Three-Dimensional Double-Walled Ultrathin Graphite Tube Conductive Scaffold with Encapsulated Germanium Nanoparticles as a High-Areal-Capacity and Cycle-Stable Anode for Lithium-Ion Batteries

The demand for lithium-ion batteries with both high power and high-energy density has attracted widespread attention as energy-storage devices for the increasing demand of consumer electronics, electric vehicles, and grid-scale storage. However, the fabrication of an advanced electrode architecture with high areal capacity, excellent cycling stability, and superior rate performance remains a long-term challenge in the development of advanced electrochemical energy-storage devices. Herein, we design an effective and general strategy to spontaneously encapsulate Ge nanoparticles into a three-dimensional double hydrophilic N-doped ultrathin graphite/void/hydrophobic ultrathin graphite tube network (Ge@3D-DHGT) with control over the position for large specific capacity (1338 mA h g–1), high rate performance (752 mA h g–1 at 40 C), and superior cycling stability (up to 1000 cycles). Toward the practical application, the as-prepared Ge@3D-DHGT electrode showed a large areal capacity (10 mA h cm–2 under 8 mA cm–2), which provides a highly promising anode with both high capacity and high rate performance. Importantly, this work provides an approach to fabricate high-areal-capacity anodes with long cycling stability and rapid charge–discharge properties with practical applications in advanced rechargeable batteries

Three-Dimensional Double-Walled Ultrathin Graphite Tube Conductive Scaffold with Encapsulated Germanium Nanoparticles as a High-Areal-Capacity and Cycle-Stable Anode for Lithium-Ion Batteries

The demand for lithium-ion batteries with both high power and high-energy density has attracted widespread attention as energy-storage devices for the increasing demand of consumer electronics, electric vehicles, and grid-scale storage. However, the fabrication of an advanced electrode architecture with high areal capacity, excellent cycling stability, and superior rate performance remains a long-term challenge in the development of advanced electrochemical energy-storage devices. Herein, we design an effective and general strategy to spontaneously encapsulate Ge nanoparticles into a three-dimensional double hydrophilic N-doped ultrathin graphite/void/hydrophobic ultrathin graphite tube network (Ge@3D-DHGT) with control over the position for large specific capacity (1338 mA h g–1), high rate performance (752 mA h g–1 at 40 C), and superior cycling stability (up to 1000 cycles). Toward the practical application, the as-prepared Ge@3D-DHGT electrode showed a large areal capacity (10 mA h cm–2 under 8 mA cm–2), which provides a highly promising anode with both high capacity and high rate performance. Importantly, this work provides an approach to fabricate high-areal-capacity anodes with long cycling stability and rapid charge–discharge properties with practical applications in advanced rechargeable batteries

Regulating Solvation Structures Enabled by the Mesoporous Material MCM-41 for Rechargeable Lithium Metal Batteries

For developing the reversible lithium metal anode, constructing an ideal solid electrolyte interphase (SEI) by regulating the Li+ solvation structure is a powerful way to overcome the major obstacles of lithium dendrite and limited Coulombic efficiency (CE). Herein, spherical mesoporous molecular sieve MCM-41 nanoparticles are coated on a commercial PP separator and used to regulate the Li+ solvation structure for lithium metal batteries (LMBs). The regulated solvation structure exhibits an agminated state with more contact ion pairs (CIPs) and ionic aggregates (AGGs), which successfully construct a homogeneous inorganic-rich SEI in the lithium anode. Meanwhile, the regulated solvation structure weakens the interaction between the solvents and Li+, resulting in low Li+ desolvation energy and uniform Li deposition. Thus, a high CE (∼96.76%), dendrite-free Li anode, and stable Li plating/stripping cycling for approximately 1000 h are achieved in the regulated carbonate-based electrolyte without any additives. Therefore, regulating the Li+ solvation structure in the electrolyte by employing a mesoporous material is a forceful way to construct an ideal SEI and harness lithium metal

An In Situ Ionic-Liquid-Assisted Synthetic Approach to Iron Fluoride/Graphene Hybrid Nanostructures as Superior Cathode Materials for Lithium Ion Batteries

A tactful ionic-liquid (IL)-assisted approach to <i>in situ</i> synthesis of iron fluoride/graphene nanosheet (GNS) hybrid nanostructures is developed. To ensure uniform dispersion and tight anchoring of the iron fluoride on graphene, we employ an IL which serves not only as a green fluoride source for the crystallization of iron fluoride nanoparticles but also as a dispersant of GNSs. Owing to the electron transfer highways created between the nanoparticles and the GNSs, the iron fluoride/GNS hybrid cathodes exhibit a remarkable improvement in both capacity and rate performance (230 mAh g^–1 at 0.1 C and 74 mAh g^–1 at 40 C). The stable adhesion of iron fluoride nanoparticles on GNSs also introduces a significant improvement in long-term cyclic performance (115 mAh g^–1 after 250 cycles even at 10 C). The superior electrochemical performance of these iron fluoride/GNS hybrids as lithium ion battery cathodes is ascribed to the robust structure of the hybrid and the synergies between iron fluoride nanoparticles and graphene

Magnetically Induced Reversible Transition between Cassie and Wenzel States of Superparamagnetic Microdroplets on Highly Hydrophobic Silicon Surface

