Graphene nanosheets for enhanced lithium storage in lithium ion batteries

Graphene nanosheets were synthesized in large quantities using a chemical approach. Field emission electron microscope observation revealed that loose graphene nanosheets agglomerated and crumpled naturally into shapes resembling flower-petals. High resolution transmission electron microscope analysis, Raman spectroscopy and ultraviolet-visible spectroscopy measurements confirmed the graphitic crystalline structure of the graphene nanosheets. The nanosheets exhibited an enhanced lithium storage capacity as anodes in lithium-ion cells and good cyclic performance.     

Three-dimensional lithium manganese phosphate microflowers for lithium-ion battery applications

The Polyvinylpyrrolidone (PVP)-assisted polyol process was employed for the synthesis of lithium manganese phosphate (LiMnPO₄) microflowers as a cathode material for Li-ion battery applications. LiMnPO₄ microflowers were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope-energy dispersion spectroscope, and impedance spectroscopy. The microflowers were highly porous with nanosized petals. CR2032 coin cells were fabricated using LiMnPO₄ microflowers’ sample and their battery characteristics were tested. The discharge capacity of LiMnPO₄ microflowers was found to be 164 mAh g⁻¹ at 0.1C. The observed high discharge capacity was attributed to the short diffusion length of Li-ion motion in the nanopetals of the LiMnPO₄ microflowers.     

锂离子电池电解质六氟磷酸锂市场分析

通过对未来5 a锂离子电池在动力电池、储能电池、数码电池市场的发展情况分析,预测锂离子电池生产的平均增长率将达到26%以上,到2025年对应锂离子电池电解液的需求量和六氟磷酸锂需求量将分别达到93.0万t和10.3万t。分析目前六氟磷酸锂产能情况和后期各生产企业扩产计划,预测六氟磷酸锂产能在2022年以前满足市场需求;若2025年以前各生产企业扩产到位,供需将会达到平衡,并且六氟磷酸锂价格趋于平稳,在原材料价格波动不大的情况下预计其价格在8.5万元/t左右。     

锂离子电池正极材料层状LiMnO2的研究进展

层状LiMnO₂是高能量密度锂离子电池关键正极材料之一,是当前的研究热点。本文比较系统地综述了目前LiMnO₂材料的国内外最新研究现状,对近期的材料制备方法和掺杂改性、表面包覆改性研究的进展情况进行了详细的分析。在已有初步实验基础上提出了将液相共沉淀与高温固相法相结合制备纳米级LiMnO₂以及阴阳离子共掺杂结合熔融浸渍包覆方法提高LiMnO₂循环性能等合成及改性方法,以提高结构稳定性及循环寿命。     

Graphene nanosheets production using liquid-phase exfoliation of pre-milled graphite in dimethylformamide and structural defects evaluation

The non-oxidation-based procedure is proposed for the production of high-quality graphene nanosheets using graphite as the raw materials. This research demonstrated a hybrid two-step production method by liquid-phase exfoliation (LPE) of Premilled graphite in Dimethylformamide (DMF) and compared it with the purely milled and just sonicated samples. However, a simple physical separation procedure composed of two centrifuge processes also designed for the separation of the products in each step. By this process, the exfoliated graphite, less-exfoliated ones and produced nanoparticles are separated, and the less-exfoliated ones are reused again in moderate sonication process. Two grades of graphene nanosheets and a grade of graphitic nanoparticles result at the end. The quality and the nature of defects in all graphene samples produced from LPE, wet milling of graphite and a combination of both, was investigated and discussed by Raman spectroscopy related indices. Raman spectra analysis indicates the adverse effect of sonication power on the in-plane defects formation in the graphene nanosheets which could be hindered by the reduction in power of sonication along with the pre-milling of the graphite. Also inductively-coupled plasma (ICP) and field emission scanning electron microscopy (FE-SEM) analysis used for further characterization of the milled-sonicated sample.     

锂离子电池负极材料钛酸锂的制备与研究

以四氯化钛、氢氧化锂为原料,采用模板法,获得前躯体（Li1.81H0.19）Ti2O5·0.262 5TiO2,再通过煅烧,得到纳米钛酸锂（Li4Ti5O12）。最佳制备工艺条件为：模板∶钛（摩尔比）为4∶1,700℃煅烧1 h。采用TEM电镜观测的粒度达到10~100 nm,XRD拟合粒径5~30 nm,比表面积达100~600 m2/g。     

Graphene oxides doped MIL-101(Cr) as anode materials for enhanced electrochemistry performance of lithium ion battery

MIL-101(Cr)/graphene oxides composites has been successfully synthesized via a facile route using a solvothermal treatment and fully characterized using powder X-ray diffraction (PXRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and infrared spectroscopy (IR). The specific capacity of MIL-101(Cr)/GO are almost twice larger than that of MIL-101(Cr) at the first discharge process and the multiple relationship maintained over 40 cycles, indicating that the electrochemical performance of MIL-101(Cr) as anode material has been improved through doping by GO.     

