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Three-electrode LiCoO2/graphite pouch cells have been used to investigate the film formation mechanism of Fluoroethylene carbonate (FEC) for high-voltage performance. It is found that the cells exhibit improved cycling performance in 5% FEC containing electrolyte in the voltage range of 3.0–4.4 V. In situ electrochemical impedance spectroscopy (EIS) results reveal that the gradual film formation process in FEC electrolyte is not a negative lithium consumption process, different from that of the base electrolyte. The characterizations from scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrate that FEC facilitates the formation of stable solid electrolyte interfaces (SEI) simultaneously on anode and cathode of the LiCoO2/graphite pouch cells with different decomposition mechanisms, which can effectively protect electrodes and prevent electrolyte decomposition on both electrodes.

Template method has been used as an important method to prepare porous materials. However, there are few reports about template method employing potassium chloride as template. Here, potassium chloride is employed as a template to prepare the porous carbon, and transition metal nitrates (Fe(NO3)2,d Co(NO3)2, Ni(NO3)2) are introduced to catalyze graphitization and to result different carbon structure during carbonization (denoted as Fe@C, Co@C and Ni@C). The Fe@C shows a formicary-like structure with an about 20 nm pore diameter and the Co@C displays a completely compact structure. Whereas, the Ni@C exhibits a foam-like structure with hierarchical porous structure consisting of macroporous frameworks, mesopores and ultrathin porous walls (∼5 nm). Its macropore and mesopore diameter is around 100 nm and 4 nm, respectively, its specific surface area is 464.5 m2 g−1. When adopted as anode material, the Ni@C presents much outstanding rate and cycling capability for lithium and sodium storage than Fe@C and Co@C, the capacity for sodium storage is 260 mAh g−1 after 100 cycles at 100 mA g−1 and 92 mAh g−1 after 1000 cycles at 1A g−1, and the capacity for lithium storage is 683 mAh g−1 after 1000 cycles at a current density of 1 A g−1.

Hollow micro-/nanostructures of metal oxides have attracted tremendous research attention in energy storage due to their unique structural advantages. Although fabrication of spherical hollow architectures have been intensively reported, rational design and facile synthesis of anisotropic hollow structures are still quite challenging, especially for those complex mixed metal oxides with well-controlled interior structures. Herein, through facile citrate-assisted hydrothermal synthesis and subsequent controlled annealing, well-defined octahedral ZnCo2O4 solid, hollow and yolk-shell micro-/nanostructures were constructed for the first time. When used as anode materials for lithium ion batteries (LIBs), the hollow ZnCo2O4 octahedron exhibits the best lithium storage properties, delivering high discharge capacities of 880 mA h g−1 over 160 cycles at 0.2 A g−1, and 650 mA h g−1 over 300 cycles at 1 A g−1. Moreover, it shows a superior high-rate performance with 60% of the specific capacity maintained even at a high current density of 5 A g−1. These features render the hollow octahedral ZnCo2O4 micro-/nanostructure a promising anode for next generation LIBs.

Structural hierarchy is ubiquitous in nature and quite important for optimizing the properties of functional materials. Carbon nanomaterials, owing to their unique and tunable physical and chemical properties, have been regarded as promising candidates for various energy storage systems. Constructing hierarchically structured carbon nanomaterials (HSCNs) can boost electrochemical performance of nanocarbons. Therefore, HSCNs have attracted tremendous research attentions in recent years. In this review, we summarized the recent progress in hierarchical structure design of carbon nanomaterials and their potential applications in different energy storage technologies. First we give a brief introduction about carbon nanomaterials and the hierarchical structure merits. Subsequently, recent research works on hierarchical structure design of carbon nanomaterials was summarized and classified according to applications in lithium-ion batteries, sodium-ion batteries, supercapacitors and lithium–sulfur batteries, respectively. In addition, the challenges of HSCNs in different applications were also concluded and reviewed. At last, design principles of HSCNs were summarized and future development trends were prospected.

The practical application of tin dioxide (SnO2) in lithium-ion batteries has been greatly hindered by its large volumetric expansion and low conductivity. Thus, a rational design of the size, geometry and the pore structure of SnO2-based nanomaterials is still a dire demand. To this end, herein we report an effective approach for engineering hollow-structured SnO2 nanospheres with adequate surface oxygen vacancies simultaneously wrapped by a nitrogen-doped graphene network (SnO2-x/N-rGO) through an electrostatic adsorption-induced self-assembly together with a thermal reduction process. The close electrostatic attraction achieved a tight and uniform combination of positively charged SnO2 nanospheres with negatively charged graphene oxide (GO), which can alleviate the aggregation and volume expansion of the entrapped SnO2 nanospheres. Subsequent thermal treatment not only ensures a significant reduction of the GO sheets accompanying nitrogen-doping, but also induces the generation of oxygen vacancies on the surface of the SnO2 hollow nanospheres, together building up a long-range and bicontinuous transfer channel for rapid electron and ion transport. Because of these structural merits, the as-built SnO2-x/N-rGO composite used as the anode material exhibits excellent robust cycling stability (∼912 mA h g-1 after 500 cycles at 0.5 A g-1 and 652 mA h g-1 after 200 cycles at 1 A g-1) and superior rate capability (309 mA h g-1 at 10 A g-1). This facile fabrication strategy may pave the way for the construction of high performance SnO2-based anode materials for potential application in advanced lithium-ion batteries.

