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Title: Using real-time electron microscopy to explore the effects of transition-metal composition on the local thermal stability in charged Li xNi yMn zCo 1-y-zO 2 cathode materials

In this study, we use in-situ transmission electron microcopy (TEM) to investigate the thermal decomposition that occurs at the surface of charged Li xNi yMn zCo 1-y-zO 2 (NMC) cathode materials of different composition (with y, z=0.8, 0.1 and 0.6, 0.2 and 0.4, 0.3), after they have been charged to their practical upper limit voltage (4.3V). By heating these materials inside the TEM, we are able to directly characterize near surface changes in both their electronic structure (using electron energy loss spectroscopy) and crystal structure and morphology (using electron diffraction and bright-field imaging). The most Ni-rich material (y, z = 0.8, 0.1) is found to be thermally unstable at significantly lower temperatures than the other compositions – this is manifested by changes in both the electronic structure and the onset of phase transitions at temperatures as low as 100°C. Electron energy loss spectroscopy indicates that the thermally induced reduction of Ni ions drives these changes, and that this is exacerbated by the presence of an additional redox reaction that occurs at 4.2V in the y, z = 0.8, 0.1 material. Exploration of individual particles shows that there are substantial variations in the onset temperatures and overall extent of these changes.more » Of the compositions studied, the composition of y, z = 0.6, 0.2 has the optimal combination of high energy density and reasonable thermal stability. The observations herein demonstrate that real time electron microscopy provide direct insight into the changes that occur in cathode materials with temperature, allowing optimization of different alloy concentrations to maximize overall performance.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [3] ;  [4]
  1. Korea Advanced Inst. Science and Technology (KAIST), Daejeon (Korea, Republic of); Korea Inst. of Science and Technology, Seoul (Korea, Republic of)
  2. Korea Inst. of Science and Technology, Wanju-gun(Korea, Republic of)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States)
  4. Korea Inst. of Science and Technology, Seoul (Korea, Republic of)
  5. Korea Advanced Inst. Science and Technology (KAIST), Daejeon (Korea, Republic of)
Publication Date:
Report Number(s):
Journal ID: ISSN 0897-4756; R&D Project: EST431; KC0207010
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 27; Journal Issue: 11; Journal ID: ISSN 0897-4756
American Chemical Society (ACS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier: