Lithium-sulfur Pouch Cells Research Articles

Improving the electrochemical performance of lithium-sulfur batteries by interface modification with a bifunctional electrolyte additive

Lithium-sulfur (Li-S) batteries with sulfur cathode and lithium anode are considered as a promising candidate in the next generation of high specific energy secondary batteries. However, the scalable application of Li-S batteries is limited by the unstable electrode/electrolyte interfaces. Herein, a novel bifunctional electrolyte additive, trifluoromethane sulfonamide (TFMSA), is introduced to stabilize both electrode/electrolyte interfaces to enhance the electrochemical performance of Li-S batteries. The TFMSA molecule can not only alleviate the passivation of the sulfur cathode surface, but also suppress Li dendrites growth and prevent the lithium anode from the corrosion of polysulfides. As a result, the assembled Li-S battery with TFMSA-containing electrolyte displays excellent long-cycle performance and rate capability. Moreover, the Li||Li symmetric cell using TFMSA electrolyte can stably cycle for 1200 h at 1 mA cm−2 and 1 mAh cm−2. The Li-S pouch cell with TFMSA also exhibits outstanding performance, indicating the prospect of practical application. This work sheds light on an innovative idea for interface modification via an electrolyte additive to overcome the inherent issues of Li-S batteries.

Thermal runaway routes of large-format lithium-sulfur pouch cell batteries

<h2>Summary</h2> Lithium-sulfur (Li-S) batteries emerge as one of the most attractive energy storage systems due to their ultra-high theoretical energy densities, but the pace of their thermal safety assessment is obviously lagging behind. Herein, by investigating the thermal runaway behavior of Li-S pouch cells from the materials level, we unprecedentedly revealed that the thermal runaway route starts from cathode-induced reactions and then gets accelerated by reactions from the anode. Besides, the solvent vaporization is verified to dominate pressure building up during thermal runaway. Moreover, Li-S batteries employing varied electrolytes with different thermal stabilities, even inorganic all solid-state electrolytes, all undergo rapid thermal runaway at a narrow temperature range due to the intrinsic thermal features of the sulfur cathode and Li metal anode sublimating, melting, and cross-reacting at high temperatures. The in-depth depicted thermal runaway routes will deliver great inspiration for mitigating the safety issues of next generation batteries.

COFs-confined multifunctional Sulfur-host design towards High-performance Lithium-sulfur batteries

Herein, a covalent organic framework (COF) confined multifunctional sulfur-host design strategy, with built-in porous catalyst and external microporous COF layer, is proposed to deal with the notorious lithium polysulfides (LiPSs) shuttle effect in lithium-sulfur (Li-S) batteries. The built-in hollow catalyst, consists of carbon supported cobalt nanodots (Co-NC) derived from ZIF-67 metal–organic framework, servers as sulfur accommodation and catalytic center for LiPSs trapping and conversion. The Co-NC is wrapped by a thin microporous TpBD-Me2 COF layer with polar functional groups, providing additional physical and chemical confinement for polysulfides shuttling. With these merits, the cell with S/Co-NC@TpBD-Me2 cathode exhibits a high initial capacity of 1178.15 mAh g−1 at 0.2C, and average 0.04% decay per cycle at 1C in 500 cycles. The cell also delivers a high rate performance (543.13 mAh g−1) up to 5C. Even at raised sulfur loading (5.71 mg cm−2) and lean electrolyte condition (E/S ratio 6.10 μL mg−1), a 4.53 mAh cm−2 high area capacity is achieved after 50 cycles. The Li-S pouch cell also achieves a specific capacity of 860.35 mAh g−1 at 0.1C after 50 cycles. This COF-confined multifunctional composite design provides an alternative strategy for the fabrication of high-performance Li-S batteries.