Graphene nanosheets as cathode catalysts for lithium-air batteries with an enhanced electrochemical performance

Graphene nanosheets have been investigated as cathode catalysts for lithium-air batteries with alkyl carbonate electrolyte. Field emission scanning electron microscopy, transmission electron microscope and Raman spectroscopy have confirmed the high quality of the as-prepared graphene nanosheets and the surface analysis has identified the mesoporous characteristic of graphene nanosheets. The electrochemical properties of graphene nanosheets as cathode catalysts in lithium-air batteries were evaluated by a galvanostatic charge/discharge testing. The reaction products on the graphene nanosheets cathode were analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. The graphene nanosheet electrodes exhibited a much better cycling stability and lower overpotential than that of the Vulcan XC-72 carbon. This work demonstrated that graphene nanosheets could be an efficient catalyst for lithium-air batteries.     

一种用于磷酸铁锂电极的水性黏结剂制备与性能研究

磷酸铁锂作为锂离子电池正极材料应用广泛。目前在其电极制备中仍采用PVDF油系黏结剂体系,可用于该电极的水性黏结剂仍需进一步研究。通过反应型乳化剂共聚苯乙烯（St）与丙烯酸异辛酯（2-EHA）制备了不同结构的磷酸铁锂正极水系黏结剂PSEHA,探讨了黏结剂对电池性能的影响。PSEHA黏结剂不含不饱和双键,抗氧化性好,较低的溶胀率可以有效防止过度溶胀导致的结构破坏,而反应型乳化剂可以解决乳化剂残留问题。采用所得最优结构黏结剂制备的磷酸铁锂电极表现出优异的电化学稳定性,扣式电池1 C循环100圈后容量保留率仍有96%,而SBR仅有93.9%;软包全电池在1 C倍率下循环170圈后容量保留率仍有98.9%。该新型水性黏结剂对促进磷酸铁锂水性体系制备有重要意义。     

The influence of the local current density on the electrochemical exfoliation of graphite in lithium-ion battery negative electrodes

The local current density related to the exfoliation process of graphite negative electrodes in mixed ethylene carbonate/propylene carbonate electrolytes was controlled by a variation of the current applied to lithium half-cells containing either single type graphite electrodes or electrodes consisting of mixtures of an exfoliating and a non-exfoliating graphite. The partial local current density attributed to graphite passivation and its distribution within the volume of the electrode was found to be a key parameter to explain differences in the exfoliation behaviour observed for graphite electrodes. The local current density is related with a local overpotential which may suppress one of several possible electrochemical processes. In a negative electrode consisting of a mixture of a non-exfoliating and an exfoliating graphite component, the exfoliation of the exfoliation-sensitive graphite component can be completely suppressed when increasing the partial local current density attributed to the graphite exfoliation process above a certain threshold, by either decreasing the amount of exfoliating graphite particles in the electrode or by increasing the total current density, i.e., the specific current. The consideration of the local current density distribution for the electrochemical processes throughout the electrode leads to a more general concept for the graphite passivation behaviour during the first lithium insertion in lithium-ion batteries.     

PVDF porous matrix with controlled microstructure prepared by TIPS process as polymer electrolyte for lithium ion battery

Poly(vinylidene fluoride) (PVDF) microporous matrix of polymer electrolyte for lithium ion battery was prepared via the thermally induced phase separation (TIPS) process using diluent mixture of dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP). Since this method has only one parameter, namely the DBP/DEHP ratio in diluent mixture, the membrane microstructure is easily and conveniently controlled. With the assistance of a pseudo-binary temperature-DBP ratio phase diagram of the PVDF-diluent mixture system, the membrane formation mechanism for different microstructures of membranes was proposed. In addition to studying the different microstructures available in TIPS process, the relationship between performance of membrane, electrochemical property of polymer electrolyte and final microstructure has been investigated in this paper.     

