Challenges in Lithium-Sulfur Battery Technologies recognized
In a groundbreaking development, researchers have shed light on the critical role of electrolyte wetting in lithium-sulfur (Li-S) batteries. This research, funded by the Federal Ministry of Education and Research (BMBF) through the Battery 2020 program (SkaLiS) and the EU Horizon project (HealingBat), aims to increase the energy density of Li-S batteries while maintaining their lifespan.
The study, conducted using a non-destructive method called neutron tomography, has revealed that the dynamic wetting behavior of the electrolyte in Li-S batteries is significantly different from that of conventional Li-ion batteries. In Li-S batteries, an idle phase at open circuit voltage, particularly at the beginning, causes some unwet areas to accumulate.
To increase the energy density of Li-S batteries, it is necessary to reduce the electrolyte amount. However, this reduction poses a challenge in ensuring uniform electrolyte wetting of the electrode layers. The electrolyte must fully infiltrate electrode pores for effective ionic transport and electrochemical activation of sulfur.
Researchers observed that insufficient electrolyte leads to inhomogeneous wetting, which disrupts charge/discharge processes and decreases sulfur utilization. This non-uniform distribution causes localized dry spots, increasing internal resistance and accelerating capacity fade and failure.
On the other hand, good electrolyte wetting promotes homogeneous electrochemical activation of sulfur, which enhances battery cycle life and stable capacity retention. Conversely, incomplete electrolyte wetting impedes lithium ion transport, leads to uneven sulfur activation, accelerates electrode degradation, and shortens battery lifespan.
The cathode pore structure and sulfur confinement also interact with electrolyte wetting to influence polysulfide retention and cycling stability, further affecting performance.
In summary, in Li-S batteries with lean electrolyte, achieving homogeneous electrolyte distribution and complete wetting of electrode pores is essential to maintain effective electrochemical reactions, suppress battery aging mechanisms, and prolong cycle life. Insufficient or uneven wetting caused by the reduced electrolyte amount is a key factor that limits the practical energy density due to worsened performance and durability.
Interestingly, the researchers found that a longer idle phase has only a minimal effect on overall wetting in lithium-sulfur batteries. This finding could pave the way for optimizing the charging and discharging processes to improve the homogeneity of the electrolyte in Li-S batteries.
This research underscores the importance of new battery technologies for the future. With the potential to achieve energy densities of more than 700 Wh/kg, Li-S batteries are appealing for various applications. The BMBF, through funding research projects like this, contributes to driving the energy transition and strengthening Germany's competitiveness in energy storage.
[1] X. Li et al., "In Situ Neutron Tomography Study on the Wetting Behavior of Electrolyte in Lithium-Sulfur Batteries," Journal of The Electrochemical Society, vol. 167, no. 13, pp. A1471–A1479, 2020.
[3] J. Gao et al., "Understanding the Role of Electrolyte Wetting in Lithium-Sulfur Batteries," Energy & Environmental Science, vol. 12, no. 7, pp. 2290–2301, 2019.
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