Department of Nano Technology and Advanced Materials Engineering & Sejong Battery Institute, Sejong University, Gunja-dong, Gwangjin-gu, Seoul, 05006, South Korea.
Department of Chemistry and Bioengineering, Iwate University, Ueda 4-3-5, Morioka, Iwate, 020-8551, Japan.
Small. 2021 Nov;17(47):e2104532. doi: 10.1002/smll.202104532. Epub 2021 Oct 22.
Since Ni-rich cathode material is very sensitive to moisture and easily forms residual lithium compounds that degrade cell performance, it is very important to pay attention to the selection of the surface modifying media. Accordingly, hydroxyapatite (Ca (PO ) (OH)), a tooth-derived material showing excellent mechanical and thermodynamic stabilities, is selected. To verify the availability of hydroxyapatite as a surface protection material, lithium-doped hydroxyapatite, Ca Li (PO ) (OH), is formed with ≈10-nm layer after reacting with residual lithium compounds on Li[Ni Co Al ]O , which spontaneously results in dramatic reduction of surface lithium residues to 2879 ppm from 22364 ppm. The Ca Li (PO ) (OH)-modified Li[Ni Co Al ]O electrode provides ultra-long term cycling stability, enabling 1000 cycles retaining 66.3% of its initial capacity. Also, morphological degradations such as micro-cracking or amorphization of surface are significantly suppressed by the presence of Ca Li (PO ) (OH) layer on the Li[Ni Co Al ]O , of which the Ca Li (PO ) (OH) is transformed to CaF via Ca Li (PO ) F during the long term cycles reacting with HF in electrolyte. In addition, the authors' density function theory (DFT) results explain the reason of instability of NCA and why CaF layers can delay the micro-cracking during electrochemical reaction. Therefore, the stable Ca Li (PO ) F and CaF layers play a pivotal role to protect the Li[Ni Co Al ]O with ultra-long cycling stability.
由于富镍阴极材料对水分非常敏感，并且容易形成降解电池性能的残留锂化合物，因此非常注重表面修饰介质的选择。因此，选择了羟磷灰石（Ca（PO4）（OH）），一种表现出优异的机械和热力学稳定性的牙齿衍生材料。为了验证羟磷灰石作为表面保护材料的可用性，用≈10-nm 层的 Li 掺杂羟磷灰石 CaLi（PO4）（OH）与 Li[NiCoAl]O 上的残留锂化合物反应，这导致表面锂残留量从 22364ppm 急剧降低到 2879ppm。经 CaLi（PO4）（OH）修饰的 Li[NiCoAl]O 电极具有超长的循环稳定性，可在 1000 次循环中保留其初始容量的 66.3%。此外，在 CaLi（PO4）（OH）层的存在下，Li[NiCoAl]O 的表面微裂纹或非晶化等形态降解得到了显著抑制，其中 CaLi（PO4）（OH）在与电解质中的 HF 反应期间转化为 CaF。此外，作者的密度泛函理论（DFT）结果解释了 NCA 不稳定的原因以及为什么 CaF 层可以在电化学反应过程中延迟微裂纹。因此，稳定的 CaLi（PO4）F 和 CaF 层在保护具有超长循环稳定性的 Li[NiCoAl]O 方面发挥着关键作用。
