Li-S batteries are promising alternatives due to their proven increased gravimetric capacity compared to Li-ion batteries. However, their development is hindered by many technical issues, one of the most challenging being the dissolution and shuttle of polysulfide species, which causes irreversible loss of cathode material leading to rapid capacity fading. Among the possible strategies to mitigate this effect, the choice of suitable solvents is easy to implement and has large room for improvement. To guide this quest, computationally-aided optimization is a powerful tool, provided that suitable descriptors are used to screen possible solvents. In this work, molecular dynamics simulations were performed for a typical lithium polysulfide Li2S6 dissolved in different solvents. Diffusion coefficients and their related activation energies were calculated, and thermodynamic properties like solvation energies and entropies were also evaluated. Additionally, a theoretical framework for computing the relative solubilities of lithium polysulfide is provided. For the set of solvents considered, we found that the system's viscosity appears as an important descriptor to correlate with different system properties. The donor number of the solvent also appears as a valid descriptor, for low-viscosity solvents. In general, it was found that higher viscosity solvents lead to lower diffusion rates and higher polysulfide solubility. These results suggest that the optimal choice to reduce the shuttle is a trade-off between high-viscosity solvents to reduce polysulfide diffusion and low-viscosity solvents to reduce its solubility, which could be further improved by properly tuning the donor number.

In this work, we evaluate the reliability of a recently developed model for estimating kinetic parameters for different materials used in lithium-ion batteries. This model considers non-interacting Li-ions being inserted under constant current conditions, assuming finite diffusion inside the particles and charge transfer limitations at the electrode/electrolyte interface. Here, we are interested in evaluating the effect of neglecting the particular insertion isotherms of the materials on the fittings made for diffusion coefficients and electrochemical rate constants. With this purpose, equilibrium isotherms of different materials are extracted from an open-access Li-ion battery parameter database. This thermodynamic information is introduced into the model to perform simulations and obtain the maximum state of charge reached as a function of C-rate. This data is then fitted to the model without interactions using our open-source Python package. The fitted values obtained for the diffusion coefficients are finally compared with the reference values from the database to estimate the accuracy of the model for different real-world systems.

In this work we have investigated the effect of slurry pH on the lithiation mechanism of silicon nanoparticle (SiNP) anodes in lithium-ion batteries. To this end, we have used a combination of lithium (7Li) and silicon (29Si) magic angle spinning nuclear magnetic resonance (MAS NMR), density functional theory (DFT), and electrochemical charge–discharge cycling. The NMR results show that different lithiation mechanisms are present depending on the pH. An acidic slurry facilitates the lithiation of SiNP, whereas a basic slurry oxidises the SiNP to form a shell of SiO/SiO2, which must be cracked before Si lithiation becomes relevant. In a basic slurry, the leading process during the first cycle is the reaction of Li+ and SiO/SiO2 to form lithium silicates. Consequently, this intermediate step leads to a greater capacity loss in the basic media than in the acidic one.

Silicon anodes hold great promise for next-generation Li-ion batteries. The main obstacle to exploiting their high performance is the challenge of linking experimental observations to atomic structures due to the amorphous nature of Li-Si alloys. We unveil the atomistic-scale structures of amorphous Li-Si using our recently developed density functional tight-binding model. Our claim is supported by the successful reproduction of experimental X-ray pair distribution functions, NMR and M\"ossbauer spectra using simple nearest neighbors models. The predicted structures are publicly available.

In this work, we develop a new tool to provide a diagnostic map for alkali-ion intercalation materials under galvanostatic conditions. These representations, stated in the form of capacity level diagrams, are built from hundreds of numerical simulations representing different experimental conditions, summarized in two dimensionless parameters: a kinetic parameter denominated Ξ and a finite diffusion parameter l. To lay the theoretical and methodological foundations, a general model is used here. This model can be adapted to the thermodynamic and kinetic framework of specific systems. We provide two representative examples.