In this work, we report a magnetic technique for reversible wetting–dewetting transitions of microdroplets on highly hydrophobic surfaces. A superparamagnetic microdroplet can be reversibly switched between the Cassie state and the Wenzel state on a highly hydrophobic microstructured silicon substrate by the application of the magnetic field. The transition can be controlled by both the intensity of the magnetic field and the concentration of the superparamagnetic Fe₃O₄ nanoparticles in the microdroplet. The magnetic force needed during the transition from the Cassie state to the Wenzel state was found to be apparently smaller than that needed in the reverse process. Such asymmetry is ascribed to the higher energy of the Cassie state compared with the Wenzel state, the change of the gravitational potential energy, and the adhesion hysteresis. This report provides a novel method of dynamically controlling liquid/solid interactions, which can not only help us to understand further the transition between the Cassie state and the Wenzel state but also potentially be used in some important applications, such as lab-on-a-chip devices and chemical microreactors

Quasi-Solid-State Polymer Electrolyte Based on Highly Concentrated LiTFSI Complexing DMF for Ambient-Temperature Rechargeable Lithium Batteries

Solid-state polymer electrolytes (SPEs) complexing a plasticizer is a valid strategy to improve the poor ionic conductivity of SPEs at ambient temperature. In this study, a quasi-SPE based on a polyurethane matrix (QSPE-PU) is constructed by regulating the contents of bis­(trifluoromethanesulfonyl) imide (LiTFSI) salt and N,N-dimethylformamide (DMF) and shows high performance in ambient-temperature rechargeable lithium batteries. Highly concentrated LiTFSI is designed to anchor DMF, decreasing the free solvent molecules in the QSPE to improve the stability with lithium metal. Meanwhile, DMF can fully dissociate the highly concentrated LiTFSI, providing more carriers. The prepared QSPE-PU40 shows a high ionic conductivity of 1.12 × 10–4 S cm–1 at ambient temperature since DMF not only provides more carriers but also enhances the movement of the polymer segments and lowers the energy barrier of lithium ion migration. Density functional theory calculations further prove that DMF facilitates the conduction of lithium ions in the QSPE system. QSPE-PU40 shows good compatibility with the lithium metal electrode by forming a stable solid electrolyte interphase during lithium plating/stripping processes. The lithium ferrophosphate (LFP)/QSPE-PU40/Li battery exhibits a high specific capacity of 138 mA h g–1 with remarkable cycling stability at 0.5 C and 30 °C (94% capacity retention after 800 cycles). More impressively, the pouch cell based on QSPE-PU40 delivers good flexibility and high safety. Such a QSPE is expected to provide an effective strategy where SPEs are applied in solid-state lithium batteries at ambient temperature and even flexible batteries for next-generation wearable devices

Enhanced Cyclability of Li–O₂ Batteries Based on TiO₂ Supported Cathodes with No Carbon or Binder

The decomposition of carbon materials and organic binders in Li–air batteries has been reported repeatedly in recent literature. The decomposition of carbon can harm the batteries’ cyclability further by catalyzing electrolyte degrading. Therefore, there is a critical need to exploit a new catalyst support substituting carbon and develop a binder free cathode preparation strategy for Li–air batteries. Herein, TiO2 nanotube arrays growing on Ti foam are used as the catalyst support to construct carbon and binder free oxygen diffusion electrodes. After being coated with Pt nanoparticles by a cool sputtering approach, the TiO2 nanotube arrays are used as cathodes of Li–O2 batteries. Benefiting from the stability of TiO2 in the discharge/charge processes, the Li–O2 batteries realize enhanced cyclability at high current densities (for instance, more than 140 cycles at 1 or 5 A g–1), within wide discharge/charge voltage windows (for instance, 1.5–4.5 V). X-ray photoelectron spectra and a scanning electron microscope image of the cathodes after cycling at 5 A g–1 150 times indicate that the TiO2 nanotubes can remain stable in the long term cycle test. 1H nuclear magnetic resonance analysis reveals that the tetraethylene glycol dimethyl ether electrolyte has no degradation, showing enhanced stability compared with that in the carbon containing batteries

Quasi-Solid-State Polymer Electrolyte Based on Highly Concentrated LiTFSI Complexing DMF for Ambient-Temperature Rechargeable Lithium Batteries

Solid-state polymer electrolytes (SPEs) complexing a plasticizer is a valid strategy to improve the poor ionic conductivity of SPEs at ambient temperature. In this study, a quasi-SPE based on a polyurethane matrix (QSPE-PU) is constructed by regulating the contents of bis­(trifluoromethanesulfonyl) imide (LiTFSI) salt and N,N-dimethylformamide (DMF) and shows high performance in ambient-temperature rechargeable lithium batteries. Highly concentrated LiTFSI is designed to anchor DMF, decreasing the free solvent molecules in the QSPE to improve the stability with lithium metal. Meanwhile, DMF can fully dissociate the highly concentrated LiTFSI, providing more carriers. The prepared QSPE-PU40 shows a high ionic conductivity of 1.12 × 10–4 S cm–1 at ambient temperature since DMF not only provides more carriers but also enhances the movement of the polymer segments and lowers the energy barrier of lithium ion migration. Density functional theory calculations further prove that DMF facilitates the conduction of lithium ions in the QSPE system. QSPE-PU40 shows good compatibility with the lithium metal electrode by forming a stable solid electrolyte interphase during lithium plating/stripping processes. The lithium ferrophosphate (LFP)/QSPE-PU40/Li battery exhibits a high specific capacity of 138 mA h g–1 with remarkable cycling stability at 0.5 C and 30 °C (94% capacity retention after 800 cycles). More impressively, the pouch cell based on QSPE-PU40 delivers good flexibility and high safety. Such a QSPE is expected to provide an effective strategy where SPEs are applied in solid-state lithium batteries at ambient temperature and even flexible batteries for next-generation wearable devices