Li1.2Mn0.54Co0.13Ni0.13O2@V2O5核壳复合材料的制备及其电化学性能

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聂文波, 肖其昌, 王京亮, 雷钢铁, 肖启振, 李朝晖. Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料的制备及其电化学性能 . 无机材料学报, 2014, 29(3): 257-263
NIE Wen-Bo, XIAO Qi-Chang, WANG Jing-Liang, LEI Gang-Tie, XIAO Qi-Zhen, LI Zhao-Hui. Preparation of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ Core-shell Composite and Its Electrochemical Properties . Journal of Inorganic Materials, 2014, 29(3): 257-263 复制到剪切板

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Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料的制备及其电化学性能

聂文波, 肖其昌, 王京亮, 雷钢铁, 肖启振, 李朝晖

湘潭大学化学学院, 环境友好化学与应用教育部重点实验室, 湘潭411105

李朝晖, 教授. E-mail:lzh69@xtu.edu.cn

聂文波(1986-), 男, 硕士研究生. E-mail:363478547@qq.com

基金:国家自然科学基金 (21174119) National Natural Science Foundation of China (21174119)

摘要

采用溶胶-凝胶技术在富锂锰基固溶体Li_1.2Mn_0.54Co_0.13Ni_0.13O₂表面包覆V₂O₅, 制备了Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料。通过扫描电镜(SEM)和透射电镜(TEM)观察其形貌, X射线衍射(XRD)分析确定其结构。结果显示, 结晶态的V₂O₅均匀包覆在类球形Li_1.2Mn_0.54Co_0.13Ni_0.13O₂颗粒表面, Li_1.2Mn_0.54Co_0.13Ni_0.13O₂材料的晶体结构在包覆前后保持不变。X射线光电子能谱(XPS)分析结果表明, 该核壳复合材料首次充电时, 锂离子嵌入V₂O₅包覆层。电化学测试结果表明, 表面包覆15%V₂O₅的核壳复合材料具有最佳的电化学性能: 0.1C倍率下放电比容量为276 mAh/g, 首次充放电库仑效率达到94%, 50次循环后容量保持率达89%。

关键词: 富锂锰基固溶体; 表面包覆; 核壳结构; 库仑效率; 锂离子电池

中图分类号:TQ174 文献标志码:A 文章编号:1000-324X(2014)03-0257-07

Preparation of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ Core-shell Composite and Its Electrochemical Properties

NIE Wen-Bo, XIAO Qi-Chang, WANG Jing-Liang, LEI Gang-Tie, XIAO Qi-Zhen, LI Zhao-Hui

Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan 411105, China

Abstract

Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell composite was prepared by coating V₂O₅ on the surface of the lithium-rich manganese-based solid solution Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ particles through Sol-Gel technology. Its morphology was observed by using scanning electronic microscope (SEM) and transition electronic microscope (TEM) while the crystal structure was calculated from the results of the X-ray diffraction (XRD). It is found that the quasi spherical core-shell composite is coated homogeneously with the crystalline V₂O₅ nanoparticles. The crystal structure of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂core is maintained after the surface coating. XPS spectra suggest that Li⁺ ions intercalate the crystal structure of the V₂O₅ shell during the first charge. The electrochemical measurements show that the core-shell composite being coated with 15% V₂O₅ could deliver an initial capacity of 276 mAh/g at the rate of 0.1C accompamied by a coulombic efficiency of 94%. It can remain 89% of the initial capacity after 50 charge/discharge cycles.

Keyword: Li-rich manganese-based solid solution; surface coating; core-shell structure; coulombic efficiency; lithium-ion battery

Show Figures

近年来, 电动汽车一直是国家科技部大力支持的重大科技项目。作为电动汽车的核心部件, 动力电池起着至关重要的作用。锂离子电池具有高能量密度、长寿命、环境友好等优点, 已经成为现阶段电动汽车的首选电源。其中, 锂离子电池的负极材料, 如工业化的石墨, 开发中的硅、合金以及金属氧化物等都具有非常高的比容量; 而正极材料LiCoO₂、LiNi_1/3Co_1/3Mn_1/3O₂、LiMn₂O₄和LiFePO₄等比容量均不超过200 mAh/g。因此, 人们必须大力开发具有更高能量密度的新型正极材料, 以提高电池的能量密度, 并降低电池成本^{[ 1]}。

富锂锰基固溶体 xLi₂MnO₃·(1- x)LiMO₂(M为Co、Ni、Mn、Fe、Cr等元素中的一种或几种)具有工作电压高(>3 V)、比容量高(~300 mAh/g)等优点, 被认为是动力锂离子电池的下一代正极材料, 成为近十年的研究热点^{[ 2, 3, 4]}。但是, 它在首次充电至4.5 V时, 伴随Li₂O从晶格中脱出, 而产生较大的不可逆容量损失, 导致首次充放电库仑效率低^{[ 5, 6]}。为了解决此问题, 人们开展了大量的研究工作, 包括表面包覆^{[ 7, 8, 9, 10, 11, 12, 13, 14]}、预处理^{[ 15, 16, 17]}、少量稀土元素掺杂^{[ 18]}以及与锂受体型正极材料共混复合^{[ 19, 20, 21]}。其中, 在富锂锰基固溶体表面包覆锂受体型正极材料, 容纳首次充电时脱出的、不可回嵌的大量锂离子, 从而降低首次充放电过程中的不可逆容量损失, 是一种有效的方法。

