Carbon‐Interconnected Ge Nanocrystals as an Anode with Ultra‐Long‐Term Cyclability for Lithium Ion Batteries

Germanium (Ge) possesses a great potential as a high‐capacity anode material for lithium ion batteries but suffers from its poor capacity retention and rate capability due to significant volume expansion by lithiation. Here, a facile synthetic route is introduced for producing nanometer‐sized Ge crystallites interconnected by carbon (GEC) via thermal decomposition of a Ge‐citrate complex followed by a calcination process in an inert atmosphere. The GEC electrode shows outstanding electrochemical performance, i.e., an almost 98.8% capacity retention of 1232 mAh g^?1, even after 1000 cycles at the rate of C/2. Importantly, a high discharge capacity of 880 mAh g^?1 is maintained at the very high rate of 10 C. The excellent anode performance of GEC stems from both effective buffering of carbon anchored to the Ge nanocrystals and the high open porosity of the GEC aggregated powder with an average pore diameter of 32 nm. Furthermore, the interfacial layer formed between Ge and carbon plays an essential role in prolonging the cycle life. The GEC electrode can be successfully employed as an anode for next generation lithium ion batteries.     

Thermo‐electrochemical Activation of an In–Cu Intermetallic Electrode for the Anode in Lithium Secondary Batteries

Lithium ion batteries (LIBs) have been emerging as a major power source for portable electronic devices and hybrid electric vehicles (HEV) with their superior performance to other competitors. The performance aspects of energy density and rate capability of LIBs should, however, be further improved for their new applications. Towards this end, many Li‐alloy materials, metal oxides, and phosphides have been tested, some of which have, however, been discarded because of poor activity at ambient temperature. Here, it is shown that the In? Cu binary intermetallic compound (Cu₇In₃), which shows no activity at room temperature as a result of activation energy required for In? Cu bond cleavage, can be made active by discharge–charge cycling at elevated temperatures. Upon lithiation at elevated temperatures (55–120 °C), the Cu₇In₃ phase is converted into nanograins of metallic Cu and a lithiated In phase (Li₁₃In₃). The underlying activation mechanism is the formation of new In‐rich phase (CuIn). The de‐lithiation temperature turns out to be the most important variable that controlling the nature of the In‐rich compounds.     

Binary Li4Ti5O12‐Li2Ti3O7 Nanocomposite as an Anode Material for Li‐Ion Batteries

Li₄Ti₅O₁₂ typically shows a flat charge/discharge curve, which usually leads to difficulty in the voltage‐based state of charge (SOC) estimation. In this study, a facile quench‐assisted solid‐state method is used to prepare a highly crystalline binary Li₄Ti₅O₁₂‐Li₂Ti₃O₇ nanocomposite. While Li₄Ti₅O₁₂ exhibits a sudden voltage rise/drop near the end of its charge/discharge curve, this binary nanocomposite has a tunable sloped voltage profile. The nanocomposite exhibits a unique lamellar morphology consisting of interconnected nanograins of ≈20 nm size with a hierarchical nanoporous structure, contributing to an enhanced rate capability with a capacity of 128 mA h g^?1 at a high C‐rate of 10 C, and excellent cycling stability.     

N‐Doped Graphene‐SnO2 Sandwich Paper for High‐Performance Lithium‐Ion Batteries

A new facile route to fabricate N‐doped graphene‐SnO₂ sandwich papers is developed. The 7,7,8,8‐tetracyanoquinodimethane anion (TCNQ^?) plays a key role for the formation of such structures as it acts as both the nitrogen source and complexing agent. If used in lithium‐ion batteries (LIBs), the material exhibits a large capacity, high rate capability, and excellent cycling stability. The superior electrochemical performance of this novel material is the result from its unique features: excellent electronic conductivity related to the sandwich structure, short transportation length for both lithium ions and electrons, and elastomeric space to accommodate volume changes upon Li insertion/extraction.     

