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Martin Winter1 A. Friesen1 M. Börner1 F.M. Schappacher1

1, Universität Münster, Münster, , Germany

Lithium ion battery (LIB) cells are established electrochemical energy storage systems with high Coulombic and energy efficiencies and high energy and power densities [1-3]. Four performance parameters are considered key for the success of future applications: High energy density, fast charging, long cycle life and enhanced safety.
The controlled safe behavior of LIBs is a critical performance requirement for commercial use, especially in large batteries for automotive and stationary energy storage (“grid”) application. In the past years several incidents occurred, that caused public attention to the safety of the technology in general, raising doubts on the implementation of LIBs in large battery applications. Moreover, the progressive development of new materials and advanced cell designs improves the cell performance continuously, but unfortunately the growing energy densities and increasing battery pack sizes raise the safety risks, too.
Measures can be taken on various levels of battery hierarchy to improve safety of LIBs. On battery system level, housing, packaging, thermal and battery management play important roles. On module level, temperature control of sensors and an intelligent battery management system help to improve safety. The cell design has a major influence on the safety of LIB cells. The heat dissipation rate during an exothermal reaction largely influenced by the cell design. If the heat dissipation rate is larger than the heat generation rate of the exothermic reaction, the cell will cool down and not reach a critical state. If the cell gets into a critical state, different safety measures like current interruption devices (CID), positive temperature coefficient elements (PTC) or burst discs are the last measures before the cell chemistry comes into play. The latest incidents with smartphones clearly prove, that we also have to address the cell chemistry. The intrinsic safety of LIBs is influenced by the anode and cathode active materials, as well as the inactive materials, like electrolyte and separator. The usually used liquid electrolyte is the most critical compound as it is volatile, flammable and in contact with every part of the LIB cell [4]. In addition, the electrolyte does decompose forming toxic components [5].
In this presentation, we will focus on intrinsic cell safety and the prominent role of the electrolyte. We will show how different additives influence the different components of a LIB cell and cell safety.
References:
[1] Wagner R, Winter M, et al., J. Appl. Electrochem., 2013, 43 (5), 481-496
[2] Placke T, Winter M, et. al. J. Solid State Electrochem., 2017, 1-26, DOI: 10.1007/s10008-017-3610-7
[3] Meister P, Winter M, Placke T, et. al. Chem. Mater., 2016, 28, 7203-7217
[4] Schmitz R W, Winter M, et. al. Prog. Solid State Ch., 2014, 42, 65-84
[5] Nowak S, Winter M, J. Electrochem. Soc., 2015, 162, A2500-A2508

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