Access to the full text of the published version may require a subscription. Rights © Tsinghua University Press and Springer-Verlag Berlin ABSTRACTThe performance of the lithium-ion cell is heavily dependent on the ability of the host electrodes to accommodate and release Li + ions from the local structure. While the choice of electrode materials may define parameters such as cell potential and capacity, the process of intercalation may be physically limited by the rate of solid-state Li + diffusion. Increased diffusion rates in lithium-ion electrodes may be achieved through a reduction in the diffusion path, accomplished by a scaling of the respective electrode dimensions.In addition, some electrodes may undergo large volume changes associated with charging and discharging, the strain of which, may be better accommodated through nanostructuring. Failure of the host to accommodate such volume changes may lead to pulverisation of the local structure and a rapid loss of capacity. In this review article, we seek to highlight a number of significant gains in the development of nanostructured lithium-ion battery architectures (both anode and cathode), as drivers of potential next-generation electrochemical energy storage devices.

The synthesis of the Li-ion conversion candidates, FeF2 and CoF2, obtained from the single source organometallic precursors [Fe(tta)3] (tta = C8H4F3O2S), and [Co(hfac)2[middle dot]2H2O] (hfac = C5H1F6O2), respectively, via a novel supercritical fluid (SCF) method is presented. The nature of the synthesis led to highly-crystalline FeF2 and CoF2 powders requiring no additional thermal treatment. The as-obtained powders were investigated for use as potential positive Li-ion conversion electrodes by means of chronopotentiometric measurements. The FeF2 cells displayed high initial capacities following electrochemical conversion (up to [similar]1100 mA h g-1 at a potential of 1.0 V vs. Li/Li+), with appreciable cyclic behaviour over 25 discharge-charge cycles. The deposition of a [similar]5 nm layer of amorphous carbon onto the surface of the active material following SCF treatment, likely facilitated adequate electron transport through an otherwise poorly conducting FeF2 phase. Similarly, CoF2 cells displayed high initial capacities (up to [similar]650 mA h g-1 at a potential of 1.2 V vs. Li/Li+), although significant capacity fading ensued in the subsequent cycles. Ex situ XRD measurements confirmed a poor reversibility in the conversion sequence for CoF2, with a complete loss of CoF2 crystallinity and the sole presence of a crystalline LiF phase following charging

Intercalation-type electrodes have now been commonly employed in today’s batteries as such materials are capable of storing and releasing lithium reversibly via topotactic transformation, conducive to small structural change, but they have limited interstitial sites to hold Li. In contrast, conversion electrodes feature high Li-storage capacity, but often undergo large structural change during (de)­lithiation, resulting in cycling instability. One exception is iron fluoride (FeF2), a conversion-type cathode that exhibits both high capacity and high cycling stability. Herein, we report a lithiation-driven topotactic transformation in a single crystal of FeF2, unveiled by in situ visualization of the spatial and crystallographic correlation between the parent and converted phases. Specifically, conversion in FeF2 resembles the intercalation process but involves transport of both Li+ and Fe2+ ions within the F-anion array, leading to formation of Fe preferentially along specific crystallographic orientations of FeF2. Throughout the process, the F-anion framework is retained, creating a checkerboard-like structure, within which the volume change is largely compensated, thereby enabling the high cyclability in FeF2. Findings from this study, with unique insights into conversion reaction mechanisms, may help to pave the way for designing conversion-type electrodes for the next-generation high energy lithium batteries.

We present the facile synthesis of crystalline V 2 O 5 nanorods and V 2 O 5 /TiO 2 nanocomposites structures by a carbon nanocage (CNC)-assisted growth process, using vanadium triisopropoxide oxide and titanium isopropoxide precursors in air at 500 C. The diameters of the resultant V 2 O 5 nanorods ranged between $10 and 70 nm, while the crystalline V 2 O 5 /TiO 2 nanocomposite structures adopted a unique morphology, due to both crystallisation and templating processes, with V 2 O 5 adopting small-diameter nanowire and nanorod morphologies surrounded by sub-30 nm TiO 2 nanoparticles. The V 2 O 5 nanorods and V 2 O 5 /TiO 2 nanocomposites were characterised by electron microscopy and X-ray diffraction techniques and subsequently reviewed as positive Li-ion electrodes. The phase-pure V 2 O 5 nanorod structures exhibited appreciable Li + storage properties over the potential range of 2.0-4.0 V vs. Li/Li + , displaying capacities of up to 288 mA h g À1 with appreciable cyclic behaviour at test rates of up to $1 C. The crystalline V 2 O 5 /TiO 2 nanocomposite structures displayed similar Li + storage properties, however, increasing molar fractions of TiO 2 led to a decline in the overall capacity versus the single-phase V 2 O 5 counterparts. Interestingly, the Li + insertion behaviour of the V 2 O 5 /TiO 2 nanocomposite displayed character more-typical of amorphous V 2 O 5 , which was ascribed to a structural buffering effect of the inactive TiO 2 phase.

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Positively charged, surfactant-free gold nanoparticles (Au NPs) with diameters ranging between 2-200 nm have been synthesised in water via a seed-mediated growth method, involving the reduction of gold(iii) chloride (AuCl3) by hydroxylamine hydrochloride (NH2OH[middle dot]HCl) in the presence of l-cysteine methyl ester hydrochloride (HSCH2CH(NH2)COOCH3[middle dot]HCl) as a capping agent. The mercapto group (-SH) on the capping ligand has a high affinity for Au, anchoring the cysteine group to the nanoparticles, whilst the ammonium group (-NH3+), formed by the presence of an amine group in slightly acidic media (pH [similar] 4.5-5), resulted in positively charged colloidal nanoparticles ([small zeta]-potential +33 to +49 mV), which was key to their electrostatic stability. Data from cytotoxicity studies performed on a range of different cell types (human and murine), including human prostate cancer cells (PC3), showed that the positively charged Au-l-cysteine-cysteine nanoparticles were less cytotoxic than positively charged Au NPs produced using commonly employed surfactant cetyl trimethyl ammonium bromide (CTAB) under similar conditions. In addition, the positively charged Au NPs could be successfully complexed with small interfering RNA (siRNA). At the cellular level, the uptake of fluorescein siRNA from the charged nanoparticles was comparable to uptake from the commercial carrier INTERFRin[trade mark sign], implying the potential application of these novel vectors for nucleic acid delivery

Both porosity and tortuosity are important measures for liquid-permeable membranes. Porosity is easily calculated from the membrane's basis weight, density and dimensions. Tortuosity cannot be assessed directly, and is commonly estimated for by the air permeability using the Gurley number. Yet tortuosity may also be determined by measuring the ionic conductivity of an electrolyte-impregnated membrane. In the present work, the resistance of stacked membrane layers impregnated with a lithium-ion electrolyte is measured using a custom designed electrochemical cell optimized for electrochemical impedance spectroscopy (EIS). Linear regression of the resistance as a function of the number of layers provides the resistance of a single membrane layer. Analysis of the linear fit provides an error-corrected ionic resistance value per membrane layer, which is subsequently used to calculate the MacMullin number and tortuosity. After validating this approach with a commercial polyolefin battery separator, polyetherimide membranes having different pore morphologies were analyzed. The tortuosity values measured through EIS (2.5-3.9) showed a poor correlation to the measured Gurley numbers (34-879 s/100cc), which demonstrates that, depending on membrane structure and composition, Gurley numbers cannot simply be used as a means to predict the effective ionic conduction properties of an electrolyte-wetted membrane.

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