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Aqueous zinc ion batteries (A-ZIBs) have been used as new alternative batteries for grid-scale electrochemical energy storage because of their low cost and environmental protection. Finding a suitable and economical cathode material, which is needed to achieve high energy density and long cycle stability, is one of the most important and arduous challenges at the present stage. Potassium manganese hexacyanoferrate (KMHCF) is a kind of Prussian blue analogue. It has the advantages of a large 3D frame structure that can accommodate the insertion/extraction of zinc ions, and is nontoxic, safe, and easy to prepare. However, regularly synthesized KMHCF has higher water and crystal defects, which reduce the possibility of zinc ions' insertion/extraction, and subsequently the discharge capacity and cycling stability. In this work, a KMHCF material with less water and low defects was obtained by adding polyvinylpyrrolidone during the synthesis process to control the reaction process. The KMHCF serves as the cathode of A-ZIBs and exhibits an excellent electrochemical performance providing a specific capacity of 140 mA h g-1 for the initial cycle at a current density of 100 mA g-1 (1 C). In particular, it can maintain a reversible capacity of 85 mA h g-1, even after 400 cycles at 1 C. Moreover, unlike the traditional zinc storage mechanism of A-ZIBs, we found that the KMHCF electrode undergoes a phase transition process when the KMHCF electrode was activated by a small current density, which is attributed to part of the Mn on the lattice site being replaced by Zn, thus forming a new stable phase to participate in the subsequent electrochemical reaction.

A lithium–sulfur (Li–S) battery has become a promising energy storage device because of its remarkable excellent specific capacity density and energy density. However, low sulfur utilization and sh...

Li-CO2 batteries have attracted worldwide attention because of their dual characteristics of high energy density and effective CO2 capture. However, the basic electrochemistry mechanism involved has been unclear, which is mainly confused by the complicated decomposition of organic electrolytes. Herein, water-in-salt (WIS, LiTFSI/H2O 21.0 mol/1 kg) has been explored as a suitable electrolyte for the first time to investigate the reaction mechanism of Li-CO2 batteries with different cathodes (carbon nanotube (CNT) and Mo2C/CNT, respectively). An Mo2C-based Li-CO2 battery with WIS delivers a higher energy efficiency of 83% and a superior cyclability, compared to those of the CNT-based counterpart cell. Through various ex/in situ qualitative/quantitative characterizations, the Mo2C-based Li-CO2 battery with WIS can operate on the reversible conversion of CO2-to-Li2C2O4 ((e-/CO2)ideal = 1) at lower discharge/charge overpotentials, while the CNT-based counterpart cell is based on the formation/decomposition of Li2CO3 ((e-/CO2)ideal ≈ 1.33) at high overpotentials. Such a difference in CO2 reduction products stems from the stronger interaction between Mo2C(101) and Li2C2O4 than that of the CNT and Li2C2O4 based on the density functional theory calculations, resulting in the selective stabilization of the intermediate product Li2C2O4 on the Mo2C surface.

Iron-based phosphate materials have been employed as cathodes for sodium-ion batteries (SIBs) because of their low cost and environmental friendliness, but the electrochemical performance of this k...

Summary Rechargeable aqueous zinc-based batteries are very attractive alternative devices for current energy storage by virtue of their low cost and high security. However, the performance of vanadium oxide cathode strongly relies on the distance of interlayer spacing. Here, we employ layered PEDOT-NH4V3O8 (PEDOT-NVO) as a cathode material, which produces an enlarged interlayer spacing of 10.8 A (against 7.8 A for the single NVO) by effectively conducting polymer intercalation. This cathode material exhibits an improved capacity of 356.8 mAh g−1 at 0.05 A g−1 and 163.6 mAh g−1, even at the highest current density of 10 A g−1 (with a high retention from 0.05 to 10 A g−1), and features an ultra-long lifetime of over 5,000 charge-discharge cycles with a capacity retention of 94.1%. A combination of mechanism analyses and theoretical calculations suggest that the oxygen vacancies and larger interlayer spacing through polymer assistance account for the improved electrochemical performance.

ConspectusBuilding rechargeable batteries for subzero temperature application is highly demanding for various specific applications including electric vehicles, grid energy storage, defense/space/subsea explorations, and so forth. Commercialized nonaqueous lithium ion batteries generally adapt to a temperature above -20 °C, which cannot well meet the requirements under colder conditions. Certain improvements have been achieved with nascent materials and electrolyte systems but have mainly been restrained to discharge and within a small rate at temperatures above -40 °C. Moreover, the recharging process of batteries based on the graphite anode still faces huge challenges from the simultaneous Li+ intercalation and potential Li stripping at subzero temperatures. Revealing the temperature-dependent evolution of physicochemical and electrochemical properties will greatly benefit our understanding of the limiting factors at low temperature, which is of significant importance.Herein, we dissect the ion movements in the liquid electrolyte and solid electrode as well as their interphase to analyze the temperature effect on Li+-diffusion behavior during charging/discharging processes. An electrolyte is the vital factor, and its ionic conductivity guarantees the smooth operation of the battery. However, it is the sluggish diffusion in the solid, especially the charge transfer at the solid electrolyte/electrode interfaces (SEI), that greatly limits the kinetics at low temperature. Many strategies have been put forward to tame electrolytes for low-temperature application. From a macroscopic point of view, multiple solvents are mixed to adjust the liquid temperature range and viscosity. With respect to the microscopic nature, research is focusing on the solvation structure by formulating the ratio of Li+ ions to solvent molecules. The binding energy of the Li+-solvent complex is crucial for the desolvation process at low temperature, which is manipulated with fluorinated solvents or other weakly solvating electrolytes. On the basis of an optimized electrolyte, electrodes and their reaction mechanism need to be coupled carefully because different materials show totally different responses to temperature change. To avoid the sluggish desolvation process or slow diffusion in the bulk intercalation compounds, several kinds of materials are summarized for low temperature use. The intercalation pseudocapacitive behavior can compensate for the kinetics to some extent, and a metal anode is a good candidate for replacing a graphite anode to build high-energy-density batteries at subzero temperature. It is also a wise choice to develop nascent battery chemistry based on the co-intercalation of solvent molecules into electrodes. Furthermore, the interfacial resistance contributes a lot at low temperature, which need be modified to accelerate the Li+ diffusion across the film. This will be linked to the electrolyte, exactly speaking, the solvation structure, to regulate the organic and inorganic components as well as the structure. Although it is difficult to investigate SEI on a graphite anode owing to its poor performance at low temperature, great efforts on Li metal anodes have offered some valuable information as reference. It is worth mentioning that the improvement in low-temperature performance calls for not only a change in the single composition but also the synergetic effect of each part in the whole battery. The elementary studies covered in this account could be taken as insight into some key strategies that help advance the low-temperature battery chemistry.

