由电解磷铁废渣制备的FePO4合成LiFePO4研究

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刘严, 王贵欣, 闫康平, 李成佳. 由电解磷铁废渣制备的FePO₄合成LiFePO₄研究 . 无机材料学报, 2012, 27(5): 475-479
LIU Yan, WANG Gui-Xin, YAN Kang-Ping, LI Cheng-Jia. Synthesis of LiFePO₄ Using FePO₄ Produced by Electrolyzing Fe_1.5P Waste Slag . Journal of Inorganic Materials, 2012, 27(5): 475-479 复制到剪切板

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由电解磷铁废渣制备的FePO₄合成LiFePO₄研究

刘严, 王贵欣, 闫康平, 李成佳

四川大学化学工程学院, 成都 610065

王贵欣, 副教授. E-mail:guixin66@scu.edu.cn

刘严(1986-), 女, 硕士研究生. E-mail:liuyan10502@126.com

基金:四川大学青年基金(07046);

摘要

在磷酸水溶液中, 以磷铁废渣为阳极、石墨为阴极, 恒流无膜电解后溶液由无色变为黄色, 用氨水调节pH值, 经过滤、洗涤、干燥, 得到淡黄色粉体, XRD和热分析结果表明该粉体组成为FePO₄·2H₂O. 在电解产物中加入LiOH·H₂O和葡萄糖, 用乙醇作溶剂充分研磨形成流变相前驱体, 在700℃氩气气氛中焙烧得到LiFePO₄/C复合物. 用动电位极化方法分析了磷铁的电解过程, 用XRD、SEM和循环伏安法(CV)研究了LiFePO₄/C复合物的结构、形貌及电化学性能. 测试结果表明LiFePO₄/C复合物没有磷铁原料的杂质峰, 氧化电位和还原电位分别在3.54和3.33 V, 说明经过阳极袋电解能够消除磷铁原料中的杂质元素影响及锂离子脱/嵌过程中极化较小.

关键词: 锂离子电池; LiFePO₄; Fe_1.5P; 电解; 循环伏安法

中图分类号:TM911 文献标志码:A 文章编号:1000-324X(2012)05-0475-05

Synthesis of LiFePO₄ Using FePO₄ Produced by Electrolyzing Fe_1.5P Waste Slag

LIU Yan, WANG Gui-Xin, YAN Kang-Ping, LI Cheng-Jia

College of Chemical Engineering, Sichuan University, Chengdu 610065, China

Fund:Sichuan University Youth Fund(07046);

Abstract

Fe_1.5P waste slag was galvanostatically electrolyzed without separator in a H₃PO₄ aqueous solution using graphite as the cathode, and the electrolyte color turned from achromatism to yellow after electrolysis. Light yellow powder was finally obtained by adjusting the value of pH using ammonia water, filtering, washing and drying in sequence. The results of XRD and TG-DTA showed that the as-electrolyzed product was FePO₄·2H₂O. The as-obtained FePO₄·2H₂O was mixed well with LiOH·H₂O and glucose to form a rheological phase precursor by using ethanol as a dispersing agent. LiFePO₄/C composite was synthesized successfully by calcining the above precursor at 700℃ in an Ar atmosphere. The electrolysis process was investigatedvia a potentiodynamic polarization method. The structure, morphology and electrochemical performance of the as-synthesized LiFePO₄/C composite were characterized by XRD, SEM and cyclic voltammetry, respectively. There was no impurity indexed peaks from Fe_1.5P raw material, and the oxidization potential and the reduction potential were at 3.54 V and 3.33 V, respectively. The good experimental results indicated that electrolysis of Fe_1.5P waste slag using an anode bag can eliminate the effect of impurities from raw material and the polarization between lithium ion intercalation and de-intercalation was low.

Keyword: lithium-ion battery; LiFePO₄; Fe_1.5P; electrolysis; cyclic voltammetry

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橄榄石型LiFePO₄具有原料丰富、放电平台稳定、热稳定性好、安全性高、环境友好等优点^{[ 1]}, 在电动车、动力工具和大规模能量存储等领域备受关注, 而低成本合成是推进其广泛应用的一个关键环节. 传统制备方法主要用单一锂盐、铁盐和磷酸盐通过高温下的碳或氢还原反应得到, 原料很难均匀混合. 为了克服传统方法的缺点、降低混料过程中的原料损失、提高原料的混合均匀度和反应物间的相接触面, 以FePO₄同时为铁源和磷源与锂盐的反应备受关注, 也是目前工业化生产LiFePO₄的一种主要方法. 2002年Prosini等^{[ 2]}利用溶液共沉淀法制备出纳米FePO₄, 其与LiI反应合成了电化学性能良好的LiFePO₄; Li等以FeSO₄^{[ 3]}和FeSO₄废渣^{[ 4]}为铁源, 用碳热还原法合成了具有较好电化学性能的LiFePO₄. 目前报道的FePO₄都是通过铁盐和磷酸盐反应得到, 亚铁盐需要进一步氧化成铁盐, 原料较贵且工序较多, 导致合成LiFePO₄的成本仍比较高.

