Stable and Highly Ion-Selective Membrane Made from Cellulose Nanocrystals for Aqueous Redox Flow Batteries.

The design of chemically stable ion-exchange membranes with high selectivity for applications in an aqueous redox flow battery (RFB) at high acid concentrations remains a significant challenge. Herein, this study designed a stable and highly ion-selective membrane by utilizing proton conductive cellulose nanocrystals (CNCs) incorporated in a semicrystalline hydrophobic poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix. The high hydrophobicity of the PVDF-HFP matrix mitigates crossover of the electrolytes, whereas the abundant and low-cost CNCs derived from wood provide high proton conductivity. The fundamental contributors for CNCs' excellent proton conductivity are the hydroxyl (-OH) functional groups, highly acidic sulfonate (-SO3H) functional groups, and the extensive intramolecular hydrogen bonding network. In addition, CNCs exhibit a mechanically and chemically stable structure in the harsh acidic electrolyte attributed to the high crystallinity (crystalline index of ∼86%). Therefore, because of the high proton conductivity, excellent ion selectivity, high chemical stability, and structural robustness, the vanadium redox flow battery (VRFB) assembled with the homogeneous CNCs and PVDF-HFP (CNC/PVDF-HFP) membrane achieved a Coulombic efficiency (CE) of 98.2%, energy efficiency (EE) of 88.2%, and a stable cycling performance for more than 650 cycles at a current density of 100 mA cm-2. The obtained membrane possesses excellent flexibility, high mechanical tensile strength, and superior selectivity. Meanwhile, the applied casting method is scalable for large-scale manufacturing.

Bone-Inspired Mineralization with Highly Aligned Cellulose Nanofibers as Template.

Bioinspired by the aligned structure and building blocks of bone, this work mineralized the aligned bacterial cellulose (BC) through in situ mineralization using CaCl2 and K2HPO4 solutions. The cellulose nanofibers were aligned by a scalable stretching process. The aligned and mineralized bacterial cellulose (AMBC) homogeneously incorporated hydroxyapatite (HAP) with a high mineral content and exhibited excellent mechanical strength. The ordered 3D structure allowed the AMBC composite to achieve a high elastic modulus and hardness and the development of a nanostructure inspired by natural bone. The AMBC composite exhibited an elastic modulus of 10.91 ± 3.26 GPa and hardness of 0.37 ± 0.18 GPa. Compared with the nonaligned mineralized bacterial cellulose (NMBC) composite with mineralized crystals of HAP randomly distributed into the BC scaffolds, the AMBC composite possessed a 210% higher elastic modulus and 95% higher hardness. The obtained AMBC composite had excellent mechanical properties by mimicking the natural structure of bone, which indicated that the organic BC aerogel with aligned nanofibers was a promising template for biomimetic mineralization.

Sulfide-Based Solid-State Electrolytes: Synthesis, Stability, and Potential for All-Solid-State Batteries.

Due to their high ionic conductivity and adeciduate mechanical features for lamination, sulfide composites have received increasing attention as solid electrolyte in all-solid-state batteries. Their smaller electronegativity and binding energy to Li ions and bigger atomic radius provide high ionic conductivity and make them attractive for practical applications. In recent years, noticeable efforts have been made to develop high-performance sulfide solid-state electrolytes. However, sulfide solid-state electrolytes still face numerous challenges including: 1) the need for a higher stability voltage window, 2) a better electrode-electrolyte interface and air stability, and 3) a cost-effective approach for large-scale manufacturing. Herein, a comprehensive update on the properties (structural and chemical), synthesis of sulfide solid-state electrolytes, and the development of sulfide-based all-solid-state batteries is provided, including electrochemical and chemical stability, interface stabilization, and their applications in high performance and safe energy storage.

Dual-Function, Tunable, Nitrogen-Doped Carbon for High-Performance Li Metal-Sulfur Full Cell.

Lithium metal-sulfur (Li-S) batteries are attracting broad interest because of their high capacity. However, the batteries experience the polysulfide shuttle effect in cathode and dendrite growth in the Li metal anode. Herein, a bifunctional and tunable mesoporous carbon sphere (MCS) that simultaneously boosts the performance of the sulfur cathode and the Li anode is designed. The MCS homogenizes the flux of Li ions and inhibits the growth of Li dendrites due to its honeycomb structure with high surface area and abundance of nitrogen sites. The Li@MCS cell exhibits a small overpotential of 29 mV and long cycling performance of 350 h under the current density of 1 mA cm-2 . Upon covering one layer of amorphous carbon on the MCS (CMCS), an individual carbon cage is able to encapsulate sulfur inside and reduce the polysulfide shuttle, which improves the cycling stability of the Li-S battery. As a result, the S@CMCS has a maximum capacity of 411 mAh g-1 for 200 cycles at a current density of 3350 mA g-1 . Based on the excellent performance, the full Li-S cell assembled with Li@MCS anode and S@CMCS cathode shows much higher capacity than a cell assembled with Li@Cu anode and S@CMCS cathode.

Bacterial-Derived, Compressible, and Hierarchical Porous Carbon for High-Performance Potassium-Ion Batteries.

Hierarchical-structured electrodes having merits of superior cycling stability and high rate performance are highly desired for next-generation energy storage. For the first time, we reported a compressible and hierarchical porous carbon nanofiber foam (CNFF) derived from a sustainable and abundant biomaterial resource, bacterial cellulose, for boosting the electrochemical performance of potassium-ion batteries. The CNFF free-standing electrode with a hierarchical porous three-dimensional structure demonstrated excellent rate performance and outstanding cyclic stability in the extended cycling test. Specifically, in the long-term cycling-stability test, the CNFF electrode maintained a stable capacity of 158 mA h g-1 after 2000 cycles at a high current density of 1000 mA g-1, which has an average capacity decay of 0.006% per cycle. After that, the CNFF electrode maintained a capacity of 141 mA h g-1 at a current density of 2000 mA g-1 for another 1500 cycles, and a capacity of 122 mA h g-1 at a current density of 5000 mA g-1 for an additional 1000 cycles. The mechanism for the outstanding performance is that the hierarchical porous and stable CNFF with high surface area and high electronic conductivity provides sufficient sites for potassium-ion storage. Furthermore, quantitative kinetics analysis has validated the capacitive- and diffusion-controlled charge-storage contributions in the carbon-foam electrode. This work will inspire the search for cost-effective and sustainable materials for potassium electrochemical energy storage.