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Large-scale stationary energy storage urgently demands to develop rechargeable batteries with low cost, high energy density, and enhanced cycling stability. Beyond conventional Li-ion batteries, secondary Li-I2 batteries based on the conversion reaction mechanism is considered as a promising next-generation energy storage device. However, Li-I2 batteries also suffer shuttle effect caused by the high solubility of iodine in the organic electrolyte. A first-principles approach is employed to probe the effect of I2 molecules on corroding the metallic Li anode surface. It is found that the I2 molecule always tends to dissociate to two I atoms on the Li surface. Electrons in the metallic substrate spontaneously migrate to I atoms, resulting in the self-discharge. According to the ab-initio molecular dynamics simulation, the metallic Li surface can be oxidized to LiI species. LiI species cannot binding to the metallic substrate strongly and will be exfoliated easily, leading to the loss of active materials and irreversible capacity fade. According to the present simulation, LiNO3 additive can also prevent the Li surface from the iodization corrosion. The NO3 - group can completely dissociate and penetrate into the Li substrate, result in forming a protective ternary compound layer. This layer can provide a strong affinity to LiI species, leading to alleviating the loss of active materials. Beyond LiNO3 additive, using N-doped graphene is another strategy to improve the battery performance. The N dopant can provide a strong attraction to trap I2 molecules. In addition, the N heteroatom can shift the Fermi energy level above the pi-antibonding states, which can enhance the reduction and dissociation of the I2 molecule.

The development of electric vehicles (EVs) and stationary energy storage demands rechargeable batteries with improved electrochemical performance. The lithium-sulfur (Li-S) battery is considered as the competitive candidate to replace the conventional Li-ion batteries based on the intercalation mechanism in the near future because the Li-S system can deliver a high energy density of ~2600 Wh/kg with low cost.1-3 The crucial challenge for commercializing Li-S batteries is the shuttle effect caused by the dissolution and migration of polysulfides (PSs), which can corrode metallic Li anode and result in the irreversible capacity loss. To prohibit the shuttle effect, S particles, even smaller S2-4 molecules, are confined in nanopores for trapping PSs.4-8 However, the lithiation of the sulfur active material always suffers from enormous volume expansion, and resulting mechanical degradation of the host material.9 Using Li2S to fabricate the Li-S battery cathode may be a promising approach to improve the battery performance.10 Previous studies on Li-O2 batteries showed that the amorphous Li2O2 has faster charge transfer kinetics than the crystalline Li2O2.11, 12 The charge transport mechanism in amorphous Li2S is not clearly understood. According to our first-principles calculations, the formation energies of charged defects in the amorphous Li2S is lower than those in the crystalline phase. Given that the charged defects are charge carriers in Li2S, the cathode fabricated by amorphous Li2S is expected to exhibit faster kinetics. Also, we investigate the delithiation process of ultra-small Li2S nanoparticle. It is found that the polaron as the charge carrier can even form in the ultra-small nanoparticle. Although the overall delithiation process can be considered as an oxidization process, local reduction reactions and the disproportionation reaction are observed in intermediate products. The final charging product can even be a cyclo-S10 ring. This study is expected to provide new insight into designing nanostructured active materials for Li-S batteries. References Yin, Y.-X.; Xin, S.; Guo, Y.-G.; Wan, L.-J. Angewandte Chemie-International Edition 2013, 52, (50), 13186-13200. Son, Y.; Lee, J.-S.; Son, Y.; Jang, J.-H.; Cho, J. Advanced Energy Materials 2015, 5, (16). Pang, Q.; Liang, X.; Kwok, C. Y.; Nazar, L. F. Nature Energy 2016, 1. Yang, Y.; Zheng, G.; Cui, Y. Chemical Society Reviews 2013, 42, (7), 3018-3032. Chen, H.; Shen, Y.; Wang, C.; Hu, C.; Lu, W.; Wu, X.; Chen, L. Journal of The Electrochemical Society 2018, 165, (1), A6034-A6042. Liu, Z.; Mukherjee, P. P. Acs Applied Materials & Interfaces 2017, 9, (6), 5263-5271. Liu, Z.; Balbuena, P. B.; Mukherjee, P. P. Journal of Physical Chemistry Letters 2017, 8, (7), 1324-1330. Liu, Z.; Balbuena, P. B.; Mukherjee, P. P. Journal of Physical Chemistry C 2017, 121, (32), 17169-17175. Barai, P.; Mistry, A.; Mukherjee, P. P. Extreme Mechanics Letters 2016, 9, 359-70. Hu, C.; Chen, H.; Xie, Y.; Fang, L.; Fang, J.; Xu, J.; Zhao, H.; Zhang, J. Journal of Materials Chemistry A 2016, 4, (47), 18284-18288. Tian, F.; Radin, M. D.; Siegel, D. J. Chemistry of Materials 2014, 26, (9), 2952-2959. Zhang, Y. L.; Cui, Q. H.; Zhang, X. M.; McKee, W. C.; Xu, Y.; Ling, S. G.; Li, H.; Zhong, G. M.; Yang, Y.; Peng, Z. Q. Angewandte Chemie-International Edition 2016, 55, (36), 10717-10721. Figure 1

