@article{35913,
  author = {Lori A Kaufman and Bryan D McCloskey},
  title = {Surface Lithium Carbonate Influences Electrolyte Degradation via Reactive Oxygen Attack in Lithium-Excess Cathode Materials},
  abstract = {<p><span>Lithium-excess layered oxide cathode materials (Li</span><sub><span>(1+<em>x</em>)</span></sub><span>TM</span><sub><span>(1–<em>x</em>)</span></sub><span>O</span><sub><span>2</span></sub><span>) for lithium-ion batteries achieve high specific capacities (≥250 mA h/g) via redox participation of both transition metals and oxygen anions. While oxygen is initially present as O</span><sup><span>2–</span></sup><span>&nbsp;in the cathode, oxidized oxygen species such as peroxo-like oxygen (O</span><sub><span class="stack">2</span></sub><sup><span class="stack">2–</span></sup><span>) and oxygen gas (O</span><sub><span>2</span></sub><span>) are known to form on charge. In this work, differential electrochemical mass spectrometry (DEMS) is used to study the mechanisms by which lithium carbonate, a common impurity, influences how these oxygen species form and react within the battery. We first show, in agreement with prior studies, that Li</span><sub><span>2</span></sub><span>CO</span><sub><span>3</span></sub><span>&nbsp;oxidizes electrochemically on charge to evolve CO</span><sub><span>2</span></sub><span>, but not O</span><sub><span>2</span></sub><span>, implying that reactive oxygen species form instead that then react with cell components to form nonvolatile products. To study the effect of Li</span><sub><span>2</span></sub><span>CO</span><sub><span>3</span></sub><span>&nbsp;on degradation processes at the cathode surface, a Li-excess cathode material Li</span><span>1.17</span><span>(Ni</span><sub><span>0.2</span></sub><span>Mn</span><sub><span>0.6</span></sub><span>Co</span><sub><span>0.2</span></sub><span>)</span><span><sub>0.83</sub></span><span>O</span><sup><span>2</span></sup><span>&nbsp;(NMC) is synthesized using a method that prevents formation of carbonate impurities in the synthesized material. Isotopically tagged lithium carbonate is then deposited on the NMC surface through controlled exposure to&nbsp;</span><sup><span>13</span></sup><span>CO</span><sub><span>2</span></sub><span>&nbsp;or C</span><sup><span>18</span></sup><span>O</span><sub><span>2</span></sub><span>&nbsp;gas. DEMS results show that when lithium carbonate is present on the cathode surface, organic fragments containing diatomic oxygen are formed on the cathode surface during charge above 4.2 V&nbsp;</span><em>versus</em><span>&nbsp;Li/Li</span><sup><span>+</span></sup><span>. Isotopic analysis indicates that the diatomic oxygen within these fragments primarily originates from the NMC lattice, with only a minor fraction originating from the Li</span><sub><span>2</span></sub><span>CO</span><sub><span>3</span></sub><span>&nbsp;itself. Our results therefore suggest that reactive oxygen released from the NMC lattice is triggered by the oxidation of surface lithium carbonate.</span></p>},
  year = {2021},
  journal = {Chemistry of Materials},
  volume = {33},
  pages = {4170 - 4176},
  month = {06/2021},
  issn = {0897-4756},
  url = {https://pubs.acs.org/doi/10.1021/acs.chemmater.1c00935},
  doi = {10.1021/acs.chemmater.1c00935},
  language = {eng},
}