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

The interface between electrodes and electrolytes largely contributes to the efficiency with which batteries convert energy. In recent years, many efforts aimed at developing better performing batteries have focused on tailoring the electrode/electrolyte interface to boost the energy density of rechargeable batteries, particularly lithium-metal batteries (LMBs).

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

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

A possible solution to overcome this key limitation of LMBs is to regulate the Li⁺ solvation structure and design new electrolytes to facilitate the formation of the solid-electrolyte interphase (SEI) and stabilize the electrode/electrolyte interface. While many studies have been focusing on these goals, very few explored how the dielectric environment in batteries contributes to stabilizing/de-stabilizing this interface.

Researchers at Zhejiang University and other institutes in China recently carried out a study exploring this research question. Their paper, published in Nature Energy, outlines a dielectric protocol that could help to address some of the issues associated with LMBs, potentially enhancing their safety and reliability.

“As the electric vehicle and energy storage markets continue to grow, the demand for LIBs will keep increasing,” Xiulin Fan, co-author of the paper, told TechXplore. “However, to achieve a low-carbon or carbon-free economy, we need batteries that perform better than current LIBs. This calls for an energy storage technology with the energy density that is higher than 500 Wh/kg, which could power electric devices much longer on a single charge compared to LIBs. Lithium metal batteries (LMBs) with metal electrodes instead of graphite electrodes have caught our attention, yet these batteries face premature death issues both in the laboratory and industry. Our main objective was thus to develop long-lasting and high-energy-density LMBs.”

The approach to designing LMBs introduced 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 batteries, their protocol ensures the integrity of cation-anion coordination, enabling the formation of the SEI from the exposure of the anion-rich electrolyte to an interfacial electric field.

“The dielectric protocol requires the cation-anion pairs to 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,” explained Fan. “This forms an anion-rich region near the electrode-electrolyte interface. Such an interfacial configuration can prioritize the anion decomposition at the interface, thereby imparting robust interfacial chemistry to Li deposits in Li-metal pouch cells.”

“At charged interfaces, cation–anion pairs arrange in a periodic oscillatory distribution,” wrote Zhang, Li and their colleagues. “A low-oscillation amplitude exacerbates the electrolyte decomposition and increases surface impedance. We propose a dielectric protocol that maintains cation–anion coordination with a high oscillation amplitude at the interfaces, addressing these issues.”

Using their newly proposed protocol, the team realized an ultra-lean electrolyte (1 g Ah⁻¹), which they tested in lithium-metal pouch cells. The resulting pouch cells were found to exhibit 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,” said Fan. “This allows us to adjust the interfacial properties by tailoring the electrolyte composition, which can improve battery performance.”

Other research groups could soon draw inspiration from 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 Li-metal batteries can lead to serious safety hazards like fires and explosions,” added Fan. “Our future work aims to enhance the cycle stability of Li-metal batteries under realistic conditions to achieve an energy storage technology that combines both high energy density and safety.”

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