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。     

不同放电功率下的储能用磷酸铁锂电池热失控特性实验研究

以某款52Ah储能用方形磷酸铁锂电池单体为对象,采用400 W的外部热源、20.8～166.4 W(1～8h)的恒功率放电以匹配电池工作状态下的热滥用条件,测量电池热失控过程中的表面温度和电压,记录热失控实验现象和关键时间点,对比研究不同放电功率对热滥用诱发热失控进程的影响.结果表明,放电操作会加速热失控的进程,且放电功率越大,热失控越早发生,从不放电到166.4 W恒功率放电,安全阀打开时间缩短了23.4％,热失控触发时间缩短了5.6％;与此同时,四组放电工况由于放出部分能量,最终热失控的严重程度有所降低,放电工况下的热失控最高温度和最大温升速率比不放电工况最高分别下降了9.0％和53.3％;另外,放电操作会造成热失控过程中电压更大的波动,后续电压下降的时间窗口前移至开阀时间附近,这将更有利于利用电压变化对热失控进行预警.总体而言,放电操作在加速热失控进程的同时,降低了热失控最终的严重程度.本工作可对电化学储能电站的日常安全运营和电池管理系统设计提供参考.     

磷酸铁锂电池及其新能源汽车启动电源性能研究

鉴于汽车启动电源铅酸电池存在严重环境污染隐患,本文采用环保型32650圆柱磷酸铁锂电池组装成25.6 V/65 A•h电池组代替铅酸电池应用于汽车启动电源,并分别对磷酸铁锂电池组的常温和低温启动能力、倍率性能和低温放电性能等进行测试。实验结果表明,电池组0.33 C放电容量为67.028 A•h,3 C放电容量为0.33 C放电容量的98.24%,电池组具有较好的倍率性能;电池组在 −30℃放电容量为额定容量的84.7%,具有良好的低温性能;电池组在25℃和 −20℃下以600 A电流放电,单串电池电压均高于放电保护电压;电池组在25℃搁置28 d之后,容量恢复率为99.37%;磷酸铁锂电池组性能均满足汽车启动电源性能要求,可以代替铅酸电池作为汽车启动电源。     

Solvothermal synthesis of hierarchical LiFePO4 microflowers as cathode materials for lithium ion batteries

Hierarchical LiFePO₄ microflowers have been successfully synthesized via a solvothermal reaction in ethanol solvent with the self-prepared ammonium iron phosphate rectangular nanoplates as a precursor, which is obtained by a simple water evaporation method beforehand. The hierarchical LiFePO₄ microflowers are self-assemblies of a number of stacked rectangular nanoplates with length of 6-8 μm, width of 1-2 μm and thickness of around 50 nm. When ethanol is replaced with the water-ethanol mixed solvent in the solvothermal reaction, LiFePO₄ micro-octahedrons instead of hierarchical microflowers can be prepared. Then both of them are respectively modified with carbon coating through a post-heat treatment and their morphologies are retained. As a cathode material for rechargeable lithium ion batteries, the carbon-coated hierarchical LiFePO₄ microflowers deliver high initial discharge capacity (162 mAh g⁻¹ at 0.1 C), excellent high-rate discharge capability (101 mAh g⁻¹ at 10 C), and cycling stability, which exhibits better electrochemical performances than carbon-coated LiFePO₄ micro-octahedrons. These enhanced electrochemical properties can be attributed to the hierarchical micro/nanostructures, which can take advantage of structure stability of micromaterials for long-term cycling. Furthermore the rectangular nanoplates as the building blocks can improve the electrochemical reaction kinetics and finally promote the rate performance.     

羧甲基壳聚糖水性粘结剂改性及其在磷酸铁锂正极的应用研究

羧甲基壳聚糖（C-CTS）作为磷酸铁锂（LiFePO4, LFP）正极水系粘结剂的两种改性方式分别是：（1）与聚环氧乙烷（PEG）共混制备C-CTS/PEG复合粘结剂;（2）在C-CTS/PEG混合体系中,以三羟甲基丙烷-三[3-(2-甲基吖丙啶基)丙酸酯]（XR-104）作为交联剂制备可交联的C-CTS/PEG/XR-104水系粘结剂。本文考察了不同C-CTS/PEG质量比复合粘结剂对LFP正极的电化学性能的影响,C-CTS/PEG的优化重量比为3∶1,此时LFP正极表现出最佳的循环稳定性。电池在0.5 C下充放电测试,140次循环后容量保持率为99%。采用差示扫描量热法（DSC）、傅里叶红外光谱仪（FTIR）和溶解实验等研究C-CTS/PEG与XR-104的交联反应,当交联剂XR-104的重量为C-CTS的1%时,LFP正极表现出最佳的电化学性能。     

交联型水性粘结剂的制备及其在磷酸铁锂正极的 应用研究

丙烯酸（AA）通过自由基接枝聚合对聚乙烯醇（PVA）进行改性,得到接枝聚合物PVA-g-PAA,并与季戊四醇（PER）交联剂共同作为磷酸铁锂（LFP）正极的交联型水性粘结剂,探讨了交联温度及不同PER使用量对LFP正极电化学性能的影响。交联温度与极片制备工艺温度相吻合,极片在烘干的过程中同时完成交联反应。当PER的加入量为PVA-g-PAA的5mol%时,LFP电极表现出最优的粘结力和电化学稳定性,在0.2 C和1 C倍率下进行充放电循环测试,PVA-g-PAA-c-5%PER在0.2 C倍率下循环100圈后的容量保持率为99.4%,PVA-g-PAA和PVDF的分别为94.4%和88.6%;PVA-g-PAA-c-5%PER在1 C高倍率下循环400圈后的容量保持率为82.6%,而PVA-g-PAA的保持率为78.8%。     

