Multifunctional Additive Enables a "5H" PEO Solid Electrolyte for High-Performance Lithium Metal Batteries.

The solid-state battery with a lithium metal anode is a promising candidate for next-generation batteries with improved energy density and safety. However, the current polymer electrolytes still cannot fulfill the demands of solid-state batteries. In this work, we propose a "5H" poly(ethylene oxide) (PEO) electrolyte via introducing a multifunctional additive of tris(pentafluorophenyl)borane (TPFPB) for high-performance lithium metal batteries. The addition of TPFPB improves the ionic conductivity from 6.08 × 10-5 to 1.54 × 10-4 S cm-1 via reducing the crystallinity of the PEO electrolyte and enhances the lithium-ion transference number from 0.19 to 0.53 via anion trapping due to its Lewis acid nature. Furthermore, the fluorine and boron segments from TPFPB can optimize the composition of the solid-electrolyte interphase and cathode-electrolyte interphase, providing a high electrochemical stability window over 4.6 V of the PEO electrolyte along with significantly improved interface stability. At last, TPFPB can ensure improved safety through a self-extinguishing effect. As a result, the "5H" electrolyte enables the Li/Li symmetric cells to achieve a stable cycle over 2200 h at the current density of 0.2 mA cm-2 with a capacity of 0.2 mA h cm-2; the LiFePO4/Li full cells with a high LFP loading of 8 mg cm-2 exhibits decay-free capacity of 140 mA h g-1 (99% capacity retention) after 100 cycles; and the NCM811/Li cells exhibit a high capacity of 160 mA h g-1 after 50 cycles at 0.5 C. This work presents an innovative approach to utilizing a "5H" electrolyte for high-performance solid-state lithium batteries.

Ether-Based High-Voltage Lithium Metal Batteries: The Road to Commercialization.

Ether-based high-voltage lithium metal batteries (HV-LMBs) are drawing growing interest due to their high compatibility with the Li metal anode. However, the commercialization of ether-based HV-LMBs still faces many challenges, including short cycle life, limited safety, and complex failure mechanisms. In this Review, we discuss recent progress achieved in ether-based electrolytes for HV-LMBs and propose a systematic design principle for the electrolyte based on three important parameters: electrochemical performance, safety, and industrial scalability. Finally, we summarize the challenges for the commercial application of ether-based HV-LMBs and suggest a roadmap for future development.

In Operando Monitoring the Stress Evolution of Silicon Anode Electrodes during Battery Operation via Optical Fiber Sensors.

Silicon (Si) anode has attracted broad attention because of its high theoretical specific capacity and low working potential. However, the severe volumetric changes of Si particles during the lithiation process cause expansion and contraction of the electrodes, which induces a repeatedly repair of solid electrolyte interphase, resulting in an excessive consuming of electrolyte and rapid capacity decay. Clearly known the deformation and stress changing at µÎµ resolution in the Si-based electrode during battery operation provides invaluable information for the battery research and development. Here, an in operando approach is developed to monitor the stress evolution of Si anode electrodes via optical fiber Bragg grating (FBG) sensors. By implanting FBG sensor at specific locations in the pouch cells with different Si anodes, the stress evolution of Si electrodes has been systematically investigated, and Δσ/areal capacity is proposed for stress assessment. The results indicate that the differences in stress evolution are nested in the morphological changes of Si particles and the evolution characteristics of electrode structures. The proposed technique provides a brand-new view for understanding the electrochemical mechanics of Si electrodes during battery operation.

Spatial differentiation and scenario simulation of cultivated land in mountainous areas of Western Hubei, China: a PLUS model.