Lithium-ion batteries are poised to play an important role in the push for electric vehicles. Electroplating and possible dendritic growth, however, have been a safety concern. Non-uniform electrodeposition and subsequent growth may cause short circuit. Apart from catastrophic failure, Li plating results in the battery performance decay as well. There is a need for a better understanding of the factors that are most critical in the nucleation and growth of Li electrodeposition and the morphology evolution thereof. The metal ion reaches the electrode surface where it is reduced. The metal atom can thereafter diffuse inside the bulk electrode or aggregate on the surface under some specific set of conditions and form a variety of structures on the electrode surface, like small islands, uniform film, mossy or filament like structure or dendrite (as schematically shown in Figure 1). Physicochemical determinants affecting electrodeposition include the adsorption energy of metal atom on electrode surface, diffusion barrier for metal atom in the bulk electrode compared to that on the electrode surface, the crystallographic nature of the electrode surface, the strength of cohesive metal-metal interaction. Beyond the nature of the electrode material, the operating temperature, current density and applied potential can also affect the electrodeposition rate, which consequently control the morphology evolution. In this study, a mesoscale interfacial modeling and analysis is presented in order to investigate the lithium electrodeposition regimes and morphology evolution. Figure 1

In the field of battery technology, the lithium-sulfur battery has been widely pursued due to high energy density and high theoretical capacity that can satisfy viability thresholds for electric vehicles. However, this elusive technology remains in the research sector due to a wealth of engineering challenges resulting from the complex chalcogenide electrochemistry. The most infamous challenge remains the polysulfide shuttle effect, in which lithium polysulfide intermediates are produced as elemental sulfur (S8) is reduced to lithium sulfide (Li2S) during the discharge cycle. Since the higher order polysulfides are soluble in organic electrolyte, battery cycling can result in dissolution of the cathode, dendrite formation upon a lithium metal anode, and introduce impedance via electrode passivation. This can ultimately cause rapid capacity fade and unstable Coulombic efficiency. This work presents a novel carbon-sulfur composite, utilizing a cost-effective, bimodal-porosity carbon substrate and a sonochemical sulfur loading technique to improve mono-dispersity in sulfur distribution. The cavity-rich carbon substrate, appropriately named carbon compartments, is synthesized through a single step heating process of commercial wheat flour. The surface area and bi-modal porosity of the carbon compartments enable high sulfur loading (ca. 70 %-wt.). Optimization of a novel fluorinated-electrolyte demonstrates radical improvement in columbic efficiency and cycling stability of the carbon-sulfur composite. The demonstrated Li-S cathode has shown stable half-cell performance (ca. 750 mAh g-1) and columbic efficiency (> 96 %) for all cycles at a current density of 28 mA g-1. Further analysis using in-depth multi-scale modeling describes the electrochemical performance of the composite. Density functional theory and ab initio molecular dynamics characterize the development and behavior of sulfur-containing compounds at the electrolyte-composite surface. Stochastic modeling of the composite microstructure describes electrochemical and physical consequences of polysulfide precipitation. This multi-scale model provides fundamental insight into the mechanisms concerning the role of carbon morphology in the polysulfide shuttle phenomenon.

The lithium-sulfur battery is a strong contender among the beyond Li-ion chemistries due to its superior capacity and energy density as compared to the conventional Li-ion cells. However, experimental evidences suggest that even the first discharge capacity is appreciably lower than the theoretical limit. This non-ideality is usually associated with the so-called “polysulfide shuttle effect”. On the cathode side, solid sulfur dissolves in the electrolyte and undergoes successive reduction to different intermediate and reduced-order sulfide ions. Due to the underlying potential and concentration gradients, these negative ions travel toward the anode and chemically oxidize the lithium metal, while being reduced simultaneously. Theoretical capacity is achieved when sulfur undergoes complete electrochemical reduction; hence the above chemical reaction(s) limit the available capacity. Lithium sulfide (Li2S) is the final discharge product which forms when the ionic product exceeds the solubility limit. This can passivate the surface, block the porous structure and may lead to the reacting species starvation in the cathode. The shuttle effect is a resultant manifestation of these coupled phenomena. In this work, a computational study is presented in order to quantify the influence of shuttle effect on the Li-S cell capacity. The model correlates concentration evolution and microstructural changes with cell performance. Based on this understanding, electrode modifications such as, cathode coating and microstructure properties are studied in order to fundamentally understand the deleterious influence of the “shuttle effect” on cell performance. Figure 1

Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density [1-6]. A typical Li-S battery operation includes multi-step electrochemical reactions and transport phenomena relevant to the “internal shuttle effect”. The insoluble final product, such as Li2S, can passivate the active cathode surface, block mass transfer channels and induce mechanical degradation, all of which negatively impact the cell performance. Each of these phenomena takes place at different spatial and temporal scales which necessitates a mesoscale approach to understand the implications of physicochemical coupling. In this regard, a coupled mesoscale model has been developed in order to study physicochemical interactions in the cathode microstructure. At the interface level, the mechanism of chemical interactions between discharge products and cathode surface is fundamentally investigated. The growth rates of precipitation thickness and coverage are predicted. At the cathode microstructure level, the surface passivation and pore blockage induced by Li2S precipitation are systematically studied. At the cell level, the mechanisms of discharge capacity loss are revealed. In summary, this mesoscale modeling framework can be employed to quantify the capacity loss due to the internal shuttle effect and other electrochemical degradation mechanisms and understand the effect of cathode microstructure (i. e. sulfur loading, specific surface area, pore size distribution) on the electrochemical performance. Acknowledgement: Financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, grant DE-EE0006832 (Program manager: Tien Duong) is gratefully acknowledged. References: P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, Nat. Mater., 11(1), 19-29 (2012). F. Y. Fan, W. C. Carter, and Y. M. Chiang, Adv. Matter., 27, 5203-5209 (2015) R. Cao, W. Xu, D. Lv, J. Xiao, and J. G. Zhang, Adv. Energy Matter., 5, 1402273 (2015) Y. X. Yin, S. Xin, Y. G. Guo, and L. J. Wan, Angew. Chem., 52(50), 13186-13200 (2013) Y. Yang, G. Y. Zheng, and Y. Cui, Chem. Soc. Rev., 42(7), 3018-3032 (2013). Z. Liu, D. Hubble, P. B. Balbuena, and P. P. Mukherjee, Phys. Chem. Chem. Phys., 17, 9032 (2015). Figure 1

Energy storage, such as lithium-ion batteries (LIBs), is key enabler for grid energy storage and vehicle electrification. The electrode microstructure, which is affected by processing scheme, plays an important role in determining the electrode property and performance.1-5In the multiphase electrode slurry, physicochemical interactions affect the assembly of active material and conductive additive particles. Additionally, the pattern of nanoparticle assembly is also affected by the solvent evaporation rate. Polymer-mediated nanoparticle assembly can be a promising method to control a composite microstructure.6 However, there are only a few studies focusing on the effect of binder interaction (such as binder molecular weight) on the electrode microstructure formation and the relative performance.7, 8 In the present study, we developed a mesoscale model accompanied by stochastic dynamics simulation to illustrate the influence of binder interaction and evaporation on microstructures during the electrode processing. Present simulations demonstrate that the lower drying temperature can produce electrode films with micropores as shown in Figs. 1 (a) ~ (c). The depth of micropores tends to increase as binder length (L) increases. Drying temperature affects binder distribution along thickness direction as shown in Fig. 1 (d). The lower drying temperature reduces the fraction of on-surface binder. Additionally, binder length also affects the binder distribution. It can be seen in Fig. 1 (d), that an increase of binder length is beneficial for keep high volume fraction of binder in the film which has implication in better mechanical stability of the electrode film. Refernces 1. J. Li, B. L. Armstrong, J. Kiggans, C. Daniel, and D. L. Wood III, Langmuir, 28 (8), 3783-3790 (2012). 2. H. Zheng, R. Yang, G. Liu, X. Song, and V. S. Battaglia, The Journal of Physical Chemistry C, 116 (7), 4875-4882 (2012). 3. G. Liu, H. Zheng, S. Kim, Y. Deng, A. Minor, X. Song, and V. Battaglia, J Electrochem Soc, 155 (12), A887-A892 (2008). 4. Z. Liu and P. P. Mukherjee, J Electrochem Soc, 161 (8), E3248-E3258 (2014). 5. Z. Liu, V. Battaglia, and P. P. Mukherjee, Langmuir, 30 (50), 15102-15113 (2014). 6. P. Akcora, H. Liu, S. K. Kumar, J. Moll, Y. Li, B. C. Benicewicz, L. S. Schadler, D. Acehan, A. Z. Panagiotopoulos, V. Pryamitsyn, V. Ganesan, J. Ilavsky, P. Thiyagarajan, R. H. Colby, and J. F. Douglas, Nat Mater, 8 (4), 354-359 (2009). 7. B.-R. Lee and E.-S. Oh, The Journal of Physical Chemistry C, 117 (9), 4404-4409 (2013). 8. N. Tasić, Z. Branković, Z. Marinković-Stanojević, and G. Branković, Science of Sintering, 44 (3), 365-372 (2012). Figure 1

