Three-Dimensional Self-Supported Ge Anode for Advanced Lithium-Ion Batteries

Three-dimensional (3D) self-supported Ge anode is one of the promising candidates to replace the traditional graphite anode material for high-performance binder-free lithium-ion batteries (LIBs). The enlarged surface area and the shortened ions/electrons transporting distance of the 3D electrode would greatly facilitate the rapid transfer of abundant lithium ions during cycling, thus achieve enhanced energy and power density during cycling. Cycle stability of the 3D self-supported Ge electrode would be improved due to the obtained enough space could effectively accommodate the large volume expansion of the Ge anode. In this review, we first describe the electrochemical properties and Li ions storage mechanism of Ge anode. Moreover, the recent advances in the 3D self-supported Ge anode architectures design are majorly illustrated and discussed. Challenges and prospects of the 3D self-supported Ge electrode are finally provided, which shed light on ways to design more reliable 3D Ge-based electrodes in energy storage systems.

Three-Dimensional Nitrogen-Doped Carbonaceous Networks Anchored with Cobalt as Separator Modification Layers for Low-Polarization and Long-Lifespan Aluminum-Sulfur Batteries

Aluminum-sulfur (Al-S) batteries have attracted extensive interest due to their high theoretical energy density, inherent safety, and low cost. However, severe polarization and poor cycling performance significantly limit the development of Al-S batteries. Herein, three-dimensional (3D) nitrogen-doped carbonaceous networks anchored with cobalt (Co@CMel-ZIF) is proposed as a separator modification layer to mitigate these issues, prepared via carbonizations of a mixture of ZIF-7, melamine, and CoCl2. It exhibits a 3D network structure with a moderate surface area and high average pore diameter, which is demonstrated to be effective in adsorbing the aluminum polysulfides and hindering the mobility of polysulfides across the separator for enhanced cyclic stability of Al-S batteries. Meanwhile, Co@CMel-ZIF are characterized by abundant catalytic pyridinic-N and Co-Nx active sites that effectively eliminate the barrier of sulfides' conversion and thereby facilitate the polarization reduction. As a result, Al-S cells based on the separator modified with Co@CMel-ZIF exhibit a low voltage polarization of 0.47 V under the current density of 50 mA g-1 at 20 °C and a high discharge specific capacity of 503 mAh g-1 after 150 cycles. In contrast, the cell employing a bare separator exhibits a polarization of 1.01 V and a discharge capacity of 300 mAh g-1 after 70 cycles under the same conditions. This work demonstrates that modifying the separators is a promising strategy to mitigate the high polarization and poor cyclability of Al-S batteries.

MoSe2 @rGO as Highly Efficient Host and Catalyst for Li-Organosulfide Battery

Organosulfides are promising high-capacity cathode materials for rechargeable lithium batteries. However, sluggish kinetics and inferior utilization impede its practical application in batteries. Rationally designing redox mediators and identifying their active moieties remain formidable challenges. Currently, as a rising star of transition metal dichalcogenides, few-layered MoSe2 decorated reduced graphene oxide (rGO) (MoSe2 @rGO) with high electronic conductivity and narrow energy band is used to manipulate electrocatalytic redox kinetics of organosulfides, thereby enhancing the battery performance. Here, an exotic MoSe2 @rGO is reported with Se defects material obtained from 2D MoSe2 growing on rGO for Li-dipentamethylenethiuram tetrasulfide (Li-PMTT) batteries. MoSe2 @rGO with Se defects has a large specific surface area, and sufficient pores, as well as exce llent catalytic ability for organosulfides conversion reactions. Therefore, the PMTT@MoSe2 @rGO cathode delivers a high reversible capacity of 405 mAh g-1 in the first cycle at 0.5 C and can maintain 238.3 mAh g-1 specific capacity after 300 cycles. This work offers an understanding of organosulfides electrochemistry toward fast and durable performance, holding great promise for developing practically feasible lithium-organosulfides battery material designs.

Electrolyte-Impregnated Mesoporous Hollow Microreactor to Supplement an Inner Reaction Pathway for Boosting the Cyclability of Li-CO2 Batteries

Li-CO2 batteries that integrate energy storage with greenhouse gas fixation have received a great deal of attention in the pursuit of carbon neutrality. However, cyclic accumulation of the insulative and insoluble Li2CO3 on the cathode surface severely restrains the battery cyclability, especially under a high depth of discharge/charge. Herein, we design and fabricate a microreactor-type catalyst by embedding Ru nanoparticles into the shells of mesoporous hollow carbon spheres. We show that both the hollow cavity and mesoporous shell are indispensable for concertedly furnishing a high activity to catalyze reversible Li2CO3 formation/decomposition. This unique structure ensures that the Ru sites masked by exterior Li2CO3 deposits during charging can resume the redox process of discharge by working with the prestored electrolyte to establish an inner reaction path. The thus fabricated Li-CO2 batteries demonstrate remarkable cyclability of 1085 cycles under 0.5 Ah g-1 and 326 cycles under 2 Ah g-1 at 1 A g-1, outshining most of the literature reports. This study highlights a smart catalyst design to boost the reversibility and cyclability of Li-CO2 batteries through an "in & out" strategy.

