DOCTORAL CANDIDATE
Iniyan Selvaraj

SUPERVISORS
Rita Baddour-Hadjean, Institut de Chimie et des Matériaux Paris-Est (ICMPE)
Dipan Kundu, University of New South Wales (UNSW)
Dr. Jean Pierre Pereira-Ramos, Institut de Chimie et des Matériaux Paris-Est (ICMPE)
Dr. Thi-Thanh Tam Nguyen, Institut de Chimie et des Matériaux Paris-Est (ICMPE)

Energy storage, Li (Na) batteries, Chemistry, Polymer science, Materials science, Solid-state chemistry, Electrochemistry

Among the various types of electrochemical energy storage technologies, Li+-ion batteries are still in the forefront and are currently playing an indispensable role in supporting our modern society. Electrochemistry of lithium-based cells presents various attractive properties: i) lithium is the lightest metal with an exceptionally low redox potential (ELi+/Li = −3.04 V/NHE); ii) Li+-ion possesses a small ionic radius that is advantageous for easy diffusion into solid; iii) Li+-ion based cell has a long cycle life with high rate capability etc. Unfortunately, lithium resources are limited: only 20 ppm as relative abundance in the Earth’s crust. Thus, many researchers try to explore new abundant and low-cost alternatives to lithium, such as sodium, potassium, or calcium. Sodium is cheap, available in a high abundance (1000 times more abundant than lithium) with very desirable redox potential, i.e., ENa+/Na = −2.71 V/NHE, only 0.3 V greater than that of lithium, and similar electrochemical behaviour.

The proposed project concerns the synthesis of new solid electrolyte membranes based on thermostable polymers and ionic liquids (ILs) for being used as ion-conducting membranes in sodium-ion batteries (SIBs). The originality of this approach lies in the use of polycyanurates (PCNs), a family of thermosetting polymers with unique intrinsic properties (high chemical and thermal resistance, low dielectric constant, and strong adhesion to conductive metals and composites) as polymer matrix for impregnating ILs. These polymers have been mainly used as binders in high-performance structural composites, especially in the aeronautical and aerospace industries, but have not yet been exploited in the microelectronics industry because of their brittleness.

Recently, we have found that the presence of a small amount of ILs during the step of forming PCN networks produces flexible conductive PCN-ILs membranes that could replace both microporous separators and flammable, volatile organic electrolytes in Li-ion batteries. Indeed, the presence of nano-domains containing ILs within these membranes would facilitate the mobility of Na+ cations while maintaining the electronic insulation even at a high temperature. They should act as a physical barrier against dendritic growth, hence reducing the risk of short circuits, thermal runaway, and explosion and thus significantly improving the safety of Na-ion batteries. Therefore, would enable the replacement of conventional graphite-based anode with metallic sodium for producing batteries with very high energy density. The impregnation of ILs would endow the membranes with ionic conductivity with improved safety issues thanks to the non-volatility, non-flammability and no leakage of impregnated ILs. Recent studies show that the use of ILs can significantly increase the electrochemical properties of a solid-state battery, such as improving the long-term stability of metal electrodes and interfacial compatibility with electrodes.