Rationally Designed Hierarchical TiO2@Fe2O3 Hollow Nanostructures for Improved Lithium Ion Storage

Hollow and hierarchical nanostructures have received wide attention in new‐generation, high‐performance, lithium ion battery (LIB) applications. Both TiO₂ and Fe₂O₃ are under current investigation because of their high structural stability (TiO₂) and high capacity (Fe₂O₃), and their low cost. Here, we demonstrate a simple strategy for the fabrication of hierarchical hollow TiO₂@Fe₂O₃ nanostructures for the application as LIB anodes. Using atomic layer deposition (ALD) and sacrificial template‐assisted hydrolysis, the resulting nanostructure combines a large surface area with a hollow interior and robust structure. As a result, such rationally designed LIB anodes exhibit a high reversible capacity (initial value 840 mAh g^?1), improved cycle stability (530 mAh g^?1 after 200 cycles at the current density of 200 mA g^?1), as well as outstanding rate capability. This ALD‐assisted fabrication strategy can be extended to other hierarchical hollow metal oxide nanostructures for favorable applications in electrochemical and optoelectronic devices.     

3D Hierarchical Porous α‐Fe2O3 Nanosheets for High‐Performance Lithium‐Ion Batteries

To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α‐Fe₂O₃ nanosheets are fabricated on copper foil and directly used as binder‐free anode for lithium‐ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g^?1 is maintained at 2 C (2.01 A g^?1) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g^?1), a capacity of 433 mA h g^?1 is retained. The unique porous 3D hierarchical nanostructure improves electronic–ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder‐free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefits leading to outstanding electrochemical performance.     

Laser Porosificated Silicon Anodes for Lithium Ion Batteries

This study presents the first laser porosificated silicon anode for lithium‐ion batteries. The pulsed laser induced pore creation improves the cycling stability of the d = 210 nm thick sputtered thin film anodes compared to plain Si. Galvanostatic cycling with a charge capacity limited to C = 932 mAh g^?1 and a 2C current rate shows a stable cycling for more than N = 600 cycles. After N = 3000 cycles the laser porosificated and crystallized Si has a remaining capacity of C₃₀₀₀ > 120 mAh g^?1. Postmortem scanning electron microscopy images after N = 3000 cycles prove that the laser porosification reduces cracks in the active layer.     

Biomimetic Spider‐Web‐Like Composites for Enhanced Rate Capability and Cycle Life of Lithium Ion Battery Anodes

It is crucial to control the structure and composition of composite anode materials to enhance the cell performance of such anode materials for lithium ion batteries. Herein, a biomimetic strategy is demonstrated for the design of high performance anode materials, inspired by the structural characteristics and working principles of sticky spider‐webs. Hierarchically porous, sticky, spider‐web‐like multiwall carbon nanotube (MWCNT) networks are prepared through a process involving ozonation, ice‐templating assembly, and thermal treatment, thereby integrating the networks with γ‐Fe₂O₃ particles. The spider‐web‐like MWCNT/γ‐Fe₂O₃ composite network not only traps the active γ‐Fe₂O₃ materials tightly but also provides fast charge transport through the 3D internetworked pathways and the mechanical integrity. Consequently, the composite web shows a high capacity of ≈822 mA h g^?1 at 0.05 A g^?1, fast rate capability with ≈72.3% retention at rates from 0.05 to 1 A g^?1, and excellent cycling stability of >88% capacity retention after 310 cycles with a Coulombic efficiency >99%. These remarkable electrochemical performances are attributed to the complementarity of the 3D spider‐web‐like structure with the strong attachment of γ‐Fe₂O₃ particles on the sticky surface. This synthetic strategy offers an environmentally safe, simple, and cost‐effective avenue for the biomimetic design of high performance energy storage materials.     

Electrokinetic Phenomena Enhanced Lithium‐Ion Transport in Leaky Film for Stable Lithium Metal Anodes

The application of lithium (Li) metal anodes in Li metal batteries has been hindered by growth of Li dendrites, which lead to short cycling life. Here a Li‐ion‐affinity leaky film as a protection layer is reported to promote a dendrite‐free Li metal anode. The leaky film induces electrokinetic phenomena to enhance Li‐ion transport, leading to a reduced Li‐ion concentration polarization and homogeneous Li‐ion distribution. As a result, the dendrite‐free Li metal anode during Li plating/stripping is demonstrated even at an extremely high deposition capacity (6 mAh cm^?2) and current density (40 mA cm^?2) with improved Coulombic efficiencies. A full cell battery with the leaky‐film protected Li metal as the anode and high‐areal‐capacity LiNi_0.8Co_0.1Mn_0.1O₂ (NCM‐811) (≈4.2 mAh cm^?2) or LiFePO₄ (≈3.8 mAh cm^?2) as the cathode shows improved cycling stability and capacity retention, even at lean electrolyte conditions.     