Modification of Nitrate Ion Enables Stable Solid Electrolyte Interphase in Lithium Metal Batteries

AbstractThe lifespan of high‐energy‐density lithium metal batteries (LMBs) is hindered by heterogeneous solid electrolyte interphase (SEI). The rational design of electrolytes is strongly considered to obtain uniform SEI in working batteries. Herein, a modification of nitrate ion (NO3−) is proposed and validated to improve the homogeneity of the SEI in practical LMBs. NO3−is connected to an ether‐based moiety to form isosorbide dinitrate (ISDN) to break the resonance structure of NO3−and improve the reducibility. The decomposition of non‐resonant −NO3in ISDN enriches SEI with abundant LiNxOyand induces uniform lithium deposition. Lithium–sulfur batteries with ISDN additives deliver a capacity retention of 83.7 % for 100 cycles compared with rapid decay with LiNO3after 55 cycles. Moreover, lithium–sulfur pouch cells with ISDN additives provide a specific energy of 319 Wh kg−1and undergo 20 cycles. This work provides a realistic reference in designing additives to modify the SEI for stabilizing LMBs.

Modification of Nitrate Ion Enables Stable Solid Electrolyte Interphase in Lithium Metal Batteries.

The lifespan of high-energy-density lithium metal batteries (LMBs) is hindered by heterogeneous solid electrolyte interphase (SEI). The rational design of electrolytes is strongly considered to obtain uniform SEI in working batteries. Herein, a modification of nitrate ion (NO3 - ) is proposed and validated to improve the homogeneity of the SEI in practical LMBs. NO3 - is connected to an ether-based moiety to form isosorbide dinitrate (ISDN) to break the resonance structure of NO3 - and improve the reducibility. The decomposition of non-resonant -NO3 in ISDN enriches SEI with abundant LiNx Oy and induces uniform lithium deposition. Lithium-sulfur batteries with ISDN additives deliver a capacity retention of 83.7 % for 100 cycles compared with rapid decay with LiNO3 after 55 cycles. Moreover, lithium-sulfur pouch cells with ISDN additives provide a specific energy of 319 Wh kg-1 and undergo 20 cycles. This work provides a realistic reference in designing additives to modify the SEI for stabilizing LMBs.

WN0.67-Embedded N-doped Graphene-Nanosheet Interlayer as efficient polysulfide catalyst and absorbant for High-Performance Lithium-Sulfur batteries

• A novel interlayer of WN 0.67 @NG for high-performance Li-S batteries is fabricated. • Multifunctional WN 0.67 @NG can be used as efficient polysulfide catalyst and absorbant. • Li-S cell with WN 0.67 @NG/PP delivers outstanding electrochemical performance. • Excellent performance is attributed to synergistic effect of WN 0.67 and nitrogen-doped graphene. Lithium-sulfur (Li-S) battery has attracted wide research attention due to its high energy density, high earth-abundance and low-cost. However, the dissolution of lithium polysulfides (LiPSs) and corresponding shuttle will lead to serious capacity degradation and worse cycling stability of Li-S batteries. To address such issues, herein, we firstly present a novel interlayer of WN 0.67 -embedded N-doped graphene-nanosheets (WN 0.67 @NG) via a facile solvothermal reaction followed by nitriding treatment. The Li-S cell equipped with WN 0.67 @NG modified polypropylene (PP) separator exhibits outstanding electrochemical performances: a long-term stability with only a capacity decay of 0.07% per cycle over 200 cycles and a large capacity of 725 mAh g −1 at 4C; interestingly, a favorable capacity of 776 mAh g −1 can be maintained after 100 cycles at 0.2C for assembled Li-S pouch cell under a high sulfur loading conditions of 4.3 mg cm −2 with lean electrolyte occupation (6 μL mg −1 ). The outstanding performance can be attributed to the following advantages of WN 0.67 @NG interlayer: the high conductivity of NG sheets can facilitate the electron transfer and act as a physical block for restricting the LiPSs shuttle; most importantly, the polar WN 0.67 nanoneedles embedded on the NG sheets not only provide abundant active sites for chemisorption and catalytic conversion of LiPSs, but also contribute to the nucleation and growth of Li 2 S; further theoretical calculations and in-situ Raman spectra clearly reveal the adsorption and catalytic conversion mechanism of WN 0.67 @NG interlayer at the molecular level. The work provides new insight into rational design and facile fabrication of multifunctional separators for industrial applications in high-performance Li-S batteries.

