Tailored Pre-Lithiation of Carbon Anodes Using Melt Deposited Thin Lithium

Abstract

The user demands for Lithium ion batteries in mobile applications and electric vehicles request steady improvement in terms of capacity and cycle life. State-of-the-art lithium ion batteries irreversibly loose about 10 % of the capacity during the first cycles due to SEI formation. Therefore, 10 % of the cathode material is not used during the rest of the cells life which results in a waste of cathode material and leads to a lowered range of battery electric vehicles. Therefore, these losses must be compensated to ensure efficient resource utilization and to further increase the capacity of the lithium ion battery.We have developed a method to compensate these capacity losses by pre-lithiation: A fast and simple approach of electrolyte-free direct contact pre-lithiation leads to targeted degrees of pre-lithiation in a range of 7-50 % for state-of-the-art graphite electrodes. The parameters pressure (0-40 MPa), temperature (20-150°C) and time (0-60 min) are used to transfer lithium from a temporary substrate to the graphite anode. This process uses 1-5 µm thin lithium films made by the Fraunhofer IWS lithium melt deposition process as a lithium source.[1] The degree of pre-lithiation can be controlled by the lithium loading of the temporary substrate. NCM full cells built with pre-lithiated graphite electrodes where electrochemically evaluated in comparison to unlithiated electrodes. They show 6.5 % capacity increase after the first cycles using the additional lithium to form the SEI during the first cycles. The parameter influence of the pre-lithiation process on the initial coulomb efficiency of cells with pre-lithiated graphite electrodes is examined in half cells showing an ICE of 99.91 % for the best parameters.This method of electrolyte-free direct contact pre-lithiation shows an efficient way to further increase the capacity of state-of-the-art LIBs with graphite electrodes by increasing the cathode material utilization. It can potentially be scaled up to a roll-to-roll process using a heated calender nip. The temporary substrates with tailored lithium loading can be processed by lithium melt deposition in an efficient way with high lithium yield and high precision.[1] K. Schönherr, B. Schumm, F. Hippauf, R. Lissy, H. Althues, C. Leyens, S. Kaskel, Chemical Engineering Journal Advances 2022, 9, 100218. Figure 1