The Importance of Electrolyte Additive Interactions: A Case Study in LNO||Graphite Battery Chemistry
Authors: Woelke Christian , Benayad Anass , Hanke Felix , Baraldi Giorgio , Echeverria Maria , Esen Ekin , Ayerbe Elixabete , Neale Alex R. , Everitt Jacqui , Hardwick Laurence J. , Yan Peng , Poterała Marcin , Wieczorek Wladyslaw , Winter Martin , Cekic-Laskovic Isidora 
Published: December 2024

The ever-growing demand for lithium-ion batteries (LIBs) and especially the requirements of high energy densities necessitates the development of advanced battery materials in order to make electro mobility and renewable energy feasible concepts for a broad application in society. However, modern electrode active materials that promise high energy densities come with numerous challenges that need to be overcome before they can be applied in commercials batteries. LiNiO2 (LNO) has drawn attention as a possible cathode active material due to its high specific capacity and absence of the critically regarded cobalt.1,2 On the flip side, LNO suffers from the formation of an ionically insulating rock salt phase on the particle surface, which leads to active material degradation and rapid capacity fading during battery operation.3

An economically viable and easily implemented approach to increase battery performance and prolong lifetime is the incorporation of functional additives into the liquid electrolyte. Usually added in small amounts, electrolyte additives can serve a multitude of functions in a battery, e. g. stabilization of electrode active materials. Since different desired effects require electrolyte additives with different functionalities, it is not uncommon that multiple additives are used at once in a mixture.4 What seems to be often neglected however, are possible direct interactions of functional electrolyte additives or their decomposition products as well as crosstalk phenomena that can significantly alter the interphase chemistries within the battery and thereby the galvanostatic cycling performance. Consideration of such effects is important for the design of novel electrolytes and especially for the accelerated discovery of materials by means of machine learning and artificial intelligence support.
In this study we implemented the sulfur-based additive benzo[d][1,3,2]dioxathiole 2,2-dioxide (DTDPh) in LNO||graphite batteries, which was able to improve the cycle life as well as the accumulated discharge energy at end of life by 45% and thus significantly outperformed the well-known film forming additive vinylene carbonate (VC). Detailed electrochemical and spectroscopic analysis revealed that DTDPh significantly alters the compositions of both negative and positive electrode interphases, despite being reduced on the negative electrode. Interestingly, the combination of DTDPh and VC causes a poorer performance than DTDPh alone, indicating a direct interaction of the two functional additives. We found strong evidence from electrochemistry and spectroscopy for a partial suppression of the effects of DTDPh by VC and propose a possible mechanism of their interaction based on DFT calculations.

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