Oxalic Acid as a Cathode Additive Increasing Rate Capability of Ni-Rich Layered Cathode Materials

Ni-rich layered cathode is known as the main limit for the fast charge of Li-ion batteries. With a focus on Ni-rich LiNi0.80Co0.10Mn0.10O2 (NCM811) cathode, two strategies have been attempted to improve the rate capability of Li-ion cells, one by breaking down the spherical secondary structure to increase the material's surface area and the other by reconstructing the native surface layer to reduce interfacial resistance between the active material and the electrolyte. In the milling process, it was found that conducting carbon buffers NCM811 particles from breaking down, and that a decrease in the content of carbon makes it possible to break down the spherical secondary structure. Because NCM811 particles are natively covered by a dense and resistive surface layer consisting mainly of alkaline residual lithium compounds (RLCs), adding an appropriate amount of H2C2O4 into the slurry is shown to dramatically reduce interfacial resistance between the cathode and electrolyte. This is because H2C2O4 reacts with RLCs to reconstruct the texture of the dense native surface layer, which allows the liquid electrolyte to permeate and wet the active material and hence reduces the electrolyte-electrode interfacial resistance. This simple process provides an operation-viable and cost-effective strategy for improving the rate capability of Li-ion batteries.