磷铁是黄磷或钙镁磷肥生产过程中产量较多的一种副产物^{[ 5]}, 价格低廉, 杂质种类和含量依矿物和反应工艺的不同而有所差别. 磷铁的密度较大, 纯度可以达到98%以上, 经处理后既可以用作锂电池负极材料^{[ 6]}, 而且可以与锂盐和补充磷源经高温反应制备LiFePO₄^{[ 7]}. 然而, 直接利用磷铁合成LiFePO₄的电化学性能受限于磷铁的纯度、组成和粒度, 对磷铁来源要求非常苛刻, 而磷铁的这些指标在生产过程中又很难保证一致, 是目前利用磷铁废渣亟待解决的一个问题. 流变相法是将反应物调制成固体颗粒和液体物质分散均匀的流变相系后反应制备材料的一种简便方法, 固体微粒悬浮在溶剂中, 相接触充分, 表面利用率高^{[ 6, 7, 8, 9, 10]}.

本工作利用电热法黄磷生产的磷铁废渣为原料, 利用阳极袋电解除去原料中的杂质元素, 通过在水溶液中恒流电解制备了高纯度FePO₄, 将其与LiOH·H₂O和葡萄糖通过流变相法合成了LiFePO₄/C复合物, 用XRD、SEM等表征了原料和产物的组成与形貌, 用循环伏安法评价了LiFePO₄/C复合物的氧化还原行为.

1 实验

1.1 电解磷铁制备FePO₄及电解过程研究

用DE-2直流电源为电解电源, 分别以放置在丙纶布阳极袋中的电热法黄磷副产磷铁废渣和高纯石墨为阳极和阴极, 在1.0 mol/L磷酸水溶液中恒流电解, 得到黄色溶液, 用氨水调节pH=3, 得到乳白色悬浊液, 经过滤、洗涤、干燥, 得到淡黄色粉末.

采用三电极体系在PAR273A电化学工作站上测试磷铁在磷酸电解液中的动电位极化曲线, 磷铁为工作电极, 石墨为辅助电极, 饱和甘汞电极SCE为参比电极, 扫描速度为5 mV/s.

1.2 LiFePO₄/C的制备

将上述烘干后的淡黄色电解产物与LiOH·H₂O和葡萄糖混合, 加入无水乙醇充分研磨至形成均一流变相前驱体, 经~300℃预烧2 h后, 再在氩气气氛管式炉中~700℃焙烧6 h, 冷却后得到灰黑色蓬松粉状产物.

1.3 模拟电池组装和循环伏安测试

将上述合成的LiFePO₄/C复合物与乙炔黑导电剂和LA132粘接剂按质量比16:3:1进行混合, 加水调制成均一浆料, 均匀涂覆在干净铝箔上, 经100℃真空干燥12 h后, 裁剪成1.2 cm²的电极片用作工作电极, 以金属锂为对电极和参比电极, LiPF₆/EC+DMC+EMC(体积比1:1:1)为电解液, Celgard2400为隔膜, 在充满氩气的手套箱中组装成2032模拟扣式电池.

为了考察材料的Li⁺脱/嵌行为, 在PAR273A电化学工作站上测试模拟电池的循环伏安曲线, 扫描电压区间为2.4 ~ 4.2 V, 扫速为0.1 mV/s.

1.4 材料表征

用XRD(飞利浦χ’pert pro MPD型X射线衍射仪)对材料的晶体结构和组成进行分析, 采用Cu Kα辐射源, 扫描速率为0.04°/min; 用TG-DTA (FRC/T-2型热分析仪, 北京光学仪器厂)分析电解产物中的结晶水含量, 空气气氛下由室温以10 ℃/min升至~850℃; 用SEM(JEOL JSM-5900LV)观察产物的形貌; 材料的氧化还原行为用上述循环伏安法测试. 用高频碳硫分析仪(CS-902, 北京万联达信科仪器有限公司)测试LiFePO₄/C产物的碳含量.

2 结果与讨论

2.1 磷铁的组分及电解过程分析

图1是磷铁原料的XRD图谱, 与标准图谱比较发现, 磷铁原料的衍射谱中只含有斜方晶系FeP (JPCDS78-1443)和六方晶系Fe₂P(JPCDS 01-1200)的峰, 没有其它杂相峰存在, 表明磷铁原料主要是由FeP和Fe₂P组成. ICP-AES分析表明Fe:P的原子比为3:2, 结合二者分析结果, 磷铁原料的组成为Fe_1.5P^{[ 6, 7]}. XRF 分析含有Ca、Si等微量杂质.

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	图1 磷铁原料的XRD图谱Fig. 1 XRD pattern of the Fe-P raw material

为了分析磷铁的电解过程, 获得最佳的电解工艺条件, 对磷铁在磷酸电解液中进行动电位极化曲线测试, 结果如图2所示. 根据PowerSuite自带软件模拟, 磷铁在磷酸水溶液中的腐蚀电位和腐蚀电流密度分别是-0.24 V和11.1 A/m²(由于磷铁为多孔材料, 实际面积在电解过程中难以获得, 这里的面积仅指磷铁暴露在电解液中的表观面积). 因此, 磷铁能够在磷酸水溶液中进行电解. 另外, 当电位 E>1.0 V时, 随着电压增大, 电流增加不明显, 说明高电位电解时能耗较高. 所以, 电解磷铁的工作电位不易大于1.0 V, 电流密度不易超过900 A/m², 文中采用11.1 A/m²电流密度对磷铁进行电解.

