Study on the characteristics of second life LiFePO4 batteries

随着电动汽车的快速发展,未来将有大量的动力电池退役,这些淘汰下来的电池仍有可观的剩余容量和寿命,可以在静态储能等领域实现梯次利用。为了提高安全性和输出性能,淘汰下来的动力电池需要在筛选之后重新串、并联成组使用。以二次利用磷酸铁锂动力电池为研究对象,研究在单体电池内阻不一致、剩余容量不一致、初始SOC不一致等情形下,电池组的并联特性,即并联电池组中各电池直流阻抗、电流不平衡度的变化情况。对于实现磷酸铁锂动力电池的梯次利用具有指导意义。     

Preparation and electrochemical performance of LiFePO4/S composite cathode materials

以提高磷酸铁锂体系动力电池的能量密度为目的,在LiFePO₄正极材料中加入少量S材料球磨制得LiFePO₄/S复合正极材料。使用X射线衍射（XRD）和扫描电子显微镜（SEM）表征了结构和形貌,并分别组装扣式电池和软包电池测试其电化学性能。结果表明,磷酸铁锂纳米颗粒致密均匀附着在硫材料表面,构成具有包覆性结构的复合材料。在不同比例的LiFePO₄/S复合材料中,硫的添加量为15%的LiFePO₄/S复合正极材料表现出最优异的电化学性能,0.1 C下的初始容量为251.5mA·h/g,循环100周之后容量保持率达94.9%。以该比例的复合材料为正极的0.5A·h软包电池,循环100周后容量保持率为86.7%。LiFePO₄作为一种极性载体,对多硫化物有一定的吸附能力,少量硫的加入可以在大幅度提高LiFePO₄材料放电容量的同时,维持优异的循环稳定性。LiFePO₄/S复合材料可为磷酸铁锂体系动力电池的发展提供新的思路。     

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。     

Application of LiFePO4 battery in DC system of new substation

随着发电站和变电站自动化程度的提高,为变电站和发电站提供通讯、调度、控制、照明等动力的直流系统显得尤为重要,直流系统为电力控制和操作提供重要的电力保障,是电力系统控制、保护的基本保障。如果直流电源系统供电不可靠失电,将导致变电站所有通讯、调度、控制、保护、照明处于瘫痪状态,无法保证变电站的安全稳定运行,在变电站站用电源事故停电情况下,整个电站失去可控性和保护,极易造成电网事故,给电网安全稳定运行带来潜在风险。直流电源是变电站的心脏,电池是电源的最后屏障,目前国网公司暂无磷酸铁锂电池的生产能力。     

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.     

Review on state of health estimation of retired lithium-ion batteries

由于电池组中电池单体之间存在性能差异,退役锂离子电池在投入梯次利用前需要借助健康状态（SOH）评估技术进行电池单体的分类与配组。健康状态评估系统的构建涉及电池建模、电池测试、数据处理、算法开发等各种技术问题。目前通过基于模型的参数识别与直接提取健康因子是构建SOH评估体系的两种主要思路。在电池模型的简化、测试工况的设计、健康因子的选择和算法的应用与优化等方面已经有了很多研究。如何在缩短电池测试时间的同时提高评估系统的泛化能力是目前该研究领域的主要问题,这些问题的解决对于SOH评估系统真正在梯次利用锂离子电池的产业化中发挥作用至关重要。在未来的研究中通过优化测试工况和数据融合等技术,有望开发出性能更好的SOH评估系统。     

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).     

Research progress of cycle phosphazenes applied in lithium ion batteries

本文回顾了环三磷腈及其衍生物的合成,阐述了其在锂离子电池电解液,正负极材料等关键材料方面的应用研究进展,并进行了相应的展望.随着锂离子电池在高容量动力及储能领域中的广泛应用,电池的安全性问题日益凸显,材料安全性是电池安全性的基本保证.磷腈化合物由于其特殊的组成和结构,具有高效阻燃与电化学稳定性,在用于改善锂离子电池安全性方面受到越来越广泛的关注.在锂离子电池电解液添加剂和共溶剂的研究中发现,磷腈化合物不仅可以改善电解液的热稳定性和阻燃性能,还可以提高电池的充放电电压和循环稳定性;同时,也可以作为正负极材料的重要组分,改善电极材料的安全性.在锂离子电池安全性领域中具有较好的研究价值和实用意义.     

