From Ionic Liquid Fragments Towards Hybrid Nanoparticles for Solid-State Lithium Ion Technology

Abstract

Secondary batteries capable of efficiently storing and delivering a large amount of electrical energy are essential elements to sustain the constantly increasing development of nomad and mobility technologies. Among the different energy storage systems, the most energetic storage systems which have flood the market are ions batteries (mainly lithium), however they suffer of one major drawback owing to overloads or short-circuits which may cause thermal runaway owing to the combustion of the liquid electrolyte. To make them safer both in use and after disposal, one possibility is to replace traditional liquid electrolyte by solid state electrolytes in the next generations of ion batteries [1]. All-solid-state batteries are capable to have longer life cycle, higher energy density and less requirements on packaging. One of key components that determines performance is solid electrolyte. In the past years many types have been investigated among which figures the types NASICON, perovskite, Argyrodite, anti-perovskite, garnet, LISICON, Li3N, sulfide and many more [2]. Nevertheless, an insufficient room-temperature ionic conductivity (10-5-10-3 σ.cm-1), lithium transport number, and poor electrode-electrolyte interface hinder the reality of these devices [3]. One other promising possibility is to use immobilized or grafted ionic liquids onto the surface of a nanometric material to ensure ion mobility [4]. These new types of hybrid materials, still modestly developed, offer mechanical strength comparable to that of solid polymer electrolytes and have been reported, by our group, to display lithium ion conductivity approaching the standards of liquid electrolytes [5]. Here we present the design of new organic/inorganic hybrid electrolytes based on nanometric zirconium and silicon dioxide and ionic liquid for ion conduction. Immobilization of the ionic liquid was realized using suitable function groups (carboxylic acid or organosilane) which formed with surface atoms a stable interaction. These new materials were carefully characterized by different techniques like FT-IR, TEM, TGA and N2-adsorption to ensure incorporation of the ionic liquid to prove the grafting and estimate the organic content of the synthesized hybrid materials. Additionally, ionic conductivity was measured by Electrochemical Impedance Spectroscopy using a specific new method specifically developed for this type of material and was completed with the determination of the electrochemical stability using cyclic voltammetry. Several parameters like material texture (particle diameter, porosity, shape…), anchoring type, molecular structure of ionic liquid fragments and surface density of the grafting were tuned to maximize ion mobility and so the conductivity. First trends linking hybrid materials structure/composition and ionic conductivity will be presented. [1] Fan, L. et al., Adv. Energy Mater., 2018, 8, 1702657. [2] Takada, K. Acta Mater., 2013, 61, 759–770. [3] Sun, C. et al., Nano Energy, 2017, 33, 363–386. [4] Lu, Y. et al., Adv. Mater., 2012, 24, 4430–4435. [5] Delacroix, S. et al., Chem. Mater., 2015, 27, 7926–7933. Fig 1. New organic/inorganic hybrid electrolytes based ionic liquids Figure 1