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	图2 磷铁在磷酸水溶液中的动电位极化曲线Fig. 2 Potentiodynamic polarization curves of the Fe_1.5P in H₃PO₄aqueous solution

磷铁Fe_1.5P可以看作FeP和Fe₂P的混合物, Fe的平均价态为+2价, P的价态为-3价, 电解时作为阳极失去电子, 总的阳极反应方程式为:

由于FeP和Fe₂P是固体, 根据Nernst方程计算平衡条件下的阳极电极电位 E_A为:

(1)

为标准电极电势, a为各离子的活度.

阴极为析氢反应:

平衡条件下的阴极电极电位 E_K为:

(2)

整个电解电池的电极电位差为:

(3)

根据电池反应的热力学方程, 电解电池的反应Gibbs自由能变Δ G为:

(4)

由此可见, Δ G与H⁺活度关系密切, 而活度与浓度成正比关系, 所以电解电池的Δ G随着电解液中H⁺活度的增大而降低, 从而使电解反应更容易进行, 降低电解过程中的能量消耗, 同时H₃PO₄为FePO₄补充磷源. 考虑到磷酸水溶液中电极材料的极化和补充磷源的量, 选用1.0 mol/L的磷酸水溶液为电解液.

2.2 磷铁的电解产物分析

电解产物焙烧前后的XRD图谱如图3所示, 从图3(a)可知, 没焙烧的电解产物没有明显的衍射峰, 可能是无定形或含有结晶水, 而经600℃空气中焙烧3 h后, 产物的衍射峰变得非常明显(图3(b)), 衍射峰位置与FePO₄ (JPCDS 29-0715)的标准图谱完全一致, 不含磷铁原料中FeP和Fe₂P的衍射峰, 说明磷铁电解后的产物经焙烧后转变为六方层状结构FePO₄.

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	图3 (a) 未焙烧, (b) 600℃空气中焙烧3 h电解产物的XRD图谱Fig. 3 XRD patterns of the electrolytic products (a) uncalcined and (b) calcined at 600℃ in air for 3 h

为了确认电解产物中是否含有结晶水, 对电解产物进行TG-DTA热分析, 结果如图4所示. 由图中曲线可以看出, 电解产物在100℃~200℃失重较多, 说明电解产物中含有结晶水. DTA曲线在127.6℃有一个明显的吸热峰, 表明电解产物中的结晶水开始失去. 因此, 127.6℃以下的失重主要来源于物理吸附水的脱去. 随着温度上升至450℃左右, TG曲线趋于稳定, 说明结晶水完全脱去. 在127.6~450℃之间的失重约为20.4%, 根据计算, 得出结晶水个数约为2.13. 结合上述XRD分析结果, 电解产物的化学式为FePO₄·2H₂O, 从而失重方程式可写为:

基于上述分析结果, 磷铁Fe_1.5P在H₃PO₄水溶液中的电解反应方程式为:

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	图4 电解产物的TG-DTA 曲线Fig. 4 TG-DTA curves of the electrolytic product

反应过程中, 只有磷铁和H₃PO₄水溶液消耗, 产物只有FePO₄·2H₂O和H₂, 容易分离, 而且大量H₂可以作为清洁能源富集利用.

2.3 由电解产物制备的LiFePO₄/C复合物及其性能分析

基于上述电解产物FePO₄·2H₂O, 添加LiOH·H₂O( n(Fe): n(P): n(Li)=1:1:1)和葡萄糖合成的LiFePO₄/C的XRD图谱如图5所示. 产物的衍射峰比较尖锐, 说明产物的晶型较好. 经碳硫分析仪测试产物的碳含量约为4.30wt%, 而XRD图中没有碳的明显特征峰, 说明产物中的碳可能以无定形形态存在^{[ 11]}.

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	图5 由电解产物合成的LiFePO₄/C的XRD图谱Fig. 5 XRD pattern of the as-synthesized LiFePO₄/C from the electrolytic product

通过JADE5.0软件分析, 衍射峰位置与LiFePO₄的标准图谱(JPCDS 40-1499)一致, 2 θ在17.1°、20.7°、25.5°、29.6°和35.5°处的主峰分别对应(020)、(011)、(111)、(121)和(131)面, 表明产物是纯相的橄榄石型LiFePO₄^{[ 7, 12, 13]}. 利用X射线衍射图的晶面指标计算出的晶胞参数为 a=0.6012 nm, b=1.0350 nm, c=0.4695 nm, 晶胞体积为 V=0.29213 nm³, 与标准样的0.6019 nm×1.0347 nm×0.4704 nm非常接近. 根据谢勒公式 ( D为晶粒尺寸(nm), λ为X光波长, β为衍射峰半高宽, θ为衍射角, k为Scherrer常数, 取值为0.89), 由上述5个强峰的半高宽计算得到的LiFePO₄/C产物的平均晶粒粒径为35.3 nm.