Hydronium-ion batteries are regarded as one of the most promising energy technologies as next-generation power sources, benefiting from their cost effectivity and sustainability merits. Herein, we propose a hydronium-ion battery which is based on an organic pyrene-4,5,9,10-tetraone anode and an inorganic MnO2@graphite felt cathode in an acid electrolyte. Its operation involves a quinone/hydroquinone redox reaction on anode and a MnO2/Mn2+ conversion reaction on cathode, in parallel with the transfer of H3O+ between two electrodes. The distinct operation mechanism affords this hydronium-ion battery an energy density up to 132.6 Wh kg−1 and a supercapacitor-comparable power density of 30.8 kW kg−1, along with a long-term cycling life over 5000 cycles. Furthermore, surprisingly, this hydronium-ion battery works well even with a frozen electrolyte under −40 °C, and superior rate performance and cycle stability remain at −70 °C., The authors show a hydronium-ion battery with an organic pyrene-4,5,9,10-tetraone anode and a MnO2@graphite cathode and H3O+ as the charge carrier. In addition to exhibiting promising energy density and power density, this battery works well even under low temperatures ranging from −40 °C to −70 °C.

Investigating the reaction mechanism and the rational design of highly efficient electrocatalysts for the oxygen evolution reaction play a key role in renewable energy applications. Here, we report a homogeneous multi-metal-site oxyhydroxide electrocatalyst (consisting of Fe doped NiOOH and Cu doped NiOOH) obtained by in situ electrochemical dealloying of the multi-metal-site alloy (consisting of FeNi3 and NiCu alloys). The in situ structural evolution process manipulates the intermediate and enhances the water oxidation performance. After dealloying, the electrochemically dealloyed catalyst exhibits a small overpotential at large current density (250 mV at 100 mA cm−2), low Tafel slope (34 mV dec−1), remarkably increased ECSA (8-fold larger than before), and superior durability for 200 h at 100 mA cm−2. This electrocatalyst presents one of the best performances among all reported transition metal-based electrocatalysts, and is even superior to the benchmark RuO2. Operando ATR FT-IR reveals that the electrochemically dealloyed electrocatalyst could manipulate the reaction path based on direct O2 evolution mechanism (DOEM) and facilitate the formation of O–O bonds. This fundamental understanding will contribute to the identification and design of the active structure of oxygen evolution electrocatalysts.

With the increase in interest in energy storage for grid applications, a rechargeable battery, as an efficient energy storage/conversion system, has been receiving great attention. However, its development has largely been stalled by the issues of high cost, safety and energy density. Here, we report an aqueous manganese–lead battery for large-scale energy storage, which involves the MnO2/Mn2+ redox as the cathode reaction and PbSO4/Pb redox as the anode reaction. The redox mechanism of MnO2/Mn2+ was investigated to improve reversibility. All materials are inexpensive and the assembled battery can work well during the penetration test. The battery shows a discharge voltage of around 1.55 V, high rate capability, and no obvious capacity decay over 10 000 cycles. Furthermore, a high volumetric low energy density of 187 W h L−1 was obtained for a pouch battery using a high-concentration electrolyte comprising 3 M MnSO4. Meanwhile, the low freezing point of the high-concentration electrolyte endowed the battery with capability to work at a low temperature of −40 °C. Owing to the low cost and high electrochemical performance, the Mn–Pb battery has great potential for grid energy storage.

A well-formulated electrolyte is proposed based on a fluorinated carboxylate ester solvent, which shows a wide electrochemical window (0-4.73 V, vs. Li+/Li), low solvation energy (10.05 kJ mol-1) and ability to maintain a liquid state at temperatures as low as -120 °C. This electrolyte produced batteries with superior electrochemical performance at low temperatures relative to carbonate-based electrolytes.

An all-solid-state sodium–sulfur (Na–S) battery using a S/CPAN (carbonized polyacrylonitrile) composite cathode and poly(ethylene oxide) (PEO) electrolyte was prepared and tested at 60 °C. The S/CP...

Aqueous rechargeable zinc batteries (ARZBs) are desirable for energy storage devices owing to their low cost and abundance of the Zn anode, but their further development is limited by a dearth of ideal cathode materials that can simultaneously possess high capacity and stability. Herein, we employ a layered structure of ammonium vanadium bronze (NH4)0.5V2O5 as the cathode material for ARZBs. The large interlayer distance supported by the NH4+ insertion not only facilitates the Zn2+-ion intercalation/deintercalation but also improves the electrochemical stability in ARZBs. As a result, the layered structural (NH4)0.5V2O5 cathode delivers a high capacity up to 418.4 mA h g-1 at a current density of 0.1 A g-1. A reversible capacity of 248.8 mA h g-1 is still retained after 2000 cycles and a capacity retention of 91.4% was maintained at 5 A g-1. Furthermore, in comparison with previously reported Zn-ion batteries, the Zn/(NH4)0.5V2O5 battery achieves a prominent high energy density of 418.4 W h kg-1 while delivering a high power density of 100 W kg-1. The results would enlighten and push the ammonium vanadium compounds to a brand new stage for the application of aqueous batteries.

Lithium-sulfur battery is garnering much of attention due to its high energy densities, low-cost active material of sulfur and variety of applications in portable electronics. High integrity and consistent qualities of the large-scale sulfur cathode with high energy have to be ensured to construct reliable and practical lithium-sulfur batteries that could supersede advancing lithium-ion batteries. Here, facile and productive approaches are developed to mass-produce functional sulfur hosts and to fabricate large-scale sulfur cathode with high sulfur loading. The functional sulfur host is synthesized by anchoring polyethylenimine at the surface of commercially available carbon at inert conditions with a scale of more than 10 g per batch via simple solution method. Combining the functionalized sulfur host with a polyacrylic acid binder allows high integrity and uniformity of the high sulfur loading cathode to be fabricated in large dimensions. Followed by this approach, the sulfur cathode, 70 × 6 cm2, is produced with the sulfur loading of >4.3 mg cm−2. It is found that 12 wt% of polyethylenimine in the functionalized sulfur host with polyacrylic acid is at optimal condition that presents stable electrochemical performances over 600 cycles.

Layered compounds with large interlayer spacing enabling ions intercalation are promising anode materials for sodium-ion and potassium-ion batteries. Herein, we prepared the high-purity layer-structured NbSe2 sheets with compatible interlayer spacing (6.30 A) via a facile solid-state vacuum sintering. The as-prepared NbSe2 was explored as anode materials for sodium and potassium batteries for the first time. The NbSe2 exhibits excellent cycle stability and rate performance for sodium storage, which provides initial reversible capacity of 116.6 mA h g−1 and retention capacity of 98.1 mA h g−1 after 100 cycles at 100 mA g−1. A capacity of 78.6 mA h g−1 was achieved even at a high current density of 4000 mA g−1. The sodium-ion storage mechanism of NbSe2 was primitively discussed in this paper. NbSe2 also demonstrates considerable potassium storage capacity and good rate performance. The results indicate that NbSe2 may be a promising anode for sodium-ion and potassium-ion batteries as a novel anode material.

The intense interest of Li-O2 battery stems from its ultrahigh theoretical energy density, but its application is still hindered by the issues of Li anode. Herein, RuO2-CNTs composite, a conventional O2 cathode catalyst in Li-O2 battery, is first utilized as an anode host for dendrite-free Li plating/stripping with high Coulombic efficiency. It is demonstrated that such excellent plating/stripping performance arises from the lithiophilicity characteristic of Ru nanoparticles (that is derived from the in-situ electrochemical conversion from RuO2 to Ru/Li2O) and buffer space provided by CNTs. Furthermore, the RuO2-CNTs electrode pre-deposited with limited Li (RuO2-CNTs@Li anode) is coupled with a RuO2-CNTs catalytic cathode to form a Li-O2 full cell, which displays an extended cycle life with dramatically improved energy density. The achieved cell shows a high stability of 200 cycles with RuO2-CNTs@Li anode (1 mg Li) that sheds light on the efficient utilization of Li anode in Li-O2 batteries.

Lithium metal is an ideal anode for high-energy rechargeable batteries at low temperature, yet hindered by the electrochemical instability with the electrolyte. Concentrated electrolytes can improve the oxidative/reductive stability, but encounter high viscosity. Herein, a co-solvent formulation was designed to resolve the dilemma. By adding electrochemically "inert" dichloromethane (DCM) as a diluent in concentrated ethyl acetate (EA)-based electrolyte, the co-solvent electrolyte demonstrated a high ionic conductivity (0.6 mS cm-1 ), low viscosity (0.35 Pa s), and wide range of potential window (0-4.85 V) at -70 °C. Spectral characterizations and simulations show these unique properties are associated with the co-solvation structure, in which high-concentration clusters of salt in the EA solvent were surrounded by mobile DCM diluent. Overall, this novel electrolyte enabled rechargeable metallic Li battery with high energy (178 Wh kg-1 ) and power (2877 W kg-1 ) at -70 °C.

Redox mediators (RMs) play pivotal roles in enhancing the performance of electrochemical energy storage and conversion systems. Unlike the widely explored areas of electrode materials, electrolytes, separators, and electrolyte additives, RMs have received little attention. This review provides a comprehensive discussion toward understanding the effects of RMs on electrochemical systems, underlying redox mechanisms, and reaction kinetics both experimentally and theoretically. Our discussion focuses on the roles of RMs in various electrochemical systems such as lithium-ion batteries, Li–O2 batteries, Li–S batteries, decoupling electrolysis, supercapacitors, and microbial fuel cells. Depending on the reaction regions where the RMs become active, we can classify them into bulk, solid–solid interfacial, solid–liquid interfacial, and cell-unit RMs. The prospect of developing RMs with effective charge transfer properties along with minimal side-effects is an exciting research direction. Moreover, the introduction of an efficient RM into an electrochemical system can fundamentally change its chemistry; in particular, the electrode reaction polarization can be considerably decreased. In this context, we discuss the key properties of RMs applied for various purposes, and the main issues are addressed.

