Air Corrosion of Layered Cathode Materials for Sodium-Ion Batteries: Cation Mixing and a Practical Suppression Strategy.

Layered oxide cathodes of sodium-ion batteries (SIBs) are considered promising candidates due to their fascinating high capacity, good cyclability, and environmental friendliness. However, the air sensitivity of layered SIB cathodes causes high electrode manufacturing costs and performance deterioration, hampering their practical application. Herein, a commercial O3-type layered Na(Ni1/3Fe1/3Mn1/3)O2 (NNFM) material is adopted to investigate the air corrosive problem and the suppression strategy. We reveal that once the layered material comes in contact with ambient air, cations migrate from transition metal (TM) layers to sodium layers at the near surface, although Na+ and TM ions show quite different ion radii. Experimental results and theoretical calculations show that more Ni/Na disorder occurs in the air-exposed O3-NNFM materials, owing to a lower Ni migration energy barrier. The cation mixing results in detrimental structural distortion, along with the formation of residual alkali species on the surface, leading to high impedance for Na+ diffusion during charge/discharge. To tackle this problem, an ultrathin and uniform hydrophobic molecular layer of perfluorodecyl trimethoxysilane is assembled on the O3-NNFM surface, which significantly suppresses unfavorable chemistry and structure degradation during air storage. The in-depth understanding of the structural degradation mechanism and suppression strategy presented in this work can facilitate high-energy cathode manufacturing from the perspective of future practical implementation and commercialization.

Anion-Reinforced Solvating Ionic Liquid Electrolytes Enabling Stable High-Nickel Cathode in Lithium-Metal Batteries.

Ionic liquid electrolytes (ILEs) are promising to develop high-safety and high-energy-density lithium-metal batteries (LMBs). Unfortunately, ILEs normally face the challenge of sluggish Li+ transport due to increased ions' clustering caused by Coulombic interactions. Here a type of anion-reinforced solvating ILEs (ASILEs) is discovered, which reduce ions' clustering by enhancing the anion-cation coordination and promoting more anions to enter the internal solvation sheath of Li+ to address this concern. The designed ASILEs, incorporating chlorinated hydrocarbons and two anions, bis(fluorosulfonyl) imide (FSI-) and bis(trifluoromethanesulfonyl) imide (TFSI-), aim to enhance Li+ transport ability, stabilize the interface of the high-nickel cathode material (LiNi0.8Co0.1Mn0.1O2, NCM811), and retain fire-retardant properties. With these ASILEs, the Li/NCM811 cell exhibits high initial specific capacity (203 mAh g-1 at 0.1 C), outstanding capacity retention (81.6% over 500 cycles at 1.0 C), and excellent average Coulombic efficiency (99.9% over 500 cycles at 1.0 C). Furthermore, an Ah-level Li/NCM811 pouch cell achieves a notable energy density of 386 Wh kg-1, indicating the practical feasibility of this electrolyte. This research offers a practical solution and fundamental guidance for the rational design of advanced ILEs, enabling the development of high-safety and high-energy-density LMBs.

Synergistic Effect of Dual Phases to Improve Lithium Storage Properties of Nb2O5.

Niobium pentoxides (Nb2O5) present great potential as next-generation anode candidates due to exceptional lithium-ion intercalation kinetics, considerably high capacity, and reasonable redox potential. Although four phases of Nb2O5 including hexagonal, orthorhombic, tetragonal, and monoclinic polymorphs show diverse characteristics in electrochemical performance, stable lifetime, high specific capacity, and fast intercalation properties cannot be delivered simultaneously with a single phase. Herein, this issue is addressed by generating a homogeneous mixture of orthorhombic and monoclinic crystals at the nanoscale. Reversible lithium-ion intercalation/deintercalation of the monoclinic phase is achieved, and exceptional lithium storage sites are created at the interface of the two phases. As a result, electrochemical features of stable lifetime from the orthorhombic phase and high specific performance from the monoclinic phase are harmoniously combined. This dual-phase Nb2O5/C nanohybrids deliver as high as 380 mA h g-1 (0.01-3.0 V) and 184 mA h g-1 (1.0-3.0 V) after 200 cycles. The essential principle of property enhancement is further confirmed through in situ XRD measurements and DFT calculations. The dual-phase concept can be further applied on electrodes with multiphases to achieve high electrochemical performance.

Localized Ligands Assist Ultrafast Multivalent-Cation Intercalation Pseudocapacitance.

