Carbon-coated graphite for anode of lithium ion rechargeable batteries: Graphite substrates for carbon coating

Anode performance in lithium ion rechargeable batteries (LIBs) was studied on four kinds of graphite powders, including synthetic graphite. Carbon-coated synthetic graphite gave a smaller irreversible capacity of about 20 mAh g⁻¹ and a better cyclic performance in an electrolyte solution of EC/DMC than natural graphite, though its discharge capacity of about 300 mAh g⁻¹ is a little smaller than natural graphite. Even in a PC-containing solution as EC/PC = 3/1, carbon-coated synthetic graphite had almost the same anode performance as in the solution without PC. Carbon coating of above 5 mass% on graphite particles was found to be effective to improve the anode performance at a low temperature of −5 °C, high retention in discharge capacity of about 90% being obtained. On both natural and synthetic graphite powders, carbon coating by the amount of 3–10 mass% at a temperature of 700–1000 °C was found to be optimum for the improvement of anode performance in LIBs, to have a lower irreversible capacity and higher retention in discharge capacity at −5 °C than without carbon coating.     

Carbon-coated graphite for anode of lithium ion rechargeable batteries: Carbon coating conditions and precursors

Carbon coating of natural graphite particles was performed by mechanical mixing of natural graphite with different carbon precursors in a scale of about 100 g. Anode performance in lithium ion rechargeable batteries was studied on the resultant carbon-coated graphite. Carbon formed on graphite particles had amorphous structure and low density. By carbon coating, a decrease in irreversible capacity of the first charge/discharge cycle in an electrolyte solution of EC/PC = 3/1 was observed, without noticeable change in discharge capacity. Carbon derived from different precursors did not give any marked difference in anode performance of carbon-coated graphite. Optimum conditions for carbon coating were determined as the coating of 4-13 mass% at 700-1000 °C. The present mechanical mixing of natural graphite and carbon precursor in powder is concluded to be a simple but sufficient process to produce carbon-coated graphite for anode material in lithium ion rechargeable batteries. As carbon precursor, PVA was shown to be one of the appreciable carbon precursors.     

Calculation on energy densities of lithium ion batteries and metallic lithium ion batteries

锂电池是理论能量密度最高的化学储能体系,估算各类锂电池电芯和单体能达到的能量密度,对于确定锂电池的发展方向和研发目标具有重要的参考价值。本工作根据主要正负极材料的比容量、电压,同时考虑非活性物质集流体、导电添加剂、黏结剂、隔膜、电解液、封装材料占比,计算了不同材料体系组成的锂离子电池和采用金属锂负极、嵌入类化合物正极的金属锂离子电池电芯的预期能量密度,并计算了18650型小型圆柱电池单体的能量密度,为电池发展路线的选择和能量密度所能达到的数值提供参考依据。同时指出,电池能量密度只是电池应用考虑的一个重要指标,面向实际应用,需要兼顾其它技术指标的实现。     

Carbon-coated SiO2 nanoparticles as anode material for lithium ion batteries

A simple approach is proposed to prepare C-SiO₂ composites as anode materials for lithium ion batteries. In this novel approach, nano-sized silica is soaked in sucrose solution and then heat treated at 900 °C under nitrogen atmosphere. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis shows that SiO₂ is embedded in amorphous carbon matrix. The electrochemical test results indicate that the electrochemical performance of the C-SiO₂ composites relates to the SiO₂ content of the composite. The C-SiO₂ composite with 50.1% SiO₂ shows the best reversible lithium storage performance. It delivers an initial discharge capacity of 536 mAh g⁻¹ and good cyclability with the capacity of above 500 mAh g⁻¹ at 50th cycle. Electrochemical impedance spectra (EIS) indicates that the carbon layer coated on SiO₂ particles can diminish interfacial impedance, which leads to its good electrochemical performance.     

Electrochemical properties of carbon-coated Si/B composite anode for lithium ion batteries

Carbon-coated Si and Si/B composite powders prepared by hydrocarbon gas (argon + 10 mol% propylene) pyrolysis were investigated as the anodes for lithium-ion batteries. Carbon-coated silicon anode demonstrated the first discharge and charge capacity as 1568 mAh g⁻¹ and 1242 mAh g⁻¹, respectively, with good capacity retention for 10 cycles. The capacity fading rate of carbon-coated Si/B composite anode decreased as the amounts of boron increased. In addition, the cycle life of carbon-coated Si/B/graphite composite anode has been significantly improved by using sodium carboxymethyl cellulose (NaCMC) and styrene butadiene rubber (SBR)/NaCMC mixture binders compared to the poly(vinylidene fluoride, PVdF) binder. A reversible capacity of about 550 mAh g⁻¹ has been achieved at 0.05 mAm g⁻¹ rate and its capacity could be maintained up to 450 mAh g⁻¹ at high rate of 0.2 mAm g⁻¹ even after 30 cycles. The improvement of the cycling performance is attributed to the lower interfacial resistance due to good electric contact between silicon particles and copper substrate.     

