Initial Reversible Capacity Research Articles

Coupling 5 d metallic and conductive Network for promoting polysulfide conversion

The reaction kinetics of lithium-sulfur (Li-S) battery mainly depends on the capture and catalytic conversion efficiency of lithium polysulfide (LiPSs). The unique electron configuration of the 5d metal and the high electrical conductivity of MXene can enhance the interaction between the catalyst and LiPSs. However, the challenge of enhancing the adsorption of LiPSs by regulating the electronic structure of the catalyst with 5d metal and MXene remains unresolved and obscure. In this work, we have developed molybdenum disulfide (MoS2)-tungsten disulfide (WS2) @MXene (MoS2-WS2@MX) heterostructure catalysts for separator coatings in Li-S batteries by introducing W and MXene for the first time. Theoretical calculations demonstrate that the 5 d metallic and conductive MXene coupling effectively modulate the orbital hybridization degree between the catalyst and LiPSs, thereby reducing the energy barrier for LiPSs conversion. Electrochemical test and in situ tests verify the effectiveness of the strategy on the adsorption and conversion of LiPSs. Consequently, the MoS2-WS2@MX based batteries exhibit high initial reversible capacity of 950.3 mAh g−1 and low capacity decay of 0.066 % per cycle over 500 cycles at 2 C, which is superior to most reported catalysts. This study provides a dual regulatory strategy for enhancing catalytic activity, offering valuable insights for the advancement of high-performance Li-S batteries.

Impact of Na-Carboxymethyl Cellulose Binder Type on Hard Carbon Performance and SEI Formation in Sodium-Ion Batteries.

The development of hard carbon (HC) electrodes using biobased binders, formulated in water solvent, is of great interest for Na-ion batteries. Five Na-carboxymethyl cellulose (CMC) binders with different molecular weights and degrees of substitution were investigated. The increase in the CMC molecular weight led to an increase in the volume of water necessary for slurry preparation and a decrease in the electrode mass loading. Moreover, the adhesion of the slurry was strongly impacted by the aluminum current collector properties. A high initial Coulombic efficiency, iCE (up to ∼90%), and reversible capacity (up to 334 mAh g-1 at C/10) were obtained in Na half-cells. Post-mortem XPS analyses performed on several electrodes under various conditions allowed a better understanding of the formation and composition of the solid electrolyte interphase (SEI) layer. The genesis of SEI was initially chemically driven: to a small extent, by HC and to a greater extent, by the Na metal. However, SEI formation was mainly governed by the electrochemical-driven degradation of the electrolyte salt and solvent. The SEI layer composed of an inorganic-rich core and an organic-rich shell significantly decreased the resistance of the HC electrode, allowing superior iCE while maintaining high capacity retention (96.2%), after 100 cycles at 1C.

Gas-phase Kirkendall effect inducing built-in bifunctional ultrafine Cu nanocrystalline integrated 3D hollow nanoporous CuxO anode towards excellent lithium storage performance

Traditional CuxO (x = 1, 2) electrodes exhibit excellent specific capacity, but the poor stress-buffering performance and inferior conductivity hinder its further application. To solve these issues, herein, we develop a built-in bifunctional ultrafine Cu nanocrystalline networks hybridized 3D hollow nanoporous CuxO (BUCN@3D-HN CuxO) integrated anode by a facile gas-phase Kirkendall effect. The 3D hollow nanoporous (3D-HN) structure can bidirectionally retard the change of stress, while the built-in ultrafine Cu nanocrystalline networks (BUCN) own the effect of providing rapid internal electron transport across the active/inert Cu/CuxO system. Benefiting from the synergistic effect of the excellent stress-buffering ability and improved electronic conductivity, the designed BUCN@3D-HN CuxO electrode delivers a high initial reversible capacity of 1.67 mAh cm−2 under the current density of 1 mA cm−2. Besides, a high capacity retention of 0.96 mAh cm−2 with a high capacity retention ratio of 85.7 % is achieved even after 800 cycles at a high rate of 4 mA cm−2. This work provides a facile yet effective method to prepare hollow nanoporous electrodes and emphasizes the significance of active/inert system, which may shed light on the design of other high-performance electrodes beyond Lithium-ion batteries.

