Fast Determination of the Limiting Ionic Diffusion Coefficient in Lithium Metal Polymer Batteries
Résumé
The energy conversion and its storage is a tremendous challenge for our society. Despite the great progress of the Lithium (Li)-ion technology based on flammable liquid electrolyte, their intrinsic instability is a strong safety issue for large-scale applications. The use of solid polymer electrolytes (SPEs) is an adequate solution in terms of safety and energy density thanks to their stability towards Li metal.[1] Moreover, as for conventional liquid electrolyte, the cationic transference number of poly(ethylene oxide) based SPE is typically below 0.2 which limits their power performance due to the formation of concentration gradient throughout the electrodes.[2] In such Li metal battery, the SPE acts as both separator and functionalized cathode binder ensuring ionic transport all over the battery. To increase the battery energy density a simple way is to use thicker cathode. Indeed, for a given electrode formulation, the energy density is directly linked to the active material loading.[3]
The goal of this study is to propose a quick and efficient methodology to optimize the thickness of the SPE and of the cathode based on charge transport parameters, which allows to determine the effective limiting Li+ diffusion coefficient. Revisiting a protocol by Doyle et al.[4] the battery power performance is rapidly established, at least 8 time faster than conventional cycling (charge-discharge steps) with a similar accuracy as depicted in Figure 1.[5] Then, by using an approach based on the Sand equation a limiting current density is determined. A unique mother curve of the capacity as a function of the limiting current density is obtained whatever the electrode and electrolyte thicknesses. Finally, the effective limiting diffusion coefficient is estimated which in turn allows to design the best electrode depending on electrolyte thickness.
References
[1] J.-M. Tarascon, M. Armand, Nature, 414 (2001) 359.
[2] M. Doyle, T. F. Fuller, J. Newman, Electrochim. Acta., 39 (1994) 2073.
[3] Z. Du, Z., D. L. Wood III, C. Daniel, S. Kalnaus, J. Li, J. Appl. Electrochem., 47 (2017) 405.
[4] M. Doyle, J. Newman, J. Reimers, J. Power Sources, 52 (1994) 211.
[5] D. Devaux, H. Leduc, P. Dumaz, M. Lecuyer, M. Deschamp, R. Bouchet, Front. Energy Res., 7 (2020) 168.