LiNi0.8Co0.15Al0.05O2 and graphite–SiOx composites have been considered as potential cathode and anode materials for next-generation batteries due to their high specific capacity. It is significant to illustrate the degradation mechanism of NCA/graphite–SiOx power batteries under various conditions for their wide application. In this study, 10 A h NCA/graphite–SiOx power batteries were prepared and their deterioration mechanism at different temperatures (25 °C, 45 °C, and 65 °C) and discharge rates (1C and 3C) was systematically investigated. The results show that the batteries experienced 15.02% and 52.17% capacity loss after 400 cycles at 25 °C and 45 °C at 1C, respectively, and 21.94% after 400 cycles at a discharge rate of 3C. The capacity loss is as high as 79.93% after only 150 cycles at 65 °C and 1C. The long-term cycling behavior of the batteries is strongly affected by temperature, whereas it is negligibly affected by the discharge rate. The reversible lithium loss from the NCA cathode and structure decay of graphite–SiOx are responsible for the capacity loss of the battery. Many lithium alkyl carbonate (Li2CO3 and ROCO2Li), fluorophosphate (LixPOyFz and LixPFy), LiF, and oxygenated species are observed on the surface of graphite–SiOx due to the decomposition of the electrolyte at high temperatures. These species are deposited on the separator and thus block the pores and hinder ion transport; this results in a great increase of battery resistance and sudden loss of battery capacity.

To develop the symmetrical electrode materials for solid oxide fuel cells (SOFCs) and to explore the facile cell fabrication technique are both meaningful and of great significance. Here a bi-functional hybrid material LaNi0.82Fe0.18O3 (LNF)/NiO was synthesized by a one-pot citrate method and further used as the quasi-symmetrical electrode catalysts for solid oxide fuel cells (SOFCs). LNF and Ni (reduced NiO) functioned as the cathode/anode catalysts. The La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) based asymmetrical tri-layered substrates were fabricated by a screen-printing assisted co-firing technique. The polarization resistances (Rp) of the infiltrated anode at 700, 650, 600 and 550 °C were only 0.08, 0.12, 0.18 and 0.3 Ω cm2, respectively. Comparably, the Rp of the infiltrated cathode were much larger, e.g., 0.18, 0.35, 0.875 and 2.55 Ω cm2 at 700, 650, 600 and 550 °C, respectively. Encouragingly, these cathode Rp values were largely reduced when discharge due to an activation process. The LNF and NiO reversibly formed and decomposed during the oxidation and reduction processes, suggesting that the LNF/NiO hybrid is a potential quasi-symmetrical SOFC electrode material. When using H2 as fuel and air as oxidant, the maximum power densities of the single cell at 650, 600 and 550 °C were as high as 928, 580 and 329 mW cm−2, respectively.

The ever-increasing boom in smart, miniaturized electronics has led to an urgent need for on-chip energy storage systems that exhibit high performance, safety, flexibility and robust integration. However, tremendous challenges exist. Here, we demonstrate the first prototype of all-solid-state planar lithium ion micro-capacitors (LIMCs) based on interdigital patterns of lithium titanate nanospheres as the anode and activated graphene as the cathode. The interdigital LIMCs were fabricated via layer-by-layer mask-assisted deposition of graphene and electrode materials, without the need for metal current collectors, additives or polymer binders. The as-assembled LIMCs delivered a record volumetric energy density of 53.5 mW h cm−3. Furthermore, they exhibited outstanding mechanical flexibility without performance degradation under repeated bending, superior electrochemical metrics and safety at a high temperature of 80 °C due to the highly stable ionogel electrolyte and the absence of a separator. Additionally, our microdevices presented remarkable modular integration of the constructed bipolar cells for boosting high voltage and capacitance. Therefore, these LIMCs hold great potential for application in future flexible and wearable electronics.

Sulfur-functionalized graphene monoliths with a high sulfur fraction (16.8 wt%) were prepared to demonstrate a high capacity (∼400 mA h g-1 at 0.1 A g-1) and ultrafast (∼120 mA h g-1 at 5 A g-1) sodium ion storage. The reversible reaction of -C-Sx-C- with sodium ions contributes to the extra capacity while a 3D graphene network guarantees high rate capability.

In this work, we propose a general template-free strategy for fabricating two-dimensional mesoporous mixed oxide nanosheets, such as metal cobaltites (MCo2O4, M = Ni, Zn) through the self-deconstruction/reconstruction of highly uniform Co-based metal glycerate nanospheres into 2D Co-based metal glycerate/hydroxide nanosheets, induced by the so-called “water treatment” process at room temperature followed by their calcination in air at 260 °C. The proposed ‘self-deconstruction/reconstruction’ strategy is highly advantageous as the resulting 2D metal cobaltite nanosheets possess very high surface areas (150–200 m2 g−1) and mesoporous features with narrow pore size distribution. In addition, our proposed method also enables the crystallization temperature to achieve pure metal cobaltite phase from the precursor phase to be lowered by 50 °C. Using the 2D mesoporous NiCo2O4 nanosheets as a representative sample, we found that they exhibit 6–20 times higher specific capacitance and greatly enhanced capacitance retention compared to the NiCo2O4 nanospheres achieved through the direct calcination of the Ni–Co glycerate nanospheres. This highlights another advantage of the proposed strategy for enhancing the electrochemical performance of the mixed oxide products for supercapacitor applications. Furthermore, the asymmetric supercapacitor (ASC) assembled using the 2D NiCo2O4 nanosheets//graphene oxide (GO) exhibits a maximum energy density of 38.53 W h kg−1, while also showing a high capacitance retention of 91% after 2000 cycles at 5 A g−1. It is expected that the proposed general method may be extended to other transition metal elements for creating 2D mixed oxide nanosheets with enhanced surface areas and improved electrochemical performance.

