Lithium-sulfur Cells Research Articles

Ultrafine Co-Species Interspersed g-C3N4 Nanosheets and Graphene as an Efficient Polysulfide Barrier to Enable High Performance Li-S Batteries.

Lithium-sulfur (Li-S) batteries are regarded as one of the promising advanced energy storage systems due to their ultrahigh capacity and energy density. However, their practical applications are still hindered by the serious shuttle effect and sluggish reaction kinetics of soluble lithium polysulfides. Herein, g-C3N4 nanosheets and graphene decorated with an ultrafine Co-species nanodot heterostructure (Co@g-C3N4/G) as separator coatings were designed following a facile approach. Such an interlayer can not only enable effective polysulfide affinity through the physical barrier and chemical binding but also simultaneously have a catalytic effect on polysulfide conversion. Because of these superior merits, the Li-S cells assembled with Co@g-C3N4/G-PP separators matched with the S/KB composites (up to ~70 wt% sulfur in the final cathode) exhibit excellent rate capability and good cyclic stability. A high specific capacity of ~860 mAh g-1 at 2.0 C as well as a capacity-fading rate of only ~0.035% per cycle over 350 cycles at 0.5 C can be achieved. This bifunctional separator can even endow a Li-S cell at a low current density to exhibit excellent cycling capability, with a capacity retention rate of ~88.4% at 0.2 C over 250 cycles. Furthermore, a Li-S cell with a Co@g-C3N4/G-PP separator possesses a stable specific capacity of 785 mAh g-1 at 0.2 C after 150 cycles and a superior capacity retention rate of ~84.6% with a high sulfur loading of ~3.0 mg cm-2. This effective polysulfide-confined separator holds good promise for promoting the further development of high-energy-density Li-S batteries.

A low-self-discharge high-loading polysulfide cathode design for lithium–sulfur cells

A low-self-discharge lithium–sulfur cell with a carbonized electrospun nanofiber substrate attains a long shelf life and stable electrochemistry with a capacity-fade rate of 0.26% per day and a long cycle life of 200 cycles after resting for 90 days.

Integrated high-sulfur-loading polysulfide/carbon cathode in lean-electrolyte cell toward high-energy-density lithium–sulfur cells with stable cyclability

A core–shell polysulfide/carbon cathode demonstrates a lean-electrolyte lithium–sulfur cell with a record low electrolyte-to-sulfur ratio (4–3 μL mg−1) and a high-sulfur-loading cathode with high electrochemical utilization and stability.

Li-S Battery Outlier Detection and Voltage Prediction using Machine Learning

State estimation is essential for enabling battery management systems (BMSs) to monitor, control, and optimize battery performance. The first step toward this is the ability to predict a battery's behavior given its input current and present state. In the early stages of new battery chemistry development, prior to commercialization, lab-fabricated battery cells might be used for characterization and BMS development. Such custom-fabricated batteries are often more prone to anomalies in their cycling behavior, including loss of connectivity and instantaneous internal shorts. The use of battery cycling data containing such anomalies can negatively affect modeling accuracy and system predictability. This paper uses the K-means clustering method to detect outlier patterns in battery cycling, thereby enabling the extraction of sanitized cycling data. A feedforward neural network is then trained to predict battery voltage one step ahead, given the input current and prior voltage history. The paper demonstrates this machine learning approach for cycling data from laboratory-fabricated lithium-sulfur (Li-S) cells. This demonstration highlights both the accuracy of the proposed voltage prediction algorithm and the degree to which the proposed outlier detection algorithm helps improve this accuracy.

Insight into the failure mechanism of large-scale cylindrical lithium-sulphur cells.

Li-S batteries with a sulphur loading content of 5 mg cm-2 were produced as large-scale 18 650 cylindrical cells. We have found that a key failure mode of cylindrical Li-S battery cells is the severe capacity fading during the galvanostatic charge-discharge process due to the corrosion of the electrodes, the electrolyte decomposition, and the severe polysulphide shuttling effect.

Laboratory Setup for Solid-State Battery Pressure Characterization and Control

As high-energy-density solid-state cells approach maturity, battery management systems must be developed to maximize the performance of these cells by monitoring and/or controlling their mechanical stress. This paper describes the design, testing, and control of a lab-scale solid-state battery cell testing system. Solid-state lithium-sulfur cells are characterized under constant volume and constant stress conditions. The testing system also uses axial displacement feedback for mixed volume/stress control and dynamic switching between control modes as a function of state-of-charge and/or charge/discharge conditions.