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。     

High-power LiFePO4 cathode materials with a continuous nano carbon network for lithium-ion batteries

To meet the requirements of high-power products (ex. electric scooters, hybrid electric vehicles, pure electric vehicles and robots), high-energy safe lithium-ion batteries need to be developed in the future. This research will focus on the microstructures and electrochemical properties of olivine-type LiFePO₄ cathode materials. The morphologies of LiFePO₄/C composite materials show spherical-type particles and have good carbon conductive networks. From the TEM bright field image and EELS mapping, the LiFePO₄/C powder shows continuous, dispersive nano-carbon network. These structures will improve electron transfer and lithium-ion diffusion for LiFePO₄ cathode materials, and increase their conductivity from 10⁻⁹ S cm⁻¹ to 10⁻³ S cm⁻¹. The electrochemical properties of LiFePO₄/C cathode material in this work demonstrated high rate capability (≥12 C) and long cycle life (≥700 cycles at a 3 C discharge rate).     

Charge-discharge rate of spinel lithium manganese oxide and olivine lithium iron phosphate in ionic liquid-based electrolytes

Rate capability of Li/spinel LiMn₂O₄ or olivine LiFePO₄ positive electrode cells containing mixed imidazolium ionic liquids electrolytes has been investigated under comparison with conventional organic solvent electrolyte and piperidinium ionic liquid. The LiMn₂O₄ electrode provides variation of rate capabilities among the ionic liquid electrolytes, while ionic liquid electrolytes provide similar extent of capacity degradation under high rate compared with organic solvent electrolyte for LiFePO₄ electrode. Such differences in electrolyte dependences of the rate capabilities can be explained in relation to parameters in the high frequency resistances on AC impedance, assumed as interfacial resistances. The rate capability of LiMn₂O₄ is somewhat related to the activation energy of the high frequency resistance, while for LiFePO₄ the resistance value appears to contribute to the rate capability.     

Uniform carbon coating drastically enhances the electrochemical performance of a Fe3O4 electrode for alkaline nickel–iron rechargeable batteries

Fe₃O₄@C composites for use in alkaline nickel-iron rechargeable batteries are synthesized via a spray drying method. SEM and TEM confirm that the Fe₃O₄@C composite is a secondary particle microsphere formed by many primary particles uniformly coated with carbon. The particles aggregate with each other, which is equivalent to forming a three-dimensional conductive mesh. The electrochemical properties of the bare Fe₃O₄ and Fe₃O₄@C composites as anode materials for alkaline nickel-iron batteries are investigated. The results show that the Fe₃O₄@C composite synthesized by spray drying exhibits considerably high discharge capacities and an excellent rate capability. The specific discharge capacity of the Fe₃O₄@C composite reaches 693.7 mAh g⁻¹ at a current density of 300 mA g⁻¹, with a charging efficiency of 92.5%. Moreover, the Fe₃O₄@C composite exhibits an admirable cycling stability with a superior capacity retention of 92.0% for 100 cycles at a current density of 300 mA g⁻¹. In addition, discharge capacities of 556.7 and 420.1 mAh g⁻¹ are achieved at high current densities of 1200 and 2400 mA g⁻¹, respectively.     

Investigation of inorganic compounds on the surface of cathode materials using Li and O K-edge XANES

Inorganic compounds on the surfaces of the cathode materials LiNi_0.80Co_0.15Al_0.05O₂ and LiCoO₂ were studied using Li and O K-edge X-ray absorption near edge structure (XANES) measurements. Rietveld analysis revealed that the LiNi_0.80Co_0.15Al_0.05O₂ sample contained 2% Li₂CO₃, while the LiCoO₂ sample was single-phase. The Li and O K-edge XANES spectra indicated that the surface of LiCoO₂ was almost free of residual Li₂CO₃. In contrast, the presence of both residual Li₂CO₃ and an additional cubic phase were observed, respectively, on and near the surface of LiNi_0.80Co_0.15Al_0.05O₂. These results demonstrate that the XANES technique, using a combination of the total electron yield and fluorescence methods, is an effective tool for probing the surfaces of cathode materials.     

Synthesis of LiFePO4/polyacenes using iron oxyhydroxide as an iron source

LiFePO₄/polyacenes (PAS) composite is synthesized by iron oxyhydroxide as a new raw material and phenol–formaldehyde resin as both reducing agent and carbon source. The mechanism of the reaction is outlined by the analysis of XRD, FTIR as well as TG/DSC. The results show that the formation of LiFePO₄ is started at 300 °C, and above 550 °C, the product can be mainly ascribed to olivine LiFePO₄. The electrochemical properties of the synthesized composites are investigated by charge–discharge tests. It is found that the prepared sample at 750 °C (S750) has a better electrochemical performance than samples prepared at other temperatures. A discharge capacity of 158 mAh g⁻¹ is delivered at 0.2 C. Under high discharge rate of 10 C, a discharge capacity of 145 mAh g⁻¹ and good capacity retention of 93% after 800 cycles are achieved. The morphology of S750 and PAS distribution in it are investigated by SEM and TEM.     

锂金属负极的研究策略

全固态电池由正极材料、固态电解质和锂金属负极组成,锂金属负极是全固态电池的重要组成部分。锂金属负极的成功应用不仅可以提高电池能量密度和安全性能,还能降低现有电化学体系的制造成本,全面取代液态锂离子电池。但在实际的应用过程当中,锂金属负极还存在着下列难以解决的问题：锂枝晶、“死锂”粉末化、体积膨胀和抗空气氧气稳定性。针对以上的问题,综述了先进的锂金属负极研究策略,并给出了解决方案,最后提出了展望。