Conventional intercalation compounds for lithium‐ion batteries (LIBs) suffer from rapid capacity fading and are even unable to charge–discharge with temperature decline, owing to the sluggish kinetics and solvation/desolvation process. In this work, a high‐performance rechargeable battery at ultralow temperature is developed by employing a nanosized Ni‐based Prussian blue (NiHCF) cathode. The battery delivers a high capacity retention of 89% (low temperature of −50 °C) and 82% (ultralow temperature of −70 °C) compared with that at +25 °C. Various characterizations and electrochemical investigations, including operando Fourier transform infrared spectra, in situ X‐ray diffraction, cyclic voltammetry response, and galvanostatic intermittent titration technique are carried out to detect the structural stability and electrochemical behavior at different temperatures. It turns out that the pseudocapacitive behavior drives the desolvation process at the interface, while fast diffusion in the bulk electrode accelerates the movement of Li+ from the interface to the bulk materials. The unique synergistic features of intercalation pseudocapacitance at the electrolyte/electrode interface and high diffusion coefficient in the bulk electrode enables the NiHCF cathode with excellent low temperature performance. These findings offer a new direction for the design of LIBs operated at low temperature., Benefitting from the synergistic effect of pseudocapacitive behavior at the interface and high diffusion coefficient in the bulk electrode, a rechargeable battery with excellent low temperature performance is realized with nanosized Ni‐based Prussian blue as cathode, exhibiting a high capacity retention of 89% at −50 °C and 82% at ultralow temperature of −70 °C compared with that at +25 °C.

Lithium ion capacitors (LIC), which can bridge the gap between lithium ion batteries and supercapacitors by combining the merits of the two systems, are thus considered as some of the most promising energy storage devices. However, the imbalances in specific capacity, high-rate behavior, and cycling lifespan between the two electrodes make it a challenge to develop LICs with high energy density at high power density output along with long cycle life. Herein, a LIC consisting of a three-dimensional carbon modified LTSO (3DC@LTSO) anode and a lignin-derived activated carbon (LDAC) cathode is designed and fabricated. These two electrode materials with desirable electrochemical properties will much favorably offset the imbalances between the two electrodes. Moreover, a novel electrode-matching strategic approach, which will further offset the imbalance between the two electrodes, is developed. Thereby, the assembled LDAC//3DC@LTSO LIC cell shows a high energy density of 115.3 W h kg−1 at 163.5 W kg−1 and a high power density of 6560 W kg−1 at 60 W h kg−1, coupled with an excellent cycling lifespan of 90% capacity retention after 6000 cycles at a current density of 2.0 A g−1. These combined results are impressive in terms of obtaining high energy density and long cycling lifespan LICs.

The vital challenge in relation to layered Ni-rich cathodes is their pronounced structural degradation originating from cation mixing at high voltage, which causes serious electrode polarization and electrochemical deterioration. Herein, an overall structural modification strategy, which integrates a Li2GeO3 coating with gradient Ge-doping, was developed to improve the structural stability and create ordered diffusion channels in a layered Ni-rich cathode via interfacial fusion at high temperature. This effective strategy significantly enhances the reversible capacity retention, voltage stability and rate capability of the layered Ni-rich cathode at high voltage. We find that the Li2GeO3 coating inhibits interfacial side reactions to enhance the surface structural stability of the cathode materials. More importantly, the gradient Ge-doping plays a critical role in suppressing cation mixing to improve the ordered channels available for Li+ ion transport. The experimental observations, corroborated by first principle calculations, further reveal that Ge-doping not only alleviates structural degradation by increasing the phase transition energy barrier for layers to form spinel-like or rock-salt phases, but also facilitates fast Li+ diffusion kinetics via reducing the diffusion barrier. Our work provides a design idea for stabilizing the surface/bulk structure of advanced cathodes for high-performance Li-ion batteries.

This work developed a facile way to mass-produce a carbon-coated TiP2O7 nanoporous microsphere (TPO-NMS) as anode material for aqueous lithium-ion batteries via solid-phase synthesis combined with spray drying method. TiP2O7 shows great prospect as anode for aqueous rechargeable lithium-ion batteries (ALIBs) in view of its appropriate intercalation potential of −0.6 V (vs. SCE) before hydrogen evolution in aqueous electrolytes. The resulting sample presents the morphology of secondary microspheres (ca. 20 μm) aggregated by carbon-coated primary nanoparticles (100 nm), in which the primary nanoparticles with uniform carbon coating and sophisticated pore structure greatly improve its electrochemical performance. Consequently, TPO-NMS delivers a reversible capacity of 90 mA h/g at 0.1 A/g, and displays enhanced rate performance and good cycling stability with capacity retention of 90% after 500 cycles at 0.2 A/g. A full cell containing TPO-NMS anode and LiMn2O4 cathode delivers a specific energy density of 63 W h/kg calculated on the total mass of anode and cathode. It also shows good rate capacity with 56% capacity maintained at 10 A/g rate (vs. 0.1 A/g), as well as long cycle life with the capacity retention of 82% after 1000 cycles at 0.5 A/g.

