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In this study, newly designed cathode material LiFeP 1-x Si x O 4 , with silicon mixed in LiFePO 4 is investigated using the density functional theory. Its most optimized structure is the olivine structure of the Pnma space group. Bonding length show the anti-site defect which hinders Li diffusivity is prevented in the LiFeP 1-x Si x O 4. Lithium migration energy barriers in the (010) path of LiFeP 1-x Si x O 4 (x = 0, 0.5, and 1) are calculated by using nudged elastic band calculations, and the average values are determined as 0.180, 0.245, and 0.280 eV for LiFePO 4 , LiFeP 0.5 Si 0.5 O 4 , and LiFeSiO 4 , respectively. This signifies that the Li ionic diffusivity is degraded thermodynamically, which is contrary to that indicates by the calculated bonding length, however, the difference is negligibly small. Furthermore, the intercalation voltage increases up to 4.97 V, depending on the Si ratio to P, and is much higher than that of the pristine cathode materials LiFePO 4 (∼3.47 V) enabling voltage optimization by Si substitution. The energy density is proportional to the intercalation voltage, hence the energy density is increased, respectively. Finally, the Total density of states show that the electronic conductivity of LiFeP 1-x Si x O 4 (x = 0–1) is better than that of LiFePO 4. • Novel cathode material LiFeP 1-x Si x O 4 is detail designed using ab-initio study. • Optimized LiFeP 1-x Si x O 4 crystal structure is olivine structure Pnma space group. • LiFeP 1-x Si x O 4 cathode material diminishes anti-site defect and enhances electronic conductivity. • LiFeP 1-x Si x O 4 cathode material overcome low intercalation voltage and control the voltage. • LiFeP 1-x Si x O 4 cathode material improves volumetric energy density. [ABSTRACT FROM AUTHOR]

In this study, we revealed the interfacial strengthening mechanism between a Stone- Thrower-Wales (STW) defective single layer graphene and polypropylene (PP), through a density functional theory (DFT) simulation and atomistic molecular dynamics simulations. In quantum mechanical simulation, the adhesion energy of propylene monomer on STW defective graphene is calculated with van der Waals interaction. An improved adsorption characteristic of propylene to the STW defective graphene is clearly observed, compared with a pristine counterpart. For deeper understanding of the adsorption, the electronic structure calculation and geometrical analysis of the adsorbed structures are also performed. In molecular dynamics simulation, three transversely isotropic nanocomposite unit cell structures consisting of PP and single layer graphene having a different number of STW defects are constructed. The stress-strain curves of nanocomposites according to the density of STW defects are obtained from uniaxial tension and shear tests. Since the properties of graphene itself are degraded by the STW defects, the overall stress-strain characteristics of nanocomposites involving the deformation of graphene are degraded by the addressed STW defects. However, in longitudinal shearing, where interfacial shearing between graphene and PP is involved, the STW defect can critically improve the shear load bearing capability. The increased interfacial shear load transfer is mostly attributed to the rippling of graphene at the STW defective sites, and the resultant surface roughness of graphene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Facilitation mechanisms of lithium ion diffusion were investigated through thermal stability, grain growth kinetics, and diffusion model. • Oxygen evolution and destruction of the layered structure were prohibited by thermal treatment at 1100 °C, securing stable lithium ion diffusion at micro-level. • High capacity retention of 96.5 % was achieved at 1C by controlled densification and coarsening based on the kinetic study of grain growth at macro -level. • The electrochemical properties showed good agreement with our developed diffusion model, suggesting the strategic way to achieve lower tortuosity and higher diffusion coefficient by controlling rapid grain growth. The performance of lithium-ion batteries is highly dependent on the morphology of the grain and structure of the electrode, which can be optimized for either high power or high energy. Despite the progress in all-solid-state batteries, the behavior of densification and coarsening has not yet been investigated on cathode. Herein, we investigated the strategies how to manipulate Li-ion diffusion at the different dimensions of micro- to macro level, facilitating the diffusion as tailoring the multi-scale path from densification to coarsening. First, the influence of microstructure on tortuosity and diffusivity was studied to understand the effect of sintering. Increased sintering time was expected to deteriorate electrochemical properties owing to lower diffusivity, and higher tortuosity. Second, the grain growth and densification behavior were studied in conjunction with the critical temperature for multi-scale tailoring without significant thermal degradation. At longer sintering times, densification was sluggish and had a monotonous increment of 2.5 %/h. However, the grain sizes greatly increased to 8.37 μm, leading isolated pores breaking. Finally, the tailored diffusivity and tortuosity were compared with the calculated results to understand intra- and inter-diffusion. Our finding provides clues to facilitate the diffusion of Li-ion by controlled densification and coarsening behavior in highly densified electrode. [ABSTRACT FROM AUTHOR]