A useful spatial pattern of cultivated land utilization in mountainous areas is a basic prerequisite for promoting efficient utilization of cultivated land and has a practical use for ensuring regional food security and rural revitalization. In this paper, we use Enshi and Lichuan cities as case studies and the PLUS model to analyze the spatial differentiation characteristics of cultivated land from 2000 to 2020. In addition, we simulated the spatial pattern of cultivated land in 2030 concerning the ecological priority scenario (scenario I) and the ecological and economic coordination scenario (scenario II). The results show that (1) the degree of cultivated land fragmentation from 2000 to 2020 is characterized as "high in the east and low in the west," and the spatial aggregation of cultivated land decreases slightly over time and that there is a risk of increasing fragmentation of cultivated land in the future. (2) The complexity of cultivated land shape shows a fluctuating decrease between 2000 and 2030, and an overall trend of landscape homogenization. (3) The spatial distribution of cultivated land is concentrated in the peak cluster depressions and river valleys. The imbalance in the distribution of cultivated land has increased in the past two decades which should be curbed in the future. (4) In 2030, concerning the ecological priority development scenario, cultivated land use tends to evolve in the direction of balanced distribution and a relatively complex shape. (5) Concerning the coordinated ecological and economic development scenario, the spatial aggregation of cultivated land is higher and the patches of cultivated land are more regular, but the distribution imbalance is more serious. The results can provide scientific references for sustainable and effective use of cultivated land in mountainous areas.

Building Practical High-Voltage Cathode Materials for Lithium-Ion Batteries.

It has long been a global imperative to develop high-energy-density lithium-ion batteries (LIBs) to meet the ever-growing electric vehicle market. One of the most effective strategies for boosting the energy density of LIBs is to increase the output voltage, which largely depends upon the cathode materials. As the most-promising cathodes for high-voltage LIBs (>4 V vs Li/Li+ ), four major categories of cathodes including lithium-rich layered oxides, nickel-rich layered oxides, spinel oxides, and high-voltage polyanionic compounds still encounter severe challenges to realize the improvement of output voltage while maintaining high capacity, fast rate capability, and long service life. This review focuses on the key links in the development of high-voltage cathode materials from the lab to industrialization. First, the failure mechanisms of the four kinds of materials are clarified, and the optimization strategies, particularly solutions that are easy for large-scale production, are considered. Then, to bridge the gap between lab and industry, the cost management, safety assessment, practical battery-performance evaluation, and sustainability of the battery technologies, are discussed. Finally, tough challenges and promising strategies for the commercialization of high-voltage cathode materials are summarized to promote the large-scale application of LIBs with high energy densities.

Solid/Quasi-Solid Phase Conversion of Sulfur in Lithium-Sulfur Battery.

The lithium-sulfur (Li-S) battery is considered as one of the most promising options because the redox couple has almost the highest theoretical specific energy (2600 Wh kg-1 ) among all solid anode-cathode candidates for rechargeable batteries. The "solid-liquid-solid" mechanism has become a dominating phase transformation process since it was first reported, although this cathode mode suffers from a tough "shuttle" phenomenon due to the dissolution of the soluble intermediate polysulfides generated during the charging-discharging process, which causes rapid loss of energy-bearing material and shortened lifespan. For decades, tremendous efforts have been made to restrict the shuttle effect. Changing sulfur conversion to "solid-solid" mode or "quasi-solid" mode, which successfully exceed the limit of the dissolution of the intermediates, and may address the root of the problem. In this review, the main focus is on the fundamental chemistry of the "solid-solid" and "quasi-solid" phase transformation of the sulfur cathode. First, the strategies of sulfur immobilization in "solid-liquid-solid" multi-phase conversions as well as the pivotal influence factors for the electrochemical conversion process are briefly introduced. Then, the different routes are summarized to realize the "solid-solid" and "quasi-solid" redox mechanisms. Finally, a perspectives on building high-energy-density Li-S batteries are provided.

Dynamic response relationship between cultivated land marginalisation and rural labour out-migration in mountainous areas in China: evidence from a vector autoregressive model.

Understanding the dynamic interaction between cultivated land marginalisation (CLM) and rural labour out-migration (RLM) is vital for the sustainable utilisation of cultivated land, particularly in mountainous areas. Most previous research focused on unilateral CLM or RLM in mountainous areas, with limited research on the dynamic response between these two factors. To address this gap, we identified the characteristics of CLM and analysed the changing trends in RLM in 19 counties of western Hubei Province, China, from 2000 to 2018. The dynamic response relationship between the two phenomena was identified using a vector autoregressive model. CLM showed a volatile trend throughout the study area, with fluctuations most evident during 2004-2007 and 2009-2015. The rural labour population showed an inverted U-shaped trend with an increase during 2003-2015 and a decrease afterward, which is consistent with the trends in socioeconomic development. The dynamic response between the two factors showed large fluctuations in the short term but a stable relationship in the long term. These findings have important implications for differentiated land management, comprehensive land improvement, and rural land use policies and indicate that the added value of agricultural products from mountainous areas should be strengthened.

