喷雾干燥-高温固相法制备纳米LiFePO4与LiFePO4/C材料及性能研究

采用喷雾干燥-高温固相法制备纳米LiFePO₄与LiFePO₄/C正极材料，用X-射线衍射，扫描电镜等对合成材料进行了表征，并对以LiFePO₄为正极的电池进行了电化学性能测试。结果表明:材料合成最佳煅烧温度为600 ℃;合成过程中由于碳对LiFePO₄晶型的生长有一定的抑制作用，相对于纯LiFePO₄材料，LiFePO₄/C材料粒径更小;并且，在此最佳合成温度下合成的LiF     

高振实密度圆饼状LiFePO4/C的制备及电化学性能

以乙二醇为溶剂,采用溶剂热法一步合成圆饼状LiFePO₄,然后以葡萄糖为碳源与合成的LiFePO₄前躯体高温烧结得到碳包覆的LiFePO₄/C复合材料,其振实密度高达1.3 g·cm^-3。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对LiFePO₄/C复合材料进行了物相和形貌表征,研究结果表明制备得到的LiFePO₄呈圆饼状,且生成的圆饼是由单晶LiFePO₄纳米片堆积而成。此外,LiFePO₄颗粒表面碳层包覆均匀。将制备的LiFePO₄/C用作锂离子电池正极材料,电化学性能测试表明其具有高的充放电比容量(在0.1C时放电,其初始放电比容量为157.7 mAh·g^-1)与良好的循环性能(500次循环后容量保持率为82.4%)。     

Mo掺杂LiFePO4正极材料的第一性原理研究

基于第一性原理密度泛函理论计算了LiFePO₄和LiFe_1-xMo_xPO₄(x=0.005,0.01,0.015,0.02,和0.025)的电子结构和锂离子扩散能垒。结果显示掺杂后的LiFe_0.99Mo_0.01PO₄样品具有最大的(101)晶面间距,由此可知LiFe_0.99Mo_0.01PO₄沿[101]晶向具有最宽的锂离子扩散通道。未掺杂的LiFePO₄的锂离子扩散能垒为4.289eV,而掺杂后LiFe_0.99Mo_0.01PO₄降为4.274eV,经过计算得出掺杂样品LiFe_0.99Mo_0.01PO₄的锂离子扩散系数增为未掺杂LiFePO₄的1.79倍,表明Mo掺杂有利于改善LiFePO₄的锂离子扩散能力。态密度图显示,掺杂Mo后导带底附近的峰强度增强,对LiFePO₄电子导电性能的提高是有利的。因此,掺杂Mo有益于提高LiFePO₄的锂离子扩散能力和电子导电能力。结合我们的实验结果比较得知,在磷酸铁锂性能的改善上,相比电子导电能力,锂离子扩散能力的提高起到了更重要的作用。     

水热法制备树叶状LiFePO4/C复合正极材料

采用柠檬酸辅助水热法合成了高分散性树叶状LiFePO₄/C复合正极材料。利用X射线衍射、傅里叶红外光谱、扫描电镜、高分辨率透射电镜和选区电子衍射分析了材料的形貌结构。结果表明,柠檬酸对树叶状LiFePO₄/C复合材料的形成具有促进作用。该材料的最大暴露晶面为(010)晶面,且分散性较好。与颗粒状LiFePO₄/C材料相比,该材料呈现出更高的放电比容量和更好的倍率性能,在0.1C和5C倍率下,放电比容量分别为158和126mAh·g^-1,其原因是由于锂离子沿[010]方向的扩散距离缩短,从而使锂离子扩散系数显著增大。     

溶剂热法合成花状分级结构LiFePO4及其电化学性能研究

以乙二醇/水为溶剂,酒石酸铵为添加剂和碳源,采用溶剂热法,制备了高振实密度(1.3g·cm^-3)的锂离子正极材料磷酸铁锂(LiFePO₄)。采用X射线衍射(XRD)、红外光谱、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对样品进行了表征。研究结果表明样品为单晶纳米片组装而成的花状三维多孔分级结构LiFePO₄。通过时间单因素实验探讨花状分级结构LiFePO₄的生长机理,其生长过程概括为:成核和生长,定向组装。电化学性能测试结果表明LiFePO₄样品具有优异的倍率性能(10C时放电比容量保持在74.8mAh·g^-1)与循环性能(50次循环后容量保持率 > 93%)。     