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, Li 12 Si 7 , Li 13 Si 4 , and Li 15 Si 4 . 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, Li 12 Si 7 , Li 13 Si 4 , and Li 15 Si 4 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We study the piezoelectric behavior of metal-doped monolayer MoS 2. Its three-dimensional charge density, work function (WF), and piezoresponse with various metal dopants are theoretically predicted based on density functional theory, and the real-time piezoelectric power of these samples is experimentally verified. Selected p -type metal dopants (Au, Ag, Pd, Pt, and Al) increase the WF of monolayer MoS 2 , affecting electron emission from the MoS 2 surface. The reason is that p -type metal dopants suppress excess electrons and prevent screening effects. A nanogenerator constructed from Au-doped monolayer MoS 2 has been used to explore the possibility of a practical device. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Li metal has been regarded as a promising anode for rechargeable batteries with high energy densities. However, the growth of Li dendrites and severe volume changes in the Li anode still hinder its practical use. Three-dimensional (3D) host structures have recently attracted significant attention as an effective strategy to resolving these problems. Herein, we demonstrate reversible Li metal storage in carbon hosts with strong Li–host interactions derived from metal-organic frameworks (MOFs). The combined experimental and computational modeling studies reveal that galvanically displaced Ag enhances Li–host interactions and the spatial distribution characteristics of Ag play a crucial role in controlling Li storage behavior and reversibility. The atomic Ag clusters trigger the outward growth of Li from the internal pores of the host and enables stable battery cycling, whereas the surface-anchored Ag nanoparticles induce uneven Li plating on the outer surface of the carbon host, resulting in a rapid performance drop. This work provides new insights into the development of advanced host materials for reversible Li anodes by utilizing strong Li–host interactions. [Display omitted] • Metal-organic framework-derived carbon hosts with galvanically introduced Ag. • Lithiophilic Ag enhances the Li–host interaction, inducing preferential Li plating. • Atomic Ag clusters in the carbon host improve the cycling stability. • Surface-anchored Ag particles cause uneven Li plating and a fast performance drop. • The morphology and distribution of lithiophilic Ag determines Li plating behavior. [ABSTRACT FROM AUTHOR]

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 LiNO 3 altering the deposited Li morphology from dendritic to spherical, are widely used as salts for electrolyte. However, the depletion of LiNO 3 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 LiNO 3 for AFBs to circumvent these issues. Experimental and theoretical studies reveal that electrolytes with high-concentration LiNO 3 (up to 2 M) can be prepared by suppressing the agglomeration of LiNO 3 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. Image 1 • A dual-salt electrolyte with high LiNO 3 content is prepared for anode-free batteries. • Enhanced solubility of LiNO 3 is understood via experimental and theoretical studies. • Dendrite-free Li and protective SEI layers are characterized by ex-/in-situ analyses. • Cell containing electrolyte shows improved electrochemical performance. [ABSTRACT FROM AUTHOR]

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. Image 1 • A strategy for improving the cycle performance of NCM cathode is presented. • The particle hardness of NCM can be effectively enhanced by Mg doping. • The enhanced particle hardness of Mg-NCM positively affects the cycle performance. • The formation of microcracks within Mg-NCM can be suppressed during cycles. [ABSTRACT FROM AUTHOR]

