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The lithium–sulfur battery is receiving intense interest because its theoretical energy density exceeds that of lithium-ion batteries at much lower cost, but practical applications are still hindered by capacity decay caused by the polysulfide shuttle. Here we report a strategy to entrap polysulfides in the cathode that relies on a chemical process, whereby a host—manganese dioxide nanosheets serve as the prototype—reacts with initially formed lithium polysulfides to form surface-bound intermediates. These function as a redox shuttle to catenate and bind ‘higher’ polysulfides, and convert them on reduction to insoluble lithium sulfide via disproportionation. The sulfur/manganese dioxide nanosheet composite with 75 wt% sulfur exhibits a reversible capacity of 1,300 mA h g −1 at moderate rates and a fade rate over 2,000 cycles of 0.036%/cycle, among the best reported to date. We furthermore show that this mechanism extends to graphene oxide and suggest it can be employed more widely. The polysulfide shuttle is a major problem leading to capacity decay in lithium–sulfur batteries. Here, the authors show that in-situ -generated thiosulfate species on a manganese oxide nanosheet act as a polysulfide mediator, which effectively prevents polysulfide dissolution, leading to enhanced cyclability.

The stable operation of lithium-based batteries at low temperatures is critical for applications in cold climates. However, low-temperature operations are plagued by insufficient dynamics in the bulk of the electrolyte and at electrode|electrolyte interfaces. Here, we report a quasi-solid-state polymer electrolyte with an ionic conductivity of 2.2 × 10 −4 S cm −1 at −20 °C. The electrolyte is prepared via in situ polymerization using a 1,3,5-trioxane-based precursor. The polymer-based electrolyte enables a dual-layered solid electrolyte interphase formation on the Li metal electrode and stabilizes the LiNi 0.8 Co 0.1 Mn 0.1 O 2 -based positive electrode, thus improving interfacial charge-transfer at low temperatures. Consequently, the growth of dendrites at the lithium metal electrode is hindered, thus enabling stable Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 coin and pouch cell operation even at −30 °C. In particular, we report a Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 coin cell cycled at −20 °C and 20 mA g −1 capable of retaining more than 75% (i.e., around 151 mAh g −1 ) of its first discharge capacity cycle at 30 °C and same specific current. Low-temperature batteries are detrimentally affected by the sluggish kinetics of the electrolyte. Here, the authors propose a quasi-solid-state polymer electrolyte capable of improving interfacial charge transfer and enabling stable Li metal cell operation even at −30 °C.

In recent years, the concept of entropy stabilization of crystal structures in oxide systems has led to an increased research activity in the field of “high entropy oxides”. These compounds comprise the incorporation of multiple metal cations into single-phase crystal structures and interactions among the various metal cations leading to interesting novel and unexpected properties. Here, we report on the reversible lithium storage properties of the high entropy oxides, the underlying mechanisms governing these properties, and the influence of entropy stabilization on the electrochemical behavior. It is found that the stabilization effect of entropy brings significant benefits for the storage capacity retention of high entropy oxides and greatly improves the cycling stability. Additionally, it is observed that the electrochemical behavior of the high entropy oxides depends on each of the metal cations present, thus providing the opportunity to tailor the electrochemical properties by simply changing the elemental composition. High entropy oxides provide a new strategy toward materials design by stabilizing single-phase crystal structures composed of multiple cations. Here, the authors apply this concept to the development of conversion-type electrode materials for lithium-ion storage and show the underlying mechanism.

The operation of traditional aqueous-electrolyte zinc-ion batteries is adversely affected by the uncontrollable growth of zinc dendrites and the occurrence of side reactions. These problems can be avoided by the development of functional hydrogel electrolytes as replacements for aqueous electrolytes. However, the mechanism by which most hydrogel electrolytes inhibit the growth of zinc dendrites on a zinc anode has not been investigated in detail, and there is a lack of a large-scale recovery method for mainstream hydrogel electrolytes. In this paper, we describe the development of a recyclable and biodegradable hydrogel electrolyte based on natural biomaterials, namely chitosan and polyaspartic acid. The distinctive adsorptivity and inducibility of chitosan and polyaspartic acid in the hydrogel electrolyte triggers a double coupling network and an associated synergistic inhibition mechanism, thereby effectively inhibiting the side reactions on the zinc anode. In addition, this hydrogel electrolyte played a crucial role in an aqueous acid-based Zinc/MnO 2 battery, by maintaining its interior two-electron redox reaction and inhibiting the formation of zinc dendrites. Furthermore, the sustainable biomass-based hydrogel electrolyte is biodegradable, and could be recovered from the Zinc/MnO 2 battery for subsequent recycling. Functional hydrogel electrolytes show promising potential for enhancing the sustainability of aqueous zinc-ion batteries. Here, the authors introduce a biomass-based hydrogel electrolyte that not only prevents side reactions on the zinc anode but also enables easy retrieval from the zinc batteries.

