Advanced Electrolyte Design for High-Energy Batteries with Li Metal and Micro-sized Silicon Anodes

To tackle the increasing environmental deterioration, the electrification of modern society needs to be fulfilled with low-cost, safe, and high-energy batteries. Lithium (Li) metal and silicon (Si) represent the ideal materials to upgrade the conventional carbonaceous anodes due to their high theoretical specific capacities (3860 mAh g^-1 of Li and 3579 mAh g^-1 of Si vs. 372 mAh g^-1 of graphite) and low electrochemical potentials (-3.04 V of Li and -2.74V of Si vs. SHE). However, extreme challenges have been put forward for effective electrolyte design to maximize the energy efficiency of these high-energy materials. The solid-electrolyte interphase (SEI) formed in the conventional carbonate electrolytes is organic-rich and unstable when facing the volume change during the charge/discharge of Li metal and Si anodes. Therefore, new electrolyte design strategies and advancements are in urgent demand to promote robust, inorganic interphases for high energy efficiency on these promising materials.<br/><br/>We present here cutting-edge electrolyte design principles considering all aspects of chemical, electrochemical, and material science, which govern the interphase formation process on both high-energy Li metal and micro-sized Si anodes and facilitate LiF SEI for long-term cell cycle performance. [1-3] We first propose an electrolyte strategy through solvent design from a synthetic chemistry perspective, promoting anion reduction, and suppressing solvent degradation, which enables high reversibility on both Li metal [1] and micro-sized Si anodes. [2] Our study further indicates that when solvent reduction is inevitable, the reductive products of the solvent should be controlled for high-modulus inorganic components, for example, Li₂O formation from sulfolane reduction, and the formation of polymerized organic ingredients need to be minimized. [3] The aggregated solvation originating from synthetic solvent design will also play a big role in the interphase formation process, therefore, both solvent stability (vs. anion stability) and solvation between Li⁺ cation and solvent/anion in the electrolytes are important driving forces for effective LiF SEI formation. By leveraging the reductive priority between the solvents and anions, we demonstrate an effective inorganic interphase (LiF or Li₂O) formation over a wide voltage range in different electrolytes. New records of cycle performance were achieved in both anode-free Cu||NCA lithium metal cells [1] and Si||NMC811 full cells using micro-sized Si anodes. [2-3]<br/><br/>In summary, we showed the potential of synthetic strategies for advanced electrolyte development, which represents a powerful tool for next-generation high-energy batteries. The successful utilization of micro-sized Si anodes with simple electrolyte innovation demonstrates great promise for cost-effective, high-energy batteries with improved safety.<br/><br/><b>Acknowledgment</b><br/>This work was supported by the U.S. Department of Energy (DOE) under award numbers DEEE0009183 and DE-EE0008202 at the University of Maryland, College Park (UMCP).<br/><br/><b>Reference</b><br/>[1] A.-M. Li, O. Borodin, T. P. Pollard, W. Zhang, N. Zhang, S. Tan, F. Chen, C. Jayawardana, B. L. Lucht, E. Hu, X.-Q. Yang, and C. Wang. Methylation enables the use of fluorine-free ether electrolytes in high-voltage lithium metal batteries. <i>Nature Chemistry</i>, 2024, <b>16</b>(6), 922-929.<br/>[2] A.-M. Li, Z. Wang, T. Lee, N. Zhang, T. Liu, W. Zhang, C. Jayawardana, M. Yeddala, B. L. Lucht, and C. Wang. Asymmetric electrolyte design for high-energy lithium-ion batteries with micro-sized alloying anodes. <i>Nature Energy</i>, 2024, 1-10.<br/>[3] A.-M. Li, Z. Wang, T. P. Pollard, W. Zhang, S. Tan, T. Liu, C. Jayawardana, S.-C. Liou, J. Rao, B. L. Lucht, E. Hu, X.-Q. Yang, O. Borodin, and C. Wang. High voltage electrolytes for lithium-ion batteries with micro-sized silicon anodes. <i>Nature Communications</i>, 2024, <b>15</b>(1), 1206.