硬碳包覆人造石墨作为锂离子电池负极材料的快充性能评价CSCD

电动汽车及混合动力汽车的发展对锂离子电池的功率特性提出了更高的要求.目前商业化的锂离子电池负极材料以石墨为主.然而石墨材料的层间距较小(0.335 nm),锂的扩散受到限制,不利于大电流充电.因此,制备和评价具有快充能力的石墨负极材料将有力推动锂离子电池在电动汽车中的应用.本文选择了一种小粒径(约6.7 μm)人造石墨,通过包覆硬碳进一步提高材料的快充性能.采用SEM、BET等表征材料的物理指标.考察材料首次充放电曲线、倍率、电化学阻抗和锂离子扩散系数等,评价硬碳包覆对快充性能的影响.     

新型锂盐氟代磺酰亚胺锂电解液对锂离子电池性能的影响CSCD

采用新型锂盐双(氟代磺酰)亚胺锂(Li FSI)代替六氟磷酸锂(Li PF_6)作为锂离子电池的电解液锂盐,配制不同浓度的Li FSI/EC+EMC+DMC(质量比1∶1∶1)电解液,用循环伏安、电化学阻抗(EIS)、恒流充放电等实验并结合Li^+迁移数、电导率和黏度等物化参数的测试,研究新型锂盐浓度和电解液物化参数对电池倍率性能的影响。结果表明与同浓度的Li PF_6电解液相比,Li FSI电解液具有更高的离子传导能力和电导率及锂离子迁移数;在0.8~1.6 mol/L的浓度范围内,含Li FSI电解液的电池相对含Li PF_6电解液的电池表现出更好的电化学性能,更适用于高性能锂离子电池;1.2 mol/L为Li FSI电解液的最优浓度,此时其电导率和锂离子迁移数均达到最大值(κ=12.39 ms/cm,t_+=0.6327),制备的锂离子电池电化学阻抗最小,倍率性能最佳。     

硬碳的预锂化及其电化学性能

以钛酸锂@活性炭复合材料作为正极,以商业化硬碳为负极同时将其与锂粉进行不同比例的复合,然后制备得到了预嵌锂硬碳//钛酸锂@活性炭锂离子电容器(LIC).本工作通过对硬碳与锂粉进行不同比例的复合制备得到了多种预嵌锂硬碳极片,然后,通过对所制备得到的预嵌锂硬碳极片组装的LIC进行了一系列电化学性能测试,研究了硬碳极片的嵌锂量对LIC比能量和比功率的影响.结果表明:将硬碳与锂粉进行复合可以在不明显减小LIC比功率的同时,大幅提升LIC的比能量,其中当硬碳与锂粉的质量比为3:1时所组装的LIC其能量密度最大可以达到29.69 W·h/kg,功率密度最大可以达到7.57 kW/kg,在电流密度为2 A/g时充放电循环2000次后容量保持率能够达到83.11％.     

三维石墨烯包封石墨的储锂性能研究

石墨由于价格低廉、电压平台稳定以及质量比容量高[372 (mA·h)/g]等优势,在锂离子电池领域已被广泛应用,但其存在振实密度较低和循环稳定性较差等不足。利用石墨和氧化石墨烯进行水热反应获得水凝胶,通过石墨烯的毛细收缩和静电自组装原理,获得具有致密结构的石墨烯包封石墨复合块体(石墨@石墨烯),使粉末石墨的振实密度从1.2 g/cm³提高到1.7 g/cm³。与石墨相比,石墨烯构筑的致密三维导电网络结构具有更优异的电化学循环稳定性和倍率性能。在0.01～2.00 V测试电压区间,石墨在0.5 A/g倍率下,经过100圈循环后放电比容量仅保持在227.4 (mA·h)/g,容量保持率仅为64.1%;而石墨@石墨烯复合材料的容量保持在353.9 (mA·h)/g,维持了98%的高容量保持率。证明石墨烯包封石墨可以有效提高石墨的振实密度以及长循环稳定性。     

基于三维电化学热耦合析锂模型的锂离子电池参数设计

锂离子电池负极析锂可能会诱发热失控,进而导致安全事故。而通过优化电池设计参数能够有效减少析锂副反应的发生,因此本工作提出一种基于三维电化学热耦合析锂模型的锂离子电池参数设计优化方法。首先,将模型参数进行分类,分别采用实验、精确测量、文献查找和参数辨识等方法获取相应的参数。同时加入可逆锂重嵌入机制和产热模型,建立三维电化学热耦合析锂模型。模型建立完成后,对模型精度进行验证,验证结果表明模型可以较好地模拟电池在常温和低温下端电压的变化,并且能够定量描述在低温大倍率充电期间电池内部的析锂程度、温度分布等非均一现象。最后,通过分析电极尺寸和极耳位置,研究电池设计参数对非均一析锂的影响。仿真结果表明：电极长度增加会导致电极区域温度差异和电流密度的不一致性增大,综合影响下使电池析锂时间略有提前,但对电池总体析锂程度影响较小;电池极耳位置处于长度方向的轴线对侧时能够有效缓解负极析锂,相对析锂程度降低了16.7%。     