图6为合成的LiFePO₄/C复合材料的SEM照片, 产物有大量细小颗粒团聚而成, 粒子表面包覆着颜色较浅的絮状物, 可能是蔗糖分解的碳层, 与文献^{[ 14, 15, 16]}报道一致.

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	图6 合成的LiFePO₄/C复合材料的SEM 照片Fig. 6 SEM image of the as-synthesized LiFePO₄/C

2.4 LiFePO₄/C复合物的氧化还原行为

图7是制备的LiFePO₄/C复合物在0.1 mV/s时的循环伏安曲线, 曲线较平滑, 在3.54和3.33 V有一对明显的氧化峰和还原峰, 分别对应着LiFePO₄中锂离子的脱出和嵌入引起的氧化反应和还原反应, 与文献报道一致^{[ 7, 12, 13]}. 曲线中没有其它杂峰出现, 说明磷铁原料中的杂质元素经阳极袋电解后对LiFePO₄/C产物的氧化还原行为没有影响. 另外, LiFePO₄/C的氧化峰和还原峰的电位差值是0.21 V, 说明合成的LiFePO₄/C在锂离子脱嵌的过程中极化比较小.

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	图7 合成的LiFePO₄/C的循环伏安曲线Fig. 7 ββCyclic voltammogram of the as-synthesized LiFePO₄/C

3 结论

在1.0 mol/L磷酸水溶液中恒流无膜电解磷化工副产物磷铁Fe_1.5P废渣, 通过用氨水调节pH值制备了纯相FePO₄, 利用动电位极化方法探讨了电解过程机理, 磷酸的加入有利于降低电解过程的能耗并补充不足的磷, 采用阳极袋消除了磷铁中的杂质对产物的影响, 用TG-DTA分析了电解产物中的结晶水含量. 基于电解产物, 分别以LiOH·H₂O为锂源和葡萄糖为碳源, 采用流变相法成功合成了较好晶型的LiFePO₄/C复合物, XRD衍射峰与标准图谱接近, 晶胞参数为 a=0.6012 nm, b=1.0350 nm, c=0.4695 nm, 晶胞体积为 V=0.29213 nm³, 平均晶粒粒径为35.3 nm, 产物由大量细小颗粒团聚而成. 循环伏安分析结果表明其氧化电位和还原电位分别在3.54和3.33 V, 锂离子在脱/嵌过程中的极化较小.

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[6]	LI Xiu-Li, WANG Gui-Xin, YAN Kang-Ping, et al. Effect of ZnO modification on the electrochemical performance of Fe_{1. 5}P. Journal of Inorganic Materials, 2010, 25(8): 877-881. [本文引用:3] [JCR: 0.531] [CJCR: 1.106]
[7]	刘睿, 王贵欣, 闫康平, 等. 由黄磷副产物磷铁合成球形LiFePO₄. 合成化学, 2010, 18(5): 639-641. [本文引用:5]
[8]	Zhou W J, Bao S J, He B L, et al. Synthesis and electrochemical properties of LiAl_{0. 05}Mn_{1. 95}O₄ by the ultrasonic assisted rheological phase method. Electrochim. Acta, 2006, 51(22): 4701-4708. [本文引用:1] [JCR: 3.777]
[9]	Liu H, Feng Y, Wang K, et al. Synthesis and electrochemical properties of Li₄Ti₅O₁₂/C composite by the PVB rheological phase method. J. Phys. Chem. Solids, 2008, 69(8): 2037-2040. [本文引用:1] [JCR: 1.527]
[10]	XU Hui, ZHONG Hui. Structure and electrochemical properties of LiCo_{0. 3}Ni_{0. 7}O₂ prepared by the rheological phase and spray drying method. Journal of Inorganic Materials, 2004, 19(3): 497-502. [本文引用:1] [JCR: 0.531] [CJCR: 1.106]
[11]	Wang Gui-Xin, Yan Kang-Ping, Yu Zuo-Long, et al. Facile synthesis and high rate capability of Li₄Ti₅O₁₂/C composite materials with controllable carbon content. J. Appl. Electrochem. , 2010 , 40(4): 821-831. [本文引用:1] [JCR: 1.836]
[12]	XIE Hui, ZHOU Zhen-Tao. Synthesis and electrochemical performances of LiFePO₄/C composites by solid state reaction. Journal of Inorganic Materials, 2007, 22(4): 631-639. [本文引用:2] [JCR: 0.531] [CJCR: 1.106]
[13]	Cheol W K, Jong S P, Kyung S L, et al. Effect of Fe₂P on the electron conductivity and electrochemical performance of LiFePO₄ synthesized by mechanical alloying using Fe³+ raw material. J. Power Sources, 2006, 163(1): 144-150. [本文引用:2] [JCR: 4.675]
[14]	YANG Shu-Ting, LIU Yu-Xia, YIN Yan-Hong, et al. Effects of Mg ion doping on the electrochemical performances and structure of LiFePO₄/C. Journal of Inorganic Materials, 2007, 22(4): 627-631. [本文引用:1] [JCR: 0.531] [CJCR: 1.106]
[15]	CHEN Zhao-Hui, Dahn J R. Reducing carbon in LiFePO₄/C composite electrodes to maximize specific energy, volumetric energy, and tap density. J. Electrochem. Soc. , 2002, 149(9): A1184-A1189. [本文引用:1] [JCR: 2.588]
[16]	LU Jun-Biao, TANG Li-Long, ZHANG Zhong-Tai, et al. Preparation and electrochemical properties of high-performance LiFePO₄. Journal of Inorganic Materials, 2005, 20(3): 666-669. [本文引用:1] [JCR: 0.531] [CJCR: 1.106]

