Low- and Zero-Cobalt Layered Oxide Cathodes for Lithium-Ion Batteries

Abstract

Lithium-ion batteries have become an integral part of our daily life, powering portable electronic devices. They are in the process of transforming the transportation sector through electrification. They are also being intensively pursued for grid storage of electricity produced from renewable sources. Cost, sustainability, and supply-chain issues are major considerations in employing lithium-ion batteries for electric vehicle (EV) and grid storage applications. In the case of EVs, energy density or driving distance between charges is a critical parameter as well. These considerations have created immense interest to reduce cobalt content or eliminate cobalt altogether in layered oxide cathodes. With this perspective, the research and development trend has been to increase the nickel content and lower the cobalt content in LiNi1-y-xMny-CozO2 (NMC) cathodes. For instance, the industry has been gradually moving from LiCoO2 with 100% Co to NMC-111 with 33% Ni and 33% Co to NMC-622 with 60% Ni and 20% Co to NMC-811 with 80% Ni and 10% Co. While the increase in Ni content offers both an increase in capacity and a reduction in cost, it is also met with serious technical challenges. As the Ni content increases beyond 60%, the cathodes suffer from poor cycle, thermal, and air stabilities. The problems become exponentially challenging as the Ni content increases. This presentation will focus on improving the cycle, thermal, and air stabilities through compositional and controlled synthesis approaches, while reducing the Co content significantly as well as eliminating it altogether to give low- and zero-cobalt layered oxide cathodes with high capacities.The low- and zero-cobalt layered oxide cathodes are synthesized by a coprecipitation of the hydroxide precursors with appropriate doping, employing a tank reactor, followed by calcining with lithium hydroxide at optimal temperatures under a flowing oxygen atmosphere. As the Ni content increases, the calcining temperature and conditions need to be sensitively controlled to obtain high-quality samples. The presentation will particularly focus on the performance evaluation and a fundamental understanding of the degradation mechanisms with cathodes containing > 90% nickel, including LiNiO2. The electrochemical performances are evaluated with full pouch cells by pairing the cathodes with graphite anode. The bulk and surface instabilities are assessed by employing a suite of advanced analytical methodologies, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), time-of-flight – secondary ion mass spectrometry (TOF-SIMS), high-resolution transmission electron microscopy (HR-TEM), etc. before and after extended cycling of full pouch cells. The presentation will also focus on assessing and improving the air stability as well as thermal stability of various compositions. Approaches to realize capacity values as high as 220 mAh/g will be presented.