Electrolessly tin-plated sulfur nanocomposite for practical lean-electrolyte lithium-sulfur cells with a high-loading sulfur cathode.

Lithium-sulfur batteries are among the most promising low-cost, high-energy-density storage devices. The high-capacity sulfur active material undergoes electrochemical conversion between the solid and liquid states. Thus, the comprehensive design of a suitable synthesis method, substrate material, and cathode configuration is essential for developing advanced sulfur cathodes with practical cell design and cell performance parameters. Herein, an electroless plating method is employed to develop a tin-plated sulfur nanocomposite. The nanosized tin plating shell effectively encapsulates a large amount of sulfur; the nanocomposite exhibits excellent high sulfur loading and content (6-10 mg cm-2 and 65-85 wt%, respectively), and the cell based on the nanocomposite exhibits a superior low electrolyte-to-sulfur ratio of 7-4 μL mg-1. In addition to these critical cell design parameters, the tin-plated sulfur nanocomposite attains outstanding electrochemical utilization and stability for 200 cycles under a broad range of cycling rates of C/20-C/2, and additional outstanding cell performance properties in terms of a high areal capacity of 6.3-11.4 mA h cm-2, a high gravimetric capacity of 520-663 mA h g-1, a high energy density of 13-24 mW h cm-2, and a low electrolyte-to-capacity ratio of 3.75 μL mA h-1.

Global Sensitivity Analysis of 0-D Lithium Sulfur Electrochemical Model

This paper examines global parameter sensitivity in a zero-dimensional lithium-sulfur (Li-S) battery model. Li-S batteries are an appealing cell chemistry due to their high theoretical energy density, abundant supply, and low cost. Due to the lack of complete understanding of the underlying working mechanisms for Li-S cells, the development of mathematical models and state estimation is still in its early stages. Model development and parameter Identification are closely associated. Both are essential for developing battery management systems (BMS) in commercialized Li-S powered applications. This paper highlights the parameter Identification challenges associated with Li-S models. Sensitivity analysis helps for parameter Identification by revealing information about parameter relevance and interdependence. Sensitivity analysis also helps in understanding different physical ranges of parameters, and their impact on model performance/response. In this work, we examine global sensitivity analysis (GSA). A key challenge for GSA, especially in Li-S batteries, is a lack of available information in the literature about a-priori distributions of Li-S parameters. This paper aims to elucidate this challenge by comparing GSA under different parameter distributions. Three model parameters are chosen in this analysis, and their sensitivities are compared under three different distributions. We find that, under certain distributions of parameters, relative importance of the parameters shifts.

High-Tap-Density Sulfur Cathodes Made Beyond 400 °C for Lithium–Sulfur Cells with Balanced Gravimetric/Volumetric Energy Densities

Lithium–sulfur cells application is hindered by imbalanced gravimetric/volumetric energy densities (EG/EV) in pouch cells, owing to constraints in cathode engineering/compactness and Li2Sn phase-conversion kinetics. By mimicking ternary-oxide cathodes, a synthetic route beyond 400 °C is proposed to make high-tap-density (maximum 2.12 g cm–3) microsphere cathodes, where sulfur and NiFe2O4 quantum-dot catalysts are sealed in N-rich carbon shells. Conformal silica package proves critical to elevate cathode thermotolerant limit over sulfur sublimation temperature and block sulfuric vapor loss, enabling polymeric carbonization and high sulfur content retention (∼70.3%). The quantum dots and enclosed N-rich carbon help shorten the electrical resistance, anchor Li2Sn molecules, and boost their phase conversions. Such cathodes exhibit high reversible capacities, great sulfur utilization, and cyclic behaviors. Packed pouch cells show balanced EG/EV and good bendability under high sulfur loading and lean-electrolyte conditions. Our strategy may offer new opportunities for other broad electrodes with low pack density and thermal instability challenges.

