Lithium Sulfide (Li₂S)/Graphene Oxide Nanospheres with Conformal Carbon Coating as a High-Rate, Long-Life Cathode for Li/S Cells

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W·h kg^–1, which is much higher than that of Li ion cells (400–600 W·h kg^–1). However, problems of the S cathode such as highly soluble intermediate species (polysulfides Li₂S_<i>n</i>, <i>n</i> = 4–8) and the insulating nature of S cause poor cycle life and low utilization of S, which prevents the practical use of Li/S cells. Here, a high-rate and long-life Li/S cell is proposed, which has a cathode material with a core–shell nanostructure comprising Li₂S nanospheres with an embedded graphene oxide (GO) sheet as a core material and a conformal carbon layer as a shell. The conformal carbon coating is easily obtained by a unique CVD coating process using a lab-designed rotating furnace without any repetitive steps. The Li₂S/GO@C cathode exhibits a high initial discharge capacity of 650 mA·h g^–1 of Li₂S (corresponding to the 942 mA·h g^–1 of S) and very low capacity decay rate of only 0.046% per cycle with a high Coulombic efficiency of up to 99.7% for 1500 cycles when cycled at the 2 C discharge rate

Zinc Phosphides as Outstanding Sodium-Ion Battery Anodes

To design a high-performance sodium-ion battery anode, binary zinc phosphides (ZnP2 and Zn3P2) were synthesized by a facile solid-state heat treatment process, and their Na storage characteristics were evaluated. The Na reactivity of ZnP2 was better than that of Zn3P2. Therefore, a C-modified ZnP2-based composite (ZnP2-C) was fabricated to achieve better electrochemical performance. To investigate the electrochemical reaction mechanism of ZnP2-C during sodiation/desodiation, various ex situ analytical techniques were employed. During sodiation, ZnP2 in the composite was transformed into NaZn13 and Na3P phases, exhibiting a one-step conversion reaction. Conversely, Zn and P in NaZn13 and Na3P, respectively, were fully recombined to the original ZnP2 phase during desodiation. Owing to the one-step conversion/recombination of ZnP2 in the composite during cycling, the ZnP2-C showed high electrochemical performance with a highly reversible capacity of 883 mA h g–1 after 130 cycles with no capacity deterioration and a fast C-rate capability of 500 mA h g–1 at 1 C and 350 mA h g–1 at 3 C

Failure Modes of Flexible LiCoO₂ Cathodes Incorporating Polyvinylidene Fluoride Binders with Different Molecular Weights

Understanding the mechanical failure modes of lithium-ion battery [Li-ion batteries (LIBs)] electrodes is exceptionally important for enabling high specific energy and flexible LIB technologies. In this work, the failure modes of lithium cobalt oxide (LCO) cathodes under repeated bending and the role of the polymer binder in improving the mechanical durability of the LCO electrodes for use in flexible LIBs are investigated. Mechanical and electrochemical evaluations of LCO electrodes (areal capacity of ≥2.5 mA h cm–2) employing poly(vinylidene fluoride) (PVDF) binder were carried out, followed by extensive optical and electron microscopies. We find that the molecular weight (MW) of the PVDF significantly influenced the surface and bulk microstructure of the LCO electrodes, particularly the distribution of carbon additive and binder, which plays a crucial role in affecting the mechanical and electrochemical properties of the electrodes. Multiple mechanical failure modes (e.g., surface scratches and microcracks) observed in the LCO electrodes subjected to repeated bending originated from the use of low MW PVDF; these failure modes were successfully mitigated by using a high MW PVDF. Remarkably, the optimized flexible LCO electrode incorporating high MW PVDF showed comparable discharge capacity retention during galvanostatic cycling after repeated bending (7000 cycles at 50 mm bending diameter) to electrodes not subjected to the repeated bending. This study highlights the importance of carrying out a comprehensive investigation of the failure mechanisms in flexible electrodes, which identified the pivotal role of the PVDF MW in the electrode microstructure and its effects on the electrode resilience to failure during repeated bending

Redox-Active Supramolecular Polymer Binders for Lithium–Sulfur Batteries That Adapt Their Transport Properties in Operando

π-Stacked perylene bisimide (PBI) molecules are implemented here as highly networked, redox-active supramolecular polymer binders in sulfur cathodes for lightweight and energy-dense Li–S batteries. We show that the in operando reduction and lithiation of these PBI binders sustainably reduces Li–S cell impedance relative to nonredox active conventional polymer binders. This lower impedance enables high-rate cycling in Li–S cells with excellent durability, a critical step toward unlocking the full potential of Li–S batteries for electric vehicles and aviation

High-Energy-Density Gallium Antimonide Compound Anode and Optimized Nanocomposite Fabrication Route for Li-Ion Batteries

