Flexible Graphene‐Wrapped Carbon Nanotube/Graphene@MnO2 3D Multilevel Porous Film for High‐Performance Lithium‐Ion Batteries

The ingenious design of a freestanding flexible electrode brings the possibility for power sources in emerging wearable electronic devices. Here, reduced graphene oxide (rGO) wraps carbon nanotubes (CNTs) and rGO tightly surrounded by MnO₂ nanosheets, forming a 3D multilevel porous conductive structure via vacuum freeze‐drying. The sandwich‐like architecture possesses multiple functions as a flexible anode for lithium‐ion batteries. Micrometer‐sized pores among the continuously waved rGO layers could extraordinarily improve ion diffusion. Nano‐sized pores among the MnO₂ nanosheets and CNT/rGO@MnO₂ particles could provide vast accessible active sites and alleviate volume change. The tight connection between MnO₂ and carbon skeleton could facilitate electron transportation and enhance structural stability. Due to the special structure, the rGO‐wrapped CNT/rGO@MnO₂ porous film as an anode shows a high capacity, excellent rate performance, and superior cycling stability (1344.2 mAh g⁻¹ over 630 cycles at 2 A g⁻¹, 608.5 mAh g⁻¹ over 1000 cycles at 7.5 A g⁻¹). Furthermore, the evolutions of microstructure and chemical valence occurring inside the electrode after cycling are investigated to illuminate the structural superiority for energy storage. The excellent electrochemical performance of this freestanding flexible electrode makes it an attractive candidate for practical application in flexible energy storage.     

Separator‐Integrated,Reversely Connectable Symmetric Lithium‐Ion Battery

A separator‐integrated, reversely connectable, symmetric lithium‐ion battery is developed based on carbon‐coated Li₃V₂(PO₄)₃ nanoparticles and polyvinylidene fluoride‐treated separators. The Li₃V₂(PO₄)₃ nanoparticles are synthesized via a facile solution route followed by calcination in Ar/H₂ atmosphere. Sucrose solution is used as the carbon source for uniform carbon coating on the Li₃V₂(PO₄)₃ nanoparticles. Both the carbon and the polyvinylidene fluoride treatments substantially improve the cycling life of the symmetric battery by preventing the dissolution and shuttle of the electroactive Li₃V₂(PO₄)₃. The obtained symmetric full cell exhibits a reversible capacity of ≈87 mA h g^–1, good cycling stability, and capacity retention of ≈70% after 70 cycles. In addition, this type of symmetric full cell can be operated in both forward and reverse connection modes, without any influence on the cycling of the battery. Furthermore, a new separator integration approach is demonstrated, which enables the direct deposition of electroactive materials for the battery assembly and does not affect the electrochemical performance. A 10‐tandem‐cell battery assembled without differentiating the electrode polarity exhibits a low thickness of ≈4.8 mm and a high output voltage of 20.8 V.     

Sulfur‐Grafted Hollow Carbon Spheres for Potassium‐Ion Battery Anodes

Sulfur‐rich carbons are minimally explored for potassium‐ion batteries (KIBs). Here, a large amount of S (38 wt%) is chemically incorporated into a carbon host, creating sulfur‐grafted hollow carbon spheres (SHCS) for KIB anodes. The SHCS architecture provides a combination of nanoscale (≈40 nm) diffusion distances and C? S chemical bonding to minimize cycling capacity decay and Coulombic efficiency (CE) loss. The SHCS exhibit a reversible capacity of 581 mAh g^?1 (at 0.025 A g^?1), which is the highest reversible capacity reported for any carbon‐based KIB anode. Electrochemical analysis of S‐free carbon spheres baseline demonstrates that both the carbon matrix and the sulfur species are highly electrochemically active. SHCS also show excellent rate capability, achieving 202, 160, and 110 mAh g^?1 at 1.5, 3, and 5 A g^?1, respectively. The electrode maintains 93% of the capacity from the 5th to 1000th cycle at 3 A g^?1, with steady‐state CE being near 100%. Raman analysis indicates reversible breakage of C? S and S? S bonds upon potassiation to 0.01 V versus K/K⁺. The galvanostatic intermittent titration technique (GITT) analysis provides voltage‐dependent K⁺ diffusion coefficients that range from 10^?10 to 10^?12 cm² s^?1 upon potassiation and depotassiation, with approximately five times higher coefficient for the former.     

Hyperporous Sponge Interconnected by Hierarchical Carbon Nanotubes as a High‐Performance Potassium‐Ion Battery Anode

Recently, commercial graphite and other carbon‐based materials have shown promising properties as the anode for potassium‐ion batteries. A fundamental problem related to those carbon electrodes, significant volume expansion, and structural instability/collapsing caused by cyclic K‐ion intercalation, remains unsolved and severely limits further development and applications of K‐ion batteries. Here, a multiwalled hierarchical carbon nanotube (HCNT) is reported to address the issue, and a reversible specific capacity of 232 mAh g^?1, excellent rate capability, and cycling stability for 500 cycles are achieved. The key structure of the HCNTs consists of an inner CNT with dense‐stacked graphitic walls and a loose‐stacked outer CNT with more disordered walls, and individual HCNTs are further interconnected into a hyperporous bulk sponge with huge macropore volume, high conductivity, and tunable modulus. It is discovered that the inner dense‐CNT serves as a robust skeleton, and collectively, the outer loose‐CNT is beneficial for K‐ion accommodation; meanwhile the hyperporous sponge facilitates reaction kinetics and offers stable surface capacitive behavior. The hierarchical carbon nanotube structure has great potential in developing high‐performance and stable‐structure electrodes for next generation K and other metal‐ion batteries.