Porous Na3Fe2(PO4)3 has been synthesized via a sol-gel method using citric acid as a metal ion complexing agent and polyvinyl alcohol as a structure-guiding agent. The obtained porous Na3Fe2(PO4)3 with particle size distribution of 40–60 nm has a typical NASICON structure in a space group of C2/c and the specific surface area is 40.2 m2 g−1. Electrochemical measurement results indicate that the initial discharge-specific capacity of porous Na3Fe2(PO4)3 is up to 92.5 mAh g−1 and maintains at 86 mAh g−1 after 200 cycles at 20 mA g−1 (92% of theoretical capacity) and the corresponding coulombic efficiency is up to 100% as well as high rate capability performance (71.5 mAh g−1 after 1000 cycles under 500 mA g−1). The excellent electrochemical properties are attributed to its particular [Fe2(PO4)3] “lantern units” stacked crystal structure and porous morphology, which significantly improves intercalation/de-intercalation kinetic of sodium ions.

To meet the growing energy demands, it is urgent for us to construct grid-scale energy storage system than can connect sustainable energy resources. Aqueous Li-ion batteries (ALIBs) have been widely investigated to become the most promising stationary power sources for sustainable energy such as wind and solar power. It is believed that advantages of ALIBs will overcome the limitations of the traditional organic lithium battery in virtue of the safety and environmentally friendly aqueous electrolyte. In the past decades, plentiful works have been devoted to enhance the performance of different types of ALIBs. In this review, we discuss the development of cathode, anode and electrolyte for acquiring the desired electrochemical performance of ALIBs. Also, the main challenges and outlook in this field are briefly discussed.

S0.87Se0.13/CPAN (carbonized polyacrylonitrile) composites material was synthesized by annealing the mixture of S (sulfur), Se (selenium) and PAN directly at 400 °C. The prepared composites was used as high capacity and stable cycling performance cathode for lithium sulfur battery. It delivers a specific capacity of 1210 mAh g−1 after 100 cycles at a constant current density of 120 mA g−1. In addition, it remains 989 mAh g−1 after 200 cycles at a current density of 300 mA g−1 with ultralow capacity fading of 0.025% per cycle. Meantime, the S0.87Se0.13/CPAN cathode exhibits extremely low self-discharge behavior. The superior electrochemical performance of S0.87Se0.13/CPAN composites should be ascribed to high S/Se ratio in S0.87Se0.13/CPAN composites and good conductivity brought by the addition of Se, which make full use of high capacity of S. Moreover, the chemical bonding between Se and S, as well as the chemical bonding between S0.87Se0.13 and CPAN decrease the loss of active material. This easy one-step synthesis procedure offers a feasible new route for the development of sulfide-based cathode material.

Because of the low cost and abundant nature of the sodium element, sodium-ion batteries (SIBs) are attracting extensive attention, and a variety of SIB cathode materials have been discovered. However, the lack of high-performance anode materials is a major challenge of SIBs. Herein, we have synthesized ultrasmall TiO2-nanoparticle-coated reduced graphene oxide (TiO2@RGO) composites by using a one-pot hydrolysis method, which are then investigated as anode materials for SIBs. The morphology of TiO2@RGO has been characterized using transmission electron microscopy, indicating that the TiO2 nanospheres uniformly grow on the surface of the RGO nanosheet. As-prepared TiO2@RGO composites exhibited a promising electrochemical performance in terms of cycling stability and rate capability, especially the initial cycle Coulombic efficiency of 60.7%, which is higher than that in previous reports. The kinetics of the electrode reaction has been investigated by cyclic voltammetry. The results indicate that the sodium-...

Silicon is an ideal candidate anode material for Li-ion batteries (LIBs). However, it suffers from rapid capacity fading due to large volume expansion upon lithium insertion. Herein, we design and fabricate highly stable carbon coated porous Mg2Si intermetallic anode material using facile mechano-thermal technique followed by carbon coating using thermal vapour deposition (TVD), toluene as carbon source. The electrode exhibits an excellent first reversible capacity of 726 mAh g−1 at a rate of 100 mA g−1. More importantly, the electrode demonstrates high rate capability (380 mAh g−1 at high rate of 2 A g−1) as well as high cycle stability, with capacity retentions of 65% over 500 cycles. These improvements are attributable to both Mg supporting medium and the uniform carbon coating, which can effectively increase the conductivity and electronic contact of the active material and protects large volume alterations during the electrochemical cycling process.

Li2TiSiO5 presents an operational potential at 0.28 V vs. Li+/Li, which could fill the voltage gap between graphite and Li4Ti5O12, showing great potential as an alternative anode material for Li-ion batteries. Apart from its advantages such as proper operational potential, excellent reversibility, low cost, environment friendly and so on, Li2TiSiO5 also suffers from two shortages of relatively low rate performance and capacity-voltage curve changing during cycling. In this work, we introduced expanded graphite as supporting medium, and successfully synthesized Li2TiSiO5 nanoparticles loaded expanded graphite composites (LTSO-EG). By dramatically reducing particle size and improving electronic conducting material, the rate performance of LTSO-EG is greatly improved compared with the amorphous carbon coated Li2TiSiO5. And most importantly, LTSO-EG displays a slope and stable capacity-voltage curve during cycling with reduced polarization.