1997

2.588

0.0

J. Electrochem. Soc.. 1997, 144(4):1188-1190

Phospho-olivines as positive-electrode materials for rechargeable lithium batteries

Padhi A K , Nanjundaswamy K S , Goodenough J B

Reversible extraction of lithium from $\text{[math]}$ (triphylite) and insertion of lithium into $\text{[math]}$ at 3.5 V vs. lithium at 0.05 mA/cm² shows this material to be an excellent candidate for the cathode of a low‐power, rechargeable lithium battery that is inexpensive, nontoxic, and environmentally benign. Electrochemical extraction was limited to ∼0.6 Li/formula unit; but even with this restriction the specific capacity is 100 to 110 mAh/g. Complete extraction of lithium was performed chemically; it gave a new phase, $\text{[math]}$ , isostructural with heterosite, $\text{[math]}$ . The $\text{[math]}$ framework of the ordered olivine $\text{[math]}$ is retained with minor displacive adjustments. Nevertheless the insertion/extraction reaction proceeds via a two‐phase process, and a reversible loss in capacity with increasing current density appears to be associated with a diffusion‐limited transfer of lithium across the two‐phase interface. Electrochemical extraction of lithium from isostructural $\text{[math]}$ (M = Mn, Co, or Ni) with an $\text{[math]}$ electrolyte was not possible; but successful extraction of lithium from $\text{[math]}$ was accomplished with maximum oxidation of the $\text{[math]}$ occurring at x = 0.5. The $\text{[math]}$ couple was oxidized first at 3.5 V followed by oxidation of the $\text{[math]}$ couple at 4.1 V vs. lithium. The $\text{[math]}$ interactions appear to destabilize the $\text{[math]}$ level and stabilize the $\text{[math]}$ level so as to make the $\text{[math]}$ energy accessible.

... 橄榄石型LiFePO₄具有原料丰富、放电平台稳定、热稳定性好、安全性高、环境友好等优点^[1], 在电动车、动力工具和大规模能量存储等领域备受关注, 而低成本合成是推进其广泛应用的一个关键环节 ...

2002

2.588

0.0

J. Electrochem. Soc. 2002, 149(7):A886-A890

A new synthetic route for preparing LiFePO₄ with enhanced electrochemical performance

Prosini P P , Carew ska M , Scaccia S

Nanocrystalline LiFePO 4 was obtained by heating amorphous nanosized LiFePO 4 . The amorphous material was obtained by lithiation of FePO 4 synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH 4 ) 2 (SO 4 ) 2 ⋅6H 2 O and NH 4 H 2 PO 4, using hydrogen peroxide as the oxidizing agent. The materials were characterized by chemical analysis, thermogravimetric and differential thermal analysis, X-ray powder diffraction, and scanning electron microscopy. The Brunauer- Emmett-Teller method was used to evaluate the specific surface area. Nanocrystalline LiFePO 4 showed very good electrochemical performance delivering about the full theoretical capacity (170 Ah kg −1 ) when cycled at the C/10 rate. A capacity fade of about 0.25% per cycle affected the material upon cycling. © 2002 The Electrochemical Society. All rights reserved.

... 2002年Prosini等^[2]利用溶液共沉淀法制备出纳米FePO₄, 其与LiI反应合成了电化学性能良好的LiFePO₄ ...

2008

0.0

J. PowerSources. 2008, 184(2):574-577

LiFePO₄ with enhanced performance synthesized by a novel synthetic route

Zheng Jun-Chao , Li Xin-Hai , Wang Zhi-Xing

Pure LiFePO₄ was synthesized by heating an amorphous LiFePO₄. The amorphous LiFePO₄ obtained through lithiation of FePO₄·xH₂O by using oxalic acid as a novel reducing agent at room temperature. FePO₄·xH₂O was prepared through co-precipitation by employing FeSO₄·7H₂O and H₃PO₄ as raw materials. X-ray diffraction (XRD), scanning electron microscopy (SEM) observations showed that LiFePO₄ composites with fine particle sizes between 100 nm and 200 nm, and with homogenous sizes distribution. The electrochemical performance of LiFePO₄ powder synthesized at 500 °C were evaluated using coin cells by galvanostatic charge/discharge. The synthesized LiFePO₄ composites showed a high electrochemical capacity of 166 mAh g⁻¹ at the 0.1C rate, and possessed a favorable capacity cycling maintenance at the 0.1C, 0.2C, 0.5C and 1C rate.

... Li等以FeSO₄^[3]和FeSO₄废渣^[4]为铁源, 用碳热还原法合成了具有较好电化学性能的LiFePO₄ ...

