A General Method to Fabricate Free-Standing Electrodes: Sulfonate Directed Synthesis and their Li⁺ Storage Properties

For materials based on a spatially varied conversion reaction, Li⁺ storage properties largely hinge on the rational design of the concurrent electronic and ionic pathways in the electrode. We herein present a scalable approach for integrating size-tunable Fe₃O₄ nanocrystals with hierarchical porous carbon foam by employing sulfonated high internal phase emulsion polymers (polyHIPE) as the carbon source and substrate. To verify the feasibility of our configuration design, the electrodes of such a type were directly evaluated in pouch cells without using an auxiliary binder or a metallic current collector: The best performing composite electrode, with optimized oxide size range, exhibits a good capacity retention of 89.7% of the first charge capacity after 100 cycles and high rate durability up to 4 A g^–1. Furthermore, this synthetic approach was also applied to develop carbon/FeS free-standing anodes using the sulfonate groups as the sulfur source, demonstrating its generic applicability to the fabrication of other free-standing electrodes with enhanced Li⁺ storage properties

Toward Solid-State 3D-Microbatteries Using Functionalized Polycarbonate-Based Polymer Electrolytes

3D microbatteries (3D-MBs) impose new demands for the selection, fabrication, and compatibility of the different battery components. Herein, solid polymer electrolytes (SPEs) based on poly­(trimethylene carbonate) (PTMC) have been implemented in 3D-MB systems. 3D electrodes of two different architectures, LiFePO₄-coated carbon foams and Cu₂O-coated Cu nanopillars, have been coated with SPEs and used in Li cells. Functionalized PTMC with hydroxyl end groups was found to enable uniform and well-covering coatings on LiFePO₄-coated carbon foams, which was difficult to achieve for nonfunctionalized polymers, but the cell cycling performance was limited. By employing a SPE prepared from a copolymer of TMC and caprolactone (CL), with higher ionic conductivity, Li cells composed of Cu₂O-coated Cu nanopillars were constructed and tested both at ambient temperature and 60 °C. The footprint areal capacity of the cells was ca. 0.02 mAh cm^–2 for an area gain factor (AF) of 2.5, and 0.2 mAh cm^–2 for a relatively dense nanopillar-array (AF = 25) at a current density of 0.008 mA cm^–2 under ambient temperature (22 ± 1 °C). These results provide new routes toward the realization of all-solid-state 3D-MBs

On the P2-Na<i>_x</i>Co_1–<i>y</i>(Mn_2/3Ni_1/3)<i>y</i>O₂ Cathode Materials for Sodium-Ion Batteries: Synthesis, Electrochemical Performance, and Redox Processes Occurring during the Electrochemical Cycling

P2-type NaMO₂ sodiated layered oxides with mixed transition metals are receiving considerable attention for use as cathodes in sodium-ion batteries. A study on solid solution (1 – <i>y</i>)­P2-Na<i>_x</i>CoO₂–(<i>y</i>)­P2-Na<i>_x</i>Mn_2/3Ni_1/3O₂ (<i>y</i> = 0, 1/3, 1/2, 2/3, 1) reveals that changing the composition of the transition metals affects the resulting structure and the stability of pure P2 phases at various temperatures of calcination. For 0 ≤ <i>y</i> ≤ 1.0, the P2-Na<i>_x</i>Co_{(1–<i>y</i>)}Mn_2<i>y</i>/3Ni_<i>y</i>/3O₂ solid-solution compounds deliver good electrochemical performance when cycled between 2.0 and 4.2 V versus Na⁺/Na with improved capacity stability in long-term cycling, especially for electrode materials with lower Co content (<i>y</i> = 1/2 and 2/3), despite lower discharge capacities being observed. The (1/2)­P2-Na<i>_x</i>CoO₂–(1/2)­P2-Na<i>_x</i>Mn_2/3Ni_1/3O₂ composition delivers a discharge capacity of 101.04 mAh g^–1 with a capacity loss of only 3% after 100 cycles and a Coulombic efficiency exceeding 99.2%. Cycling this material to a higher cutoff voltage of 4.5 V versus Na⁺/Na increases the specific discharge capacity to ≈140 mAh g^–1 due to the appearance of a well-defined high-voltage plateau, but after only 20 cycles, capacity retention declines to 88% and Coulombic efficiency drops to around 97%. In situ X-ray absorption near-edge structure measurements conducted on composition Na<i>_x</i>Co_1/2Mn_1/3Ni_1/6O₂ (<i>y</i> = 1/2) in the two potential windows studied help elucidate the operating potential of each transition metal redox couple. It also reveals that at the high-voltage plateau, all of the transition metals are stable, raising the suspicion of possible contribution of oxygen ions in the high-voltage plateau