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Surface enrichment and diffusion enabling gradient-doping and coating of Ni-rich cathode toward Li-ion batteries.

ABSTRACT: Critical barriers to layered Ni-rich cathode commercialisation include their rapid capacity fading and thermal runaway from crystal disintegration and their interfacial instability. Structure combines surface modification is the ultimate choice to overcome these. Here, a synchronous gradient Al-doped and LiAlO₂-coated LiNi_0.9Co_0.1O₂ cathode is designed and prepared by using an oxalate-assisted deposition and subsequent thermally driven diffusion method. Theoretical calculations, in situ X-ray diffraction results and finite-element simulation verify that Al³⁺ moves to the tetrahedral interstices prior to Ni²⁺ that eliminates the Li/Ni disorder and internal structure stress. The Li⁺-conductive LiAlO₂ skin prevents electrolyte penetration of the boundaries and reduces side reactions. These help the Ni-rich cathode maintain a 97.4% cycle performance after 100 cycles, and a rapid charging ability of 127.7 mAh g^-1 at 20 C. A 3.5-Ah pouch cell with the cathode and graphite anode showed more than a 500-long cycle life with only a 5.6% capacity loss.

SUBMITTER: Yu H

PROVIDER: S-EPMC8316340 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature

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Surface enrichment and diffusion enabling gradient-doping and coating of Ni-rich cathode toward Li-ion batteries.

Yu Haifeng H Cao Yueqiang Y Chen Long L Hu Yanjie Y Duan Xuezhi X Dai Sheng S Li Chunzhong C Jiang Hao H

Nature communications 20210727 1

Critical barriers to layered Ni-rich cathode commercialisation include their rapid capacity fading and thermal runaway from crystal disintegration and their interfacial instability. Structure combines surface modification is the ultimate choice to overcome these. Here, a synchronous gradient Al-doped and LiAlO2-coated LiNi0.9Co0.1O2 cathode is designed and prepared by using an oxalate-assisted deposition and subsequent thermally driven diffusion method ...[more]

PMID: 34315905

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Project description:The chemical and electrochemical reactions at the positive electrode-electrolyte interface in Li-ion batteries are hugely influential on cycle life and safety. Ni-rich layered transition metal oxides exhibit higher interfacial reactivity than their lower Ni-content analogues, reacting via mechanisms that are poorly understood. Here, we study the pivotal role of the electrolyte solvent, specifically cyclic ethylene carbonate (EC) and linear ethyl methyl carbonate (EMC), in determining the interfacial reactivity at charged LiNi0.33Mn0.33Co0.33O2 (NMC111) and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells. While NMC111 exhibits similar parasitic currents with EC-containing and EC-free electrolytes during high voltage holds in NMC/Li4Ti5O12 (LTO) cells, this is not the case for NMC811. Online gas analysis reveals that the solvent-dependent reactivity for Ni-rich cathodes is related to the extent of lattice oxygen release and accompanying electrolyte decomposition, which is higher for EC-containing than EC-free electrolytes. Combined findings from electrochemical impedance spectroscopy (EIS), TEM, solution NMR, ICP, and XPS reveal that the electrolyte solvent has a profound impact on the degradation of the Ni-rich cathode and the electrolyte. Higher lattice oxygen release with EC-containing electrolytes is coupled with higher cathode interfacial impedance, a thicker oxygen-deficient rock-salt surface reconstruction layer, more electrolyte solvent and salt breakdown, and higher amounts of transition metal dissolution. These processes are suppressed in the EC-free electrolyte, highlighting the incompatibility between Ni-rich cathodes and conventional electrolyte solvents. Finally, new mechanistic insights into the chemical oxidation pathways of electrolyte solvents and, critically, the knock-on chemical and electrochemical reactions that further degrade the electrolyte and electrodes curtailing battery lifetime are provided.

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Surface enrichment and diffusion enabling gradient-doping and coating of Ni-rich cathode toward Li-ion batteries.

Publications

Surface enrichment and diffusion enabling gradient-doping and coating of Ni-rich cathode toward Li-ion batteries.

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