An organometallic compound of ferrocene is first investigated as a promising anode for lithium-ion batteries. The electrochemical properties of ferrocene are conducted by galvanostatic charge and discharge. The ferrocene anode exhibits a high reversible capacity and great cycling stability, as well as superior rate capability. The electrochemical reaction of ferrocene is semi-reversible and some metallic Fe remains in the electrode even after delithiation. The metallic Fe formed in electrode and the stable solid electrolyte interphase should be responsible for its excellent electrochemical performance.

The traditional oxygen reduction/evolution reaction (ORR/OER) catalysts are mainly noble metal-based materials, but their scarcity and instability impede their practical applications, especially in Zn–air batteries. Hence, identifying a bifunctional catalyst with low-cost and high-stability is very crucial for Zn–air batteries. Herein, we report a simple method to prepare core–shell-structured Co@Co3O4 nanoparticles encapsulated into N-doped carbon polyhedra by carbonization and controlled oxidation of metal–organic frameworks (MOFs), which are then applied as a bifunctional catalyst for Zn–air batteries. Using such a configuration, enhanced performances, including a high power density of ∼64 mW cm−2, a stable voltage profile over 80 h battery operation with four mechanical recharges, a small discharge/charge overpotential of ∼0.66 V and a long-life of 100 cycles for 200 h operation at 5 mA cm−2, have been achieved. These excellent performances can be attributed to abundant graphited carbon and CNTs, high N-doping, plentiful pores, the synergy between the semiconductive Co3O4-coating layer and the conductive Co bulk, and the uniform Co@Co3O4 nanoparticles in this catalyst which effectively improve electrical conductivity/ion transfer and further concertedly promote the catalytic activity towards the ORR/OER. Moreover, the belt-shaped polymer Zn–air battery with this catalyst also shows good electrochemical stability under different deformations.

Cost-effective and highly efficient electrocatalysts for hydrogen evolution reactions (HERs) are crucial and highly desired in the sustainable energy field. Despite tremendous efforts on the development of alternative catalysts, platinum (Pt) is still the most efficient catalyst for HERs. Nevertheless, it remains a great challenge to output sufficient catalytic activity with a low Pt loading. In this research, Prussian blue analogues (PBA) of nickel hexacyanoferrate (Ni3[Fe(CN)6]2) nanocubes were used as the active substrate to enhance the HER activity of Pt by fabricating a Pt-Ni3[Fe(CN)6]2 interface. The Ni species of Ni3[Fe(CN)6]2 play key roles in contributing to the water dissociation and improving the HER kinetics, as well as helping to maintain the catalytic activity of Pt during a long-term durability test in both acidic and alkaline media. As a result, the new Ni3[Fe(CN)6]2/Pt hybrid catalyst exhibits a superior catalytic property for HERs in both sulfuric acid (H2SO4) and potassium hydroxide with a low Pt loading of only 4.0%. Impressively, a low overpotential of 59 mV is achieved at current density of 10 mA cm−2 in H2SO4, and a high mass current density of 3.75 mA μg Pt−1 is obtained at an overpotential of 70 mV, which outperforms currently reported Pt-based catalysts in acid electrolyte. It is believed that this work will inspire the design of PBA-based hybrid nanomaterials with improved or new functionalities for energy conversion and catalysis applications.

As a high-voltage and earth-abundant element, in recent years, alluaudite, Na2+2xFe2−x(SO4)3, has been regarded as a highly promising cathode material of sodium ion batteries with higher energy density. However, the critical environmental sensitivity and limited conductivity of this kind of sulfate-based (SO42−) polyanionic material has led to its poor crystal stability and inferior intercalation ability. Herein, we report the design of nitrogen-doped graphene under low temperature conditions as an evolutionary modification approach to prepare the Na2+2xFe2−x(SO4)3; namely, an alluaudite sulfate Na2+2xFe2−x(SO4)3@N-rGO composite was prepared by a facile co-precipitation method assisted by the nitrogen-doped graphene. It is therefore surprising that the three-dimensional graphene-based network provides continuous electron pathways; thus, the Na2+2xFe2−x(SO4)3@N-rGO composite exhibits improved electronic conductivity and excellent sodium insertion capability, as well as the electrochemical performance. As a result, it delivers a reversible capacity of 93.2 mA h g−1 with average redox potential of 3.8 V (vs. Na+/Na) at 0.05C; when the discharge rate increased to 10C, it delivers 56.3 mA h g−1 and an amazing capacity retention of 83% is achieved after 400 cycles. On the other hand, the doped nitrogen species plays a huge role on improving the electron-donating ability of the graphene layer, which effectively protects the easily oxidized host material from deterioration, giving the material longer stability in a normal oxygen-containing atmosphere. We believe that this work may lead to a promising, low cost, suitable sodium ion battery material for next-generation large-scale energy storage devices.

Manganese oxides (MnO2) are regarded as typical and promising electrode materials for supercapacitors. However, the practical electrochemical performance of MnO2 is far from its theoretical value. Nowadays, numerous efforts are being devoted to the design and preparation of nanostructured MnO2 with the aim of improving its electrochemical properties. In this work, ultralong MnO2 nanowires were fabricated in a process induced by carbon quantum dots (CQDs); subsequently, a binder-free flexible electrode membrane was easily obtained by vacuum filtration of the MnO2 nanowires. The effects of the CQDs not only induced the formation of one-dimensional nanostructured MnO2, but also significantly improved the wettability between electrode and electrolyte. In other words, the MnO2 membrane demonstrated a superhydrophilic character in aqueous solution, indicating the sufficient and abundant contact probability between electrode and electrolyte. The binder-free flexible MnO2 electrode exhibited a preeminent specific...

