No abstract

Energy storage technology has received significant attention for portable electronic devices, electric vehicle propulsion, bulk electricity storage at power stations, and load leveling of renewable sources, such as solar energy and wind power. Lithium ion batteries have dominated most of the first two applications. For the last two cases, however, moving beyond lithium batteries to the element that lies below-sodium-is a sensible step that offers sustainability and cost-effectiveness. This requires an evaluation of the science underpinning these devices, including the discovery of new materials, their electrochemistry, and an increased understanding of ion mobility based on computational methods. The Review considers some of the current scientific issues underpinning sodium ion batteries.

The safety, affordability, and impressive electrochemical performance of many Zn-ion batteries (ZIBs) has recently triggered an overwhelming literature surge. As is typical for a new area, initial enthusiasm and high expectations have now been replaced by a more measured period of research that reaches deep into the underlying factors controlling electrochemical properties. Rather than battery metrics, this review focuses on fundamental aspects of the chemistry of ZIBs that are the least understood and on which there has been progress over the last few years. We provide guidance for future research regarding (1) the significant challenge of proton/Zn 2+ co-intercalation in aqueous media, (2) limitations to conversion chemistry that often accompanies ZIB electrochemistry, (3) positive aspects of facile Zn 2+ (de)intercalation in nonaqueous electrolytes and organic cathode materials, (4) the desolvation penalty at electrode-electrolyte interfaces, (5) solutions for controlling Zn dendritic growth, and (6) suggested electrochemistry protocols for the field.

The lithium-sulphur battery relies on the reversible conversion between sulphur and Li 2 S and is highly appealing for energy storage owing to its low cost and high energy density. Porous carbons are typically used as sulfur hosts, but they do not adsorb the hydrophilic polysulphide intermediates or adhere well to Li 2 S, resulting in pronounced capacity fading. Here we report a different strategy based on an inherently polar, high surface area metallic oxide cathode host and show that it mitigates polysulphide dissolution by forming an excellent interface with Li 2 S. Complementary physical and electrochemical probes demonstrate strong polysulphide/Li 2 S binding with this 'sulphiphilic' host and provide experimental evidence for surface-mediated redox chemistry. In a lithium-sulphur cell, Ti 4 O 7 /S cathodes provide a discharge capacity of 1,070 mAh g À 1 at intermediate rates and a doubling in capacity retention with respect to a typical conductive carbon electrode, at practical sulphur mass fractions up to 70 wt%. Stable cycling performance is demonstrated at high rates over 500 cycles.

Comparison of intercalation of Zn2+ in layered V3O7·H2O in non-aqueous and aqueous electrolytes reveals a much higher desolvation penalty at the non-aqueous interface, a major factor in dictating the kinetics.

Aqueous zinc batteries are highly attractive for large-scale storage applications owing to their inherent safety, low-cost, and durability. Yet, their advancement is hindered by a dearth of positive host materials (cathode) due to sluggish diffusion of Zn 2+ inside solid inorganic frameworks. Here, we report a novel organic host, tetrachloro-1,4-benzoquinone (also called: p-Chloranil), which due to its inherently soft crystal structure can provide reversible and efficient Zn 2+ storage. It delivers a high capacity of ≥200 mAh g-1 with a very small voltage polarization of 50 mV in a flat plateau around 1.1 V, which equate to an attractive specific energy of > 200 Wh kg-1 at an unparalleled energy efficiency (~95%). As unraveled by density functional theory (DFT) calculations, the molecular columns in p-Chloranil undergo a twisted rotation to accommodate Zn 2+ , thus restricting the volume change (-2.7%) during cycling. In-depth characterizations using operando X-ray

Nanostructured sulfur host materials that embrace both high electronic conductivity and strong chemisorption towards polysulfides are central to enable high performance Li–S batteries.

Aqueous Zn-ion batteries, which are being proposed as large scale energy storage solutions due to their unparalleled safety and cost advantage, are comprised of a positive host (cathode) material, a metallic zinc anode, and a mildly acidic aqueous electrolyte (pH ~ 3 -7). Typically, the charge storage mechanism is believed to be reversible Zn 2+ (de)intercalation in the cathode host, with the exception of α-MnO2, for which multiple vastly different and contradicting mechanisms have been proposed. However, our present study, combining electrochemical, operando X-ray diffraction (XRD), electron microscopy in conjunction with energy dispersive X-ray spectroscopy (EDX), and in situ pH evolution analyses on two oxide hosts -tunneled α-MnO2 and layered V3O7•H2O vis-à-vis two non-oxide hostslayered VS2 and tunneled Zn3[Fe(CN)6]2, suggests that oxides and non-oxides follow two dissimilar charge storage mechanisms. While the oxides behave as dominant proton intercalation materials, the non-oxides undergo exclusive zinc intercalation.Stabilization of the H + on the hydroxyl terminated oxide surface is revealed to facilitate the proton 2 intercalation by a preliminary molecular dynamics simulation study. Proton intercalation for both oxides leads to the precipitation of layered double hydroxide (LDH) -Zn4SO4(OH)6•5H2O with ZnSO4/H2O electrolyte and a triflate anion (CF3SO3 -) based LDH with Zn(SO3CF3)2/H2O electrolyte -on the electrode surface. The LDH precipitation buffers the pH of the electrolytes to a mildly acidic value, sustaining the proton intercalation to deliver large specific capacities for the oxides. Moreover, we also show that the stability of the LDH precipitate is crucial for the rechargeability of the oxide cathodes, revealing a critical link between the charge storage mechanism and the performance of the oxide hosts in aqueous zinc batteries.