Li、Li-C电极表面化学和形态表征研究方法

本文综述了 L i、Li- C电极表面化学、形态研究的特点 ,论述了 FTIR、XPS和 AFM在研究 Li、Li- C电极的表面化学和形态中的应用及优缺点。

A review of the carbon coating of the silicon anode in highperformance lithium-ion batteries

In the development of rechargeable lithium ion batteries(LIBs),silicon anodes have attracted much attention because of their extremely high theoretical capacity,relatively low Li-insertion voltage and the availability of silicon resources.However,their large volume expansion and fragile solid electrolyte interface(SEI)film hinder their commercial application.To solve these problems,Si has been combined with various carbon materials to increase their structural stability and improve their interface properties.The use of different carbon materials,such as amorphous carbon and graphite,as three-dimensional(3D)protective anode coatings that help buffer mechanical strain and isolate the electrolyte is detailed,and novel methods for applying the coatings are outlined.However,carbon materials used as a protective layer still have some disadvantages,necessitating their modification.Recent developments have focused on modifying the protective carbon shells,and substitutes for the carbon have been suggested.

Preparation and performance of hierarchically porous carbons as oxygen electrodes for lithium oxygen batteries

The hierarchically porous carbons （HPCs） were prepared by sol-gel selassembly technology in different surfactant concentrations and were used as the potential electrode for lithium oxygen batteries. The physical and electrochemical properties of the as-prepared HPCs were investigated by filed emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM）, nitrogen adsorption-desorption isotherm and galvanostatic charge/discharge. The results indicate that all of the HPCs mainly possess mesoporous structure with nearly similar pore size distribution. Using the HPCs as the electrode, a high discharge capacity for lithium oxygen battery can be achieved, and the discharge capacity increases with the specific surface area. Especially, the HPCs-3 oxygen electrode with CTAB concentration of 0.27 mol/L exhibits good capacity retention through controlling discharge depth to 800 mA·h/g and the highest discharge capacity of 2050 mA·h/g at a rate of 0.1 mA/cm2.

Calculation model of edge carbon atoms in graphite particles for anode of lithium-ion batteries

Based on the hexagonal crystallite model of graphite,the electrochemical characteristics of carbon atoms on the edge and basal plane were proposed by analyzing graphite crystal structure and bonds of carbon atoms in different sites.A spherical close-packed model for graphite particle was developed.The fractions of surface carbon atoms（SCA） and edge carbon atoms（ECA） were derived in the expression of crystallographic parameters and particle size,and the effects of ECA on the initial irreversible capacity and the mechanisms of action were analyzed and verified.The results show that the atoms on the edge are more active for electrochemical reactions,such as electrolyte decomposition and tendency to form stable bond with other atoms and groups.For the practical graphite particle,corresponding modifying factors were introduced to revise the difference in calculating results.The revised expression is suitable for the calculation of the fractions of SCA and ECA for carbon materials such as graphite,disordered carbon and modified graphite.

Vapor-grown carbon fibers enhanced sulfur-multi walled carbon nanotubes composite cathode for lithium/sulfur batteries

Vapor-grown carbon fibers （VGCFs） were introduced as conductive additives for sulfur-multiwalled carbon nanotubes （S-MWCNTs） composite cathode of lithium-sulfur batteries. The performance of S-MWCNTs composite cathodes with carbon black and VGCFs as sole conductive additives was investigated using scanning electron microscopy （SEM）, galvanostatic charge-discharge tests and electrochemical impedance spectroscopy （EIS）. The results show that the S-MWCNTs composite cathode with VGCFs displays a network-like morphology and exhibits higher activity and better cycle durability compared with the composite cathode with carbon black, delivering an initial discharge capacity of 1254 mA＆#183;h/g and a capacity of 716 mA＆#183;h/g after 40 cycles at 335 mA/g. The interconnected VGCFs can provide a stable conductive network, suppress the aggregation of cathode materials and residual lithium sulfide and maintain the porosity of cathode, and therefore the electrochemical performance of S-MWCNTs composite cathode is enhanced.