2009

4.675

0.0

... Li等以FeSO₄^[3]和FeSO₄废渣^[4]为铁源, 用碳热还原法合成了具有较好电化学性能的LiFePO₄ ...

1990

0.0

... 磷铁是黄磷或钙镁磷肥生产过程中产量较多的一种副产物^[5], 价格低廉, 杂质种类和含量依矿物和反应工艺的不同而有所差别 ...

2010

0.531

1.106

Journal of Inorganic Materials. 2010, 25(8):877-881 DOI:10.3724/SP.J.1077.2010.00877

Effect of ZnO modification on the electrochemical performance of Fe_1.5P

(School of Chemical Engineering, Sichuan University, Chengdu 610065, China)

ZnO-modified Fe_1.5P powders were synthesized successfully via a rheological phase method. X-ray diffractometry (XRD) was utilized to analyze the composition. TEM was used to characterize the morphology. The effects of ZnO modification on the electrochemical performance of the Fe_1.5P were investigated using constant current charge/discharge method, cyclic voltammogram, and electrochemical impedance spectrograph (EIS). The experimental results show that ZnO modification can enhance the rate performance of Fe_1.5P. The first discharge capacity of the ZnO-modified Fe_1.5P is 837.5mAh/g, and 69.7% higher than that of the pristine Fe_1.5P. After 215 cycles, the discharge capacity of the Fe_1.5P at 12C rate is increased to 144.3%. Furthermore, ZnO modification improve 330% of the recovery discharge capability of the Fe_1.5P at 0.1C rate. In addition, in comparison with the pristine Fe_1.5P, ZnO modification reduce 87.9% of the SEIingd SEI film resistance R_SEI, 87% of the charge transfer resistance R_d, and 13.2% of the Warburg impedance W_b from the diffusion of lithium ions, while can improve 86.6% of the diffusion efficiency of lithium ions.

用流变相法制备了ZnO修饰Fe_1.5P电极材料, 用X射线衍射仪对产物进行成分分析, 用透射电镜表征形貌, 用恒流充放电法、循环伏安法和电化学阻抗谱法研究了ZnO修饰对Fe_1.5P电化学性能的影响. 实验结果表明: ZnO修饰能够提高Fe_1.5P的倍率特性, 使Fe_1.5P的首次放电容量提高~69.7％, 达到837.5 mAh/g, 经过215次循环后, 将Fe_1.5P在12 C倍率下的放电容量提高~144.3%, 而且将Fe_1.5P在0.1 C倍率下的恢复放电容量提高~330％; 另外, ZnO修饰Fe_1.5P的SEI膜阻抗R_SEI、电荷传递阻抗R_d和Li⁺扩散的Warburg阻抗Wb分别降低~87.9％、~87％和~13.2％, 将锂离子扩散系数提高~86.6%.

... 磷铁的密度较大, 纯度可以达到98%以上, 经处理后既可以用作锂电池负极材料^[6], 而且可以与锂盐和补充磷源经高温反应制备LiFePO₄^[7] ...

... 流变相法是将反应物调制成固体颗粒和液体物质分散均匀的流变相系后反应制备材料的一种简便方法, 固体微粒悬浮在溶剂中, 相接触充分, 表面利用率高^[6,7,8,9,10] ...

... 5P^[6,7] ...

2010

0.0

... 磷铁的密度较大, 纯度可以达到98%以上, 经处理后既可以用作锂电池负极材料^[6], 而且可以与锂盐和补充磷源经高温反应制备LiFePO₄^[7] ...

... 5P^[6,7] ...

... 处的主峰分别对应(020)、(011)、(111)、(121)和(131)面, 表明产物是纯相的橄榄石型LiFePO₄^[7,12,13] ...

... 33 V有一对明显的氧化峰和还原峰, 分别对应着LiFePO₄中锂离子的脱出和嵌入引起的氧化反应和还原反应, 与文献报道一致^[7,12,13] ...

2006

3.777

0.0

Electrochim. Acta. 2006, 51(22):4701-4708 DOI:10.1016/j.electacta.2006.01.011

Synthesis and electrochemical properties of LiAl_0.05Mn_1.95O₄ by the ultrasonic assisted rheological phase method

Abstract

Pure-phase and well-crystallized spinel LiAl_0.05Mn_1.95O₄ powders were successfully synthesized by a simple ultrasonic assisted rheological phase (UARP) method. The structure and morphology properties of this as-prepared powder compared with the pristine LiMn₂O₄ and LiAl_0.05Mn_1.95O₄ obtained from the solid-state reaction (SSR) method were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties focused on the LiAl_0.05Mn_1.95O₄ by this new method have also been investigated in detail. According to these tests results, it is obviously to see that the newly prepared sample delivers a relatively high initial discharge capacity of 111.6 mAh g⁻¹, presents excellent rate capability and reversibility, and shows good cycling stability with capacity retention of 90.6% after 70 cycles. Meanwhile, the electrochemical impedance spectroscopy (EIS) investigations were employed to study the electrochemical process of Li⁺ ions with the synthesized LiAl_0.05Mn_1.95O₄ electrode in detail.