Lithium-sulfur (Li-S) battery is a promising energy storage technology, which offers improved performance in terms of higher energy density and material sustainability owing to the abundance of sulfur (S) as the active material. However, one of the key challenges centers on insoluble discharge product formation in the cathode and concomitant internal shuttle effect [1-5]. The polysulfide (such as Li2S) formation poses a deleterious consequence on the electrode microstructural change, thereby impacting the transport and electrochemical properties and ultimately resulting in capacity fade. In this regard, the cathode architecture plays an important role in determining the Li-S battery performance. A desirable electrode microstructure should effectively deter the dissolution of polysulfide, and facilitate lithium ion transport. This warrants a fundamental understanding of the physicochemical interplay resulting from the underlying microstructure-transport-performance interaction. In this work, a mesoscale computational model, shown schematically in Fig.1, will be presented in order to fundamentally investigate the morphology evolution due to Li2S precipitation and the resulting influence on the electrode microstructural and performance attributes. Acknowledgement: Financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, grant DE-EE0006832 (Program manager: Dr. Tien Duong) is gratefully acknowledged. References: 1. P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, Nat Mater, 11(1), 19-29 (2012). 2. Y. Yang, G. Y. Zheng, and Y. Cui, Chem Soc Rev, 42(7), 3018-3032 (2013). 3. X. Ji, K. T. Lee, and L. F. Nazar, Nat Mater, 8(6), 500-506 (2009). 4. X. Ji, S. Evers, R. Black, and L. F. Nazar, Nat Commun, 2, 325 (2011). 5. Z. Liu, D. Hubble, P. B. Balbuena, and P. P. Mukherjee, Phys Chem Chem Phys, 17, 9032 (2015). Figure 1

Lithium-ion batteries (LIB) are currently considered as the primary choice for electric drive vehicles. The electrode microstructure and composition play an important role in determining the performance of the LIB. To this end, the processing of the multi-phase slurry consisting of active nanoparticles, conductive additives, binder and solvent determines the electrochemical properties and performance of the electrode. Morphology and the size of the active nanoparticles affect the LIB performance due to large active surface area, short diffusion length and fast kinetics. On the contrary, the aggregation of the active nanoparticles might have a detrimental effect. Therefore, fundamental understanding of the aggregation behavior of the active particles in the slurry is of paramount importance. In this regard, the evaporation dynamics of the slurry is a key factor which determines the microstructural heterogeneity of the electrode. The morphology of the aggregated particles is governed by a variety of physicochemical factors such as interaction between nanoparticles, diffusion rate of the nanoparticles and evaporation rate of the solvent. In this work, we present a mesoscale modeling approach in order to investigate the influence of evaporation on active particle assembly in LIB electrode processing. Our mesoscale model is based on a coarse-grain formalism combining lattice gas and kinetic Monte Carlo methodologies. We will present a comprehensive study of the active particle aggregation behavior and resultant influence due to the (1) evaporation rate of the solvent, (2) active particle and binder interaction, and (3) active particle morphology. Figure 1 shows representative aggregation characteristics of different active particle morphology. Reference J. Li, B. L. Armstrong, J. Kiggans, C. Daniel and D. L. Wood, Langmuir, 28, 3783-3790 (2012). J. Li, C. Daniel and D. L. Wood, Journal of Power Sources, 196, 2452-2460 (2011). H. Zheng, R. Yang, G. Liu, X. Song and V. S. Battaglia, Journal of Physical Chemestry C, 116, 4875-4882 (2012). E. Rabani, D. R. Reichman, P. L. Geissler and L.ha E. Brus, Nature, 426, 271-274 (2003).