Recently, researchers at the Sustainable Power and Energy Center of the University of California, San Diego, published their findings in Nature where they introduced a novel cathode material for solid-state lithium-sulfur batteries. This material exhibits high conductivity and structural reparability, overcoming the limitations of traditional sulfur cathodes. This advancement holds promise in bringing lithium-sulfur batteries closer to industrial application.
Solid-state lithium-sulfur batteries, composed of a solid electrolyte, a lithium metal anode, and a sulfur cathode, are rechargeable batteries. Due to their higher energy density and lower cost, they are poised to become alternatives to conventional lithium-ion batteries.
These batteries store twice as much energy per kilogram as lithium-ion batteries. This means they could double the range of electric vehicles without increasing the weight of the battery pack. Moreover, their abundant and readily available source materials make them an economically viable and environmentally friendly option.
However, the characteristics of sulfur cathodes have hindered the development of solid-state lithium-sulfur batteries. Sulfur is not only a poor electronic conductor, but sulfur cathodes also undergo significant expansion and contraction during charge and discharge cycles, leading to structural damage and weakened contact with the solid electrolyte.
These issues diminish the cathode's ability to transfer charges, affecting the overall performance and lifespan of solid-state batteries.
The novel cathode material developed by the research team consists of crystals composed of sulfur and iodine. By introducing iodine molecules into the sulfur crystal structure, they increased the conductivity of the cathode material by 11 orders of magnitude, or 100 billion times, compared to crystals made solely of sulfur.
On the other hand, since iodine disrupts the intermolecular bonds holding sulfur molecules together, the damage is just enough to lower the melting point of this new crystal material to a mere 65 degrees Celsius. As a result, after charging the battery, repairing the damaged interface during cycling is as easy as remelting the cathode.
This capability is crucial for addressing the accumulated damage at the cathode-electrolyte interface due to repeated charge and discharge cycles.
To validate the effectiveness of this novel cathode material, the researchers constructed a test battery and subjected it to repeated charge and discharge cycles. The battery remained stable over more than 400 cycles and retained 87% of its capacity.
This iodine-doped sulfur cathode offers a unique concept for overcoming the main barrier to the commercialization of solid-state lithium-sulfur batteries. The team notes that the low melting point of the novel cathode material enables interface repair, making it a potential enabling solution for high-energy-density solid-state batteries.
"This discovery has the potential to address one of the major challenges introduced by solid-state lithium-sulfur batteries by significantly extending the battery's lifespan," says co-author Christopher Brooks, Chief Scientist at Honda Research Institute USA. "The battery can self-repair simply by raising the temperature, which could significantly prolong the entire lifecycle of the battery, creating potential pathways for practical applications of solid-state batteries."
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