High Areal Capacity, Long Cycle Life Li-Air Batteries Enabled by Nano/Micro Hierarchical Porous Cathode.

The limited cycle life of Li-air batteries (LABs) with high areal capacity remains the chief challenge that hinders their practical applications. Here, the study proposes a hierarchical porous electrode (HPE) design strategy, in which porous MnO nanoflowers are built into mesopore/macropore electrodes through a combination of chemical dealloying and physical de-templating procedures. The MnO nanoflowers with 10-30 nm pore provides active sites to catalyze the O2 reduction and decomposition of discharged products. The 5-10 µm macroscopic pores in the cathode serve as channels of O2 transportation and facilitate the electrolyte permeation. The proposed HPE exhibits a full discharge capacity of 17.49 mAh cm-2 and stable cycle life >2000 h with a limited capacity of 6 mAh cm-2 . These results suggest that the HPE design strategy for LABs can simultaneously provide large capacity and robust cycle life, which is promising for advanced metal-air batteries.

Asymmetric Swelling Behaviors of High-Energy-Density Lithium-Ion Batteries with a SiOx /Graphite Composite Anode.

The battery swelling originated from the electrode swelling is a big obstacle for the practical application of high-energy-density lithium-ion batteries (HED-LIBs). Herein, the HED-LIBs are constructed by SiOx /graphite composite anode and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathode and their swelling behaviors are investigated at the cell, electrode, and particle scales. there are three expansion stages during the charging while one expansion followed by two contraction stages during the discharging process. The expansion ratio is in direct proportion to the ratio of SiOx content and about 10 times larger than that of the cathode. A 100 nm thick double-layer solid electrolyte interface, comprises LiF, Li2 O, and Li2 CO3 , forms on the surface of the SiOx particles, and evolves into a 300 nm thick triple-layer after cycling. The performance degradation of HED-LIBs is associated with the expansion of anodes, increase in resistance, and consumption of Li in the anodes during cycling. This study is expected to guide the future selection and design of HED-LIBs and battery packs.

CO2 Capture Membrane for Long-Cycle Lithium-Air Battery.

Lithium-air batteries (LABs) have attracted extensive attention due to their ultra-high energy density. At present, most LABs are operated in pure oxygen (O2) since carbon dioxide (CO2) under ambient air will participate in the battery reaction and generate an irreversible by-product of lithium carbonate (Li2CO3), which will seriously affect the performance of the battery. Here, to solve this problem, we propose to prepare a CO2 capture membrane (CCM) by loading activated carbon encapsulated with lithium hydroxide (LiOH@AC) onto activated carbon fiber felt (ACFF). The effect of the LiOH@AC loading amount on ACFF has been carefully investigated, and CCM has an ultra-high CO2 adsorption performance (137 cm3 g-1) and excellent O2 transmission performance by loading 80 wt% LiOH@AC onto ACFF. The optimized CCM is further applied as a paster on the outside of the LAB. As a result, the specific capacity performance of LAB displays a sharp increase from 27,948 to 36,252 mAh g-1, and the cycle time is extended from 220 h to 310 h operating in a 4% CO2 concentration environment. The concept of carbon capture paster opens a simple and direct way for LABs operating in the atmosphere.

Hierarchical Sulfide-Rich Modification Layer on SiO/C Anode for Low-Temperature Li-Ion Batteries.

The silicon oxide/graphite (SiO/C) composite anode represents one of the promising candidates for next generation Li-ion batteries over 400 Wh kg-1 . However, the rapid capacity decay and potential safety risks at low temperature restrict their widely practical applications. Herein, the fabrication of sulfide-rich solid electrolyte interface (SEI) layer on surface of SiO/C anode to boost the reversible Li-storage performance at low temperature is reported. Different from the traditional SEI layer, the present modification layer is composed of inorganic-organic hybrid components with three continuous layers as disclosed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The result shows that ROSO2 Li, ROCO2 Li, and LiF uniformly distribute over different layers. When coupled with LiNi0.8 Co0.1 Mn0.1 O2 cathode, the capacity retention achieves 73% at -20 °C. The first principle calculations demonstrate that the gradient adsorption of sulfide-rich surface layer and traditional intermediate layer can promote the desolvation of Li+ at low temperature. Meanwhile, the inner LiF-rich layer with rapid ionic diffusion capability can inhibit dendrite growth. These results offer new perspective of developing advanced SiO/C anode and low-temperature Li-ion batteries.

