Next-gen batteries: enabled by spatial atomic layer interfacing

Li-ion batteries have emerged as the key energy storage technology, not only in portable electronics & gadgets but also in electric vehicles (EV) and grid-storage. A combination of high energy density anodes such as silicon or lithium, and Ni- or Li-rich cathode1,2 is necessary to achieve the targeted energy density of >350 Wh/Kg. The challenge is that such extreme redox-chemistries bring safety issues and degradation3, especially at the electrode-electrolyte interfaces4. In order to improve safety, solid polymer electrolytes5 and ceramic electrolytes6 are proposed to replace liquid electrolyte composed of organic solvents, which are highly flammable and toxic. However, most of the solid electrolytes and also the conventional liquid electrolyte (to a lesser extent), has either oxidative or reductive instability against the new generation electrodes leading to capacity degradation during cycling. In brief, most of the safety and capacity degradation issues arise from the incompatibility of electrodes and electrolytes, i.e. highly unstable interfaces. Thus, an optimized interface is the key to the success of new generation Li-ion battery in terms of stability and safety. The preffered way to achieve this is by creating artificial electrode-electrolyte interfaces that are stable against the electrochemical environment and has the ability to protect the electrode as well as electrolyte surfaces from degradation by acting as a lithium conducting barrier. These interfaces can be formed either in-situ using electrolyte additives or ex-situ via chemical or physical methods. However, in the state-of-the-art cells, the above methods have not yet been shown to guaranty the required uniform atomic layer interfacial coating at an industrial scale. The relative newcomer in this field is atomic layer deposition (ALD), has the potential to play a big role in interfacial-engineering owing to its ability to achieve conformal interfacial coatings at an atomic scale7. However, conventional vacuum-based ALD is not compatible with the high throughput roll-to-roll battery electrode production. Here, spatial ALD (sALD)8 technology, an advanced version of ALD at ambient pressure, is a prime choice due to its reel-to-reel scalability and higher throughput. TNO-Holst center has established roll-to-roll sALD in the past several years for various applications. Wide range of materials including metal, metal oxides, nitrides, sulfides, organic, polymer, and polymers are possible using sALD depending upon the chemistry and reactivity at the electrode surfaces. We will showcase various sALD films Al2O3, TiO2, ZnO, etc., which are specifically tailored to address various issues such as lithium dendrite formation, interface stabilization, cathode degradation protection, etc. Thanks to the selective deposition reaction of sALD, the passivation coatings at interfaces can reach all the way down within a thick commercial electrode (50-60μm). Furthermore, our pinhole-free sALD-LiPON electrolyte thin films with Li-ion conductivity >10-7 S/cm will be presented.