Improved electrochemical performance of modified natural graphite anode for lithium secondary batteries

Modified natural graphite is synthesized by surface coating and graphitizing process on the base of spherical natural graphite. The modified natural graphite is examined discharge capacity and coulombic efficiency for the initial charge–discharge cycle. Modification process results in marked improvement in electrochemical performance for a larger discharge capacity and better coulombic efficiency. The mechanism of the enhancement are investigated by means of X-ray powder diffraction, scan electron microscopy, and physical parameters examination. The proportion of rhombohedral crystal structure was reduced by the heat treatment process. The modified natural graphite exhibits 40 mAh g⁻¹ reduction in the first irreversible capacity while the reversible capacity increased by 16 mAh g⁻¹ in comparison with pristine graphite electrode. Also, it has an excellent capacity retention of ∼94% after 100 cycles and ∼87% after 300 cycles.     

Carbon-coated MoO3 nanobelts as anode materials for lithium-ion batteries

MoO₃ nanobelts are synthesized by a simple hydrothermal route followed by carbon coating. The effects of the carbon coating on the nanobelts are investigated by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS), a transmission electron microscope (TEM), and galvanostatic cycling. As observed from the TEM and SEM images, the C-MoO₃ nanobelts have a diameter of 150 nm and a length of 5-8 μm. In the electrochemical results, the C-MoO₃ nanobelts exhibit excellent cycling stability after being cycled at a current rate of 0.1 C, maintaining their capacity at 1064 mAh g⁻¹ after 50 cycles. These results are better than those for a bare MoO₃ nanobelt electrode. The excellent electrochemical performance of the C-MoO₃ nanobelts can be attributed to the effects of the carbon coating which stabilizes the structure of the MoO₃, enhances the ionic/electrical conductivity, and moreover, can serve as a buffering agent to absorb the volume expansion during the Li⁺ intercalation process.     

固态锂电池研发愿景和策略

很多新兴技术领域对可充放电池的能量密度不断提出新的期望和要求,已经远远超过目前电池实际达到的水平。尽早理解如何提高电池的能量密度, 如何兼顾其它综合技术指标的实现,尽早确定较为可行的技术路线,是目前学术界、产业界关心的重要问题。本文作者根据对目前液态锂离子电池和固态金属锂电池的科学与技术研发现状的理解,小结了固态锂电池目前仍需要解决的主要科学与技术问题,并提出了可能的解决方案。从规模制造的角度,比较了四种含有不同形式固体电解质材料电池的特点,预测了固态锂电池的技术路线和实现时间。最后列举了日本、美国、中国政府最近提出的未来可充放电池中长期发展技术目标,分析了固态锂电池实现这些技术指标的可能性并预测了时间节点。     

A review of international safety testing standards and regulations for lithium ion power batteries

研究了国内外具有代表性的动力锂电池安全性测试标准及规范,包括ISO 12405、IEC 62660、SAE J2464、SAE J2929、UL 2580、ECE R100-02、GB/T 31485、GB/T 31467.3和FreedomCAR。将安全性测试项目分为机械安全性、环境安全性和电气安全性3类,详细介绍了各试验项目在不同标准规范的具体参数,总结了我国国标与国外标准的异同,最后指出了现行标准规范中的不足,提出了改进意见。     

Fundamental scientific aspects of lithium ion batteries(Ⅺ)--Lithium air and lithium sulfur batteries

提高能量密度是可充放锂电池研发最重要的目标.近年来,锂硫电池与锂空气电池由于具有高的理论能量密度而受到广泛关注,这两种电池仍然面临较多的科学与技术问题,处于电池开发早期研究阶段.在本文中,重点介绍了锂空气电池的基本工作原理,基本结构组成,所面临的问题和两种特殊体系的锂空气电池, 同时简要介绍了锂硫电池.     