Graphitic Carbon Nanocage as a Stable and High Power Anode for Potassium‐Ion Batteries

As an emerging electrochemical energy storage device, potassium‐ion batteries (PIBs) have drawn growing interest due to the resource‐abundance and low cost of potassium. Graphite‐based materials, as the most common anodes for commercial Li‐ion batteries, have a very low capacity when used an anode for Na‐ion batteries, but they show reasonable capacities as anodes for PIBs. The practical application of graphitic materials in PIBs suffers from poor cyclability, however, due to the large interlayer expansion/shrinkage caused by the intercalation/deintercalation of potassium ions. Here, a highly graphitic carbon nanocage (CNC) is reported as a PIBs anode, which exhibits excellent cyclability and superior depotassiation capacity of 175 mAh g^?1 at 35 C. The potassium storage mechanism in CNC is revealed by cyclic voltammetry as due to redox reactions (intercalation/deintercalation) and double‐layer capacitance (surface adsorption/desorption). The present results give new insights into structural design for graphitic anode materials in PIBs and understanding the double‐layer capacitance effect in alkali metal ion batteries.     

Vanadate‐Based Materials for Li‐Ion Batteries: The Search for Anodes for Practical Applications

While the practical application of electrode materials depends intensively on the Li⁺ ion storage mechanisms correlating ultimately with the coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling, only intercalation‐type electrode materials have proven viable for commercialization up to now. This paper reviews the promising anode materials of metal vanadates (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni, Li) that have high capacity, low cost, and abundant resource, and also discusses the related Li⁺ ion storage mechanism. It is concluded that most of these (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni) exhibit irreversible redox reactions upon lithiation/delithiation accompanied by large volume expansion, which is not favorable for industrial applications. In particular, Li₃VO₄ with specific intercalation Li⁺ ion storage mechanism and compatible merits of safety and energy density exhibits great potential for practical application. This review systematically summarizes the latest progress in Li₃VO₄ research, including the representative fabrication approaches for advanced morphology and state‐of‐the‐art technologies to boost performance and the morphology variation associated with Li⁺ ion storage mechanisms. Furthermore, an outlook on where breakthroughs for Li₃VO₄ may be most likely achieved will be provided.     

Bismuth Microparticles as Advanced Anodes for Potassium‐Ion Battery

Potassium‐ion batteries (KIBs) are important alternatives to lithium‐ and sodium‐ion batteries. Herein, microsized a Bi electrode delivers exceptional potassium storage capacity, stability, and rate capability by the formation of an elastic and adhesive oligomer‐containing solid electrolyte interface with the assistance of diglyme electrolytes. The kinetics‐controlled K–Bi phase transitions are unraveled combining electrochemical profiles, in situ X‐ray diffraction and density functional theory calculations. Reversible, stepwise Bi–KBi₂–K₃Bi₂–K₃Bi transitions govern the electrochemical processes after the initial continuous surface potassiation. The Bi electrode outperforms the other anode counterparts considering both capacity and potential. This work provides critical insights into the rational design of high‐performance anode materials for KIBs.     

Mo‐Based Ultrasmall Nanoparticles on Hierarchical Carbon Nanosheets for Superior Lithium Ion Storage and Hydrogen Generation Catalysis

Constructing 3D hierarchical architecture consisting of 2D hybrid nanosheets is very critical to achieve uppermost and stable electrochemical performance for both lithium‐ion batteries (LIBs) and hydrogen evolution reaction (HER). Herein, a simple synthesis of uniform 3D microspheres assembled from carbon nanosheets with the incorporated MoO₂ nanoclusters is demonstrated. The MoO₂ nanoclusters can be readily converted into the molybdenum carbide (Mo₂C) nanocrystals by using high temperature treatment. Such assembling architecture is highly particular for preventing Mo‐based ultrasmall nanoparticles from coalescing or oxidizing and endowing them with rapid electron transfer. Consequently, the MoO₂/C hybrids as LIB anode materials deliver a specific capacity of 625 mA h g^?1 at 1600 mA g^?1 even after 1000 cycles, which is among the best reported values for MoO₂‐based electrode materials. Moreover, the Mo₂C/C hybrids also exhibit excellent electrocatalytic activity for HER with small overpotential and robust durability in both acid and alkaline media. The present work highlights the importance of designing 3D structure and controlling ultrasmall Mo‐based nanoparticles for enhancing electrochemical energy conversion and storage applications.     

