Dielectric protocol leads to high energy density in Li-metal pouch cells

The interface between electrodes and electrolytes contributes greatly to the efficiency with which batteries convert energy. In recent years, many efforts to develop higher-performance batteries have focused on tailoring the electrode/electrolyte interface to increase the energy density of rechargeable batteries, particularly lithium-metal hydride (LMB).

LMBs are promising battery solutions that incorporate Li metal anodes, instead of the graphite-based anodes typically used by lithium-ion (LiB) batteries. Compared to LiBs, these batteries could feature significantly higher energy densities and faster charging speeds.

However, many LMBs developed so far have significant limitations, such as high manufacturing costs, low Coulomb efficiency, and the growth of Li dendrites during charging. Li dendrites are tree-like structures based on Li metal that can form on the surface of anodes during battery charging, increasing the risk of overheating and potential fires, while reducing the performance of a battery.

A possible solution to overcome this key limitation of LMBs is to regulate the Li⁺ solvation structure and design of novel electrolytes to facilitate the formation of the solid electrolyte interphase (SEI) and stabilize the electrode/electrolyte interface. Although many studies have focused on these objectives, very few have explored how the dielectric environment of batteries contributes to stabilize/destabilize this interface.

Researchers from Zhejiang University and other institutes in China recently conducted a study exploring this research question. Their paper, published in Natural energydescribes a dielectric protocol that could help address some of the issues associated with LMBs, potentially improving their safety and reliability.

“As the electric vehicle and energy storage markets continue to grow, the demand for lithium-ion batteries will continue to increase,” Xiulin Fan, co-author of the study, told TechXplore. “However, to achieve a low-carbon or carbon-free economy, we need batteries that perform better than current lithium-ion batteries. This requires energy storage technology with an energy density greater than 500 Wh/kg, which could power electrical devices for much longer on a single charge compared to lithium-ion batteries. Lithium-ion metal batteries (LMBs) with metal electrodes instead of graphite electrodes have caught our attention, but these batteries face premature death issues both in the laboratory and in industry. Therefore, our main goal was to develop durable and high-energy-density lithium-ion metal batteries.”

The LMB design approach presented in the researchers’ paper considers the effects of the interfacial electric field, which can be modulated via a battery’s dielectrics, on the electrode/electrolyte interphase. By regulating the dielectric medium used in the batteries, their protocol ensures the integrity of the cation-anion coordination, allowing the formation of the SEI from the exposure of the anion-rich electrolyte to an interfacial electric field.

“The dielectric protocol requires that the cation-anion pairs be placed in a non-solvating solvent with a high dielectric constant, which can protect the cation-anion pairs from dissociation by the electric field,” Fan explained. “This forms an anion-rich region near the electrode-electrolyte interface. Such an interface configuration can prioritize the decomposition of anions at the interface, thus imparting robust interface chemistry to Li deposition in Li-metal pouch cells.”

“At charged interfaces, cation-anion pairs organize into a periodic oscillatory distribution,” Zhang, Li, and colleagues wrote. “A low oscillation amplitude exacerbates electrolyte decomposition and increases surface impedance. We propose a dielectric protocol that maintains cation-anion coordination with a high oscillation amplitude at interfaces, which overcomes these problems.”

Using their newly proposed protocol, the team achieved an ultra-lean electrolyte (1 g Ah⁻¹), which they tested in lithium-metal pouch cells. The resulting pouch cells were found to have a remarkable energy density of 500 Wh kg⁻¹ .

“This work reveals the spatial distribution of anions and cations on the charged electrode-electrolyte interface,” Fan said. “This allows us to tune the interfacial properties by tailoring the electrolyte composition, which can improve battery performance.”

Other research groups may soon be inspired by this research team’s dielectric-mediated approach to prepare other promising electrolytes for LMBs. Collectively, these efforts could contribute to the development of more reliable high-density battery solutions.

“The high energy density of lithium-metal batteries can lead to serious safety risks, such as fires and explosions,” Fan added. “Our future work aims to improve the cycle stability of lithium-metal batteries under realistic conditions to achieve an energy storage technology that combines both high energy density and improved safety.”

© 2024 Science X Network