Tailoring Na2FePO4F nanoparticles as the high-rate capability and Long-life cathode towards fast chargeable sodium-ion full batteries

Na2FePO4F (NFPF) with two-dimensional channels for transferring Na ions is considered as the promising cathode material for high-performance sodium-ion batteries (SIBs), while the electrochemical performance in full-cell devices remains unsatisfactory. Here, we developed a method combining high-boiling organic solvents assisted colloidal synthesis (HOS-CS) and subsequent calcination for preparing 20–30 nm of NFPF nanoparticles (NPs) wrapped by conductive carbon as the efficient cathode. HOS-CS demonstrated merits in terms of high utilization of precursors, high synthetic efficiency, and uniform distribution of both sizes and composition of NPs. Impressively, the as-obtained NFPF/C/MWCNTs delivered a reversible capacity up to 118.4 mAh/g at 0.1C. As a bonus, the full-cell configuration fabricated via NFPF/C/MWCNTs cathode and hard carbon (HC) anode demonstrated extraordinary rate capability and cyclic stability. Even at an ultrahigh rate of 10C, 54.7 mAh/g of initial reversible capacity and nearly 80.7 % of capacity retention after 200 cycles were achieved, highlighting the great potentials of NFPF/C/MWCNTs||HC full cell for practical applications in the fields of fast chargeable SIBs. This work offers a novel synthetic method for the preparation of efficient NFPF-based cathode.

Electronic Modulation and Symmetry‐Breaking Engineering of Single‐Atom Catalysts Driving Long‐Cycling Li−S Battery

AbstractDeveloping efficient and durable single‐atom catalysts is vitally important for the sulfur redox reaction (SROR) in Li−S battery, while it remains enormous challenging. Herein, undercoordinated Ni−N3 moieties anchored on N,S‐codoped porous carbon (Ni−NSC) is obtained to enhance the SROR. The experiments and theoretical calculations indicate that the symmetry‐breaking charge transfer in Ni single‐atom catalyst originates from tuning effect of sulfur atoms mediated Ni−N3 moieties, which can both facilitate the chemical adsorption by formation of N−Ni⋅⋅⋅Sn2−, and achieve a rapid redox conversion of polysulfides because of the enhanced electron transfer. As results, the Ni−NSC based Li−S battery delivers a very high initial reversible capacity (1025 mAh g−1 at 1 C), as well as outstanding cycling‐stability for 2400 cycles at 2 C and 3 C, respectively. Noteworthy, the areal capacity can reach 7.8 mAh cm−2 at 0.05 C and a retention capacity of 4.7 mAh cm−2 after 100 cycles at 0.2 C for Ni−NSC based Li−S battery with sulfur loading of 5.88 mg cm−2. This work provides profound insight for rational optimizing microscopic electronic density of active site to promoting SROR in metal‐sulfur batteries.

Electronic Modulation and Symmetry-Breaking Engineering of Single-Atom Catalysts Driving Long-Cycling Li-S Battery.

Developing efficient and durable single-atom catalysts is vitally important for the sulfur redox reaction (SROR) in Li-S battery, while it remains enormous challenging. Herein, undercoordinated Ni-N3 moieties anchored on N,S-codoped porous carbon (Ni-NSC) is obtained to enhance the SROR. The experiments and theoretical calculations indicate that the symmetry-breaking charge transfer in Ni single-atom catalyst originates from tuning effect of sulfur atoms mediated Ni-N3 moieties, which can both facilitate the chemical adsorption by formation of N-Ni⋅⋅⋅Sn 2-, and achieve a rapid redox conversion of polysulfides because of the enhanced electron transfer. As results, the Ni-NSC based Li-S battery delivers a very high initial reversible capacity (1025 mAh g-1 at 1 C), as well as outstanding cycling-stability for 2400 cycles at 2 C and 3 C, respectively. Noteworthy, the areal capacity can reach 7.8 mAh cm-2 at 0.05 C and a retention capacity of 4.7 mAh cm-2 after 100 cycles at 0.2 C for Ni-NSC based Li-S battery with sulfur loading of 5.88 mg cm-2. This work provides profound insight for rational optimizing microscopic electronic density of active site to promoting SROR in metal-sulfur batteries.

