Understanding the dynamics of lithium diffusion within solid-state electrodes is pivotal for advancing high-performance batteries. Conventionally, lithium diffusion within solid-solution battery particles has been assumed to be solely driven in the direction of minimizing the concentration gradient, resulting in a monotonous lithium distribution. However, employing operando scanning transmission X-ray microscopy, this study has revealed the presence of non-monotonous dense and dilute concentration domains of lithium within individual single-crystalline LiNi 1/3 Mn 1/3 Co 1/3 O 2 particles at the nanoscale during charging and discharging processes. Our findings advocate that the formation of Li-dense and -dilute domains is associated with nanoscopic non-uniform strain fields, challenging conventional solid-solution lithium diffusion models that rely solely on the concentration gradient as the driving force. Bragg coherent X-ray diffraction imaging verified such non-uniform nanoscopic intraparticle strain fields, which may cause the direction of lithium diffusion to deviate from the direction of the concentration gradient. Moreover, we have identified that Li-dilute domains near the surface could be manipulated in situ to enhance rate-capability. This study paves a new avenue for understanding solid-state diffusion at the nanoscale, enabling the fabrication of high-performance batteries.
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