Synergized Tricomponent All-Inorganics Solid Electrolyte for Highly Stable Solid-State Li-Ion Batteries

Garnet-type oxide Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) features superior ionic conductivity and good stability toward lithium (Li) metal, but requires high-temperature sintering (≈1200 °C) that induces high fabrication cost, poor mechanical processability, and high interface resistance. Here, a novel high-performance tricomponent composite solid electrolyte (CSE) comprising LLZTO-4LiBH4 /xLi3 BN2 H8 is reported, which is prepared by ball milling the LLZTO-4LiBH4  mixture followed by hand milling with Li3 BN2 H8 . Green pellets fabricated by heating the cold-pressed CSE powders at 120 °C offer ultrafast room-temperature ionic conductivity (≈1.73 × 10-3  S cm-1  at 30 °C) and ultrahigh Li-ion transference number (≈0.9999), which enable the Li|Li symmetrical cells to cycle over 1600 h at 30 °C with only 30 mV of overpotential. Moreover, the Li|CSE|TiS2  full cells deliver 201 mAh g-1  of capacity with long cyclability. These outstanding performances are due to the low open porosity in the electrolyte pellets as well as the high intrinsic ionic conductivity and easy deformability of Li3 BN2 H8 .

Anchoring and Catalytic Effects of rGO Supported VS2 Nanosheets Enable High-Performance Li-Organosulfur Battery

As a high-energy-density cathode material, organosulfur has great potential for lithium batteries. However, their practical application is plagued by electronic/ionic insulation and sluggish redox kinetics. Hence, our strategy is to design a self-weaving, freestanding host material by introducing reduced graphene oxide-supported VS₂ nanosheets (VS₂ -rGO) and carbon nanotubes (CNTs) for lithium-phenyl tetrasulfide (Li-PTS) batteries. Unique host materials not only provide physicochemical confinement of active materials to boost the utilization but also catalyze the conversion of active materials to accelerate redox kinetics. Therefore, Li-PTS cell based on the 3D VS₂ -rGO-CNTs (VSGC) host material shows excellent cyclability, with a slow capacity decay rate of 0.08% per cycle over 500 cycles at 0.5 C, and a high areal capacity of 3.1 mAh cm^-2 with the PTS loading of 7.2 mg cm^-2 . More importantly, the potential for practical applications is highlighted by the flexible pouch cell with a high areal capacity (4.1 mAh cm^-2 ) and a low electrolyte/PTS ratio (3.5 µL mg^-1 ). This work sheds light on elevating the electrochemical performance of Li-organosulfur batteries through the effective catalytic and adsorbed host material.

Enhanced Cyclability of LiNi0.6Co0.2Mn0.2O2 Cathodes by Integrating a Spinel Interphase in the Grain Boundary

Nickel-rich layered oxides are promising cathode materials for high-energy-density lithium-ion batteries. Unfortunately, the interfacial instability and intergranular cracks result in fast capacity fading and voltage fading during battery cycling. To address these issues, a coherent spinel interphase in the grain boundary of LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) was successfully constructed via solution infusion and heat treatment. The results showed that the spinel (LiMn₂O₄) interphase could significantly reduce the formation of intergranular cracks during cycling. Meanwhile, the spinel structure on the primary particles effectively suppressed surface degradation, realizing the reduction of interface charge-transfer resistance and electrochemical polarization. As a result, the spinel-modified NCM cathode materials display superior electrochemical cyclability. The 1 wt % spinel phase-modified NCM delivers a discharge capacity of 154.1 mAh g^-1 after 300 cycles (1 C, 3-4.3 V) with an excellent capacity retention of 93%.

Walking and cycling for health: A multi-group analysis of path models between genders

AIMS

Walking and cycling are beneficial for urban adults' health. Transport and recreation are modifiable domains of major physical activity resources. The purposes of this study were to explore associations among psychological and environmental factors, walking and cycling behaviours and quality of life by developing a path model and comparing gender differences.

DESIGN

A cross-sectional study.

METHODS

Participants were community-dwelling healthy urban adults aged 20-65 years. Data were collected between September 2019 and June 2020 by self-reported questionnaires, including health beliefs, the neighbourhood environment, walking and cycling behaviours and the World Health Organization Quality-of-Life Scale. An ANCOVA, chi-squared tests, partial least squares-path model and a multi-group analysis were performed for statistical analyses.

RESULTS

In total, 1294 valid responses were received, which included 41.27% men and 58.73% women. Men had lower walking behaviours and better self-efficacy than women. The developed path model indicated an acceptable model fit. Significant path coefficients were found among psychological and environmental factors, walking and cycling behaviours and quality of life. The path model between men and women found no significant differences in any path coefficients. Significant path coefficients of environmental factors with cycling behaviour and of walking behaviour with quality of life were found in men but not in women.

CONCLUSION

Improving individuals' health beliefs, self-efficacy and perceived walkability and cyclability is a beneficial strategy for promoting physical activity. Walking and cycling behaviours are recommended to improve the quality of life of urban adult populations.

