in-situ-neutron-powder-diffraction-using-custom-made-lithium-ion

<em>In Situ</em> Neutron Powder Diffraction Using Custom-made Lithium-ion Batteries

Li-ion batteries are widely used in portable electronic devices and are considered as promising candidates for higher-energy applications such as electric ...

University of Wollongong

Australian Nuclear Science and Technology Organisation

Sodium-ion batteries can be the best alternative to lithium-ion batteries, because of their similar electrochemistry, nontoxicity, and elemental abundance and the low cost of sodium. They still stand in need of better cathodes in terms of their structural and electrochemical aspects. Accordingly, the present study reports the first example of the preparation of Na2/3(Fe1/2Mn1/2)O2 hierarchical nanofibers by electrospinning. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically, resulting in enhanced cyclability when compared to nanoparticles, with initial discharge capacity of ∼195 mAh g(-1). This is attributed to the good interconnection among the fibers, with well-guided charge transfers and better electrolyte contacts.

Electrospun P2-type Na(2/3)(Fe(1/2)Mn(1/2))O2 hierarchical nanofibers as cathode material for sodium-ion batteries.

Structural phase transitions can be used to alter the properties of a material without adding any additional elements and are therefore of significant technological value. It was found that the hexagonal-SnS2 phase can be transformed into the orthorhombic-SnS phase after an annealing step in an argon atmosphere, and the thus transformed SnS shows enhanced sodium-ion storage performance over that of the SnS2, which is attributed to its structural advantages. Here, we provide the first report on a SnS@graphene architecture for application as a sodium-ion battery anode, which is built from two-dimensional SnS and graphene nanosheets as complementary building blocks. The as-prepared SnS@graphene hybrid nanostructured composite delivers an excellent specific capacity of 940 mAh g(-1)and impressive rate capability of 492 and 308 mAh g(-1) after 250 cycles at the current densities of 810 and 7290 mA g(-1), respectively. The performance was found to be much better than those of most reported anode materials for Na-ion batteries. On the basis of combined ex situ Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ex situ X-ray diffraction, the formation mechanism of SnS@graphene and the synergistic Na-storage reactions of SnS in the anode are discussed in detail. The SnS experienced a two-structural-phase transformation mechanism (orthorhombic-SnS to cubic-Sn to orthorhombic-Na3.75Sn), while the SnS2 experienced a three-structural-phase transformation mechanism (hexagonal-SnS2 to tetragonal-Sn to orthorhombic-Na3.75Sn) during the sodiation process. The lesser structural changes of SnS during the conversion are expected to lead to good structural stability and excellent cycling stability in its sodium-ion battery performance. These results demonstrate that the SnS@graphene architecture offers unique characteristics suitable for high-performance energy storage application.

Enhanced sodium-ion battery performance by structural phase transition from two-dimensional hexagonal-SnS2 to orthorhombic-SnS.

The development of cathode materials with high capacity and cycle stability is essential to emerging electric-vehicle technologies, however, of serious environmental concern is that materials with these properties developed so far contain the toxic and expensive Co. We report here the Li-rich, Co-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode material, prepared via a template-free, one-step wet-chemical method followed by conventional annealing in an oxygen atmosphere. The cathode has an unprecedented level of cation mixing, where the electrochemically-active component contains four elements at the transition-metal (3a) site and 20% Ni at the active Li site (3b). We find Ni(2+)/Ni(3+)/Ni(4+) to be the active redox-center of the cathode with lithiation/delithiation occurring via a solid-solution reaction where the lattice responds approximately linearly with cycling, differing to that observed for iso-structural commercial cathodes with a lower level of cation mixing. The composite cathode has ∼75% active material and delivers an initial discharge-capacity of ∼103 mA h g(-1) with a reasonable capacity retention of ∼84.4% after 100 cycles. Notably, the electrochemically-active component possesses a capacity of ∼139 mA h g(-1), approaching that of the commercialized LiCoO2 and Li(Ni1/3Mn1/3Co1/3)O2 materials. Importantly, our operando neutron powder-diffraction results suggest excellent structural stability of this active component, which exhibits ∼80% less change in its stacking-axis than for LiCoO2 with approximately the same capacity, a characteristic that may be exploited to enhance significantly the capacity retention of this and similar materials.

Article	Year
Electrospun P2-type Na(2/3)(Fe(1/2)Mn(1/2))O2 hierarchical nanofibers as cathode material for sodium-ion batteries. ACS applied materials & interfaces\| PubMed ID: 24905950	2014
Enhanced sodium-ion battery performance by structural phase transition from two-dimensional hexagonal-SnS2 to orthorhombic-SnS. ACS nano\| PubMed ID: 25010575	2014
Electrochemistry and structure of the cobalt-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode. Physical chemistry chemical physics : PCCP\| PubMed ID: 25337805	2014

Wei Kong Pang

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