Atomic Layer Deposition of Nanocomposite Fluoride Coatings for Li-Ion Batteries

Abstract

The energy storage market is projected to reach >$50 billion in the next five years. Major segments of this market consist of rechargeable lithium-ion batteries for consumer electronics, electric vehicles (automobiles, drones, aviation and space applications) and stationary storage for smart grids. For all these applications, high energies and capacities are required to meet the needs of consumer demands and economic viability. However, in order to meet these demands, lithium-ion materials must operate successfully at relatively high voltages (i.e. ≥ ~4.4V vs. Li/Li+) in practical cells. In particular, the cathode/electrolyte interfaces must be stabilized to prevent deleterious electrochemical reactions which can cause transition metal dissolution, capacity fade, and cell failure. The conventional approach to stabilize cathode surfaces is to use protective coatings consisting mostly of metal oxides such as TiO2, ZrO2, HfO2, and Al2O3. However, despite nearly two decades of research and development, these metal oxide coatings are still susceptible to chemical attack by hydrogen fluoride (HF) that forms in the liquid electrolyte during battery cycling. The HF dissolves the metal oxide coatings exposing the underlying cathode material. To resolve the issues related to HF and improve electrode-surface stability, we have developed atomic layer deposition (ALD) based, nanocomposite fluoride coatings that resist dissolution by HF. We have added ultrathin nanocomposite fluoride coatings on various cathode materials such as conventional LiCoO2, various NMCs-(e.g., LiMO2, M=Mn, Ni, Co), and Li/Mn-rich, layered-layered-spinel (LLS) composite cathodes. These coatings are found to significantly improve the stability and performance of the cathodes in lithium-ion cells. Here we will present ALD growth of nanocomposite fluorides for Li-ion batteries and some of the latest electrochemical results.