IMPACTS

What problem did the study address? A large proportion of urban adult populations still have insufficient physical activity globally. It is essential that implications from an overall perspective of psychological and environmental factors and their interactions be integrated to develop efficient strategies for promoting physical activity and quality of life. What were the main findings? The developed path model with an acceptable model fit found that psychological and environmental factors were important in explaining urban adults' walking and cycling behaviours and quality of life. Differences were not found between men's and women's path models. Where and on whom will the research have impact? Improving urban adults' psychological and environmental factors might be an efficient strategy for promoting sufficient physical activity. Men's low engagement in walking behaviours should garner increased attention. Providing equal opportunities for both genders to engage in walking and cycling behaviours are recommended for health promotion in urban regions.

Carbon Uniformly Distributed SiOx/C Composite with Excellent Structure Stability for High Performance Lithium-Ion Batteries

Silicon oxides (SiOx, 0<x<2) has been considered as one of the most promising candidate materials for high specific energy anode materials and attracted extensive attention. However, there are still some shortcomings within SiOx that extremely limit its promotion in industry, especially the large volume expansion and poor conductivity. Reasonable design of silicon oxides (SiOx) electrode material is very important to improve its energy storage performance. Here, we fabricated a novel porous SiOx/C nanohybrids based on the facile sol-gel method followed by pyrolysis, in which carbon and SiOx not only exhibited uniform distribution at the nanoscale, the stability of SiOx/C network can also be easily adjusted via controlling the hydrolysis and condensation rate of precursors in situ. Thanks to the excellent electrical conductivity and structural stability of carbon, uniform distribution of SiOx and carbon at the nanoscale, as well as the porous structure. The SiOx/C(50) electrode, with the most appropriate carbon content, delivered a high lithium storage capacity and excellent cyclability. Specifically, a reversible capacity of 808 mA h g^-1 can be achieved at 100 mA g^-1 , retaining 666 mA h g^-1 after 100 cycles. And the reversible capacity still retained ∼550 mAh g^-1 after 1200 cycles at a current density of 0.5 A g^-1 .

Enhanced Performance of ΔTad upon Frequent Alternating Magnetic Fields in FeRh Alloys by Introducing Second Phases

The cyclability and frequency dependence of the adiabatic temperature change (ΔT_ad) under an alternating magnetic field (AMF) are significantly important from the viewpoint of refrigeration application. Our studies demonstrated, by direct measurements, that the cyclability and low-magnetic-field performance of ΔT_ad in FeRh alloys can be largely enhanced by introducing second phases. The ΔT_ad under a 1.8 T, 0.13 Hz AMF is reduced by 14%, which is much better than that (40-50%) of monophase FeRh previously reported. More importantly, the introduction of second phases enables the antiferromagnetic-ferromagnetic phase transition to be driven by a lower magnetic field. Thus, ΔT_ad is significantly enhanced under a 0.62 T, 1 Hz AMF, and its value is 70% larger than that of monophase FeRh previously reported. Although frequency dependence of ΔT_ad occurs, the specific cooling power largely increases by 11 times from 0.17 to 1.9 W/g, as the frequency increases from 1 to 18.4 Hz under an AMF of 0.62 T. Our analysis of the phase transition dynamics based on magnetic relaxation measurements indicates that the activation energy barrier is lowered owing to the existence of second phases in FeRh alloys, which should be responsible for the reduction of the driving field. This work provides an effective way to enhance the cyclability and low-magnetic-field performance of ΔT_ad under an AMF in FeRh alloys by introducing second phases.

Electrochemical Performance of Na3V2(PO4)2F3 Electrode Material in a Symmetric Cell

A NASICON-based Na3V2(PO4)2F3 (NVPF) cathode material is reported herein as a potential symmetric cell electrode material. The symmetric cell was active from 0 to 3.5 V and showed a capacity of 85 mAh/g at 0.1 C. With cycling, the NVPF symmetric cell showed a very long and stable cycle life, having a capacity retention of 61% after 1000 cycles at 1 C. The diffusion coefficient calculated from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT) was found to be ~10-9-10-11, suggesting a smooth diffusion of Na+ in the NVPF symmetric cell. The electrochemical impedance spectroscopy (EIS) carried out during cycling showed increases in bulk resistance, solid electrolyte interphase (SEI) resistance, and charge transfer resistance with the number of cycles, explaining the origin of capacity fade in the NVPF symmetric cell. Finally, the postmortem analysis of the symmetric cell after 1000 cycles at a 1 C rate indicated that the intercalation/de-intercalation of sodium into/from the host structure occurred without any major structural destabilization in both the cathode and anode. However, there was slight distortion in the cathode structure observed, which resulted in capacity loss of the symmetric cell. The promising electrochemical performance of NVPF in the symmetric cell makes it attractive for developing long-life and cost-effective batteries.