Reconstruction of Conformal Nanoscale MnO on Graphene as a High‐Capacity and Long‐Life Anode Material for Lithium Ion Batteries

To tackle the issue of inferior cycle stability and rate capability for MnO anode materials in lithium ion batteries, a facile strategy is explored to prepare a hybrid material consisting of MnO nanocrystals grown on conductive graphene nanosheets. The prepared MnO/graphene hybrid anode exhibits a reversible capacity as high as 2014.1 mAh g^?1 after 150 discharge/charge cycles at 200 mA g^?1, excellent rate capability (625.8 mAh g^?1 at 3000 mA g^?1), and superior cyclability (843.3 mAh g^?1 even after 400 discharge/charge cycles at 2000 mA g^?1 with only 0.01% capacity loss per cycle). The results suggest that the reconstruction of the MnO/graphene electrodes is intrinsic due to conversion reactions. A long‐term stable nanoarchitecture of graphene‐supported ultrafine manganese oxide nanoparticles is formed upon cycling, which yields a long‐life anode material for lithium ion batteries. The lithiation and delithiation behavior suggests that the further oxidation of Mn(II ) to Mn(IV ) and the interfacial lithium storage upon cycling contribute to the enhanced specific capacity. The excellent rate capability benefits from the presence of conductive graphene and a short transportation length for both lithium ions and electrons. Moreover, the as‐formed hybrid nanostructure of MnO on graphene may help achieve faster kinetics of conversion reactions.     

Iron Oxide Nanoparticle and Graphene Nanoribbon Composite as an Anode Material for High‐Performance Li‐Ion Batteries

A composite material made of graphene nanoribbons and iron oxide nanoparticles provides a remarkable route to lithium‐ion battery anode with high specific capacity and cycle stability. At a rate of 100 mA/g, the material exhibits a high discharge capacity of ~910 mAh/g after 134 cycles, which is >90% of the theoretical li‐ion storage capacity of iron oxide. Carbon black, carbon nanotubes, and graphene flakes have been employed by researchers to achieve conductivity and stability in lithium‐ion electrode materials. Herein, the use of graphene nanoribbons as a conductive platform on which iron oxide nanoparticles are formed combines the advantages of long carbon nanotubes and flat graphene surfaces. The high capacity over prolonged cycling achieved is due to the synergy between an electrically percolating networks of conductive graphene nanoribbons and the high lithium‐ion storage capability of iron oxide nanoparticles.     

锂离子电池正极材料纳米LiFePO_4

综述了LiFePO4的晶体结构、充放电机理、电化学性能、存在问题以及纳米技术近年来在LiFePO4中应用的最新进展。纳米LiFePO4的制备方法主要有高温固相反应法、水热合成法、溶胶凝胶法、微波合成法等。材料的粒径大小及分布、离子和电子的传导能力对产品的电化学性能影响较大,在制备时采用惰性气氛、掺杂改性以及控制晶粒的生长尺寸是关键,电极材料的微纳米化对锂离子电池的电化学性能和循环性能的改善有着显著的意义,展望了纳米正极材料LiFePO4用于锂离子电池的未来前景。     

Fabrication of Electrospinning‐Derived Carbon Nanofiber Webs for the Anode Material of Lithium‐Ion Secondary Batteries

A carbon nanofiber‐based electrode, exhibiting a large accessible surface area (derived from the nanometer‐sized fiber diameter), high carbon purity (without binder), relatively high electrical conductivity, structural integrity, thin web macromorphology, a large reversible capacity (ca. 450 mA h g^–1), and a relatively linearly inclined voltage profile, is fabricated by nanofiber formation via electrospinning of a polymer solution and its subsequent thermal treatment. It is envisaged that these characteristics of this novel carbon material will make it an ideal candidate for the anode material of high‐power lithium‐ion batteries (where a high current is critically needed), owing to the highly reduced lithium‐ion diffusion path within the active material.     

Ultrasmall Sn Nanoparticles Embedded in Carbon as High‐Performance Anode for Sodium‐Ion Batteries

Designed as a high‐capacity, high‐rate, and long‐cycle life anode for sodium‐ion batteries, ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network (denoted as 8‐Sn@C) is prepared using an aerosol spray pyrolysis method. Instrumental analyses show that 8‐Sn@C nanocomposite with 46 wt% Sn and a BET surface area of 150.43 m² g^?1 delivers an initial reversible capacity of ≈493.6 mA h g^?1 at the current density of 200 mA g^?1, a high‐rate capacity of 349 mA h g^?1 even at 4000 mA g^?1, and a stable capacity of ≈415 mA h g^?1 after 500 cycles at 1000 mA g^?1. The remarkable electrochemical performance of 8‐Sn@C is owing to the synergetic effects between the well‐dispersed ultrasmall Sn nanoparticles and the conductive carbon network. This unique structure of very‐fine Sn nanoparticles embedded in the porous carbon network can effectively suppress the volume fluctuation and particle aggregation of tin during prolonged sodiation/desodiation process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sn anode.     