The improved discharge performance of Li/CFx batteries by using multi-walled carbon nanotubes as conductive additive

The discharge performance of Li/CF_x (x = 1) battery is improved by using multi-walled carbon nanotubes (MWCNTs) as an alternative conductive additive. Compared with the battery using acetylene black as conductive additive at the same amount, the Li/CF_x battery using MWCNTs as conductive additive has higher specific capacity and energy density as well as smoother voltage plateau, especially at higher discharge rate. The specific capacity at discharge rate of 1 C is improved by nearly 26% when MWCNTs are employed as conductive additive. Meanwhile, it is also found that the discharge performance is able to be tuned by the amount of MWCNTs and the battery containing more MWCNTs is favorable to be discharged at higher rates. The specific capacity of Li/CF_x battery with 11.09 wt.% MWCNTs is approximately 712 mAh g⁻¹ at the discharge rate of 1 C. It is proposed that the formed three-dimensional networks of MWCNTs in cathode, which enlarges the contact area of interphase and facilitates electrons delivery, accelerates the rates of lithium ion diffusion into the fluorinated layers and electrons transport in cathode at the same time, which improves the discharge performance of Li/CF_x battery subsequently, especially at higher rates.     

Polytriphenylamine: A high power and high capacity cathode material for rechargeable lithium batteries

Polytriphenylamine (PTPAn) was chemically synthesized and tested as a cathode material for high-rate storage and delivery of electrochemical energy. It is found that the polymer has not only superior high power capability but also high energy density at prolonged cycling. At a moderate rate of 0.5C, PTPAn gives a high average discharge voltage of 3.8 V and quite a high capacity of 103 mAh g⁻¹, which is very close to the theoretical capacity (109 mAh g⁻¹) as expected from one electron transfer per triphenylamine monomer. Even cycled at a very high rate of 20C, the polymer can still deliver a capacity of 90 mAh g⁻¹ at 1000th cycle with a nearly 100% coulombic efficiency. The excellent electrochemical performances of PTPAn are explained from the structural specificity of the polymer where the radical redox centers are stabilized and protected by conductive polymeric backbone, making the radical redox and charge-transporting processes kinetically facile for high-rate charge and discharge.     

Research progress on cathode materials for high energy density lithium ion batteries

便携式电子设备的微型化、轻量化与电动汽车、电网储能设备的飞速发展,对高能量密度的锂离子电池的研发和性能表现提出了越来越高的要求。锂离子电池正极材料是锂离子电池的核心,其提供锂离子并参与电化学反应,因此改善正极材料性能是提高锂离子电池能量密度的关键。人们需要进一步研究开发成本较低、安全性更好的高能量密度新型锂离子电池正极材料。本文主要从提升正极材料的比容量和工作电压两方面介绍三元、富锂锰基材料和高电位镍锰酸锂等高比能量正极材料的介尺度结构设计、制备与性能调控研发进展。     

Improving electrochemical properties and structural stability of lithium manganese silicates as cathode materials for lithium ion batteries via introducing lithium excess

The serious capacity decay caused by structural amorphization is still a major issue for polyanion-type lithium manganese silicates (Li₂MnSiO₄) as cathode material for lithium ion batteries. In this work, a new strategy for alleviating the structural instability via the introduction of excess lithium into the host crystal lattice is provided. A comprehensive study demonstrates that the required energy for the extraction/insertion of lithium ions into host crystal lattice was decreased as a result of changed local environment of cations in the compound after the excess lithium occupancy in lattice. Importantly, it was found that Li-rich samples deliver higher reversible capacity and increased average potential than pristine sample, indicating the improved energy density of polyanion-type Li_{2 + 2x}Mn_{1 − x}SiO₄/C_. Additionally, the structure of Li2.2 sample was kept intact, while the Li2.0 sample was transformed to amorphous state at 200 mA h g⁻¹ during the initial charging process by controlling the charge cut-off potential. As expected, the introduction of a certain amount of excess lithium into Li₂MnSiO₄ is explored as a route to achieving increased capacity with more movable lithium, while maintaining its structural stability and cyclic stability.     

