AAC  >> Vol. 8 No. 4 (November 2018)

    煅烧温度对523型镍钴锰酸锂正极材料电化学性能的影响
    Effects of Calcination Temperature on Electrochemical Properties of 523-Type Lithium Nickel-Cobalt-Manganese Oxide as Positive Electrode Materials

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作者:  

王北平,邹忠利,黄 安,汪 青:北方民族大学材料科学与工程学院,宁夏 银川

关键词:
锂离子电池过渡金属氧化物煅烧温度电化学性能Lithium Ion Battery Transition Metal Oxides Calcination Temperature Electrochemical Property

摘要:

研究了煅烧温度对镍钴锰酸锂的物相和电化学性能的影响。利用液相共沉淀法 + 固相煅烧工艺制备了目标产物,并综合利用XRD、恒电流充放电技术及交流阻抗技术对材料物相和电化学性能进行了表征。结果表明,900℃下煅烧获得的产物层状结构发育完全,结晶度高,离子混排度低,首次放电比容量达到166.3 mAh∙g−1,2C下放电比容量为73.2 mAh∙g−1。900℃产物的电荷转移阻抗较小,提高了锂离子的扩散速度,有利于倍率充放电性能的改善。

The effect of calcination temperature on the phase and electrochemical properties of lithium nickel-cobalt-manganese oxide was studied. The target product was prepared by liquid phase co-precipitation and solid phase calcination, and the phase and electrochemical properties of the material were characterized by XRD, constant current charge-discharge technique and AC imped-ance technique. The results show that the product obtained by calcination at 900˚C has a well-developed layered structure, high crystallinity and low ionic mixing. The initial discharge capacity is up to 166.3 mAh∙g−1. The charge transfer impedance of the product is small, which im-proves the diffusion rate of lithium ion and improves charge/discharge rate.




1. 引言

锂离子电池具有高的工作电压和能量密度、长循环寿命等优点,广泛应用于电子产品、电动工具和电动汽车等领域,并逐渐扩展应用到电站储能领域。其正极材料是提高电池性能的重要因素。近年来,三元过渡金属氧化物LiNi1−x−yCoxMnyO2 (0 < x < 1,0 < y < 1)受到了越来越多的关注和研究 [1] [2] [3] 。与LiCoO2比较,三元过渡金属氧化物降低了材料成本,向商业化应用领域逐步拓展。但该类材料的高倍率充放电性能不如LiCoO2,限制了其在某些领域的应用。为提高此类材料的结构稳定性和电化学性能,研究人员从多方面进行了改进:1) 采用金属元素进行掺杂,如Zn、Nd和Nb等 [4] [5] [6] ;2) 采用包覆材料进行表面改性,如La2O3、Mn3(PO4)2和PEDOT等 [7] [8] [9] ;3) 构筑浓度梯度结构 [10] ;4) 形成固溶体 [11] ;5) 其他制备技术与工艺优化 [12] [13] ;6) 形貌控制 [14] [15] 。这些努力在提高材料结构稳定性和电化学性能方面取得了一定的成功。

本论文研究了镍钴锰酸锂LiNi0.5Co0.2Mn0.3O2制备过程中煅烧温度对物相和电化学性能的影响,综合利用XRD、恒电流充放电等测试技术对产物性能进行了表征。

2. 实验

采用硫酸镍、硫酸钴和硫酸锰按照摩尔比为0.5:0.2:0.3的比例,将上述试剂溶解于通有氮气的100 mL去离子水中,配置成2 mol/L的混合溶液。在60℃水浴条件下,逐滴加入氨水控制溶液PH值为11,再逐滴加入NaOH,快速搅拌反应6 h,再陈化反应8 h,洗涤至中性。在80℃真空烘箱中干燥10 h,得到氢氧化物前驱体。将该前驱体与碳酸锂充分混合后在马弗炉中于800℃、900℃煅烧10 h,得到目标产物。

粉末XRD测试在X Pert-Pro仪器上进行,2θ = 10˚~80˚,步速2˚/min。将产物、导电炭黑和聚偏氟乙烯(PVDF)按照质量比为85:10:5的比例混合均匀,加入适量的N-甲基吡咯烷酮(NMP),充分搅拌后得到均匀浆料,将其涂敷在铝箔后于80℃在真空烘箱中烘干10 h。之后切片,在充满氩气的手套箱中将电极片、Celgard 2400隔膜、金属锂片(对电极)组装成扣式电池,电解液为1M LiPF6的碳酸乙烯酯/碳酸二甲酯(体积比为1:1)的溶液。恒流充放电测试电压范围为2.5~4.3 V,在武汉蓝电电池测试仪进行。交流阻抗在电化学工作站(上海辰华CHI660E)上进行测试,其中电压扰幅5 mV,频率范围0.01~10 kHz。

