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The realisation of fast-charging lithium-ion batteries with long cycle lifetimes is hindered by the uncontrollable plating of metallic Li on the graphite anode during high-rate charging. Here we report that surface engineering of graphite with a cooperative biphasic MoOx–MoPx promoter improves the charging rate and suppresses Li plating without compromising energy density. We design and synthesise MoOx–MoPx/graphite via controllable and scalable surface engineering, i.e., the deposition of a MoOx nanolayer on the graphite surface, followed by vapour-induced partial phase transformation of MoOx to MoPx. A variety of analytical studies combined with thermodynamic calculations demonstrate that MoOx effectively mitigates the formation of resistive films on the graphite surface, while MoPx hosts Li+ at relatively high potentials via a fast intercalation reaction and plays a dominant role in lowering the Li+ adsorption energy. The MoOx–MoPx/graphite anode exhibits a fast-charging capability (, Fast-charging of lithium-ion batteries is hindered by the uncontrollable plating of metallic Li on the graphite anode during cycling. Here, the authors demonstrate the fast chargeability and long cycle lifetimes via surface engineering of graphite with a cooperative biphasic MoOx–MoPx promoter.

Solid polymer electrolytes (SPEs) have been received significant attention due to their inherent advantages of high safety and high electrochemical stability as fast Li-ion conductors. However, conventional SPEs of dual-ion conductors (i.e., conducting both anions and cations) are prone to induce concentration polarization and thus decrease in ionic conductivities, which remains a significant hurdle for their practical applications. Here, we propose a new host of porous aromatic frameworks (PAFs) as a promising single Li-ion conducting SPEs. PAF1 is one of the promising types for crystalline polymers with the integration of aromatic organic building units into a 3-dimensional framework, having plenty of voids space inside. By covalently tethering the sulfonate on aromatic groups, anions are immobilized onto the frameworks, and the exchanging process of protons with Li-ions makes it perform as a fast Li-ionic conductor. Consequently, Li sulfonated PAF1 (denoted as Li-SPAF1) shows superior ion-conducting properties of 0.102 mS cm−1 at room temperature with the activation energy of 0.21 eV. It is demonstrated that the aromatic groups have high chemical and thermal stabilities, even stable with Li metal, which is advantageous for delivering stable electrochemical performances. Also, the structure and conduction mechanism are theoretically investigated by using density functional theory calculations.

Despite a variety of advantages over the presently dominant vanadium redox flow batteries, the commercialization of iron–chromium redox flow batteries (ICRFBs) is hindered by sluggish Cr2+/Cr3+ redox reactions and vulnerability to the hydrogen evolution reaction (HER). To address these issues, here, we report a promising electrocatalyst comprising Ketjenblack (KB) carbon with embedded bismuth nanoparticles (Bi-C). The uniform incorporation of Bi nanoparticles into KB carbon via a simple reduction process excellently promotes the electrochemical activity of Cr2+/Cr3+ redox reactions while retarding the HER. A combination of experimental analysis and density functional theory (DFT) calculations indicates that these phenomena are attributable to the synergistic effect of Bi and KB, which inhibits hydrogen evolution and provides active sites to enhance the Cr2+/Cr3+ redox reaction, respectively. An ICRFB cell containing the Bi-C catalyst as the negative electrode exhibits a high energy efficiency of 86.54% with excellent capacity retention during charge–discharge cycling at room temperature. This study offers an intelligent hybrid material as a useful design principle for electrocatalysts capable of addressing the critical problems in ICRFBs.

Ether-based organic liquid electrolytes (OLEs) have been commonly used in lithium–oxygen batteries (LOBs); however, they become unstable and cause rapid performance degradation during LOB operation. To address these problems, in this study we propose an OLE-free cathode architecture based on a Li+-selective solid membrane (LSSM). An LSSM with a seamless duplex (dense/porous) architecture is prepared by a tape casting process combined with co-sintering, and carbon nanotubes (CNTs) decorated with Au nanoparticles (CNT@Au) are directly formed on its porous framework. We show that the duplex-LSSM can effectively protect the metallic Li anode from parasitic reactions with impurity species and improve the cycling stability of Li. Furthermore, an LOB assembled with the duplex-LSSM and CNT@Au components exhibits a discharge capacity as high as 3650 mAh g−1 and improved cycling stability (>140 cycles) compared to a conventional OLE-based LOB; this can be explained in terms of the combined advantages provided by the OLE-free cathode and the LSSM-protected Li anode.

