The CIRCE project focuses on failure mechanisms occurring in high capacity batteries with aprotic electrolytes. The project will last 24 months and will imply the cooperation of three permanent Sapienza Staff (Sergio Brutti, Camillo La Mesa and Domenico Stranges), one non-permanent post-doc (Giorgia Greco) and one PhD student (Mariarosaria Tuccillo)
The main goal of the project is to study the fundamental chemical mechanisms underneath the irreversible degradation upon abuse of the battery constituents (i.e. electrodes, electrolytes) leading to gas release.
The project tackles two closely interacting activities that address:
(a) the fundamental understanding of thermal and photochemical degradation reacions of aprotic electrolytes/solvents
(b) the interplay between solid consitutents of batteries (electrodes, separators, countercollectors, cages) and the liquid aprotic electrolyte in abuse conditions.
In summary this project focuses on the study of the parasitic chemistry activated by thermal/electrochemical abuse leading to gas release in high capacity batteries with aprotic electrolytes. We adopt a bottom-up approach starting from the unexplored analysis of the thermal and photochemical degradation of electrodes/electrolytes to rationalize the complexity of the gas release reactions in full LIBs under abuse conditions. This fundamental knowledge will pave the way for the identification of mitigation strategies to reduce flammability and toxic gas release.
The current formulation of lithium-ion batteries (LIBs) is constituted by LiCoO2/graphite and a carbonate-based electrolyte with LiPF6 salt [1]. This formulation cannot be simply upscaled from mobile electronics to transportation due to costs, environmental malignity, and chemical hazards upon abuse [2].
The proposed project investigates the degradation chemistry and gas release mitigation strategies of an innovative LIB formulation demonstrated by us previously [3]. In our formulation a high capacity Co-free lithium iron phosphate, i.e. LiFePO4, is coupled with a high capacity silicon-carbon composite and the carbonate based electrolyte is improved by adding trifluoromethyl sulphonyl imide based ionic liquids able to enhance thermal stability and resilience upon abuse. This combination of innovative materials discloses remarkable enhancement compared to the state-of-the-art in terms of environmental benignity, safety and performance [3].
The CIRCE project starts from this solid background and tackles the investigation of the failure mechanisms of this innovative LIB formulation to foster further innovations to mitigate the gas release upon thermal abuse. The project tackles TWO parallel closely interacting activities:
(1) Analysis of the thermal stability of electrode materials by monitoring structural alterations and gas release upon cycling in batteries.
(2) Investigation of the degradation mechanism at high temperature of electrolyte components by identification of the pyrolysis elementary steps and well as photodissiciation mechanims
The first relevant innovation pursued is to shed light on the multiphase chemical reactivity at high temperature of electrodes (activity 1) and the development of a comprehensive reactive scheme of the thermal breakdown of the electrolytes (activity 2). These two goals aim at paving a fundamental description of the degradation chemistry at high temperature of the constituent elements of our innovative LIB formulation that leads to gas release.
In the literature the description of the most relevant degradation chemistry routes in LIBs leading to gas release have been investigated in the past (see as examples [4,5]). The most relevant understanding consolidated in the literature is the remarkable dependence of the parasitic chemistry on the interaction between the different constituent elements of any full LIB formulation [6,7].
Once established, this analysis of the degradation chemistry of our LIB formulation will allow to evaluate the relative merit of the possible mitigation strategies (i.e. the use of lithium oxide and lithium hydroxide as electrode/separators additives) able to minimize the gas release. The adoption of these mitigation strategies has been discussed in the literature for different LIB formulations [7] and will be preliminary considered for further advancement beyond this project.
In summary this project tackles the study of the parasitic chemistry leading to gas release in an innovative LIB formulation. We adopt a bottom-up approach starting from the unexplored analysis of the thermal degradation of electrodes/electrolytes with multiple complex techniques.
This goal is in line with the commitments of the new Horizon Europe research program starting in 2021 (Pillar II 'Global Challenges and European Industrial Competitiveness' in Cluster 'Climate, Energy and Mobility') and tackle challenges outlines by the Battery Europe and Battery2030+ UE initiatives.
[1] B. Scrosati, J. Garche, J. Power Sources. 195 (2010) 2419¿2430. [2] M. Hu, X. Pang, Z. Zhou, J. Power Sources. 237 (2013) 229¿242. [3] A.Celeste, L.Silvestri, M.Agostini, M.Sadd, S.Palumbo, J.K.Panda, A.Matic, V.Pellegrini, S.Brutti, Batteries & Supercaps (2020) in press, https://doi.org/10.1002/batt.202000070; [4] W.Kong et al. J.Power Sources 142 (2005) 285-291 [5] Y.Fernandes et al. J. Power Sources 414 (2019) 250-261 [6] Z.Liao et al. J. En.Chem, 49 (2020) 124-135. [7] S.Nowak. M.Winter. J.Electrochem. Soc. 162 (2015) A2500¿A2508