Rechargeable batteries based on multivalent cation (Mvn+ , n>1) carriers are considered potentially low-cost alternatives to lithium-ion batteries. However, the high charge-density Mvn+ carriers generally lead to sluggish kinetics and poor structural stability in cathode materials. Herein, we report an Mvn+ storage via intercalation pseudocapacitance mechanism in a 2D bivalve-like organic framework featured with localized ligands. By switching from conventional intercalation to localized ligand-assisted-intercalation pseudocapacitance, the organic cathode exhibits unprecedented fast kinetics with little structural change upon intercalation. It thus enables an excellent power density of 57 kW kg-1 over 20000 cycles for Ca2+ storage and a power density of 14 kW kg-1 with a long cycling life over 45000 cycles for Zn2+ storage. This work may provide a largely unexploited route toward constructing a local dynamic coordination microstructure for ultrafast Mvn+ storage.

Polyfluorinated crosslinker-based solid polymer electrolytes for long-cycling 4.5 V lithium metal batteries.

Solid polymer electrolytes (SPEs), which are favorable to form intimate interfacial contacts with electrodes, are promising electrolyte of choice for long-cycling lithium metal batteries (LMBs). However, typical SPEs with easily oxidized oxygen-bearing polar groups exhibit narrow electrochemical stability window (ESW), making it impractical to increase specific capacity and energy density of SPE based LMBs with charging cut-off voltage of 4.5 V or higher. Here, we apply a polyfluorinated crosslinker to enhance oxidation resistance of SPEs. The crosslinked network facilitates transmission of the inductive electron-withdrawing effect of polyfluorinated segments. As a result, polyfluorinated crosslinked SPE exhibits a wide ESW, and the Li|SPE|LiNi0.5Co0.2Mn0.3O2 cell with a cutoff voltage of 4.5 V delivers a high discharge specific capacity of ~164.19 mAh g-1 at 0.5 C and capacity retention of ~90% after 200 cycles. This work opens a direction in developing SPEs for long-cycling high-voltage LMBs by using polyfluorinated crosslinking strategy.

Ion Co-storage in Porous Organic Frameworks through On-site Coulomb Interactions for High Energy and Power Density Batteries.

Fast and continuous ion insertion is blocked in the common electrodes operating with widely accepted single-ion storage mechanism, primarily due to Coulomb repulsion between the same ions. It results in an irreconcilable conflict between capacity and rate performance. Herein, we designed a porous organic framework with novel multiple-ion co-storage modes, including PF6 - /Li+ , OTF- /Mg2+ , and OTF- /Zn2+ co-storage. The Coulomb interactions between cationic and anionic carriers in the framework can significantly promote electrode kinetics, by rejuvenating fast ion carrier migration toward framework interior. Consequently, the framework via PF6 - /Li+ co-storage mode shows a high energy density of 878 Wh kg-1 cycled more than 20 000 cycles, with an excellent power density of 28 kW kg-1 that is already comparable to commercial supercapacitors. The both greatly improved energy and power densities via the co-storage mode may pave a way for exploring new electrodes that are not available from common single-ion electrodes.

Simultaneous Stabilization of Lithium Anode and Cathode using Hyperconjugative Electrolytes for High-voltage Lithium Metal Batteries.

Although great progress has been made in new electrolytes for lithium metal batteries (LMBs), the intrinsic relationship between electrolyte composition and cell performance remains unclear due to the lack of valid quantization method. Here, we proposed the concept of negative center of electrostatic potential (NCESP) and Mayer bond order (MBO) to describe solvent capability, which highly relate to solvation structure and oxidation potential, respectively. Based on established principles, the selected electrolyte with 1.7 M LiFSI in methoxytrimethylsilane (MOTMS)/ (trifluoromethyl)trimethylsilane (TFMTMS) shows unique hyperconjugation nature to stabilize both Li anode and high-voltage cathode. The 4.6 V 30 µm Li||4.5 mAh cm-2 lithium cobalt oxide (LCO) (low N/P ratio of 1.3) cell with our electrolyte shows stable cycling with 91 % capacity retention over 200 cycles. The bottom-up design concept of electrolyte opens up a general strategy for advancing high-voltage LMBs.

Boosting Perovskite Solar Cells Efficiency and Stability: Interfacial Passivation of Crosslinked Fullerene Eliminates the "Burn-in" Decay.

