Understanding Voltage Hysteresis for High-Energy-Density Li–S Batteries

Li–S batteries are promising candidates for next-generation energy storage technologies owing to their high theoretical capacity and low weight and the wide availability of S. The addition of Se to S is considered a rational design principle to regulate the polarization of Li–S cells intrinsically. Moreover, the electrochemical utilization of solid-state Li2–xS (0.0 ≤ x ≤ 1.0) provides sufficiently high theoretical specific capacity (836 mA h g–1) and long-term stability. However, solid-state Se-doped Li–S compounds during (de)­lithiation have not been studied in detail. Therefore, we performed combined experimental and theoretical studies to reveal the reduction of polarization by Se doping owing to multiple factors that were previously assumed to be negligible. Experimentally, the polarization reduction in Se-doped Li2S is dependent on the electronic, ionic, and thermodynamic properties of the Se dopant. Theoretically, Se doping simultaneously lowers the formation energy, bond symmetry of Li–S­(Se), energy required for structural changes, and electronic stability, resulting in the reduction of polarization. Our concrete understanding of the two types of Li–S electrodes can aid the design of advanced high-energy solid-state Li–S batteries

Graphene–Li₂S–Carbon Nanocomposite for Lithium–Sulfur Batteries

Lithium sulfide (Li₂S) with a high theoretical specific capacity of 1166mAh g^–1 is a promising cathode material for next-generation Li–S batteries with high specific energy. However, low conductivity of Li₂S and polysulfide dissolution during cycling are known to limit the rate performance and cycle life of these batteries. Here, we report on the successful development and application of a nanocomposite cathode comprising graphene covered by Li₂S nanoparticles and protected from undesirable interactions with electrolytes. We used a modification of our previously reported low cost, scalable, and high-throughput solution-based method to deposit Li₂S on graphene. A dropwise infiltration allowed us to keep the size of the heterogeneously nucleated Li₂S particles smaller and more uniform than what we previously achieved. This, in turn, increased capacity utilization and contributed to improved rate performance and stability. The use of a highly conductive graphene backbone further increased cell rate performance. A synergetic combination of a protective layer vapor-deposited on the material during synthesis and <i>in situ</i> formed protective surface layer allowed us to retain ∼97% of the initial capacity of ∼1040 mAh g_s^–1 at <i>C</i>/2 after over 700 cycles in the assembled cells. The achieved combination of high rate performance and ultrahigh stability is very promising

Deciphering Enhanced Solid-State Kinetics of Li–S Batteries via Te Doping

Owing to their high gravimetric energy, low cost, and wide availability of required materials, Li–S batteries (LSBs) are considered as a promising next-generation energy storage technology. However, the sluggish redox kinetics and dissolution of lithium polysulfides during the electrochemical reactions are key problems to overcome. The improvement of the long-term cycle life of LSBs solely by converting insoluble solid-state electrolyte-soluble lithium polysulfides (LiPSs) (Li2Sx, where 1 ≤ x ≤ 2, 836 mAh g–1) is an ingenious method, but solid-state LiPS conversion has sluggish redox kinetics owing to the intrinsically low electrical conductivity of solid-state LiPS compounds (Li2S and Li2S2). This study applied Te doping to S cathodes and conducted experimental and theoretical analyses on the Te-doped solid-state LiPSs to investigate the effect of Te on the redox kinetics of the solid-state LiPS conversions for high-performance LSBs. The qualitative and quantitative electrochemical characterization demonstrated that Te induced an increase in the kinetics. Furthermore, the enhanced kinetics were explained at the atomic scale by the theoretical thermodynamics and chemomechanics investigations. The design of high-performance LSBs will benefit the strong understanding of Te-doped S electrodes in solid-state conversion

Microwave-Mediated Stabilization and Carbonization of Polyacrylonitrile/Super‑P Composite: Carbon Anodes with High Nitrogen Content for Lithium Ion Batteries

