Understory fuel loads and the impact factors of Quercus mongolica natural secondary forest in Hebei Pro-vince, China.

We investigated understory fuel loads of Quercus mongolica natural secondary forests in Hebei Province, China. We analyzed the effects of stand factors, topographic factors, and ground cover factors on the quantity and composition of fuel, established the dynamic models of understory fuel loads, and proposed management measures. The results showed that the understory total fuel load in Q. mongolica natural secondary forests was 11.68 t·hm-2, which exceeded the forest fire potential threshold (10 t·hm-2). The understory dead fuel load was mainly humus, and the understory living fuel load was mainly shrubs. The 1 h time-lag fuel load increased significantly with increasing canopy density, stand density, stand age, and litter thickness. The 10 h time-lag fuel load increased signi-ficantly with increasing stand density, average tree height, and litter thickness. Humus load decreased significantly with increasing altitude and increased significantly with increasing humus thickness. Herb load increased significantly with increasing sunny slope orientation and herbal coverage. Shrub load increased significantly with increasing slope degree, shrub coverage, and humus thickness. Understory total fuel load decreased significantly with increasing altitude, and increased significantly with increasing stand density, humus thickness, and litter thickness. The results of stepwise regression analysis indicated that stand density, humus thickness, and altitude could better predict the understory total fuel load (Radj2=0.775). Therefore, more attention should be paid on the control of stand density of Q. mongolica natural secondary forest in Hebei Province. Cleaning of litters and humus on the ground would help prevent forest fires scientifically and effectively.

On-site building of a Zn2+-conductive interfacial layer via short-circuit energization for stable Zn anode.

Aqueous zinc ion batteries (ZIBs) show great potential in large-scale energy storage systems for their advantages of high safety, low cost, high capacity, and environmental friendliness. However, the poor performance of Zn metal anode seriously hinders the application of ZIBs. Herein, we use the zinc-ion intercalatable V2O5·nH2O (VO) as the interface modification material, for the first time, to on-site build a Zn2+-conductive ZnxV2O5·nH2O (ZnVO) interfacial layer via the spontaneous short-circuit reaction between the pre-fabricated VO film and Zn metal foil. Compared with the bare Zn, the ZnVO-coated Zn anode exhibits better electrochemical performances with dendrite-free Zn deposits, lower polarization, higher coulombic efficiency over 99% after long cycles and 10 times higher cycle life, which is confirmed by constructing Zn symmetrical cell and Zn|ZnSO4 + Li2SO4|LiFePO4 full cell.

Shaping Li Deposits from Wild Dendrites to Regular Crystals via the Ferroelectric Effect.

Manipulating the Li plating behavior remains a challenging task toward Li-based high-energy batteries. Generally, the Li plating process is kinetically controlled by ion transport, concentration gradient, local electric field, etc. A myriad of strategies have been developed for homogenizing the kinetics; however, such kinetics-controlled Li plating nature is barely changed. Herein, a ferroelectric substrate comprised of homogeneously distributed BaTiO3 was deployed and the Li plating behavior was transferred from a kinetic-controlled to a thermodynamic-preferred mode via ferroelectric effect. Such Li deposits with uniform hexagonal and cubic shapes are highly in accord with the thermodynamic principle where the body-centered cubic Li is apt to expose more (110) facets as possible to maximally minimize its surface energy. The mechanism was later confirmed due to the spontaneous polarization of BTO particles trigged by an applied electric field. The instantly generated reverse polarized field and charged ends not only neutralized the electric field but also leveled the ion distribution at the interface.

In Situ Formed LiZn Alloy Skeleton for Stable Lithium Anodes.