The Cover Feature represents a 3-D plot of the loading status of a battery particle material as a function of two galvanostatic dimensionless parameters l and Ξ that depend on the physical properties of the material (particle size d, diffusion coefficient D, intercalation rate constant k0) and the loading rate Cr. More information can be found in the Research Article by Ezequiel P. M. Leiva and co-workers.

The present study focuses on the effect of using different aqueous based binders, prepared in basic and acidic medium, on the electrochemical performance of silicon nanoparticle-based anodes. The slurries were prepared with sodium alginate (ALG), polyacrylic acid (PAA) and sodium carboxymethylcellulose (CMC) at different pHs (3.00 and 10.00), and compared with the standard PVDF binder. In order to analyze the interactions present in each case thermogravimetric analysis, rheological characterization, SEM, and XPS studies were carried out. The impact of the viscosity and different functional groups present in each polymer on the electrochemical perfor-mance was also thoroughly evaluated.

A sustainable cow hair-based biocarbon/sulfur composite was prepared via a melt-diffusion process and used as cathode for lithium-sulfur (Li-S) batteries, exhibiting high capacity, good rate capability, and excellent cyclability. The effect of the activation process during the formation of the biocarbon was deeply analyzed by thermogravimetry, N-2 adsorption, X-ray photoelectron spectroscopy, scanning and transmission electron microcopy, among others. A correlation between the composition and the surface area with the electrochemical performance was found. The best results were obtained using an activated sample and composite electrode containing 73 wt % sulfur, which present an initial discharge capacity of around 1200 mAh/g and 799 mAh/g after 100 cycles at a current density of 0.1 A/g. Moreover, a specific capacity of similar to 701 mAh/g was measured at 1 C. The great electrochemical performance of this electrode in Li-S batteries is attributed to the porous carbon structure. Taking into account that hair is one of the major waste produced in the leather sector, this work presents a promising approach to reuse this material by giving it added value through the preparation of carbon/sulfur composites for high-performance Li-S batteries.

We present a coarse-grained carbon black model consisting of nanoparticles with sizes comparable to that found in experimental samples. The parameters of the interaction potential are estimated from surface energy values. The relaxed geometry of the systems is obtained by simulated annealing. The pore size distribution (PSD) of the calculated porous materials is presented. The results of the simulations are in good agreement with PSD obtained from experimental measurements reported in the literature. This work paves the way towards realistic microstructural models of carbonaceous porous materials.

Composite polymer electrolytes (CPE) are a very promising strategy for using lithium metal anodes safely. These electrolytes are formed by polymeric matrices in which ceramic nanoparticles are incorporated to modify their mechanical and conduction properties. In this work a methacrylate-based polymer matrix containing 63 wt% of ZrO2 nanoparticles (NPs) was prepared and tested as electrolyte for lithium metal batteries. The prepared CPE shows a higher ionic conductivity than the polymer matrix without ZrO2 NPs and a higher lithium transport number than Celgard with liquid electrolyte and stabilizes the processes of deposition-dissolution of lithium with respect to the reference cell, thus prolonging the cycling time without short circuits. Finally, the compatibility of the CPE with a LiFePO4 cathode was verified, achieving a stable cycling at 1.0 C and at ambient temperature, with an impressive capacity of 140.18 mAh g(-1) even after 250 cycles. (C) 2021 Elsevier Ltd. All rights reserved.

Lithium-sulfur (Li-S) batteries are seen as a promising technology to satisfy the increasing demand for high energy density batteries for portable electronic devices and electric vehicles. However, they present different well-known drawbacks such as the solubility, deposition, and shuttle effect of lithium polysulfides that limit their practical applications. Additives or mediators can play a critical role to solve these problems. Tris (2-carboxyethyl) phosphine (TCEP) is mostly used in biological applications as a shear agent to cut higher-order polysulfides (Li2Sx , x>6) to low-order polysulfide (Li2Sx , x<4). Using this property, we incorporate TCEP in the cathode’s composition and test their electrochemical performance compared with cathodes without TCEP. When phosphine is present, not only a decrease in the energy barrier for the reduction reaction, but also a higher specific capacity is observed. The role of TCEP as a critical component is deeply studied by XPS and discussed herein.