The Fabrication of ZIF-L Derived Zns/Mos2@NC Anode Materials for Remarkable Lithium-Ion Storage.

The enhancement of electrochemical performance in lithium-ion batteries can be achieved through the incorporation of MoS2 with carbon materials and various metal sulfides. In this study, a ZnS/MoS2 heterostructure was developed, featuring a two-dimensional nitrogen-doped carbon nanosheet (NC) backbone. The synthesis of ZnMoZIF-L precursors was accomplished by introducing a Mo source in a 1 : 1 molar ratio during the ZIF-L synthesis process. Following high-temperature carbonization and vulcanization treatment, ZnS/MoS2@NC composite materials were successfully synthesized. Compared to the unvulcanized ZnO/MoO3@NC and MoS2 samples, the ZnS/MoS2@NC composite exhibits remarkable lithium storage performance. At a current density of 500 mA g-1, the initial reversible capacity capacity is still as high as 1674 mAh g-1. Furthermore, this composite material demonstrates optimal rate capabilities and a significant contribution to pseudocapacitance. The nitrogen-doped carbon framework effectively mitigates volume changes, while the heterostructural design provides more active sites for lithium-ions, thereby enhancing lithium storage performance.

Synergistic effect of P2, O3 phase on biphasic layered oxide with enhanced electrochemical performance for sodium storage

Oxides with a layered structure are regarded as prospective candidates for use as cathodes in the next generation of sodium ion batteries. These materials, which exhibit a P2 structure and O3 structure, possess distinctive advantages that give rise to disparate electrochemical performance. Herein, a thermodynamically and kinetically stable P2/O3 biphasic layered oxide with a chemical formula of K0.05Na0.8Ni0.5Mn0.5O2 is synthesized using a simplistic high temperature solid-state method. P2 phase enhances the structural stability of the material, while O3 phase provides additional sodium storage sites, thereby increasing the material’s capacity. The joint action of the two phases results in an improvement in the electrochemical characteristics. Moreover, the Ni-Mn-based layered oxide is enhanced by Fe-substitution, which effectively mitigates the Jahn-Teller effect caused by Mn3+, thereby improving the comprehensive electrochemical performance of the cathode. The Fe-doped specimen offers 102.8 mAh g−1 as the initial reversible discharge capacity under a high current density of 200 mA g−1, and a high capacity retention amounting to 83.17 % is attained after 200 cycles. In addition, the structural development of the P2/O3 biphasic sample during Na+ extraction/insertion was elucidated by in situ XRD. This paper employs the advantages of P2 and O3 phases to augment material electrochemical characteristics and verifies the possibility of the P2/O3 biphasic structure by density functional theory (DFT) calculations, providing new ideas for biphasic sodium ion battery cathode materials.

Synthesis of nano cubic microstructure LiNi0.8Co0.1Mn0.1O2 cathode materials via rapid precipitation assisted with hydrothermal treatment

In this work, a modified Ni-rich cathode material LiNi0.8Co0.1Mn0.1O2 with a unique nano cubic microstructure is successfully synthesized via a rapid precipitation assisted with hydrothermal treatment. The formation of this distinctive microstructure is attributed to the homogeneous rapid precipitation in microreactor, which predominantly generates uniform crystal nuclei. The as-prepared material with nano-/microstructure shows superior initial reversible capacity (205.3 mAh·g−1 at 2.7–4.3 V) and rate capability (163.9 mAh·g−1 at 5 C). Additionally, it maintains a high capacity (188.2 mAh·g−1) with a retention of 87.2 % at 1 C after 200 cycles, demonstrating outstanding cycling stability. Our work presents a straightforward and efficient approach for producing nano-cubic microstructure layered cathode materials.

