High energy density primary cathode with a mixed electron/ion interface

The Alkynyl π Bond of sp-C Enhanced Rapid, Reversible Li-C Coupling to Accelerate Reaction Kinetics of Lithium Ions

Graphdiyne (GDY) is a promising anode for rechargeable batteries with high capacity, outstanding cyclic stability, and low diffusion energy. The unique structure of GDY endows distinctive mechanisms for metal-ion storage, and it is of great significance to further visualize the complex reaction kinetics of the redox process. Here, we systematically tracked the reaction kinetics and provided mechanistic insights into the lithium ions in the GDY to reveal the feature of the cation-π effect. It has been demonstrated that, unlike only one π bond in sp2-C, π electrons provided by one of the two alkynyl π bonds in sp-C can achieve proper interaction and speedy capture of lithium ions; thus, reversible Li-C coupling can be formed between electron-rich sp-C and lithium ions. In addition to interlayer intercalation in sp2-C regions, nanopores filling triangular-like cavities composed of highly conjugated sp-C contribute to the major capacity in flat voltage plateau regions. Therefore, a capture/pores filling-intercalation hybrid mechanism can be found in GDY. The coexistence of sp and sp2 carbon enables GDY electrodes with rapid Li+ diffusion, high capacity of over 1435 mAh g-1, extraordinary rate capability, and cyclic stability for more than 10000 cycles at 10A g-1. These results provide guidance for developing advanced carbon electrodes with optimized reaction kinetics for rechargeable batteries.

The Accurate Synthesis of a Multiscale Metallic Interface on Graphdiyne

The accurate construction of composite material systems containing graphdiyne (GDY) and other metallic materials has promoted the formation of innovative structures and practical applications in the fields of energy, catalysis, optoelectronics, and biomedicine. To fulfill the practical requirements, the precise formation of multiscale interfaces over a wide range, from single atoms to nanostructures, plays an important role in the optimization of the structural design and properties. The intrinsic correlations between the structure, synthesis process, characteristic properties, and device performance are systematically investigated. This review outlines the current research achievements regarding the controlled formation of multiscale metallic interfaces on GDY. Synthetic strategies for interface regulation, as well as the correlation between the structure and performance, are presented. Furthermore, innovative research ideas for the design and synthesis of functional metal-based materials loaded onto GDY-based substances are also provided, demonstrating the promising application potential of GDY-based materials.

Microcrystalline Nanofiber Electrode with Adaptive Intrinsic Structure and Microscopic Interface

A strategy of microcrystalline aggregation is proposed to fabricate energy storage electrode with outstanding capacity and stability. Carbon-rich electrode (BDTG) functionalized with benzo[1,2-b:4,5-b']dithiophene units and butadiyne segments are prepared. The linear conjugate chains pack as microcrystalline nanofibers on nanoscale, which further aggregates to form a porous interpenetrating network. The microcrystalline aggregation feature of BDTG exhibit stable structure during long cycling test, revealing the following advantage in structure and property. The stretchable butadiyne linker facilitates reversible adsorption and desorption of Li with the aid of adjacent sulfur heteroatom. The alkyne-alkene transition exhibits intrinsic structural stability of microcrystalline region in BDTG electrodes. Meanwhile, alkynyl groups and sulfur heteroatoms on the surface of BDTG nanofibers participate in the formation of microscopic interface, providing a stable interfacial contact between BDTG electrodes and adjacent electrolyte. As a proof-of-concept, BDTG-based electrode shows high capacity (1430 mAh g-1 at 50 mA g-1) and excellent cycle performance (8000 cycles under 5 A g-1) in half-cell of lithium-ion batteries, and a reversible capacity of 120 mAh g-1 is obtained under the current density of 2 C in full-cell. This work shows microcrystalline aggregation is beneficial to realize adaptive intrinsic structure and interface contact during the charge-discharge process.

Electrolyte Engineering Empowers Li||CFx Batteries to Achieve High Energy Density and Low Self-Discharge at Harsh Conditions

Given its exceptional theoretical energy density (over 2000 Wh kg-1), lithium||carbon fluoride (Li||CFx) battery has garnered global attention. N-methylpyrrolidone (NMP)-based electrolyte is regarded as one promising candidate for tremendously enhancing the energy density of Li||CFx battery, provided self-discharge challenges can be resolved. This study successfully achieves a low self-discharge (LSD) and desirable electrochemical performance in Li||CFx batteries at high temperatures by utilizing NMP as the solvent and incorporating additional ingredients, including vinylene carbonate additive, as well as the dual-salt systems formed by LiBF4 with three different Li salts, namely lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and LiNO3. The experimental results unfold that the proposed methods not only minimize aluminum current collector corrosion, but also effectively passivate the Li metal anode. Among them, LiNO3 exhibits the most pronounced effect that achieves an energy density of ≈2400 Wh kg-1 at a current density of 10 mA g-1 at 30 °C, nearly 0% capacity-fade rate after 300 h of storage at 60 °C, and the capability to maintain a stable open-circuit voltage over 4000 h. This work provides a distinctive perspective on how to realize both high energy density and LSD rates at high temperature of Li||CFx battery.

Revealing the Mechano-Electrochemical Coupling Behavior and Discharge Mechanism of Fluorinated Carbon Cathodes toward High-Power Lithium Primary Batteries

Unclear reaction mechanisms and unsatisfactory power performance hinder the further development of advanced lithium/fluorinated carbon (Li/CFx ) batteries. Herein, the mechano-electrochemical coupling behavior of a CFx cathode is investigated by in situ monitoring strain/stress using digital image correlation (DIC) techniques, electrochemical methods, and theoretical equations. The DIC monitoring results present the distribution and dynamic evolution of the plane strain and indicate strong dependence toward the material structure and discharge rate. The average plane principal strain of fully discharged 2D fluorinated graphene nanosheets (FGNSs) at 0.5 C is 0.50%, which is only 38.5% that of conventional bulk-structure CFx . Furthermore, the superior structural stability of the FGNSs is demonstrated by the microstructure and component characterization before and after discharge. The plane stress evolution is calculated based on theoretical equations, and the contributions of electrochemical and mechanical factors are examined and discussed. Subsequently, a structure-dependent three-region discharge mechanism for CFx electrodes is proposed from a mechanical perspective. Additionally, the surface deformation of Li/FGNSs pouch cells formed during the discharge process is monitored using in situ DIC. This study reveals the discharge mechanism of Li/CFx batteries and facilitates the design of advanced CFx materials.