2008

1.527

0.0

2004

0.531

1.106

Journal of Inorganic Materials. 2004, 19(3):497-502

Structure and electrochemical properties of LiCo_0.3Ni_0.7O₂ prepared by the rheological phase and spray drying method

1.Dept. of Material and Bio. Engineering of Chengdu University of Technology; Chengdu 610059; China; 2. LeiLi High-tech Development Co.; Ltd; Chengdu 610045; China

The cathode materials LiCo_0.3Ni_0.7O₂ were prepared from Co_0.3Ni_0.7(OH)₂
and LiOH·H₂O dispersed in the organic solution by the rheological phase and spray drying method in air at different sintering temperature for
16h. The TG-DTA analysis, XRD analysis, SEM and electrochemical tests were used to study the physical and the electrochemical performances
of the materials. The results indicate that molecular level completely mixing of the raw materials of samples made by our method makes the
sintering temperature drop to a lower temperature and the resulted sample has an excellent layered structure and the cation mixing and
nonstoichiometric products are effectively restrained when sintered at 700℃. The material(sintered at 700℃) cycled between 2.80～4.25V shows a high initial capacity of 172mAh/g with an efficiency of 90.8% and its irreversible capacity only 16mAh/g.
91% of the initial discharge capacity remains after 40 cycles.

以Co_0.3Ni_0.7(OH)₂和LiOH·H₂O为原料,在含羟基的有机溶剂水溶液中浸渍呈流变相,用喷雾干燥后于空气中在不同的温度下煅烧16h制备层状LiCo_0.3Ni_0.7O₂正极材料,用XRD、TG-DTA、SEM以及激光粒度测试等表征了材料的晶体结构与理化性能。结果表明,由本法可降低样品合成的反应温度和对反应气氛的严格要求,制备出的样品可有效抑制材料中阳离子混排及非化学计量产物的出现,大大降低材料的首次不可逆放电容量,提高材料的首次放电效率.经700℃煅烧16h合成出的样品首次放电容量达172mAh/g,首次放电效率可达90.8％,循环40次后容量仅衰减9％,显示出优良的电化学性能.

2010

1.836

0.0

J. Appl. Electrochem. 2010, 40(4):821-831 DOI:10.1007/s10800-009-0065-2

Facile synthesis and high rate capability of Li₄Ti₅O₁₂/C composite materials with controllable carbon content

1.Sichuan University School of Chemical Engineering 610065 Chengdu China 2.Chinese Academy of Sciences Chengdu Institute of Organic Chemistry 610041 Chengdu China

A modified ball-milling-assisted green solid reaction method is provided to prepare Li₄Ti₅O₁₂/C composite materials with controllable carbon content. Thermal analysis was utilized to investigate the reaction process and the temperature for eliminating carbon. The added carbon and the time for eliminating the carbon can affect the particle size and greatly improve the cycling stability and rate performance. Besides, the particle size can reach ~60 nm, the Li₄Ti₅O₁₂ eliminated carbon at 600 °C has ~178% higher discharge capacity than that without added carbon after 500 cycles under the same conditions. As for the Li₄Ti₅O₁₂ with a carbon weight of 10.6%, the second discharge capacity can reach 177.2 and 120.8 mAh g⁻¹ at 1 and 20 C rates, respectively. Its discharge capacity still remains at 118.3 mAh g⁻¹ after 500 cycles under various current rates. The results are comparable to those of the reported Li₄Ti₅O₁₂/PAS composite.

... 30wt%, 而XRD图中没有碳的明显特征峰, 说明产物中的碳可能以无定形形态存在^[11] ...

2007

0.531

1.106

Journal of Inorganic Materials. 2007, 22(4):631-639 DOI:10.3724/SP.J.1077.2007.00631

Synthesis and electrochemical performances of LiFePO₄/C composites by solid state reaction

1. Electrochemical and Biologic Department, Zhong Shan College, University of Electronic Science and Technology of China, Zhongshan 528402, China; 2. College of Material Science & Engineering, South China University of Technology, Guangzhou 510640, China

The LiFePO₄/C composite cathode materials for lithiumion batteries were synthesized by a solid state reduction method. The crystalline structure, morphology of particles, and electrochemical performance of the sample were investigated by -ray diffraction, scanning electron microscope, charge-discharge test and cyclic voltammetry. The results show that the composite synthesized at 700℃ has a simple pure olivetype phase with small particles, and uniformly distribution of gain sizes, and shows the best electrochemical performances with 1^st discharge specific capacity 150.3mAh/g and 20 th discharge specific capacity retention ratio 99.2% at 0.1C rate. It also shows good rate capability with 131.4mAh/g, 122.1mAh/g at the high rate of 1.0C and 2.0C, respectively. With the excellent characteristic to resist overcharge, this composite can retain its microstructure even after long time overcharge, but it is vulnerable to overdischarge.