尽管已有文献报道, 富锂锰基固溶体与V₂O₅复合可以改善其首次充放电库仑效率^{[ 19]}, 但是文献[19]中无定形V₂O₅未均匀包覆在固溶体颗粒表面, 且无定形V₂O₅的嵌-脱锂可逆性差, 导致其循环性能不佳。另外, 关于表面包覆结晶态V₂O₅改善富锂锰基固溶体的首次充放电库仑效率和循环性能的工作鲜有报道。本工作在Li_1.2Mn_0.54Co_0.13Ni_0.13O₂(0.5Li₂MnO₃·0.5LiNi_1/3Co_1/3Mn_1/3O₂)电极材料表面包覆结晶态V₂O₅纳米层, 合成核壳复合材料。通过循环伏安测试、交流阻抗测试和恒流充放电测试, 研究核壳复合材料中V₂O₅对首次充放电库仑效率和循环性能的影响。

1 实验方法

1.1 试剂

醋酸锰、醋酸钴、醋酸镍和醋酸锂均从上海国药集团购买, 柠檬酸和草酸从广东汕头西陇化工厂购买, 偏钒酸铵从湘中精细化学品厂购买, 所有试剂均为分析纯。

1.2 分析与测试

采用场发射扫描电镜(FESEM, Hitachi S-4800)和高分辨分析透射电子显微镜(TEM, Jeol JEM-2010)观察颗粒形貌, 加速电压分别为15 kV和200 kV。采用多晶粉末高级衍射仪(Bruker D8)对材料进行物相分析, 以 Cu K_α为辐射源(λ=0.15406 nm), 工作电压和工作电流分别为45 kV和50 mA。X射线光电子能谱(XPS, Perkin Elmer PHI 5000C ESCA), 单色Al K_α (1486.6 eV)光源, 以C1s (284.6 eV)为标准。循环伏安测试在EG&G 273电化学分析系统上进行, 首次扫描起始电位均为模拟电解池的开路电压, 在2.0~4.8 V区间以0.2 mV/s的速度扫描。恒流充放电测试在Arbin 2000电池测试仪上进行, 电流密度为30 mA/g。

1.3 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料的制备

采用溶胶-凝胶法合成Li_1.2Mn_0.54Co_0.13Ni_0.13O₂^{[ 22]}。首先, 按化学式的摩尔计量比分别称取醋酸锰、醋酸钴和醋酸镍溶于适量去离子水中。然后, 在80℃恒温水浴中, 不断搅拌下缓慢滴加醋酸锂和柠檬酸的混合溶液(醋酸锂的质量稍过量化学式计算量的5%, 柠檬酸用量为所有金属离子摩尔数的10%), 滴加完后用氨水调节混合溶液的pH为7.0~8.0, 置于80℃恒温箱中凝胶。升温至100℃干燥后, 在450℃空气气氛中预烧10 h, 研磨压片后再在空气气氛中900℃煅烧10 h, 快速冷却至室温得到Li_1.2Mn_0.54Co_0.13Ni_0.13O₂粉末。然后, 在去离子水中, 加入相当于水质量10%的Li_1.2Mn_0.54Co_0.13Ni_0.13O₂粉末, 超声搅拌2 h。再按比例加入NH₄VO₃并溶解, 按文献[23]的方法制备V₂O₅溶胶, 100℃恒温干燥。最后, 得到的混合物经400℃空气煅烧4 h, 研磨过筛(25 μm), 得到Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料粉末。其中, 表面包覆0、5%、10%、15%和20% V₂O₅的核壳复合材料样品分别记为LMS0、LMS1、LMS2、LMS3和LMS4。

按前述包覆层的合成方法制备纯V₂O₅电极材料。

1.4 研究电极的制备和电池组装

将核壳复合电极材料与乙炔黑、PVDF按质量比80:10:10混合, 加入适量N-甲基吡咯烷酮(NMP), 搅拌, 调制成均匀浆料, 均匀涂布于铝箔上, 120℃真空干燥过夜, 冲裁成φ12 mm的电极圆片。在手套箱中, 将制作的电极片、Celgard 2300多孔膜和锂片组装成CR 2016型扣式电池, 电池中滴加高压电解液(LBC326, 深圳新宙邦公司)。