微米橄榄石型LiFePO4的水热合成优化

为深入研究大颗粒磷酸铁锂(LiFePO₄)锂离子电池正极材料的性能衰退机理并据此改善其体积能量密度和功率密度, 进而切实推进该材料在电动汽车、混合动力汽车和电站储能等领域的高效广泛应用, 本文通过优化水热合成条件制备了粒径为2 μm的均匀微米LiFePO₄颗粒粉末. 在未经任何改性(包覆或掺杂)的情况下,该材料表现出本征大颗粒LiFePO₄典型的充放电和循环性能, 可作为后续研究的代表样品进一步考察大颗粒材料相对纳米材料性能衰退的机制和根本原因, 最终通过有的放矢地改性手段获得高密度、高能量和高功率的LiFePO₄ 正极材料. 实验结果表明, 增加反应物浓度、水热温度和保温时间以及降低溶液pH 值均有利于LiFePO₄颗粒的长大. 通过比较不同粒径的LiFePO₄的电化学性能确证了其随颗粒尺寸的增大而衰退. 当颗粒大小由0.7 μm增加到16.5 μm时, LiFePO₄在0.1C倍率下的放电比容量由152 mAh·g^-1下降至80 mAh·g^-1.同时, 1C倍率下的循环测试结果表明, 颗粒尺寸越大, LiFePO₄的容量衰减愈严重.     

鸟巢状分级结构LiFePO4的合成及其电化学性能研究

采用溶剂热法,以乙二醇为溶剂,P₁₂₃为软模板剂,制备了锂离子电池正极材料磷酸铁锂(LiFePO₄),其振实密度约为1.2g·cm^-3。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)和BET对样品的成分、晶型,形貌和孔结构进行了表征。结果表明：鸟巢状LiFePO₄由单晶纳米片组成,具有开放的三维多孔分级结构。通过时间单因素实验探讨鸟巢状分级结构LiFePO₄的生长机理,其生长过程可以概括为：成核定向生长团聚定向生长。电化学性能测试结果表明材料在0.1C倍率下充放电时,其首次放电比容量达132.5mAh·g^-1。     

MoO3氧化物掺杂改善LiFePO4 / 乙炔黑电化学性能研究

采用MoO₃氧化物前驱物对磷酸铁锂(LiFePO₄)进行少量的掺杂，并用XRD、SEM、CV及恒流充放电测试对产物进行了研究。研究表明，少量的掺杂并未影响到LiFePO₄的晶体结构，但却能够在一定程度上改善LiFePO₄的电化学性能。其中650 ℃焙烧的1% Mo掺杂的LiFePO₄材料性能较好，该材料在以0.2 C的倍率充放电时，充放电曲线具有平稳的电压平台和较大的充放电容量，首次放电容量能达到     

纺锤体形LiFePO4锂离子电池正极材料的制备与性能

采用低温溶剂热法合成了LiFePO₄, 并通过热处理方法制备出LiFePO₄/C锂离子电池复合正极材料. 利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱以及恒电流充放电测试等方法对样品进行结构表征和充放电性能测试. 结果表明: 采用丙三醇(甘油)为溶剂, 低温条件下(120 °C)合成的LiFePO₄具有橄榄石型晶体结构, 呈纺锤体形貌, 且具有粒径分布均匀的特点. 热处理后制备的LiFePO₄/C复合正极材料仍呈纺锤体形貌, 且表现出了优良的充放电性能. 室温下以0.1C倍率恒流充放电, LiFePO₄/C的首次放电比容量达到147.2 mAh·g^-1, 50次循环后放电比容量仍然保持在136.3 mAh·g^-1. 当倍率为0.2C、0.5C和1C时, 样品的平均放电比容量分别在130、120和108 mAh·g^-1左右.     

球磨方式对锂离子正极材料LiFePO4性能的影响

采用高温固相合成法制备橄榄石型的LiFePO₄正极材料，在合成过程中分别采用湿法球磨和干法球磨两种球磨方式。用X-射线衍射，扫描电镜，激光粒度测试等对合成材料进行表征，并对以LiFePO₄为正极的电池进行电化学性能测试。结果表明，相对于干法球磨，湿法球磨制备的LiFePO₄样品具有更好的电化学性能，0.2C放电的首次放电比容量为134.9 mAh·g^-1，并有优良的大电流放电性能及循环性能。这主要是因为采用湿法球磨制备的LiFePO₄材料物相较纯、粒径均匀，与导电添加剂的接触更加紧密，从而提高了LiFePO₄材料电化学性能。     