A novel fast estimation and regroup method of retired lithium-ion battery cells

With the commercialization of the electric vehicles, the large-scale lithium-ion cells as the power of electric vehicles are to be retired. The second-use of retired cells is of great significance to improve the battery economy. A fast classification and regroup evaluation method of the retired lithium-ion cells are proposed in this paper to improve the classification efficiency of retired lithium-ion cells and adapt to the regroup under different conditions. The lithium-ion cells after being balanced in parallel are charged in series with a constant current. A support vector regression (SVR) model with the parameters optimized by the particle swarm optimization (PSO) algorithm is built for the fast capacity estimation and the error will not exceed 0.3%. Different cells regrouped means different performance. In order to improve the consistency of retired cells and satisfy different using conditions, a Weighted-K-means algorithm is proposed in this paper to regroup the cells with the known capacity and internal resistance. The classification method is evaluated by the voltage consistency of cells using different working conditions, which indicates capacity occupied a large proportion can meet the requirement of energy condition meanwhile keep a good consistency. But the resistance will dominate in algorithm under conditions which have requirement for instantaneous power.     

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.     

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。     

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.     

Preparation and characterization of Ti-doped LiFePO4 cathode materials for lithium-ion batteries

Olivine structured LiFePO₄ (lithium iron phosphate) and Ti⁴⁺-doped LiFe_1−xTi_xPO₄ (0.01 ≤ x ≤ 0.09) powders were synthesized via a solution route followed by heat-treatment at 700 °C for 8 h under N₂ flowing atmosphere. The compositions, crystalline structure, morphology, carbon content, and specific surface area of the prepared powders were investigated with ICP-OES, XRD, TEM, SEM, EA, and BET. Capacity retention study was used to investigate the effects of Ti⁴⁺ partial substitution on the intercalation/de-intercalation of Li⁺ ions in the olivine structured cathode materials. Among the prepared powders, LiFe_0.97Ti_0.03PO₄ manifests the most promising cycling performance as it was cycled with C/10, C/5, C/2, 1C, 2C, and 3C rate. It showed initial discharge capacity of 135 mAh g⁻¹ at 30 °C with C/10 rate. From the results of GSAS refinement for the prepared samples, the doped-Ti⁴⁺ ions did not occupy the Fe²⁺ sites as expected. However, the occupancy of the doped Ti⁴⁺ ions are still not clear, and theoretical calculations are needed for further studies. From the variation of lattice parameters calculated by the least square method without refinement, it suggested that Ti⁴⁺-doped LiFePO₄ samples formed solid solutions at low doping levels while TiO₂ was also observed with TEM in samples prepared with doping level higher than 5 mol%.     

Application of SiO/C composite anode material for lithium -ion batteries

硅基材料因其较高的比容量而受到研究者广泛的关注。本文选取高比容量SiOx与NG复合材料作为锂离子电池负极材料,研究了不同SiO/C复合比例对全电池的能量密度和循环性能的影响。不同比例SiOx/C复合材料的首次容量和首次效率有明显差别。与石墨材料相比,SiOx/C复合材料的膨胀程度略有增加。随着SiOx比例的增加,全电池的能量密度先是上升然后下降,但其循环稳定性却有所降低。当SiOx比例在4%时,全电池能量密度提升1.2%,500周循环后容量保持率在80%以上,可以满足商业化锂离子电池的使用要求。     

