Abstract
Electrochemical energy storage devices based on Li-ion cells currently power almost all electronic devices and power tools. The development of new Li-ion cell configurations by incorporating innovative functional components (electrode materials and electrolyte formulations) will allow to bring this technology beyond mobile electronics and to boost performance largely beyond the state-of-the-art. Here we demonstrate a new full Li-ion cell constituted by a high-potential cathode material, i.e. LiNi0.5Mn1.5O4, a safe nanostructured anode material, i.e. TiO2, and a composite electrolyte made by a mixture of an ionic liquid suitable for high potential applications, i.e. Pyr1,4PF6, a lithium salt, i.e. LiPF6, and standard organic carbonates. The final cell configuration is able to reversibly cycle lithium for thousands of cycles at 1000 mAg−1 and a capacity retention of 65% at cycle 2000.
Highlights
Energy conversion and storage are key enabling technologies that will pave the way in the XXI century to mass electro-mobility, smart-grids of continental-size and realistic reduction of CO2 emissions
The key-innovation stands in the unique combination of (a) a nanostructure TiO2-based negative electrode with a tailored 1-D tubular morphology; (b) a LiNi0.5Mn1.5O4-based positive electrode (LNMO) with a finely tuned stoichiometry and a surface layer obtained through a single-stage, simple, cheap and easy-scalable mechanochemical milling route followed by high temperature annealing in air; and (c) a composite liquid electrolyte formed by a mixture of LiPF6, ethylene carbonate, dimethyl carbonate and N-n-butyl-N-methylpyrrolidinium hexafluorophosphate (Py14PF6) ionic liquid with optimized composition[4]
Preliminary X-ray Photoelectron Spectroscopy (XPS) data suggest that this native surface layer is mainly constituted by Cr(III) oxide and spontaneously grows on the surface of well-formed crystalline iron-doped LNMO particles at 800 °C
Summary
Energy conversion and storage are key enabling technologies that will pave the way in the XXI century to mass electro-mobility, smart-grids of continental-size and realistic reduction of CO2 emissions. The key-innovation stands in the unique combination of (a) a nanostructure TiO2-based negative electrode with a tailored 1-D tubular morphology; (b) a LiNi0.5Mn1.5O4-based positive electrode (LNMO) with a finely tuned stoichiometry and a surface layer obtained through a single-stage, simple, cheap and easy-scalable mechanochemical milling route followed by high temperature annealing in air; and (c) a composite liquid electrolyte formed by a mixture of LiPF6, ethylene carbonate, dimethyl carbonate and N-n-butyl-N-methylpyrrolidinium hexafluorophosphate (Py14PF6) ionic liquid with optimized composition[4] This full cell configuration is able to provide outstanding performance in terms of power density and cycling life, in combination with an intrinsically higher safety, compared to commercial cells, provided by the ionic liquid component, and lower costs as well as an improved environmental compatibility due to the absence of cobalt in the cathode material. Only the combination of a suitable lattice doping with coating layers through complex and expensive multi-stage synthetic procedures is apparently able to lead to materials with superior properties in lithium cells[12]
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