Solid-State Double-Network Hydrogel Redox Electrolytes for High-Performance Flexible Supercapacitors

Flexible supercapacitors have great potential applications in wearable and portable electronics, but their practical applications were limited due to the low energy density and mechanical flexibility of solid-state electrolytes used for the construction of flexible supercapacitors. In this study, we first report the solid-state double-network (DN) hydrogel electrolytes (HEs) incorporated with Na₂MoO₄ redox additives. It is found that the solid-state DN HEs with Na₂MoO₄ redox additives exhibit high electrochemical performance, excellent mechanical properties, and fast self-recovery features. We then demonstrate novel symmetric supercapacitors (SSCs) incorporated with the solid-state Na₂MoO₄ DN HEs and the active carbon cloths as the electrodes. The SSCs exhibit a specific capacitance of 84 mF/cm² at a current density of 1 mA/cm² and an energy density of 70 μWh/cm² at a power density of 3800 μWh/cm². Moreover, the SSCs retain approximately 80% capacitance retention after 7000 charge/discharge cycles, which indicates that the SSCs possess excellent flexibility and stability. All of these results demonstrate that the SSCs incorporated with the solid-state Na₂MoO₄ DN HEs as energy-storage devices have great practical applications in wearable and portable electronics.

Identifying the Association between Surface Heterogeneity and Electrochemical Properties in Graphite

Graphite materials for commercial Li-ion batteries usually undergo special treatment to control specific parameters such as particle size, shape, and surface area to have desirable electrochemical properties. Graphite surfaces can be classified into basal and edge planes in the aspect of the structure of carbons, with the existing defect sites such as functional groups and dislocations. The solid-electrolyte interphase (SEI) mostly forms at the edge plane and defect sites, as Li-ions only intercalate through these non-basal planes, whereas the electrochemical properties of graphite largely depend on its surface heterogeneity due to the difference of reactivity on each plane. In order to quantify the detailed surface structure of graphite materials, local-absorption isotherms were utilized, and the analyzed nanostructural parameters of various commercial graphite samples were correlated with the electrochemical properties of each graphite anode. Thereby, we have confirmed that the fraction of non-basal plane and fast-charging capability has strong linear relations. The pore/non-basal sites are also related to the cycle life by affecting the SEI formation, and the determination of surface heterogeneity and pores of graphite materials can provide powerful parameters that imply the electrochemical performances of commercial graphite.

Study of Anion Exchange Membrane Properties Incorporating N-spirocyclic Quaternary Ammonium Cations and Aqueous Organic Redox Flow Battery Performance

Flexible cross-linked anion exchange membranes (AEMs) based on poly (p-phenylene oxide) grafted with N-spirocyclic quaternary ammonium cations were synthesized via UV-induced free-radical polymerization by using diallylpiperidinium chloride as an ionic monomer. Five membranes with ion exchange capacity (IEC) varying between 1.5 to 2.8 mmol Cl-·g-1 polymer were obtained and the correlation between IEC, water uptake, state of water in the membrane and ionic conductivity was studied. In the second part of this study, the influence of properties of four of these membranes on cell cycling stability and performance was investigated in an aqueous organic redox flow battery (AORFB) employing dimethyl viologen (MV) and N,N,N-2,2,6,6-heptamethylpiperidinyl oxy-4-ammonium chloride (TMA-TEMPO). The influence of membrane properties on cell cycling stability and performance was studied. At low-current density (20 mA·cm-2), the best capacity retention was obtained with lower IEC membranes for which the water uptake, freezable water and TMA-TEMPO and MV crossover are low. However, at a high current density (80 mA·cm-2), membrane resistance plays an important role and a membrane with moderate IEC, more precisely, moderate ion conductivity and water uptake was found to maintain the best overall cell performance. The results in this work contribute to the basic understanding of the relationship between membrane properties and cell performance, providing insights guiding the development of advanced membranes to improve the efficiency and power capability for AORFB systems.

Highly Stable and Recyclable Sequestration of CO2 Using Supported Melamine on Layered-Chain Clay Mineral

A type of highly stable and recyclable clay-based composite was developed for sequestration of CO₂, which was synthesized by loading melamine (MEL) onto attapulgite (ATT) via a wet impregnation method. The synthesized materials were characterized by N₂ adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and transmission electron microscopy (TEM). By means of thermal and acidic treatments more active sites of ATT were exposed, and large surface areas were obtained. The MEL molecules were well combined with those exposed sites, which enhanced stability and cyclability for CO₂ sequestration. On the basis of CO₂ adsorption-desorption measurements, the composite of ATT-MEL was found to have a higher CO₂ adsorption capacity (4.91 cm³/g) which was much higher than that of CO₂ absorption on bare MEL (1.30 cm³/g) at 30 °C. After ten cycles of reusing, the composite exhibited even higher capacity for CO₂ adsorption by an increased percentage of 5.91% (30 °C) and 5.77% (70 °C) compared to the capacity in the first cycle. The reason lies in the strong interaction between melamine and attapulgite matrix which was further confirmed by DFT calculations. The MEL was validated to have advantages over aliphatic amines (TEPA) in modifying ATT to get high stability of CO₂-adsorbents.

