Multilayer Graphene as a Cathode Conductive Additive in Lithium-Ion Pouch Cells: A Correlation of Changes in Electrolyte Uptake and Composition of the Electrode Electrolyte Interface with Enhanced Cycling Stability

Abstract

The electrochemical performance of the lithium-ion battery is significantly affected by the choice of electrode conductive additives. In this study, a mixed conductive additive with an equal proportion of multilayer-graphene (MLG) and carbon black (CB) is used in LiNi1/3Mn1/3Co1/3O2 (NMC-CB-MLG) electrodes. The electrochemical performance of these electrodes is compared at coin cell and pouch cell formats with that of the LiNi1/3Mn1/3Co1/3O2 (NMC) electrodes prepared with CB alone as a conductive additive (NMC-CB). While CB independently increases rate capability, mixing MLG with CB as a conductive additive enhances cycling stability. The pouch cells fabricated using the NMC-CB-MLG electrode show a superior capacity retention of 80% after 730 cycles at 1C, compared to 65% at 320 cycles of NMC-CB. The differences in the capacity retention of both cells are correlated with the electrolyte uptake and stability of the electrode–electrolyte interface (EEI) due to changes in the chemical composition as investigated using X-ray photoelectron spectroscopy. The main reasons for the capacity fade of NMC-CB are explained by the formed unstable EEI and cathode electrode cracking, which lead to loss of lithium inventory and loss of active materials. This study concludes that MLG mixed with CB can be used as a conductive additive in commercial large-format lithium-ion high energy cells.