Ordered macroporous V-doped ZnO framework impregnated with microporous carbon nanocages as multifunctional sulfur reservoir in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as a promising energy storage device. However, their practical application is still hindered by the unsatisfactory cyclability and slow reaction kinetics. Here, we propose a conductive oxide-based macro-microporous framework, where ZIF-8-derived N-doped carbon (NC) nanocages are embedded within the three-dimensionally ordered macroporous (3DOM) V-doped ZnO matrix, as a high-performance sulfur host for Li-S batteries. The unique framework provides large surface area and high porosity for sulfur accommodation, while the V-doped ZnO skeleton enables a highly conducive substrate for electrochemical reactions. More importantly, such hybrid structure imposes strong fixation and effective catalysis of polysulfides, rendering reversible and rapid sulfur redox reactions. Due to these synergistic effects, the 3DOM [email protected]/S cathode exhibits an excellent cycling stability with a low capacity fading rate of 0.043 % per cycle during 500 cycles at 1C and a good rate capability of 767.6 mAh g−1 at 3C. Moreover, a high initial areal capacity of 4.4 mAh cm−2 was also achieved under a high sulfur loading of 5.8 mg cm−2 with a low E/S ratio of 4.4 μL mg−1 in coin cells, as well as decent flexibility and stable cycling in Li-S pouch cell configuration.

Operando Radiography and Multimodal Analysis of Lithium–Sulfur Pouch Cells—Electrolyte Dependent Morphology Evolution at the Cathode

AbstractIn recent years, the technology readiness level of next‐generation lithium–sulfur (Li/S) batteries has shifted from coin cell to pouch cell dimensions. Promising optimizations of the electrodes, electrolytes, active materials, and additives lead to improved performance and cycling stability. However, new challenges arise with the pouch cell design and engineering (including electrode stacking and electrolyte filling), which influence the mechanistic processes of the cell. This study presents an unprecedented multimodal operando investigation of Li/S batteries on a pouch cell level and provides an inside view of material transformations during battery cycling, using X‐ray radiography, electrochemical impedance spectroscopy, and spatially resolved temperature monitoring. With the comparison of two different electrolytes, new experimental details about sulfur and lithium sulfide deposition and dissolution processes are revealed and related to electrolyte and temperature distribution. Operando impedance measurements on monolayer pouch cells yield a clear correlation of electrochemical and macroscopic radiographic observations. Understanding the monolayer cells’ behavior represents an optimal foundation for further studies on multilayer pouch cell prototypes and demonstrators with the developed operando setup. Herein the proof of principle for correlated measurement methods on pouch cell level is shown, and the experimental proof of concept for sulfur crystal suppression in sparingly solvating electrolyte is visualized.

Modeling of the temporal evolution of polysulfide chains within the lithium-sulfur battery

The lithium-sulfur battery belongs to the group of promising technologies known as post lithium-ion batteries, due to its high specific capacity of 1672 Ahkg−1, specific energy density of around 2600 Whkg−1 and the expected low price. Due to low performance, capacity fading and low coulombic efficiency, the commercialization is slow. The complex mechanisms of precipitation and dissolution of the individual polysulfide chains are described in a mathematical model. The model is based on the Nernst-formulation (concentration dependence) and the Butler-Volmer-equation (reaction kinetics). In the mathematical model, the evolution as well as the appearance of the individual polysulfide chains are described as a function of the C-rate. In this model, the nucleation of the precipitating solid and the recrystallization are represented. Depending on the state of charge, the model predicts the precipitation/dissolution and the appearance of the individual polysulfide chains. A prototype lithium-sulfur pouch cell is experimentally investigated, and the yielded measurement results are related to the model. The mathematical description could be used as foundation for mechanical studies, as well as for control algorithms (battery-management-system) to monitor the individual cells.