3. 结果与讨论

3.1. 物相分析

图1是800℃和900℃下制备所得产物XRD谱图。800℃产物的(006)/(102)、(110)/(108)两对特征峰中未见明显分峰,表明产物的层状结构发育尚不完全。900℃的(006)/(102)、(110)/(108)两对特征峰分峰明显,形成了良好的层状结构。I(003)/I(104)强度比是离子混排度的一个重要指标,值越大,离子混排程度越低。经计算,800℃产物和900℃产物I (003)/I(104)强度比分别为0.9625和1.3112,这表明800℃产物存在较为严重的离子混排,而900℃产物的离子混排得到了有效控制。同时,900℃产物的峰型更加尖锐,结晶度更高。

Figure 1. XRD patterns of the products obtained at 800/900˚C

图1. 800℃和900℃煅烧所得产物的XRD谱图

3.2. 电化学性能

图2是800℃和900℃煅烧所得产物的首次充放电曲线。900℃产物首次充电比容量为160.5 mAh∙g−1,首次放电比容量为166.3 mAh∙g−1,库伦效率为103.6%,800℃产物的首次放电比容量为121.5 mAh∙g−1,库伦效率为97.1%。相对于800℃,900℃产物的首次放电比容量增加了27.0%。这主要由于900℃产物的离子混排度较低,为锂离子在晶格中占位提供了更多的活性位点。

Figure 2. The first charge/discharge curves of the products obtained at 800/900˚C

图2. 800℃和900℃煅烧所得产物的首次充放电曲线

图3是800℃和900℃煅烧所得产物的高倍率性能曲线。900℃产物在2C电流密度下放电比容量为73.2 mAh∙g−1,800℃产物在2C电流密度下放电比容量为60.2 mAh∙g−1。900℃下产物的高倍率充放电性能得到提高,这主要是由于900℃下产物的层状结构发育完全,结晶度高,离子混排度低,为锂离子在晶体内部的扩散提供了空间和通道,有利于高倍率充放电性能的改善。

Figure 3. High rate performance of the products obtained at 800/900˚C

图3. 800℃和900℃煅烧所得产物的倍率性能

图4是800℃和900℃煅烧所得产物的交流阻抗谱图。为进一步讨论煅烧温度对产物动力学性能的影响,对800℃和900℃的产物进行了交流阻抗测试。利用等效电路原理,模拟计算相应阻抗。其中Rs为溶液电阻,高频区半圆代表表面膜阻抗Rsf,对应着锂离子通过阴极颗粒界面迁移阻抗;中频区半圆代表电荷转移阻抗Rct,对应电极和电解液之间的电荷转移阻抗。低频区直线代表Warburg阻抗Zw,对应着锂离子在晶体中的扩散速度。900℃产物的Rsf和Rct为9.2 Ω和53.5 Ω,明显小于800℃产物的Rsf (58.3 Ω)、Rct (129.4 Ω)。这表明900℃下所得产物的锂离子扩散速度更快,从而提高材料的高倍率充放电性能。

Figure 4. EIS spectra of the products obtained at 800/900˚C

图4. 800℃和900℃煅烧所得产物的交流阻抗谱图

4. 结论

本文采用液相共沉淀 + 固相煅烧方法制备了523型镍钴锰酸锂,考察了煅烧温度对材料物相和电化学性能的影响。结果表明,900℃下煅烧获得的产物层状结构发育完全,结晶度高,离子混排度低,首次放电比容量达到166.3 mAh∙g−1,5C下放电比容量为73.2 mAh∙g−1。900℃产物的电荷转移阻抗较小,提高了锂离子的扩散速度,有利于倍率充放电性能的改善。

基金项目

中科院“西部之光”人才培养计划一般项目,宁夏自然科学基金项目(NZ17096)。

文章引用:
王北平, 邹忠利, 黄安, 汪青. 煅烧温度对523型镍钴锰酸锂正极材料电化学性能的影响[J]. 分析化学进展, 2018, 8(4): 198-203. https://doi.org/10.12677/AAC.2018.84024

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