Progress in research on Li–CO_2 batteries: Mechanism, catalyst and performance

Rechargeable Li-CO2 batteries provide a promising new approach for carbon capture and energy storage technology. However, their practical application is limited by many challenges despite much progress in this technology. Recent development in Li-CO2 batteries is presented. The reaction mechanism with an air cathode, operating temperatures used, electrochemical performance under different CO2 concentrations, stability of the battery in different electrolytes, and utilization of different cathode materials were emphasized. At last, challenges and perspectives were also present- ed. This review provides a deep understanding of Li-CO2 batteries and offers important guidelines for developing reversible and high efficiency Li-CO2 batteries.

Relationship between initial efficiency and structure parameters of carbon anode material for Li-ion battery

The initial efficiency is a very important criterion for carbon anode material of Li-ion battery.The relationship between initial efficiency and structure parameters of carbon anode material of Li-ion battery was investigated by an artificial intelligence approach called Random Forests using D10,D50,D90,BET specific surface area and TP density as inputs,initial efficiency as output.The results give good classification performance with 91%accuracy.The variable importance analysis results show the impact of 5 variables on the initial efficiency descends in the order of D90,TP density,BET specific surface area,D50 and D10;smaller D90 and larger TP density have positive impact on initial efficiency.The contribution of BET specific surface area on classification is only 18.74%,which indicates the shortcoming of BET specific surface area as a widely used parameter for initial efficiency evaluation.

Effects of carbon sources on electrochemical performance of Li_4Ti_5O_(12)/C composite anode materials

Li4Ti5O12/C composite materials were synthesized by two-step solid state reaction method with glucose, sucrose, and starch as carbon sources, respectively. The effects of carbon sources on the structure, morphology, and electrochemical performance of Li4Ti5O12/C composite materials were investigated by SEM, XRD and electrochemical tests. The results indicate that carbon sources have almost no effect on the structure of Li4Ti5O12/C composite materials. The initial discharge capacities of the Li4Ti1O12/C composite materials are slightly lower than those of as-synthesized Li4Ti5O12. However, Li4Ti5O12/C composite materials show better electrochemical rate performance than the as-synthesized Li4Ti5O12. The capacity retention （79%） of the Li4Ti5O12/C composite materials with starch as carbon source, is higher than that of Li4Ti5O12/C composite materials with glucose and sucrose as carbon source at current rate of 2.0C.

Synthesis and characterization of porous monodisperse carbon spheres/selenium composite for high-performance rechargeable Li-Se batteries

In order to find the appropriate material to load selenium for higher performance of rechargeable Li-Se batteries,the resorcinol-formaldehyde resins derived monodisperse carbon spheres(RFCS)/Se composites were fabricated by the melting-diffusion method.The RFCS were obtained from initial carbonization of resorcinol-formaldehyde resins and subsequent KOH activation.Three kinds of samples of the RFCS/Se composites with different mass ratios were characterized by XRD,Raman spectroscopy,SEM,BET and EDS tests,which demonstrate that the samples with diverse mass fractions of selenium have distinct interior structure.The most suitable RFCS/Se composite is found to be the RFCS/Se-50 composite,which delivers a high reversible capacity of 643.9 mA·h/g after 100 cycles at current density of 0.2C.

Effect of Carbon Content on Electrochemical Properties of LiFePO4/C Composite Cathode

Olivine-type LiFePO4/C composite cathode materials were synthesized by a solid-state reaction method in an inert atmosphere. The glucose was added as conductive precursors before the formation of the crystalline phase. The effects of glucose content on the properties of as-synthesized cathode materials were investigated. The crystal structure and the electrochemical performance were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, laser particle-size distribution measurement and electrochemical performance testing. The material has a single crystal olivine structure with grain-sizes ca. 100-200 nm. SEM micrographs and the corresponding energy dispersive spectrometer （EDS） data confirm that the carbon particulates produced by glucose pyrogenation are uniformly dispersed among the LiFePO4 grains, ensuring a good electronic contact. Impedance spectroscopy was used to investigate the ohmic and kinetic contributions to the cell performance. It is found that increasing the carbon content leads to a reduction of the cell impedance due to the reduction of the charge transfer resistance. The galvanostatically charge and discharge tests show that the material obtained by adding 10% C （by mass） gives a maximum discharge capacity of 140.8mA·h·g^-1 at the same rate （C/10）. The material also displays a more stable cycle-life than the others.