Small amounts of two-dimensional (2D) graphene sheets are usually added into a polymer matrix to fabricate nanocomposites with improved mechanical and functional properties. Further enhancements of these properties beyond those of ordinary nanocomposites require much higher loadings of well-dispersed fillers, preferably in the form of an interconnected network with the preferential orientation along the direction of interest. However, the assembly of 2D fillers to form such a three-dimensional (3D) network remains a formidable task. Herein, a totally new approach is developed to fabricate a high-density 3D multilayer graphene web with interconnected, in-plane oriented graphene struts based on the versatile chemical vapor deposition technique. The continuous high-quality graphene network within the epoxy composites leads to exceptional electrical and thermal conductivities of 50 S cm−1 and 8.8 Wm−1 K−1, respectively. The high filler loading of 8.3 wt% also gives rise to a remarkable fracture toughness of 2.18 MPa m1/2, well over 100% enhancement over the neat epoxy. The simultaneous achievements of both remarkable transport properties and fracture toughness at these levels by an identical nanocomposite are unprecedented and have never been reported previously. The combination of unrivalled electrical and thermal conductivities with extraordinary fracture resistance offers the composites unique opportunities for multi-functional applications.

Most of the catalysts in lithium sulfur (Li-S) batteries present low electronic conductivity and the lithium polysulfides (LiPSs) must diffuse onto the surface of the carbon materials to achieve their conversion reaction. It is a significant challenge to achieve the instantaneous transformation of LiPSs to Li2 S in Li-S batteries to suppress the shuttle effect of LiPSs. Herein, a unique electron and ion co-conductive catalyst of carbon-coated Li1.4 Al0.4 Ti1.6 (PO4 )3 (C@LATP) is developed, which not only possesses strong adsorption to LiPSs, but, more importantly, also promotes the instantaneous conversion reaction of LiPSs to Li2 S. The C@LATP nanoparticles as catalytic active sites can synchronously and efficiently provide both Li ions and electrons to facilitate the conversion reaction of LiPSs. The conversion reaction path of LiPSs using C@LATP changes from traditional "adsorption-diffusion-conversion" to novel "adsorption-conversion," which effectively lowers the decomposition barrier of Li2 S6 and promotes faster conversion of LiPSs. The shuttle effect of LiPSs is considerably suppressed and utilization of sulfur is greatly improved. The Li-S batteries using C@LATP present excellent rate, cycling, and self-discharge properties. This work highlights the significance of electron and ion co-conductive solid-state electrolytes for the instantaneous transformation of LiPSs in advanced Li-S batteries.

The combination of various fillers can improve the thermal conductivity of polymer composites, because an efficient heat conduction network synergistically formed in matrix. The synergistic effect of two fillers, carbon fiber and alumina particle, in polydimethylsiloxane (PDMS) is investigated in this work. A filler combination results in higher thermally conductive composite than any of the single filler. The volume ratio of 4:1 shows the greatest thermal conductivity. The thermal conductivity of PDMS composite filled with 24 vol% carbon fiber and 6 vol% alumina reaches 7.91 W m−1K−1, which was 34% higher than that of 30 vol% CF/PDMS. The combined filler composite also shown better process performance due to the lower viscosity. The synergy is attributed to the optimized heat transfer network and reduced interfacial thermal resistance. Therefore, a combined filler achieved better thermally conductive performance and better process performance with cost-effective source materials.

The pore structural designability of wood-derived hard carbons (WDHCs) lays an optimal foundation for acquiring a cost-efficient and green anode material for sodium-ion batteries. Here, a WDHCs material was reported for high-capacity and cycling-stable sodium storage through a pore forming-opening strategy. Associated with the natural holey texture of wood, the WDHCs displays a hierarchical pore structure by a precise chemical treatment and a high-temperature carbonization, creating the straight channels and plentiful closed nanopores. This well-constructed channel structure is conducive to the penetration of electrolyte and the transport of sodium ions. The closed nanopores constructed by the curved graphene layers are gradually unfolded upon cycling, thus providing higher reversible capacity in the platform zone. The surface-controlled pseudocapacitive reaction favored ultrafast ion transport mainly contributes to sodium storage capacity. As a result, the developed optimal anodes harvest a high sodium storage capacity of 439 mAh g−1 at 0.1 A g−1, and excellent long-term cycling stability of 248 mA h g−1 at 0.1 A g−1 over 500 cycles as well as the capacity retention close to 100%. The galvanostatic intermittent titration technique combined with electrochemical impedance spectroscopy proved that the WDHCs anode has fast charge transport kinetics, thus exhibiting excellent rate performance.

The interfacial issues between garnet electrolyte and Li metal hinder the application of garnet electrolyte in solid-state Li metal batteries. Herein, a three-dimensional (3D) porous Zn layer (PZL) is magnetron sputtered on the surface of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) to construct a 3D Li–Zn alloy layer at the LLZTO/Li interface by melting Li metal into PZL. The 3D Li–Zn alloy effectively reduces the LLZTO/Li interfacial impedance from 319.8 Ω cm2 to an extremely low value of 1.9 Ω cm2. Meanwhile, the 3D alloy skeleton can enhance the transport kinetics and promote uniform distribution of Li ion at interface to inhibit the growth of Li dendrites. More importantly, the volume expansion of interface between LLZO and Li metal anode is effectively suppressed due to the host role of 3D Li–Zn alloy interface. The Li/LLZTO@PZL/Li symmetrical battery achieves a high critical current density of 2 mA cm−2 for one cycle. The all-solid-state LiNi0.5Co0.2Mn0.3O2 (NCM523)/LLZTO@PZL/Li battery with a high cathode loading of 4.9 mg cm−2 delivers a high specific capacity of 143.8 mAh g−1 after 170 cycles. The 3D alloy interface is significant for enhancing the interfacial stability of high capacity all-solid-state lithium metal batteries.