Synthesis of Nanosize Quasispherical MgFe2O4 and Study of Electrochemical Properties as Anode of Lithium Ion Batteries

In this work, nanosize MgFe₂O₄ spinel with quasispherical shape was prepared as anode material for lithium ion batteries by the hydroxide coprecipitation method. The crystal structure, composition, and morphology of the as-prepared powders were characterized by means of x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy, and scanning electron microscopy (SEM), respectively. The XRD and SEM data revealed that the material as-prepared at 900°C was of high crystallinity and quasispherical with diameter of about 100 nm. A reaction mechanism is proposed. The?electrochemical properties were evaluated by cyclic voltammetry and galvanostatic charge–discharge studies. The sample calcined at 900°C delivered a higher initial discharge capacity (1200 mAh g^?1) and better cyclability. The enhanced electrochemical behavior was ascribed to the nanosize and the better crystallinity of the spherical powder. All the results suggest that nanosize quasispherical MgFe₂O₄ is a promising candidate anode material for lithium ion batteries.     

Preparation of Short Carbon Nanotubes and Application as an Electrode Material in Li‐Ion Batteries

A new approach is developed for cutting conventional micrometer‐long entangled carbon nanotubes (CNTs) to short ca. 200 nm long segments with excellent dispersion. CNTs with different lengths are used as anode materials in Li‐ion batteries. The reversible capacity of the Li‐ion batteries is increased and the irreversible capacity is decreased upon shortening the length of the CNTs. The reason for this is that the insertion/extraction of Li ions is easier into/from short CNTs as compared to long CNTs because of the shortened length and the presence of lateral defects. Moreover, short CNTs have a lower electrical resistance and Warburg prefactor, resulting in better rate performance at high current densities. The present study suggests that short segments of CNTs obtained by cutting long CNTs may possess novel properties that may be useful for a wide variety of applications.     

Synthesis,Structure Transformation,and Electrochemical Properties of Li2MgSi as a Novel Anode for Li‐lon Batteries

In this work, a novel hexagonal Li₂MgSi anode is successfully prepared through a hydrogen‐driven chemical reaction technique. Electrochemical tests indicate significantly improved cycling stability for the as‐synthesized Li₂MgSi compared with that of Mg₂Si. Ball‐milling treatment induces a polymorphic transformation of Li₂MgSi from a hexagonal structure to a cubic structure, suggesting that the cubic Li₂MgSi is a metastable phase. The post‐24‐h‐milled Li₂MgSi delivers a maximum capacity of 807.8 mAh g^?1, which is much higher than that of pristine Li₂MgSi. In particular, the post‐24‐h‐milled Li₂MgSi retains 50% of its capacity after 100 cycles, which is superior to cycling stability of Mg₂Si. XRD analyses correlated with CV measurements do not demonstrate the dissociation of metallic Mg and/or Li–Mg alloy involved in the lithiation of Mg₂Si for the Li₂MgSi anode, which contributes to the improved lithium storage performance of the Li₂MgSi anode. The findings presented in this work are very useful for the design and synthesis of novel intermetallic compounds for lithium storage as anode materials of Li‐ion batteries.     

Super‐Aligned Carbon Nanotube Films as Current Collectors for Lightweight and Flexible Lithium Ion Batteries

Carbon nanotube (CNT) current collectors with excellent flexibility, extremely low density (0.04 mg cm^?2), and tunable thickness are fabricated by cross‐stacking continuous CNT films drawn from super‐aligned CNT arrays. Compared with metal current collectors, better wetting, stronger adhesion, greater mechanical durability, and lower contact resistance are demonstrated at the electrode/CNT interface. Electrodes with CNT current collectors show improvements in cycling stability, rate capability, and gravimetric energy density over those with metal current collectors. These results suggest that CNT films can function as a promising type of current collector for lightweight and flexible lithium ion batteries with high energy density.     