Accelerated Hydrogen "Spill-Over" Enhances Anode Performance of Tensile Strained Pd-Based Fuel Cell Electrocatalysts.

Development of efficient electrocatalysts usually relies on half-cell electrochemical tests for rapid material screening, which however are not always consistent with the associated full cell evaluation. This study designs a tensile-strained Pd anode and reveals that with a lower apparent activity toward the hydrogen oxidation reaction as compared to the unstrained one, it exhibits a surprisingly high activity in proton exchange membrane fuel cells (PEMFCs). With an ultralow Pd loading of 4.5 µg cm-2 , the tensile-strained Pd achieves a maximum power density of 1048 mW cm-2 , indicating a 30-fold improvement in power efficiency than that of commercial Pd/C, nearly four times of that of the unstrained one. This discrepancy can be ascribed to the hydrogen-rich surface in the H2 atmosphere of PEMFCs owing to the accelerated hydrogen "spill-over" in the tensile-strained Pd with a standout hydrogen storage property.

Wide-temperature rechargeable Li metal batteries enabled by an in-situ fabricated composite gel electrolyte with a hierarchical structure.

Lithium metal batteries (LMBs) are well recognized as promising next-generation high energy density batteries, but the uncontrollable Li dendrites growth and the volatilization/gas production of electrolytes, which become extremely worse at low and high temperatures, restrict their practical utilizations. In this work, a hierarchically structured polymerized gel electrolyte (HGE), which was composed of an inorganic (LixGa86In14 alloy and LiCl salt)/organic (polymerized tetrahydrofuran (THF)) hybrid layer and the bulk polymerized THF electrolyte, was proposed to achieve a steady performance of LMBs over a wide temperature range of -20-55 °C. The HGE fabrication can be completed within assembled cells with a simultaneously occurring replacement-polymerization-alloying reaction, which helps decrease the interfacial resistance and enhance the stability and ion diffusion under both low and high temperatures. The use of THF with low polarity also ensures high ion conductivity under low temperatures. With such HGE, the Li symmetric cells showed low overpotential under 10 mA/cm2 with a capacity of 10 mAh/cm2 over a 1200 h cycling, and the full cell coupled with Li4Ti5O12 demonstrated high capacity retention over 5000 cycles at room temperature. Besides, the symmetric cells showed low overpotentials of 12 mV at 55 °C and 80 mV at -20 °C at 2 mA/cm2 after a 1000 h cycling, and the full cell revealed the high capacity retention of 93.5% at 55 °C and 88.8% at -20 °C after 1500 cycles under a high current density of 1000 mA/g. This work shows a hierarchically structured polymerized electrolyte design for advanced Li batteries workable under broad temperatures.

Immobilizing Ceramic Electrolyte Particles into a Gel Matrix Formed In Situ for Stable Li-Metal Batteries.

Hybrid solid/gel electrolytes (SGEs) have generated much research attentions because of their capability to suppress Li dendrite growth and improve battery safety. However, the interfacial compatibility of the electrode/electrolyte or polymer/inorganic ceramics within hybrid electrolytes remains challenging for practical applications. Herein, an SGE is fabricated by confining ceramic particles (Li7La3Zr2O12; LLZO) into in situ formed tetraethylene glycol dimethyl ether (G4)-based gel electrolytes within assembled cells. A hierarchical layered structure is formed when LLZO settles near the Li anode within the liquid electrolyte during the gradual gelatinization process. Good interfacial compatibility is obtained from good contact with the liquid G4 component. The LLZO layer also serves as an ionic sieve to redistribute the Li deposition. This SGE endows stable Li stripping/plating cycling over 800 h at 0.5 mA/cm2 (60 °C). Moreover, Li-metal batteries with an SGE coupled with LiFePO4 and an air cathode both exhibit superior cycling performance. This work presents a promising strategy for hierarchically layered SGEs for high-performance Li-metal batteries.

Prevention of Na Corrosion and Dendrite Growth for Long-Life Flexible Na-Air Batteries.