A nitrogen (N)-doped porous carbon sheet is prepared by in situ polymerization of pyrrole on both sides of graphene oxide, following which the polypyrrole layers are then transformed to the N-doped porous carbon layers during the following carbonization, and a sandwich structure is formed. Such a sheet-like structure possesses a high specific surface area and, more importantly, guarantees the sufficient utilization of the N-doping active porous sites. The internal graphene layer acts as an excellent electron pathway, and meanwhile, the external thin and porous carbon layer helps to decrease the ion diffusion resistance during electrochemical reactions. As a result, this sandwich structure exhibits prominent catalytic activity toward the oxygen reduction reaction in alkaline media, as evidenced by a more positive onset potential, a larger diffusion-limited current, better durability and poison-tolerance than commercial Pt/C. This study shows a novel method of using graphene to template the traditional poro...

Vanadium pentoxide (V2O5) is considered a promising cathode material for advanced lithium-ion batteries owing to its high specific capacity and low cost. However, the application of V2O5-based electrodes has been hindered because of their inferior conductivity, cycling stability, and power performance. Herein, hierarchical sisal-like V2O5 microstructures consisting of primary one-dimensional (1D) nanobelts with [001] facets orientation growth and rich oxygen vacancies are synthesized through a facile hydrothermal process using polyoxyethylene-20-cetyl-ether as the surface control agent, followed by calcination. The primary 1D nanobelt shortens the transfer path of electrons and ions, and the stable {001} facets could reduce the side reaction at the interface of electrode/electrolyte, simultaneously. Moreover, the formation of low valence state vanadium would generate the oxygen vacancies to facilitate lithium-ion diffusion. As a result, the sisal-like V2O5 manifests excellent electrochemical performances, including high specific capacity (297 mA h g-1 at a current of 0.1 C) and robust cycling performance (capacity fading 0.06% per cycle). This work develops a controllable method to craft the hierarchical sisal-like V2O5 microstructures with excellent high rate and long-term cyclic stability.

As a promising candidate for large-scale energy storage systems, sodium-ion batteries (SIBs) are experiencing a rapid development. Organic conjugated carboxylic acid anodes not only have tailorable electrochemical properties but also are easily accessible. However, the low stability and electrical conductivity hamper their practical applications. In this study, disodium terephthalate (Na2 TP), the most favorable organic conjugated carboxylic acid anode material for SIBs, was proposed to integrate with graphene oxide (GO) by an anti-solvent precipitation process, which ensures the uniform and tight coating of GO on the Na2 TP surface. GO is electrochemically reduced during the first several cycles of the electrochemical measurement, which buffers the volume change and improves the electrical conductivity of Na2 TP, resulting in a better cyclic and rate performance. The incorporation of only 5 wt % GO onto Na2 TP leads to a reversible capability of 235 mA h g-1 after 100 cycles at a current rate of 0.1 C, which is the best among the state of the art organic anodes for SIBs. The one-step synthesis together with the low costs of the raw materials show a promise for the scalable preparation of anode materials for practical SIBs.

In this paper, a novel route using lithium polyacrylate (PAALi) as dual-functional lithium source was developed to produce layered oxide cathodes. The PAALi was in-situ polymerized on the surface of Ni1/3Co1/3Mn1/3(OH)2 precursor. By means of spray drying, spherical powders composed of PAALi wrapped around the precursor were prepared. The organic compound PAALi can function as a particle size control agent as well as the highly dispersed lithium source in the proposed route. It can transform to carbon coating layers during pre-heat treatment at 450 °C under inert atmosphere. Those carbon coating layers not only significantly reduce agglomeration of particles and limit growth of the particle size, but also provide enough inner voids and paths after the subsequent sintering at 900 °C. The produced layered cathodes can deliver capacity retention of 84.4% after 200 cycles at 1C and a capacity of 110.5 mA h g−1 at 10C. In comparison, the sample prepared with traditional lithium source only delivers capacity retention of 63.0% after 200 cycles at 1C and 70.9 mA h g−1 at 10C. The proposed route using PAALi as lithium source is potentially generalized to a broad application in the preparation of high-performance electrode materials.

Multicomponent composites with an atomic-scale distribution of different component and an integrated lattice structure may manifest an enhanced synergistic effect compared to the mechanical mixture. In this paper, multicomponent Zn0.12Co0.88CO3 composite with high tap density (2.11 g cm−3) synthesized via one-step solvothermal method, which exhibits hexagonal structure similar to that of the monocomponent cobalt carbonate (CoCO3). The Zn-substitution could significantly improve the charge and discharge capacity of CoCO3 from 1001.6 mAh g−1 to 1253.7 mAh g−1 at 0.2 C. When the Zn-substituted CoCO3 is embedded in carbon nanotubes (CNT) network, the rate performance of Zn0.12Co0.88CO3 can be improved greatly. The resulting Zn0.12Co0.88CO3/CNT exhibits outstanding rate performance, delivering a reversible capacity of 1098.4, 840.8, and 610.7 mAh g−1 at 0.5, 1 and 2 C, respectively. The excellent performance of Zn0.12Co0.88CO3/CNT is ascribed to the unique micro-sphere structure with carbon nanotubes. The elastic CNT networks are introduced to wrap the Zn0.12Co0.88CO3, which can not only provide a highly conductive network for electron transfer, but also serve as a buffer to alleviate the aggregation and volume changes of Zn0.12Co0.88CO3 nanoparticles. The Zn0.12Co0.88CO3/CNT composite may serve as a novel high-capacity LIBs anode material for practical application, and a facile strategic approach is introduced for the full-molar-ratio synthesis of multicomponent composites.

