High power and capacity of LiNi0.5Mn1.5O4 thin films cathodes prepared by pulsed laser deposition

Graphical abstract: Lithium secondary batteries using LiNi0.5Mn1.5O4 (LNMO) films as a cathode material were prepared by pulsed laser deposition on stainless steel substrates. X-ray diffraction and Field-emission Scanning Electron Microscope results show that the film deposited at 750 °C exhibits good crystallinity with well-defined grains structure. As shown in the results of X-ray photoelectron spectroscopy, the average oxidation state of Mn is increased gradually with rising substrate temperature, besides, small amounts of Fe ions can also be seen on the surface of the samples, which can affect the electrochemical properties of the samples. Charge/discharge behavior of the batteries under a high cutoff voltage of 4.9 V vs. Li was highly improved by using Li-rich samples. Excess of lithium in these samples can combine with the impurities to obtain various Li–Fe modified LNMO thin films at high annealing temperature, which exhibit larger specific capacity and higher rate capability. Especially, when the substrate temperature increases to 750 °C, the reversible capacity maintains 116.8 mAh g (1 after 100 cycles at 0.5C, and the Coulombic efficiency is nearly a constant value of 98%. It also exhibits excellent rate capability. As the rates increase to 5 and 10C, about 95.4 and 92.3% of its initial capacity at 0.2C can be retained. The rate capability of the samples can be shown as follows (Li-rich Sample A (550 °C), B (650 °C), and C (750 °C); Stoichiometric Sample D (750 °C)). -- Highlights: • Well-crystallized and high-stabilized spinel LNMO film cathode with excess of lithium was synthesized on stainless steel substrates by pulsed laser deposition technique. • The discharge capacity of the sample deposited at 750 °C decreases slightly to 116.8 mAh g−1 at 0.5C after 100 cycles with a stable Coulombic efficiency of 98%. • It also exhibits excellent rate capability. As the rates increase to 5 and 10C, about 95.4 and 92.3% of its initial capacity at 0.2C can be retained. -- Abstract: Lithium secondary batteries using LiNi0.5Mn1.5O4 films as a cathode material were prepared by pulsed laser deposition on stainless steel substrates. X-ray diffraction and Field-emission Scanning Electron Microscope results show that the film deposited at 750 °C exhibits good crystallinity with well-defined grains structure. Charge/discharge behavior of the batteries under a high cutoff voltage of 4.9 V vs. Li was highly improved by using Li-rich samples, which exhibits larger specific capacity and higher rate capability. Especially, when the substrate temperature increases to 750 °C, the reversible capacity maintains 116.8 mAh g−1 after 100 cycles at 0.5C, and the Coulombic efficiency is almost a constant value of 98%. It also exhibits excellent rate capability, as the rates increase to 5 and 10C, and about 95.4% and 92.3% of its initial capacity at 0.2C can be retained