Graphene/nanosized silicon composites for lithium battery anodes with improved cycling stability

Graphene/nanosized silicon composites were prepared and used for lithium battery anodes. Two types of graphene samples were used and their composites with nanosized silicon were prepared in different ways. In the first method, graphene oxide (GO) and nanosized silicon particles were homogeneously mixed in aqueous solution and then the dry samples were annealed at 500 °C to give thermally reduced GO and nanosized silicon composites. In the second method, the graphene sample was prepared by fast heat treatment of expandable graphite at 1050 °C and the graphene/nanosized silicon composites were then prepared by mechanical blending. In both cases, homogeneous composites were formed and the presence of graphene in the composites has been proved to effectively enhance the cycling stability of silicon anode in the lithium-ion batteries. The significant enhancement on cycling stability could be ascribed to the high conductivity of the graphene materials and absorption of volume changes of silicon by graphene sheets during the lithiation/delithiation process. In particular, the composites using thermally expanded graphite exhibited not only more excellent cycling performance, but also higher specific capacity of 2753 mAh/g because the graphene sheets prepared by this method have fewer structural defects than thermally reduced GO.     

Bamboo-like amorphous carbon nanotubes clad in ultrathin nickel oxide nanosheets for lithium-ion battery electrodes with long cycle life

In this work, we report the synthesis of one-dimensional (1-D) hierarchical NiO nanosheets covering bamboo-like amorphous CNT composites (NiO@CNT) via a facile and a low-cost solution route based on sulfonated polymeric nanotubes (PNTs) used simultaneously as both, a template, and a source of nano-structured carbon derived by a low-temperature thermal carbonization treatment. The electrochemical performance of the NiO@CNT composite electrode indicate that this novel hybrid nanostructure is potentially capable of delivering excellent reversible capacity when used as an anode material in a lithium-ion battery (LIB). A large discharge capacity of 1034 mAh g⁻¹ is delivered by the NiO@CNT composite even after 300 cycles at a relatively high current density of 800 mA g⁻¹, with an average coulombic efficiency of 98.1%. A significant achievement in the reversible capacity of the NiO@CNT composite is attributed to the outstanding nanostructure resulting in synergistic effects of the hollow amorphous CNT backbone and ultrathin NiO nanosheets. Furthermore, the generic solution method to fabricate 1-D metal oxides@amorphous CNT nanostructures, developed in this work, is expected to have a wide range of applications in improving the properties of transition metal oxides.     

High performance binder-free reduced graphene oxide nanosheets/Cu foam anode for lithium ion battery

Binder-free combination of reduced graphene oxide with Cu foam (RGO/Cu foam) anode for lithium ion battery was designed and achieved via one-step facile electro-reduction. The as-prepared composite RGO/Cu foam anode were studied in terms of scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR), Raman, galvanostatic charge/discharge, cyclic voltammogram and AC impedance. As expected, graphene oxide nanosheets were indeed successfully electro-reduced to large degree and tightly combined with Cu foam without any additional polymer binder. Moreover, the integrated RGO/Cu foam electrode delivered high reversible capacity of 1196.2 mAh/g at 0.25 A/g, indicating satisfactory electrochemical performances. High Li-storage activity, large surface area, high conductivity of RGO nanosheets and the binder-free combination with porous Cu foam should be jointly responsible for high electrochemical performances.     

Fish-scale-like nano-porous membrane based on zeolite nanosheets for long stable zinc-based flow battery

Zinc-based flow batteries receive widespread attention due to their advantages of low cost and high energy density. However, zinc dendrites are easy to appear during the charge process, pierce the membrane and thus destroy the battery, which seriously restrict its further development. In this article, MFI-type zeolite nanosheets (ns-MFIs) with high mechanical strength and hydrophobicity are in situ introduced to porous polymer membranes, which spontaneously form turnup fish-scale-like structure through the one-step phase inversion/surface segregation process. This special structure well disperses mechanical energy to provide effective protection characteristics to resist the penetration of zinc dendrites, and meanwhile promotes the uniform zinc depositions on the electrode by alleviating the water migration and accelerating zincate ion diffusion, so as to prolong the cycle life of the battery for more than 600 cycles, which is 4 times and 2.5 times longer than the commercial Nafion 212 and pristine porous polymer membrane, respectively. Moreover, the sub-nano size pores and high-aspect-ratio of ns-MFIs afford membranes extra ion sieving ability and transport area for the charging-balancing ions OH⁻ to ensure superior battery performance, delivering an average coulombic efficiency (CE) of ~98.5%, voltage efficiency (VE) of ~83.2%, and energy efficiency (EE) of ~81.9% at 80 mA/cm².     