Rechargeable Na-air batteries (NABs) based on abundant Na resources are generating great interest due to their high energy density and low cost. However, Na anode corrosion in ambient air and the growth of abnormal dendrites lead to insufficient cycle performance and safety hazards. Effectively protecting the Na anode from corrosion and inducing the uniform Na plating and stripping are therefore of vital importance for practical application. We herein report a NAB with in situ formed gel electrolyte and Na anode with trace residual Li. The gel electrolyte is obtained within cells through cross-linking Li ethylenediamine at the anode surface with tetraethylene glycol dimethyl ether (G4) from the liquid electrolyte. The gel can effectively prevent H2O and O2 crossover, thus delaying Na anode corrosion and electrolyte decomposition. Na dendrite growth was suppressed by the electrostatic shield effect of Li+ from the modified Li layer. Benefiting from these improvements, the NAB achieves a robust cycle performance over 2000 h in opened ambient air, which is superior to previous results. Gelation of the electrolyte prevents liquid leakage during battery bending, facilitating greater cell flexibility, which could lead to the development of NABs suitable for wearable electronic devices in ambient air.

A Strategy To Prepare High-Quality Monocrystalline Graphene: Inducing Graphene Growth with Seeding Chemical Vapor Deposition and Its Mechanism.

High-quality monocrystalline graphene has gained considerable attention in fundamental physics, materials science, and nanoelectronics. However, the performance of the graphene obtained by chemical synthesis methods is currently significantly restricted by the crystal quality. Herein, a seeding chemical vapor deposition (SCVD) method is designed to cultivate high-quality monocrystalline graphene on a Cu(111) substrate with hexagonal boron nitride (h-BN) as the seed crystal. Combining the experimental and theoretical research, the nucleation behavior of the growth-induced graphene on the h-BN seed crystal is investigated, and the induced growth mechanism on the Cu(111) substrate is studied. The results show that the h-BN seed crystal can dramatically reduce the adsorption energy of active carbon atoms and the energy barrier for C-C aggregation at the BN/Cu(111) step, thus promoting graphene growth around the h-BN seed. Large monocrystalline graphene domains are obtained by the proposed SCVD method. Further study shows that the growth-induced graphene has good crystal quality and could maintain high structural integrity. This new strategy can be applied for growing high-quality graphene and other two-dimensional materials.

A stable tunnel-type NaGe3/2Mn1/2O4 anode for Na-ion batteries.

Tunnel-type NaGe3/2Mn1/2O4 was fabricated for anode of sodium ion batteries, delivering a discharge capacity of 200.32 mAh g-1 and an ultra-low potential platform compared with that of pure Na4Ge9O20 (NGO). The results of X-ray photoelectron spectroscopy (XPS) demonstrate that Ge redox occurs, and partial substitution of Mn effectively improves the Na-storage properties compared to those of NGO.

A "directed precursor self-assembly" strategy for the facile synthesis of heteropoly blues: crystal structures, formation mechanism and electron distribution.

Recent research studies demonstrated that heteropoly blues (reduced polyoxometalates) could act as a special kind of solid material with potential functions in antiviral activity, and photocatalytic, photothermal and semiconducting properties. In this work, we develop a "directed precursor self-assembly" strategy for the facile synthesis of heteropoly blues (HPBs), so four representative HPBs [GeW10MoO40], [GeMoMoO40], [P2W16MoO62] and [P2W12MoMoO62] have been synthesized and structurally characterized. These four heteropoly blue compounds were synthesized by the solution self-assembly reaction of a precursor [MoO4(H2O)2(ox)2]2- with vacant polyoxometalates. Electrospray ionization mass spectrometry (ESI-MS) was used to analyze the assembly mechanism of these HPBs. A detailed study on the magnetic properties was also carried out, which shows that the number of MoV and their locations are capable of adjusting the electron distribution in HPBs.

Unveiling the structural evolution of 1T SnS2 anode upon lithiation/delithiation by TEM.

Herein, the definite structure-dependent evolution process upon lithiation/delithiation and clear atomic images of pure 1T-phase SnS2 were obtained for the first time, illustrating the different insertion-conversion-desertion processes of discharge/charge plateaus. Also, 1T SnS2 exhibited advantages over commercial SnS2 (mixed with 1T and 1H phases) in cell resistance and lithium-storage performance.

