Freeze-Drying-Assisted Synthesis of Porous SnO2 /rGO Xerogels as Anode Materials for Highly Reversible Lithium/Sodium Storage

Oxygen-Rich Carbon Nitrides from an Eutectic Template Strategy Stabilize Ni, Fe Nanosites for Electrocatalytic Oxygen Evolution

Functionalized porous carbons are central to various important applications such as energy storage and conversion. Here, a simple synthetic route to prepare oxygen-rich carbon nitrides (CNOs) decorated with stable Ni and Fe-nanosites is demonstrated. The CNOs are prepared via a salt templating method using ribose and adenine as precursors and CaCl₂ ·2H₂ O as a template. The formation of supramolecular eutectic complexes between CaCl₂ ·2H₂ O and ribose at relatively low temperatures facilitates the formation of a homogeneous starting mixture, promotes the condensation of ribose through the dehydrating effect of CaCl₂ ·2H₂ O to covalent frameworks, and finally generates homogeneous CNOs. As a specific of the recipe, the condensation of the precursors at higher temperatures and the removal of water promotes the recrystallization of CaCl₂ (T < T_m = 772 °C), which then acts as a hard porogen. Due to salt catalysis, CNOs with oxygen and nitrogen contents as high as 12 and 20 wt%, respectively, can be obtained, while heteroatom content stayed about unchanged even at higher temperatures of synthesis, pointing to the extraordinarily high stability of the materials. After decorating Ni and Fe-nanosites onto the CNOs, the materials exhibit high activity and stability for electrochemical oxygen evolution reaction with an overpotential of 351 mV.

Binary-Metal Mn2SnO4 Nanoparticles and Sn Confined in a Cubic Frame with N-Doped Carbon for Enhanced Lithium and Sodium Storage

Sn-based materials have been popularly researched as anodes for energy storage due to their high theoretical capacity. However, the sluggish reaction kinetics and unsatisfied cycling stability caused by poor conductivity and dramatic volume expansion are still pivotal barriers for the development of Sn-based materials as anodes. In this work, the binary-metal Mn₂SnO₄ nanoparticles and Sn encapsulated in N-doped carbon (Sn@Mn₂SnO₄-NC) were fabricated by multistep reactions and employed as the anode for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The coexistence of binary metals (Sn and Mn) can improve intrinsic conductivity. Simultaneously, hollow architecture along with carbon relieves internal stress and prevents structural collapse. A Sn@Mn₂SnO₄-NC anode delivers an appealing capacity of 1039.5 mAh g^-1 for 100 cycles at 100 mA g^-1 and 823.8 mAh g^-1 for 600 cycles at 1000 mA g^-1 in LIBs. When evaluated as an anode in SIBs, the Sn@Mn₂SnO₄-NC anode tolerates up to 7000 cycles at 2000 mA g^-1 and maintains a capacity of 185.8 mAh g^-1. Quantified kinetic investigations demonstrate the high contribution of pseudocapacitive effects during the cycle process. Furthermore, density functional theory (DFT) calculations further verify that introduction of the second metal (Mn) improves the conductivity of the material, which is favorable for charge transport. This work is expected to provide a feasible preparation strategy for binary-metal materials to enhance the performance of lithium- and sodium-ion batteries.

SnO2 Nanoflake Arrays Coated with Polypyrrole on a Carbon Cloth as Flexible Anodes for Sodium-Ion Batteries

SnO₂ has been extensively studied as an anode material for sodium-ion batteries, which, however, has long been subjected to poor conductivity and large volume expansion accompanied with an unsatisfactory electrochemical performance. Here, novel interlaced SnO₂ nanoflakes are synthesized directly on a carbon cloth collector via hydrothermal and annealing treatment and then coated with polypyrrole (PPy) via electrodeposition. The as-prepared flexible SnO₂@PPy on the carbon cloth exhibits a high initial capacity of 1172.1 mAh g^-1 and an outstanding cycling stability with 85% capacity retention after 300 cycles at 0.1 A g^-1, which can be contributed to the interlaced SnO₂ nanoflakes as well as the coating of PPy. This result shows promising potential for construction of an electrode in high-performance energy storage fields.