Leah A. Riley

Ultrathin Direct Atomic Layer Deposition on Composite Electrodes for Highly Durable and Safe Li‐Ion Batteries

Abstract : In order to employ Li-ion batteries (LIBs) in next-generation hybrid electric and/or plug-in hybrid electric vehicles (HEVs and PHEVs), LIBs must satisfy many requirements: electrodes with long lifetimes (fabricated from inexpensive environmentally benign materials), stability over a wide temperature range, high energy density, and high rate capability. Establishing long-term durability while operating at realistic temperatures (5000 charge-depleting cycles, 15 year calendar life, and a range from -46 deg C to +66 deg C) for a battery that does not fail catastrophically remains a significant challenge. Recently, surface modifications of electrode materials have been explored as viable paths to improve the performance of LIBs for vehicular applications. Here we clearly demonstrate that conformal ultrathin protective coating by inactive metal oxide without disrupting inter-particle electronic pathway can be realized by atomic layer deposition (ALD) directly performed on a composite electrode, which leads to significant improvement of both long-term durability and safety of NG anode. Also ALD coatings are significantly more promising than efforts that have been previously reported.

Conformal Surface Coatings to Enable High Volume Expansion Li-Ion Anode Materials

An alumina surface coating is demonstrated to improve electrochemical performance of MoO(3) nanoparticles as high capacity/high-volume expansion anodes for Li-ion batteries. Thin, conformal surface coatings were grown using atomic layer deposition (ALD) that relies on self-limiting surface reactions. ALD coatings were tested on both individual nanoparticles and prefabricated electrodes containing conductive additive and binder. The coated and non-coated materials were characterized using transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. Importantly, increased stability and capacity retention was only observed when the fully fabricated electrode was coated. The alumina layer both improves the adhesion of the entire electrode, during volume expansion/contraction and protects the nanoparticle surfaces. Coating the entire electrode also allows for an important carbothermal reduction process that occurs during electrode pre-heat treatment. ALD is thus demonstrated as a novel and necessary method that may be employed to coat the tortuous network of a battery electrode.

Improved Mechanical Integrity of ALD-Coated Composite Electrodes for Li-Ion Batteries

Mechanical properties of composite anodes coated with by atomic layer deposition (ALD) were examined using nanoindentation and nanoscratching. Significant improvement in adhesion to the current collector for the ALD-coated is observed. This improved adhesion enables enhanced electrical conductivity for these high capacity/high volume expansion materials, suggesting the potential of these coatings for high-energy density Li-ion batteries suitable for vehicular applications.