Understanding Material Compatibility in CO2 Capture Systems Using Molten Alkali Metal Borates

Molten alkali metal borates have been proposed as energy-efficient sorbents for the low-cost capture of CO₂ at high temperatures. The molten sorbents could help to mitigate global warming by capturing CO₂ from industrial sources and preventing the release of CO₂ into the atmosphere. However, these novel materials operate under harsh conditions, introducing challenges of which material compatibility is one of the most important. Other than platinum, where a less than 0.1% change in performance was observed over 1000 h of continuous use, few materials were found to be compatible with the molten salts. Common ceramics, steels, and superalloys were eliminated from consideration due to corrosive oxidation of the substrate and contamination of the melt resulting in chemical degradation and reduction in the sorbent's working capacity. A high-purity nickel alloy, Nickel 200/201, with a protective oxide layer was found to perform optimally with regards to both corrosive degradation and chemical degradation. Modest corrosion rates on the order of 0.3-0.5 mm/year were estimated, and the sorbent capacity was found to drop by between a manageable 0.5 and 20% over 100 h. Various protective measures are proposed, and future work suggested, to ensure that material compatibility does not limit the potential of molten alkali metal borates to reduce CO₂ emissions and contribute to a clean energy future.

Chemomechanical Design Factors for High Performance in Manganese-Based Spinel Cathode Materials for Advanced Sodium-Ion Batteries

Manganese-based spinel cathode materials for sodium-ion batteries (SIBs) are promising candidates for next-generation batteries; especially, Na[Ni_0.5Mn_1.5]O₄ (NNMO) should get attention because of its relatively high operating voltage and firm octahedral host structure. Here, first-principles calculations and the phase field method are used to elucidate the reasons for the low performance of NNMO compared with Li[Ni_0.5Mn_1.5]O₄, and we determine the requirements for realizing high-performance cathode materials for SIBs. Owing to the Ni²⁺/Ni⁴⁺ double redox, NNMO could operate at a high voltage; however, the large Na⁺ increases the local site energy of the redox center, promoting electron extraction from the redox center, leading to unexpected voltage loss. Additionally, the homogeneous free energy confirms that NNMO would undergo phase separation into fully intercalated and deintercalated phases, inducing lattice misfits along the interfaces of the two phases. Particularly, a higher phase transition barrier and large Na⁺ cause fast phase separation, inducing increased polarization and severe stress field upon cycling. The present analysis with comprehensive first-principles calculations and the phase field method provides three critical factors toward high electrochemical performance: (i) strengthening Ni-O bonding to avoid undesirable voltage loss, (ii) increasing the vacancy/Na solubility during (de)sodiation to enhance cyclability, and (iii) suppressing the structural distortion during (de)sodiation to prevent mechanical failure. Based on these crucial points, additionally, we suggest the M-pillared Na_1-xM_x[Ni_0.5Mn_1.5]O₄ (monovalent or divalent species, M), where the M works to strengthen the redox center for improved energy density and to alleviate the drastic structural change and voltage hysteresis for better cyclability, would have superior electrochemical performance as a cathode material for SIBs.

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

To develop ternary transition-metal germanate anodes with superior lithium storage performances for lithium-ion batteries, a novel capacity counterbalance approach in one compound is designed by introducing an electrocatalytic conversion-type component with a positive cycling trend to compensate the negative cycling trend of the GeO₂ component. Novel cobalt germanate hydroxide (CGH) nanoplates chemically bonded on reduced graphene oxide (RGO) sheets are thus synthesized with a mild one-pot hydrothermal approach, constructing maximal face-to-face contact interfaces with interfacial bonds to boost the electrochemical conversion reactions. Furthermore, the hydroxyl groups (Co-OH) of CGH nanoplates are regulated by thermal annealing treatments, thus controlling the capacity contribution resulting from the electrocatalytic conversion reaction of LiOH to exactly offset the capacity fading of GeO₂. The results on the CGH electrodes at different cycling potentials confirm the stepwise electrochemical reactions of Co, GeO₂, and LiOH. The equilibrium of these electrochemical reactions ensures a stable cycling capacity without obvious fluctuations. Consequently, the optimal CGH/RGO hybrid anode delivers a reversible capacity as high as 1136 mA h g^-1 at 0.1 A g^-1 until 100 cycles. It also exhibits a long cyclability with a retained capacity of 560 mA h g^-1 at 1 A g^-1 until 1000 cycles. This work demonstrates a general and efficient capacity counterbalance method to highly boost lithium storage performances in terms of high capacity and long-term cyclability.