Perovskite solar cells (PSCs) longevity is nowadays the bottleneck for their full commercial exploitation. Although lot of research is ongoing, the initial decay of the output power - an effect known as "burn-in" degradation happening in the first 100 h - is still unavoidable, significantly reducing the overall performance (typically of >20%). In this paper, the origin of the "burn-in" degradation in n-i-p type PSCs is demonstrated that is directly related to Li+ ions migration coming from the SnO2 electron transporting layer visualized by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements. To block the ion movement, a thin cross-linked [6,6]-phenyl-C61-butyric acid methyl ester layer on top of the SnO2 layer is introduced, resulting in Li+ immobilization. This results in the elimination of the "burn-in" degradation, showing for the first time a zero "burn-in" loss in the performances while boosting device power conversion efficiency to >22% for triple-cation-based PSCs and >24% for formamidinium-based (FAPbI3 ) PSCs, proving the general validity of this approach and creating a new framework for the realization of stable PSCs devices.

Ionic Liquid-Type Additive for Lithium Metal Batteries Operated in LiPF6 Based-Electrolyte Containing 2500 ppm H2O.

The presence of trace amounts of moisture in the electrolyte can cause hydrolysis of LiPF6 and deteriorate the stability of lithium metal batteries. Herein, we propose a multifunctional ionic liquid-type additive constituting a 1-methyl-1-butyl pyrrolidium cation (Py14+) and an acetate anion (CH3COO-) (denoted as IL-AC in this study), which can effectively adsorb the trace moisture and thus prevent the hydrolysis of LiPF6 via intermolecular interactions. The prepared IL-AC can also remove HF to suppress the dissolution of transition metal ions from cathode materials through the reaction CH3COO- + HF → CH3COOH + F-. Compared with the baseline electrolyte, the contents of HF and transition metal ions are significantly lower in the electrolyte with 0.5% IL-AC. Upon the addition of 0.5% IL-AC additive and 2500 ppm H2O, the Li||NCM811 battery shows a capacity of 153.7 mAh g-1 after 300 cycles, while the Li||LNMO battery possesses stable capacity retention of 93.22% after 500 cycles at 1C and a Coulombic efficiency greater than 99%. Thus, this work provides a convenient and effective method to absorb trace amounts of water and remove HF in the electrolyte and provides a new path for the expensive and tedious process of water removal from the electrolyte in industry.

An Approach for Time Synchronization of Wireless Accelerometer Sensors Using Frequency-Squeezing-Based Operational Modal Analysis.

Wireless sensor networks usually suffer from the issue of time synchronization discrepancy due to environmental effects or clock management collapse. This will result in time delays between the dynamic responses collected by wireless sensors. If non-synchronized dynamic response data are directly used for structural modal identification, it leads to the misestimation of modal parameters. To overcome the non-synchronization issue, this study proposes a time synchronization approach to detect and correct asynchronous dynamic responses based on frequency domain decomposition (FDD) with frequency-squeezing processing (FSP). By imposing the expected relationship between modal phase angles extracted from the first-order singular value spectrum, the time lags between different sensors can be estimated, and synchronization can be achieved. The effectiveness of the proposed approach is fully demonstrated by numerical and experimental studies, as well as field measurement of a large-span spatial structure. The results verify that the proposed approach is effective for the time synchronization of wireless accelerometer sensors.

A preoperative prediction model based on Lymphocyte-C-reactive protein ratio predicts postoperative anastomotic leakage in patients with colorectal carcinoma: a retrospective study.

BACKGROUND & AIMS: Lymphocyte-C-reactive Protein Ratio (LCR) has been demonstrated as a promising new marker for predicting surgical and oncological outcomes in colorectal carcinoma (CRC). However, anastomotic leakage (AL) is also likely related to this inflammatory marker. Herein, we aimed to identify preoperative predictors of AL and build and develop a novel model able to identify patients at risk of developing AL. METHODS: We collected 858 patients with CRC undergoing elective radical operation between 2007 and 2018 at a single center were retrospectively reviewed. We performed univariable and multivariable analyses and built a multivariable model that predicts AL based on preoperative factors. Propensity adjustment was used to correct the bias introduced by non-random matching of the LCR. The model's performance was evaluated by using the area under the receiver operator characteristic curves (AUROCs), decision curve analysis (DCA), Brier scores, D statistics, and R2 values. RESULTS: Age, nutrition risk screening 2002 (NRS2002) score, tumor location and LCR, together with hemoglobin < 90 g/l, were independent predictors of AL. The models built on these variables showed good performance (internal validation: c-statistic = 0.851 (95%CI 0.803-0.965), Brier score = 0.049; temporal validation: c-statistic = 0.777 (95%CI 0.823-0.979), Brier score = 0.096). A regression equation to predict the AL was also established by multiple linear regression analysis: [Age(≥ 60 year) × 1.281] + [NRS2002(≥ 3) × 1.341] + [Tumor location(pt.) × 1.348]-[LCR(≤ 6000) × 1.593]-[Hemoglobin(< 90 g/L) × 1.589]-6.12. CONCLUSION: Preoperative LCR is an independent predictive factor for AL. A novel model combining LCR values, age, tumor location, and NRS2002 provided an excellent preoperative prediction of AL in patients with CRC. The nomogram can help clinical decision-making and support future research.

