Bending‐Tolerant Anodes for Lithium‐Metal Batteries

Bendable energy‐storage systems with high energy density are demanded for conformal electronics. Lithium‐metal batteries including lithium–sulfur and lithium–oxygen cells have much higher theoretical energy density than lithium‐ion batteries. Reckoned as the ideal anode, however, Li has many challenges when directly used, especially its tendency to form dendrite. Under bending conditions, the Li‐dendrite growth can be further aggravated due to bending‐induced local plastic deformation and Li‐filaments pulverization. Here, the Li‐metal anodes are made bending tolerant by integrating Li into bendable scaffolds such as reduced graphene oxide (r‐GO) films. In the composites, the bending stress is largely dissipated by the scaffolds. The scaffolds have increased available surface for homogeneous Li plating and minimize volume fluctuation of Li electrodes during cycling. Significantly improved cycling performance under bending conditions is achieved. With the bending‐tolerant r‐GO/Li‐metal anode, bendable lithium–sulfur and lithium–oxygen batteries with long cycling stability are realized. A bendable integrated solar cell–battery system charged by light with stable output and a series connected bendable battery pack with higher voltage is also demonstrated. It is anticipated that this bending‐tolerant anode can be combined with further electrolytes and cathodes to develop new bendable energy systems.     

Covalent‐Organic‐Framework‐Based Li–CO2 Batteries

Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials constructed from designer molecular building blocks that are linked and extended periodically via covalent bonds. Their high stability, open channels, and ease of functionalization suggest that they can function as a useful cathode material in reversible lithium batteries. Here, a COF constructed from hydrazone/hydrazide‐containing molecular units, which shows good CO₂ sequestration properties, is reported. The COF is hybridized to Ru‐nanoparticle‐coated carbon nanotubes, and the composite is found to function as highly efficient cathode in a Li–CO₂ battery. The robust 1D channels in the COF serve as CO₂^– and lithium‐ion‐diffusion channels and improve the kinetics of electrochemical reactions. The COF‐based Li–CO₂ battery exhibits an ultrahigh capacity of 27 348 mAh g^?1 at a current density of 200 mA g^?1, and a low cut‐off overpotential of 1.24 V within a limiting capacity of 1000 mAh g^?1. The rate performance of the battery is improved considerably with the use of the COF at the cathode, where the battery shows a slow decay of discharge voltage from a current density of 0.1 to 4 A g^?1. The COF‐based battery runs for 200 cycles when discharged/charged at a high current density of 1 A g^?1.     

3‐D Integrated All‐Solid‐State Rechargeable Batteries

Portable society urgently calls for integrated energy supplies. This holds for autonomous devices but even more so for future medical implants. Evidently, rechargeable integrated all‐solid‐state batteries will play a key role in these fields, enabling miniaturization, preventing electrode degradation upon cycling and electrolyte leakage. Planar solid‐state thin film batteries are rapidly emerging but reveal several potential drawbacks, such as a relatively low energy density and the use of highly reactive lithium. Thin film Si‐intercalation electrodes covered with a solid‐state electrolyte are found to combine a high storage capacity of 3500 mAh g^–1 with high cycle life, enabling to integrate batteries in Si. Based on the excellent intercalation chemistry of Si, a new 3D‐integrated all‐solid‐state battery concept is proposed. High aspect ratio cavities and features, etched in silicon, will yield large surface area batteries with anticipated energy density of about 5 mWh μm^–1 cm^–2, i.e. more than 3 orders of magnitude higher than that of integrated capacitors.     

CuO Nanoplates for High‐Performance Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are promising alternatives to lithium‐ion batteries because of the abundance and low cost of K. However, an important challenge faced by KIBs is the search for high‐capacity materials that can hold large‐diameter K ions. Herein, copper oxide (CuO) nanoplates are synthesized as high‐performance anode materials for KIBs. CuO nanoplates with a thickness of ≈20 nm afford a large electrode–electrolyte contact interface and short K⁺ ion diffusion distance. As a consequence, a reversible capacity of 342.5 mAh g^?1 is delivered by the as‐prepared CuO nanoplate electrode at 0.2 A g^?1. Even after 100 cycles at a high current density of 1.0 A g^?1, the capacity of the electrode remains over 206 mAh g^?1, which is among the best values for KIB anodes reported in the literature. Moreover, a conversion reaction occurs at the CuO anode. Cu nanoparticles form during the first potassiation process and reoxidize to Cu₂O during the depotassiation process. Thereafter, the conversion reaction proceeds between the as‐formed Cu₂O and Cu, yielding a reversible theoretical capacity of 374 mAh g^?1. Considering their low cost, easy preparation, and environmental benignity, CuO nanoplates are promising KIB anode materials.