Building flexibly porous conductive skeleton inlaid with surface oxygen-dominated MXene as an amphiphilic nanoreactor for stable Li-S pouch batteries

The severe polysulfides shuttling, sluggish conversion kinetics and uncontrollable growth of lithium dendrites greatly restrict the progress of lithium-sulfur (Li-S) battery. Guided by first-principles calculations, in this work, a porous carbon nanofiber with an oxygen-dominated Ti3C2 MXene nanosheet (denoted as O-Ti3C2@CNF) is designed and synthesized as an all-purpose interlayer for the Li-S system. The oxygen-functionalized strategy is achieved by stepwisely controllable surface modifications and moderate oxygen regulation, forming an oxygen-rich MXene surface. On the one hand, the MXene and porous carbon nanofiber collaboratively construct a 3D conductive scaffold, which renders strong physical/chemical affinity and fast reaction kinetics toward sulfur species. On the other hand, the O-Ti3C2@CNF enables the high-flux Li diffusion and achieves the dendrite-free Li anode due to its 3D architecture with abundantly lithophilic active centers. Based on the abovementioned merits, a practical, flexible Li-S pouch battery was assembled by employing a symmetrical interlayer design, which delivered an excellent areal capacity of 5.2 mAh cm−2 over 30 cycles (under the conditions of sulfur loading up to 6.7 mg cm−2 and electrolyte to sulfur ratio of 6.0 mL g−1). The symmetrically designed interlayer as amphiphilic membrane nanoreactor may inspire the material engineering in practical Li-S pouch cells.

Polysulfide regulation vs anode modification: Perspectives on commercializing lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are considered the promising energy-storage devices to replace the aging lithium-ion batteries. Indeed, they have gained much attention in both academia and industry due to their high theoretical energy density. Although significant progress has been achieved in the field of academia, the same thing cannot be stated for the commercial production of Li–S batteries. This is evidenced by the fact that only a few studies have demonstrated a pouch-cell approach. Thus, it is important to realize the significant gap between academic research and the real-world production of lithium–sulfur cells. In this perspective, we discuss the issues and challenges behind the large-scale production of Li–S batteries; moreover, we highlight the recent advances in the development of lithium–sulfur pouch cells that are achieved either by polysulfide regulation or by anode modification. We hope that this review will attract more attention to the development of lithium–sulfur pouch cells to overcome the practical hurdles of large-scale production.

Influence of external stack pressure on the performance of Li-S pouch cell

The lithium-sulfur (Li-S) cell system is promising to satisfy the increasing need for cost-efficient energy storage with high theoretical energies due to the enormous theoretical gravimetrical capacity and the abundance of sulfur. Furthermore, the technology readiness level of Li-S batteries increased steadily in recent years due to extensive research, as well as the number of reported prototype cells. However, an often ignored test parameter is the application of external pressure to the cell stack. In this study, the influence of external pressure on the performance of Li-S cells is investigated. Therefore, five-layered pouch cells with solvent-free processed cathodes are assembled. These cells are tested under lean electrolyte conditions (electrolyte to sulfur ratio of 4.5 µl mg(S)−1). To evaluate the influence of the used electrolyte system either the state-of-the-art 1,2-dimethoxyethane/1,3-dioxolane electrolyte or the sparing polysulfide solvating hexyl methyl ether/1,3-dioxolane electrolyte is deployed. The impact of pressure application is evaluated electrochemically as well as by post-mortem focused ion beam-scanning electron microscopy of the cycled electrodes. Moreover, a technique for infiltration of sulfur into the carbon host matrix is presented, discussed, and successfully implemented.