Rationally designed carbon-coated Fe304 coaxial nanotubes with hierarchical porosity as high-rate anodes for lithium ion batteries

Fe3O4 is a promising high-capacity anode material for lithium ion batteries, but challenges including short cycle life and low rate capability hinder its widespread implementation. In this work, a well-defined tubular structure constructed by carbon-coated Fe3O4 has been successfully fabricated with hierarchically porous structure, high surface area, and suitable thickness of carbon layer. Such purposely designed hybrid nanostructures have an enhanced electronic/ionic conductivity, stable electrode/electrolyte interface, and physical buffering effect arising from the nanoscale combination of carbon with Fe3O4, as well as the hollow, aligned and hierarchically porous architectures. When used as an anode material for a lithium-ion half cell, the carbon-coated hierarchical Fe3O4 nanotubes showed excellent cycling performance with a specific capacity of 1,020 mAh.g^-1 at 200 mA.g^-1 after 150 cycles, a capacity retention of ca. 103%. Even at a higher current density of 1,000 mA·g^-1, a capacity of 840 mAh·g^-1 is retained after 300 cycles with no capacity loss. In particular, a superior rate capability can be obtained with a stable capacity of 355 mAh.g^-1 at 8,000 mA·g^-1. The encouraging results indicate that hierarchically tubular hybrid nanostructures can have important implications for the development of high-rate electrodes for future rechargeable lithium ion batteries （LIBs）.

Hybrid Silicon-Carbon Nanostructured Composites as Superior Anodes for Lithium Ion Batteries

We have successfully fabricated a hybrid silicon-carbon nanostructured composite with large area （about 25.5 in^2） in a simple fashion using a conventional sputtering system. When used as the anode in lithium ion batteries, the uniformly deposited amorphous silicon （a-Si） works as the active material to store electrical energy, and the pre-coated carbon nanofibers （CNFs） serve as both the electron conducting pathway and a strain/stress relaxation layer for the sputtered a-Si layers during the intercalation process of lithium ions. As a result, the as-fabricated lithium ion batteries, with deposited a-Si thicknesses of 200 nm or 300 nm, not only exhibit a high specific capacity of 〉2000 mA.h/g, but also show a good capacity retention of over 80% and Coulombic efficiency of 〉98% after a large number of charge/discharge experiments. Our approach offers an efficient and scalable method to obtain silicon-carbon nanostructured composites for application in lithium ion batteries.

TiO2 nanotube branched tree on a carbon nanofiber nanostructure as an anode for high energy and power lithium ion batteries

The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes （NTs） branched onto a carbon nanofiber （CNF） ＂tree＂ that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited -10 times higher areal energy density and excellent rate capability （discharge capacity of -150 mA.h.g-1 at a current density of 1,000 mA·g-1）. Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity （mA·h·cm-2） as well as excellent rate capability.

Ball-flower-like carbon microspheres via a three-dimensional replication strategy as a high-capacity cathode in lithium–oxygen batteries