"First-Cycle Effect" of Trace Li2S in a High-Performance Sulfur Cathode.

Lithium-sulfur battery is one of the most promising choices for next-generation batteries due to its high theoretical energy density and natural abundance. However, the sulfur cathode undergoes a stepwise reduction process and generates multiple soluble polysulfide intermediates; for the further conversion from the dissolved intermediates to the final solid product (Li2S), the surface nucleation barrier limits the speed of the electrochemical precipitation, resulting in serious polysulfide diffusion loss and low sulfur utilization. Herein, the trace Li2S (tLi2S) is modified on the carbon fiber (CF) skeleton as preloaded crystal nuclei to boost the electrokinetics of Li2S deposition in the initial cycle. The trace Li2S decreases the nucleation barrier on the modified electrode (tLi2S@CF), resulting in a high initial capacity of 1423 mAh g-1 for the Li2S6 catholyte (0.2 C), which corresponds to a nearly 100% utilization of Li2S6. Furthermore, the trace Li2S nuclei induce a uniform distribution of the redeposited active materials, and the uniform distribution persists in the following cycles, which benefits the cycle life significantly. The sulfur cathode based on the tLi2S@CF matrix maintains a capacity of 1106 mAh g-1 at 1 C rate after 100 cycles. The strategy can provide a new avenue for the rational design of the sulfur cathode.

Effects of land use transition on ecological vulnerability in poverty-stricken mountainous areas of China: A complex network approach.

Poverty-stricken mountainous areas are often subject to ecological vulnerability, and land use transition is a major factor affecting that vulnerability. Land use transition forms a complex network comprised of different land use types which interact with each other and respond to external environment processes, resulting in dynamics. This study develops complex network approach with cascade failure model to quantitatively explore the effects of land use transition on ecological vulnerability from the holistic and dynamic perspective. The study analyzes the characteristics of land use transition, identifying key transition types and simulating their impact on ecological vulnerability in 16 poverty-stricken mountainous counties in western Hubei Province, China, with the following findings. (1) The heterogeneity of change in agricultural land and construction land is significant; from 1990 to 2015, a short-term increase in the amount of agricultural land is followed by a gradual reduction, while the amount of construction land increased continuously. (2) Agricultural land is the dominant output land type, exported mainly to construction land and water area, and construction land is the dominant input land type, imported mainly from agricultural land. Sparse woods, woods, and dryland are the key land use types in the study area. (3) the critical points for maintaining resilience of ecosystem are 80% or higher for cultivated land and 80% or higher for woodland. (4) For the tolerance parameter α, 20% increase in cultivated land and a 10% increase in woodland would enhance ecosystem resilience and reduce its damage degree to corresponding land use transition. These findings are important points of reference for the sustainable management of poverty-stricken mountainous counties in western Hubei Province and in China more generally. They also have policy implications for land resources, especially in terms of the alleviation of poverty and the coordination between ecological protection and economic development.

A Supramolecular Complex of C60 -S with High-Density Active Sites as a Cathode for Lithium-Sulfur Batteries.

The well-known "shuttle effect" of the intermediate lithium polysulfides (LiPSs) and low sulfur utilization hinder the practical application of lithium-sulfur (Li-S) batteries. Herein, we describe a novel C60 -S supramolecular complex with high-density active sites for LiPS adsorption that was formed by a simple one-step process as a cathode material for Li-S batteries. Benefiting from the cocrystal structure, 100 % of the C60 molecules in the complex can offer active sites to adsorb LiPSs and catalyze their conversion. Furthermore, the lithiated C60 cores promote internal ion transport inside the composite cathode. At a low electrolyte/sulfur ratio of 5 µL mg-1 , the C60 -S cathode with a sulfur loading of 4 mg cm-2 exhibited a high capacity of 809 mAh g-1 (3.2 mAh cm-2 ). The development of the C60 -S supramolecular complex will inspire the invention of a new family of S/fullerenes as cathodes for high-performance Li-S batteries and extend the application of fullerenes.

An inverted U-shaped curve relating farmland vulnerability to biological disasters: Implications for sustainable intensification in China.