Orchestrating multiple cobalt compounds via a unique dual-templating design towards enhanced sulfur conversion kinetics

The intrinsic polysulfide shuttling and sluggish redox kinetics plague lithium-sulfur (Li-S) batteries with fast capacity fading and poor rate capability. Doping heteroatoms and embedding polar motifs into carbonaceous materials have been reckoned highly effective to promote both polysulfide trapping and catalytic sulfur conversion. Herein, we report polyaniline (PANi)-derived hierarchical carbon capsule co-doped with Co, S, N, F (MHCC) as the sulfur host, synthesized through a dual-template strategy exploiting Escherichia coli as the primary bio-template and ordered mesoporous silica as the secondary pore-forming template. The resulting capsular composite comprises a hollow core surrounded by a mesoporous shell, expressing a variety of active sites including Co-Nx, Co9S8, and CoF2 that synergistically boost the redox kinetics via strong chemisorption and catalytic effects. The Li-S cell with the sulfur/MHCC cathode delivers a high initial discharge capacity of 1331 mAh g−1 at 0.2 C and a long-term lifespan of 700 cycles at 2 C. Moreover, an areal capacity of 8.2 mAh cm−2 is achieved at a high sulfur loading of 8 mg cm−2. This study paves the way for the deployment of green Li-S batteries based on natural products through hierarchical structure design and catalytic engineering.

ВЛИЯНИЕ СВОЙСТВ УГЛЕРОДНЫХ МАТЕРИАЛОВ НА УДЕЛЬНУЮ ЭНЕРГИЮ И ДЛИТЕЛЬНОСТЬ ЦИКЛИРОВАНИЯ ЛИТИЙ-СЕРНЫХ АККУМУЛЯТОРОВ

The effect of the structure and the specific surface area of carbon materials, contained in positive electrodes, on the peculiarities of cycling of lithium-sulfur cells (the depth of electrochemical reduction of sulfur and lithium polysulfides, the changes in capacity and Coulomb efficiency of cycling) was studied. The studies showed that the depth of electrochemical transformations of sulfur and lithium polysulfides depended not only on the specific surface area of the carbon material contained in positive electrodes, but also on the structure and the surface morphology of the carbon material particles.

Flexible Freestanding Thin Polyethylene Oxide‐Based Film as Artificial Solid–Electrolyte Interface to Protect Lithium Metal in Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) that utilize sulfur and lithium (Li) metal as electrode materials are highly attractive for transportation applications due to their high theoretical gravimetric energy density. However, two major challenges currently impede the commercialization of LSB, which are the formation of Li dendrites and polysulfide shuttling. To mitigate these two effects, a protective film or artificial solid–electrolyte interface (SEI) can be applied directly to the Li‐metal surface. Herein, the preparation of freestanding polyethylene oxide (PEO)‐based films using tape casting as a scalable coating technique is presented. Moreover, the films are applied directly to the Li surface via a solvent‐free method. To demonstrate the suitability of the developed PEO‐based films, the long‐term cycling performance of the lithium–sulfur cells is discussed. It is shown that the cells with the Li‐metal surface protected by PEO‐based films achieve better stability and reproducibility, reaching ≈400 mA h g S−1 after 250 cycles compared to ≈200 mA h g S−1 after 250 cycles for the bare Li‐metal electrode. An extensive postmortem analysis of the Li‐metal electrode surface with scanning electron microscopy is additionally shown, revealing that the PEO‐based artificial SEIs form uniformly with a low level of defect layers at the interface with the Li‐metal electrode, which indicates the creation of a stable SEI.

High-loading polysulfide/cement cathode for the manufacture of dynamically and statically stable lean-electrolyte lithium–sulfur batteries

In order to design lithium-sulfur cells for practical viability in the high-density energy storage, the exploitation of the effective contribution of the large amount of active-material mass to the high specific capacity at a lean-electrolyte condition must be considered. However, this is limited by the insulating nature of solid-state sulfur/sulfide, and the diffusion loss of the liquid-state polysulfides. In this study, Portland cement is adopted as a reinforcement material to design a high-loading polysulfide/cement cathode with sulfur loading and content of 8.64 mg cm−2 and 60 wt%, respectively. The nonporous cement exhibits a high polysulfide-trapping capability and low electrolyte consumption, which enable the high-sulfur-loading cathode to achieve record low electrolyte-to-sulfur ratios of 7–3 μL mg−1, with high gravimetric capacity and areal capacity of the cathode (i.e., 768 mA h g−1 and 11.06 mA h cm−2, respectively) and dynamically/statically electrochemical stability with 90% capacity retention after 100 cycles and a 1-month rest.

An Experimentally Parameterized Equivalent Circuit Model of a Solid-State Lithium-Sulfur Battery

This paper presents and parameterizes an equivalent circuit model of an all-solid-state lithium-sulfur battery cell, filling a gap in the literature associated with low computational intensity models suitable for embedded battery management applications. The paper addresses this gap by parameterizing a three-state equivalent circuit model using experimental pulse power characterization data from a laboratory-fabricated lithium-sulfur cell. The cell is mechanically loaded during electrical cycling to achieve maximum ionic conductivity and consistent capacity. A nested combination of linear and nonlinear least squares regression is used to estimate the model parameters. The model captures slow cycling and fast pulse charge/discharge dynamics within 34 mV RMS error. The series resistance changes significantly at high/low states of charge and low C-rates. A sensitivity analysis determines that accurately modeling the dependence of resistance on C-rate and state of charge is important for model fidelity.