The robust porous architectures of active materials are highly desired for oxygen electrodes in lithium–oxygen batteries to enable high capacities and excellent reversibility. Herein, we report a novel three-dimensional replication strategy to fabricate three-dimensional architecture of porous carbon for oxygen electrodes in lithium–oxygen batteries. As a demonstration, ball-flower-like carbon microspheres assembled with tortuous hollow carbon nanosheets are successfully prepared by completely replicating the morphology of the nanostructured zinc oxide template and utilizing the polydopamine coating layer as the carbon source.When used as the active material for oxygen electrodes, the three-dimensional porous architecture of the prepared ballflower-like carbon microspheres can accommodate the discharge product lithium peroxide and simultaneously maintain the ions and gas diffusion paths. Moreover, their high degrees of defectiveness by nitrogen doping provide sufficient active sites for oxygen reduction/evolution reaction.Thus the prepared ball-flower-like carbon microspheres demonstrate a high capacity of 9,163.7 mA h g-1 and excellent reversibility. This work presents an effective way to prepare three-dimensional architectures of porous carbon by replicating the controllable nanostructures of transition metal oxide templates for energy storage and conversion applications.

A high-capacity graphene/mesocarbon microbead composite anode for lithium-ion batteries

The graphene/mesocarbon microbead(MCMB)composite is assessed as an anode material with a high capacity for lithium-ion batteries.The composite electrode exhibits improved cycling stability and rate capability,delivering a high initial charge/discharge capacity of 421.4 mA·h/g/494.8 mA·h/g as well as an excellent capacity retention over 500 cycles at a current density of 40 mA/g.At a higher current density of 800 mA/g,the electrode still retains 35%of its initial capacity which exceeds the capacity retention of pure graphene or MCMB reference electrodes.Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the composite electrode favors electrochemical kinetics as compared with graphene and MCMB separately.Superior electrochemical properties suggest a strong synergetic effect between highly conductive graphene and MCMB.

Soft template PEG-assisted synthesis of Fe_3O_4@C nanocomposite as superior anode materials for lithium-ion batteries

Carbon-encapsulated Fe3O4 composites were successfully fabricated via hydrothermal method and ex- amined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The Fe3O4@C nanocomposite as an anode material with novel structure demonstrated excellent electrochemical performance, with enhanced specific reversible current density of 50 mA/g capacity （950 mAh/g at the after 50 cycles）, remarkable rate capability （more than 650 mAh/g even at the current density of 1,000 mAJg） and good cycle ability with less capacity fading （2.4 % after 50 cycles）. Two factors have been attributed to the ultrahigh electrochemical perfor- mance： Firstly, the 30- to 50-nm spherical structure with a short diffusion pathway and the amorphous carbon layer could not only provide extra space for buffering the volumetric change during the continuous charging-dis- charging but also improve the whole conductivity of the Fe3O4@C nanocomposite electrode; secondly, the syner- gistic effects of Fe304 and carbon could avoid Fe304 direct exposure to the electrolyte and maintain the structural stabilization of Fe3O4@C nanocomposite. It was suggested that the Fe3O4@C nanocomposite could be suitable as analternative anode for lithium-ion batteries with a high ap- plication potential.

Nano-structured red phosphorus/porous carbon as a superior anode for lithium and sodium-ion batteries

To enhance electrochemical performance of li- thium or sodium-ion batteries （LIBs or NIBs）, active materials are usually filled in porous conductive particles to produce anode composites. However, it is still challenging to achieve high performance anode composites with high specific capa- city, excellent rate performance, high initial Coulombic effi- ciency （ICE） and long cycle life. Based on these requirements, we design and fabricate activated carbon-coated carbon na- notubes （AC@CNT） with hierarchical structures containing micro- and meso-pores. A new structure of phosphorus/car- bon composite （P@AC@CNT） is prepared by confining red P in porous carbon through a vaporization-condensation-con- version method. The micro-pores are filled with P, while the meso-pores remain unoccupied, and the pore openings on the particle surface are sealed by P. Due to the unique structure of P@AC@CNT, it displays a high specific capacity of 1674 mA h g-i at 0.2 C, ultrahigh ICE of 92.2%, excellent rate per- formance of 1116 mA h g-i at 6 C, and significantly enhanced cycle stability for LIBs. The application of P@AC@CNT in NIBs is further explored. This method for the fabrication of the special composites with improved electrochemical per- formance can be extended to other energy storage applica- tions.