Investigation of novel Nanolayer coating technique for Li-ion batteries

The push for the electrification of vehicles has prompted extensive research on high-energy active materials for the electrodes. Lithium cobalt oxide (LiCoO₂), which has been used as the cathode for the past three decades, does not meet the increasing demands due to its limited practical capacity. Because of this, nickel-based cathodes containing cobalt and manganese (NMC) have been widely researched, as they exhibit a higher practical capacity. In NMC, nickel provides a high capacity, cobalt improves the rate capability and manganese maintains the structural stability. One factor limiting the capacity of NMC is the cut-off potential used, which is generally about 4.3 V. The potential can typically be increased to 4.5V to get more capacity, however, the surface undergoes a reconstruction (from a layered to a rock-salt structure) upon high-voltage cycling [1]. This surface reconstruction is responsible for capacity fading and impedance build up, preventing high-voltage operation.

In order to circumvent the structural reconstruction, a conformal coating can be applied onto the cathode surface to prevent any changes to the cathode surface. Currently, coatings are generally performed via a solution-based process. These do not require expensive tools and can be done relatively quickly. However, it is hard to control the thickness of the layer and conformal coating is not always obtained. Using vapour-based techniques, such as atomic layer deposition (ALD), conformal coatings can be achieved, however, complex machinery is required, and the deposition process is much slower than solution-based methods. Recently, a facile new method, called condensed layer deposition (CLD), has been developed which takes advantage of the interfacial tension between a polar and non-polar liquid to achieve a conformal coating without the need for complex equipment [2].

In this thesis, you will investigate the CLD method for its capability of conformal coating the dense particle composite active material layers in batteries. The coating surface will be characterised by techniques such as Raman, EDX and SEM. The student will then test the efficiency of the coating, using electrochemical methods.

1. Lin, F.; Markus, I. M.; Nordlund, D.; Weng, T.-C.; Asta, M. D.; Xin, H. L.; Doeff, M. M. Nature Communications 2014,5, 3529.
2. Jasim, A. M.; He, X.; White, T. A.; Xing, Y. Communications Materials2020, 1, 1–7.