2 结果与讨论

2.1 XRD分析

图1为样品LMS0、LMS3及V₂O₅的XRD图谱, 由图可知, 未包覆样品Li_1.2Mn_0.54Co_0.13Ni_0.13O₂(LMS0)中, 衍射峰2 θ=18.8°、36.9°、37.8°、38.5°、44.7°、48.8°、58.8°、64.3°、65.4°和68.7°分别对应(003)、(101)、(006)、(012)、(104)、(015)、(107)、(018)、(110)和(113)晶面。这些特征衍射峰表明, 此材料属于六方晶系、R m空间点群, 具有典型的α-NaFeO₂层状岩盐结构^{[ 22]}。位于20.1°和21.7°的微弱衍射峰对应(020)和(110)晶面, 表明Li₂MnO₃组分中Li与Mn按1:2的比例交替排列形成的一种超晶格有序排列, 归属于单斜晶系、C2/m点群^{[ 24]}。图1中(003)与(104)衍射峰强度的比值( I₍₀₀₃₎/ I₍₁₀₄₎)为1.30, (006)/(012)和(018)/(110)两组衍射峰分裂明显, 说明制备的Li_1.2Mn_0.54Co_0.13Ni_0.13O₂具有良好的层状结构。在其表面包覆V₂O₅后, 属于富锂锰基固溶体结构的所有特征衍射峰的位置基本不变, 表明经过400℃热处理后, 复合材料中富锂锰基固溶体的晶体结构保持不变。根据高温煅烧的V₂O₅的XRD特征衍射峰^{[ 23]}, 从图1可以看出V₂O₅属于斜方相、Pmmn空间点群 (JCPDS 41-1426), 在复合材料中, 其(110)晶面对应的衍射峰(26.1°)消失, (200)晶面对应的衍射峰15.2°负移至13.9°。由布拉格方程2 d·sin θ= λ, 可以计算出(200)晶面的层间距由0.29 nm增大到0.32 nm。消失的特征衍射峰表明, V₂O₅在富锂锰基固溶体表面结晶生长时, 某些晶面的生长受到抑制, 图中用*标注的XRD衍射峰仍可归属于V₂O₅。

2.2 形貌分析

图2为Li_1.2Mn_0.54Co_0.13Ni_0.13O₂材料和Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料(LMS3)的SEM照片, 图3为核壳复合材料LMS3的TEM照片及其EDX分析结果。图2(a)显示, 未包覆的Li_1.2Mn_0.54Co_0.13Ni_0.13O₂材料表面光滑, 颗粒为类球形, 粒径尺寸为100~300 nm, 有一定程度的团聚现象。包覆V₂O₅后的样品颗粒表面变得粗糙(图2(b))。V₂O₅溶胶经煅烧处理后, 生成粒径为10~20 nm的纳米颗粒(图3(b)), 沉积在富锂锰基固溶体颗粒表面, 形成均匀的约50 nm厚的包覆层(图3a)。包覆层不是非常均匀和致密, 一些裸露点引起富锂锰基固溶体与电解质溶液的接触, 这可能不利于核壳复合材料的循环性能, 但是包覆层疏松又有利于锂离子在电极材料表面的迁移。图3(c)为表面包覆层中V₂O₅晶粒的HRTEM照片, 可以看到其层间距约为0.32 nm。图3(d)为选定区域的EDX分析谱图, 结果显示表面包覆层为钒的氧化物。图中C、Al、Si和P元素可能来自透射电镜制样过程中引入的杂质。

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	图 1 V₂O₅、Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料(LMS3)和Li_1.2Mn_0.54Co_0.13Ni_0.13O₂(LMS0)的XRD图谱Fig. 1 XRD patterns of V₂O₅, Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell composite (LMS3) and Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ (LMS0)

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	图2 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂(a)和Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料(b)的SEM照片Fig. 2 SEM images of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂(a) and Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell composite

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	图 3 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料TEM照片(a, b), 包覆层中V₂O₅的HRTEM照片(c)及其EDX图谱(d)Fig. 3 TEM images of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell composite (a, b), HRTEM image of the V₂O₅ in the shell (c) and its EDX spectrum (d)

2.3 XPS分析

图4为LMS3样品未充电(a)和首次充电至4.8 V后(b)的V2p_2/3XPS图谱及其充放电前后的XRD图谱(c)。由图4可知, 未充电样品中位于517.6和516.4 eV的V2p_3/2能带信号峰分别对应于V⁵⁺ 2p_3/2和V⁴⁺ 2p_3/2^{[ 25]}, 前者的积分面积远大于后者, 表明充电前V₂O₅包覆层的V元素主要为+5价。充电至4.8 V后, V₂O₅包覆层的V⁵⁺ 2p_3/2和V⁴⁺ 2p_3/2信号峰的位置基本不变, 但是V⁴⁺ 2p_3/2信号峰的积分面积明显增大, 表明V₂O₅包覆层发生了电化学反应: V₂O₅ + xLi⁺ + xe^- → Li _xV₂O₅, 从而引起部分V元素价态的降低, 导致充电后核壳复合材料包覆层中+4价V元素的相对含量增加。由图4(c)可知, 样品首次充电至4.8V后, 16.5°、24.7°、50.5°和60.3°出现较明显的衍射峰(*标注), 可能是Li _xV₂O₅的XRD衍射峰^{[ 26, 27, 28]}, x的数值大小还有待进一步研究, 该工作正在进行中。

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	图4 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料(LMS3)未充电(a)和首次充电至4.8 V后(b)的V2p_2/3 XPS图谱, 及其首次充电至4.8 V后XRD图谱(c)Fig. 4 XPS spectra of V2p_2/3 in the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅core-shell composite (LMS3) before (a) and after (b) charged to 4.8 V in the first cycle, and their XRD patterns

2.4 电化学性能

图5为不同V₂O₅表面包覆量的Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料在2.0~4.8 V范围(a, b, c)和V₂O₅样品在2.0~4.5 V范围(d)的循环伏安曲线图。由图5可知, 随着V₂O₅包覆量的增加, 富锂锰基固溶体材料首次循环中两个特征氧化峰发生

