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Dual function Li-reactive coating from residual lithium on Ni-rich NCM cathode material for Lithium-ion batteries.

ABSTRACT: In this study, lithium phosphate (Li₃PO₄) is coated on the surface of Ni-rich LiNi_0.91Co_0.06Mn_0.03O₂ cathode material to enhance its cyclability and rate performance. The process is carried-out by achieving dual benefits, reduction of residual lithium compounds by converting them into Li₃PO₄ coating material. The 0.1 mol.% Li₃PO₄ (LiP) sample exhibits a capacity retention of 82% while the pristine NCM shows only 68.1% after 100 cycles. In addition, the LiP-0.1 NCM delivers high discharge capacities (161.9 mAh g^-1 at 3C, 144.3 mAh g^-1 at 4C and 94.6 mAh g^-1 at 5C) as compared to the pristine NCM (129.3 mAh g^-1 at 3C, 67.4 mAh g^-1 at 4C and 33.4 mAh g^-1 at 5C) in the voltage range of 3.0-4.3 V. In addition, the irreversible phase transition has also suppressed in the coated sample which is confirmed by cyclic voltammetry. Our study suggests that Li₃PO₄ coating reduces the polarization and acts as protecting layer between the electrode and electrolyte that results in the superior electrochemical performance.

SUBMITTER: Sattar T

PROVIDER: S-EPMC8452671 | biostudies-literature |

REPOSITORIES: biostudies-literature

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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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Dual function Li-reactive coating from residual lithium on Ni-rich NCM cathode material for Lithium-ion batteries.

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