Abstract
Ni-rich LiNi0.8Co0.1Mn0.1O2 oxide has been modified by ultrathin Al2O3 coatings via atomic layer deposition (ALD) at a growth rate of 1.12 Å/cycle. All characterizations results including TEM, SEM, XRD and XPS together confirm high conformality and uniformity of the resultant Al2O3 layer on the surface of LiNi0.8Co0.1Mn0.1O2 particles. Coating thickness of the Al2O3 layer is optimized at ~2 nm, corresponding to 20 ALD cycles to enhance the electrochemical performance of Ni-rich cathode materials at extended voltage ranges. As a result, 20 Al2O3 ALD-coated LiNi0.8Co0.1Mn0.1O2 cathode material can deliver an initial discharge capacity of 212.8 mAh/g, and an associated coulombic efficiency of 84.0% at 0.1 C in a broad voltage range of 2.7–4.6 V vs. Li+/Li in the first cycle, which were both higher than 198.2 mAh/g and 76.1% of the pristine LiNi0.8Co0.1Mn0.1O2 without the Al2O3 protection. Comparative differential capacity (dQ/dV) profiles and electrochemical impedance spectra (EIS) recorded in the first and 100th cycles indicated significant Al2O3 ALD coating effects on suppressing phase transitions and electrochemical polarity of the Ni-rich LiNi0.8Co0.1Mn0.1O2 core during reversible lithiation/delithiation. This work offers oxide-based surface modifications with precise thickness control at an atomic level for enhanced electrochemical performance of Ni-rich cathode materials at extended voltage ranges.
Highlights
Lithium ion batteries have been dominantly applied in hybrid electric vehicles (HEVs) and pure electric vehicles (EVs) [1,2], which significantly enhances our living environment
Thickness of the resultant oxide coatings can be precisely controlled at the Angstrom or atomic monolayer level, which is determined by the number of atomic layer deposition (ALD) cycles
Enhanced cycling stability of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material in an extended voltage voltage range has been realized by surface modification of ultrathin Al2 O3 coating through atomic range has been realized by surface modification of ultrathin Al2O3 coating through atomic layer layer deposition
Summary
Lithium ion batteries have been dominantly applied in hybrid electric vehicles (HEVs) and pure electric vehicles (EVs) [1,2], which significantly enhances our living environment. Because of the rapid development of practical Si–C composite anode materials, developing high-performance cathode materials with high specific capacity, high working potential, excellent cycle life, reliable safety, and low cost has become an urgent requirement [7,8,9]. Li-excess and Ni-rich layered oxides have been extensively investigated as high-energy cathode materials for superior lithium ion batteries [10,11]. The other is low coulombic efficiency in the first cycle that results from the initial electrochemical activation of the Li+ -inactive Li2 MnO3 component [10,12,13]. These two problems impede practical applications of Li-excess cathode materials. Ni-rich layered oxides have been considered as feasible cathode materials by offering a reversible capacity of ~200 mAh/g and a stable working voltage at ~3.8 V vs. Li+ /Li
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