Cobalt Hydroxide Carbonate/Reduced Graphene Oxide Anodes Enabled by a Confined Step-by-Step Electrochemical Catalytic Conversion Process for High Lithium Storage Capacity and Excellent Cyclability with a Low Variance Coefficient

Transition metal carbonates/hydroxides have attracted much attention as appealing anode materials due to their considerable reversible electrochemical catalytic conversion capacity. However, their serious positive or negative trends with cycles caused by the electrochemical catalytic conversion seriously affect their practical applications. Herein, novel one-dimensional cobalt hydroxide carbonate (CHC) nanomaterials are tightly anchored on reduced graphene oxide (RGO) sheets via a facile one-pot hydrothermal synthesis, forming surface-confined domains to further restrict the electrochemical catalytic conversion process. The analysis on the cycled electrodes at varied potentials confirms that the added capacity of CHC arises from the step-by-step reversible reactions of Li₂CO₃ and LiOH under the electrochemical catalysis of Co metal generated by the conversion reaction of CHC. The reversible reaction of Li₂CO₃ is followed closely by that of LiOH in the discharge process, while the order is opposite in the charge process. Such a step-by-step electrochemical catalytic conversion process could confine each other to accommodate the volume change and avoid side reactions. The confined effect is further enhanced by limiting the width and length of the CHC, which are determined by regulating the nucleation and growth of CHC on the surface of RGO, leading to an extraordinary cyclability. The optimized CHC/RGO hybrid maintains a high reversible capacity of 1110 mA h g^-1 after 100 cycles at 0.1 A g^-1, which is much higher than the theoretical value of CHC (506 mA h g^-1) on the basis of the recognized conversion reaction. Furthermore, it keeps high reversible capacities of 755 and 506 mA h g^-1 after 200 cycles at 1 and 2 A g^-1, respectively, exhibiting a high-rate cyclability with the lowest coefficient of variance of 9.4% among the reported ones. The confined step-by-step electrochemical catalytic conversion process facilitates high lithium storage capacity and satisfactory cyclability with a pretty low variance coefficient.

A Co-Doped MnO2 Catalyst for Li-CO2 Batteries with Low Overpotential and Ultrahigh Cyclability

Li-CO₂ batteries can not only capture CO₂ to solve the greenhouse effect but also serve as next-generation energy storage devices on the merits of economical, environmentally-friendly, and sustainable aspects. However, these batteries are suffering from two main drawbacks: high overpotential and poor cyclability, severely postponing the acceleration of their applications. Herein, a new Co-doped alpha-MnO₂ nanowire catalyst is prepared for rechargeable Li-CO₂ batteries, which exhibits a high capacity (8160 mA h g^-1 at a current density of 100 mA g^-1 ), a low overpotential (≈0.73 V), and an ultrahigh cyclability (over 500 cycles at a current density of 100 mA g^-1 ), exceeding those of Li-CO₂ batteries reported so far. The reaction mechanisms are interpreted depending on in situ experimental observations in combination with density functional theory calculations. The outstanding electrochemical properties are mostly associated with a high conductivity, a large fraction of hierarchical channels, and a unique Co interstitial doping, which might be of benefit for the diffusion of CO₂ , the reversibility of Li₂ CO₃ products, and the prohibition of side reactions between electrolyte and electrode. These results shed light on both CO₂ fixation and new Li-CO₂ batteries for energy storage.

SnP3/Carbon Nanocomposite as an Anode Material for Potassium-Ion Batteries

New anode materials with large capacity and long cyclability for next-generation potassium-ion batteries (PIBs) are required. PIBs are in the initial stage of investigation and only a few anode materials have been explored. In this study, for the first time, an SnP₃/C nanocomposite with superior cyclability and rate performance was evaluated as an anode for PIBs. The SnP₃/C nanocomposite was synthesized by a facile and cost-effective high-energy ball-milling technique. The SnP₃/C electrode delivered a first reversible capacity of 410 mAh g^-1 and maintained 408 mAh g^-1 after 50 cycles at a specific current of 50 mA g^-1. After 80 cycles at a high specific current of 500 mA g^-1, a high capacity of 225 mAh g^-1 remained. From a crystallographic analysis, it was suggested that the SnP₃/C nanocomposite underwent a sequential and reversible conversion and alloying reactions. The excellent cycling stability and rate capability of the SnP₃/C electrode were attributed to the nanosized SnP₃ particles and carbon buffer layer, which supplied channels for the migration of K-ions and mitigated the stress induced by a large volume change during potassiation/depotassiation. In addition, a full cell composed of the SnP₃/C nanocomposite anode and potassium Prussian blue cathode exhibited a reversible capacity of 305 mAh g^-1 at a specific current of 30 mA g^-1 and retained 71.7% of the original capacity after 30 cycles. These results are important for understanding the electrochemical process of the SnP₃/C nanocomposite and using the SnP₃/C as an anode for PIBs.

Enhancement of Ultrahigh Rate Chargeability by Interfacial Nanodot BaTiO3 Treatment on LiCoO2 Cathode Thin Film Batteries

Nanodot BaTiO₃ supported LiCoO₂ cathode thin films can dramatically improve high-rate chargeability and cyclability. The prepared BaTiO₃ nanodot is <3 nm in height and 35 nm in diameter, and its coverage is <5%. Supported by high dielectric constant materials on the surface of cathode materials, Li ion (Li⁺) can intercalate through robust Li paths around the triple-phase interface consisting of the dielectric, cathode, and electrolyte. The current concentration around the triple-phase interface is observed by the finite element method and is in good agreement with the experimental data. The interfacial resistance between the cathode and electrolyte with nanodot BaTiO₃ is smaller than that without nanodot BaTiO₃. The decomposition of the organic solvent electrolyte can prevent the fabrication of a solid electrolyte interface around the triple-phase interface. Li⁺ paths may be created at non solid electrolyte interface covered regions by the strong current concentration originating from high dielectric constant materials on the cathode. Robust Li⁺ paths lead to excellent chargeability and cyclability.