Lithium metal is the most promising anode for developing high-energy density rechargeable batteries because of its ultrahigh theoretical capacity and extremely low reduction potential. However, the formation of dendritic lithium and the huge volume change of the anode during the charge/discharge process severely hinder the practical application of the lithium anode. Obtaining high-performance, simple methods that can simultaneously modify the interface and restrict the volume change of the Li anode are highly required. Herein, the lithiophilic Zn nanoparticles are introduced into molten lithium directly to obtain a composite anode filled with in situ formed LiZn alloy rods. These micrometer-sized alloy rods can serve as a skeleton to provide a large number of lithium deposition sites as well as volume suppression for lithium deposition. Benefiting from these two aspects, the composite anode exhibits superior electrochemical performance by means of lowering the overpotential and prolonging the cycle life of symmetrical cells. Furthermore, the full cell paired with this composite anode and LiFePO4 cathode also demonstrates a better capacity retention than its counterpart with raw Li anode.

Level the Conversion/Alloying Voltage Gap by Grafting the Endogenetic Sb2Te3 Building Block into Layered GeTe to Build Ge2Sb2Te5 for Li-Ion Batteries.

Many research efforts for advanced Li-ion batteries have been made to design new material with large capacity and long cycle life, but little attention has been paid to regulate the voltage platform until now. Although quite attractive for the binary Ge-based chalcogenides, challenge is that a large potential gap as well as incongruous reaction kinetics is typically found between their conversion step (>1.6 V) and alloying region (<0.4 V). Herein, we propose an endogenetic structural design by grafting Sb2Te3 building block into layered GeTe to establish a ternary Ge2Sb2Te5 compound, which can effectively level such a big potential gap. Turning from semiconductive GeTe into metallic conductive Ge2Sb2Te5, the reaction kinetics can be enhanced. The LixTe formation step in Ge2Sb2Te5 is found declined to 1.30 V, and the enlistment of Sb (∼0.78 V) bridges the conversion and alloying plateau; thus, the incongruous reaction kinetics and large potential gap between the conversion-alloying step can be alleviated. Furthermore, there is a spatially confined and synergistic effect among Te, Sb, and Ge components, conducting the LixTe and LixGe processes in a more harmonious and gentle way. Therefore, Ge2Sb2Te5 exhibites much enhanced cyclability and rate performance, with 546 mAh/g remained at 2000 mA/g. This unique design strategy can be leveraged to manipulate the voltage profile of other compounds.

Investigation of the temperature-dependent behaviours of Li metal anode.

Effects of temperature on Li nucleation/deposition behaviours and electrochemical performances are thoroughly investigated. Higher temperature leads to lower nucleation density with larger deposit sizes due to the reduced surface migration barrier and accelerated ion diffusion, plus better lifespans and coulombic efficiency owing to the relatively conducive morphology characteristics and a favorable SEI layer.

An Autotransferable g-C3 N4 Li+ -Modulating Layer toward Stable Lithium Anodes.

Commercial deployment of lithium anodes has been severely impeded by the poor battery safety, unsatisfying cycling lifespan, and efficiency. Recently, building artificial interfacial layers over a lithium anode was regarded as an effective strategy to stabilize the electrode. However, the fabrications reported so far have mostly been conducted directly upon lithium foil, often requiring stringent reaction conditions with indispensable inert environment protection and highly specialized reagents due to the high reactivity of metallic lithium. Besides, the uneven lithium-ion flux across the lithium surface should be more powerfully tailored via mighty interfacial layer materials. Herein, g-C3 N4 is employed as a Li+ -modulating material and a brand-new autotransferable strategy to fabricate this interfacial layer for Li anodes without any inert atmosphere protection and limitation of chemical regents is developed. The g-C3 N4 film is filtrated on the separator in air using a common alcohol solution and then perfectly autotransferred to the lithium surface by electrolyte wetting during normal cell assembly. The abundant nitrogen species within g-C3 N4 nanosheets can form transient LiN bonds to powerfully stabilize the lithium-ion flux and thus enable a CE over 99% for 900 cycles and smooth deposition at high current densities and capacities, surpassing most previous works.

Single Additive with Dual Functional-Ions for Stabilizing Lithium Anodes.

