Electrochemical characterization of bi-layered graphite anodes combining high and low porosity in lithium-ion cells to improve cell performance

Lithium-ion batteries have been implemented worldwide in portable devices. Furthermore, they are strong candidates to facilitate the upcoming revolution associated with the electrification of vehicles. Nowadays, these cells are based on transition metal oxides in the positive electrode and graphite in the negative electrode. Despite focusing many efforts on developing novel materials for enhancing the performance of lithium-based batteries, there is still room for improvement by working on the electrode characteristics with widely industry-implemented and trustable state-of-the-art materials. In this work, we developed and characterized graphite electrodes with bi-layered structure consisting of two layers with different porosity. These electrodes were tested both in half and full coin cell configuration, the latter using LiNi0.6Mn0.2Co0.2O2 as the positive electrode. Regular single-layer graphite electrodes with the same average porosity and loading were also elaborated and tested for comparison. Galvanostatic cycling, power tests and impedance spectroscopy were combined with post-mortem characterization to understand the influence of the multi-layer structure onto the electrochemical response. Results show that the bi-layered structure provides enhanced capacity retention during the beginning of life of cells. However, this advantage is lost when the repeated lithiation-delithiation cycles of graphite affect the pore size of the lower porosity layer. In any case, it is evidenced that by modulating the coating method and therefore the macroscopic properties of graphite, it is possible to have a significant impact on its electrochemical characteristics. This should be of high interest for battery manufacturers facing the uncertainties associated with the processing and implementation of novel materials.