Ti3C2Tx MXene coated 3D ordered macroporous germanium anodes for Li-ion batteries with enhanced cycling stability and fast Li-ion mobility

The current trend in electronic device development and electric vehicle technology has resulted in A growing need for negative electrode materials that possess high capacity and quick Li-ion transport properties. Ge-based materials are considered the very promising candidates owing to their high theoretical capacity and facile alloying reaction with Li. In order to enhance the rate of Li-ion diffusion and account for the volume change of over 300 %, a Ti3C2Tx MXene coated 3D ordered macroporous germanium (3DOM Ge@MXene) structure was successfully developed. The 3DOM Ge@MXene provides a 1490 mAh g−1 initial reversible capacity at 0.32 A g−1. Additionally, after 100 cycles, it displays a consistent cycling ability of 1034 mAh g−1. The MXene coating also improves the material's Li-ion rapid transfer performance, with Li-ion diffusion coefficient of 1.35 × 10−10 cm2s−1 for anodic and 2.2 × 10−10 cm2s−1 for cathodic.

Understanding the Structural and Electrochemical Properties of Anion‐Redox O3‐Na[Li1/3Mn2/3]O2 Cathode for Sodium‐Ion Batteries

AbstractActivating anionic redox is an effective strategy for enhancing the capacity of cathode materials in both lithium‐ion and sodium‐ion batteries. However, the fundamental mechanisms of O3‐type sodium anionic redox cathodes remain poorly understood due to the limited availability of such materials, despite their inherent advantages such as high initial sodium content and high reversible capacity. Herein, we employ multiple characterization methods to elucidate the structural and electrochemical properties of O3‐Na[Li1/3Mn2/3]O2, a promising sodium anionic redox cathode developed recently, with a particular focus on the effect of cutoff voltages during electrochemical aging. Our synchrotron powder X‐ray diffraction results indicate that charging the material to voltages above 4.1 V induces substantial structural changes, which compromise the structural and electrochemical reversibility of the material. This is corroborated by more rapid capacity decay and increased impedance, attributed to severe degradation on both the surface and in the bulk, as evidenced by the formation of lower valence manganese compounds. Furthermore, increasing the lower cutoff voltage for the discharge process effectively suppresses surface degradation, thereby improving cycling stability. This work offers a comprehensive understanding of a pivotal sodium anionic redox cathode material, providing valuable insights that can drive the development of advanced materials for sodium‐ion batteries.

Coal-based graphene derived from different coal ranks: exceptional sodium storage performance in sodium-ion batteries.

Coal is a premium carbon material precursor as anode materials for sodium-ion batteries (SIBs). Additionally, developing anode materials with large capacity and rapid charging performance is essential for the advancement of SIBs. Consequently, in this work, coal-based reduced graphene oxide (CrGO) was prepared as an anode materials for SIBs by a modified Hummers-high temperature thermal reduction method with different ranks of coal (coal-based graphite, CG) as a precursor. The CG prepared from higher-rank coal exhibits a higher degree of graphitization, and its graphene layers are easier to exfoliate. The unique microstructure of CrGO provides stability during the sodium storage process and exhibits fast ion capacitive adsorption behavior, enhancing reaction kinetics. CrGO, with an initial reversible capacity of up to 331 mA h g-1 at a current density of 0.03 A g-1, achieves a specific capacity of 75 mA h g-1, even at a high current density of 10 A g-1. Notably, CrGO also maintains a good specific capacity of 123 mA h g-1 after 1000 cycles at a current density of 1 A g-1, with a capacity retention rate of 91.8%. This study highlights the potential for using coal-derived materials in the development of high-performance anode materials for SIBs, promoting the green and high-value utilization of coal.