以Fe₂O₃为铁源, 用环氧树脂对反应前驱体进行包覆, 通过固相还原法制备了LiFePO₄/C复合正极材料. 采用XRD、SEM、循环伏安以及充放电测试等方法对其晶体结构、表观形貌和电化学性能进行了研究. 研究结果表明, 煅烧温度对材料的电化学性能有较大影响, 在700℃煅烧所得产物为单一的橄榄石型晶体结构, 粒径分布较均匀, 且具有良好的电化学性能. 以0.1C倍率进行充放电, 其首次放电容量为150.3mAh/g, 充放电循环20周后, 容量保持率达99.2%; 以1.0、2.0C倍率进行充放电, 其首次放电容量分别为131.4和122.1mAh/g. 其在过充条件下的电性能也佳, 过充后还能继续放电, 但在过放电条件下, 其电性能迅速劣化.

... 处的主峰分别对应(020)、(011)、(111)、(121)和(131)面, 表明产物是纯相的橄榄石型LiFePO₄^[7,12,13] ...

... 33 V有一对明显的氧化峰和还原峰, 分别对应着LiFePO₄中锂离子的脱出和嵌入引起的氧化反应和还原反应, 与文献报道一致^[7,12,13] ...

2006

4.675

0.0

... 处的主峰分别对应(020)、(011)、(111)、(121)和(131)面, 表明产物是纯相的橄榄石型LiFePO₄^[7,12,13] ...

... 33 V有一对明显的氧化峰和还原峰, 分别对应着LiFePO₄中锂离子的脱出和嵌入引起的氧化反应和还原反应, 与文献报道一致^[7,12,13] ...

2007

0.531

1.106

Journal of Inorganic Materials. 2007, 22(4):627-631 DOI:10.3724/SP.J.1077.2007.00627

Effects of Mg ion doping on the electrochemical performances and structure of LiFePO₄/C

1. College of Chemistry and Environmental Science, Henna Normal University, Xinxiang 453007, China; 2. Research Institute of New Energy & Material Engineering of Henan Province, Xinxiang 453007, China; 3. Zhongke Science & Technology CO. Ltd, Xinxiang 453002, China

Stoichiometric Mg doped LiFePO₄/C cathode material was synthesized through a templatesolid state reaction in an inert atmosphere using magnesium lactate as dopant and part of carbon source. Effects of Mg²⁺ doping on the electrochemical and physical performances of the cathode materials were investigated. At 1/3C discharge rate, the secondly reversible specific capacity of the Mg-doped LiFePO₄/C is nearly 20mAh/g higher than that of the undoped one. After 20 cycles, the capacity of the former is 162.1mAh/g, 22mAh/g higher than that of the latter. Impedance R ct of the Mg-doped material is 120Ω, while that of the undoped material is 180Ω. The tap density of Mg-doped material is
also improved by 0.229g·cm^-3 compared with undoped material.

以乳酸镁做为Mg²⁺的掺杂源和部分的碳源, 在惰性氛围下用模板-固相合成法合成了掺Mg²⁺的LiFePO₄/C复合正极材料, 考察了Mg²⁺对于目标化合物电化学和物理性能的影响. 研究结果表明, 在C/3倍率下材料掺杂前后第二个循环的放电容量分别为140.5和159.9mAh/g, 循环20次后容量为140.4 和162.1mAh/g. 电化学交流阻抗表明, 掺杂后的材料阻抗R_ct从180Ω 减小到120Ω. 掺杂后振实密度比掺杂前提高了0.229g·cm^-3.

... 图6为合成的LiFePO₄/C复合材料的SEM照片, 产物有大量细小颗粒团聚而成, 粒子表面包覆着颜色较浅的絮状物, 可能是蔗糖分解的碳层, 与文献^[14,15,16]报道一致 ...

2002

2.588

0.0

2005

0.531

1.106

Journal of Inorganic Materials. 2005, 20(3):666-669

Preparation and electrochemical properties of high-performance LiFePO₄

Department of Materials Sciences and Engineering; State Key Laboratory of New Ceramics and Fine Processing; Tsinghua University; Beijing 100084; China

Carbon covered LiFePO₄ powders with the microstructure of submicro-particles aggregated 5.01wt% carbon content,
and the diameter of aggregated particle of 10μm were synthesized by solid state sintering processing. The capacity and cycle performance were studied
at the charge and discharge rate of C/10, C/5, C/2 and 1C. The results show that below the rate of C/2, the voltage platform and capacity is not sensitive to the rate.
When the rate is increased to 1C, the capacity is decreased and the voltage platform is increased in charge processing and decreased in discharge
processing. Along with the increasing of cycle number, the capacity is increased to its saturate value. After 30 cycles, the capacities are
131.7, 129.1, 123.5 and 114.4 mAh/g, respectively.

通过固相法合成了裂解碳包覆的具有亚微米球形颗粒团簇微结构的LiFePO₄粉体材料.材料中裂解碳百分含量为5.01%,一次颗粒粒径在200-600nm,团簇体粒径在10μm左右. 在0.1、0.2、0.5和1C的充放电速率下,研究了材料的比容量和循环稳定性的变化.当充放电速率<1C时,随着充放电速率的增大,材料的充放电平台和比容量并不随速率的增大而发生较大变化,当充放电速率≥1C时,材料的充放电电压平台迅速升高(充电)或降低(放电),比容量也有较大的降低;随着充放电次数的增加,材料的比容量有所增加,然后趋于稳定.在30 个循环后材料的放电比容量分别为:131.7、129.1、123.5和114.4mAh/g.