Lithium-sulfur (Li-S) batteries exhibit a significantly higher theoretical energy density compared to lithium-ion (Li-ion) batteries, with Li-S reaching up to about 500 Wh/kg versus the typical 150-250 Wh/kg range for Li-ion batteries. This higher energy density implies Li-S batteries have the potential to deliver more energy per unit mass, making them attractive for applications demanding high energy storage, such as electric vehicles or large-scale energy storage.
However, when considering overall system efficiency—particularly in practical, real-world use—the situation is nuanced:
- Energy Density vs. Practical Efficiency: While Li-S batteries have a much higher theoretical energy density, their practical energy density can be reduced by factors such as the need for conductive additives (due to sulfur’s poor electrical conductivity) and the volume expansion (~80%) during charge-discharge cycles, which can cause mechanical degradation and capacity loss. These factors lower the effective usable energy density and decrease cycle life.
- Cycle Life and Coulombic Efficiency: Li-ion batteries tend to have higher Coulombic efficiency (up to 99%) and longer cycle life, meaning they retain capacity over many charge-discharge cycles better than Li-S batteries. Li-S batteries suffer from capacity fading mainly due to polysulfide dissolution in the electrolyte, which affects their long-term energy retention and system efficiency.
- System-Level Efficiency Considerations: Although Li-S batteries promise a lighter and potentially cheaper solution with higher theoretical energy density, their system efficiency is currently limited by shorter lifespan, lower cycling stability, and mechanical and chemical challenges. Li-ion batteries, with their mature technology, deliver more consistent, high-efficiency performance over longer periods despite their lower theoretical energy density.
In summary, lithium-sulfur batteries offer superior theoretical energy density and lighter weight, which can translate to higher potential system energy efficiency by weight. However, due to practical challenges like shorter cycle life, capacity fade, and mechanical issues, their overall system efficiency in real-world applications currently lags behind lithium-ion batteries, which maintain higher Coulombic efficiency and better long-term performance. The trade-off is between high theoretical energy density versus proven durable efficiency and longevity.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-the-energy-density-of-lithium-sulfur-batteries-compare-to-lithium-ion-batteries-in-terms-of-overall-system-efficiency/