Control of N/P ratios and cut-off voltage for Silicon-Based Li-ion batteries

High-energy density and unwavering safety standards form the cornerstone of new energy vehicle development, necessitating the design of power batteries that seamlessly integrate these critical qualities. Key to this endeavor is the enhancement of energy density at the architectural level, focusing on the optimization of the N/P ratio—a move that demands a holistic evaluation extending beyond mere comparisons of cathode and anode capacities to include initial efficiency, and both reversible and irreversible capacities. Departing from traditional N/P ratio designs requires meticulous optimization. This research introduces a novel N/P ratio design methodology, termed the “Water Cup Model”, for lithium-ion batteries (LIBs), effectively addressing capacity loss issues endemic to conventional designs. This approach, under consistent cathode material and areal capacity conditions, increases the batteries’ specific energy by approximately 5 Wh/kg, without compromising safety. Further innovation is achieved by incorporating a voltage regulation coefficient, λ, allowing for precise adjustment of the cut-off discharge voltage and facilitating the selection of high-performance silicon-based anode materials. Comparative assessments of energy density and cycling performance affirm the superiority of our optimized N/P ratio strategy against conventional methods. This strategy’s core lies in its capacity to significantly boost energy density without extensive modifications to the battery’s internal makeup, relying solely on the precise management of the N/P ratio to ensure safety is not compromised by energy density enhancements. This seminal work lays down a cost-effective, robust framework for advancing high-performance LIB technology, contributing pivotal insights to the field.

Nanodiamond-Assisted High-Performance Sodium-Ion Batteries with Weakly Solvated Ether Electrolyte at -40°C.

Realizing high performances of sodium-ion batteries (SIBs) working at low temperatures is a pressing need for the commercial applications of SIBs. In this work, nanodiamonds (NDs) are introduced in diglyme electrolytes (ND-Diglyme) to significantly improve the low-temperature performances of SIBs. The corresponding SIB achieves an initial reversible specific capacity of 324mA h g-1 at -40°C (slightly decreased from 357mA h g-1 at 25°C) and shows a capacity retention ratio of ≈82% after 100 cycles at 0.1 A g-1. Moreover, it shows a capacity as high as 40mA h g-1 at 1 A g-1, nearly five times the date of the pure Diglyme electrolyte. Experimentally reveals that introducing NDs is helpful in inhibiting dendrite growth and improving the cyclic stability of anode at LT, because the ND with strong adsorption to sodium ions can not only assist in forming an effective solid electrolyte interface rich with NaF and Na2CO3 but also effectively reduce the activation energy (decreased from 426.68 to 370.51 meV) during the charge transfer processes. Hence, the proposed ND-assisted weakly ether electrolyte in this study presents a viable electrolyte additive solution to fulfill the rising low-temperature demands of SIBs.

Nickle-doped covalent organic frameworks/carbon nanotubes composite for high-performance lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are considered as one of the most promising next-generation energy storage systems. To mitigate the shuttle effect of lithium polysulfides (LiPSs) in LSBs, the rational design of sulfur hosts with high physical confinement and catalytic activity is critical to enhance the performance of LSBs. Here, we successfully prepare a nickle-doped covalent organic frameworks/carbon nanotubes composite (Ni/COFs/CNTs) as the sulfur host in LSBs. COFs can confine and immobilize sulfur species. Moreover, CNTs and Ni nanoparticles can provide fastelectrontransferpathways. Thus, Ni/COFs/CNTs composite can alleviate the shuttle effect during the cycling processes.The S/Ni/COFs/CNTs cathode displays a high initial reversible capacity of 1068.6 mAh g−1 and a high capacity retention (83.3 %) after 100 cycles at 0.1C. This work provides a useful strategy to the rational design of sulfur hosts for LSBs.

Chemically Bonded Biphase Coating of Ni-Rich Layered Oxides with Enhanced High-Voltage Tolerance and Long-Cycle Stability.

Stabilizing the crystalline structure and surface chemistry of Ni-rich layered oxides is critical for enhancing their capacity output and cycle life at a high cutoff voltage. Herein, we adopted a simple one-step solid-state method by directly sintering the Ni0.9Co0.1(OH)2 precursor with LiOH and Ta2O5, to simultaneously achieve the bulk material synthesis of LiNi0.9Co0.1O2 and in situ construction of a rock-salt Ta-doped interphase and an amorphous LiTaO3 outer layer, forming a chemically bonded surface biphase coating on LiNi0.9Co0.1O2. Such a cathode architectural design has been demonstrated with superior advantages: (1) eliminating surface residual alkali, (2) strengthening the layered oxygen lattice, (3) suppressing bulk-phase transformation, and (4) facilitating Li-ion transport. The obtained cathode exhibits excellent electrochemical performance, including a high initial reversible capacity of 180.3 mAh g-1 at 1.0 C with 85.5% retention after 300 cycles (2.8-4.35 V) and a high initial reversible capacity of 182.5 mAh g-1 at 0.2 C with 87.6% retention after 100 cycles (2.8-4.5 V). Notably, this facile and scalable electrode engineering makes Ni-rich layered oxides promising for practical applications.

