Sharma Ankur, Rajkamal A, Kobi Sushobhan, Kumar Bachu Sravan, Paidi Anil Kumar, Chatterjee Abhijit, Mukhopadhyay Amartya
Department of Chemical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India.
High Temperature and Energy Materials Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India.
ACS Appl Mater Interfaces. 2021 Jun 9;13(22):25836-25849. doi: 10.1021/acsami.1c01347. Epub 2021 May 24.
"Layered"/"cation-ordered"/O3-type Li-T-oxides (T: transition metal) suffer from structural instability due to "T migration" from the T layer to the Li layer upon Li removal (., "cation disordering"). This phenomenon gets exacerbated upon excessive Li removal, with Ni ions being particularly prone to migration. When used as cathode material in Li-ion batteries, the "T migration" and associated structural changes cause rapid impedance buildup and capacity fade, thus limiting the cell voltages to ≤4.3 V for stable operation and lowering the usable Li-storage capacity (concomitantly, energy density). Looking closely at the "T migration" pathway, one realizes that the tetrahedral site (-site) of the Li layer forms an intermediate site. Accordingly, the present work explores a new idea concerning suppression of "Ni migration" by "blocking" the intermediate crystallographic site (., the -site) with a dopant, which is the most stable at that site. In this regard, density functional theory (DFT)-based simulations indicate that the concerned -site is energetically the most preferred and stable site for Zn. Detailed analysis of crystallographic data (including bond valence sum) obtained with the as-prepared Zn-doped Li-NMC supports the same. Furthermore, the simulations also predict that Zn doping is likely to suppress "Ni migration" upon Li removal. Supporting these predictions, galvanostatic delithiation/lithiation studies with Zn-doped and undoped Li-NMCs demonstrate significantly improved cyclic stability, near-complete suppression of "cation mixing", and negligible buildup of impedance (as well as potential hysteresis) for the former, even upon being subjected to long-term cycling using a high upper cut-off potential of 4.7 V (vs Li/Li). Accordingly, such subtle tuning of the composition and structure, in the light of electronic configuration of the dopant and specific crystallographic site occupancy, is likely to pave the way toward the development of Ni-containing stable high voltage O3-type Li-T-oxide cathodes for the next-generation Li-ion batteries.
“层状”/“阳离子有序”/O3型锂-过渡金属氧化物（T：过渡金属）由于在脱锂过程中“T迁移”（即从T层迁移到Li层，也就是“阳离子无序化”）而存在结构不稳定性。这种现象在过度脱锂时会加剧，其中镍离子尤其容易迁移。当用作锂离子电池的阴极材料时，“T迁移”及相关的结构变化会导致快速的阻抗增加和容量衰减，从而将电池电压限制在≤4.3V以实现稳定运行，并降低可用的锂存储容量（相应地，能量密度）。仔细研究“T迁移”途径会发现，Li层的四面体位置（-位置）形成了一个中间位置。因此，本工作探索了一个新想法，即通过用一种在该位置最稳定的掺杂剂“阻塞”中间晶体学位置（即-位置）来抑制“镍迁移”。在这方面，基于密度泛函理论（DFT）的模拟表明，所关注的-位置在能量上是锌最优先且最稳定的位置。对所制备的锌掺杂锂镍锰钴氧化物获得的晶体学数据（包括键价和）进行的详细分析也支持了这一点。此外，模拟还预测锌掺杂可能会在脱锂时抑制“镍迁移”。对锌掺杂和未掺杂的锂镍锰钴氧化物进行的恒电流脱锂/锂化研究支持了这些预测，结果表明前者具有显著改善的循环稳定性、几乎完全抑制了“阳离子混合”，并且即使在使用4.7V（相对于Li/Li）的高上限截止电位进行长期循环时，阻抗（以及电位滞后）的增加也可忽略不计。因此，根据掺杂剂的电子构型和特定晶体学位置占据情况对组成和结构进行这种微妙的调整，可能会为下一代锂离子电池开发含镍稳定高压O3型锂-过渡金属氧化物阴极铺平道路。