Sustainable farmland intensification is necessary in order to harmonize relationships between food security, socioeconomic development, and ecological civilization. However, the degradation of farmland sustainability because of biological disasters represents a major challenge if we are to achieve this intensification. Our understanding of farmland vulnerability to biological disasters (FVBD) remains relatively rudimentary and subjective, limiting its effectiveness as a tool for farmland sustainability analysis. Limited research has also been carried out on FVBD changes taking into account human decisions on farmland use. The aim of this study is to achieve a novel understanding of FVBD change and its implications for sustainable intensification using evidence from Chinese farmland use. A theoretical framework based on an inverted U-shaped curve that depicts FVBD as well as an assessment framework for FVBD were established using induced substitution of agricultural production. Across China and considering 15 provincial districts with scarce farmland, the relationship between FVBD and socio-economic development was identified as consistent with an inverted U-shaped curve at both national and provincial levels. FVBD values in 2016 across Southern China, on the Huang-Huai-Hai Plain, and on the middle-lower Yangtze Plain were 45.44, 40.58, and 37.22, respectively. These values also decreased in provinces on the middle-lower Yangtze Plain between 1995 and 2016, but increased markedly across provinces in Southern China and on the Huang-Huai-Hai Plain. Contributions to FVBD changes during stages of growth and decline were also analyzed between 1995 and 2016. An inverted U-shaped curve was effective in investigating the responses of farmland sustainability to a range of alternative future socioeconomic development pathways. Thus, in the Chinese settings, a typical country with scarce farmland, policies on FVBD control are essential if we are to promote sustainable farmland intensification. The findings of this work are important and present us with a new way to understand FVBD from a human perspective.

Impacts of Precipitation and Temperature on Changes in the Terrestrial Ecosystem Pattern in the Yangtze River Economic Belt, China.

The terrestrial ecosystem plays an important role in maintaining an ecological balance, protecting the ecological environment, and promoting the sustainable development of human beings. The impacts of precipitation, temperature, and other natural factors on terrestrial ecosystem pattern change (TEPC) are the basis for promoting the healthy development of the terrestrial ecosystem. This paper took the Yangtze River Economic Belt (YREB) as the study area, analyzed the temporal and spatial characteristics of TEPC from 1995 to 2015, and used spatial transfer matrix and terrestrial ecosystem pattern dynamic degree models to analyze the area transformation between different terrestrial ecosystem types. A bivariate spatial autocorrelation model and a panel data regression model were used to study the impacts of precipitation and temperature on TEPC. The results show that: (1) The basic pattern of the terrestrial ecosystem developed in a relatively stable manner from 1995 to 2005 in the YREB, and transformations between the farmland ecosystem, forest ecosystem, and grassland ecosystem were more frequent. The temporal and spatial evolution of precipitation and temperature in the YREB showed significant regional differences. (2) There was a significant negative bivariate global spatial autocorrelation effect of precipitation and temperature on the area change of the forest ecosystem, and a positive effect on the area change of the settlement ecosystem. The local spatial correlation between precipitation or temperature and the terrestrial ecosystem showed significant scattered distribution characteristics. (3) The impacts of precipitation and temperature on TEPC showed significant regional characteristics on the provincial scale. The impact utility in the tail region is basically negative, while both positive and negative effects exist in the central and head regions of the YREB. Moreover, the impact showed significant spatial heterogeneity on the city scale. (4) The Chinese government has promulgated policies and measures for strategic planning, ecological environment protection, and economic support, which could effectively promote ecological and sustainable development of the YREB and promote the coordinated development of the ecology, economy, and society in China.

A Lithium-Ion Pump Based on Piezoelectric Effect for Improved Rechargeability of Lithium Metal Anode.

