28 Feb Chemicals for improved batteries – Lithium & Sodium

Safer liquid electrolytes are of paramount for the development of new generations of batteries. Liquid electrolytes of today’s LIBs are usually composed of conductive carbonate solvent and lithium salt. However, some potentially serious safety threats may be caused by the liquid electrolyte system. First, leaking organic solvent can make toxic effects on the human body when battery packing is damaged. Furthermore, low ignition point and low boiling point generate serious threats, such as thermal runaway when the battery is overcharged and discharged. Moreover, the characteristics of liquid aggravate performance deterioration and the side reactions between electrode and electrolyte, which are common reasons for electrolyte system failure.[4] Narrow working temperature, decomposition under high voltage, and the inability to suppress lithium dendrite make the traditional liquid electrolyte no longer satisfied with the high-energy battery of the future.[5]

For this purpose, use of additives and non-flammable organic liquid electrolytes has proven to be an effective strategy. For instance, a review from R. Gond and coworkers[6] put forward the advantage of phosphorous containing solvents as flame retardant, the use of fluorinated compounds as non-flammable and more stable solvents and finally the introduction of inorganic liquid electrolytes due to their inherent noncombustible properties. SPECIFIC POLYMERS has a large portfolio of potential additives bearing aforementioned functions.

Solid state batteries, including ceramic and polymer electrolytes, are among the emerging solutions. Solid polymer electrolytes (SPEs) are attracting major interest due to their small volume change during the charging/discharging process, high level of safety and ease of manufacturing.[7] Most of the SPEs are currently made up of polyethylene glycol (PEO), polycarbonates, polypropylene glycol (PPO) or polyesters. As displayed by X. Zhang et al.,[8] composition and architecture of polymer electrolytes play a significant role on the battery performances by promoting SPE self-organization or reducing its crystallinity or its glass transition temperature. SPECIFIC POLYMERS proposes alternative PEO-based and cyclic carbonate monomers and polymers to develop SPE with advanced properties.

Moreover, while traditional electrolytes are dual-ion conductors, i.e., both cations and anions are mobile in the polymer network, SPECIFIC POLYMERS gives access to single-ion conductors (SICs) by commercializing functional monomers and homopolymers bearing LiTFSI group namely LiMTFSI (SP-49-023), LiSTFSI (SP-59-011), PMTFSILi (SP-4P-6-004). J. Gao et al.,[9] put forward that SIC has advantages over binary-ion conductors such as their high ionic selectivity against lithium approaching unity, their high oxidation voltage (>4.0V) as well as their resistance to dendrite formation since SICs allow lithium plating and stripping evenly during the charging/discharging process. For instance, in a paper of J. L. Olmedo-Martínez et al,[10] the PMTFSILi was mixed with different molecular weight of PEO. The impact of PMTFSILi on the crystallization and conductivity of the blends was explored in detail and it was proved that PMTFSLi has ability to reduce PEO crystallinity due to a great miscibility between both polymers. The highest ionic conductivity of 2.1 × 10⁻⁴ S/cm at 70°C was obtained with a 50/50 composition blends. Finally, it has been demonstrated by L. Porcarelli and coworkers[11] a thermally-cured LiMTFSI/PEO-based single-ion conducting polymer gel electrolyte displaying simultaneously transference number (t_Li+) ~1 and ion conductivity of ~10^-4 S/cm at 25°C.