Temperature-Dependent Li Storage Performance in Nanoporous Cu-Ge-Al Alloy.

The performance fading process and safety concerns of lithium ion batteries at low temperature (LT) prohibit their application in cold climates. The alloy-type electrodes demonstrate great potentials in stable and dendrite-free anodes at LT. Herein, we report a temperature-dependent Li storage performance in Al-based nanoporous alloy anode. The nanoporous-structured Cu-Ge-Al ternary alloys (NP-CuGeAl) have been designed and prepared by selectively etching Al out. The high-Al-content NP-CuGeAl (acid etching for 6 h, named CGA-6) is composed of multi-intermetallic compounds (denoted as M xN y, M, N = Cu, Al, Ge) with bimodal porous architectures. Investigated as anode at room temperature, the CGA-6 delivers a capacity as high as 479.7 mAh g-1 at 0.5 A g-1 of over 1020 cycles, and the low-Al-content ones show improved LT electrochemical performance. At -20 °C, the CGA-48 (acid etching for 48 h) shows much better performance as compared with the CGA-6. In Situ transmission electron microscopy and ex situ characterizations confirm that the M xN y/Li zM xN y couples are highly reversible and the porous structure is durable upon battery cycling.

Spider-Web-Inspired Nanocomposite-Modified Separator: Structural and Chemical Cooperativity Inhibiting the Shuttle Effect in Li-S Batteries.

Despite their high theoretical capacity density (1675 mAh g-1), the application of Li-S batteries has been seriously hindered by the shuttle effect of polysulfides. Here, inspired by the working principle of natural spider webs, we synthesized a spider-web-like nanocomposite in which many hollow mesoporous silica (mSiO2) nanospheres/Co nanoparticles were threaded by interconnected nitrogen-doped carbon nanotubes (NCNTs). Then the nanocomposite (denoted as Co/mSiO2-NCNTs) was coated on the commercial separator by a simple infiltration to mitigate the above issue. The intimate combination of three-dimensional conductive networks (NCNTs) with abundant polysulfide adsorbent sites (SiO2 and N)/polysulfide conversion catalysts (Co and Co-N x species) allows the Co/mSiO2-NCNTs coating layer to not only effectively capture polysulfides via both physical confinement and chemical bonding but also accelerate the redox kinetics of polysulfides significantly. Furthermore, the combination of ex situ experiment and theoretical calculation demonstrates that the reversible adsorption/desorption of polysulfides on mSiO2 nanospheres benefits uniform deposition of Li2S2/Li2S on the conductive networks, which contributes to long-term cycling stability. As a result, Li-S batteries with Co/mSiO2-NCNTs-coated separators exhibited both excellent cycling stability and rate performance.

Induced growth of quasi-free-standing graphene on SiC substrates.

Free-standing graphene grown on SiC substrates is desirable for micro- and nano-electronic device applications. In this work, an induced growth method to fabricate quasi-free-standing graphene on SiC was proposed, where graphene nucleation sites were generated on the SiC substrate and active carbon sources were subsequently introduced to grow graphene centered along the established nucleation sites. The structure and morphology of the cultivated graphene were characterized by using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). Compared to the traditional epitaxial growth methods on SiC substrates, this approach shows a significant reduction of the buffer layer. This study provides an efficient method for growing quasi-free-standing graphene on SiC substrates and is believed to be able to broaden the application of graphene in electronic devices as SiC is an intrinsically outstanding wide bandgap semiconductor.

Graphene Nucleation Preference at CuO Defects Rather Than Cu2O on Cu(111): A Combination of DFT Calculation and Experiment.

It is well-known that reducing the nucleation density is an effective way to enhance the growth quality of graphene. In this work, we explore the mechanism of graphene nucleation and growth around CuO defects on a Cu(111) substrate by using density functional theory combined with the nudged elastic band method. The defect formation mechanism at the initial nucleation stage is also studied. Our calculation results of the C adsorption energy and the reaction barrier of C-C dimer formation illustrate that the initial nucleation of graphene could be promoted by artificially introducing CuO defects on a Cu(111) surface and the nucleation on the clean Cu(111) substrate could thus be suppressed. These conclusions have been verified by graphene growth experiments using a chemical vapor deposition method. Further studies showed that graphene grown around CuO "seed crystals" could maintain its structural integrity without significantly producing defective carbon rings. This work provides a fundamental understanding and theoretical guidance for the controllable preparation of large-dimension and high-quality graphene by artificially introducing CuO seeds.

