An effective approach to improve electrochemical performance of thick electrodes

Abstract

Increasing areal active material loading by thick electrodes is a direct and effective approach to improve the energy density of lithium-ion batteries (LIBs). However, it may also induce large polarization effects and reduce the active material utilization, especially under high charge/discharge current densities. In this work, dual-layered LiNi0.8Co0.15Al0.05O2 (NCA) cathodes with high areal capacity of about 5 mAh/cm2 and gradient porosity are prepared via a layer-by-layer method, in which carbon nanotubes (CNTs) and Super P (SP) carbon are used to build the electron conducting networks as well as to adjust the porosity. It is demonstrated that the CNT-SP cathode, which uses CNTs as the conductive agent in the lower layer (close to the current collector) and SP as the conductive agent in the upper layer (close to the separator), provides the highest areal capacity of 4.81 mAh/cm2 among all configurations studied (CNT-SP, SP-SP, SP-CNT, and CNT-CNT). And it exhibits high capacity retention of 99.5% over 100 cycles in NCA||graphite full pouch cells at current density of 0.2 C rate. The excellent performance of the thick CNT-SP cathode is attributed to the construction of favorable conductive networks which can provide effective and reliable paths for electron transport and Li+ diffusion. Moreover, a thinner electrode/electrolyte interphase layer is found to form in the CNT-SP electrode. This research reveals a viable approach for ameliorating the significant polarization effects and limited active material utilization in thick electrodes through alternate configurations of the conductive agents, which can be easily adopted in state-of-the-art battery manufacturing processes.