Lithium-ion batteries (LIBs) are key enablers for achieving net-zero emission by transitioning from fossil fuels to renewable energy. This study introduces a GaSb compound anode and optimized nanocomposite fabrication route for superior LIBs. First, to utilize the synergistic effect of Ga and Sb, their GaSb compound was synthesized using a simple thermal solid-state reaction. Furthermore, the anode performance and reaction mechanisms of GaSb and elemental Ga and Sb with Li ions are demonstrated fully using cutting-edge analysis tools. Second, two nanocomposite fabrication routes are suggested to obtain optimized GaSb anodes for LIBs: (1) reduced graphene oxide (rGO)-decorated GaSb nanocomposite (GaSb/rGO) by a chemical modification and (2) amorphous C (a-C)-decorated GaSb nanocomposite (GaSb/a-C) by a mechanical modification. Among the nanocomposites, the GaSb/a-C shows better electrochemical performance, achieved by the three-step nanoconfinement and stabilization of tiny GaSb crystallites (approximately 2–4 nm) homogeneously embedded in the carbon matrix. The proposed GaSb/a-C anode exhibits highly reversible gravimetric/volumetric capacities, long-term cyclability, and excellent high rate capabilities, which are much better than conventional graphite anodes. In this study, we provide an insight into the reaction mechanism of GaSb with Li ions and suggest a high-energy-density GaSb compound anode for LIBs

Direct Visualization of Lithium Polysulfides and Their Suppression in Liquid Electrolyte

Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene liquid cell electron microscopy, we have visualized formation and diffusion of Li-PS simultaneous with morphological and phase evolutions of sulfur nanoparticles during lithiation. We found that the morphological changes and Li-PS diffusion are retarded by ionic liquid (IL) addition into electrolyte. Chronoamperometric shuttle current measurement confirms that IL addition lowers the experimental diffusion coefficient of Li-PS by 2 orders of magnitude relative to that in IL-free electrolyte and thus suppresses the Li-PS shuttle current, which accounts for better cyclability and Coulombic efficiency of the Li/S cell. This study provides significant insights into electrolyte design to inhibit the polysulfide shuttle phenomenon

Three-Dimensionally Aligned Sulfur Electrodes by Directional Freeze Tape Casting

Rational design of sulfur electrodes is exceptionally important in enabling a high-performance lithium/sulfur cell. Constructing a continuous pore structure of the sulfur electrode that enables facile lithium ion transport into the electrode and mitigates the reconstruction of sulfur is a key factor for enhancing the electrochemical performance. Here, we report a three-dimensionally (3D) aligned sulfur electrode cast onto conventional aluminum foil by directional freeze tape casting. The 3D aligned sulfur–graphene oxide (S–GO) electrode consisting of few micron thick S–GO layers with 10–20 μm interlayer spacings demonstrates significant improvement in the performance of the Li/S cell. Moreover, the freeze tape cast graphene oxide electrode exhibits homogeneous reconfiguration behavior in the polysulfide catholyte cell tests and demonstrated extended cycling capability with only 4% decay of the specific capacity over 200 cycles. This work emphasizes the critical importance of proper structural design for sulfur–carbonaceous composite electrodes

Direct Visualization of Lithium Polysulfides and Their Suppression in Liquid Electrolyte

Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene liquid cell electron microscopy, we have visualized formation and diffusion of Li-PS simultaneous with morphological and phase evolutions of sulfur nanoparticles during lithiation. We found that the morphological changes and Li-PS diffusion are retarded by ionic liquid (IL) addition into electrolyte. Chronoamperometric shuttle current measurement confirms that IL addition lowers the experimental diffusion coefficient of Li-PS by 2 orders of magnitude relative to that in IL-free electrolyte and thus suppresses the Li-PS shuttle current, which accounts for better cyclability and Coulombic efficiency of the Li/S cell. This study provides significant insights into electrolyte design to inhibit the polysulfide shuttle phenomenon

Direct Visualization of Lithium Polysulfides and Their Suppression in Liquid Electrolyte

Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene liquid cell electron microscopy, we have visualized formation and diffusion of Li-PS simultaneous with morphological and phase evolutions of sulfur nanoparticles during lithiation. We found that the morphological changes and Li-PS diffusion are retarded by ionic liquid (IL) addition into electrolyte. Chronoamperometric shuttle current measurement confirms that IL addition lowers the experimental diffusion coefficient of Li-PS by 2 orders of magnitude relative to that in IL-free electrolyte and thus suppresses the Li-PS shuttle current, which accounts for better cyclability and Coulombic efficiency of the Li/S cell. This study provides significant insights into electrolyte design to inhibit the polysulfide shuttle phenomenon

Direct Visualization of Lithium Polysulfides and Their Suppression in Liquid Electrolyte

Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene liquid cell electron microscopy, we have visualized formation and diffusion of Li-PS simultaneous with morphological and phase evolutions of sulfur nanoparticles during lithiation. We found that the morphological changes and Li-PS diffusion are retarded by ionic liquid (IL) addition into electrolyte. Chronoamperometric shuttle current measurement confirms that IL addition lowers the experimental diffusion coefficient of Li-PS by 2 orders of magnitude relative to that in IL-free electrolyte and thus suppresses the Li-PS shuttle current, which accounts for better cyclability and Coulombic efficiency of the Li/S cell. This study provides significant insights into electrolyte design to inhibit the polysulfide shuttle phenomenon