Synthesis and Characterization of the Lithium-Rich Core-Shell Cathodes with Low Irreversible Capacity and Mitigated Voltage Fade
Synthesis and Characterization of the Lithium-Rich Core-Shell Cathodes with Low Irreversible Capacity and Mitigated Voltage Fade
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DOI：
10.1021/acs.chemmater.5b00617
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发表时间：
2015-05-12
影响因子：
8.6
通讯作者：
Dahn, J. R.
中科院分区：
文献类型：
--
作者：
Li, Jing;Camardese, John;Dahn, J. R.
富锂层状Ni-Mn-Co氧化物材料在过去的十年中得到了广泛的研究。富Mn材料具有严重的电压衰减问题，并且富Ni材料具有差的热稳定性并且容易氧化有机碳酸盐电解质。核-壳（CS）策略使用富Ni材料作为核和富Mn材料作为壳，可以在混合系统中平衡这些材料的优点和缺点。本文介绍的富锂CS材料与仅核和仅壳样品相比显示出大大改善的整体电化学性能。能量色散光谱结果表明，与制备的氢氧化物前体相比，在900 ℃下烧结后，在核和壳相之间存在过渡金属的扩散。仍然保持富Mn壳，而仅在前体中的壳中的Co在整个颗粒中近似均匀。具有最佳锂含量的CS样品表现出低的不可逆容量（IRC），以及高容量和优异的容量保持率。样品CS2-3（0.67Li（1+x）中的第三个样品）（Ni0.67Mn0.33）（1-x）O-2中心点0.33Li（1+y）（Ni0.4Mn0.5Co0.1）（1-y）O-2 CS2系列）的可逆容量与218 mAh/g相似，为12.3%（类似于30 mAh/g）的不可逆容量（IRC）和在30 ° C下以类似于C/20的速率到4.6V的40次循环后98%的容量保持率。微分电容对电势（dQ/dV对V）分析证实CS样品的电池具有稳定的阻抗以及非常稳定的平均电压。显然，富Mn壳可以有效地保护富Ni核免于与电解质反应，同时富Ni核呈现高且稳定的平均电压。
Lithium-rich layered Ni-Mn-Co oxide materials have been intensely studied in the past decade. Mn-rich materials have serious voltage fade issues, and the Ni-rich materials have poor thermal stability and readily oxidize the organic carbonate electrolyte. Core-shell (CS) strategies that use Ni-rich material as the core and Mn-rich materials as the shell can balance the pros and cons of these materials in a hybrid system. The lithium-rich CS materials introduced here show much improved overall electrochemical performance compared to the core-only and shell-only samples. Energy dispersive spectroscopy results show that there was diffusion of transition metals between the core and shell phases after sintering at 900 degrees C compared to the prepared hydroxide precursors. A Mn-rich shell was still maintained whereas the Co which was only in the shell in the precursor was approximately homogeneous throughout the particles. The CS samples with optimal lithium content showed low irreversible capacity (IRC), as well as high capacity and excellent capacity retention. Sample CS2-3 (the third sample in the 0.67Li(1+x)(Ni0.67Mn0.33)(1-x)O-2 center dot 0.33Li(1+y)(Ni0.4Mn0.5Co0.1)(1-y)O-2 CS2 series) had a reversible capacity of similar to 218 mAh/g with 12.3% (similar to 30 mAh/g) irreversible capacity (IRC) and 98% capacity retention after 40 cycles to 4.6 V at 30 degrees C at a rate of similar to C/20. Differential capacity versus potential (dQ/dV versus V) analysis confirmed that cells of the CS samples had stable impedance as well as a very stable average voltage. Apparently, the Mn-rich shell can effectively protect the Ni-rich core from reactions with the electrolyte while the Ni-rich core renders a high and stable average voltage.