Li-ion batteries from LiFePO4 cathode and anatase/graphene composite anode for stationary energy storage

Li-ion batteries made from LiFePO₄ cathode and anatase TiO₂/graphene composite anode were investigated for potential application in stationary energy storage. Fine-structured LiFePO₄ was synthesized by a novel molten surfactant approach whereas anatase TiO₂/graphene nanocomposite was prepared via self-assembly method. The full cell that operated at 1.6 V demonstrated negligible fade even after more than 700 cycles at measured 1 C rate. While with relative lower energy density than traditional Li-ion chemistries interested for vehicle applications, the Li-ion batteries based on LiFePO₄/TiO₂ combination potentially offers long life and low cost, along with safety, all which are critical to the stationary applications.     

Low-temperature synthesis of a green material for lithium-ion batteries cathode

Abstract

Battery technology is an important anthropogenic source of the heavy metals which are highly threatening to human health. A category of rechargeable lithium batteries that is of great interest is the set of batteries where the cathode material is a lithium iron phosphate (LiFePO₄). LiFePO₄ is an environmentally friendly and safe lithium-ion battery cathode material, but it has a key limitation, and that is its extremely low-electronic conductivity, a problem that can be greatly overcome by zinc-doping LiFePO₄. For the first time to our knowledge, a low-temperature method, that is advantageous both economically and technologically, for the synthesis of a zinc-doped LiFePO₄ is presented. Since the method appears to be applicable for synthesizing various zinc-doped LiFePO₄ compounds with the general formula LiFe_1?x Zn _x PO₄ (0<x<1), it is very promising for the production of a green cathode material for lithium-ion batteries.     

Carbon Fiber Reinforced LiFePO<Subscript>4</Subscript>-Based Three-Dimensional Bulk Electrodes with Metal-Current-Collector- and Binder-Free Design

Conductive hierarchically porous LiFePO₄ blocks enhanced by carbon fiber were successfully obtained, which is benefited from nice sinter-activity of hydrothermal synthesized LiFePO₄. In combination with hierarchically porous and carbon-fiber-reinforced electric-conductive topologies, metal-current-collector- and binder-free design, the as-prepared bulk electrodes present excellent rate capability and cycle life. Our proofof- concept study on LiFePO₄-based bulk electrodes shows facile approach to improve energy density and lower cost of Li-ion batteries.     

Anode-Free Lithium Metal Batteries Based on an Ultrathin and Respirable Interphase Layer

Anode-free lithium (Li) metal batteries are desirable candidates in pursuit of high-energy-density batteries. However, their poor cycling performances originated from the unsatisfactory reversibility of Li plating/stripping remains a grand challenge. Here we show a facile and scalable approach to produce high-performing anode-free Li metal batteries using a bioinspired and ultrathin (250 nm) interphase layer comprised of triethylamine germanate. The derived tertiary amine and Li_xGe alloy showed enhanced adsorption energy that significantly promoted Li-ion adsorption, nucleation and deposition, contributing to a reversible expansion/shrinkage process upon Li plating/stripping. Impressive Li plating/stripping Coulombic efficiencies (CEs) of ≈99.3 % were achieved for 250 cycles in Li/Cu cells. In addition, the anode-free LiFePO₄ full batteries demonstrated maximal energy and power densities of 527 Wh kg⁻¹ and 1554 W kg⁻¹, respectively, and remarkable cycling stability (over 250 cycles with an average CE of 99.4 %) at a practical areal capacity of ≈3 mAh cm⁻², the highest among state-of-the-art anode-free LiFePO₄ batteries. Our ultrathin and respirable interphase layer presents a promising way to fully unlock large-scale production of anode-free batteries.     

A general solution-chemistry route to the synthesis LiMPO4 (M=Mn, Fe, and Co) nanocrystals with [010] orientation for lithium ion batteries

A general and efficient solvothermal strategy has been developed for the preparation of lithium transition metal phosphate microstructures (LiMnPO₄, LiFePO₄, and LiCoPO₄), employing ethanol as the solvent, LiI as the Li source, metal salts as the M sources, H₃PO₄ as the phosphorus source, and poly(vinyl pyrrolidone) (PVP) as the carbon source and template. This route features low cost, environmental benign, and one-step process for the cathode material production of Li-ion batteries without any complicated experimental setups and sophisticated operations. The as-synthesized LiMPO₄ microstructures exhibit unique, well-shaped and favorable structures, which are self-assembled from microplates or microrods. The b axis is the preferred crystal growth orientation of the products, resulting in a shorter lithium ion diffusion path. The LiFePO₄ microstructures show an excellent cycling stability without capacity fading up to 50 cycles when they are used as a cathode material in lithium-ion batteries.     