Unraveling the impact of pore length on the conversion reaction of Fe3O4/carbon anodes in lithium-ion batteries

Despite numerous studies investigating Fe3O4/porous carbon anode materials for high-performance lithium-ion batteries (LIBs), the inherent limitations of the Fe3O4 conversion reaction, such as low reversibility and sluggish kinetics, continue to pose significant challenges. While modifying the porous structure of Fe3O4 anodes has demonstrated considerable promise in overcoming these limitations, the precise relationship between the porous structure and Fe3O4 conversion behavior still remains unclear. Here, we explore the impact of the pore length of the anode active material on the electrochemical performance of LIBs. Using two different composites of Fe3O4 and porous carbon with varying pore lengths as model materials, we conduct various in-depth electrochemical and ex-situ analyses. Our findings confirm that a shorter pore length facilitates higher Li+ ion diffusivity compared to longer pore length. Consequently, the conversion reaction of Fe3O4 to Fe and Li2O during lithiation process can be expedited, leading to a decrease in the resistance at the solid electrolyte interphase. As a result, we demonstrate that shortening the pore length of the porous anode composite materials can enhance the initial Coulombic efficiency (CE), reversible capacity, and rate capability of LIBs.

Exploring a New, Scalable Synthesis Route to Disordered Rock Salt (DRX) Cathode Materials

The global demand for lithium-ion batteries (LIBs) is ever-increasing as many nations seek to achieve a net carbon neutrality by the late 2030s. LiNi x Mn y Co1–x–y O2, (NMC) is one of the most widely-used Li-ion cathode active materials. Despite its excellent performance (e.g., reversible capacities up to ~220 mA h g–1 and 500+ cycles), NMC contains both Ni and Co, which are expensive and have vulnerable supply chains. Li-excess disordered rock salt (DRX) materials are promising new cathode materials that utilize earth-abundant transition metals such as Mn and Ti. Through a combination of cationic and anionic charge compensation, DRX materials can attain specific energies ≥700 Wh kg–1. Doping F– into the DRX structure (Li1+x Mn y Ti2–1–x–y O2–z F z ) has been reported to improve the material’s cycling stability. Despite their promising properties, most DRX cathodes are prepared through solid-state synthesis routes which require high-energy milling, provide little-to-no control over the particle morphology, and are difficult to scale.In this work, we developed a scalable combustion synthesis route (the glycine nitrate process) to produce high purity, high performance DRX cathodes. More specifically, we prepared two DRX precursors with nominal compositions of Li1.2Mn0.5Ti0.3O1.95 and Li1.2Mn0.7Ti0.1O1.85. When the precursors were heated under Ar to 1000 °C for 1 – 4 h, only 50% Li1.2Mn0.5Ti0.3O1.95 adopted a DRX structure, and no DRX formed for Li1.2Mn0.7Ti0.1O1.85. However, adding LiF to the precursors facilitates DRX phase formation during annealing and yields high purity DRX powders with the nominal compositions Li1.25Mn0.5Ti0.3O1.95F0.05 and Li1.35Mn0.7Ti0.1O1.85F0.15. In situ X-ray diffraction was employed to study the synthesis process, revealing DRX begins to form at just 600 °C, which is much lower than traditional solid-state routes. Furthermore, electrochemical tests on the Li1.35Mn0.7Ti0.1O1.85F0.15 cathode reveal these materials attain excellent performance with initial reversible capacities up to 215 mA h g–1 and stable cycling performance. These promising results demonstrate that combustion synthesis is a viable method for the scale-up of DRX materials.This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and was sponsored by the Vehicle Technologies Office (VTO) under the Office of Energy Efficiency and Renewable Energy (EERE). Some measurements were conducted at the Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.

