The truth about the 1st cycle Coulombic efficiency of LiNi1/3Co1/3Mn1/3O2 (NCM) cathodes
The truth about the 1st cycle Coulombic efficiency of LiNi1/3Co1/3Mn1/3O2 (NCM) cathodes
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DOI：
10.1039/c5cp07718d
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发表时间：
2016-02-07
影响因子：
3.3
通讯作者：
Winter, M.
中科院分区：
文献类型：
--
作者：
Kasnatscheew, J.;Evertz, M.;Winter, M.
在NCM/Li半电池中，对LiNi1/3Co1/3Mn1/3O2(NCM)在4.6V对Li/Li+的第一循环库仑效率(CE)进行了广泛的研究。可以证明，所观察到的总比容量损失的大部分(总计36.3 mA h g(-1))是可逆的，并且是由动力学限制引起的，即放电过程中的受阻锂化反应。通过在放电截止电位处采取恒定电位(Cp)的措施，使锂离子电池的放电容量提高了22.1 mA·h·g(-1)。通过电感耦合等离子体发射光谱仪测定NCM中Li+的含量，可以证明CP步骤中的这种容量增加是一种再硫化过程。此外，比容量损失约为。4.2 mAh·g(-1)可确定为室温下与NCM正极材料的本征反应。总体而言，不到10.0 Ma h g(-1)(占总容量损失的28%)可以归因于不可逆反应，主要是NCM的不可逆结构变化。因此，寄生反应，如氧化电解液分解，对不可逆容量的影响可以忽略不计，也可以用在线MS证明。因此，到目前为止，提取Li+的量(“Li+萃取率‘)的确定是不正确的，必须用电荷容量(=脱硫量)除以理论容量来计算。在NCM/石墨全电池中，由于石墨中不可逆的Li+损失，在恒压(CV)步骤中的可靠量比半电池中的小。
The 1st cycle Coulombic efficiency (CE) of LiNi1/3Co1/3Mn1/3O2 (NCM) at 4.6 V vs. Li/Li+ has been extensively investigated in NCM/Li half cells. It could be proven that the major part of the observed overall specific capacity loss (in total 36.3 mA h g(-1)) is reversible and induced by kinetic limitations, namely an impeded lithiation reaction during discharge. A measure facilitating the lithiation reaction, i.e. a constant potential (CP) step at the discharge cut-off potential, results in an increase in specific discharge capacity of 22.1 mA h g(-1). This capacity increase during the CP step could be proven as a relithiation process by Li+ content determination in NCM via an ICP-OES measurement. In addition, a specific capacity loss of approx. 4.2 mA h g(-1) could be determined as an intrinsic reaction to the NCM cathode material at room temperature (RT). In total, less than 10.0 mA h g(-1) (=28% of the overall capacity loss) can be attributed to irreversible reactions, mainly to irreversible structural changes of NCM. Thus, the impact of parasitic reactions, such as oxidative electrolyte decomposition, on the irreversible capacity is negligible and could also be proven by on-line MS. As a consequence, the determination of the amount of extracted Li+ ("Li+ extraction ratio'') so far has been incorrect and must be calculated by the charge capacity (=delithiation amount) divided by the theoretical capacity. In a NCM/graphite full cell the relithiation amount during the constant voltage (CV) step is smaller than in the half cell, due to irreversible Li+ loss at graphite.