Origin of Fracture‐Resistance to Large Volume Change in Cu‐Substituted Co3O4 Electrodes

The electrode materials conducive to conversion reactions undergo large volume change in cycles which restrict their further development. It has been demonstrated that incorporation of a third element into metal oxides can improve the cycling stability while the mechanism remains unknown. Here, an in situ and ex situ electron microscopy investigation of structural evolutions of Cu‐substituted Co₃O₄ supplemented by first‐principles calculations is reported to reveal the mechanism. An interconnected framework of ultrathin metallic copper formed provides a high conductivity backbone and cohesive support to accommodate the volume change and has a cube‐on‐cube orientation relationship with Li₂O. In charge, a portion of Cu metal is oxidized to CuO, which maintains a cube‐on‐cube orientation relationship with Cu. The Co metal and oxides remain as nanoclusters (less than 5 nm) thus active in subsequent cycles. This adaptive architecture accommodates the formation of Li₂O in the discharge cycle and underpins the catalytic activity of Li₂O decomposition in the charge cycle.     

Ti‐Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium‐based oxides including TiO₂ and M‐Ti‐O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium‐ion batteries, sodium‐ion batteries, and hybrid pseudocapacitors. Further, Ti‐based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in‐depth understanding on the morphologies control, surface engineering, bulk‐phase doping of Ti‐based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti‐based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium‐ion batteries to sodium‐ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.     

Quasi‐Monolayer Black Phosphorus with High Mobility and Air Stability

Black phosphorus (BP) exhibits thickness‐dependent band gap and high electronic mobility. The chemical intercalation of BP with alkali metal has attracted attention recently due to the generation of universal superconductivity regardless of the type of alkali metals. However, both ultrathin BP, as well as alkali metal‐intercalated BP, are highly unstable and corrode rapidly under ambient conditions. This study demonstrates that alkali metal hydride intercalation decouples monolayer to few layers BP from the bulk BP, allowing an optical gap of ≈1.7 eV and an electronic gap of 1.98 eV to be measured by photoluminescence and electron energy loss spectroscopy at the intercalated regions. Raman and transport measurements confirm that chemically intercalated BP exhibits enhanced stability, while maintaining a high hole mobility of up to ≈800 cm² V^?1 s^?1 and on/off ratio exceeding 10³. The use of alkali metal hydrides as intercalants should be applicable to a wide range of layered 2D materials and pave the way for generating highly stable, quasi‐monolayer 2D materials.     

Sandwiched Thin‐Film Anode of Chemically Bonded Black Phosphorus/Graphene Hybrid for Lithium‐Ion Battery

A facile vacuum filtration method is applied for the first time to construct sandwich‐structure anode. Two layers of graphene stacks sandwich a composite of black phosphorus (BP), which not only protect BP from quickly degenerating but also serve as current collector instead of copper foil. The BP composite, reduced graphene oxide coated on BP via chemical bonding, is simply synthesized by solvothermal reaction at 140 °C. The sandwiched film anode used for lithium‐ion battery exhibits reversible capacities of 1401 mAh g^?1 during the 200th cycle at current density of 100 mA g^?1 indicating superior cycle performance. Besides, this facile vacuum filtration method may also be available for other anode material with well dispersion in N‐methyl pyrrolidone (NMP).     

Self‐Activating,Capacitive Anion Intercalation Enables High‐Power Graphite Cathodes

Developing high‐power cathodes is crucial to construct next‐generation quick‐charge batteries for electric transportation and grid applications. However, this mainly relies on nanoengineering strategies at the expense of low scalability and high battery cost. Another option is provided herein to build high‐power cathodes by exploiting inexpensive bulk graphite as the active electrode material, where anion intercalation is involved. With the assistance of a strong alginate binder, the disintegration problem of graphite cathodes due to the large volume variation of >130% is well suppressed, making it possible to investigate the intrinsic electrochemical behavior and to elucidate the charge storage kinetics of graphite cathodes. Ultrahigh power capability up to 42.9 kW kg^?1 at the energy density of >300 Wh kg^?1 (based on graphite mass) and long cycling life over 10 000 cycles are achieved, much higher than those of conventional cathode materials for Li‐ion batteries. A self‐activating and capacitive anion intercalation into graphite is discovered for the first time, making graphite a new intrinsic intercalation‐pseudocapacitance cathode material. The finding highlights the kinetical difference of anion intercalation (as cathode) from cation intercalation (as anode) into graphitic carbon materials, and new high‐power energy storage devices will be inspired.     

