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J Am Chem Soc. 2016 Oct 12;138(40):13326-13334. Epub 2016 Sep 30.

Tuning of Thermal Stability in Layered Li(NixMnyCoz)O2.

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School of Advanced Materials, Peking University, Shenzhen Graduate School , Shenzhen 518055, People's Republic of China.
Electrochemical Technology Program, Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Shenzhen Tianjiao Technology Development Co., Ltd. , Shenzhen 518119, People's Republic of China.
Shenzhen OptimumNano Energy Co., Ltd , Shenzhen 518118, People's Republic of China.
Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory , 902 Battelle Boulevard, Richland, Washington 99352, United States.


Understanding and further designing new layered Li(NixMnyCoz)O2 (NMC) (x + y + z = 1) materials with optimized thermal stability is important to rechargeable Li batteries (LIBs) for electrical vehicles (EV). Using ab initio calculations combined with experiments, we clarified how the thermal stability of NMC materials can be tuned by the most unstable oxygen, which is determined by the local coordination structure unit (LCSU) of oxygen (TM(Ni, Mn, Co)3-O-Li3-x'): each O atom bonds with three transition metals (TM) from the TM-layer and three to zero Li from fully discharged to charged states from the Li-layer. Under this model, how the lithium content, valence states of Ni, contents of Ni, Mn, and Co, and Ni/Li disorder to tune the thermal stability of NMC materials by affecting the sites, content, and the release temperature of the most unstable oxygen is proposed. The synergistic effect between Li vacancies and raised valence state of Ni during delithiation process can aggravate instability of oxygen, and oxygen coordinated with more nickel (especially with high valence state) in LSCU becomes more unstable at a fixed delithiation state. The Ni/Li mixing would decrease the thermal stability of the "Ni═Mn" group NMC materials but benefit the thermal stability of "Ni-rich" group, because the Ni in the Li layer would form 180° Ni-O-Ni super exchange chains in "Ni-rich" NMC materials. Mn and Co doping can tune the initial valence state of Ni, local coordination environment of oxygen, and the Ni/Li disorder, thus to tune the thermal stability directly.


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