Transition Metal Oxide Anodes for Electrochemical Energy Storage in Lithium‐ and Sodium‐Ion Batteries

Lithium‐ion batteries (LIBs) with outstanding energy and power density have been extensively investigated in recent years, rendering them the most suitable energy storage technology for application in emerging markets such as electric vehicles and stationary storage. More recently, sodium, one of the most abundant elements on earth, exhibiting similar physicochemical properties as lithium, has been gaining increasing attention for the development of sodium‐ion batteries (SIBs) in order to address the concern about Li availability and cost—especially with regard to stationary applications for which size and volume of the battery are of less importance. Compared with traditional intercalation reactions, conversion reaction‐based transition metal oxides (TMOs) are prospective anode materials for rechargeable batteries thanks to their low cost and high gravimetric specific capacities. In this review, the recent progress and remaining challenges of conversion reactions for LIBs and SIBs are discussed, covering an overview about the different synthesis methods, morphological characteristics, as well as their electrochemical performance. Potential future research directions and a perspective toward the practical application of TMOs for electrochemical energy storage are also provided.     

MXene‐Based Mesoporous Nanosheets Toward Superior Lithium Ion Conductors

Although solid polymer electrolytes have some intrinsic advantages in synthesis and film processing compared with inorganic solid electrolytes, low ionic conductivities and mechanical moduli hamper their practical applications in lithium‐based batteries. Here, an efficient strategy is developed to produce a unique solid polymer electrolyte containing MXene‐based mesoporous silica nanosheets with a sandwich structure, which are fabricated via controllable hydrolysis of tetraethyl orthosilicate around the surface of MXene‐Ti₃C₂ under the direction of cationic surfactants. Such unique nanosheets not only exhibit individual, thin, and insulated features, but also possess abundant functional groups in mesopores and on the surface, which are favorable for the formation of Lewis acid–base interactions with anions in polymer electrolytes such as poly(propylene oxide) elastomer, enabling the fast Li⁺ transportation at the mesoporous nanosheets/polymer interfaces. As a consequence, a solid polymer electrolyte with high ionic conductivity of 4.6 × 10^?4 S cm^?1, high Young's modulus of 10.5 MPa, and long‐term electrochemical stability is achieved.     

An Upgraded Lithium Ion Battery Based on a Polymeric Separator Incorporated with Anode Active Materials

Structural/compositional characteristics at the anode/electrolyte interface are of paramount importance for the practical performance of lithium ion batteries, including cyclic stability, rate capacity, and operational safety. The anode‐electrolyte interface with traditional separator technology is featured with inevitable phase discontinuity and fails to support the stable operation of lithium ion batteries based on large‐capacity anodes with structural change in charges/discharges, such as transition metal oxide anodes. In this work, an anode/electrolyte framework based on an oxide anode and an active‐oxide‐incorporated separator is proposed for the first time and investigated for lithium ion batteries. The architecture builds a robust anode‐separator interface in LIBs, shortens Li⁺ diffusion path, accelerates electron transport, and mitigates the volume change of the oxide anode in electrochemical reactions. Remarkably, 4 wt% CuO addition in the separator leads to a 17% enhancement in the overall capacity of a battery with a CuO anode. The battery delivers an unparalleled record reversible capacity of 637.2 mAh g^?1 with a 99% capacity retention after 100 charge/discharge cycles at 0.5 C. The high performance are attributed to the robust anode‐separator interface, which gives rise to enhanced interaction between the oxide anode and the same‐oxide‐incorporated composite in the separator.     

Li4Ti5O12 Nanoparticles Embedded in a Mesoporous Carbon Matrix as a Superior Anode Material for High Rate Lithium Ion Batteries

A mesoporous Li₄Ti₅O₁₂/C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK‐3 as a hard template. Modified CMK‐3 template is impregnated with Li₄Ti₅O₁₂ precursor, followed by heat treatment at 750 °C for 6 h under N₂. Li₄Ti₅O₁₂ nanocrystals of up to several tens of nanometers are successfully synthesized in micrometer‐sized porous carbon foam to form a highly conductive network, as confirmed by field emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, and nitrogen sorption isotherms. The composite is then evaluated as an anode material for lithium ion batteries. It exhibits greatly improved electrochemical performance compared with bulk Li₄Ti₅O₁₂, and shows an excellent rate capability (73.4 mA h g^?1 at 80 C) with significantly enhanced cycling performance (only 5.6% capacity loss after 1000 cycles at a high rate of 20 C). The greatly enhanced lithium storage properties of the mesoporous Li₄Ti₅O₁₂/C nanocomposite may be attributed to the interpenetrating conductive carbon network, ordered mesoporous structure, and the small Li₄Ti₅O₁₂ nanocrystallites that increase the ionic and electronic conduction throughout the electrode.