Overview of the modeling of lithium-ion batteries

简述了锂离子电池等效电路模型和电化学模型的研究进展。由于具有耗时短、技术开发效率高等优点,仿真模型被广泛应用于锂离子电池衰减机制分析、状态诊断及寿命预测。锂离子电池仿真模型主要包括等效电路模型和电化学机理模型。等效电路模型主要应用于锂离子电池荷电状态诊断。电化学机理模型主要应用于锂离子电池衰减机制分析和健康状态诊断,并为寿命预测提供技术支持。等效电路模型的结构过于单一,在锂离子电池寿命后期适用性降低。电化学机理模型结构复杂,计算量大,在线性应用能力较差。总结了现阶段常用的锂离子电池等效电路模型和电化学模型的建模原理及模型结构,阐述了每种模型在电池研究中的具体应用,并分析了其各自的优势及局限性。通过以上分析,并结合最新的建模理论,对建立具有高精度、高适用性锂离子电池仿真模型的研究方向进行了展望。     

Operational reliability and economy evaluation of reusing retired batteries in composite power systems

To support a long-term sustainable electric future, there is ongoing development of electric vehicles, and thus, a serious problem is rising regarding recycling and the echelon application of batteries retired from electric vehicles. Herein, we propose to reuse such retired vehicle batteries as large-scale storage, based on which the operational reliability and the economy of composite generation and transmission systems are analyzed. In details, Gaussian functions were fitted according to data obtained using a holistic aging model. The proposed aging method simulated the capacity degradation of the retired batteries, with a low state of health, under various operating conditions. A universal generating function was adopted for probabilistic modeling of the capacity for battery modules consisting of hundreds of cells. The feasibility and effectiveness of using retired batteries in composite power systems were verified. The test results show that a significant investment can be saved, and system reliability improved, compared with systems without retired batteries. Finally, a method for scheduling the second retirement of retired batteries was established from the perspective of asset management.     

A review of processes and technologies for the recycling of lithium-ion secondary batteries

The purpose of this paper is to review the current status of the recycling technologies of spent lithium-ion secondary batteries. It introduced the structure and components of the lithium-ion secondary batteries, summarized all kinds of single recycling processes from spent lithium-ion secondary batteries and presented some examples of typical combined recycling processes. Also, the problems and prospect of the studies of their recycling technologies have been put forward.     

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%。     

Electrospun zeolitic imidazolate framework‐derived nitrogen‐doped carbon nanofibers with high performance for lithium‐sulfur batteries

Three‐dimensional (3D) nitrogen‐doped carbon nanofibers (N‐CNFs) which were originating from nitrogen‐containing zeolitic imidazolate framework‐8 (ZIF‐8) were obtained by a combined electrospinning/carbonization technique. The pores uniformly distributed in N‐CNFs result in the improvement of electrical conductivity, increasing of BET surface area (142.82 m² g^?1), and high porosity. The as‐synthesized 3D free‐standing N‐CNFs membrane was applied as the current collector and binder free containing Li₂S₆ catholyte for lithium‐sulfur batteries. As a novel composite cathode, the free‐standing N‐CNFs/Li₂S₆ membrane shows more stable electrochemical behavior than the CNFs/Li₂S₆ membrane, exhibiting a high first‐cycle discharge specific capacity of 1175 mAh g^?1at 0.1 C and keeping discharge specific capacity of 702 mAh g^?1 at higher rate. More importantly, as the sulfur mass in cathodes was increased at 7.11 mg, the N‐CNFs/Li₂S₆ membrane delivered 467 mAh g^?1after 150 cycles at 0.2 C. The excellent electrochemical properties of N‐CNFs/Li₂S₆ membrane can be ascribed to synergistic effects of high porosity and nitrogen‐doping in N‐CNFs from carbonized ZIF‐8, illustrating collective effects of physisorption and chemisorption for lithium polysulfides in discharge‐charge processes.     

High temperature electrochemical performance of nanosized LiFePO4

The electrochemical performance of LiFePO₄ was tested at temperatures up to 150 °C for micrometric and nanometric size samples. Among the latter, both highly defective samples obtained by direct precipitation and annealed samples were tested. The comparison of voltage composition profiles for these samples coupled to GITT experiments allowed to conclude that defects seem to be the major factor in inducing the solid solution behaviour at room temperature. Good capacity retention is exhibited upon prolonged cycling at 100 °C in EC LiBOB electrolyte, also for nanosized samples that still maintain 75% of the initial capacity after 170 cycles. These results prove that the enhanced thermal stability of such electrolytes can be extended to temperatures much higher than those usually tested.