Room temperature all-solid-state lithium batteries based on a soluble organic cage ionic conductor.

All solid-state lithium batteries (SSLBs) are poised to have higher energy density and better safety than current liquid-based Li-ion batteries, but a central requirement is effective ionic conduction pathways throughout the entire cell. Here we develop a catholyte based on an emerging class of porous materials, porous organic cages (POCs). A key feature of these Li+ conducting POCs is their solution-processibility. They can be dissolved in a cathode slurry, which allows the fabrication of solid-state cathodes using the conventional slurry coating method. These Li+ conducting cages recrystallize and grow on the surface of the cathode particles during the coating process and are therefore dispersed uniformly in the slurry-coated cathodes to form a highly effective ion-conducting network. This catholyte is shown to be compatible with cathode active materials such as LiFePO4, LiCoO2 and LiNi0.5Co0.2Mn0.3O2, and results in SSLBs with decent electrochemical performance at room temperature.

Emcoating Architecture Construction via CO2 /H2 Coupling Treatment Doubles Reversible Capacity of NbO2 /C Anode.

As a promising alternative as lithium-ion anode, niobium dioxide appeals to researchers due to high theoretical capacity and good electron conductivity. However, rarely work about NbO2 based high performance anode is reported. Here, NbO2 nanoparticles emcoated in continuous carbon matrix is constructed through CO2 /H2 coupling treatment. CO2 activation introduces unique carbon emcoating structure, which builds interconnected electron conductive network with low carbon content. Furthermore, crystallographic phase of NbO2 is enhanced during H2 treatment, which increases the lithium storage ability. Electrochemical performance of NbO2 anodes is significantly improved based on the carbon emcoating structure. A high reversible capacity of 391 mAh g-1 is retained after 350 cycles at 0.2 C. Additionally, at a current density of 1 A g-1 , the reversible capacity reaches 139 mAh g-1 . Compared with conventional NbO2 /C nanohybrids, the lithium diffusion coefficient of carbon-emcoated sample shows improvement of three orders of magnitude. Moreover, the in situ XRD investigation shows a reversible lithium insertion behaviour with a limited volume change.

Photocatalytic Abstraction of Hydrogen Atoms from Water Using Hydroxylated Graphitic Carbon Nitride for Hydrogenative Coupling Reactions.

Employing pure water, the ultimate green source of hydrogen donor to initiate chemical reactions that involve a hydrogen atom transfer (HAT) step is fascinating but challenging due to its large H-O bond dissociation energy (BDEH-O =5.1 eV). Many approaches have been explored to stimulate water for hydrogenative reactions, but the efficiency and productivity still require significant enhancement. Here, we show that the surface hydroxylated graphitic carbon nitride (gCN-OH) only requires 2.25 eV to activate H-O bonds in water, enabling abstraction of hydrogen atoms via dehydrogenation of pure water into hydrogen peroxide under visible light irradiation. The gCN-OH presents a stable catalytic performance for hydrogenative N-N coupling, pinacol-type coupling and dehalogenative C-C coupling, all with high yield and efficiency, even under solar radiation, featuring extensive impacts in using renewable energy for a cleaner process in dye, electronic, and pharmaceutical industries.

True Reaction Sites on Discharge in Li-O2 Batteries.

In the pursuit of an advanced Li-O2 battery, the true reaction sites in the cathode determined its cell performance and the catalyst design. When the first layer of insulating Li2O2 solid is deposited on the electrode substrate during discharging, the following O2 reduction to Li2O2 could take place either at the electrode|Li2O2 interface or at the Li2O2|electrolyte interface. The mechanism decides the strategies of catalyst design; however, it is still mysterious. Here, we used rotate ring-disk electrode to deposit a dense Li2O2 film and labeled the Li2O2 product with 16O/18O isotope. By identification of the distribution of the Li216O2 and Li218O2 in the Li2O2 film using new characteristic signals of Li216O2 and Li218O2, our results show that O2 is reduced to Li2O2 at both interfaces. A sandwich structure of Li218O2|Li216O2|Li218O2 was identified at the electrode surface when the electrode was discharged under 16O2 and then 18O2. The electrode|Li2O2 interface is the major reaction site, and it contributes to 75% of the overall reaction. This new mechanism raises new challenges and new strategies for the catalyst design of Li-O2 batteries.

