Atomic layer deposition (ALD) coating provides precision surface engineering through a gas phase chemical process that sequentially exposes a material substrate surface to alternating precursor molecules. These precursor molecules react with the surface during each pulse to form a uniform coating on the substrate surface. ALD precursors are self-limiting in that they only deposit one layer at a time. This process is non-directional with no line-of-sight restrictions as gas molecules can diffuse to coat all surfaces.
ALD technology is used to coat nanoparticles and deposit inorganic materials such as metals, oxides, sulphides, nitrides, phosphates fluorides, selenides, and tellurides. Organic polymers (molecular layer deposition) and hybrid inorganic/organic mixtures can also be deposited onto substrate surfaces.
Surface engineering of interfaces is becoming increasingly important in pushing the bounds of next-generation high-performance materials across a myriad of applications, ranging from batteries, catalysts, and 3D printing to displays, pharma, and many other markets.
Battery performance and degradation is defined at the many surface interfaces that exist between cell components. ALD is a method that can control those interfaces particularly for the cathode and anode active materials but also for solid electrolytes and separators.
Surface Engineering Conventional Cathode Materials
ALD coatings on nickel-rich NMC, NCA, and LCO cathode materials have been demonstrated to extend cycle life, improve safety, increase charge rate capability, reduce resistance growth, and increase energy density.
ALD can stabilize surfaces and enable higher voltage operation, with corresponding increases of up to 20% energy density. The abuse tolerance and safety of the cell is dramatically improved with a 2X threshold on thermal runaway and a reduced probability and magnitude for an event. When used to increase cell voltage, ALD coatings can lead to an overall reduction in battery pack cost on a $/kWr basis by utilizing more of the existing capacity inherent in the battery. Furthermore, growth of internal resistance is dramatically lowered with cycle life on batteries with ALD coated cathodes and anodes.
Surface Engineering Emerging Cathode Materials
Surface engineering of high voltage cathode material can increase energy density and in some cases may reduce the number of cells necessary for the required nominal voltage. It can also enable alternative cobalt-free chemistries such as lithium-nickel-manganese-oxide (LNMO), which are attractive for reducing critical, price volatile materials such as cobalt. However, this comes with the trade-off of less energy density.
LMNO can achieve near parity on energy density with other conventional chemistries at a much more affordable price if it can be operated at a higher nominal voltage. However, this requires surface engineering to achieve an encapsulation coating that will provide a meaningful cycle life at higher voltages for industry use. Forge Nano’s ALD coating can provide LNMO surface engineering that is capable of extending the life-time of this high voltage material.
Surface Engineering Anode Materials
ALD coating of both natural and synthetic graphite anodes can also produce substantial benefits for battery cycle life, charge rate capability and safety. Surface engineering of graphite anodes can reduce the rate of SEI growth on the anode surface, thereby increasing performance with a higher cycle life. High conductivity coatings can be engineered to improve the rate capability of graphite anodes including performance at lower temperatures.
ALD coated graphite anodes can decouple or delay the onset of the cascading series of side reactions that lead to safety-related thermal runaway events. In addition to improving the performance of conventional graphite anodes, Forge Nano’s surface engineering technology is also being applied for the use of emerging silicon anodes. This includes the future development of organic polymeric coatings and hybrid inorganic-organic coatings with enough flexibility for nano-silicon materials to ‘breathe’ during lithiation while maintaining their structural integrity.
Surface Engineering of Battery Cells with Forge Nano
Forge Nano is a world leader in the successful surface engineering of Li-ion battery cells with improved precision and cost. Our ALD coating processes enhance the capabilities, longevity, and safety of battery cell devices through surface engineering of conventional cathodes and anodes, novel high voltage cathodes, and emerging silicon anodes. ALD can also be applied beyond Li-ion battery technologies such as solid state electrolytes, lithium metal anodes, and to engineering of the interfaces between these materials and other battery components to enable future breakthrough batteries.