Rational Design of Statically and Dynamically Stable Lithium-Sulfur Batteries with High Sulfur Loading and Low Electrolyte/Sulfur Ratio

The primary challenge with lithium-sulfur battery research is the design of sulfur cathodes that exhibit high electrochemical efficiency and stability while keeping the sulfur content and loading high and the electrolyte/sulfur ratio low. With a systematic investigation, a novel graphene/cotton-carbon cathode is presented here that enables sulfur loading and content as high as 46 mg cm^-2 and 70 wt% with an electrolyte/sulfur ratio of as low as only 5. The graphene/cotton-carbon cathodes deliver peak capacities of 926 and 765 mA h g^-1 , respectively, at C/10 and C/5 rates, which translate into high areal, gravimetric, and volumetric capacities of, respectively, 43 and 35 mA h cm^-2 , 648 and 536 mA h g^-1 , and 1067 and 881 mA h cm^-3 with a stable cyclability. They also exhibit superior cell-storage capability with 95% capacity-retention, a low self-discharge constant of just 0.0012 per day, and stable poststorage cyclability after storing over a long period of six months. This work demonstrates a viable approach to develop lithium-sulfur batteries with practical energy densities exceeding that of lithium-ion batteries.

Facile Synthesis of Si@SiC Composite as an Anode Material for Lithium-Ion Batteries

Here, we propose a simple method for direct synthesis of a Si@SiC composite derived from a SiO₂@C precursor via a Mg thermal reduction method as an anode material for Li-ion batteries. Owing to the extremely high exothermic reaction between SiO₂ and Mg, along with the presence of carbon, SiC can be spontaneously produced with the formation of Si. The synthesized Si@SiC was composed of well-mixed SiC and Si nanocrystallites. The SiC content of the Si@SiC was adjusted by tuning the carbon content of the precursor. Among the resultant Si@SiC materials, the Si@SiC-0.5 sample, which was produced from a precursor containing 4.37 wt % of carbon, exhibits excellent electrochemical characteristics, such as a high first discharge capacity of 1642 mAh g^-1 and 53.9% capacity retention following 200 cycles at a rate of 0.1C. Even at a high rate of 10C, a high reversible capacity of 454 mAh g^-1 was obtained. Surprisingly, at a fixed discharge rate of C/20, the Si@SiC-0.5 electrode delivered a high capacity of 989 mAh g^-1 at a charge rate of 20C. In addition, a full cell fabricated by coupling a lithiated Si@SiC-0.5 anode and a LiCoO₂ cathode exhibits excellent cyclability over 50 cycles. This outstanding electrochemical performance of Si@SiC-0.5 is attributed to the SiC phase, which acts as a buffer layer that stabilizes the nanostructure of the Si active phase and enhances the electrical conductivity of the electrode.

Novel Co2 VO4 Anodes Using Ultralight 3D Metallic Current Collector and Carbon Sandwiched Structures for High-Performance Li-Ion Batteries

A novel spinel Co₂ VO₄ is studied as the Li-ion battery anode material and it is sandwiched with a 3D ultralight porous current collector (PCC) and amorphous carbon. Co₂ VO₄ demonstrates the high capacity and excellent cyclability because of the mixed lithium storage mechanisms. The 3D composite structure requires no binders and replaces the conventional current collector (Cu foil) with a 3D ultralight porous metal scaffold, yielding the high electrode-based capacity. Such a novel composite anode also enables the close adhesion of Co₂ VO₄ to the PCC scaffold. The resulting monolithic electrode has the rapid electron pathway and stable mechanical properties, which lead to the excellent rate capabilities and cycling properties. At a current density of 1 A g^-1 , the PCC and carbon sandwiched Co₂ VO₄ anode is able to deliver a stable reversible capacity of about 706.8 mAh g^-1 after 1000 cycles. Generally, this study not only develops a new Co₂ VO₄ anode with high capacity and good cyclability, but also demonstrates an alternative approach to improve the electrochemical properties of high capacity anode materials by using ultralight porous metallic current collector instead of heavy copper foil.

Designed Formulation of Se-Impregnated N-Containing Hollow Core Mesoporous Shell Carbon Spheres: Multifunctional Potential Cathode for Li-Se and Na-Se Batteries

Nitrogen-containing carbon spheres with hollow core and mesoporous shell (NHCS), capable of confining Se at levels as high as 72 wt % has been demonstrated to exhibit appreciable electrochemical behavior with 52 and 61 wt % Se loading. In particular, 52 wt % Se confined NHCS cathode exhibits 265 mAh/g at 10C rate and retains 75% of initial capacity at 2C rate up to 10 000 cycles with an insignificant decay of 0.0025% per cycle, which is an ever first report on the extended cycle life of Li-Se batteries. Due to the negligible difference found between the transport kinetics of Se and that of Li₂Se, irrespective of the cycling rate, 52 wt % Se @ NHCS performs better at high rates. Furthermore, capacity is governed by the extent of utilization of confined Se and cycle life by the extent of mitigation of volume expansion. Accordingly, rate capability studies recommend 52 wt % Se loaded cathode above 2C rate and 61 wt % Se loading up to 2C rate. Furthermore, NHCS/Se-52 cathode demonstrates suitability for Na-Se batteries by exhibiting 339 and 219 mAh/g of capacity at rates of C/5 and 2C rates, respectively. NHCS with select Se concentration could thus be exploited for multifunctional cathode behavior in Li-Se and Na-Se systems.