A new charging mode of Li-ion batteries with LiFePO<Subscript>4</Subscript>/C composites under low temperature

Li-ion batteries with LiFePO₄/C composites are difficult to be charged at low temperatures. In order to improve the low temperature performance of LiFePO₄/C power batteries, the charge–discharge characteristics were studied at different temperatures, and a new charging mode under low temperature was proposed. In the new charging mode, the batteries were excited by current pulses with the charge rates between 0.75 C and 2 C, while the discharge rates between 3 and 4 C before the conventional charging (CC–CV). Results showed that the surface temperature of Li-ion battery ascended to 3 °C at the end of pulse cycling when the environment temperature was −10 °C. Comparing with the conventional charging, the whole charge time was cut by 36 min (23.4%) and the capacity was 7.1% more at the same discharge rate, respectively.     

Enhancement of electrochemical properties of niobium‐doped LiFePO4/C synthesized by sol–gel method

LiFePO₄/C and LiFe_1–xNb _xPO₄/C composites were synthesized using a sol–gel method. The influence of niobium doping on the constitution, morphology, and electrochemical properties of the samples was studied in detail. X‐Ray diffraction patterns indicate that appropriate Nb doping does not alter seriously the structure of LiFePO₄. Electrochemical characterization of the electrodes showed that the Li‐ion batteries based on LiFe_1–xNb _xPO₄/C electrode exhibited better charge/discharge performance than those based on LiFePO₄/C. The LiFe_0.95Nb_0.05PO₄/C‐based cell had the specific capacity of 157, 121, and 85 mAh/g at 0.2, 2, and 5 C, respectively, in comparison with 126, 94, and 52 mAh/g for the LiFePO₄/C cell. The results show that the addition of niobium promotes the electrochemical performance of the materials especially at high charge/discharge rates of the battery.     

Polymer wiring of insulating electrode materials: An approach to improve energy density of lithium-ion batteries

The poor electronic conductivity of LiFePO₄ has been one of the major issues impeding it from achieving high power and energy density lithium-ion batteries. In this communication, a novel polymer-wiring concept was proposed to improve the conduction of the insulating electrode material. By using a polymer with tethered “swing” redox active molecules (S) attached on a polymer chain, as the standard redox potential of S matches closely the Fermi level of LiFePO₄, electronic communication between the redox molecule and LiFePO₄ is established. Upon charging, S is oxidized at the current collector to S⁺, which then delivers the charge (holes) to the LiFePO₄ particles by intermolecular hopping assisted by a “swing” – type motion of the shuttle molecule. And Li⁺ is extracted. Upon discharging, the above process is just reversed. Preliminary studies with redox polymer consisting of poly (4-vinylpyridine) and phenoxazine moiety tethered with a C₁₂ alkyl chain have shown promising result with carbon-free LiFePO₄, where effective electron exchange between the shuttle molecule and LiFePO₄ has been observed. In addition, as the redox polymer itself could act as binder, we anticipate that the polymer-wiring concept would provide a viable approach to conducting-additive and binder free electrode for high energy density batteries.     

Determination of the Lamb-Mössbauer factors of LiFePO4 and FePO4 for electrochemical in situ and operando measurements in Li-ion batteries

⁵⁷Fe Mössbauer spectroscopy is a powerful tool to investigate redox reactions during in electrochemical lithium insertion/extraction processes. Electrochemical oxidation of LiFe^IIPO₄ (triphylite) in Li-ion batteries results in Fe^IIIPO₄ (heterosite). LiFePO₄ was synthesized by solid state reaction at 800 °C under Ar flow from Li₂CO₃, FeC₂O₄·2H₂O and NH₄H₂PO₄ precursors in stoichiometric composition. FePO₄ was prepared from chemical oxidation of LiFePO₄ using bromine as oxidative agent. For both materials a complete ⁵⁷Fe Mössbauer study as a function of the temperature has been carried out. The Debye temperatures are found to be θ_M=336 K for LiFePO₄ and θ_M=359 K for FePO₄, leading to Lamb-Mössbauer factors f_300 K=0.73 and 0.77, respectively. These data will be useful for a precise estimation of the relative amounts of each species in a mixture.