C-rate related diffusion process of the graphite electrode by in situ experiment and analysis

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The diffusion process and mechanism play important roles in the lithium storage performance of electrode materials, which directly affects the electrochemical performance of lithium-ion batteries. In this paper, we propose an in situ experimental method based on the phase evolution to observe the diffusion process. An optical acquisition system with an electrochemical battery as the core was constructed. Using the electrochromic characteristics of graphite electrodes, the phase evolution information is displayed in real time. Based on the above experimental method, diffusion process observation experiments at different charge/discharge rates (C-rates) were carried out, and it was found that there was a rate-dependent corresponding relationship among the potential, phase transition, and lithium content. The results show that a high C-rate accelerates the phase evolution process, reduces the formation potential of the new phase, shortens the duration of the phase transition, and results in a multiphase coexistence state in the electrode. In addition, the effect of acceleration induced by a high C-rate on the diffusion process in the electrode is staged: the early and middle acceleration is significant, but the later acceleration is slow. From the perspective of the energy, this is because there is competition between the diffusion-driving energy and the energy barrier. Therefore, optimization with a balance between the battery capacity and lithiation rate is proposed.