Among various two-dimensional compounds, transition metal dichalcogenides (TMDs or MX2) are a group of materials attracting growing research interest for potential applications as battery electrodes. Here we systematically investigate the electrochemical performance of a series of MX2 (M = Mo, W, Nb, Ta; X = S, Se) upon Li/Na intercalation through first-principles calculations. MoX2 and WX2 were found to have lower voltages while those of NbX2 and TaX2 were higher than 1.5 V. By applying the rigid-band model, we found that the energy gained for electrons to transfer from Li/Na to MX2 could serve as a descriptor for characterizing voltages of MX2.The linear relation between the descriptor and voltages is useful for screening candidates for electrodes with desired voltage. Migration barriers for Li/Na ions were approximately 0.3 eV in MoX2/WX2 and 0.5 eV in NbX2/TaX2. The low barriers suggest a reasonable rate performance when these TMDs are used as electrodes. By stacking different MX2 with distinct proper...

The rapid development of lithium (Li)-ion and sodium (Na)-ion batteries requires advanced solid electrolytes that possess both favorable electrochemical performance and safety assurance. Herein we report a hierarchical poly (ionic liquid)-based solid electrolyte (HPILSE) for high-safety Li-ion and Na-ion batteries. This hybrid solid electrolyte is fabricated via in situ polymerizing 1,4-bis[3-(2-acryloyloxyethyl)imidazolium-1-yl]butane bis[bis(trifluoromethanesulfonyl)imide] (C1-4TFSI) monomer in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI)-based electrolyte which is filled in poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDDATFSI) porous membrane. The well-designed hierarchical structure simultaneously provides the prepared HPILSE with high ionic conductivity (>10 −3 S cm −1 at 25 °C), satisfied electrochemical stability, inherent incombustibility, good mechanical strength and flexibility. More intriguingly, the in situ assembled LiFePO 4 /Li and Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 /Na cells using HPILSE exhibit superior cycling performances with high specific capacities. Both the excellent performance of HPILSE and the simple fabricating process of HPILSE-based solid-state cells make it potentially as one of the most promising electrolyte materials for next generation Li-ion and Na-ion batteries.

The lithium-ion batteries show extremely poor cycling performance at low temperature. The main degradation mechanism is not clear. To address the fading mechanism, the cycling degradation of commercial LiFePO4/mesocarbon microbead (MCMB) batteries under various charge rate (1/10C, 1/3C, 1/2C, and 1C) at −10 °C is systematically investigated using nondestructive tests combining with post-mortem analysis. The low-temperature charging under high charge rates of 1/3C, 1/2C, and 1C results in severe lithium plating, which leads to extremely serious capacity loss. In contrast, no lithium plating occurred under low charge rate of 1/10C. The lithium plating on the anode surface leads to consumption of active lithium ions and electrolyte, which causes the capacity decay and increases ohmic resistance (R b) with cycling number under high charge rates. The lithium plating on the anode surface is partially reversible, which brings about the capacity recovery of batteries after 80 cycles at 25 °C. The above results are proved by the followed post-mortem measurements. The evolution of the surface morphologies of MCMB electrodes upon cycling shows that a layer composed of rod-like lithium is formed on the anode surface.

In this study, commercial Li(Ni1/3Co1/3Mn1/3)O2/graphite (NCM/C) lithium-ion batteries were cycled at −10 °C under different current rates ranging from 0.2 C to 1C. Electrochemical measurements and post-mortem analysis were performed to identify the root causes of the degradation in the electrochemical performance of the cells. The results reveal that apart from the increase of lithium plating on the anode, there is a considerable and abnormal capacity loss on the NCM cathode with the increase in current rate. The different degradation mechanisms including the loss of lithium inventory (LLI) and the specific capacity loss of NCM material (LAM) during cycling at −10 °C were analyzed quantitatively. It is shown that the evolution trend of LLI with the increase in current rate (8.6%, 35.0%, 55.8% for 0.2 C, 0.5 C and 1 C respectively) corresponds closely to that of the capacity loss of the full-cells (8.6%, 45.5%, 63.6% for 0.2 C, 0.5 C and 1 C, respectively), which is different to the trend of LAM (7.2%, 8.8%, 22.3% for 0.2 C, 0.5 C and 1 C, respectively). Further analysis by XRD and HR-TEM clearly indicates that the crystallinity of the hexagonal layered structure of NCM was greatly impaired after low-temperature cycling at −10 °C, and spinel phase can be observed among the layered structure.

Well-controlled nanostructures and a high fraction of Sn/Li2O interface are critical to enhance the coulombic efficiency and cyclic performance of SnO2-based electrodes for lithium-ion batteries (LIBs). Polydopamine (PDA)-coated SnO2 nanocrystals, composed of hundreds of PDA-coated “corn-like” SnO2 nanoparticles (diameter ca. 5 nm) decorated along a “cob”, addressed the irreversibility issue of SnO2-based electrodes. The PDA-coated SnO2 were crafted by capitalizing on rationally designed bottlebrush-like hydroxypropyl cellulose-graft-poly (acrylic acid) (HPC-g-PAA) as a template and was coated with PDA to construct a passivating solid-electrolyte interphase (SEI) layer. In combination, the corn-like nanostructure and the protective PDA coating contributed to a PDA-coated SnO2 electrode with excellent rate capability, superior long-term stability over 300 cycles, and high Sn→SnO2 reversibility.

