Department of Mechanical, Aerospace and Nuclear Engineering , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States.
Department of Mechanical and Industrial Engineering, Newark College of Engineering , New Jersey Institute of Technology (NJIT) , Newark , New Jersey 07102 , United States.
ACS Appl Mater Interfaces. 2018 Apr 25;10(16):13442-13451. doi: 10.1021/acsami.8b00258. Epub 2018 Apr 12.
High specific capacity anode materials such as silicon (Si) are increasingly being explored for next-generation, high performance lithium (Li)-ion batteries. In this context, Si films are advantageous compared to Si nanoparticle based anodes since in films the free volume between nanoparticles is eliminated, resulting in very high volumetric energy density. However, Si undergoes volume expansion (contraction) under lithiation (delithiation) of up to 300%. This large volume expansion leads to stress build-up at the interface between the Si film and the current collector, leading to delamination of Si from the surface of the current collector. To prevent this, adhesion promotors (such as chromium interlayers) are often used to strengthen the interface between the Si and the current collector. Here, we show that such approaches are in fact counter-productive and that far better electrochemical stability can be obtained by engineering a van der Waals "slippery" interface between the Si film and the current collector. This can be accomplished by simply coating the current collector surface with graphene sheets. For such an interface, the Si film slips with respect to the current collector under lithiation/delithiation, while retaining electrical contact with the current collector. Molecular dynamics simulations indicate (i) less stress build-up and (ii) less stress "cycling" on a van der Waals slippery substrate as opposed to a fixed interface. Electrochemical testing confirms more stable performance and much higher Coulombic efficiency for Si films deposited on graphene-coated nickel (i.e., slippery interface) as compared to conventional nickel current collectors.
高比容量的阳极材料，如硅（Si），越来越多地被用于下一代高性能锂离子（Li）电池。在这种情况下，与基于 Si 纳米颗粒的阳极相比，Si 薄膜具有优势，因为在薄膜中，纳米颗粒之间的自由体积被消除，从而产生了非常高的体积能量密度。然而，Si 在锂化（脱锂）过程中会经历高达 300%的体积膨胀（收缩）。这种大的体积膨胀会导致 Si 薄膜与集流体之间的界面处产生应力积累，从而导致 Si 从集流体表面分层。为了防止这种情况，通常使用附着力促进剂（如铬中间层）来增强 Si 和集流体之间的界面。在这里，我们表明，事实上，这种方法适得其反，通过在 Si 薄膜和集流体之间构建范德华“光滑”界面，可以获得更好的电化学稳定性。这可以通过简单地在集流体表面涂覆石墨烯片来实现。对于这种界面，在锂化/脱锂过程中，Si 薄膜相对于集流体滑动，同时保持与集流体的电接触。分子动力学模拟表明，与固定界面相比，范德华光滑衬底上的应力积累（i）更少，（ii）应力“循环”更少。电化学测试证实，与传统的镍集流体相比，沉积在石墨烯涂覆的镍（即光滑界面）上的 Si 薄膜具有更稳定的性能和更高的库仑效率。