Ternary Transition Metal Sulfide as High Real Energy Cathode for Lithium-Sulfur Pouch Cell Under Lean Electrolyte Conditions.

Fabrication of a highly porous sulfur host and using excess electrolyte is a common strategy to enhance sulfur utilization. However, flooded electrolyte limits the practical energy density of Li-S pouch cells. In this study, a novel Fe0.34 Co0.33 Ni0.33 S2 (FCN) is proposed as host for sulfur to realize Ah-level Li-S full cells demonstrating excellent electrochemical performances under 2 µLmg-1 lean electrolyte conditions. Moreover, Kelvin probe force microscopy shows that the FCN surface contains positive charge with a potential of ≈70 mV, improving the binding of polysulfides through Lewis acid base interaction. In particular, the FCN@S possesses inherent electrochemical activity of simultaneous anionic and cationic redox for lithium storage in the voltage window of 1.8-2.1 V, which additionally contributes to the specific capacity. Due to the low carbon content (≈10wt%), the sulfur loading is as high as ≈6mg cm-2 , approaching an outstanding energy density of 394.9 and 267.2Wh kg-1 at the current density of 1.5 and 4mA cm-2 , respectively. Moreover, after 60 cycles at 1.5mA cm-2 , the pouch cell still retains an energy of 300.2Wh kg-1 . This study represents a milestone in the practical applications of high-energy Li-S batteries.

Two Birds with One Stone: Interfacial Engineering of Multifunctional Janus Separator for Lithium-Sulfur Batteries.

Li-dendrite growth and unsatisfactory sulfur cathode performance are two core problems that restrict the practical applications of lithium-sulfur batteries (LSBs). Here, an all-in-one design concept for a Janus separator, enabled by the interfacial engineering strategy, is proposed to improve the performance of LSBs. At the interface of the anode/separator, the thin functionalized composite layer contains high-elastic-modulus and high-thermal-conductivity boron nitride nanosheets and oxygen-group-grafted cellulose nanofibers (BNNs@CNFs), by which the formation of "hot spots" can be effectively avoid, the Li-ion flux homogenized, and dendrite growth suppressed. Meanwhile, at the interface between the separator and the cathode, the homogenously exposed single-atom Ru on the surface of reduced graphene oxide (rGO@Ru SAs) can "trap" polysulfides and reduce the activation energy to boost their conversion kinetics. Consequently, the LSBs show a high capacity of 460 mAh g-1 at 5C and ultrastable cycling performance with an ultralow capacity decay rate of 0.046% per cycle over 800 cycles. To further demonstrate the practical prospect of the Janus separator, a lithium-sulfur pouch cell using the Janus separator delivers a cell-level energy density of 310.2Wh kg-1 . This study provides a promising strategy to simultaneously tackle the challenges facing the Li anode and the sulfur cathode in LSBs.

Lithiated Sulfur-Incorporated, Polymeric Cathode for Durable Lithium-Sulfur Batteries with Promoted Redox Kinetics.

Even though lithium-sulfur (Li-S) batteries have made much progress in terms of the delivered specific capacity and cycling stability by the encapsulation of sulfur within conductive carbon matrixes or polar materials, challenges such as low active sulfur utilization and unacceptable Coulombic efficiency are still hindering their commercial use. Herein, a lithium-rich conjugated sulfur-incorporated, polymeric material based on poly(Li2S6-r-1,3-diisopropenylbenzene) (DIB) is developed as a cathode material for high rate and stable Li-S batteries. Motivated by extra Li+ ions affording fast Li+ redox kinetics across the conjugated aromatic backbones, the Li-rich sulfur-based copolymer exhibits high delivery capacities (934 mAh g-1 at 120 cycles), impressive rate capabilities (727 mAh g-1 even under a current of 2 A g-1), and long electrochemical cycling performance over 500 cycles. Moreover, by use of the elastic nature and thermoplastic properties of the sulfur-incorporated, polymeric material, a prototype of a flexible Li-S pouch cell is constructed by using a poly(Li2S6-r-DIB) copolymer cathode and paired with the flexible carbon cloth/Si/Li anode, which exhibits stable electrochemical performance (658 mAh g-1 after 100 cycles) and operational capability even under folding at various angle (30°, 60°, 90°, 120°, 150°, 180°). This work extends the molecular-design approach to obtaining a high-performance organosulfur cathode material by introducing extra Li+ ions to promote redox kinetics, which provides valuable guidance for the development of high-performance Li-S batteries for practical applications.