Accessing Cation and Anion Redox in a 1-D Iron-Chalcogenide, Na3Fe2S4-XSex (x = 0, 2, & 4), in Na-Ion Batteries

The utilization of anionic redox activity is gaining significant interest in chalcogen based alkali-ion batteries. In this study, we are reporting reversible Na-ion (de)intercalation in one-dimensional structure of Na3Fe2S4-xSex (x = 0, 2, and 4). The crystal structure of Na3Fe0.5 2+Fe0.5 3+Q4 (Q = S and Se) can be visualized as a mixed valent iron, Fe2+/Fe3+ , forming infinite edge-shared chain of FeQ 4 tetrahedra with Na-ion residing in the interchain voids. While cycling the cathodes within a potential range of 1.5 – 2.5 V vs. Na/Na+, we could reversibly (de)intercalate one mole of Na from the structure. Mössbauer spectroscopy reveals a complete Fe2+ to Fe3+ oxidation in all the charged samples. Substitution of less electronegative Se2– in the structure systematically lowers the Fe2+/3+ redox couple during cycling. After 100 cycles at 1C rate, the cathode retains 83 % of its initial reversible capacity. While cycling the same cathode at a higher voltage range of 1.5 – 3.0 V, we observed a flat plateau profile at ~2.6 V with capacity reaching 255 mAh/g for Na3Fe2S4 cathode. This high capacity can be directly attributed to the anion oxidation for the charge compensation process during ~3.0 Na-ion deintercalation as supported by XPS analysis. The flat plateau profile further decreases from 2.6 to 2.5 V with the substitution of Se2–. The GITT results show two distinct kinetic behavior for the cation (fast) and anion (sluggish) redox. The decoupling of cation and anion redox in this system can enable us to understand and optimize the utilization of both redox chemistries to achieve a high energy density cathode.

High-Temperature Lithium-Sulfur Batteries with Commercial Paper-Derived Solid-State Electrolyte

Solid-state lithium-sulfur (Li-S) battery technologies could power future electric mobility due to their potential high energy density. However, the current solid-state Li-S batteries face several challenges, such as high internal impedance at the electrode/electrolyte interfaces, shuttling of lithium polysulfides, and Li dendrite formation. Herein, we introduced a novel Li-rich cellulose-based solid-state electrolyte in combination with sulfurized polyacrylonitrile (SPAN, 36.5 wt.% S) cathode, leading to durable Li-S batteries for high-temperature applications. We utilized SPAN due to its reasonable conductivity, high reversible capacity, and stable cycling performance. The solid-state electrolyte in this study was prepared by infusing Li ions (Li+) into a copper-coordinated cellulosic paper. The infusion of Li+ was carried out by soaking the copper-treated paper in a 1 M LiTFSI in EC0.5DME0.25DOL0.25 solution (where subscripts indicate the volume fraction), followed by complete evaporation of the solvents. Three types of cellulosic paper were explored, from which the commercial copy paper resulted in the highest area-normalized conductance of 24.4 mS cm-2 and Li-ion transference number of 0.76 at 50 °C. At this temperature, the Li-SPAN cells with paper-based electrolyte delivered an initial reversible capacity of 1536 mAh gs -1 at 168 mA gs -1 (0.1C). After high-temperature cycling for 150 cycles at 0.5C, the Li-SPAN cells exhibited an exceptional capacity retention of 82.2% (from 982 to 807 mAh gs -1). The conformability of the paper-based electrolyte ensures good interfacial contact with the SPAN and Li electrodes. As a result, when this solid-state Li-S battery was subjected to fast charging/discharging (1C) at 50 °C, it delivered a reversible capacity of 670 mAh gs -1. In this talk, we will outline the results from our electron microscopy, X-ray diffraction measurements, electrochemical impedance spectroscopy, and cyclic voltammetry studies on Li-S cells to unravel the superior performance of paper-based Li-S batteries at high temperatures. Figure 1