Garcia Juan C, Bareño Javier, Chen Guoying, Croy Jason R, Iddir Hakim
Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA.
Phys Chem Chem Phys. 2020 Nov 14;22(42):24490-24497. doi: 10.1039/d0cp03942j. Epub 2020 Oct 22.
The composition, structure and phase transformations occurring on cathode surfaces greatly affect the performance of Li-ion batteries. Li-Ion diffusion and surface-electrolyte interaction are two major phenomena that impact the capacity and cell impedance. The effects of surface reconstruction (SR) of cathode materials on the performance of Li-ion batteries are of current interest. However, the origin and evolution of the SR are still not well understood. In this work, density functional theory (DFT) calculations are used to investigate the processes taking place during surface segregation and reconstruction. Facet dependent segregation was found in Li(NiMnCo)O (NMC) cathodes. Specifically, Co tends to segregate to the (104) surface of the primary particles within the transition metal layer, while Ni ions tend to segregate to the (012) surface in the Li layer, forming a SR. Experimental evidence shows the SR to be epitaxial with the bulk of the as-synthesized material, and the new SR phase is pinned to the NMC unit cell leading to a strained SR. Here, we show that strain can stabilize a spinel structure of the SR layers. Understanding the effects of surface strain opens a new avenue for the design of cathode materials with enhanced surface properties.
阴极表面发生的成分、结构和相变极大地影响锂离子电池的性能。锂离子扩散和表面-电解质相互作用是影响电池容量和内阻的两个主要现象。阴极材料的表面重构（SR）对锂离子电池性能的影响是当前研究的热点。然而，SR的起源和演变仍未得到很好的理解。在这项工作中，采用密度泛函理论（DFT）计算来研究表面偏析和重构过程中发生的情况。在Li（NiMnCo）O（NMC）阴极中发现了面依赖偏析。具体而言，Co倾向于在过渡金属层内偏析到一次颗粒的（104）表面，而Ni离子倾向于在Li层偏析到（012）表面，形成SR。实验证据表明，SR与合成材料的主体是外延的，并且新的SR相固定在NMC晶胞上，导致SR产生应变。在这里，我们表明应变可以稳定SR层的尖晶石结构。了解表面应变的影响为设计具有增强表面性能的阴极材料开辟了一条新途径。
