Advanced Solid-State Electrolytes Based on Charge-Transfer Complexes for Lithium Batteries
Authors: Celle Caroline , Tessier Noeline , Kunert Romain , Bernard Laurent , Picard Lionel , Lecuyer Margaud , Dechamps Marc 
Published: December 2024

Electrifying mobility and implementing more renewable energies in our energy mix to reduce global warming and limit the climate crisis will be two targets that will require massive energy storage devices in the near future. Li batteries is one of the most promising technology for electrochemical storage to meet these challenges requiring safe and high performance cells. Li metal batteries and solid state electrolytes SSE may try to tackle these safety[1] and energy densities[2] challenges. Research pay attention to the development of several families of SSE based on oxide, sulfur or polymer moieties exhibiting pros and cons in terms of stability, safety, processability and cell and module integration. Despite their ease of processability, polymer based SSE suffur from their low ionic conductivity at room temperature and poor chemical stability towards Li metal[3]. Recently, a new class of organic materials based on charge-transfer complexes (CTCs) is drawing attention. The donor / acceptor couple associated with a lithium salt shows great ionic conduction properties up to 0,1-1 mS.cm-1 at room temperature[4]. This complexes are widely studied as fast electronic conductors for decades while their potential for ionic electrolytes, where low electronic conductivity is mandatory to prevent self-discharge, has to be studied in depth [5].

In this presentation, we will share our latest results on solid electrolytes made up of organic charge-transfer complexes. Both small molecules and polymers will be investigated to synthesize SSE by mixing it with a lithium salt. Donor and acceptor chemical structures, CTC / Li salt molar ratios will be modified to tune salt dissociation and ionic conductive properties of the SSE. While these electrolytes are currently processed as powders, fabricating films thanks to the use of binders will further improve the overall ionic conductivity. Molar ratio of CTC / binder and salt will be modified to develop optimized formulations allowing to easily process electrolytes and catholytes for full cell characterization. Ionic conductivities up to 0,02 mS.cm-1 were obtained at room temperature and are currently being improved with work on formulation and sample processing. Incorporate very low content of plasticizers might be used to improve room temperature properties. Electrochemical stability in full cell integration and competitive SSE ionic conductivity will also be shown. Advanced characterization will be used to understand the way it works to reduce the lack of sample reproducibility and to investigate these new ionic transport mechanisms involved through these materials.

[1] L. Yue et al, Energy Storage Mater, 5 (2016) 139-165.

[2] X. Cheng et al, Chem. Rev., 117 (2017) 10403-10473.

[3] J. Mindemark et al, Prog. Polym. Sci., 81 (2018) 114-143.

[4] K. Hatakeyama-Sato et al, ACS Appl. Electron. Mater., 2 (2020) 2211-2217.

[5] Yang et al., ASC Energy letters, (2023), 8, 2426-2431.