Infiltration of sulfur into microporous carbon enables the use of carbonate-based electrolytes due to the formation of a compact cathode electrolyte interface. Passivation of the surface prevents direct contact between electrolyte and sulfur. Consequently, the mechanism of sulfur conversion is changed to a quasi-solid-state mechanism with a single sloping plateau related to sulfur conversion in the narrow pores. The narrow size of pores determines the overall pore volume of the microporous carbon and with that sulfur maximum ratio within carbon-sulfur composite. Additionally, a confinement of sulfur in the narrow pores has an impact on sulfur conversion into Li 2 S 2 /Li 2 S due to volumetric changes when sulfur is reduced. In this work, we show that the degree of the conversion of sulfur into end discharge products can be extended by lowering the cutoff potential during the discharge process. A higher degree of conversion process causes cracks in the carbon structure enabling a significant increase of capacity while a compact and flexible passivation layer prevents contact with the electrolyte. Quasi solid-state reduction of sulfur is kinetically more favored compared to the consequent oxidation process. Electrochemical impedance spectroscopy measurements show diffusional restrictions in the lower part of the discharge curve that can be correlated with hindered transport due to volumetric changes caused by the reduction of sulfur into Li 2 S 2 /Li 2 S.

Understanding and optimizing single particle rate behaviour is normally challenging in composite commercial lithium-ion electrode materials. In this regard, recent experimental research has addressed the electrochemical Li-ion intercalation in individual nanosized particles. Here, we present a thorough theoretical analysis of the Li+ intercalation voltammetric behaviour in single nano/micro-scale LiMn2O4 (LMO) particles, incorporating realistic interactions between inserted ions. A transparent 2-dimensional zone diagram representation of kinetic-diffusional behaviour is provided that allows rapid diagnosis of the reversibility and diffusion length of the system depending on the particle geometry. We provide an Excel file where the boundary lines of the zone diagram can be rapidly recalculated by setting input values of the rate constant, k0 and diffusion coefficient,D . The model framework elucidates the heterogeneous behaviour of nanosized particles with similar sizes but different shapes. Hence, we present here an outlook for realistic multiscale modelling of real materials.

Complex materials composed of two and three elements with high Li-ion storage capacity are investigated and tested as lithium-ion battery (LiB) negative electrodes. Namely, anodes containing tin, silicon, and graphite show very good performance because of the large gravimetric and volumetric capacity of silicon and structural support provided by tin and graphite. The performance of the composites during the first cycles was studied using ex situ magic angle spinning (MAS) 7Li Nuclear Magnetic Resonance (NMR), density functional theory (DFT) calculations, and electrochemical techniques. The best performance was obtained for Sn/Si/graphite in a 1 : 1 : 1 proportion, due to an emergent effect of the interaction between Sn and Si. The results suggest a stabilization effect of Sn over Si, providing a physical constraint that prevents Si pulverization. This mechanism ensures good cyclability over more than one hundred cycles, low capacity fading and high specific capacity.

The utilization of low-value, abundant and sustainable biomass materials for high-value energy storage application is remarkable important nowadays. Among the most promising next generation energy storage batteries, we can find lithium-sulfur batteries that have a high theoretical specific capacity and high energy density. In the present article we propose the use of peanut shells, a regional industrial waste of high availability and polluting level, as a source of carbonaceous material for the preparation of sulfur cathode of this kind of batteries. Different carbons were obtained from pyrolysis of peanut shells by changing the conditions of the synthesis, which was performed through acid or basic pre-treatment of the biomass. The effects of these treatments in the physical characteristics of the carbonaceous materials and their performance as cathodes in lithium-sulfur batteries were studied. Chemical treatments of shells before pyrolysis , as well as the post-pyrolysis treatment of the produced carbons have , influence impact on the porosity of the final materials , and therefore on their electrochemical performance. The best electrode carbon was obtained from acid-treated peanut shells (and washed after pyrolysis) obtaining an initial specific capacity of 778 mAh/g with high cycling stability and a coulombic efficiency higher than 95 %. We also compare the performance of the best peanut shells-derived biocarbon with one commercial carbon (Super P). In this work, we study a simple route to develop low-cost carbon materials arising from residual ?? biomass which may extend their use in energy storage applications.