Lithiation Mechanism of Tunnel‐Structured MnO2 Electrode Investigated by In Situ Transmission Electron Microscopy

Manganese oxide (α‐MnO₂) has been considered a promising energy material, including as a lithium‐based battery electrode candidate, due to its environmental friendliness. Thanks to its unique 1D [2 × 2] tunnel structure, α‐MnO₂ can be applied to a cathode by insertion reaction and to an anode by conversion reaction in corresponding voltage ranges, in a lithium‐based battery. Numerous reports have attributed its remarkable performance to its unique tunnel structure; however, the precise electrochemical reaction mechanism remains unknown. In this study, finding of the lithiation mechanism of α‐MnO₂ nanowire by in situ transmission electron microscopy (TEM) is reported. By elaborately modifying the existing in situ TEM experimental technique, rapid lithium‐ion diffusion through the tunnels is verified. Furthermore, by tracing the full lithiation procedure, the evolution of the MnO intermediate phase and the development of the MnO and Li₂O phases with preferred orientations is demonstrated, which explains how the conversion reaction occurs in α‐MnO₂ material. This study provides a comprehensive understanding of the electrochemical lithiation process and mechanism of α‐MnO₂ material, in addition to the introduction of an improved in situ TEM biasing technique.     

Fe2VO4 Hierarchical Porous Microparticles Prepared via a Facile Surface Solvation Treatment for High‐Performance Lithium and Sodium Storage

Preventing the aggregation of nanosized electrode materials is a key point to fully utilize the advantage of the high capacity. In this work, a facile and low‐cost surface solvation treatment is developed to synthesize Fe₂VO₄ hierarchical porous microparticles, which efficiently prevents the aggregation of the Fe₂VO₄ primary nanoparticles. The reaction between alcohol molecules and surface hydroxy groups is confirmed by density functional theory calculations and Fourier transform infrared spectroscopy. The electrochemical mechanism of Fe₂VO₄ as lithium‐ion battery anode is characterized by in situ X‐ray diffraction for the first time. This electrode material is capable of delivering a high reversible discharge capacity of 799 mA h g^?1 at 0.5 A g^?1 with a high initial coulombic efficiency of 79%, and the capacity retention is 78% after 500 cycles. Moreover, a remarkable reversible discharge capacity of 679 mA h g^?1 is achieved at 5 A g^?1. Furthermore, when tested as sodium‐ion battery anode, a high reversible capacity of 382 mA h g^?1 can be delivered at the current density of 1 A g^?1, which still retains at 229 mA h g^?1 after 1000 cycles. The superior electrochemical performance makes it a potential anode material for high‐rate and long‐life lithium/sodium‐ion batteries.     

Ultrafast Sodium/Potassium‐Ion Intercalation into Hierarchically Porous Thin Carbon Shells

The large‐scale application of sodium/potassium‐ion batteries is severely limited by the low and slow charge storage dynamics of electrode materials. The crystalline carbons exhibit poor insertion capability of large Na⁺/K⁺ ions, which limits the storage capability of Na/K batteries. Herein, porous S and N co‐doped thin carbon (S/N@C) with shell‐like (shell size ≈20–30 nm, shell wall ≈8–10 nm) morphology for enhanced Na⁺/K⁺ storage is presented. Thanks to the hollow structure and thin shell‐wall, S/N@C exhibits an excellent Na⁺/K⁺ storage capability with fast mass transport at higher current densities, leading to limited compromise over charge storage at high charge/discharge rates. The S/N@C delivers a high reversible capacity of 448 mAh g^‐1 for Na battery, at the current density of 100 mA g^‐1 and maintains a discharge capacity up to 337 mAh g^‐1 at 1000 mA g^‐1. Owing to shortened diffusion pathways, S/N@C delivers an unprecedented discharge capacity of 204 and 169 mAh g^‐1 at extremely high current densities of 16 000 and 32 000 mA g^‐1, respectively, with excellent reversible capacity for 4500 cycles. Moreover, S/N@C exhibits high K⁺ storage capability (320 mAh g^‐1 at current density of 50 mA g^‐1) and excellent cyclic life.     

A Top‐Down Strategy toward SnSb In‐Plane Nanoconfined 3D N‐Doped Porous Graphene Composite Microspheres for High Performance Na‐Ion Battery Anode

Engineering of 3D graphene/metal composites with ultrasmall sized metal and robust metal–graphene interfacial interaction for energy storage application is still a challenge and rarely reported. In this work, a facile top‐down strategy is developed for the preparation of SnSb‐in‐plane nanoconfined 3D N‐doped porous graphene networks for sodium ion battery anodes, which are composed of several tens of interconnected empty N‐graphene boxes in‐plane firmly embedded with ultrasmall SnSb nanocrystals. The all‐around encapsulation (plane‐to‐plane contact) architecture that provides a large interface between N‐graphene and SnSb nanocrystal not only effectively enhances the electron conductivity and structural integrity of the overall electrode, but also offers excess interfacial sodium storage, thus leading to much enhanced high‐rate sodium storage capacity and stability, which has been proven by both experimental results and first‐principles simulations. Moreover, this top‐down strategy can enable new paths to the low‐cost and high‐yield synthesis of 3D graphene/metal composites for applications in energy‐related fields and beyond.     