Phase-engineering strategy of MoS2 nanosheets embedded in Bronze-TiO2 nanobelts for boosting lithium storage

Regulating the molybdenum disulfide (MoS₂) anodes with controllable phase and structure shows promising application for advanced lithium-ion storage performance. Herein, phase- and structure-regulated 1T@2H MoS₂ nanosheet @TiO₂–B nanobelts are synthesized via a facile hydrothermal and ammoniation strategy. The stable 1T@2H MoS₂ is revealed by the formation of N–Mo covalent bonds via subtle structural analysis, including XPS, Raman and TEM analysis. TiO₂ nanobelts serve as the backbone for MoS₂ nanosheets to form highly active edged nanostructure. As a proof-of-concept study, this well-devised 1T@2H MoS₂@TiO₂–B electrode delivers much higher capacities of 830 mA h g^?1 at 100 mA g^?1 after 200 cycles. Even at a large rate of 2000 mA g^?1, the reversible capacity was still maintained at 530 mA h g^?1 after 1000 cycles. In addition, the EIS, GITT and pseudocapacitance analyses further demonstrate the introduced 1T MoS₂ not only boost the lithium-ion diffusion coefficient, but also modify the electrochemical kinetics of the composite anodes. This concept of phase engineering strategy will open opportunities for advanced energy storage applications and beyond.     

基于正交层次法的锂离子电池热管散热模组数值模拟分析

设计了锂离子电池热管-铝板嵌合式散热模组,增大热管与电池接触面积,强化换热。利用数值模拟和正交试验层次分析研究了影响模组散热性能各因素的具体影响权重,进行参数优选。结果表明:各试验方案下电池模组的温差均控制在3℃以内,均温性能优异;各因素对最高温度的影响程度依次为:热管冷凝段对流传热系数>热管冷凝段长度>铝板厚度>热管间距;结合层次分析确定最佳参数组合为热管冷凝段对流传热系数25 W·m^-2·K^-1、热管长度117 mm、铝板厚度2 mm、热管间距20 mm,该方案下电池以2C倍率放电至20%模组的最高温度为41.60℃,温差为1.35℃,满足散热要求。     

锂离子电池大电流放电过程模拟研究

随着锂离子电池的广泛应用,电池以更大功率、更高倍率运行的需求日益迫切,探索锂离子电池大电流运行时的电-热行为及内部关键参数演化十分必要。建立了锂离子电池的电化学-热(ECT)模型和电池材料的热滥用模型,模拟了方形单层LiCoO₂/C电芯在不同放电电流下的电-热行为,对比分析了电池分别以1C和14C倍率放电时电池内部关键电化学参数的演化过程。结果表明:随着放电电流增加,电池内部积聚的热量会引发材料的放热反应,有引发电池热失控的可能性;大电流放电过程电解液中锂离子浓度、输运电流密度、过电势、电解质电势和固相颗粒表面的锂离子浓度波动较大,在电池内部相关区域形成了明显的浓度差、密度差和电势差。     

基于相变材料的锂离子电池热管理性能

锂离子电池（lithium-ion battery,LIB）作为目前应用最广泛的储能电池之一,在电动汽车等行业发挥着至关重要的作用。电池的温度是影响LIB性能及安全性的重要因素,因此电池热管理（battery thermal management,BTM）至关重要。目前,利用相变材料（phase change material,PCM）进行相变冷却的热管理方式因其潜热高、不需消耗额外能量的优点已成为一种很有前途的方法。本文针对8节并联18650LIB的电池组性能进行了数值模拟及实验研究,探究了石蜡基复合相变材料（composite phase change material,CPCM）物性参数（包括热导率、熔点、相变潜热和材料厚度）对本文设计的电池组热管理性能的影响。结果表明,纯石蜡用于BTM可将3C放电下的电池最高温度降低28.0%,向石蜡中添加膨胀石墨后可使CPCM的热管理性能进一步提升,CPCM的热导率为2.0W/(m·K)时可将3C放电下的电池最高温度进一步降低5.42℃,继续增大CPCM热导率对热管理性能的提升较小。在综合考虑电池组的最高温度和温度均匀性的情况下,为得到在本文所设计的锂离子电池组最佳热管理性能,CPCM的热导率为2.0W/(m·K)、熔点应在36~38℃之间、相变潜热在212J/g左右、CPCM的厚度为4mm时最优。