Abstract
Although the two active redox centers in Li-rich cathodes, including the anionic and cationic contributions, can enable Li-ion batteries to achieve outstanding specific energy, their behaviors at different current densities have not been clarified. Here, we provide a comparative study of transition metals (TMs) and oxygen redox activities by directly accessing their oxidation states in Li-rich materials operated at very different current rates. Our data reveal that the oxidation of oxygen in the near-surface region is at the same level for electrodes cycled with a wide range of current rates, indicating a reaction gradient of lattice oxygen redox reactions. The oxidation process of lattice oxygen is found to be dynamically compatible with that of the TMs. Combining the results of first principles calculations and complementary experimental findings, we propose a detailed mechanism of structural distortion from octahedral Li to tetrahedral Li and the role of oxygen vacancy in Li+ diffusion. It is found that fast delithiation occurring at high current densities can easily cause local structural transformation, leading to a limited Li+ diffusion rate and consequently suppressing rate capability.
| Original language | English |
|---|---|
| Pages (from-to) | 4137-4147 |
| Number of pages | 11 |
| Journal | Energy and Environmental Science |
| Volume | 15 |
| Issue number | 10 |
| DOIs | |
| State | Published - Jul 18 2022 |
Funding
X. H and R. K were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office, under the Advanced Battery Materials Research (BMR) Program of the US Department of Energy under Contract No. DE-AC02-05CH11231. Computational studies by Z. Z and A. J were funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Materials Project program KC23MP). This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231 using NERSC award BES-ERCAP0018557. Soft X-ray spectroscopy results were collected at the Advanced Light Source, a US DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Research at Lawrence Berkeley National Laboratory is partially supported by the Energy Biosciences Institute through the EBI-Shell program.