较明显的变化。其中, 未包覆样品在第一次循环中, 于4.3 V和4.7 V出现两个氧化峰(图5a), 第二、三次循环中变化为4.0 V一个氧化峰。表面包覆5%的V₂O₅后, 样品位于4.7 V的氧化峰消失, 只有4.6 V一个氧化峰, 随后变化为4.2 V一个氧化峰(图5b)。随V₂O₅的表面包覆量增加至15%, 样品在首次循环中于4.4 V出现一个弱氧化肩峰, 随后基本消失(图5c)。此外, 由图5(d)可知, V₂O₅有多对氧化还原峰, 随着循环次数的增加, 峰形基本不变, 峰积分面积衰减程度低, 表明合成的V₂O₅有较好的循环性能。这些氧化还原峰在复合材料中均有所体现, 且随着循环次数的增加, 峰的形状保持, 峰的积分面积衰减程度也较低(图5c)。结果说明, 在核壳复合材料首次充电时, V₂O₅被嵌入Li⁺离子, 生成具有电化学活性的Li _xV₂O₅; 在复合材料首次放电时, Li _xV₂O₅脱出Li⁺离子, 补充富锂锰基固溶体首次放电的容量损失。因此, 首次循环中, 未包覆样品的氧化峰积分面积明显大于其还原峰积分面积; 而包覆15% V₂O₅的样品的还原峰积分面积与氧化峰积分面积相差无几。

图6为室温下、不同V₂O₅表面包覆量的Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料30 mA/g电流密度的首次充放电曲线, 其中插图为样品LMS3局部电压范围的放电曲线。由图6可知, 所有样品首次充电至4.5 V时, 充电曲线出现明显的电压平台。随着V₂O₅包覆量的增加, 样品的充电曲线中4.5 V电压平台缩短, 低于4.0 V范围的充电电压降低。这可能是由于充电时少量锂离子嵌入V₂O₅层间, 部分电子被消耗, 生成了具有电化学活性的Li _xV₂O₅。因此, 核壳复合材料的首次充电容量随着V₂O₅包覆量的增加而降低。由于首次充电时, 核壳复合材料(LMS3)中的V₂O₅已经被嵌入锂离子, 所以其首次放电曲线在3.25、2.57和2.25 V出现电压平台, 相当于Li _xV₂O₅的放电平台^{[ 23]}。

所有样品的首次充放电参数见表1, 由表中数据可知, 随着V₂O₅包覆量的增大, 核壳复合材料的充电容量逐渐降低, 而放电容量逐渐增高, 不可逆容量损失从未包覆样品的95 mAh/g逐渐减小到20%包覆样品的-1 mAh/g, 不可逆容量损失几乎为零, 库仑效率接近100%。核壳复合材料的不可逆容量损失降低的原因可能有以下两个方面: 一方面, V₂O₅作为主体材料能接受富锂锰基固溶体首次充电时脱出的Li₂O; 另一方面, V₂O₅作为一种电化学活性物质, 单独作为电极材料在4.0~2.0 V电压区间放电时, 具有约300 mAh/g的容量^{[ 23]}。因此, 表面包覆20%的V₂O₅后, Li_1.2Mn_0.54Co_0.13Ni_0.13O₂首次放电时的不可逆容量损失几乎为零, 同时放电容量还能保持为279 mAh/g。

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	图 5 样品LMS0(a)、LMS1(b)、LMS3(c)和V₂O₅(d)的循环伏安曲线Fig. 5 Cyclic voltammograms of the samples LMS0 (a), LMS1 (b), LMS3 (c) and V₂O₅ (d)

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	图6 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料的首次充放电曲线Fig. 6 First charge/discharge profiles of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell compositesInset is local discharge curves of sample LMS3

在室温下, 以30 mA/g的电流密度充放电, Li_1.2-Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料和V₂O₅的循环性能如图7所示。由图7可知, 随着循环次数的增加, 未包覆V₂O₅样品的容量衰减比包覆样品的快。50次循环后, 纯Li_1.2Mn_0.54Co_0.13Ni_0.13O₂材料放电容量为187 mAh/g, 容量保持率约72%; 表面包覆5%、10%、15%和20 % V₂O₅的核壳复合材料的放电容量分别为214、224、245和235 mAh/g, 对应的容量保持率分别为80%、82%、89%和85%。由于V₂O₅均匀包覆在固溶体颗粒表面, 该包覆层可以有效地阻碍富锂锰基固溶体颗粒与电解质溶液的直接接触, 从而降低其在循环过程中因Jahn-Teller效应生成的Mn²⁺的溶解速度^{[ 8, 12, 14, 29]}; 此外, 实验制备Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料时, V₂O₅包覆层经

表1 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料的首次充放电参数过高温处理具有较高的结晶度, 因此, 所得的核壳复合材料具有优越的循环性能。 Table 1 First discharge/charge parameters of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell composites in the first cycle

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	图 7 Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料及V₂O₅的循环性能Fig. 7 Cycling performances of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅ core-shell composites and V₂O₅

图8为未包覆样品LMS0 (a)和包覆样品LMS3(b)充电至4.5 V后, 循环20次前后的交流阻抗谱的Nyquist曲线图。由图8可知, 曲线由一个变形的半圆和一条直线组成, 前者与电荷转移阻抗 R_ct有关, 后者则与锂离子在电极固相的扩散过程有关。半圆的左端点对应的实阻抗 Z_re数值为模拟电解池(即CR2016纽扣电池)的欧姆电阻 R_s, 右端点对应的实阻抗数值涉及电荷转移阻抗 R_ct, 拟合的等效电路见图8(a), 由等效电路得到的阻抗参数列于表2中。分析表2数据可知, 循环20次后, 包覆样品的电荷转移阻抗明显低于未包覆样品。结果表明, 在循环过程中, 由于表面包覆层隔离了富锂固溶体电极材料和电解质溶液, 避免电解质溶液成分在电极材料表面生成钝化膜, 从而降低了电极材料表面生成SEI (sold electrolyte interface)膜的厚度。同时, 电极中原有微孔结构的变化小, 保证了锂离子的顺利扩散^{[ 14, 30]}。

