(Invited) Intercalation Chemistry of Oxides

The lithium-ion battery technology is based on intercalation chemistry phenomenon. The 2019 Chemistry Nobel Laurette Stanley Whittingham was the first to show in 1976 how the intercalation phenomenon can be utilized to realize a rechargeable lithium battery. He demonstrated the concept with a lithium-metal anode and a layered titanium sulfide cathode. Since then the field of intercalation chemistry for electrical energy storage has evolved during the past four decades, encompassing a variety of materials and intercalation working ions, such as monovalent lithium, sodium, and potassium, divalent magnesium, calcium, and zinc, and trivalent aluminum ions. Among the intercalation materials, oxides are at the forefront with rich fundamental structural chemistry and electrochemistry as well as with profound technological and societal impact. Accordingly, this presentation will focus on the richness and complexities of the intercalation chemistry of transition-metal oxides. The scientific and technological impact of the intercalation chemistry of oxides is illustrated by the three families of cathodes for practical lithium-ion batteries: layered oxides, spinel oxides, and polyanion oxides. The presentation will first provide a comparison of these three families of oxides, pointing out the pros and cons with respect to employing them as electrodes in rechargeable batteries as well as their limiting features from a fundamental solid-state chemistry point of view. Particularly, the structural and chemical features that impact the charge-storage capacity, operating voltage, rate capability, and practical energy density will be discussed. As we move forward, the layered oxide cathodes have become the prime candidates from an energy density consideration point of view, particularly for portable electronics and electric vehicles. However, bulk and surface instabilities during charge-discharge limit their practical energy density and cycle life, while the use of significant amounts of cobalt in them poses concerns on sustainability, cost, and supply-chain issues. Therefore, the presentation will then focus on layered oxide cathodes with high nickel contents and very low or no cobalt content to increase the energy density and lower the cost. Particularly, the role of modifications in chemical compositions through cationic substitutions on the cycle, thermal, and air instabilities will be discussed from a fundamental solid-state chemistry point of view. The use of advanced analytical techniques, such as in-situ x-ray diffraction, x-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry, scanning electron microscopy, high-resolution transmission electron microscopy, and differential scanning calorimetry in understanding the intricacies of the cathodes and mitigating the problems will be presented.