Solid

Jul 11, 2023

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Researchers from the University of Bayreuth, Germany, with partners from China, have made a significant breakthrough in battery technology. Using an innovative nitrate-based additive, they have successfully developed a new solid-state lithium-metal battery that is both stable and potentially long-lasting. This, the research team stresses, underscores the importance of molecular design in creating effective additives for quasi-solid-state electrolytes.

Professor Doctor Francesco Ciucci, Chair of Electrode Design for Electrochemical Energy Systems at the University of Bayreuth, collaborated with research partners from China to resolve incompatibility issues between lithium nitrate and 1,3-dioxolane (DOL) in quasi-solid battery electrolytes by integrating a novel nitrate-based additive. This is a significant development as, in the past, such incompatibility issues made such batteries very difficult to create or scale to production.

The team's discovery now enables the development of solid-state lithium metal batteries that are highly safe, durable, and easy to produce while maintaining the manufacturing methods used for conventional liquid batteries.

In their experiments, they tried making different versions of these batteries and found that a particular type, the lithium-sulfur (Li-S) cell, performed especially well. Li-S batteries have the potential for very high energy density. This means they can store a lot of energy for their weight, which is especially valuable for applications like aviation or electric vehicles where weight matters. Apart from the high energy density, sulfur is abundant and cheap, which could make Li-S batteries more cost-effective compared to other battery technologies if the technical challenges are addressed.

Prof. Dr. Francesco Ciucci et al, 2023.

But, until now, Li-S cells have suffered from poor cycle life and stability.

"The batteries' solid-state nature ensures a high level of safety while their manufacturing remains straightforward," explained Prof. Ciucci. "We demonstrated the approach's universality by creating various types of lithium-metal batteries. Notably, the manufactured pouch Li-S cell exhibits superior performance compared to previously documented pouch Li-S cells," he added.

Professor Ciucci and his research team introduced a new additive, triethylene glycol dinitrate, which is specifically designed to enable the polymerization of DOL. The research team showed that concomitant with polymerization, forming a nitrogen-rich solid electrolyte interphase layer suppresses detrimental parasitic reactions and increases the battery's efficiency.

Based on the study findings, several battery cells were developed. Among them, lab-scale, button-type cells could be charged and discharged more than 2,000 times. A 1.7 Ah Li-S pouch cell with a high energy density of 304 Wh kg-1 and stable cycling was also fabricated.

This discovery is a big step forward in battery technology. It shows the importance of designing molecules correctly to make better batteries. "This study underscores the importance of molecular structure design in creating effective additives for quasi-solid-state electrolytes. It represents a significant advancement in the practical feasibility of employing poly-DOL-based quasi-solid-state electrolytes in lithium metal batteries," explained Prof. Ciucci.

You can view the study for yourself in the journal Energy & Environmental Science.

Study abstract:

The in situ polymerization of quasi-solid-state electrolytes (QSSEs) is emerging as a promising approach for [developing] scalable, safe, and high-performance quasi-solid-state lithium–metal batteries. In this context, poly-DOL-based electrolytes are particularly attractive due to their wide electrochemical window and strong compatibility with lithium metal. To enhance the stability of lithium metal, LiNO3 is frequently added as it creates an effective Li3N-rich solid electrolyte interphase on the surface of the lithium metal anode. However, LiNO3 prevents DOL's ring-opening polymerization, making the two compounds incompatible. To address this issue, this work develops triethylene glycol dinitrate (TEGDN), a novel nitrate-based additive, to replace LiNO3. Like LiNO3, TEGDN forms a dense, nitrogen-rich solid electrolyte interphase on the surface of lithium, protecting it from parasitic reactions. However, unlike LiNO3, TEGDN does not interfere with the polymerization of DOL, allowing the fabrication of a highly effective electrolyte that delivers an ionic conductivity of 2.87 mS cm−1 and an oxidation stability potential of 4.28 V at room temperature. To demonstrate the viability of this approach, a Li|LiFePO4 coin-type cell cycling stably more than 2000 times at 1C is fabricated. In addition, a 1.7 A h pouch-type lithium-sulfur cell with an initial specific energy of 304 W h kg−1 and a capacity retention of 79.9% after 50 cycles is prepared. In short, the present study proposed a new additive to resolve poly-DOL and LiNO3 incompatibility for the first time developing in situ polymerized quasi-solid-state batteries that exhibit remarkable capacity and stability by forming an N-rich solid electrolyte interphase.