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	图8 未包覆样品LMS0 (a)和包覆样品LMS3(b)在循环20次前后的Nyquist曲线Fig. 8 Nyquist curves of the pristine (a) and the core-shell samples (b) before and after 20 cycles

表2 等效电路的阻抗参数 Table 2 Impedance parameters of the equipment circuit

3 结论

在Li_1.2Mn_0.54Co_0.13Ni_0.13O₂材料表面成功地包覆了晶态V₂O₅, 制备了Li_1.2Mn_0.54Co_0.13Ni_0.13O₂@V₂O₅核壳复合材料。

1) 包覆V₂O₅后, 富锂锰基固溶体材料的晶体结构未发生改变, 所得核壳复合材料首次充电时, 锂离子嵌入V₂O₅包覆层, 放电时嵌锂V₂O₅放出容量, 弥补LiO₂脱出固溶体晶格引起的不可逆容量损失, 提高了首次充放电的库仑效率。

2) 包覆15% V₂O₅的核壳复合材料0.1C倍率的首次充放电库仑效率达到94%, 放电比容量为276 mAh/g, 50次循环后容量保持率达89%, 循环性能最好。

因此, 在Li_1.2Mn_0.54Co_0.13Ni_0.13O₂材料表面包覆晶态V₂O₅, 不仅可以提高首次充放电库仑效率, 而且能改善循环性能, 是一种值得深入研究的改性方法。

参考文献

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2012

0.817

0.752

Science in China(Series B). 2012, 42(8):1252 - 1262 DOI:10.1360/032012-382

Advance of lithium ion batteries: The 16th International Meeting on Lithium Batteries

锂离子电池及材料发展前瞻——第16届国际锂电会议评述

ZHANG JianBo⁵, LIANG Fan², GAO XuePing³, LI JianGang⁴, FAN LiZhen², HE XiangMing^1,5*

张剑波^⑤, 连芳^②, 高学平^③, 李建刚^④, 范丽珍^②, 何向明^①⑤*

1 Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing100084, China ;
2 School of Material Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China ;
3 Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071, China ;
4 School of Chemical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, China;
5 The State Key Laboratory of Automotive Safety and Energy, Beijing 100084, China

The International Meeting on Lithium Batteries (IMLB), which are held every two years, promotes international collaboration and cooperation and provides a forum for scientists and engineers to discuss fundamentals, innovations and applications in the field of lithium ion batteries. Meanwhile the meeting provides an opportunity for exchanging new ideas and latest results and sharing inspirations. Advance of lithium ion batteries reported in the 16th International Meeting on Lithium Batteries (The IMLB-16, Jeju, Korea, June 17 to 22, 2012) is summarized in this paper. Lithium-rich manganese-based materials, lithium titanate material, 5V spinel materials and nano-silicon anode materials become new hotspots for research. The improvement of silicon anode material and the polymer electrolyte are key areas to further improve safety and energy density of lithium-ion batteries. The lithium-sulfur batteries, lithium-air batteries and super capacitors are research areas of increasing importance.

每两年举行一次的国际锂电会议(IMLB)旨在促进国际合作和交流, 为在锂离子电池领域工作的科学家和工程师提供一个讨论锂电基础研究和技术革新的论坛. 本文总结了2012年6月17~22日在韩国济州岛召开的第16届国际锂电会议的学术报告情况. 具有较好安全性的磷酸铁锂正极材料和具有较高倍率特性和较好循环性能的纳米电极材料依然是研究热点; 同时可以看到, 富锂锰基材料、钛酸锂材料、5V尖晶石材料和纳米硅负极材料成为新的研究热点; 而锂硫电池、锂空气电池和超级电容器等新电池体系正在引起大家的兴趣和关注.

... 因此, 人们必须大力开发具有更高能量密度的新型正极材料, 以提高电池的能量密度, 并降低电池成本^[1] ...

2013

0.531

1.106

... (1-x)LiMO₂(M为Co、Ni、Mn、Fe、Cr等元素中的一种或几种)具有工作电压高(>3 V)、比容量高(~300 mAh/g)等优点, 被认为是动力锂离子电池的下一代正极材料, 成为近十年的研究热点^[2,3,4] ...