硫系电解液添加剂对镍钴锰酸锂//石墨锂离子电池性能的影响北大核心CSCD

本工作系统研究了6种添加剂[碳酸亚乙烯酯(VC)、亚硫酸乙烯酯(ES)、硫酸乙烯酯(DTD)、1,3-丙二醇环硫酸酯(PCS)、1,3-丙烷磺酸内酯(PS)、1,3-丙烯磺酸内酯(PST)]对镍钴锰酸锂(NCM111)//石墨体系锂离子电池电化学性能的影响,通过对比首次充放电效率、放电容量、倍率特性、低温放电能力、高温存储性能以及循环寿命等发现:VC在各方面性能比较均衡,碳碳双键(C=C)能够改善成膜特性,循环性能优异,可独立使用;ES在化成、循环和存储过程中因电解液持续分解而胀气,无法单独使用;硫酸酯添加剂(DTD和PCS)能够明显降低阻抗并提升低温性能,但高温性能稍差;磺酸内酯添加剂(PS和PST)对抑制高温胀气效果突出,含有双功能基团的PST循环性能及抑制电压衰减的能力优于PS,但低温阻抗较高。综合对比发现,单组分硫系添加剂在某些性能方面有自己的特色,但也存在显而易见的缺陷,无法独立使用。通过与VC进行等比例复配,硫系添加剂循环性能差的问题得以解决,而高首效、低内阻、大倍率和高温稳定性等特色功能得以保持,二元联用后的综合性能显著优于单组分添加剂,采用添加剂联用方式来改善电池综合性能是较佳选择。     

锂离子电池析锂及析锂回嵌行为的三电极分析

利用三电极电池研究了锂离子电池在不同条件下的析锂行为,并通过X射线衍射(XRD)及原子吸收(AAS)进行了相应的材料表征.结果表明,当锂离子电池在充电过程发生析锂时,其负极对参比的电势曲线在接近0V左右会出现析锂电势平台,在接下来的放电过程中同样在0V附近出现析锂回嵌的电势平台.因此充放电过程中在0 V新出现的平台可以...     

基于外特性方法的锂离子电池析锂及可逆锂回嵌定量分析北大核心CSCD

锂离子电池因其高能量密度、高循环寿命等优势被广泛应用,然而由析锂导致的电池可用锂离子损失,会降低电池自产热温度,严重影响锂离子电池的寿命与安全,锂回嵌可部分缓解析锂对电池的影响。本文基于锂离子电池低温运行实验数据,分别采用差分电压法(DVA)、开路电压法(VRP)和DVA-VRP联合法对电池的析锂及可逆锂回嵌进行定量分析,并结合电化学模型对析锂量计算结果进行了验证。研究发现,DVA特征值随着电池的老化向容量减少方向移动,VRP的特征电压平台向时间减少的方向移动,且这两种方法的析锂特征值呈线性关系,拟合直线随搁置时间的增加向原点平移。VRP结合仿真可准确预测可逆锂,缺点是耗时较长;DVA法在电池运行初期对可逆锂的预测与VRP-仿真法相差不大,但随着电池的老化,预测误差逐步增大。DVA-VRP联合法在保留VRP准确度的前提下,弥补了DVA和VRP误差大、时间成本高的不足,可在较短时间内实现对电池可逆锂的初步预测,为锂离子电池的安全评估提供了重要参考。     

使用工况对锂离子电池电化学性能的影响

[目的]锂离子电池储能技术在近年来得到快速发展和广泛应用,但在实际应用中发现具体使用工况对锂离子电池储能的实际使用寿命和盈利能力有着巨大影响,文章旨在研究使用工况对于锂离子电池电化学性能的影响,为今后的锂离子电池储能项目建设提供参考。[方法]测试并分析工作荷电区间、放电倍率、工作温度对锂离子电池实际工作性能的影响。[结果]充放电荷电区间、使用倍率、工作温度都会对锂离子电池的实际工作性能产生巨大影响。一方面,适当调节充放电荷电区间会明显提高电池的使用寿命;另一方面,目前调频储能项目常用的2 C配置方式会明显降低锂离子电池的使用寿命,而将倍率降低至1 C配置虽然会增加初始投资,但有望获得更低的周期度电成本。此外,温度控制对锂离子电池的使用寿命也极为重要,即使是个位数的温度差异也有可能造成长期使用后显著的电池不一致性。[结论]锂离子电池储能具有响应速度快、调节精度高、配置灵活等优点,随着“碳达峰、碳中和”工作的深入和电力市场的逐步建设,锂离子电池储能将会在提高电能质量方面发挥重要作用。注重使用工况对于锂离子电池性能的影响将会进一步提高锂离子电池储能的使用效能。要根据实际应用需求实际设计电池的...     