Lithium metal (Li) is an ideal anode for designing high-energy Li metal batteries (LMBs) due to its high specific capacity (3860 mAh g−1) and lowest electrochemical potential. However, the practical use of Li is currently impeded by uncontrollable dendritic growth during repeated Li plating and stripping, causing serious safety hazards such as electrical short circuits. To regulate Li growth behavior, various solid electrolyte interfaces (SEIs) have been explored. Despite intensive efforts, further understanding of the dendritic growth mechanism is still required. In this respect, herein, we clarify the origin and growth mechanism of Li dendrites by evaluating the critical role of an artificial SEI using a finite element method. Based on our theoretical study, we suggest that the relatively low ionic conductivity of the SEI layer is responsible for facilitating the growth of Li dendrites and the growth can be effectively suppressed by employing an artificial SEI with a higher ionic conductivity. The high-conductivity artificial SEI regulates local current distributions, directly affecting the growth of Li dendrites as determined by measuring the current density, exchange current density, and geometry. Our findings provide new insight into the design of artificial SEIs for improving the cycling performance of advanced LMBs.

Background Mucosal healing (MH) is one of the treatment targets in patients with ulcerative colitis (UC). However, it has been suggested that even in patients with MH, disease prognosis depends on histologic activity. This study aimed to evaluate histologic features predicting disease prognosis and their relationship with endoscopic findings in UC patients with MH. Methods We retrospectively reviewed the data of patients with UC who underwent colonoscopy or sigmoidoscopy with biopsy and evaluated eight histological features, including chronic inflammatory infiltrate, neutrophils in epithelium, ulceration, acute inflammatory cell infiltrate, basal plasmacytosis and serrated architectural abnormalities, as well as Nancy index (NI). Histologic variables predicting disease progression defined as starting corticosteroid, biologics, or small molecule agent, or undergoing clinical relapse or surgical operation were evaluated, and correlated with endoscopic findings. Results A total 194 biopsy specimens of 103 patients were evaluated. The highest grades of each histologic item were analyzed when biopsies were performed at multiple sites in one patient. 30.6% showed NI ≤ 1 (no acute inflammatory infiltrate) in 49 patients with endoscopic remission. Among 68 patients with MH, only 24.8% achieved NI ≤ 1. Mucosal friability in endoscopic findings was significantly associated with moderate-to-severe active histologic status (NI ≥3) (46.2% vs 80.0%, P=0.013), and patients with NI ≥3 showed significantly higher rates of disease progression during 13.7-month follow-up period (5.1% vs 19.0%, P=0.21). Ulceration and serrated architectural abnormalities were significantly associated with disease progression, and serrated architectural abnormalities was an independent risk factor in multivariate analysis (odds ratio 2.691 (95% confidence interval: 1.047–6.915), P=0.04). Conclusion Mucosal friability in endoscopic findings reflects moderate-to-severe active histologic status, and presence of serrated architectural abnormalities predicts disease progression in UC patients with MH. These findings may help identify patients need closer monitoring.

Despite their potential for achieving high energy density, anode-free batteries (AFBs) suffer from poor cycling stability caused by uncontrollable Li-metal deposition. To improve the reversibility of Li by physically preventing Li dendrite growth and minimizing the side reaction area between Li and the free solvent, two representative salts, lithium bis(fluorosulfonyl)imide (LiFSI) forming a robust/conductive LiF-based solid electrolyte interphase (SEI) layer, and LiNO3 altering the deposited Li morphology from dendritic to spherical, are widely used as salts for electrolyte. However, the depletion of LiNO3 by continuous consumption during cycling is a problem due to its low solubility. Thus, here, we report the use of high-concentration dual-salt electrolyte consisting of LiFSI and LiNO3 for AFBs to circumvent these issues. Experimental and theoretical studies reveal that electrolytes with high-concentration LiNO3 (up to 2 M) can be prepared by suppressing the agglomeration of LiNO3 in 1,2-dimethoxyethane (DME) in the presence of LiFSI. Because of the densely packed Li without dendrite, the formation of a protective SEI layer, and the alleviation of electrolyte oxidation as well as Al corrosion, the AFBs with this electrolyte achieve good cycling performance by reversible operation of Li. This work demonstrates the importance of electrolyte engineering for highly stable AFBs.

The mechanical properties of cathode materials are among the critical factors that directly affect the lifespan of lithium-ion batteries (LIBs). However, a significant challenge remains in understanding the exact mechanism of mechanical degradation of present cathode materials that results in significant loss of performance during long-term operation. Herein, a comparative study on the correlation between mechanical strength (e.g. particle hardness) and cycle performance of the cathode materials (particularly those with layered structures) is presented. By improving the particle hardness of cathode materials via Mg doping, the formation of undesirable microcracks within the particles during cycling can be effectively suppressed, thus improving cycle performance. Structural and electrochemical analyses are performed in order to further elucidate the mechanical degradation mechanism of LIBs during repeat cycles, and identify a possible approach to the enhancement of electrochemical performance and long-term durability in present cathode materials.