2012

0.869

1.044

Acta Physico-Chimica Sinica. 2012, 28(4):823 - 830 DOI:10.3866/PKU.WHXB201202102

Preparation and Characterization of xLi₂MnO₃·(1-x)Li[Ni_1/3Mn_1/3Co_1/3]O₂ Cathode Materials for Lithium-Ion Batteries

锂离子电池正极材料xLi₂MnO₃·(1-x)Li[Ni_1/3Mn_1/3Co_1/3]O₂的制备及表征

WANG Zhao, WU Feng, SU Yue-Feng, BAO Li-Ying, CHEN Lai, LI Ning, CHEN Shi

王昭, 吴锋, 苏岳锋, 包丽颖, 陈来, 李宁, 陈实

National Development Center of Hi-Tech Green Materials, School of Chemical Engineering & Environment, Beijing Institute of Technology, Beijing 100081, P. R. China

The lithium rich cathode materials xLi₂MnO₃·(1-x)Li[Ni_1/3Mn_1/3Co_1/3]O₂ (x=0.4, 0.5, 0.6) were successfully synthesized via sol-gel method with calcination in air. The transition metal acetate, lithium acetate, and citric acid were used as raw materials. The as-prepared materials were characterized by X-ray diffraction (XRD), scaning electron microscopy (SEM), and electrochemical tests. The material 0.5Li₂MnO₃·0.5LiNi_1/3Mn_1/3Co_1/3]O₂, which was obtained after calcination at 900 °C for 12 h, exhibited fine microstructures and good electrochemical performance. When cycled at 2.0-4.8 V with a current density of 20 mA·g^-1 at room temperature, 0.5Li₂MnO₃·0.5LiNi_1/3Mn_1/3Co_1/3]O₂ delivered a initial discharge specific capacity of 260.0 mAh·g^-1, and maintained a capacity of 244.7 mAh·g^-1 after 40 cycles (capacity retention 94.12%).

以过渡金属乙酸盐和乙酸锂为原料, 柠檬酸为螯合剂, 通过溶胶-凝胶法结合高温煅烧法制备了锂离子电池富锂锰基正极材料xLi₂MnO₃·(1-x)Li[Ni_1/3Mn_1/3Co_1/3]O₂, 采用X射线衍射(XRD), 扫描电子显微镜(SEM)和电化学性能测试对所得样品的结构, 形貌及电化学性能进行了表征. 结果表明: x=0.5时, 在900 °C下煅烧12 h得到颗粒均匀细小的层状xLi₂MnO₃·(1-x)Li[Ni_1/3Mn_1/3Co_1/3]O₂材料, 并具有良好的电化学性能, 在室温下以20mA·g^-1的电流密度充放电, 2.0-4.8 V电位范围内首次放电比容量高达260.0 mAh·g^-1, 循环40次后放电比容量为244.7 mAh·g^-1, 容量保持率为94.12%.

2007

5.968

0.0

2011

0.67

0.95

Progress in Chemistry. 2011, 23(10):2038 - 2044

Li-Rich Layer-Structured Cathode Materials for Li-Ion Batteries

锂离子电池用富锂层状正极材料

Wu Chengren^1,2, Zhao Changchun^1*, Wang Zhaoxiang^2*, Chen Liquan²

吴承仁^1,2, 赵长春^1*, 王兆翔^2*, 陈立泉²

1. School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China;
2. Laboratory for Solid State Ionics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

Electrode materials are important building blocks of lithium ion batteries. The capacity of the anode material is usually more than 300 mAh/g while that of the cathode is still around 150 mAh/g. The capacity of the cathode materials has become a bottleneck to the improvement of the electrochemical performances of lithium ion battery. Li-rich layer-structured Li_1+xA_1-xO₂ (A = Mn, Ni, Co, Ti, Zr, etc.) cathode materials caught the attention of the scientists in the past decade due to high reversible capacity (200 mAh/g or more). These materials can also be written as xLi₂MO₃·(1-x)LiM'O₂(M = Mn, Ti, Zr; M' = Mn, Ni, Co; 0≤x≤1). In this review, we introduce the synthesis methods, structure and the charge-discharge mechanism of this type of materials. More attention will be paid to the improvement to their electrochemical properties by surface (coating) and bulk (doping) modification. At the end of this review, the problems and prospects of the research on these cathode materials are commented.

Contents
1 Introduction
2 Structure of Li-rich layer-structured cathode materials
3 Synthesis of Li-rich layer-structured cathode materials
4 Charge-discharge mechanism
5 Surface and structural modification
5.1 Surface modification
5.2 Acidic treatment
5.3 Fluorine doping
5.4 Pre-cycling treatment
6 Prospects

正极材料与负极材料是锂离子电池重要组成部分。目前锂离子电池负极材料比容量通常在300mAh/g以上,而正极材料比容量始终徘徊在150mAh/g。正极材料正在成为锂离子电池性能进一步提升的瓶颈。富锂层状正极材料是一类新型正极材料,其可逆容量在200mAh/g以上,其高容量特性引起人们的广泛关注。这类材料可以用xLi₂MO₃·(1-x)LiM'O₂(M 为Mn, Ti, Zr之一或任意组合; M'为Mn, Ni, Co之一或任意组合; 0≤x≤1)形式表示。由于其组成与结构的特殊性,这类富锂层状正极材料的充放电机理也不同于其它含锂过渡金属氧化物正极材料。本文介绍富锂层状正极材料的合成、结构与充放电机理,重点介绍近年来通过改性提高其电化学性能方面的研究进展,指出目前富锂材料研究中存在的问题,探讨未来的研究重点。

... 5 V时, 伴随Li₂O从晶格中脱出, 而产生较大的不可逆容量损失, 导致首次充放电库仑效率低^[5,6] ...

