Advanced Batteries & Ceramics Laboratory (formerly, High Temperature and Energy Materials Laboratory), Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai400076, India.
Thick and Thin Films Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai400076, India.
ACS Appl Mater Interfaces. 2023 Jan 11;15(1):782-794. doi: 10.1021/acsami.2c15054. Epub 2023 Jan 3.
Ni-containing "layered"/cation-ordered LiTOs (T = transition metal) suffer from Ni-migration to the Li-layer at the unit cell level, concomitant transformation to a spinel/rock salt structure, hindrance toward Li-transport, and, thus, fading in Li-storage capacity during electrochemical cycling (i.e., repeated delithiation/lithiation), especially upon deep delithiation (i.e., going to high states-of-charge). Against this backdrop, our previously reported work [ 2021, 13, 25836-25849] revealed a new concept toward blocking the Ni-migration pathway by placing Zn (which lacks octahedral site preference) in the tetrahedral site of the Li-layer, which, otherwise, serves as an intermediate site for the Ni-migration to the Li-layer. This, nearly completely, suppressed the Ni-migration, despite being deep delithiated up to a potential of 4.7 V (vs Li/Li) and, thus, resulted in significant improvement in the high-voltage cyclic stability. In this regard, by way of conducting operando synchrotron X-ray diffraction, operando stress measurements, and 3D atom probe tomography, the present work throws deeper insights into the effects of such Zn-doping toward enhancing the structural-mechanical-compositional integrity of Li-NMCs upon being subjected to deep delithiation. These studies, as reported here, have provided direct lines of evidence toward notable suppression of the variations of lattice parameters of Li-NMCs, including complete prevention of the detrimental "-axis collapse" at high states-of-charges and concomitant slower-cum-lower electrode stress development, in the presence of the Zn-dopant. Furthermore, the Zn-dopant has been found to also prevent the formation of Ni-enriched regions at the nanoscaled levels in Li-NMCs (i.e., Li/Ni-segregation or "structural densification") even upon being subjected to 100 charge/discharge cycles involving deep delithiation (i.e., up to 4.7 V). Such detailed insights based on direct/real-time lines of evidence, which reveal important correlations between the suppression of Ni-migration and high-voltage compositional-structural-mechanical stability, hold immense significance toward the development of high capacity and stable "layered" Li-T-oxide based cathode materials for the next-generation Li-ion batteries.
含镍的“层状”/阳离子有序 LiTO（T 为过渡金属）在单元胞水平上会发生镍迁移到锂层的现象，同时伴随着尖晶石/岩盐结构的转变、锂离子传输受阻，以及电化学循环过程中（即反复脱锂/锂化），尤其是在深度脱锂（即达到高荷电状态）时，锂存储容量的衰减。针对这一背景，我们之前的研究工作[2021，13，25836-25849]提出了一个新概念，通过将（不具有八面体位置偏好的）锌置于锂层的四面体位置，可以阻止镍迁移途径，而锂层的四面体位置通常是镍迁移到锂层的中间位置。这几乎完全抑制了镍迁移，尽管深度脱锂至 4.7 V（相对于 Li/Li），从而显著提高了高压循环稳定性。在这方面，通过同步辐射 X 射线衍射、原位应力测量和 3D 原子探针断层扫描，本工作深入探讨了锌掺杂对深度脱锂时 Li-NMC 结构-力学-组成完整性的增强作用。正如这里所报道的，这些研究为抑制 Li-NMC 晶格参数的变化提供了直接的证据，包括在高荷电状态下完全防止有害的“c 轴坍塌”以及伴随而来的电极应力发展缓慢，在锌掺杂的情况下。此外，研究发现锌掺杂剂还可以防止在纳米尺度上形成富镍区域，即使在经历 100 次深度脱锂的充放电循环（即高达 4.7 V）时也是如此。这些基于直接/实时证据的详细见解，揭示了抑制镍迁移和高压组成-结构-力学稳定性之间的重要相关性，对于开发下一代锂离子电池用高容量和稳定的“层状”Li-T-氧化物正极材料具有重要意义。