动力锂离子电池正极材料磷酸铁锂的研究进展

磷酸铁锂具有价廉、环保、热稳定性好等优点,是理想的锂离子动力电池正极材料之一,因此受到行业的广泛关注。本文阐述了磷酸铁锂的结构和性能特点,介绍了磷酸铁锂的制备方法和研究新进展,基于目前研究现状讨论了存在的问题。     

Effect of annealing on the electrochemical properties of ramsdellite-type lithium titanium oxide

Lithium titanium oxide (LTO) with a ramsdellite structure is an advantageous anode for lithium ion secondary batteries, because of its positive potential, which is beneficial for safety reasons. In addition, compared with other titanate anodes, it has a superior theoretical capacity of 321 mA h g⁻¹, which is close to the capacity of a practical carbonaceous anode. Our study showed that this ramsdellite-type LTO had a high discharge capacity that is stable at 250 mA h g⁻¹ at a current density of 1 mA cm⁻². However, this high capacity is only achieved by employing as-synthesized ramsdellite LTO powder. When the same powder was stored and the same evaluation was carried out, the resulting capacity was 200 mA h g⁻¹, which is lower than the capacity of as-synthesized powder. An annealing applied to the ramsdellite LTO powder appeared to restore the capacity loss after storage. Annealing at 250 °C for 5 h produced the best performance, which was even better than that obtained using the as-synthesized ramsdellite LTO powder. Moreover, we investigated the surface property of ramsdellite LTO and found that the presence of a carbon derivative is apparently responsible for blocking the Li ions insertion/extraction, and thus reducing the capacity.     

Effect of covalently bonded polysiloxane multilayers on the electrochemical behavior of graphite electrode in lithium ion batteries

Polysiloxane multilayers were covalently bonded to the surface of natural graphite particles via diazonium chemistry and silylation reaction. The as-prepared graphite exhibited excellent discharge–charge behavior as negative electrode materials in lithium ion batteries. The improvement in the electrochemical performance of the graphite electrodes was attributed to the formation of a stable and flexible passive film on their surfaces. It was also revealed that the chemical compositions of the multilayers exerted influence on the electrochemical behavior of the graphite electrodes. The result of this study presents a new strategy to the formation of elastic and strong passive film on the graphite electrode via molecular design. Owing to the diversity of polysilxoane multilayers, this method also enables researchers to control the surface chemistries of carbonaceous materials with flexibility.     

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.     

Studies of electrochemical properties of lithium cobalt oxide

The electrochemical characteristics of high-temperature (HT) LiCoO₂ (900 °C) and low-temperature (LT) LiCoO₂ (450 °C) were studied. From cyclic voltammetry results, lithium intercalating into LT-LiCoO₂ generates two current peaks at 3.8 and 3.3 V, respectively, which is contrast to the intercalation of lithium into HT-LiCoO₂. The resistance of lithium extraction is smaller than that of lithium insertion. The diffusion coefficients of Li⁺ ions in LiCoO₂ have an order of 10⁹⁻ cm²/s.     

Effect of particle size on lithium intercalation rates in natural graphite

The intercalation rate of Li⁺-ions in flake natural graphite with particle size that ranged from 2 to 40 μm was investigated. The amount of Li⁺-ions that intercalate at different rates was determined from measurement of the reversible capacity during deintercalation in 1 M LiClO₄/1:1 (volume ratio) ethylene carbonate–dimethyl carbonate. The key issues in this study are the role of particle size and fraction of edge sites on the rate of intercalation and deintercalation of Li⁺-ions. At low specific current (15.5 mA/g carbon), the composition of lithiated graphite approaches the theoretical value, x=1 in Li_xC₆, except for the natural graphite with the largest particle size. However, x decreases with an increase in specific current for all particle sizes. This trend suggests that slow solid-state diffusion of Li⁺-ions limits the intercalation capacity in graphite. The flake natural graphite with a particle size of 12 μm may provide the optimum combination of reversible capacity and irreversible capacity loss in the electrolyte and discharge rates used in this study.     

Preparation and electrochemical properties of double-metal nitrides containing lithium

A study is reported of the preparation, chemical composition, and crystal structure of binary compounds of Li₃N with other nitrides, i.e., Mg₃N₂, AlN, BN, and Si₃N₄. Most of the crystal structures are related to an antifluorite system. Except for LiMgN, the compounds are pure lithium ion conductors. A new compound, Li₈SiN₄, has the highest lithium ion conductivity (viz., 1 × 10⁻³ S m⁻¹ at 298 K) of the double-metal nitrides investigated.     