Recently, the lithium–oxygen (Li–O2) battery has attracted much interest due to its ultrahigh theoretical energy density. However, its potential application is limited by an unstable electrolyte system, low round-trip efficiency, and poor cyclic performance. In this study, we present a new electrolyte based on N,N′-dimethylpropyleneurea (DMPU) applied for the Li–O2 battery. This electrolyte possesses high ionic conductivity and achieves a low discharge/charge voltage gap of 0.6 V, which is mainly due to the possible one-electron charge transfer mechanism. The introduction of the antioxidant butylatedhydroxytoluene (BHT) as an additive stabilizes the superoxide radical by chemical adsorption and improves the cyclic performance remarkably. Thus, this new electrolyte system may be one of the candidates for Li–O2 batteries.

An in-depth understanding of (de)lithiation induced phase transition in electrode materials is crucial to grasp their structure–property relationships and provide guidance to the design of more desirable electrodes. By operando synchrotron XRD (SXRD) measurement and Density Functional Theory (DFT) based calculations, we discover a reversible first-order phase transition for the first time during (de)lithiation of CeO2 nanoparticles. The LixCeO2 compound phase is identified to possess the same fluorite crystal structure with FM3M space group as that of the pristine CeO2 nanoparticles. The SXRD determined lattice constant of the LixCeO2 compound phase is 0.551 nm, larger than that of 0.541 nm of the pristine CeO2 phase. The DFT calculations further reveal that the Li induced redistribution of electrons causes the increase in the Ce–O covalent bonding, the shuffling of Ce and O atoms, and the jump expansion of lattice constant, thereby resulting in the first-order phase transition. Discovering the new phase ...

Sliced orange-shaped ZnCo 2 O 4 (SOS-ZCO) constructed by radically aligned subunit nanoparticles is solvothermally synthesized for the first time. When used as lithium-ion battery (LIB) anode, SOS-ZCO demonstrates excellent electrochemical performances benefiting from its advantageous structural features. It shows a high reversible capacity of 890 mA h g −1 at 0.2 A g −1 and good rate capability with capacity retention of 47% at 5 A g −1 . Moreover, it displays a superior cycling stability with 96.5% capacity retention over 130 cycles at 0.2 A g −1 and 92.3% capacity retention over 300 cycles at 1 A g −1 . It is noteworthy that during high-rate cycling, SOS-ZCO anode does not show common pulverization phenomenon to form irregular morphology, but experiences regular morphology transformation. In the first 100 high-rate cycles, SOS-ZCO anode transforms into a network of randomly arranged nanowires with high firmness, leading to negligible capacity fading in the following 200 cycles. Therefore, novel SOS-ZCO micro-/nanostructure exhibits great potential for high-performance LIB anode.

Titanium oxide (TiO2) has attracted great interest as a promising anode material for lithium (Li) ion batteries (LIBs) and sodium (Na) ion batteries (SIBs). However, the key factors that dictate the Li-ion and Na-ion storage and transportation in TiO2 remain unclear. Herein, we report a facile hydrolysis route to crafting a variety of high tap-density TiO2 spheres with controllable size and hierarchical pores. The Li-ion and Na-ion storage properties based on these TiO2 spheres were systematically investigated. The pore distribution and the size of TiO2 spheres were found to exert profound influence on the Li-ion and Na-ion storage and transportation. The Li-ion storage and transportation in dense TiO2 spheres was dependent mainly upon the micropore distribution and volume and independent of the size of spheres. In contrast, the excellent Na-ion storage and transportation in TiO2 spheres was enabled by the loose structure with a large macroscopic pore volume and shortened Na-ion diffusion length. High tap-density TiO2 spheres (1.06 g cm−3) with superior Li-ion and Na-ion storage properties were produced, exhibiting a Li-ion storage specific capacity of 189 mA h g−1 at 1C and a high capacity retention of 88.1% after 100 cycles, and a Na-ion storage specific capacity of 184 mA h g−1 at 1C and capacity retention of 90.5% after 200 cycles. The ability to understand the critical factors controlling the Li-ion and Na-ion storage in high tap-density TiO2 spheres enables their implementation for practical applications in Li-ion and Na-ion batteries.

Titanium dioxide (TiO2) mesocrystals consist of a large number of subunits possessing distinct characteristics of large surface area, high crystallinity and large density and are considered as promising potential materials for energy storage and conversion, sensing, and photocatalysis. Therefore, it is significant to develop a robust and universal method to synthesize and precisely tune the TiO2 mesocrystals at low temperatures. However, this is still a big challenge and has not been largely achieved. In this context, we develop a robust method of synthesizing TiO2 mesocrystals by a facile hydrolysis and evolution process induced by acetic acid (HAc) solution at 80 °C using TiN as a starting material. The size and crystallinity of the TiO2 mesocrystals can be easily tuned by adjusting the HAc content and reaction time. The HAc governs the transformation of TiO2 from the amorphous state to the anatase phase at a low temperature (80 °C). The average size of the TiO2 mesocrystals can be tuned from ∼100 nm to 20 nm by changing the HAc content. TiO2 mesocrystals with a spindle-like morphology were formed and the tiny anatase TiO2 grains were grown along the same orientation [001] plane, which exhibits excellent electrochemical performance for lithium-ion storage. The specific capacity at 1C is 180 mA h g−1 and the retention is 92.9% after 100 cycles. Thereby, this study presents a universal method of crafting anatase TiO2 mesocrystals at low temperatures.