The dendritic lithium formation and sustained lithium consumption caused by the uncontrollable side reactions between lithium and electrolytes seriously restrict the applications of lithium anodes in high-energy density batteries, especially in carbonate electrolytes. Ameliorating the surface status of lithium anodes is critical for modulating lithium deposition behavior and improving the cycling stability of lithium metal batteries. Herein, magnesium chloride salt is first reported as a carbonate electrolyte additive for lithium surface modification by in situ reaction. It is proved that both Cl- and Mg2+ play important roles in building a stable electrode/electrolyte interface with a fast Li+ diffusion property. The coexistence of inorganic LiCl and metallic Mg species in the interface can effectively decrease the surface side reactions, lower interphase resistance, promote Li ions diffusion, and result in uniform lithium deposition. The electrochemical tests show that the reversible utilization rate of lithium for Li/Cu asymmetrical cells increases by 10% and the polarization of Li/Li symmetrical cells is reduced noteworthily with such an additive. Furthermore, a significant improved cycling performance of Li/Li4T5O12 full cells is also achieved.

Layer Structured Materials for Advanced Energy Storage and Conversion.

Owing to the strong in-plane chemical bonds and weak van der Waals force between adjacent layers, investigations of layer structured materials have long been the hotspots in energy-related fields. The intrinsic large interlayer space endows them capabilities of guest ion intercalation, fast ion diffusion, and swift charge transfer along the channels. Meanwhile, the well-maintained in-plane integrity contributes to exceptional mechanical properties. This anisotropic structural feature is also conducive to effective chemical combination, exfoliation, or self-assembly into various nanoarchitectures, accompanied by the introduction of defects, lattice strains, and phase transformation. This review starts with a brief introduction of typical layered materials and their crystal structures, then the structural characteristics and structure oriented unique applications in batteries, capacitors, catalysis, flexible devices, etc., are highlighted. It is surprising to observe that layered materials possess: (1) high reactivity, high reversibility, and enhanced performance via forming additional chemical bonds in alkali-metal ion batteries; (2) facile phase modulation, great feasibility for in-plane/sandwich device design, and cation intercalation enabled high capacitance in supercapacitors; (3) promoted structural diversity, effective strain engineering, and capabilities to function as ideal supporting materials/templates in electrocatalysis field. Finally, the future prospects and challenges faced by layered materials are also outlined.

Reviving Lithium-Metal Anodes for Next-Generation High-Energy Batteries.

Lithium-metal batteries (LMBs), as one of the most promising next-generation high-energy-density storage devices, are able to meet the rigid demands of new industries. However, the direct utilization of metallic lithium can induce harsh safety issues, inferior rate and cycle performance, or anode pulverization inside the cells. These drawbacks severely hinder the commercialization of LMBs. Here, an up-to-date review of the behavior of lithium ions upon deposition/dissolution, and the failure mechanisms of lithium-metal anodes is presented. It has been shown that the primary causes consist of the growth of lithium dendrites due to large polarization and a strong electric field at the vicinity of the anode, the hyperactivity of metallic lithium, and hostless infinite volume changes upon cycling. The recent advances in liquid organic electrolyte (LOE) systems through modulating the local current density, anion depletion, lithium flux, the anode-electrolyte interface, or the mechanical strength of the interlayers are highlighted. Concrete strategies including tailoring the anode structures, optimizing the electrolytes, building artificial anode-electrolyte interfaces, and functionalizing the protective interlayers are summarized in detail. Furthermore, the challenges remaining in LOE systems are outlined, and the future perspectives of introducing solid-state electrolytes to radically address safety issues are presented.

Ultrafine potassium titanate nanowires: a new Ti-based anode for sodium ion batteries.

K2Ti6O13 with an analogous tunnel structure to Na2Ti6O13 is proposed as a new anode for sodium-ion batteries. By fabricating ultrafine nanowires growing perpendicularly to the Na(+) diffusion direction, the K2Ti6O13 nanowires show a much enhanced capacity (186 mA h g(-1)) as well as good rate capability for sodium storage.