锂离子电池炭负极材料结构及嵌锂机理研究进展

炭材料取代金属锂作为负极后,锂离子电池在商业应用上取得了成功,并以其高能量密度在各种电子设备上广泛使用.锂离子电池的性能很大程度上取决于炭负极材料的微观结构,不同种类的炭材料其电化学性能有很大差别.对近几年所研究的可逆储锂炭材料进行了综述,着重总结了炭负极材料的种类、结构及其嵌锂机理,并展望了锂离子电池炭负极材料的研究进展.     

Solvent‐Exchange Strategy toward Aqueous Dispersible MoS2 Nanosheets and Their Nitrogen‐Rich Carbon Sphere Nanocomposites for Efficient Lithium/Sodium Ion Storage

Major challenges in developing 2D transition‐metal disulfides (TMDs) as anode materials for lithium/sodium ion batteries (LIBs/SIBs) lie in rational design and targeted synthesis of TMD‐based nanocomposite structures with precisely controlled ion and electron transport. Herein, a general and scalable solvent‐exchange strategy is presented for uniform dispersion of few‐layer MoS₂ (f‐MoS₂) from high‐boiling‐point solvents (N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethyl formaldehyde (DMF), etc.) into low‐boiling‐point solvents (water, ethanol, etc.). The solvent‐exchange strategy dramatically simplifies high‐yield production of dispersible MoS₂ nanosheets as well as facilitates subsequent decoration of MoS₂ for various applications. As a demonstration, MoS₂‐decorated nitrogen‐rich carbon spheres (MoS₂‐NCS) are prepared via in situ growth of polypyrrole and subsequent pyrolysis. Benefiting from its ultrathin feature, largely exposed active surface, highly conductive framework and excellent structural integrity, the 2D core–shell architecture of MoS₂‐NCS exhibits an outstanding reversible capacity and excellent cycling performance, achieving high initial discharge capacity of 1087.5 and 508.6 mA h g^?1 at 0.1 A g^?1, capacity retentions of 95.6% and 94.2% after 500 and 250 charge/discharge cycles at 1 A g^?1, for lithium/sodium ion storages, respectively.     

Confined Amorphous Red Phosphorus in MOF‐Derived N‐Doped Microporous Carbon as a Superior Anode for Sodium‐Ion Battery

Red phosphorus (P) has attracted intense attention as promising anode material for high‐energy density sodium‐ion batteries (NIBs), owing to its high sodium storage theoretical capacity (2595 mAh g^?1). Nevertheless, natural insulating property and large volume variation of red P during cycling result in extremely low electrochemical activity, leading to poor electrochemical performance. Herein, the authors demonstrate a rational strategy to improve sodium storage performance of red P by confining nanosized amorphous red P into zeolitic imidazolate framework‐8 (ZIF‐8) ‐derived nitrogen‐doped microporous carbon matrix (denoted as P@N‐MPC). When used as anode for NIBs, the P@N‐MPC composite displays a high reversible specific capacity of ≈600 mAh g^?1 at 0.15 A g^?1 and improved rate capacity (≈450 mAh g^?1 at 1 A g^?1 after 1000 cycles with an extremely low capacity fading rate of 0.02% per cycle). The superior sodium storage performance of the P@N‐MPC is mainly attributed to the novel structure. The N‐doped porous carbon with sub‐1 nm micropore facilitates the rapid diffusion of organic electrolyte ions and improves the conductivity of the encapsulated red P. Furthermore, the porous carbon matrix can buffer the volume change of red P during repeat sodiation/desodiation process, keeping the structure intact after long cycle life.     

Enhanced Intercalation Dynamics and Stability of Engineered Micro/Nano‐Structured Electrode Materials: Vanadium Oxide Mesocrystals

An additive and template free process is developed for the facile synthesis of VO₂(B) mesocrystals via the solvothermal reaction of oxalic acid and vanadium pentoxide. The six‐armed star architectures are composed of stacked nanosheets homoepitaxially oriented along the [100] crystallographic register with respect to one another, as confirmed by means of selected area electron diffraction and electron microscopy. It is proposed that the mesocrystal formation mechanism proceeds through classical as well as non‐classical crystallization processes, and is possibly facilitated or promoted by the presence of a reducing/chelating agent. The synthesized VO₂(B) mesocrystals are tested as a cathodic electrode material for lithium‐ion batteries, and show good capacity at discharge rates ranging from 150–1500 mA g^?1 and a cyclic stability of 195 mA h g^?1 over fifty cycles. The superb electrochemical performance of the VO₂(B) mesocrystals is attributed to the porous and oriented superstructure that ensures large surface area for redox reaction and short diffusion distances. The mesocrystalline structure ensures that all the surfaces are in intimate contact with the electrolyte, and that lithium‐ion intercalation occurs uniformly throughout the entire electrode. The exposed (100) facets also lead to fast lithium intercalation, and the homoepitaxial stacking of nanosheets offers a strong inner‐sheet binding force that leads to better accommodation of the strain induced during cycling, thus circumventing the capacity fading issues typically associated with VO₂(B) electrodes.