Multi-functional yolk-shell structured materials and their applications for high-performance lithium ion battery and lithium sulfur battery

Lithium-ion (Li-ion) and lithium-sulfur (Li-S) cells have aroused widespread concern regarding as prospective compositions for most commonly energy storage devices because of high specific capacity and excellent energy density. But some weaknesses still exist such as high cost and low theoretical specific capacity of Li-ion cell, which is difficult to meet people's increasing demand for high energy density. And unsatisfactory conductivity and notorious “shuttle effect” of lithium polysulfides (LiPSs) for Li-S cell, which will affect the commercialization. In various structures of battery materials, yolk-shell structured materials, possessing hollow shell and interior core, show outstanding applied potential for the cells because of having appropriate pore sizes, abundant active sites, prevented aggregation of active materials, accommodated volume expansions and more facilitated channels for electrons and Li+ transportation and functional groups to effectively adsorb LiPSs. Thus many novel yolk-shell structured materials are applied to cell materials to resolve the problems mentioned above. In this review, recent progresses on yolk-shell structured materials used in the cells including their preparation methods, geometric morphology design, action mechanisms in enhancing electrochemical performances and safety are generalized. Then we have a sufficient discussion for yolk-shell structured materials in the cells and build structure-function relationships between structured materials and cell performances. At last, some challenges and suggestions about their preparations, functional modifications and actual applications of yolk-shell structured materials in the cells are summarized. We hope the review can attract more people's attention and conduct more researches on yolk-shell structured materials for various secondary batteries.

Design of spherical TiN/Nb4N5 heterostructure as bifunctional adsorption/catalytic material for lithium sulfur batteries

Lithium sulfur (Li-S) battery is the typical representative of the new generation secondary batteries, but its practical application is greatly hindered by the shuttle effect of lithium polysulfides (LiPSs) and sluggish electrochemical reaction kinetics. In this work, a spherical TiN/Nb 4 N 5 heterostructure is produced by nitridation of TiNb 2 O 7 microsphere and then used as an adsorption and catalytic material to fabricate modified polypropylene separator in Li-S batteries. Visual adsorption tests show that the TiN/Nb 4 N 5 heterostructure has better adsorption capacity of LiPSs than that of TiNb 2 O 7 microsphere precursor. The TiN/Nb 4 N 5 heterostructure also exhibits superior catalytic performance to accelerate the redox reaction kinetics of LiPSs conversion. The Li-S cell assembled with TiN/Nb 4 N 5 modified separator can deliver an initial discharge capacity of 917 mAh g -1 at 0.2 C, and a reversible capacity of 663.2 mAh g -1 after 200 cycles, higher than the cell assembled with TiNb 2 O 7 modified separator (555.4 mAh g -1 ) and pristine separator (385.1 mAh g -1 ). In short, this work provides a simple synthetic method to obtain a TiN/Nb 4 N 5 heterostructure with enhanced electrochemical performance of Li-S batteries. • TiN/Nb 4 N 5 heterostructure is synthesized by nitriding TiNb 2 O 7 microsphere; • TiN/Nb 4 N 5 heterostructure has strong adsorptive/catalytic conversion capability for polysulfides; • Li-S cell assembled with TiN/Nb 4 N 5 modified separator shows excellent electrochemical performance.

Molecular polysulfide-scavenging sulfurized–triazine polymer enable high energy density Li-S battery under lean electrolyte