A free-standing flexible anode material for sodium storage with sandwich-structured characteristics was fabricated by modified vacuum filtration, consisting of stacked layers of Na2Ti3O7 nanowires@carbon nanotubes (NTO NW@CNT) and graphene oxide. The NTO NWs have a larger specific surface area for Na+ insertion/extraction with shortened ion diffusion pathways, accelerating the charge transfer/collection kinetics. The added CNTs both facilitate the uniform dispersion of the nanowires and nanotubes and also contribute to the connectivity of the nanowires, improving their conductivity. More importantly, the unique sandwichlike layered-structured film not only provides large numbers of electron-transfer channels and promotes the reaction kinetics during the charging and discharging process but also ensures the structural stability of the NTO NWs and the electrode. Electrochemical measurements suggest that this rationally designed structure endows the electrode with a high specific capacity and excellent cycling performance. A satisfactory reversible capacity as high as 92.5 mA h g–1 was achieved after 100 cycles at 2C; subsequently, the electrode also delivered 59.9 mA h g–1 after a further 100 cycles at 5C. Furthermore, after the rate performance test, the electrode could be continuously cycled for 100 cycles at a current density of 0.2C, which demonstrated that durable cyclic capacity with a high reversible capacity of 114.1 mA h g–1 was retained. This novel and low-cost fabrication procedure is readily scalable and provides a promising avenue for potential industrial applications.

Summary Flexible energy storage devices are attracting extensive attention, but most of the reported flexible batteries and supercapacitors use either strong acid or base or toxic flammable organic solutions as electrolytes, which pose potential safety issues when worn by humans or implanted into the body. Here, we present a highly safe family of flexible sodium-ion batteries (SIBs) based on a Na 0.44 MnO 2 cathode, a nano-sized NaTi 2 (PO 4 ) 3 @C anode, and various aqueous electrolytes containing Na + . The resulting belt- and fiber-shaped aqueous SIBs exhibit high volumetric energy and power density, high flexibility, and long life and thus can be safely applied in wearable electronic devices. When normal saline or cell-culture medium is used as the electrolyte, these SIBs can still work well, indicating potential application in implantable electronic devices. The fiber-shaped electrodes in Na + -containing aqueous electrolytes exhibit an electrochemical deoxygenation function, which could be applied in biological and medical fields.

Li 4 Ti 5 O 12 as one of the commercialized materials, is famous for its excellent reversibility, but also suffered from two drawbacks- low theoretical capacity and difficulty in SOC estimation. In this study, we report a Li 4 Ti 5 O 12 nanowire/Fe 3 O 4 nanoparticle compound synthesized by hydrothermal method as anode material for lithium ion battery. By in-situ synthesizing Fe 3 O 4 nanoparticles on the surface of Li 4 Ti 5 O 12 nanowire, particle size of Fe 3 O 4 is remarkably reduced and this resulting in good reversibility of electrode. Moreover, this Li 4 Ti 5 O 12 nanowire/Fe 3 O 4 nanoparticle compound exhibits much larger capacity than pure-phase Li 4 Ti 5 O 12 . And most importantly, the Li 4 Ti 5 O 12 nanowire/Fe 3 O 4 nanoparticle compound displays a slope voltage profile, which makes the voltage based SOC estimation much easier than Li 4 Ti 5 O 12.

The utilization of CO2 in Li-CO2 batteries is attracting extensive attention. However, the poor rechargeability and low applied current density have remained the Achilles' heel of this energy device. The gel polymer electrolyte (GPE), which is composed of a polymer matrix filled with tetraglyme-based liquid electrolyte, was used to fabricate a rechargeable Li-CO2 battery with a carbon nanotube-based gas electrode. The discharge product of Li2 CO3 formed in the GPE-based Li-CO2 battery exhibits a particle-shaped morphology with poor crystallinity, which is different from the contiguous polymer-like and crystalline discharge product in conventional Li-CO2 battery using a liquid electrolyte. Accordingly, the GPE-based battery shows much improved electrochemical performance. The achieved cycle life (60 cycles) and rate capability (maximum applied current density of 500 mA g-1 ) are much higher than most of previous reports, which points a new way to develop high-performance Li-CO2 batteries.

The magnesium-metal battery, which consists of a cathode, a Mg-metal anode, and a nonaqueous electrolyte, is a safer and less expensive alternative to the popular Li-ion battery. However, the performance of Mg batteries is greatly limited by the low electrochemical oxidative stability of nonaqueous electrolytes, the slow Mg2+ diffusion into the cathode, and the irreversibility of Mg striping and plating on the Mg metal anode. Here, we report the first Mg-ion battery using a Mg2+ aqueous electrolyte, nickel hexacyanoferrate cathode, and polyimide anode. The operation depends on Mg2+ intercalation–deintercalation at the cathode and reversible enolization at the anode, accompanied by Mg2+ transport between cathode and anode. The cell exhibits a maximum cell voltage of 1.5 V and a supercapacitor-like high power, and it can be cycled 5000 times. This system points the way to improved Mg-based rechargeable batteries.

Although hard carbons holds the most promise as anodes for practical sodium-ion batteries, high cost and low initial coulomb efficiency (ICE) limit their commercial application. In the present work, we develop an efficient solvothermal stabilization method to fabricate hard carbon spheres with high carbon yield from the wheat starch precursor. As anode for sodium-ion batteries, the obtained samples deliver not only a high capacity above 300 mAh g−1, but also an enhanced initial coulombic efficiency up to 90% and long cycle stability. Furthermore, when coupled with Na0.9[Cu0.22Fe0.30Mn0.48]O2 as cathode electrode, the full cell exhibited a high ICE of 85%, an average voltage of 3.2V and excellent stability during 300 cycles charging and discharging. These desirable electrochemical performances, combined with the renewable precursor and efficient synthesis route, make the obtained hard carbon sphere a promising anode for practical material for sodium-ion batteries.