Lithium metal is widely studied as the "crown jewel" of potential anode materials due to its high specific capacity and low redox potential. Unfortunately, the Li dendrite growth limits its commercialization. Previous research has revealed that the uniform Li-ion flux on electrode surface plays a vital role in achieving homogeneous Li deposition. In this work, a new strategy is developed by introducing a multifunctional Li-ion pump to improve the homogenous distribution of Li ions. Via coating a ß-phase of poly(vinylidene fluoride) (ß-PF) film on Cu foil (Cu@ß-PF), a piezoelectric potential across such film is established near the electrode surface because of its piezoelectric property, which serves as a driving force to regulate the migration of Li ions across the film. As a result, uniform Li-ion distribution is attained, and the Cu@ß-PF shows coulombic efficiency around 99% throughout 200 cycles. Meanwhile, the lithium-sulfur full cell paired with Li-Cu@ß-PF anode exhibits excellent performance. This facile strategy via regulating the Li-ion migration provides a new perspective for safe and reliable Li metal anode.

Ether-compatible sulfurized polyacrylonitrile cathode with excellent performance enabled by fast kinetics via selenium doping.

Sulfurized polyacrylonitrile is suggested to contain Sn (n ≤ 4) and shows good electrochemical performance in carbonate electrolytes for lithium sulfur batteries. However inferior results in ether electrolytes suggest that high solubility of Li2Sn (n ≤ 4) trumps the limited redox conversion, leading to dissolution and shuttling. Here, we introduce a small amount of selenium in sulfurized polyacrylonitrile to accelerate the redox conversion, delivering excellent performance in both carbonate and ether electrolytes, including high reversible capacity (1300 mA h g-1 at 0.2 A g-1), 84% active material utilization and high rate (capacity up to 900 mA h g-1 at 10 A g-1). These cathodes can undergo 800 cycles with nearly 100% Coulombic efficiency and ultralow 0.029% capacity decay per cycle. Polysulfide dissolution is successfully suppressed by enhanced reaction kinetics. This work demonstrates an ether compatible sulfur cathode involving intermediate Li2Sn (n ≤ 4), attractive rate and cycling performance, and a promising solution towards applicable lithium-sulfur batteries.

Biomimetic Root-like TiN/C@S Nanofiber as a Freestanding Cathode with High Sulfur Loading for Lithium-Sulfur Batteries.

It is a tough issue to achieve high electrochemical performance and high sulfur loading simultaneously, which is of important significance for practical Li-S batteries applications. Inspired by the transportation system of the plant root in nature, a biomimetic root-like carbon/titanium nitride (TiN/C) composite nanofiber is designed as a freestanding current collector for the high sulfur loading cathode. Like the plant root which absorbs water and oxygen from soil and transfers them to the trunk and branches, the root-like TiN/C matrix provides high-efficiency polysulfide, electron, and electrolyte transfer for the redox reactions via its three-dimensional-porous interconnected structure. In the meantime, TiN can not only anchor the polysulfides via the polar Ti-S and N-S bond but also further facilitate the redox reaction because of its high catalytic effect. With 4 mg cm-2 sulfur loading, the TiN/C@S cathode delivers a high initial discharge capacity of 983 mA h g-1 at 0.2 C current density; after 300 charge/discharge cycles, the discharge capacity remains 685 mA h g-1, corresponding to a capacity decay rate of ∼0.1%. Even when the sulfur loading is increased to 10.5 mg cm-2, the cell still delivers a high capacity of 790 mA h g-1 and a decent cycle life. We believe that this novel biomimetic root-like structure can provide some inspiration for the rational structure design of the high-energy lithium-sulfur batteries and other composite electrode materials.

Free-Standing Mn3O4@CNF/S Paper Cathodes with High Sulfur Loading for Lithium-Sulfur Batteries.

Free-standing paper cathodes with layer-by-layer structure are synthesized for high-loading lithium-sulfur (Li-S) battery. Sulfur is loaded in a three-dimensional (3D) interconnected nitrogen-doped carbon nanofiber (CNF) framework impregnated with Mn3O4 nanoparticles. The 3D interconnected CNF framework creates an architecture with outstanding mechanical properties. Synergetic effects generated from physical and chemical entrapment could effectively suppress the dissolution and diffusion of the polysulfides. Electrochemical measurements suggest that the rationally designed structure endows the electrode with high utilization of sulfur and good cycle performance. Specifically, the cathode with a high areal sulfur loading of 11 mg cm-2 exhibits a reversible areal capacity over 8 mAh cm-2. The fabrication procedure is of low cost and readily scalable. We believe that this work will provide a promising choice for potential practical applications.

Granadilla-Inspired Structure Design for Conversion/Alloy-Reaction Electrode with Integrated Lithium Storage Behaviors.