Lean electrolyte with low electrolyte/sulfur (E/S) ratio is a crucial step for the advancement of high energy density lithium-sulfur (Li-S) batteries. However, the low E/S introduces serious kinetics issues where the cell can only last for a few cycles. Here, aiming to overcome the operational constraints, we rationally design covalently grafted sulfurized–triazine polymeric (STP) cathodes housing > 60% sulfur capable of cycling under lean electrolyte. As-developed STP cathodes at lean E/S: 4, 6, and 8 µL mgs–1 show improved sulfur reactivity and cycle-life, delivering 522, 574, and 601 mAh gs–1 at the 200th cycle. Further, at sulfur loading 5 mg cm–2 with E/S: 6 µL mgs–1, the Li-S cell exhibits 588 mAh gs–1 capacity with 93% Coulombic efficiency. Experimental and modeling tools reveal that the triazine cathode support allows covalent grafting and good wettability beneficial for facile Li ion and sulfur reactivity. As a result, the generated polysulfide is concurrently regulated in a molecularly fashion via bulk-immobilization involving abundant pyridinic–N and pyrrolic–N to confine within the electrode. Extending to construct a practical lean Li-S pouch cell with sulfur, lithium, and electrolyte accounting 53.7% cell's mass delivers an energy density of 371 Wh kg–1 that is par to the predicted values under lean electrolyte. Our study provides an invaluable resource in a potential way and future directions for developing practical high energy Li-S batteries.

Влияние поверхностной ёмкости положительных электродов на длительность циклирования литий-серных аккумуляторов

The effect of sulfur content in positive electrodes (the surface capacity of sulfur electrodes) on the characteristics (such as the depth of sulfur electrochemical reduction, changes in capacitance and Coulomb efficiency during cycle life) of lithium-sulfur cells with electrolytes based on sulfolane was studied. It was shown that the reason for the capacitance decrease of the lithium-sulfur cells at the early stage of its cycle life is the displacement of sulfur of the porous positive electrode from the rear regions into the front ones. It was established that in order to achieve the maximum possible specific energy of the lithium-sulfur batteries with the electrolytes based on sulfolane, the surface capacitance of the positive electrodes should be in the range of 2-3 mA·h/cm2.

Asymmetric N-coordinated iron single-atom catalysts supported on graphitic carbon for polysulfide conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with extremely high theoretical energy density are expected to be the next-generation energy storage systems. However, the electrochemical performance of Li-S batteries is still restricted by the shuttle effect of lithium polysulfides (LiPSs) resulting from their sluggish conversion kinetics. Herein, we demonstrated a coordination-confinement-pyrolysis strategy to fabricate iron single-atom catalysts (Fe SACs) supported on graphitic carbon nanocapsules (GCNC) by using imine (-RC = N-)-enriched polymer as precursors, aiming at suppressing the shuttle effect in Li-S batteries via simultaneously enhancing LiPSs confinement and catalytic conversion. The in-depth experiment investigations have revealed that the as-obtained N-doped carbon nanocapsules with ample hollow channels and large specific surface area (SSA) enable efficient adsorption and confinement for LiPS intermediates. Further, the isolated Fe SACs anchored on highly conductive graphitic carbon frameworks show an asymmetric N-coordinated active moiety (Fe-N5) that ensures fast redox kinetics of LiPSs and solid Li2S/Li2S2 products. As a result, the Li-S cell with a functional separator modified by the Fe-N5/GCNC exhibits a much-increased specific capacity of 1125 mAh/g at 0.1 C, excellent rate capability of 627 mAh/g at 2 C, and remarkable long-term cycling stability with a low capacity decay of 0.0386 % per cycle upon 1000 cycles. This work presents a useful strategy to fabricate high-activity SACs coupled with hollow graphitic carbon frameworks and to accelerate the catalytic conversion kinetics of LiPS intermediates for high-performance Li-S batteries.

Lithium Sulfide Batteries: Addressing the Kinetic Barriers and High First Charge Overpotential.

Ever-rising global energy demands and the desperate need for green energy inevitably require next-generation energy storage systems. Lithium-sulfur (Li-S) batteries are a promising candidate as their conversion redox reaction offers superior high energy capacity and lower costs as compared to current intercalation type lithium-ion technology. Li2S with a prelithiated cathode can, in principle, capture the high capacity while reducing some of the issues in conventional Li-S cells utilizing metallic lithium anodes and elemental sulfur cathodes. However, it also faces its own set of technical issues, including the insulating nature and the notorious shuttling effect that plagues the Li-S system. In addition, the high activation potential also hinders its electrochemical performance. To lower the high conversion barrier, key parameters of charge/ion transfer kinetics have to be considered in improving the reaction kinetics. This Review of lithium sulfide batteries examines the recent progress in this rapidly growing field, beginning with the revisiting of the fundamentals, working principles, and challenges of the Li-S system as well as the Li2S cathode. The strategies adopted and methods that have been devised to overcome these issues are discussed in detail, by focusing on the synthesis of the nanoparticles, the structuring of the functional matrixes, and the promoting of the reaction kinetics through additives, aiming at providing a broad view of paths that can lead to a market viable Li2S cathode in the near future.