The instability of organic/inorganic hybrid perovskite solar cells (PSCs) has motivated the development of the inorganic halide PSCs. However, the representative inorganic CsPbI 3 still suffers from phase instability in ambient air and an unfavorable wide bandgap (1.75 eV), thereby limiting its efficiency. In this study, a binary metal composition of Pb:Sn = 4:6 in CsPb 1-x Sn x I 3 is found to stabilize the cubic CsPbI 3 phase and reduce its bandgap. Based on the parental CsPb 0.4 Sn 0.6 I 3 , compositional engineering is further conducted for CsPb 0.4 Sn 0.6 I 3-y Br y perovskites. After introducing a suitable Br content (y = 0.6), there are remarkable improvements in the crystalline quality and a denser morphology in the perovskite films. Furthermore, in the novel inorganic CsPb 0.4 Sn 0.6 I 2.4 Br 0.6 perovskite, trap-assisted recombination is effectively suppressed, with a desirable narrow bandgap of 1.35 eV. As a result, the corresponding PSC delivered an unprecedented efficiency of 12.34%, which is the highest among the inorganic Sn-rich (Sn > 50%) PSCs reported to date. Additionally, the unencapsulated PSC demonstrates impressive long-term air stability, which exceeds the performance of 100% Pb-based inorganic CsPbI 3 and/or CsPbI 2 Br PSCs reported. This near-infrared absorbing (~930 nm) inorganic PSC with exceptional efficiency, durability and Pb-reduction generates a promising route for further progress of perovskite-based photovoltaics. Image 1 • All-inorganic CsPbI 3 suffers from phase instability, wide bandgap, and toxic-Pb. • The partial Pb-replacement by Sn (x = 0.6) stabilizes the cubic CsPbI 3 and reduces bandgap. • The suitable Br addition suppresses trap-assisted recombination of CsPb 0.4 Sn 0.6 I 3 with a narrow bandgap of 1.35 eV. • A record efficiency of 12.34% for inorganic Sn-rich perovskite solar cell is demonstrated based on CsPb 0.4 Sn 0.6 I 2.4 Br 0.6. [ABSTRACT FROM AUTHOR]

The true potential of Mg–S batteries is not yet realized despite its great advantages in material cost and safety. This is due to the lethargic reaction kinetics involved in the dissociation of Mg polysulfide (MgPS) on the cathode. Herein, we propose nitrogen–doped mesoporous carbon (N d MC) materials with suitable nitrogen content and surface moieties that can be utilized as catalytic hosts to enhance polysulfide fragmentation and electron access to the redox active sites in Mg–S batteries. In controlled N d MC, the surface nitrogen atoms located at the pyridinic positions can strongly bind MgPS and accelerate the reduction of MgPS to MgS, while the graphitic wall structure facilitates facile electron transport to the reaction sites. This synergic effect enables the composite electrode made of tuned N d MC and sulfur to exhibit an enhanced reversible capacity and good cycling capacity retention in Mg–S batteries. This study offers a new strategy for improving the performance of Mg–S batteries by fine-tuning the structural properties of the carbon hosts. [Display omitted] • N-doped graphitic mesoporous carbon is utilized as a host for S 8 imbibition. • Suitable surface moiety and wall structure of carbon host is proposed. • The pyridinic-N stronly binds MgPS and accelerates its dissociation. • Synergic effect enables an enhanced performance for Mg–S batteries. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Li dendrite growth in Li-metal batteries was probed using a finite element method. • The effects of natural and artificial SEIs on Li growth morphology were studied. • Nonuniform current density at electrolyte-electrode interface caused dendrite growth. • Dendrite growth was suppressed by a high-ionic-conductivity artificial SEI. • The results help secure the stable cycling of Li-metal anodes in Li-metal batteries. [ABSTRACT FROM AUTHOR]