Liquid Ammonia Chemical Lithiation: An Approach for High-Energy and High-Voltage Si–Graphite|Li_1+xNi_0.5Mn_1.5O₄ Li-Ion Batteries

Chemical lithiation using lithium metal dissolved in liquid ammonia is introduced for the first time as a viable, potentially scalable method to overlithiate cathode materials, in this case, the 5 V spinel Li_1+xNi_0.5Mn_1.5O₄. In this formula the value of x represents the amount of extra lithium inserted into the spinel. Such overlithiated cathodes can subsequently be used to prelithiate high-energy anodes in a lithium-ion battery configuration during the first charge step. Lithiated 5 V spinel Li_1+xNi_0.5Mn_1.5O₄ cathode materials prepared by this technique show higher first delithiation capacities, confirming the chemically inserted lithium is electrochemically active. Full cells with a Si–graphite anode and the Li_1+xNi_0.5Mn_1.5O₄ (x = 0.62) cathode show a 23% higher reversible capacity in the first cycle than LiNi_0.5Mn_1.5O₄ baseline cells and improved capacity retention. The extra chemically inserted lithium therefore sacrificially compensates for the loss of lithium at the anode, allowing higher utilization of the cathode capacity in following cycles.