Homogeneous CoO on Graphene for Binder‐Free and Ultralong‐Life Lithium Ion Batteries

Ultralong cycle life, high energy, and power density rechargeable lithium‐ion batteries are crucial to the ever‐increasing large‐scale electric energy storage for renewable energy and sustainable road transport. However, the commercial graphite anode cannot perform this challenging task due to its low theoretical capacity and poor rate‐capability performance. Metal oxides hold much higher capacity but still are plagued by low rate capability and serious capacity degradation. Here, a novel strategy is developed to prepare binder‐free and mechanically robust CoO/graphene electrodes, wherein homogenous and full coating of β‐Co(OH)₂ nanosheets on graphene, through a novel electrostatic induced spread growth method, plays a key role. The combined advantages of large 2D surface and moderate inflexibility of the as‐obtained β‐Co(OH)₂/graphene hybrid enables its easy coating on Cu foil by a simple layer‐by‐layer stacking process. Devices made with these electrodes exhibit high rate capability over a temperature range from 0 to 55 °C and, most importantly, maintain excellent cycle stability up to 5000 cycles even at a high current density.     

High Performance 3D Si/Ge Nanorods Array Anode Buffered by TiN/Ti Interlayer for Sodium‐Ion Batteries

3D micro/nanobatteries in high energy and power densities are drawing more and more interest due to the urgent demand of them in integrating with numerous micro/nanoscale electronic devices, such as smart dust, miniaturized sensors, actuators, BioMEMS chips, and so on. In this study, the electrochemical performances of 3D hexagonal match‐like Si/Ge nanorod (NR) arrays buffered by TiN/Ti interlayer, which are fabricated on Si substrates by a cost‐effective, wafer scale, and Si‐compatible process are demonstrated and systematically investigated as the anode in sodium‐ion batteries. The optimized Si/TiN/Ti/Ge composite NR array anode displays superior areal/specific capacities and cycling stability by reason of their favorable 3D nanostructures and the effective conductive layers of TiN/Ti thin films. Sodium‐ion insertion behaviors are experimentally investigated in postmorphologies and elemental information of the cycled composite anode, and theoretically studied by the first principles calculation upon the adsorption and diffusion energies of sodium in Ge unit cell. The preferential diffusion of sodium in Ge structure over in Si lattice is evidently proved. The successful configuration of these distinctive wafer‐scale Si‐based Na‐ion micro/nanobattery anodes can provide insight into exploring and designing new Si/Ge‐based electrode materials, which can be integrated into micro‐electronic devices as on chip power systems in the future.     

Graphene‐Based Mesoporous SnO2 with Enhanced Electrochemical Performance for Lithium‐Ion Batteries

Graphene‐based metal oxides generally show outstanding electrochemical performance due to the superior properties of graphene. However, the aggregation of active metal oxide nanoparticles on the graphene surface may result in a capacity fading and poor cycle performance. Here, a mesostructured graphene‐based SnO₂ composite is prepared through in situ growth of SnO₂ particles on the graphene surface using cetyltrimethylammonium bromide as the structure‐directing agent. This novel mesoporous composite inherits the advantages of graphene nanosheets and mesoporous materials and exhibits higher reversible capacity, better cycle performance, and better rate capability compared to pure mesoporous SnO₂ and graphene‐based nonporous SnO₂. It is concluded that the synergetic effect between graphene and mesostructure benefits the improvement of the electrochemical properties of the hybrid composites. This facile method may offer an attractive alternative approach for preparation of the graphene‐based mesoporous composites as high‐ performance electrodes for lithium‐ion batteries.     

Carbon Nanotube‐Encapsulated Noble Metal Nanoparticle Hybrid as a Cathode Material for Li‐Oxygen Batteries

Although Li‐oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end‐opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT‐encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li₂O₂ nanocrystals on CNT surfaces instead of localized distribution of Li₂O₂ aggregation, thus providing efficient charge transfer for the decomposition of Li₂O₂.     

FeO0.7F1.3/C Nanocomposite as a High‐Capacity Cathode Material for Sodium‐Ion Batteries

Searching high capacity cathode materials is one of the most important fields of the research and development of sodium‐ion batteries (SIBs). Here, we report a FeO_0.7F_1.3/C nanocomposite synthesized via a solution process as a new cathode material for SIBs. This material exhibits a high initial discharge capacity of 496 mAh g^?1 in a sodium cell at 50 °C. From the 3^rd to 50^th cycle, the capacity fading is only 0.14% per cycle (from 388 mAh g^?1 at 3^rd the cycle to 360 mAh g^?1 at the 50^th cycle), demonstrating superior cyclability. A high energy density of 650 Wh kg^?1 is obtained at the material level. The reaction mechanism studies of FeO_0.7F_1.3/C with sodium show a hybridized mechanism of both intercalation and conversion reaction.