Flexible Lithium-Air Battery in Ambient Air with an In†Situ Formed Gel Electrolyte.

Flexible Li-air batteries (LABs) have been considered as promising power sources for wearable electronics owing to its higher energy density. However, when operated in ambient air, problems arise, such as Li anode passivation, poor cycle life as well as leakage of liquid electrolyte. Herein, we present a LAB with a tetraethylene glycol dimethyl ether (TEGDME, G4) gel electrolyte, in which the gel is formed in situ through a cross-linking reaction between the liquid G4 and the lithium ethylenediamine (LiEDA) grown on the surface of Li anode. We demonstrate that the gel can efficiently alleviate the corrosion of the Li anode, and thus the LAB shows a cycle performance over 1175 hours (humidity: 10 % to 40 %), which is much superior to previous reports. Furthermore, the in situ formed gel enhances the electrode/electrolyte interfacial contact, which thus enables the cable-type LAB to exhibit a great flexibility.

Rechargeable Al-CO2 Batteries for Reversible Utilization of CO2.

The excessive emission of CO2 and the energy crisis are two major issues facing humanity. Thus, the electrochemical reduction of CO2 and its utilization in metal-CO2 batteries have attracted wide attention because the batteries can simultaneously accelerate CO2 fixation/utilization and energy storage/release. Here, rechargeable Al-CO2 batteries are proposed and realized, which use chemically stable Al as the anode. The batteries display small discharge/charge voltage gaps down to 0.091 V and high energy efficiencies up to 87.7%, indicating an efficient battery performance. Their chemical reaction mechanism to produce the performance is revealed to be 4Al + 9CO2 ↔ 2Al2 (CO3 )3 + 3C, by which CO2 is reversibly utilized. These batteries are envisaged to effectively and safely serve as a potential CO2 fixation/utilization strategy with stable Al.

Yucca fern shaped CuO nanowires on Cu foam for remitting capacity fading of Li-ion battery anodes.

To remit capacity fading of lithium ion battery (LIB) anodes, freestanding yucca fern shaped CuO nanowires (NWs) on Cu foams are fabricated as anodes by combining facile and scalable anodization of copper foams followed by calcination. The porous and radial configuration of the hierarchical CuO NWs on the Cu foam substrate guarantees the remarkably improved electrochemical performance with durable cycle stability and excellent rate capability compared with CuO NWs on Cu foils. The reversible capacity remains 461.5 mAh/g after 100 repeated cycles at a current density of 100 mA/g, and a capacity of 150.6 mAh/g even at a high rate of 1000 mA/g. By examining the surface morphology of the cycled samples, possible performance fading route is proposed. The 3D CuO NWs network with a porous architecture simutaneously reduces the ion diffusion distances, promotes the electrolyte permeation and electronic conductivity. This novel strategy might open a new window to develop durable CuO based composite anodes for LIBs.

Synergetic enhancement of the electronic/ionic conductivity of a Li-ion battery by fabrication of a carbon-coated nanoporous SnOxSb alloy anode.

The major obstacles which prohibit the practical applications of alloy-type anodes include insufficient ionic/electronic transportations and structural failures. Herein, we report the fabrication of a carbon-coated nanoporous SnSb alloy (NP-SnOxSb@C) and its application as an anode in Li-ion batteries (LIBs). The as-fabricated NP-SnOxSb@C is characterized by SEM and TEM and demonstrates a bi-continuous nanoporous structure. Amorphous carbon is found to be uniformly coated on the alloy surface. When used as an anode for LIB, NP-SnOxSb@C displays a high capacity (850 mA h g-1 after the 50th cycle) and good rate performance of 664 mA h g-1 at 2000 mA g-1. The improved electrochemical performance is mainly due to a high Li+ diffusion coefficient and low charge transfer resistance between the nanoporous structure and conductive carbon layer. The facile material fabrication process and good electrochemical performance enable the practical utilization of this anode for high-performance LIBs.