Lithium ion batteries (LIBs) with high power density, extended life time, and enhanced safety properties are promising energy storage devices for pure/hybrid electric vehicles and grid energy storage. Conventional graphite anodes suffer from limited rate capability and great safety concerns. Thus the development of efficient electrode materials with long cycle stability, excellent rate capability and enhanced safety is crucial for high-power LIBs. Spinel Li4Ti5O12 (LTO) has emerged as a competitive anode material for high-power LIBs due to its high safety, excellent high rate capability and extremely long cycling stability. However, the severe gas generation and associated swelling observed in soft-pack batteries during charge/discharge cycles and storage, which are accelerated under elevated temperatures, become a main obstacle to the large-scale application of LTO-based LIBs. Further understanding on the severe gassing behavior in LTO-based LIBs is quite necessary since it not only seriously deteriorates their power density and cycling stability, but also leads to great safety concerns. To date, there are some research reports that specifically refer to the gassing behavior of LTO electrodes. However, there is no critical review that concentrates exclusively on the gassing of LTO-based batteries. Hence, this review aims to provide an up-to-date and comprehensive summary of the gassing behavior in LTO-based LIBs. Details will be given specifically on the influencing factors, possible gassing mechanisms, and state-of-the art remedies. An insight into the future research of LTO-based battery development is given.

Metal–organic frameworks (MOFs) have gained significant attention as precursors for the fabrication of porous hybrid materials due to their highly controllable composition, structure and pore size. However, at present, MOF-derived materials have rarely been investigated as anode materials for sodium-ion batteries. In this work, we report the fabrication of a Ni-doped Co/CoO/N-doped carbon (NC) hybrid using bimetallic Ni–Co-ZIF as the starting precursor. The resulting Ni-doped Co/CoO/NC hybrid is highly microporous with a high specific surface area of 552 m2 g−1. When employed as an anode material for sodium-ion batteries, the Ni-doped Co/CoO/NC hybrid exhibited both good rate performance with a high discharge capacity of 218 mA h g−1 at a high current density of 500 mA g−1 and good cycling stability, as a high discharge capacity of 218.7 mA h g−1 can be retained after 100 cycles at 500 mA g−1, corresponding to a high capacity retention of 87.5%. The excellent electrochemical performance of the Ni-doped Co/CoO/NC hybrid for SIBs may be attributed to the synergistic effects of various factors, including: (i) the presence of a carbon matrix which provides protection against aggregation and pulverization during sodiation/desodiation; (ii) the highly microporous nature along with the presence of a few mesopores which facilitates better insertion/de-insertion of Na+ ions; (iii) the Ni-doping which introduces defect sites into the atomic structure of CoO via partial substitution, thus enhancing the conductivity of the cobalt oxide (CoO) component and hence, the overall hybrid material, and (iv) the N-doping which promotes a faster migration speed of sodium ions (Na+) across the carbon layer by creating defect sites, thereby improving the conductivity of the carbon frameworks in the hybrid material.

Sodium metal batteries suffer from severe capacity decay due to the continuous side-reactions between sodium metal anode and conventional carbonate electrolyte using porous glass fiber (GF) membranes as the separator, especially at elevated temperature. Moreover, sodium dendrites preferentially propagate through the low-modulus pores and cause severe safety issues. Here a compact gel polymer electrolyte (GF-GPE) with high ionic conductivity is developed by tightly immobilizing liquid electrolyte in polymer matrix embedded in GF membranes. The extensive interaction between the liquid electrolyte and polymer matrix promotes the formation of a stable Na/GF-GPE interface to effectively reduce the side reactions at both room and elevated temperature. The GF-GPE could regulate the depth concentration profile of NaF, a key solid electrolyte interphase (SEI) component, to deter sodium dendrites formation and side reactions. As a result, the Na3V2(PO4)3/GF-GPE/Na cell presents outstanding cycling stability. Its capacity retention after 2000 cycles at 1C under room temperature is as high as 95% and that after 500 cycles at 60 °C reaches 84%. This study successfully develops a robust and scalable approach by using a compact gel polymer electrolyte to achieve stable sodium metal anodes at room and elevated temperature.

Li

Sodium metal batteries have potentially high energy densities, but severe sodium-dendrite growth and side reactions prevent their practical applications, especially at high temperatures. Herein, we design an inorganic ionic conductor/gel polymer electrolyte composite, where uniformly cross-linked beta alumina nanowires are compactly coated by a poly(vinylidene fluoride-co-hexafluoropropylene)-based gel polymer electrolyte through their strong molecular interactions. These beta alumina nanowires combined with the gel polymer layer create dense and homogeneous solid-liquid hybrid sodium-ion transportation channels through and along the nanowires, which promote uniform sodium deposition and formation of a stable and flat solid electrolyte interface on the sodium metal anode. Side reactions between the sodium metal and liquid electrolyte, as well as sodium dendrite formation, are successfully suppressed, especially at 60 °C. The sodium vanadium phosphate/sodium full cells with composite electrolyte exhibit 95.3% and 78.8% capacity retention after 1000 cycles at 1 C at 25 °C and 60 °C, respectively., Here the authors show a beta alumina nanowires/gel polymer composite electrolyte design. The dense and homogeneous solid-liquid hybrid sodium-ion transportation channels promote uniform sodium deposition and stripping and significantly improve the performance of a Na metal battery.