The interaction of polysulfides with oxidized graphene layers containing functional groups (hydroxyl, epoxy and carboxyl groups) is analyzed using first-principles calculations, with the aim of using these structures to prevent polysulfide migration in lithium-sulfur batteries. An estimation of the residence time of the polysulfide on the oxidized surface is made based on transition state theory, with the finding that the studied oxidized graphene surfaces are not good enough candidates to prevent polysulfide migration in lithium-sulfur batteries. Even a value of 1.45 eV of the binding energy of the polysulfide to the surface is not enough to retain polysulfide for an important residence time.

Motivated by the abundant experimental work in the area of Li-ion batteries, in the present work we characterize via computer simulations the structure of Si-Li amorphous alloys in a wide range of compositions. Using a reactive force field we propose a novel accelerated exploration of local minima to obtain amorphous structures close to equilibrium. The features of this system analyzed for different alloy compositions are the partial radial distribution functions g(r), the first and second nearest neighbour coordination numbers and the short-order structure. The complex structure of the second peak of the Si-Li g(r) is elucidated using a cluster-connection analysis.

Nowadays, there is an evident need to improve the current Li-ion battery systems, in order to make them more reliable, durable and safe. Regarding this objective, the application of composite materials -based mainly on the combination of Si, Sn and carbon- appears as a very promising alternative for future anode materials. However, despite the great amount of publications dealing with this topic, there is not a systematic study that allows interpreting and understanding how the combination of these materials affects the electrochemical performance of the anodes prepared with them. In light of this need, in this work we propose a straightforward ball-milling procedure to prepare Sn/Si/graphite composites with different mass proportions of each material. For all compositions, a systematic study was performed in order to determine how each material affects the specific capacity, capacity fading and stability towards a change in loading current. We found that the material prepared with Sn(33)Si(33)C(33)appears to be the most promising one, delivering a reversible capacity of 906.9 mAh g(-1)even after 120 cycles at 0.5 A g(-1), thus encouraging the development of new composites based on these materials for industrial applications.

Lithium (Li) metal has been considered as an important anode candidate to reach more powerful energy storage devices with higher gravimetric and volumetric capacities. Nevertheless, the growth of high surface area lithium (HSAL) and dendrites during the stripping/deposition of Li causes safety concerns and a low cycle life of Li metal batteries. Here, we report the obtained results for protection of metallic lithium surface by using a gel polymer ionic liquid cross-linked by activation with UV radiation (UV-PIL). The UV-PIL protects Li against the constant degradation caused by the formation of unstable lithium metal electrolyte interphase and cell dry out due to continuous electrolyte consumption. We observed retarded growth of dendrites when lithium metal was protected with UV-PIL, and due to the lower ionic conductivity of UV-PIL, some differences of mass transport are present compared to carbonate-based liquid electrolyte. Nevertheless, the UV-PIL@Li negative electrode was successfully applied in a Li-ion battery with a lithium iron phosphate (LFP) positive electrode, showing similar behavior compared to the bare Li surface.

High-power high-density lithium rechargeable batteries are necessary to meet the energy demand of electric vehicles and high-power stationary grids. Here, we present a straightforward method for obtaining carbon nanofibers (CNFs) as a polysulfide barrier in Li-S cells, resulting in a significant increase in cell performance. CNFs were coated both on the separator and on the cathode. The CNF-coated cathode showed a specific capacity of 1010 mA h g−1 after 250 cycles at 0.2 C, with a capacity fading of 0.021% per cycle. In addition, at 1 C, it delivered 946 mA h g−1, thus presenting a fast Li+ transport with a good capacity. This result turns CNFs-coated cathodes into a promising system for obtaining high-performance Li-S cells.