Lithium Nitride for Prelithiating Anodes to Reduce Capacity Losses in Li-Ion Batteries
The Richardson Lab has developed a new method for prelithiating anodes to compensate for the first-cycle capacity loss associated with conventional lithium-ion batteries. The prelithiated anodes supply lithium for the irreversible reactions that occur upon initial charging, such as decomposition of the electrolyte to form a solid electrolyte interphase (SEI) layer on the anode. Since lithium ions from the cathode are not consumed in SEI formation, the battery capacity is retained.
Anode materials such as graphite, silicon, aluminum, magnesium or tin are partially lithiated via lithium-nitride metathesis reactions. Some powders are mixed by ball milling, which produces a faster and more uniform reaction. The mixtures are then heat-treated at 250-350 °C to form lithium-containing anode materials and by-products such as inert nitrides (Mg3N2 or AlN) or N2 gas in the case of Si and Sn. To prelithiate graphite anodes, carbon is added to a mixture of Li3N with just enough Mg or Al to produce only lithium and not an Mg or Al alloy. The free lithium then reacts with the carbon.
Using lithium nitride rather than lithium metal for prelithiating anode materials has several advantages, including ease of handling and mixing (Li3N is a hard powder as opposed to a soft, gummy metal) and lower cost. By partially prelithiating carbon anodes with this method, it may be possible to increase the capacity of conventional lithium-ion cells by 10% without any significant change in the manufacturing processes and with little increased cost. This technique may also help accelerate the introduction of alternative anodes containing silicon, tin, or other metalloids by reducing capacity losses (Figure 1) and preconditioning of the precursor microstructures.
Currently, the Richardson Lab is investigating the limits of prelithiation, the effects of prelithiation on cycling efficiency and reversible capacity, the influence of binders and conductive additives, and the need for added safety precautions when handling prelithiated materials.