Nguyen Julie A, Becker Abigayle, Kanhaiya Krishan, Heinz Hendrik, Weimer Alan W
Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States.
ACS Appl Mater Interfaces. 2024 Jan 10;16(1):1861-1875. doi: 10.1021/acsami.3c15080. Epub 2023 Dec 21.
Alumina surface coatings are commonly applied to layered oxide cathode particles for lithium-ion battery applications. Atomic layer deposition (ALD) is one such surface coating technique, and ultrathin alumina ALD films (<2 nm) are shown to improve the electrochemical performance of LiNiMnCoO materials, with groups hypothesizing that a beneficial Li-Al-O product is being formed during the alumina ALD process. However, the atomic structure of these films is still not well understood, and quantifying the interface of ultrathin (∼1 nm) ALD films is an arduous experimental task. Here, we perform molecular dynamics simulations of amorphous alumina films of varying thickness in contact with the (0001) LiCoO (LCO) surface to quantify the film nanostructure. We calculate elemental mass density profiles through the films and observe that the Li-Al-O interphase extends ∼2 nm from the LCO surface. Additionally, we observe layering of Al and O atoms at the LCO-film interface that extends for ∼1.5 nm. To access the short-range order of the amorphous film, we calculated the Al coordination numbers through the film. We find that while Al is the prevailing coordination environment, significant amounts of Al exist at the interface between the LiCoO surface and the film. Taken together, these principal findings point to a pseudomorphic Li-Al-O overlayer that approximates the underlying layered LiCoO lattice but does not exactly replicate it. Additionally, with sufficient thickness, the Li-Al-O film transitions to an amorphous alumina structure. We anticipate that our findings on the ALD-like, Li-Al-O film nanostructure can be applied to other layered LiNiMnCoO materials because of their shared crystal structure with LiCoO. This work provides insight into the nanostructure of amorphous ALD alumina films to help inform their use as protective coatings for Li-ion battery cathode active materials.
氧化铝表面涂层通常应用于用于锂离子电池的层状氧化物阴极颗粒。原子层沉积（ALD）就是这样一种表面涂层技术，超薄氧化铝ALD薄膜（<2纳米）被证明可以改善LiNiMnCoO材料的电化学性能，有研究团队推测在氧化铝ALD过程中会形成有益的Li-Al-O产物。然而，这些薄膜的原子结构仍未得到很好的理解，并且量化超薄（约1纳米）ALD薄膜的界面是一项艰巨的实验任务。在此，我们对与（0001）LiCoO（LCO）表面接触的不同厚度的非晶氧化铝薄膜进行分子动力学模拟，以量化薄膜的纳米结构。我们计算了穿过薄膜的元素质量密度分布，并观察到Li-Al-O界面相从LCO表面延伸约2纳米。此外，我们在LCO-薄膜界面处观察到Al和O原子的分层，其延伸约1.5纳米。为了探究非晶薄膜的短程有序性，我们计算了穿过薄膜的Al配位数。我们发现，虽然Al是主要的配位环境，但在LiCoO表面和薄膜之间的界面处存在大量的Al。综合这些主要发现表明，存在一种拟同形的Li-Al-O覆盖层，它近似于下面的层状LiCoO晶格，但并不完全复制它。此外，当厚度足够时，Li-Al-O薄膜会转变为非晶氧化铝结构。我们预计，由于我们关于类ALD的Li-Al-O薄膜纳米结构的发现与LiCoO具有共同的晶体结构，因此可以应用于其他层状LiNiMnCoO材料。这项工作为非晶ALD氧化铝薄膜的纳米结构提供了见解，有助于为其作为锂离子电池阴极活性材料的保护涂层的应用提供参考。
