Strain-associated nanoscale fluctuating lithium transport within single-crystalline LiNi1/3Mn1/3Co1/3O2 cathode particles
Danwon Lee, Chihyun Nam, Juwon Kim, S. Y. Hwang, Bonho Koo, Hyejeong Hyun, Jinkyu Chung, Sungjae Seo, Munsoo Song, Jaejung Song, Myeongjun Kim, Daan Hein Alsem, Norman Salmon, Su Yong Lee, Yeonchoo Cho, Namdong Kim, David A. Shapiro, Jongwoo Lim
Abstract
Solid-state lithium diffusion dynamics are critical for the rate capability and longevity of Li-ion batteries. Conventionally, nanoscale lithium diffusion within individual battery particles has been simplified as being primarily driven by concentration gradients, despite the associated processes inducing local lattice expansion, contraction, and strain fields. Using operando scanning transmission soft X-ray microscopy with high spatial resolution and chemical sensitivity to track nanoscale intraparticle lithium transport, and post-cycling Bragg coherent diffraction X-ray imaging to directly reveal three-dimensional intraparticle strain fields, we uncover strain-associated lithium transport dynamics within single-crystalline LiNi1/3Mn1/3Co1/3O2 (scNMC) particles during cycling. Contrary to the expected thermodynamic solid-solution behavior of scNMC, our observations reveal near-uniform but fluctuating regions of lithium-dense and lithium-dilute areas during cycling. These fluctuations suggest that nanoscale lithium diffusion can proceed counter to concentration gradients. Additionally, we demonstrate that an increased presence of lithium-dilute regions near the surface enhances lithium surface insertion kinetics, emphasizing the importance of controlling surface lithium distribution to improve rate performance. Our study provides insights into nanoscale solid-state ion transport, with potential applications in batteries, solid-state fuel cells, and memristors. Lithium-ion batteries rely on lithium diffusion within particles, traditionally assumed to follow concentration gradients. Here, authors use X-ray microscopy to track lithium movement in single particles, discovering that lithium can move against concentration gradients due to strain effects.