K.V. Carballo, X. Meng
University of Arkansas,
United States
Keywords: lithium metal batteries (LMBs), lithium metal (Li), LiNi0.8Mn0.1Co0.1 (NMC811), atomic layer deposition (ALD), molecular layer deposition (MLD)
Summary:
Lithium metal batteries (LMBs) have been proposed as an alternative technology over state-of-the-art lithium-ion batteries (LIBs), featuring the replacement of the traditional graphite anodes (372 mAh/g) by high-capacity lithium metal (Li, 3,860 mAh/g) and therefore a 50% increase in energy density. In this respect, coupling Li anodes with high-capacity layered nickel-rich oxides (e.g., LiNi0.8Mn0.1Co0.1O2, or NMC811 for short) is among the most popular pursuits. The resulting Li||NMC811 LMBs have a potential to achieve an energy density of 400 Wh/kg, much higher than ~250 Wh/kg of current LIBs. Although very promising, Li||NMC811 LMBs have been hindered from commercialization by severe structural and interfacial issues at both their anode and cathode. On the anode side, Li anodes suffer from dendrite growth and continuous formation of unstable solid electrolyte interphase (SEI). These two intertwined issues are self-accelerated and jointly lead to the depletion of electrolytes and cyclable Li. Additionally, Li dendrites also are possible to grow into the cathode side and thereby cause fire and explosion. On the cathode side, NMC811 experiences many issues due to its structural degradation and interfacial instability. To address all these issues, we utilized two powerful thin-film deposition techniques, atomic layer deposition (ALD) and molecular layer deposition (MLD), which are capable of forming uniform and conformal protective coatings over both the anode and cathode to tackle the structural and interfacial issues. To this end, we for the first time disclosed that sulfides are an important class of coating materials having some unique functions to address the issues of NMC811, which can be applied. On the other hand, we developed novel lithicone coatings via MLD, which exhibit exceptional ionic conductivity and stability as protective coatings of Li anodes. We verified that they can remarkably inhibit SEI formation and Li dendritic growth, leading to long term cycling stability of Li||Li cells. Very compellingly, we demonstrated that these ALD sulfide coatings are compatible with the MLD lithicone coatings in Li||NMC811 cells. In addition to boosting the stability of both the anode and cathode, they could work synergistically to mitigate the crosstalk between the anode and cathode to maximize the performance of the resultant Li||NMC811 cells. All these efforts together pave a feasible technical pathway for commercializing the Li||NMC811 LMBs.