Conversion/alloy-reaction electrode materials promise much higher energy density than the commonly used ones based on intercalation chemistries. However, the low electronic conductivity and, specially, the large volume expansion upon lithiation hinder their practical applications. Here, for the first time, a unique granadilla-inspired structure was designed to prepare the conversion/alloy-reaction anode of carbon coated tin/calcium tin oxide (C@void@Sn/CaSnO3) ternary composite. The granadilla-inspired structure ensures the intimate contact between the Sn/CaSnO3 nanoparticles and the carbon matrix, providing not only conductive networks for electron transport and a short distance for Li+ diffusion but also effective space for the electrode volume expansion toward conversion/alloy reaction. Moreover, the unique structure possesses abundant solid-solid interfaces between the three components as well as solid-liquid interfaces between nanoparticles and electrolyte, contributing to a large percent (58%) of interfacial charge (thus capacity). The integration of alloy-reaction, conversion-reaction, and interfacial lithium storage endows the hybrid electrode with a high capacity and long cycling life, holding great promise for next-generation high-capacity lithium-ion batteries.

Hierarchical nitrogen-doped porous graphene/reduced fluorographene/sulfur hybrids for high-performance lithium-sulfur batteries.

It is a great challenge to obtain high performance cathodes with a high sulfur loading and good cycle performance due to the dissolution of intermediate lithium polysulfides in lithium-sulfur batteries. Herein, we report a novel hierarchical hybrid composed of nitrogen-doped porous graphene (NG), reduced fluorographene or graphene fluoride (RFG), and sulfur as a composite cathode in the Li-S batteries. In comparison with sulfur composites based on only either nitrogen-doped porous graphene or pure reduced fluorographene, the hierarchical hybrid of RFG, NG, and sulfur (NG-RFG/S) shows a better reversible capacity and rate capability performance due to a better confinement effect of lithium polysulfides and sulfur. The NG-RFG/S cathode with ∼63.2% S content exhibits a high discharge capacity of 1120 mA h g-1 and retains 632 mA h g-1 after 100 cycles at 0.1C. At the higher rate of 0.5C, the cell still maintains a discharge capacity of about 300 mA h g-1 after 800 cycles, which reveals the great potential of this hybrid cathode for long-cycle-life, high energy density storage applications.

SnO2 as a high-efficiency polysulfide trap in lithium-sulfur batteries.

The ithium-sulfur battery stands as one of the most promising successors of traditional lithium-ion batteries due to its super high theoretical energy density, but practical application still suffers from the shuttle effect arising from soluble intermediate polysulfides. Here, we report SnO2 as a chemical adsorbent for polysulfides. As an interlayer between the cathode and separator, SnO2 gives better results to prevent the polysulfides from diffusing to the lithium anode than as a modifier of the carbon matrix directly. The lithium-sulfur battery with an SnO2 interlayer delivers an initial reversible capacity of 996 mA h g(-1) and retains 832 mA h g(-1) at the 100(th) discharge at 0.5 C, with a fading rate of only 0.19% per cycle. The improvements benefit from the quasi-open space provided by the interlayer configuration for the diffused sulfur species, which can largely relieve the loss of active substances caused by the volume effect during the lithiation/delithiation process.

Rational synthesis of carbon-coated hollow Ge nanocrystals with enhanced lithium-storage properties.

High-capacity anode materials based on alloy-type group IV elements always have large volume expansion during lithiation when they are used in lithium-ion batteries. Designing hollow structures is a well-established strategy to accommodate the volume change because of sufficient internal void space. Here we report a facile template-free route to prepare hollow Ge nanospheres without using any templates through a quasi-microemulsion method. Ge nanocrystals are preferably self-assembled along the interface of liquid vesicles between water and tetrahydrofuran, and well-defined hollow architectures of ∼50 nm in diameter are formed. Both the wall thickness and hollow interiors can be easily tuned. After subsequent carbon coating via pyrolysis of acetylene, the as-formed Ge@C nanocomposite with hollow interiors exhibits a highly reversible capacity of about 920 mA h g(-1) at 200 mA g(-1) over 50 cycles, and excellent rate capability. The small size and the high structural integrity of hollow Ge@C structures contribute to the superior lithium-storage performances.