Semi-Immobilized Molecular Electrocatalysts for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries constitute promising next-generation energy storage devices due to the ultrahigh theoretical energy density of 2600 Wh kg-1. However, the multiphase sulfur redox reactions with sophisticated homogeneous and heterogeneous electrochemical processes are sluggish in kinetics, thus requiring targeted and high-efficient electrocatalysts. Herein, a semi-immobilized molecular electrocatalyst is designed to tailor the characters of the sulfur redox reactions in working Li-S batteries. Specifically, porphyrin active sites are covalently grafted onto conductive and flexible polypyrrole linkers on graphene current collectors. The electrocatalyst with the semi-immobilized active sites exhibits homogeneous and heterogeneous functions simultaneously, performing enhanced redox kinetics and a regulated phase transition mode. The efficiency of the semi-immobilizing strategy is further verified in practical Li-S batteries that realize superior rate performances and long lifespan as well as a 343 Wh kg-1 high-energy-density Li-S pouch cell. This contribution not only proposes an efficient semi-immobilizing electrocatalyst design strategy to promote the Li-S battery performances but also inspires electrocatalyst development facing analogous multiphase electrochemical energy processes.

Thirty-minute synthesis of hierarchically ordered sulfur particles enables high-energy, flexible lithium-sulfur batteries

An innovative lithium-sulfur (Li-S) battery technology is proposed that provides high energy density, fast charging, and mechanical flexibility. Via the rapid (30 min) one-pot reaction of elemental sulfur and vinyl phosphonic acid (VPA), SVPA microparticles containing dissimilar sulfur allotropes were developed. The spontaneous formation of wrinkles and pores on the particles facilitates electrolyte access and alleviates mechanical stress during battery cycling. The large surface area created by the ordered sulfur domains enhances lithium diffusion coefficients and facilitates polysulfide conversion kinetics in the Li-S cells, leading to a high discharge capacity of 1529 mAh·g −1 at 0.05 C and excellent rate performance (721 mAh·g −1 at 7 C). Additionally, owing to the inherent electrode porosity imparted by SVPA microparticles, a high areal capacity of ~5 mAh·cm −2 is obtained at increased cathode loadings. Abundant phosphonate moieties at the surfaces and interfaces of particles act as effective chemical anchors for lithium polysulfides, thereby mitigating the shuttle effects, which can prolong cycle lives at various C rates. The impressive properties of the SVPA microparticles are demonstrated for Li-S pouch cells, which exhibit stable operation under various deformations and highlight the SVPA microparticles as a promising candidate for next-generation Li-S batteries for wearable electronics A simple but radical approach is proposed to advance sulfur electrodes with smart nanostructures via the rapid one-pot reaction between elemental sulfur and vinyl phosphonic acid. This study serves as a platform for the development of next-generation Li-S batteries with high energy density, rate capability, and mechanical flexibility. • Hierarchically ordered sulfur electrodes were developed via rapid, solvent-free synthesis of SVPA microparticles. • The ordered sulfur domains and abundant phosphonate moieties at wrinkled surfaces of SVPA improved redox kinetics and cathode integrity. • Li-S batteries based on SVPA microparticles empowered one of the highest areal capacity, excellent rate capability and flexible characteristics