Designing composite structures of active materials is critical for high-performance lithium-ion batteries, as it determines the reversibility of lithium-ion insertion and extraction of the electrodes. The V

Sodium-ion batteries (SIBs) are promising for large-scale energy storage systems and carbon materials are the most likely candidates for their electrodes. The existence of defects in carbon materials is crucial for increasing the sodium storage ability. However, both the reversible capacity and efficiency need to be further improved. Functionalization is a direct and feasible approach to address this issue. Based on the structural changes in carbon materials produced by surface functionalization, three basic categories are defined: heteroatom doping, grafting of functional groups, and the shielding of defects. Heteroatom doping can improve the electrochemical reactivity, and the grafting of functional groups can promote both the diffusion-controlled bulk process and surface-confined capacitive process. The shielding of defects can further increase the efficiency and cyclic stability without sacrificing reversible capacity. In this Review, recent progresses in the ways to produce surface functionalization are presented and the related impact on the physical and chemical properties of carbon materials is discussed. Moreover, the critical issues, challenges, and possibilities for future research are summarized.

Ether based electrolytes have surfaced as alternatives to conventional carbonates allowing for enhanced electrochemical performance of sodium-ion batteries; however, the primary source of the improvement remains poorly understood. Here we show that coupling titanium dioxide and other anode materials with diglyme does enable higher efficiency and reversible capacity than those for the combination involving ester electrolytes. Importantly, the electrolyte dependent performance is revealed to be the result of the different structural evolution induced by a varied sodiation depth. A suit of characterizations show that the energy barrier to charge transfer at the interface between electrolyte and electrode is the factor that dominates the interfacial electrochemical characteristics and therefore the energy storage properties. Our study proposes a reliable parameter to assess the intricate sodiation dynamics in sodium-ion batteries and could guide the design of aprotic electrolytes for next generation rechargeable batteries.

Solid electrolytes are considered as strong alternatives for conventional liquid electrolytes to overcome the safety issues of next-generation high-energy-density lithium metal batteries (LMBs). Although Li

Ether based electrolytes have surfaced as alternatives to conventional carbonates allowing for enhanced electrochemical performance of sodium-ion batteries; however, the primary source of the improvement remains poorly understood. Here we show that coupling titanium dioxide and other anode materials with diglyme does enable higher efficiency and reversible capacity than those for the combination involving ester electrolytes. Importantly, the electrolyte dependent performance is revealed to be the result of the different structural evolution induced by a varied sodiation depth. A suit of characterizations show that the energy barrier to charge transfer at the interface between electrolyte and electrode is the factor that dominates the interfacial electrochemical characteristics and therefore the energy storage properties. Our study proposes a reliable parameter to assess the intricate sodiation dynamics in sodium-ion batteries and could guide the design of aprotic electrolytes for next generation rechargeable batteries., Sodium ion batteries are known to benefit from the use of ether electrolytes. Here the authors reveal the origin showing that the energy barrier of charge transfer at the electrolyte/electrode interface dominates the interfacial electrochemical characteristics and is favorably small.

It is a huge challenge for high-tap-density electrodes to achieve high volumetric energy density but without compromising the ionic transportation. Herein, we prepared compact Li4Ti5O12 (LTO) microspheres consisting of densely packed primary nanoparticles. The real space distribution of lithium ions inside the compact LTO was revealed by using scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) to identify the function of grain boundaries for lithium ion transportation during lithiation. The as-prepared LTO microspheres possess a high tap density (1.23 g cm-3) and an ultra-small specific surface area (2.40 m2 g-1). Impressively, the compact LTO microspheres present excellent electrochemical performance. At high rates of 5C, 10C and 20C, the LTO microspheres show a specific capacity of 146.6, 138.2 and 111 mA h g-1, respectively. The capacity retention remains at 97.8% at 5C after 500 cycles. The STEM-EELS results indicate that the lithiation reaction of LTO is firstly initiated at grain boundaries during the high rate lithiation process and then diffuses to the bulk area. The abundant grain boundaries in compact LTO microspheres can form a highly efficient conductive network to preferentially transport the ions, which contributes to high volumetric and gravimetric energy density simultaneously.

Catalysis is an effective remedy for the fast capacity decay of lithium-sulfur batteries induced by the shuttling of lithium polysulfides (LiPSs), but too strong adsorption ability of many catalysts toward LiPSs increases the risk of catalyst passivation and restricts the diffusion of LiPSs for conversion. Herein, perovskite bimetallic hydroxide (CoSn(OH)6 ) nanocages are prepared, which are further wrapped by reduced graphene oxide (rGO) as the catalytic host for sulfur. Because of the coordinated valence state of Co and Sn and the intrinsic defect of the perovskite structure, such bimetallic hydroxide delivers moderate adsorption ability and enhanced catalytic activity toward LiPS conversion. Coupled with the hollow structure and the wrapped rGO as double physical barriers, the redox reaction kinetics, and sulfur utilization are effectively improved with such a host. The assembled battery delivers a good rate performance with a high capacity of 644 mAh g-1 at 2 C and long stability with a capacity decay of 0.068% per cycle over 600 cycles at 1 C. Even with a higher sulfur loading of 3.2 mg cm-2 and a low electrolyte/sulfur ratio of 5 µL mg-1 , the battery still shows high sulfur utilization and good cycling stability.

Graphyne, a kind of sp-sp2 hybrid all-carbon two-dimensional material, is currently one of the most interesting carbon allotropes besides graphene. It has potential applications and characteristic properties because of its unique electronic structure. First,the concept and properties of graphyne are summarized, then the characteristic properties of graphynes and their potential applications are reviewed, before some methods and ways to synthesize the two-dimensional structures are proposed, and finally a short perspective on the study of graphynesis given.

A rubidium nitrate (RbNO3) additive coordinated with 18‐crown‐6 crown ether is proposed to stabilize the lithium metal anode in the carbonate electrolyte. A coordination reaction between them promotes the dissolution of NO3− ions to form a dense and Li3N‐rich solid electrolyte interface and generates the Rb(18‐crown‐6)+ complexes as stable shielding ions to suppress dendrite growth.