Small coin cell batteries are predominantly used for testing lithium-ion batteries (LIBs) in academia because they require small amounts of material and are easy to assemble. However, insufficient attention is given to difference in cell performance that arises from the differences in format between coin cells used by academic researchers and pouch or cylindrical cells which are used in industry. In this article, we compare coin cells and pouch cells of different size with exactly the same electrode materials, electrolyte, and electrochemical conditions. We show the battery impedance changes substantially depending on the cell format using techniques including Electrochemical Impedance Spectroscopy (EIS) and Galvanostatic Intermittent Titration Technique (GITT). Using full cell NCA-graphite LIBs, we demonstrate that this difference in impedance has important knock-on effects on the battery rate performance due to ohmic polarization and the battery life time due to Li metal plating on the anode. We hope this work will help researchers getting a better idea of how small coin cell formats impact the cell performance and help predicting improvements that can be achieved by implementing larger cell formats.

Li-rich layered cathode materials have been considered the most promising candidates for large-scale Li-ion batteries due to their low cost and high reversible capacity. However, these materials have many drawbacks that hinder commercialization, such as low initial efficiency and cyclability at elevated temperatures. To overcome these barriers, we propose an efficient and effective surface modification method, in which chemical activation (acid treatment) and LiCoPO₄ coating were carried out simultaneously. During the synthesis, the lithium ions were extracted from the lattice, leading to improved Columbic efficiency, and these ions were used for the formation of LiCoPO₄. The Ni and Co doped spinel phase was formed at the surface of the host material, which gives rise to the facile pathway for lithium ions. The LiCoPO₄ and highly doped spinel on the surface acted as double protection layers that effectively prevented side reactions on the surface at 60 ℃. Moreover, the transition metal migration of the modified cathode was weakened, due to the presence of the spinel structure at the surface. Consequently, the newly developed Li-rich cathode material exhibited a high 1st efficiency of 94%, improved capacity retention of 82% during 100 cycles at 60 ℃, and superior rate capability of 62% at 12C (1C = 200 mA/g) rate at 24 ℃. In addition, the thermal stability of the modified cathode was significantly improved as compared to that of a bare counterpart at 4.6 V, showing a 60% decrease in the total heat generation.