Ultralong Cycle Life Achieved by a Natural Plant: Miscanthus × giganteus for Lithium Oxygen Batteries

Large energy-storage systems and electric vehicles require energy devices with high power and high energy density. Lithium oxygen (Li-O₂) batteries could achieve high energy density, but they are still facing problems such as low practical capacity and poor cyclability. Here, we prepare activated carbons (MGACs) based on the natural plant Miscanthus × giganteus (MG) through slow pyrolysis. It possesses a large surface area, plenty of active sites, and high porosity, which are beneficial to the utilization of oxygen electrode in Li-O₂ batteries. The MGACs-based oxygen electrode delivers a high specific capacity of 9400 mAh/g at 0.02 mA/cm², and long cycle life of 601 cycles (with a cutoff capacity of 500 mAh/g) and 295 cycles (with a cutoff capacity of 1000 mAh/g) at 0.2 mA/cm², respectively. Additionally, the material exhibits high rate capability and high reversibility, which is a promising candidate for the application in Li-O₂ batteries.

Polymer-Templated Formation of Polydopamine-Coated SnO2 Nanocrystals: Anodes for Cyclable Lithium-Ion Batteries

Well-controlled nanostructures and a high fraction of Sn/Li₂ O 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.

A New Route Toward Improved Sodium Ion Batteries: A Multifunctional Fluffy Na0.67FePO4/CNT Nanocactus

To improve the performance of energy storage systems, the rational design of new electrode configurations is a strategic initiative. Here, we present a novel monodisperse fluffy alluaudite Na0.67FePO4, prepared by a modified solvothermal method, as promising electrode for sodium ion battery. This porous Na0.67FePO4 with nanocactus-like morphology is composed by nanorods within an open three-dimensional structure. This unique nanocactus-based morphology offers three important advantages when used as electrode for sodium ion battery: (i) provides an open frame structure for a large Na+ ions transport; (ii) reduces the sodium ion and electron transport path by ≈20 nm; (iii) offers a large surface area for a more efficient interface between the electrode and the electrolyte. The electrochemical investigation revealed that this fluffy Na0.67FePO4 nanocactus exhibits the high discharge capacity of 138 mAh g(-1). Moreover, a battery with a Na0.67FePO4/CNT hybrid electrode delivered a discharge capacity as high as ≈143 mAh g(-1), coupled to an excellent stable cyclability (no obvious capacity fading over 50 cycles at a current rate of 5 mA g(-1)). This enhanced mechanism was studied by means of absorption measurements and ex situ XAFS characterizations. Results of the characterization of the Na0.67FePO4 suggests that the outstanding performance can be associated with the unique fluffy nanocactus morphology.

Embedded into graphene Ge nanoparticles highly dispersed on vertically aligned graphene with excellent electrochemical performance for lithium storage

Decreasing particle size has always been reported to be an efficient way to improve cyclability of Li-alloying based LIBs. However, nanoparticles (NPs) tend to agglomerate and evolve into lumps, which in turn limits the cycling performance. In this report, we prepared a unique nanostructure, graphene-coated Ge NPs are highly dispersed on vertically aligned graphene (Ge@graphene/VAGN), to avoid particle agglomeration and pulverization. Remarkable structure stability of the sample leads to excellent cycling stability. Upon cycling, the anode exhibits a high capacity of 1014 mAh g(-1), with nearly no capacity loss in 90 cycles. Rate performance shows that even at the high current density of 13 A g(-1), the anode could still deliver a higher capacity than that of graphite.

Carbon-, binder-, and precious metal-free cathodes for non-aqueous lithium-oxygen batteries: nanoflake-decorated nanoneedle oxide arrays

Rechargeable lithium-oxygen (Li-O2) batteries have higher theoretical energy densities than today's lithium-ion batteries and are consequently considered to be an attractive energy storage technology to enable long-range electric vehicles. The main constituents comprising a cathode of a lithium-oxygen (Li-O2) battery, such as carbon and binders, suffer from irreversible decomposition, leading to significant performance degradation. Here, carbon- and binder-free cathodes based on nonprecious metal oxides are designed and fabricated for Li-O2 batteries. A novel structure of the oxide-only cathode having a high porosity and a large surface area is proposed that consists of numerous one-dimensional nanoneedle arrays decorated with thin nanoflakes. These oxide-only cathodes with the tailored architecture show high specific capacities and remarkably reduced charge potentials (in comparison with a carbon-only cathode) as well as excellent cyclability (250 cycles).