Currently, there is considerable interest in developing advanced rechargeable batteries that boast efficient distribution of electricity and economic feasibility for use in large-scale energy storage systems. Rechargeable aqueous zinc batteries are promising alternatives to lithium-ion batteries in terms of rate performance, cost, and safety. In this investigation, we employ Cu 3 (HHTP) 2 , a two-dimensional (2D) conductive metal-organic framework (MOF) with large one-dimensional channels, as a zinc battery cathode. Owing to its unique structure, hydrated Zn 2+ ions which are inserted directly into the host structure, Cu 3 (HHTP) 2 , allow high diffusion rate and low interfacial resistance which enable the Cu 3 (HHTP) 2 cathode to follow the intercalation pseudocapacitance mechanism. Cu 3 (HHTP) 2 exhibits a high reversible capacity of 228 mAh g −1 at 50 mA g −1 . At a high current density of 4000 mA g −1 (~18 C), 75.0% of the initial capacity is maintained after 500 cycles. These results provide key insights into high-performance, 2D conductive MOF designs for battery electrodes. Aqueous zinc batteries are promising candidates for large scale energy storage systems but development of the cathode material remains a challenge. Here, the authors show a conductive 2D metal-organic framework involving intercalation pseudocapacitance mechanism for enhanced rate capability.

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 −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. In lithium-sulfur batteries, many porous conductive carbon materials are proposed to confine soluble polysulfides, but the efficiency is generally low. Here, the authors use a Magnéli phase of titanium oxide as the cathode host and electron conduit, which binds the lithium (poly)sulfides well, leading to excellent battery performance.

To achieve good rate capability of lithium metal anodes for high-energy-density batteries, one fundamental challenge is the slow lithium diffusion at the interface. Here we report an interpenetrated, three-dimensional lithium metal/lithium tin alloy nanocomposite foil realized by a simple calendering and folding process of lithium and tin foils, and spontaneous alloying reactions. The strong affinity between the metallic lithium and lithium tin alloy as mixed electronic and ionic conducting networks, and their abundant interfaces enable ultrafast charger diffusion across the entire electrode. We demonstrate that a lithium/lithium tin alloy foil electrode sustains stable lithium stripping/plating under 30 mA cm −2 and 5 mAh cm −2 with a very low overpotential of 20 mV for 200 cycles in a commercial carbonate electrolyte. Cycled under 6  C (6.6 mA cm −2 ), a 1.0 mAh cm −2 LiNi 0.6 Co 0.2 Mn 0.2 O 2 electrode maintains a substantial 74% of its capacity by pairing with such anode. Sluggish lithium diffusion on the surface of Li metal anodes poses a fundamental challenge. Here the authors report a Li/Li 22 Sn 5 alloy design to address this issue. The composite anode sustains stable Li stripping/plating cycling with a low overpotential of 20 mV under 30 mA cm −2  in a commercial carbonate electrolyte.

The main components and, most notably, the concentration of the non-aqueous electrolyte solution have not significantly changed since the commercialization of Li-ion batteries in the early 1990s. However, the quest for electrochemical energy storage systems with high-energy content has driven researchers to reconsider the suitability of the “standard” one molar concentration and look toward highly concentrated electrolyte solutions. However, the interplay between the fundamental electrolyte properties and the cell performance is not consistent with what would be expected based only on the electrolyte ionic conductivity. Here, the recent progress and future perspectives on the correlation between the physicochemical properties of non-standard electrolyte solutions and their ability to improve the energy storage performances of lithium-based batteries are discussed. The quest for high-energy electrochemical energy storage systems has driven researchers to look toward highly concentrated electrolytes. Here, the author discusses the recent progress and future perspectives of such electrolytes and their ability to improve the performances of lithium-based batteries.

Cobalt hydroxide is a promising electrode material for supercapacitors due to the high capacitance and long cyclability. However, the energy storage/conversion mechanism of cobalt hydroxide is still vague at the atomic level. Here we shed light on how cobalt hydroxide functions as a supercapacitor electrode at operando conditions. We find that the high specific capacitance and long cycling life of cobalt hydroxide involve a complete modification of the electrode morphology, which is usually believed to be unfavourable but in fact has little influence on the performance. The conversion during the charge/discharge process is free of any massive structural evolution, but with some tiny shuffling or adjustments of atom/ion species. The results not only unravel that the potential of supercapacitors could heavily rely on the underlying structural similarities of switching phases but also pave the way for future material design for supercapacitors, batteries and hybrid devices. Developing high-performance hybrid energy storage devices requires improved understanding of the mechanism that governs the electrochemical reactions. Here, the authors show the atomic-level working process of cobalt hydroxide electrode for pseudocapacitors.

Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of materials that have attracted attention as energy storage materials. MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution; most other MAX phases have not been explored. Here a redox-controlled A-site etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX-phase precursors with A elements Si, Zn and Ga. A negative electrode of Ti 3 C 2 MXene material obtained through this molten salt synthesis method delivers a Li + storage capacity of up to 738 C g −1 (205 mAh g −1 ) with high charge–discharge rate and a pseudocapacitive-like electrochemical signature in 1 M LiPF 6 carbonate-based electrolyte. MXenes prepared via this molten salt synthesis route may prove suitable for use as high-rate negative-electrode materials for electrochemical energy storage applications. Two-dimensional transition metal carbides and nitrides, known as MXenes, are currently considered as energy storage materials. A generic Lewis acidic etching route for preparing high-rate negative-electrode MXenes with enhanced electrochemical performance in non-aqueous electrolyte is now proposed.