Conductive Al-Doped ZnO Framework Embedded with Catalytic Nanocages as a Multistage-Porous Sulfur Host in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries possess many practical challenges including the lithium polysulfide (LiPS) "shuttle effect" and their sluggish conversion kinetics. To address these issues, a unique hierarchical porous architecture, combining highly conductive ordered macroporous skeleton and embedded microporous particles is rationally designed as a dual-effective polysulfide immobilizer and conversion promoter. In this nanoporous architecture, Al-doped ZnO (AZO) acts as a conductive macroporous framework, profiting chemical anchoring of LiPS as well as facilitating electrolyte infiltration and ion diffusion; Co nanoparticle-anchored N-doped carbon (Co-NC) derived from CoZn-metal-organic framework is embedded in the macropores to further strengthen the LiPS adsorption, catalytically accelerating conversion kinetics of LiPS simultaneously. Consequently, the Co-NC@AZO/S cathode delivers a notable rate capability of 635.5 mA h g-1 at 5 C. A high area capacity of about 5.8 mA h cm-2 with a mass loading of 6.8 mg cm-2 is also achieved under a lean electrolyte (E/S = 5.7). Additionally, the Li-S pouch cells equipped with Co-NC@AZO can be extended to sulfur loading as high as 4.0 mg cm-2, delivering a superb capability of 897.5 mA h g-1 after 100 cycles. This work puts forward a design for stably cycled and practically viable Li-S batteries.

An Experimental Study on Prototype Lithium–Sulfur Cells for Aging Analysis and State-of-Health Estimation

Lithium-sulfur (Li-S) batteries offer potential for higher gravimetric energy density in comparison to lithium-ion batteries. Since they behave quite different from lithium-ion batteries, distinctive approaches to state estimation and battery management are required to be developed specifically for them. This article describes an experimental work to model and perform real-time estimation of the progression of use-induced aging in prototype Li-S cells. To do that, state-of-the-art 19-Ah Li-S pouch cells were subject to cycling tests in order to determine progressive changes in parameters of a nonlinear equivalent-circuit-network (ECN) model due to aging. A state-of-health (SoH) estimation algorithm was then designed to work based on identifying ECN parameters using forgetting-factor recursive least squares (FFRLS). Two techniques, nonlinear curve fitting and support vector machine (SVM) classification, were used to generate SoH values according to the identified parameters. The results demonstrate that Li-S cell's SoH can be estimated with an acceptable level of accuracy of 96.7% using the proposed method under realistic driving conditions. Another important outcome was that the “power fade” in Li-S cells happens at a much slower rate than the “capacity fade” which is a useful feature for applications where consistency of power delivery is important.

Investigation on Cycling and Calendar Aging Processes of 3.4 Ah Lithium-Sulfur Pouch Cells

Much attention has been paid to rechargeable lithium-sulfur batteries (Li–SBs) due to their high theoretical specific capacity, high theoretical energy density, and affordable cost. However, their rapid c fading capacity has been one of the key defects in their commercialization. It is believed that sulfuric cathode degradation is driven mainly by passivation of the cathode surface by Li2S at discharge, polysulfide shuttle (reducing the amount of active sulfur at the cathode, passivation of anode surface), and volume changes in the sulfuric cathode. These degradation mechanisms are significant during cycling, and the polysulfide shuttle is strongly present during storage at a high state-of-charge (SOC). Thus, storage at 50% SOC is used to evaluate the effect of the remaining degradation processes on the cell’s performance. In this work, unlike most of the other previous observations that were performed at small-scale cells (coin cells), 3.4 Ah pouch Li–SBs were tested using cycling and calendar aging protocols, and their performance indicators were analyzed. As expected, the fade capacity of the cycling aging cells was greater than that of the calendar aging cells. Additionally, the measurements for the calendar aging cells indicate that, contrary to the expectation of stopping the solubility of long-chain polysulfides and not attending the shuttle effect, these phenomena occur continuously under open-circuit conditions.