The Fabrication of Pd Single Atoms/Clusters on COF Layers as Co-catalysts for Photocatalytic H2 Evolution.

The particle size of co-catalysts significantly affects the activity of semiconductors in photocatalysis. Herein, we report that the photocatalytic H2 evolution (PHE) activity of a visible light responsive covalent organic framework (COF) layer supported on SiO2 nanoparticles was greatly promoted from 47.7 to 85.5 µmol/h by decreasing the particle size of the Pd co-catalyst from 3.3 nm to single atoms/clusters. A PHE rate of 156 mmol gCOF-1 h-1 and apparent quantum efficiency up to 7.3% were achieved with the Pd SAs/Cs co-catalyst. The relationship between the activity of Pd in H2 dissociation, proton reduction, and PHE rate suggests that the promotion effect of Pd SAs/Cs is mainly attributed to their enhancement in charge separation of COF layers rather than proton reduction. Furthermore, a photoactive film was fabricated and steady production of H2 was achieved under visible light irradiation and static conditions. The optimization of the particle size of co-catalysts provides an efficient method for enhancing the photocatalytic activity of semiconductors.

Practical Prelithiation of 4.5 V LiCoO2 ||Graphite Batteries by a Passivated Lithium-Carbon Composite.

Prelithiation can replenish active Li into the battery to compensate the Li consumption due to the formation of solid electrolyte interphase (SEI) on the electrode surface, therefore improving the energy density of Li-ion batteries (LIBs), especially for batteries using electrode materials with low initial Coulombic efficiency (ICE). However, practical prelithiation in LIBs is a challenge since most lithiated compounds with high specific capacity are unstable and industrially incompatible. Herein, an effective prelithiation strategy is demonstrated by using a lithium-carbon (Li-C) microsphere composite. These Li-C microspheres are passivated by a self-assembled monolayer of octadecylphosphonic acid, which suppresses the reaction between Li and commonly used slurry solvent 1-methyl-2-pyrrolidinone (NMP). After the addition of passivated Li-C into the NMP-based graphite slurry, the ICE of the graphite||Li half-cell boosts from 88.5% to 100.5%. In a 4.5 V LiCoO2 (LCO)||graphite full-cell, the supplementary Li source avoids excessive delithiation of LCO, thus suppressing the destructive phase transformation at high delithiation potential. As a result, the prelithiated LCO||graphite full-cell presents an initial discharge capacity of 201 mAh g-1 and the capacity retention after 100 cycles increases by 7.1 %. This work provides a practical approach for developing high energy density and long cycle life LIBs.

Room-Temperature All-Solid-State Sodium Battery Based on Bulk Interfacial Superionic Conductor.

All-solid-state sodium batteries (ASSSBs) are attractive alternatives to lithium-ion batteries for grid-scale energy storage due to their high safety and ubiquitous distribution of Na sources. A critical component for ASSSB is sodium-ion conducting solid-state electrolyte (SSE). Here, we report a high-performance sodium-ion SSE with the recently developed bulk interfacial superionic conductor (BISC) concept. The ionic conductivity and areal conductance of the Na+ BISC at 25 °C reaches 6.5 × 10-4 S cm-1 and 260 mS cm-2, respectively. Using NaxCo0.7Mn0.3O2 (x ≈ 1.0, NaCMO) as the cathode active material, all-solid-state Na||NaCMO batteries exhibiting small overpotential and ∼180 cycle life are demonstrated under room temperature. This approach may also be used to prepare other metal ion, such as Mg2+, Al3+, and K+, based all-solid-state batteries.

Self-Assembled Monolayers for Batteries.

Current studies in the Li-battery field are focusing on building systems with higher energy density than ever before. The path toward this goal, however, should not ignore aspects such as safety, stability, and cycling life. These issues frequently originate from interfacial instability, and therefore, precise surface chemistry that allows for accurate control of material surface and interfaces is much in demand for advanced battery research. Molecular self-assembly as a surface chemistry tool is considered to surpass many conventional coating techniques due to its intrinsic merits such as spontaneous organization, molecular-scale uniformity, and structural diversity. Recent publications have demonstrated the power of self-assembled monolayers (SAMs) in addressing pressing issues in the battery field such as the chemical stability of Li, but many more investigations are needed to fully explore the potential and impact of this technique on energy storage. This perspective is the first of its kind devoted to SAMs in batteries and related materials. Recent research progress on SAMs in batteries is reviewed and mainly falls in two categories, including the improvement of chemical stability and the regulation of nucleation in conversion electrode reactions. Future applications and consideration of SAMs in energy storage are discussed. We believe these summaries and outlooks are highly stimulative and may benefit future advancements in battery chemistry.