First quantitatively correct mechanism for decomposition of a standard electrolyte during lithium-ion batteries cycling

Significance 

Recently, the use of lithium-ion batteries in various applications such as smartphones has gained popularity owing to their durability, high specific capacity and high energy density. In particular, their potential use in electric cars and airplanes has attracted significant attention of researchers leading to a keen interest in their electrochemical charging and discharging processes. However, the realization of the full potential of lithium-ion batteries has remained a great challenge due to the difficulty in understanding the aging and gas evolution processes during cycling. In a recently published literature, the authors demonstrated the influence of the high voltage-based cathode materials on the efficiency rate of the lithium battery.

The cutoff voltage, however, did not hinder the release of gases at both anode and cathode. Therefore, to enhance the efficiency of lithium-ion batteries, understanding the gaseous evolution in lithium-ion batteries especially under high voltage and temperature conditions is highly desirable.

Alternatively, a two-chamber cell with separated anode and cathode has been used to identify the gases released at cathode and anode during the cycling process. During cycling of lithium-ion batteries, CO2 and CO gases were produced at the cathode while C2H4, CO, and H2 were produced at the anode. Even though there is no generally accepted mechanism explaining the generation of gases during lithium-ion battery cycling, electrochemical decomposition of the carbonate electrolyte has been associated with the release of hydrogen at the electrodes. Recently, the role of the atomic oxygen released from the cathode has shown a considerable influence in the CO2 and CO generation mechanism.

To this end, understanding the underlying mechanism responsible for the generation of gases and other side products is of great importance in preventing battery degradation and aging. A group of researchers at Don State Technical University: Dr. Nikolay Galushkin, Nataliya Yazvinskaya and Dr. Dmitriy Galushkin proposed a mechanism explaining the electrolyte decomposition and its influence on the generation of gases and side products during the cycling of lithium-ion cells. Fundamentally, the authors investigated the release of gases during cycling in the voltage range of 2.6-4.2V and 2.6-4.8V at a temperature of 25 and 60°C. Furthermore, the effects of the electrochemical reaction due to the electrolyte decomposition was evaluated. They purposed to quantitatively explain the resulting gases and the ratios between them. The work is currently published in Journal of The Electrochemical Society.

The authors observed that the electrolyte decomposition resulted in the release of CO, H2, and CO2 gases. This was attributed to the direct influence of the electrochemical reaction of electrolyte decomposition in the evolution of the H2 and CO as well as the influence of the additional chemical reaction on the CO2 generation. This further explained the observed variance in the CO2 /CO ratio ranging from 0.82-2.42 at the same electrochemical reaction depending on the various cycling conditions. Furthermore, the authors noted several advantages of the electrolyte decomposition mechanism during cell cycling. For instance, it enabled a quantitative explanation of the ratios between the gases for the first time and explanation of the factors affecting the evolution of the gases. Altogether, the proposed electrolyte decomposition mechanism provides insights that will further advance both theoretical and experimental understanding of the cycling of lithium-ion cells.

Nikolay Galushkin said in a statement to Advances in Engineering, that “the study is important because, first, in the standard electrolyte (LP57), mainly ethylene carbonate (EC) decomposes during сycling of lithium-ion cells, as linear carbonates decompose into gases 5 times less efficiently than EC”. He then added “Secondly, the mechanism of electrolyte decomposition during cycling of lithium-ion cells was first established, which quantitatively explains all known experimental results. Thirdly, within the framework of the established mechanism of electrolyte decomposition, it was experimentally proved for the first time that a potential-independent H2 evolution is a consequence of its adsorption in pores of powdered graphite on anode”. He then highlighted that “Electrochemical reactions leading to generation of gases and other side products in the process of cells cycling lead to the degradation and aging of cells. In addition, during cells cycling, hydrogen accumulates in the anode, which sharply increases the likelihood of thermal runaway in lithium-ion cells. The established mechanism of electrolyte decomposition for the first time provides a quantitatively correct explanation of these undesirable phenomena. Only the knowledge of the electrochemical mechanism of any process allows them to optimally manage and effectively deal with such undesirable phenomena as cells aging and thermal runaway”.

Authors’ research interests include:

First, the study of electrochemical processes in alkaline, acid and lithium-ion batteries, such as thermal runaway, electrolyte decomposition, batteries aging processes, etc.

They first established quantitatively correct mechanism of decomposition of the electrolyte during the cycling of lithium-ion batteries, which corresponds to all experimental results. There were determined the electrochemical reactions describing the gases generation.

They experimentally proved that the thermal runaway in alkaline and acid batteries is connected with a powerful exothermic reaction initiation of the recombination of the atomic hydrogen accumulated in the electrodes, which runs in line with the electrochemical mechanism.

Secondly, the research and development of hydrogen storage systems meeting the criteria for on-board hydrogen storage systems that have been defined by the US Department of Energy. They received experimentally high-capacity metal hydrides. The capacity of the metal-hydrides as a hydrogen absorber was quantified as 20.1 wt% and 400 kg m-3. This value exceed three times the earlier data obtained by traditional methods for any reversible metal hydrides, including magnesium hydride or complex hydrides, also they are far exceed the criteria for hydrogen storage systems established by US DOE.

Third, the modeling of processes in electrochemical batteries to develop battery models suitable for practical use in electric vehicles.

First quantitatively correct mechanism for the decomposition of a standard electrolyte during lithium-ion batteries cycling - Advances in Engineering

About the author

Dr. Nikolay Galushkin is a professor at Don State Technical University, Russia. He heads a research laboratory “Electrochemical and hydrogen energy”. He received Dr.Sc. in Engineering from the South-Russian State Polytechnical University in 1998.

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About the author

Nataliya Yazvinskaya is an associate professor at Don State Technical University, Russia. She is a senior researcher of laboratory “Electrochemical and hydrogen energy”. She received Cand.Sc. in Engineering from the South-Russian State Polytechnical University in 2006.

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About the author

Dr. Dmitriy Galushkin is a professor at Don State Technical University, Russia. He is a leading scientist of laboratory “Electrochemical and hydrogen energy”. He received Dr.Sc. in Engineering from the South-Russian State Polytechnical University in 2010.

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Reference

Galushkin, N., Yazvinskaya, N., & Galushkin, D. (2019). Mechanism of Gases Generation during Lithium-Ion Batteries Cycling. Journal of The Electrochemical Society, 166(6), A897-A908.

Go To Journal of The Electrochemical Society

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