Probing Depth-Dependent Transition-Metal Redox of Lithium Nickel, Manganese, and Cobalt Oxides in Li-Ion Batteries.

Layered lithium nickel, manganese, and cobalt oxides (NMC) are among the most promising commercial positive electrodes in the past decades. Understanding the detailed surface and bulk redox processes of Ni-rich NMC can provide useful insights into material design options to boost reversible capacity and cycle life. Both hard X-ray absorption (XAS) of metal K-edges and soft XAS of metal L-edges collected from charged LiNiMnCoO (NMC622) and LiNiMnCoO (NMC811) showed that the charge capacity up to removing ∼0.

Enhanced Cycling Performance of Ni-Rich Positive Electrodes (NMC) in Li-Ion Batteries by Reducing Electrolyte Free-Solvent Activity.

The interfacial (electro)chemical reactions between electrode and electrolyte dictate the cycling stability of Li-ion batteries. Previous experimental and computational results have shown that replacing Mn and Co with Ni in layered LiNiMnCoO (NMC) positive electrodes promotes the dehydrogenation of carbonate-based electrolytes on the oxide surface, which generates protic species to decompose LiPF in the electrolyte. In this study, we utilized this understanding to stabilize LiNiMnCoO (NMC811) by decreasing free-solvent activity in the electrolyte through controlling salt concentration and salt dissociativity.

Revealing Electronic Signature of Lattice Oxygen Redox in Lithium Ruthenates and Implications for High-Energy Li-ion Battery Material Designs.

Anion redox in lithium transition metal oxides such as LiRuO and LiMnO has catalyzed intensive research efforts to find transition metal oxides with anion redox that may boost the energy density of lithium-ion batteries. The physical origin of observed anion redox remains debated, and more direct experimental evidence is needed. In this work, we have shown electronic signatures of oxygen-oxygen coupling, direct evidence central to lattice oxygen redox (O/(O)), in charged LiRuO after Ru oxidation (Ru/Ru) upon first-electron removal with lithium de-intercalation.

Chemical Reactivity Descriptor for the Oxide-Electrolyte Interface in Li-Ion Batteries.

Understanding electrochemical and chemical reactions at the electrode-electrolyte interface is of fundamental importance for the safety and cycle life of Li-ion batteries. Positive electrode materials such as layered transition metal oxides exhibit different degrees of chemical reactivity with commonly used carbonate-based electrolytes. Here we employed density functional theory methods to compare the energetics of four different chemical reactions between ethylene carbonate (EC) and layered (LiMO) and rocksalt (MO) oxide surfaces.