cycles with no indication of dendrite growth [2].

Conclusion:

Lithium-sulphur batteries are hypothetically better than their Li-ion counterparts due to its theoretically higher energy density. With more investment of talent and resources into Li-S technologies, previous barriers of short lifespan are being removed. However, the technology is not commercially viable yet, and cells still remain difficult to purchase.

 

References 

[1] Cheaper, lighter and more energy-dense: The promise of lithium-sulphur batteries

[2] https://busycontinent.com/li-s-energy-ipo-to-commercialise-lithium-sulphur-battery-technology/

Research doc: https://docs.google.com/document/d/1G-2JSGkFClgKntsU9nRUn5EJfz5LqiOg_uemWq6tjvE/edit?usp=sharing