Star-shaped lithium nitride passivation layer obtained by atmospheric-pressure plasma treatment for rechargeable lithium metal batteries

Lithium metal anodes are indispensable to realize the maximum energy density in future generation batteries. However, the lithium surface must be ‘protected’ to suppress its high reactivity and to stabilize its deposition and dissolution. Here, we report a process to form a lithium nitride (Li₃N) protective layer on lithium by a two-minute treatment in a dielectric barrier discharge (DBD) plasma. The process does not require low-pressure conditions or time-intensive post-treatments. The passivation layer is characterized by a unique, hexagonal bipyramid morphology, with α-Li₃N crystals stacked to form pillar-like structures. Such an arrangement is shown to be favorable for fast Li⁺ ion diffusion and dendrite prevention, as demonstrated by the stable Li plating/stripping of symmetric cells with passivated lithium (500 cycles compared to 150 cycles with bare lithium) at 1 mA/cm². Full cells with LiNi_0.33Mn_0.33Co_0.33O₂ (NMC111) cathode and passivated lithium anode retain 74% of their initial capacity after 300 cycles at 1C rate, by which time the cells with bare Li anode fail completely. This approach promises to be a practical solution for lithium passivation at industrial scale.