Lithium-metal batteries are a promising next-generation battery technology due to their potential for significantly higher energy densities compared to current lithium-ion batteries. However, the primary limitation of lithium-metal cells is their short lifespan. Researchers at the University of Science and Technology of China, along with other institutes, recently introduced a groundbreaking electrolyte design that addresses this issue and could lead to highly performing lithium-metal pouch cells with longer lifespans. This innovative electrolyte, presented in a paper in Nature Energy, features a unique nanometer-scale solvation structure that has the potential to accelerate the practical applications of lithium-metal batteries.
One of the major challenges of lithium-metal batteries introduced to date is their limited cycle life of approximately 50 cycles, significantly lower than commercial lithium-ion batteries. The growth of lithium dendrites, high reactivity of lithium-metal, and high-voltage transition metal cathodes contribute to the constant degradation of the electrolyte in lithium-metal cells. Despite extensive efforts by researchers worldwide, the performance of lithium-metal batteries remains unsatisfactory in terms of energy density and cycle life. The instability of the interfaces between electrolyte and electrodes is a key factor in the degradation process.
Approximately five years ago, Prof. Shuhong Jiao and her colleagues developed an electrolyte that can stabilize both the anode-electrolyte and cathode-electrolyte interfaces in lithium-metal battery cells, effectively suppressing electrolyte degradation. Their innovative electrolyte design leverages microscopic physicochemical processes inside lithium-metal batteries to enhance battery performance. By utilizing commercially available and affordable molecules, the research team focused on tuning the solvation structure of the electrolyte at the mesoscopic level. The unique solvation structure of their electrolyte, known as ‘compact ion-pair aggregate (CIPA),’ plays a critical role in promoting battery stability.
The electrolyte introduced by Prof. Jiao and her colleagues features large compact aggregates of lithium-anion ion pairs with coordination bonding, forming the CIPA structure. This design leads to a collective reduction on the lithium-metal anode, where anions in the CIPA structure are rapidly decomposed on the surface of the lithium, creating a thin and stable solid electrolyte interface (SEI). The SEI, rich in inorganic components, suppresses the constant decomposition of the electrolyte and enables homogeneous lithium deposition, reducing specific areas of lithium-metal anode and promoting battery stability.
The novel electrolyte exhibits good oxidative stability and effectively suppresses the dissolution of transition metal elements from the cathode, improving the stability of the cathode interface. The combined stabilization of the lithium-electrolyte interface and the cathode interface results in stable cycling for an extended number of cycles. In initial tests, a 500 Wh/kg lithium-metal pouch cell using the new electrolyte retained 91% of its energy after 130 cycles. The researchers aim to further extend the cycle life of these pouch cells to over 1,000 cycles while exploring battery systems with even higher energy densities.
The recent breakthrough in electrolyte design for lithium-metal batteries opens up new possibilities for enhancing battery performance and extending cycle life. The innovative solvation structure introduced by Prof. Jiao and her team offers a new avenue for electrolyte design in lithium-metal batteries. As researchers worldwide continue to explore the potential of this groundbreaking electrolyte, the advancement of lithium-metal battery technology towards higher energy densities and longer lifespans becomes increasingly promising.
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