2012

0.0

0.95

Chinese Science Bulletin. 2012, 57(10):794 - 804 DOI:10.1360/972011-610

Review of manganese-based solid solution xLi[Li_1/3Mn_2/3]O₂·(1-x)LiMO₂

锂离子电池正极材料富锂锰基固溶体的研究进展

DU Ke, HU GuoRong

杜柯, 胡国荣

School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China

Lithium-enriched manganese-based solid solution xLi[Li_1/3Mn_2/3]O₂&·(1-x)LiMO₂ is a new cathode material for lithium ion batteries. Its reversible discharge specific capacity is higher than 250 mAh/g, which is about twice that of present applied cathode materials. This material is a potential electrode material for next generation lithium ion batteries with high energy density. However, its other electrochemical properties such as power character, low temperature performance and safety at high end-of voltage do not satisfy the needs of batteries for application in electric or hybrid electric vehicles. Much research on xLi[Li_1/3Mn_2/3]O₂·(1-x)LiMO₂ has been published, which has been reviewed in this paper as three parts: reaction mechanism, synthesis and improvement of performance. In addition to research results, the use of xLi[Li_1/3Mn_2/3]O₂&·(1-x)LiMO₂ in industry is briefly described. Directions for future research are also suggested.

富锂锰基固溶体xLi[Li_1/3Mn_2/3]O₂·(1-x)LiMO₂ 具有超过目前所用正极材料1 倍的高比容量, 是很有潜力的下一代锂离子电池用正极材料, 但是其他电化学性能, 特别是功率特性尚不能满足应用要求. 从机理研究、合成工艺和性能改进3 方面综述了富锂锰基固溶体型锂离子电池正极材料xLi[Li_1/3Mn_2/3]O₂·(1-x)LiMO₂ 的研究现状, 提出了下一步的研究思路和方向.

... 5 V时, 伴随Li₂O从晶格中脱出, 而产生较大的不可逆容量损失, 导致首次充放电库仑效率低^[5,6] ...

2011

0.0

... 为了解决此问题, 人们开展了大量的研究工作, 包括表面包覆^{[7,8,9,10,11,12,13,14]}、预处理^[15,16,17]、少量稀土元素掺杂^[18]以及与锂受体型正极材料共混复合^[19,20,21] ...

2013

3.777

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... 由于V₂O₅均匀包覆在固溶体颗粒表面, 该包覆层可以有效地阻碍富锂锰基固溶体颗粒与电解质溶液的直接接触, 从而降低其在循环过程中因Jahn-Teller效应生成的Mn²⁺的溶解速度^[8,12,14,29] ...

2012

5.968

0.0

2013

4.675

0.0

2012

5.968

0.0

2013

4.675

0.0

2013

0.0

2013

4.675

0.0

... 同时, 电极中原有微孔结构的变化小, 保证了锂离子的顺利扩散^[14,30] ...

2012

5.968

0.0

2013

4.675

0.0

2012

0.72

0.914

Chinese Journal of Inorganic Chemistry. 2012, 28(5):983 - 988.

Modification of Li[Li_0.2Ni_0.2Mn_0.6]O₂ as Cathode Material for Rechargeable Lithium Batteries by Acid-Leaching

锂离子电池正极材料Li[Li_0.2Ni_0.2Mn_0.6]O₂的酸浸改性研究

HUANG XIA, YANG FEI, HU GUO-RONG, et al. Modification of Li[Li_0.2Ni_0.2Mn_0.6]O₂ as cathode material for rechargeable lithium batteries by acid-leaching. Chinese Journal of Inorganic Chemistry, 2012, 28(5): 983-988.

杜　柯, 黄　霞, 杨　菲, 胡国荣, 彭忠东

In order to improve the initial discharge efficiency of Li[Li_0.2Ni_0.2Mn_0.6]O₂ as cathode material for rechargeable lithium batteries, Li[Li_0.2Ni_0.2Mn_0.6]O₂ synthesized by a solid state method was preconditioned in acids. The product was characterized by XRD and SEM. It is found that the first discharge efficiency of Li[Li_0.2Ni_0.2Mn_0.6]O₂ after acid treatment had been greatly improved, but the mid-voltage sharply decreased. The treatment with 0.5 mol·L^-1 HNO₃ for 5 h was the best result, the efficiency reached 86.7%, meanwhile, the discharge capacity reached maximum faster than before. The reason of acid leaching modification was attributed to the appearance of the spinel structure Li₄Mn₅O₁₂ phase with rich lithium.

为提高锂离子电池正极材料Li[Li_0.2Ni_0.2Mn_0.6]O₂的首次充放电效率，对固相法合成的该材料进行了酸浸的改性研究。通过X射线衍射(XRD)、扫描电子显微镜(SEM)对所得样品的结构、形貌进行了表征。结果表明，Li[Li_0.2Ni_0.2Mn_0.6]O₂经过酸处理后，首次放电效率得到了较大的提高，但是放电中值电压明显下降。其中，0.5 mol·L^-1的硝酸浸泡5 h的效果最佳，首次放电效率达到了86.7%，同时放电容量达到最大值的循环次数大大减少。酸浸改性的原因被归结于材料表面出现了富锂尖晶石结构Li₄Mn₅O₁₂相。

2012

3.777

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2009

4.425

0.0

Electrochemistry Communications. 2009, 11(1):84 - 86 DOI:10.1016/j.elecom.2008.10.036

High capacity Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–V₂O₅ composite cathodes with low irreversible capacity loss for lithium ion batteries

GAO J, KIM J, MANTHIRAM A. High capacity Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-V₂O₅ composite cathodes with low irreversible capacity loss for lithium ion batteries. Electrochem. Commun., 2009, 11(1): 84-86.