Oxygen-redox of layer-structured metal-oxide cathodes has drawn great attention as an effective approach to break through the bottleneck of their capacity limit. However, reversible oxygen-redox can only be obtained in the high-voltage region (usually over 3.5 V) in current metal-oxide cathodes. Here, we realize reversible oxygen-redox in a wide voltage range of 1.5-4.5 V in a P2-layered Na0.7 Mg0.2 [Fe0.2 Mn0.6 □0.2 ]O2 cathode material, where intrinsic vacancies are located in transition-metal (TM) sites and Mg-ions are located in Na sites. Mg-ions in the Na layer serve as "pillars" to stabilize the layered structure during electrochemical cycling, especially in the high-voltage region. Intrinsic vacancies in the TM layer create the local configurations of "□-O-□", "Na-O-□" and "Mg-O-□" to trigger oxygen-redox in the whole voltage range of charge-discharge. Time-resolved techniques demonstrate that the P2 phase is well maintained in a wide potential window range of 1.5-4.5 V even at 10 C. It is revealed that charge compensation from Mn- and O-ions contributes to the whole voltage range of 1.5-4.5 V, while the redox of Fe-ions only contributes to the high-voltage region of 3.0-4.5 V. The orphaned electrons in the nonbonding 2p orbitals of O that point toward TM-vacancy sites are responsible for reversible oxygen-redox, and Mg-ions in Na sites suppress oxygen release effectively.

Power performance of lithium-ion batteries (LIBs) is generally controlled by the Li + diffusion within crystalline framework of electrode materials, and thus nano-sized electrode materials with shortened diffusion length have been widely used to build high power LIBs. However, the undesired effects from nano-sized electrode materials, such as low tap density, low thermal stability and increased interface also discount the overall performance of LIBs. Accordingly, it is desired to develop high power LIBs with micro-sized electrode materials. Herein, we demonstrate that hard carbon displays fast Li-storage kinetics which is not controlled by Li + diffusion in the crystalline framework. Furthermore, it is found that micro-sized spinel LiNi 0.5 Mn 1.5 O 4 and LiMn 2 O 4 have high rate performance, owing to their three-dimensional channels for Li + diffusion. Finally, the micro-sized spinel LiNi 0.5 Mn 1.5 O 4 (or Li 1.1 Mn 2 O 4 ) and micro-sized hard carbon are used as cathode and anode, respectively, to fabricate the full cells that exhibit supercapacitor-like high power performance. The achieved results point a way to develop high power LIBs besides nano-sizing electrode materials.

Sodium-ion batteries have been considered as promising alternatives to the current lithium-ion batteries owing to their low cost and abundant raw material. The major challenge of their practical implementation is the lack of favourable anode material. Spinel Li4Ti5O12 has been regarded as a potential anode material for its superior capability of sodium-ion storage and relatively appropriate operating voltage. However, the low intrinsic ionic and electronic conductivity of spinel Li4Ti5O12 still remains as its major drawback. Herein, carbon-coated Li4Ti5O12 nanoparticles have been synthesized through a solid-state reaction and a chemical vapour deposition method and used as an anode material for sodium-ion battery. The composite structure demonstrates excellent stability and an initial discharge specific capacity of 120.1 mA h g−1, which is maintained at 101.5 mA h g−1 after 500 cycles corresponding to 85% of capacity retention at a current density of 0.1 A g−1. In addition, a full cell was fabricated with carbon-coated Na3V2(PO4)3 as a positive electrode, which displayed discharge specific capacities of 138.5 mA h g−1 that was maintained at 114.7 mA h g−1 after 50 cycles at a current density of 0.05 A g−1, and the capacity retention was 82.8%. The results indicated that the Li4Ti5O12 nanoparticle with a carbon layer shows a promising electrochemical performance as anode materials in sodium-ion batteries.

Na3V2(PO4)3 (NVP) is considered a promising potential electrode material for both the cathode and anode in sodium ion batteries. Recently, flexible sodium ion batteries have attracted increased attention regarding their use as energy storage devices compatible with portable electronics, roll-up displays, implantable devices, and other applications. Here, a feasible strategy was adopted to prepare binder-free, mechanically robust, and paper-like carbon-coated NVP/reduced graphene oxide (NVP@C@rGO) electrodes. Combining the advantages of the large 2D rGO surface and nano-composite sandwich-like microstructure, the as-fabricated feasible NVP@C@rGO electrode demonstrated high reversible capacities and good rate capabilities both as a cathodic and as an anodic material. In addition to the half cell fabricated using a pure Na foil as the counter electrode, an interesting symmetric full cell constructed with NVP@C@rGO//NVP@C@rGO was systemically studied. The optimum design of the full cell exhibited good electrochemical performance, with 1.7 V as the output voltage plateau and a satisfactory capacity of 74.1 mA h g−1 at 0.5C. Up to 10C, this sodium full cell still exhibited stable capacity. Under arbitrary bending conditions, this flexible full cell can still exhibit a stable and safe electrochemical performance. This work may lead to a promising, low cost sodium full cell strategy for next-generation flexible energy storage devices.