Structural, magnetic and electrochemical properties of lithium iron orthosilicate

We report the structural and electronic characterization of Li₂FeSiO₄ synthesized by solid-state reaction. X-ray diffraction, Raman scattering, Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and magnetization measurements are analyzed. Magnetic susceptibility experiments give evidence that Li₂FeSiO₄ powders possess an antiferromagnetic ordering below T_N = 25 K due to long range Fe–O–Li–O–Fe interactions. Analysis of the paramagnetic region giving the Curie–Weiss parameters θ_p = −93.5 K and C_p = 4.13 emu K mol⁻¹ shows the divalent state of Fe cations. Electron paramagnetic resonance experiments confirm this electronic configuration. Electrochemical measurements were carried out in lithium cells with LiTFSI in a poly(ethylene oxide) (PEO) polymer electrolyte at 80 °C. The resulting cyclic voltammogram indicates a stable structure for the first cycle with redox peaks at 2.80 and 2.74 V versus Li⁰/Li⁺.     

Surface reactivity of graphite materials and their surface passivation during the first electrochemical lithium insertion

The surface passivation of TIMREX^® SLX50 graphite powder was studied as received and after heat treatment at 2500 °C in an inert gas atmosphere by differential electrochemical mass spectrometry in electrochemical lithium half-cells. 1 M LiPF₆ in ethylene carbonate and either a dimethyl carbonate, propylene carbonate or 1-fluoro ethylene carbonate co-solvent was used as electrolyte systems in these half-cells. The SEI-film formation properties of both graphite materials were correlated with their active surface area (ASA), being responsible for the interactions between the carbon and the electrolyte system. The active surface area was determined from the amount of CO and CO₂ gas desorbed at temperatures up to 950 °C from the graphite material surface after chemisorption of oxygen at 300 °C. The structural ordering at the graphite surface increased significantly during the heat treatment of the SLX50 graphite material as indicated by the significant decrease of the ASA value. The increased surface crystallinity was confirmed by krypton gas adsorption, Raman spectroscopy as well as temperature-programmed desorption. This increased structural ordering seemed to be the parameter being responsible for a hindered passivation of the heat-treated SLX50 causing partial exfoliation of the graphite structure during the first electrochemical lithium insertion in the ethylene carbonate/dimethyl carbonate electrolyte. In the case of the ethylene carbonate/1-fluoro ethylene carbonate electrolyte system, primarily the fluoro compound is responsible for the graphite passivation. In this electrolyte system, pristine SLX50 and the less reactive, heat-treated SLX50 graphite showed significantly different SEI-film formation mechanisms. In contrast, no difference in the passivation mechanism could be identified for different graphite surfaces in the ethylene carbonate electrolyte system with propylene carbonate as co-solvent.     

Improving electrochemical properties of lithium iron phosphate by addition of vanadium

The poor conductivity, resulting from the low lithium-ion diffusion rate and low electronic conductivity in the LiFePO₄ phase, has posed a bottleneck for commercial applications. Well-crystallized LiFePO₄-based powders with vanadium addition were synthesized with solution method. The synthesized powders are coated with carbon. The powder containing the well-mixed LiFePO₄ and Li₃V₂(PO₄)₃ phases (LFVP) with narrow distributed particle size ranging between 0.5 and 2.5 μm exhibits improved electrochemical performance. The small particle size and the presence of the electronically conductive mixed phases can be the reasons why the cells containing LFVP exhibit the high discharge capacity of about 100 mAh g⁻¹ at 10 C, whereas the samples with single phase, such as LiFePO₄ and Li₃V₂(PO₄)₃, have the discharge capacity less than 80 Ah g⁻¹ at the same rate.     

锂盐对LAGP-PEO复合固体电解质及全固态LFP锂离子电池性能的影响

将Li1.5Al0.5Ge1.5(PO4)3（LAGP）与少量PEO(LiX)复合,采用溶液浇注法制备了以LAGP为主相的固体复合电解质,研究了LiClO4、LiTFSI、LiBOB 3种锂盐对固体复合电解质离子电导率、电化学稳定窗口、与锂负极界面的化学稳定性和电化学稳定性的影响以及锂盐种类对LFP固态电池循环及倍率性能的影响。研究结果表明,采用LiClO4、LiTFSI、LiBOB 3种锂盐制备的固体复合电解质分解电压均超过5 V,具有较好的电化学稳定性。LAGP-PEO(LiTSFI)固体复合电解质的离子电导率以及室温对锂界面的稳定性相对更高。LAGP-PEO (LiBOB)与锂的界面在60 ℃时相对更稳定。与之对应,采用LAGP-PEO(LiTSFI)和LAGP-PEO(LiBOB)固体复合电解质的LFP全固态电池,分别在25 ℃和60 ℃具有最高的比容量和最好的循环稳定性。