Abstract

With an aim to suppress the huge irreversible capacity loss encountered in high capacity layered oxide solid solutions between Li₂MnO₃ and LiMO₂ (M = Mn, Ni, and Co), layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–V₂O₅ composite cathodes with various V₂O₅ contents have been investigated. The irreversible capacity loss decreases from 68 mAh/g at 100% Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ to 0 mAh/g around 89 wt.% Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–11 wt.% V₂O₅ as the lithium-free V₂O₅ serves as an insertion host to accommodate the lithium ions that could not be inserted back into the layered lattice after the first charge. The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–V₂O₅ composite cathodes with about 10–12 wt.% V₂O₅ exhibit an attractive discharge capacity of close to 300 mAh/g with little irreversible capacity loss and good cyclability.

... 尽管已有文献报道, 富锂锰基固溶体与V₂O₅复合可以改善其首次充放电库仑效率^[19], 但是文献[19]中无定形V₂O₅未均匀包覆在固溶体颗粒表面, 且无定形V₂O₅的嵌-脱锂可逆性差, 导致其循环性能不佳 ...

2011

2.588

0.0

2009

4.675

0.0

2012

0.0

... 13O₂^[22] ...

... -NaFeO₂层状岩盐结构^[22] ...

2013

3.777

0.0

... 根据高温煅烧的V₂O₅的XRD特征衍射峰^[23], 从图1可以看出V₂O₅属于斜方相、Pmmn空间点群 (JCPDS 41-1426), 在复合材料中, 其(110)晶面对应的衍射峰(26 ...

... 25 V出现电压平台, 相当于Li_xV₂O₅的放电平台^[23] ...

... 0 V电压区间放电时, 具有约300 mAh/g的容量^[23] ...

2008

8.238

0.0

... 的微弱衍射峰对应(020)和(110)晶面, 表明Li₂MnO₃组分中Li与Mn按1:2的比例交替排列形成的一种超晶格有序排列, 归属于单斜晶系、C2/m点群^[24] ...

2006

1.22

0.0

... 4 eV的V2p_3/2能带信号峰分别对应于V⁵⁺ 2p_3/2和V⁴⁺ 2p_3/2^[25], 前者的积分面积远大于后者, 表明充电前V₂O₅包覆层的V元素主要为+5价 ...

0.0

... 出现较明显的衍射峰(*标注), 可能是Li_xV₂O₅的XRD衍射峰^[26,27,28], x的数值大小还有待进一步研究, 该工作正在进行中 ...

2010

4.425

0.0

Electrochemistry Communications. 2010, 12(9):1154 - 1157 DOI:10.1016/j.elecom.2010.05.045

Li_xV₂O₅ nanobelts for high capacity lithium-ion battery cathodes

SEMENENKO D A, ITKIS D M, POMERANTSEVA E A, et al. Li_xV₂O₅ nanobelts for high capacity lithium-ion battery cathodes. Electrochem. Commun., 2010, 12(9): 1154-1157.

Abstract

5–10 μm long, typically 200–300 nm wide, and several nanometers thick Li_xV₂O₅ (× ∼ 0.8) nanobelts with the δ-type crystal structure were synthesized by a hydrothermal treatment of Li⁺-exchanged V₂O₅ gel. When dried at 200 °C under vacuum prior to electrochemical testing, the as-prepared nanobelts underwent the well-known δ → ε → γ-phase transition giving a mixture of ε and γ phases as a nanocomposite electrode material. Such a simple preparation procedure guarantees a yield of material with drastically enhanced initial discharge specific capacity of 490 mAh/g and great cyclability. The enhanced electrochemical performance is attributed to the complex of experimental procedures including post-synthesis treatment of the single-crystalline Li_xV₂O₅ nanobelts.

... 出现较明显的衍射峰(*标注), 可能是Li_xV₂O₅的XRD衍射峰^[26,27,28], x的数值大小还有待进一步研究, 该工作正在进行中 ...

1997

2.046

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... 出现较明显的衍射峰(*标注), 可能是Li_xV₂O₅的XRD衍射峰^[26,27,28], x的数值大小还有待进一步研究, 该工作正在进行中 ...

2013

0.0

2010

4.425

0.0

Electrochemistry Communications. 2010, 12(6):750 - 753 DOI:10.1016/j.elecom.2010.03.024

Carbon-coated high capacity layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ cathodes

Liu J, Wang Q Y, Reeja-Jayan B, et al. Carbon-coated high capacity layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ cathodes. Electrochem. Commun., 2010, 12(6): 750-753.

Abstract

Electrodes fabricated with the layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ have been coated with carbon by a thermal evaporation process and characterized. The carbon coating enhances the sample surface conductivity by 40% without degrading the layered oxide. The carbon-coated cathodes exhibit much improved rate capability and cycling performance than the bare cathode. Electrochemical impedance spectroscopy (EIS) data reveal that the improved electrochemical performances of the carbon-coated sample are due to the suppression of the solid-electrolyte interfacial (SEI) layer and faster kinetics of both the lithium-ion diffusion through surface layer and the charge transfer reaction.

... 同时, 电极中原有微孔结构的变化小, 保证了锂离子的顺利扩散^[14,30] ...