Deciphering Interfacial Reactions via Optical Sensing to Tune the Interphase Chemistry for Optimized Na‐Ion Electrolyte Formulation

Abstract

Interphases, solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI) are the key influencers in determining battery life and performance. Especially, for technologies such as sodium ion batteries that are in development stage, it is crucial to tune the interphase chemistry without which it suffers at present from poor performance metrics for reaching real-life applications. In this study, we utilize optical sensors as a tool to follow operando, the thermal events of interfacial reactions and established the role of different electrolyte additives during the SEI/CEI formation. Using the acquired knowledge from sensing, together with complementary studies in Na-ion full-cells, we propose a new electrolyte formulation that showed stable cycling performance at 0-55 °C with very low self-discharge and improved safety due to mitigated 2 gassing during cycling. Finally, we nurture our studies by transferring the know-hows to prototype cylindrical 18650 cells. We hope such findings will accelerate the practical development of Na-ion batteries.

Rechargeable Batteries of the Future—The State of the Art from a BATTERY 2030+ Perspective

“…The deeper analysis of heat information deciphered the thermodynamic parameters such as enthalpy and entropy, pertaining to the phase transitions and cell ageing. Furthermore, the simultaneous monitoring of heat and pressure decoded the exothermic reactions and gas evolutions during the SEI and CEI formations, [223,224] and thereby accelerated the screening of the electrolyte additives. This work was further extended by showing that Rayleigh back scattering could be used to monitor the temperature in 18 650 cells along its axial dimension with a resolution up to 0.05 pixel mm −1 Rayleigh sensors, unlike FBGs, are less expensive to manufacture, but require a more expensive interrogation system and greater calculation resources to analyze the large amount of data generated.…”

Practicality of methyl acetate as a co-solvent for fast charging Na-ion battery electrolytes

“…In summary, a noteworthy increase in ionic conductivity was observed here with the addition of MA/EA is ascribed to the low drag force experienced by ions (which were already well dissociated by EC-PC) during their migration. In order to improve the electrochemical stability of MA/ EA containing electrolyte, the mixture of 4 additives namely, 0.5% NaODFB, 3% VC, 3% SN and 0.2% TMSPi, recently studied by our group [42] is added into the MA/ EA co-solvent containing electrolytes. The electrolyte formulations thus obtained with these additives are mentioned hereafter with the extension 'Add ' in their name for simplicity purposes.…”

“…Moreover, the polarization of the cell or ∆V is calculated as average discharge voltage subtracted from average charge voltage, which suggests impedance growth in the cell [51]. The slippage values of NVPF and HC electrodes indicate the parasitic reactions and (or) mass losses at the respective electrodes, and its calculation method is described elsewhere [42,52].…”

“…Therefore, in the present study, we explored the impact of adding methyl acetate (MA) and/or ethyl acetate on the Na-ion electrolyte's conductivity and electrochemical performance of our reference electrolyte containing 4 additives namely sodium oxalato(difluoro)borate (NaODFB), vinylene carbonate (VC), succinonitrile (SN), and tris-trimethylsilylphosphite (TMSPi). These additives form a good passivation film and lead to good performance at room temperature and high temperature [42]. With the incorporation of MA the charge transfer resistance is significantly reduced, thus less polarization and greater capacity are achieved at low temperatures (0 C).…”

Monitoring battery electrolyte chemistry via in-operando tilted fiber Bragg grating sensors

“…We previously demonstrated the use of fiber Bragg grating (FBG) sensors, inscribed either in single-mode fiber (SMF) or in microstructured fiber (MOF) that was placed inside a battery, to monitor changes in multiple parameters such as temperature (T) and pressure (P) in real-world conditions 4,16 with high sensitivity and space resolution 17 . However, in such a configuration, the fiber acts as a true waveguide with the traveling light being fully transparent to the fiber-surrounding environment.…”