Most synthetic carbonaceous anode materials for lithium-ion batteries (LIBs) are fabricated through a two-step heat-treatment process involving stabilization and carbonization. In this study, the stabilization and carbonization processes were accomplished via microwave treatment in significantly reduced time to fabricate carbonaceous anode materials for LIBs. Polymeric precursors for carbon materials, such as polyacrylonitrile (PAN), cannot be heat treated via the microwave because of their weak microwave-absorption properties. To address the issue, Super-P, carbon nanoparticles with an excellent microwave absorbing property, was adopted as a microwave initiator. On mixing a small amount of Super-P with PAN, Super-P acted as an efficient microwave absorber, and the temperature of the PAN/Super-P composite rapidly increased upon microwave treatment. Consequently, the stabilization time was reduced from 60 to 30 min when microwave irradiation was used to heat the PAN/Super-P composite. More significantly, the carbon sample could be fabricated by using only 1 min of microwave treatment, whereas convection heating required more than 200 min. Additionally, the carbonaceous materials obtained after microwave heating over shorter time periods were endowed with a high nitrogen content. The nitrogen content of microwave-heated carbon was 8.89%, whereas that of the convection carbonized counterpart was only 4.63%. Both pyridinic and graphitic nitrogen, which have been reported to improve the electrochemical performance, were noticeably higher in microwave-heated carbon. The synthesized microwave-assisted carbon material exhibited notable enhancements in the reversible capacity, rate performance, and cyclic stability. In summary, microwave-assisted stabilization and carbonization techniques offer options for the fast production of carbon anodes with excellent electrochemical performance and may be used for developing practical and high-performance battery anodes

Aqueous Quaternary Polymer Binder Enabling Long-Life Lithium–Sulfur Batteries by Multifunctional Physicochemical Properties

Lithium–sulfur batteries (LSBs) have been considered promising candidates for application in high-density energy storage systems owing to their high gravimetric and volumetric energy densities. However, LSB technology faces many barriers from the intrinsic properties of active materials that need to be solved to realize high-performance LSBs. Herein, an aqueous binder, that is, PPCP, based on polyethyleneimine (PEI), polyvinylpyrrolidone (PVP), citric acid (CA), and polyethylene oxide (PEO), was developed. The synthesized PPCP binder has incredible mechanical properties, suitable viscosity, and essential functional groups for developing an effective and reliable LSB system. This study demonstrates that CA is crucial in cross-linking PEI–PVP polymer molecules, and PEO segments significantly enhance the flexibility of the PPCP binder; thus, the binder can mechanically stabilize the cathode structure over many operating cycles. The redistribution of active materials during the charge–discharge processes and reduction of the shuttle effect originate from the excellent chemical interactions of PPCP with lithium polysulfides, which is confirmed by the density functional theory calculation, enabling an ultra-long electrochemical cycle life of 1800 cycles with a low decay rate of 0.0278% cycle–1

Enhancing the Stability of Sulfur Cathodes in Li–S Cells via in Situ Formation of a Solid Electrolyte Layer

Enhancing the performance of rechargeable lithium (Li)–sulfur (S) batteries is one of most popular topics in a battery field because of their low cost and high specific energy. However, S experiences dissolution during its electrochemical reactions; hence, maintaining its initial capacity is challenging. Protecting the S cathode with a Li ion conducting layer that acts as a barrier for polysulfide transport is an attractive strategy, but formation of such protective layers typically involves significant effort and cost. Here, we report a facile route to form a conformal solid electrolyte layer on S cathodes in situ using a carbonate solvent. The chemically and mechanically stable and Li ion conducting protective layer is formed by inducing electrolyte reduction and polymerization reactions on the cathode surface. The layer serves as a polysulfide’s barrier, successfully helping to retain S active material in the carbon pores. In addition, it helps to improve the performance of Li anodes

Continuous-Flow Synthesis of Carbon-Coated Silicon/Iron Silicide Secondary Particles for Li-Ion Batteries

The development of better Li-ion battery (LIB) electrodes requires an orchestrated effort to improve the active materials as well as the electron and ion transport in the electrode. In this paper, iron silicide is studied as an anode material for LIBs because of its higher conductivity and lower volume expansion compared to pure Si particles. In addition, carbon nanotubes (CNTs) can be synthesized from the surface of iron-silicides using a continuous flow coating process where precursors are first spray dried into micrometer-scale secondary particles and are then flown through a chemical vapor deposition (CVD) reactor. Some CNTs are formed inside the secondary particles, which are important for short-range electrical transport and good utilization of the active material. Surface-bound CNTs on the secondary particles may help establish a long-range conductivity. We also observed that these spherical secondary particles allow for better electrode coating quality, cyclability, and rate performance than unstructured materials with the same composition. The developed electrodes retain a gravimetric capacity of 1150 mAh/g over 300 cycles at 1A/g as well as a 43% capacity retention at a rate of 5 C. Further, blended electrodes with graphite delivered a 539 mAh/g with high electrode density (∼1.6 g/cm3) and areal capacity (∼3.5 mAh/cm2) with stable cycling performance