Synthesis and Electrochemical Characterization of Novel Electrolyte Additives for High Performance in Lithium-Ion Batteries with Si-Based Anodes

Abstract

Silicon is a promising active material for the anode in lithium-ion batteries (LIB), since it enables much higher energy densities than graphite - the state-of the art material for LIB-anodes. However, the utilization of silicon brings many challenges, which originate mainly from the enormous volume change between the lithiated and delithiated state (300%). One of the consequences is a constant re-formation of the solid electrolyte interphase (SEI), which is accompanied by a loss of active Li+. This leads to a strong capacity fading, which results in a very short cycle life. [1]An efficient and economical approach to tackle these problems is the utilization of additives in the electrolyte. Additives are small molecules or salts that decompose during the first cycles of the battery life resulting in an interphase with modified composition and thereby an improved SEI. Depending on the additive the SEI can reduce the impedance of the cell and help to maintain the structural stability of the anode. [2]In this work four new additives were synthesized and electrochemically tested with a silicon-based anode. Improvements regarding capacity retention were found for all additives in half-cell measurements. Hence, after 500 cycles additive 1 showed a 26 % increased capacity retention, while additive 4 induced an improvement of 43 % compared to the base electrolyte. Electrochemical impedance measurements were conducted and simulated directly after the formation as well as after 100 cycles. The resistance of the first semi-circle showed a reduction of 40 % and 26 % after formation and 100 cycles respectively, when the additive 1 is used. The second semi-circle showed no significant change after formation, but a 27 % reduction of resistance after 100 cycles, when the additive 1 is used. The semi-circles can be attributed to the Li ion migration in the SEI. Therefore, the SEI build from the decomposition of additive 1 favours charge-transfer compared to the SEI build from the base electrolyte. Scanning electron microscopy (SEM) images of lithiated and delithiated electrodes show smaller cracks on the surface when using additive 1 compared to the electrode treated with the base electrolyte. This phenomenon shows an increased cohesive force of the new formed SEI mitigating the effects of the enormous volume expansion in the electrode.[1] Zuo X., Zhu J., Müller-Buschbaum P. & Cheng Y.-J. Silicon based lithium-ion battery anodes: A chronicle perspective review. Nano Energy. 31, 213-143; 10.1016/j.nanoen.2016.11.013 (2017)[2] Eshetu, G.G., Zhang, H., Judez, X. et al. Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes. Nat Commun 12, 5459; 10.1038/s41467-021-25334-8 (2021) Figure 1