The kinetics of lithium atoms in various Li–Si binary compounds are investigated using density functional theory calculations and kinetic Monte Carlo calculations. The values of the Li migration energy barriers are identified by NEB calculations with vacancy–mediated, interstitial and exchange migration mechanisms in crystalline LiSi, Li12Si7, Li13Si4, and Li15Si4. A comparison of these NEB results shows that the vacancy–mediated Li migration is identified as the dominant diffusion mechanisms in Li–Si compounds. The diffusion coefficients of Li in Li–Si compounds at room temperature are determined by KMC simulation. From the KMC results, the recalculated migration energy barriers in LiSi, Li12Si7, Li13Si4, and Li15Si4 correspond to 0.306, 0.301, 0.367 and 0.320 eV, respectively. Compared to the Li migration energy barrier of 0.6 eV in crystalline Si, the drastic reduction in the Li migration energy barriers in the lithiated silicon indicates that the initial lithiation of the Si anode is the rate-limiting step. Furthermore, it is also found that Si migration is possible in Li–rich configurations. On the basis of these findings, the underlying mechanisms of kinetics on the atomic scale details are elucidated.

The electrochemical performance of Li-ion batteries strongly depends on the interaction between atomic scale and micro scale phenomena in high capacity electrode materials such as silicon and sulfur. Local thermodynamic interactions between host and guest species on atomic-scale significantly influence transfer kinetics and deformation kinematics on the micro-scale. We propose a multi-scale model to characterize the electrochemical and mechanical response of an amorphous silicon thin film during discharge/charge cycling. In the atomic-scale simulation, the stress-dependent energy barrier for the migration of lithium and the molar excess Gibbs free energy were calculated using density functional theory. These atomic-scale effects account for the nonlinear lithium diffusion behavior in the continuum simulation. In the continuum simulation, we considered the coupled diffusion and large deformation model on the cell-scale to determine the non-equilibrium cell potential as a function of the surface lithium concentration using Butler-Volmer kinetics. We clearly show that Li macroscopic kinetics is significantly affected by the stress induced by the volumetric strain associated with diffusion and the mixing formation energy of Li x Si. Our simulation results demonstrate that the multi-scale model is consistent with experimental observations at different C-rates.

To meet the growing demand for high-power lithium-ion batteries (LIBs), the development of advanced materials is crucial because they play a central role in energy storage technologies. Although graphite is widely used as the most popular anode material, the rate capability and thermal stability of graphite should be further improved for extending the applications of LIBs into emerging markets like electric vehicles and personal mobility devices. With this in mind, we propose off-stoichiometric TiO2-x-decorated graphite as a potential anode material for practical use in high-power LIBs. Thanks to the high electrical conductivity and thermal resistance of off-stoichiometric TiO2-x induced by an in situ carbothermal reduction process, the rate capability and thermal stability of graphite can be notably enhanced. The TiO2-x-decorated graphite offers a high capacity retention of 76.9% even after 100 cycles at a current density of 1C. We believe that this work can provide more opportunities to explore highly reliable anode materials offering high-energy and high-power characteristics for advanced LIBs.

A diffusion induced stress (DIS) model based on the finite element method was used to analyze mechanical stress within a multiscale framework for silicon nanowire anodes designed for use in Li-ion batteries. With a prelithiated nanowire, the mechanical moduli of lithium silicide and the migration energy barriers of lithium were calculated by density functional theory method, while the diffusion constants for lithium silicide were obtained using kinetic Monte Carlo simulations. Unlike previous DIS analyses, this multiscale approach reveals a decreasing hoop stress with increasing lithium concentration. Furthermore, an increase in the diffusion coefficient with Li concentration was also found to be a much more significant factor than the reduction in the mechanical moduli, causing a prelithiated silicon anode to experience lower stress levels than pristine silicon. On the basis of this finding, it is concluded that prelithiation reduces the loss in cycling performance that typically occurs due largely to an excess of induced stress.

Energetics and kinetics of Li insertion into c-Si and a-Si systems are investigated using the density functional (DFT) theory calculations and kinetic Monte Carlo (KMC) simulations. DFT formation energies show the mechanism of phase separation between crystalline silicon and amorphous lithium silicide. Both crystalline and amorphous Si show similar trends in volume expansion and phase transition under lithiation, and kinetics of Li diffusion in bulk silicon (from DFT and KMC) shows a big difference between c-Si and a-Si. The Li migration barrier is 0.6 eV in c-Si, and quickly decreases to 0.4 eV under increasing Li concentration or Si volume expansion. To simulate Li diffusion in amorphous silicon using KMC, we have developed a formulation for environment dependent migration energy barriers of Li in a-Si using a volume dependent function. KMC simulations are performed for Li diffusion in both c-Si and a-Si, and the diffusion coefficient of Li in a-Si is an order of magnitude larger than in c-Si. These studies help to understand mechanisms of lithiation with atomic scale details and elucidate the phase separation between c-Si and lithium silicide.

In this paper, we device stress-diffusion full coupling multiscale analysis method for battery electrode simulation. In proposed method, the diffusive and mechanical properties of electrode material depend on Li concentration are estimated using density function theory(DFT) simulation. Then, stress-diffusion full coupling continuum formulation based on finite element method(FEM) is constructed with the diffusive and mechanical properties calculated from DFT simulation. Finally, silicon nanowire anode charge and discharge simulations are performed using the proposed method. Through numerical examples, the stress-diffusion full coupling method shows more resonable results than previous one way continuum analysis.