Progress on high energy density lithium batteries by CAS battery research group

提高动力电池的能量密度将显著延长续航里程,对发展电动汽车具有重要的意义.中国科学院在2013年底部署了中国科学院战略性先导科技专项,通过合作研究,积极探索了第三代锂离子电池,固态锂电池,锂-硫电池和锂-空气电池等电池体系.其中,采用纳米硅碳负极,富锂正极的24 A·h的锂离子电池单体,质量能量密度达到374 W·h/kg,体积能量密度达到577 W·h/L.8 A·h固态聚合物锂电池60 ℃下能量密度达到240 W·h/kg,基于无机陶瓷固态电解质的固态锂电池室温下能量密度达到240 W·h/kg.37 A·h的锂硫电池单体室温能量密度达到566 W·h/kg,50 ℃达到616 W·h/kg.5 A·h锂空气电池单体能量密度达到526 W·h/kg.目前这些样品电池在综合技术指标方面离实际应用还有较大的距离,需要进一步深入细致的进行基础科学与关键技术方面的研究.从长远考虑,电池能量密度的提高必然进一步增加电池安全性风险,因此不同形式的固态锂电池将是未来长续航动力锂电池的发展方向.     

Polysulfide rubber-based sulfur-rich composites as cathode material for high energy lithium/sulfur batteries

Novel sulfur-rich polymer composites were prepared from the commercial polysulfide rubber through facile vulcanization methods and were firstly used as cathode material for lithium/sulfur batteries. The sulfur enriched in the composites includes three parts, the first part was inserted into the main chains of the polysulfide rubber, the second part formed insoluble polysulfide (-S_n-)through self-polymerization and the third part was trapped inside the network of the above two polymer chains. The obtained sulfur-rich polymer composites have high sulfur content over 80%. Compared with the pure sulfur electrode, the composites showed better cycle stability and coulomb efficiency.     

Experimental measurement and analysis methods of cyclic voltammetry for lithium batteries

循环伏安作为一种重要的电化学测试方法,在电化学领域尤其是锂电池的研究中有着广泛的应用,常用于电极反应可逆性、电极反应机理及电极反应动力学参数的研究。本文介绍了循环伏安的基本原理、测试方法以及常用仪器,并结合实际案例,具体分析了循环伏安在锂电池电极材料反应机理、电极过程动力学以及电解液电化学稳定性方面的应用研究。     

New electrolytes based on glutaronitrile for high energy/power Li-ion batteries

Glutaronitrile, CN[CH₂]₃CN, is evaluated as a co-solvent in thermally and (anodically) electrochemically stable electrolyte mixtures suitable for high energy/power Li-ion batteries. Linear sweep voltammetry scans indicate an electrochemical anodic stability of more than 6 V versus Li⁺/Li for the 1 M LiTFSI electrolytes. Glutaronitrile and its ethylene carbonate electrolyte solutions show high ionic conductivities and low viscosities reaching 5 mS cm⁻¹ and 7 cP, respectively, at 20 °C. Aluminum corrosion tests of the solutions showed an improved protective resistance up to 4.4 V. Lithium ion batteries incorporating graphite as an anode and LiCoO₂ as the cathode material were assembled using a glutaronitrile electrolyte mixture, whose stability on graphite was greatly enhanced by the use of ethylene carbonate as a co-solvent and Li (bioxalatoborate) (LiBOB) as a co-salt, and these cells showed moderately good discharge capacities with low capacity fade up to the 100th cycle.     

Effect of carbon coating on thermal stability of natural graphite spheres used as anode materials in lithium-ion batteries

To investigate the effect of non-graphitic carbon coatings on the thermal stability of spherical natural graphite at elevated temperature, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements are performed. Data from DSC studies show that the thermal stability of the surface modified natural graphite electrode is improved. The surface modification results in a decrease in the BET surface specific area. An improvement in coulombic efficiency and a reduction in irreversible capacity are also observed for the carbon-coated natural graphite. X-ray diffraction analysis confirms that carbon coating alleviates the release of intercalated lithium from natural graphite at an elevated temperature and acts as a protective layer against electrolyte attack.     

Research progress in blending modification cathode materials for lithium ion batteries

本文简述了国内外锂离子电池正极材料共混改性的研究进展。正极材料是锂离子电池重要组成部分，是决定锂离子电池能量密度和成本的关键因素。共混改性具有制备工艺简单、材料性能一致性容易控制、综合成本较低等优点，在钴酸锂、锰酸锂、磷酸铁锂和三元材料电池制造中得到应用。国内外通过对正极材料共混改性机理研究，发现共混改性是材料改善电化学性能、降低成本、提升安全性能的有效途径，并有望发展成为依据材料特性指导锂离子电池高性能电极设计的重要方法。同时在正极材料共混改性方面亟需加强共混材料物性匹配、充放电机制选取、共混工艺研究，该方法也为高镍、富锂锰基等新一代正极材料工业化应用提供了工艺参考。