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

Ryoichi Tatara; Yang Yu; Pinar Karayaylali; Averey K Chan; Yirui Zhang; Roland Jung; Filippo Maglia; Livia Giordano; Yang Shao-Horn

doi:10.1021/acsami.9b11942

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

ACS Appl Mater Interfaces. 2019 Sep 25;11(38):34973-34988. doi: 10.1021/acsami.9b11942. Epub 2019 Sep 13.

Authors

Ryoichi Tatara, Yang Yu, Pinar Karayaylali, Averey K Chan¹, Yirui Zhang, Roland Jung², Filippo Maglia², Livia Giordano, Yang Shao-Horn

Affiliations

¹ Department of Materials , Imperial College London , Royal School of Mines Building, Prince Consort Road , London SW7 2AZ , U.K.
² BMW Group , Petuelring 130 80788 Munich , Germany.

PMID: 31433154
DOI: 10.1021/acsami.9b11942

Abstract

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 LiNi_xMn_yCo_1-x-yO₂ (NMC) positive electrodes promotes the dehydrogenation of carbonate-based electrolytes on the oxide surface, which generates protic species to decompose LiPF₆ in the electrolyte. In this study, we utilized this understanding to stabilize LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) by decreasing free-solvent activity in the electrolyte through controlling salt concentration and salt dissociativity. Infrared spectroscopy revealed that highly concentrated electrolytes with low free-solvent activity had no dehydrogenation of ethylene carbonate, which could be attributed to slow kinetics of dissociative adsorption of Li⁺-coordinated solvents on oxide surfaces. The increased stability of the concentrated electrolyte against solvent dehydrogenation gave rise to high capacity retention of NMC811 with capacities greater than 150 mA h g^-1 (77% retention) after 500 cycles without oxide-coating and Ni-concentration gradients or electrolyte additives.

Keywords: Activity; Concentrated Electrolyte; Electrode−electrolyte Interface; Li-ion Batteries; NMC; Ni-rich Positive Electrodes; Solvation Structure.