Quantifying degradation mechanisms in a high performance parallel hybrid lithium-ion supercapacitor induced by long term cycling at high current rates

International audienceUnderstanding the degradation pathways of electrode materials is a key to develop more reliable Li-ion technologies along with an increased energy density and power rate. This study aims to demonstrate the benefits of the combined use of X-ray based characterization techniques and electrochemical assessment for thorough multi-scale anlaysis to elucidate the aging mechanisms of a Li 4 Ti 5 O 12 /AC//LiMn 2 O 4 /AC parallel hybrid lithium-ion supercapacitor. Analyses performed on samples extracted from full stack representative of industrial battery application, show that irreversible modifications are observed at all length scales on both electrodes. At the negative, the disaggregation and corrosion of the LTO active material, as well as AC particle cracking and electrode film delamination have been observed.In the meantime, drastic cracking of the AC and LMO active material along with important micro-strain increase at the crystallite level for LMO as well as Mn 3+ dissolution are reported at the positive. The formation of a cathode electrolyte interface (CEI) is also reported. These structural and chemical changes have been identified as precursors to important polarization increase, Li inventory loss and furthermore capacity fading leading thus to device failure.</div

Durability of carbon-supported manganese oxide nanoparticles for the oxygen reduction reaction (ORR) in alkaline medium

International audienceMnOx/C-based electrocatalysts, prepared by the chemical deposition of manganese oxide nanoparticles on carbon, were tested towards the Oxygen Reduction Reaction (ORR) in their as-synthesized state and after ageing, either in ambient air for a year (mild ageing) or in an O2-saturated molar KOH solution at 80 °C for three weeks (premature ageing). For each electrocatalyst, the morphology and composition were characterised using TEM, XRD and chemical analysis. ORR kinetic parameters were evaluated using the Rotating Disk Electrode (RDE) and Rotating Ring Disk Electrode (RRDE) setups. Whilst the oxygen reduction activity of the electrocatalysts barely changes after mild ageing, it decreases after premature ageing following dramatic modifications to both the chemical and crystalline structures of the carbon-supported MnOx nanoparticles. The peroxide yield also sharply increases after premature ageing. Doping MnOx/C with nickel or magnesium divalent cations is beneficial since it improves both the catalytic activity and selectivity towards the 4-electron ORR pathway, even after ageing