Quantifying Degradation Mechanisms in a High-Performance Parallel Hybrid Lithium-Ion Supercapacitor Induced by Long Term Cycling at High Current Rates

Abstract

Understanding 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 Li4Ti5O12/AC//LiMn2O4/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 electrode, 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 Mn3+ dissolution are reported at the positive. The formation of a cathode electrolyte interface 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.