Development of Operando Bimodal Atomic Force Microscopy System for Real-Time Nanomechanical Mapping of Electrode Cross-Sections in All-Solid-State Lithium-Ion Battery Configuration
Authors: Putra Ridwan Pratama , Matsushita Kyosuke , Ohnishi Tsuyoshi , Masuda Takuya 
Published: December 2024

All-solid-state lithium-ion batteries (ASSLBs) have garnered considerable attention as the next-generation electrochemical energy storage systems due to their high chemical safety and wide electrochemical potential windows1. Among the available candidates for ASSLB negative electrodes, silicon is a promising material because of its extremely high theoretical capacity and low lithiation/delithiation potential2. However, Si is known to undergo severe structural changes during electrochemical lithiation/delithiation, as revealed by our previous operando studies using a laboratory-based X-ray photoelectron spectroscopy setup3,4. These dramatic structural changes may result in a significant volume expansion/contraction, leading to particle cracking, pulverization, and electrode failure. Hence, the understanding and control of such physicochemical phenomena are critical to prevent nanomechanical and electrochemical degradation of the electrode.

In this talk, we will introduce our newly developed operando bimodal atomic force microscopy (AFM) system which enables real-time nanomechanical monitoring of an amorphous Si thin film electrode during electrochemical lithiation/delithiation, simultaneously with cross-sectional topography imaging5. An ASSLB cell composed of 3 µm-thick Si thin film/500 µm-thick Li6.6La3Zr1.6Ta0.4O12 (LLZT) solid electrolyte/50 µm-thick Li foil (Si/LLZT/Li) was fabricated, and its cross-section was smoothened by an Ar-ion beam prior to carrying out the nanomechanical mapping on the Si/LLZT interface. The nanomechanical mapping was performed during the first electrochemical lithiation and delithiation within a potential window of 0.01-1.20 V vs. Li+/Li under Ar atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm).

Nanomechanical property maps of the Si electrode, in the form of Young’s modulus maps, were successfully acquired as a function of apparent Li content x in lithium silicide (Li
x
Si), together with real-time topography images. At the first lithiation, the average Young’s modulus drastically decreased due to the formation of Li
x
Si from pristine Si, followed by a moderate modulus reduction up to a capacity of 3300 mAh g-1 (x = 3.46 in Li
x
Si). Throughout the successive delithiation up to 1467 mAh g-1 (x = 1.54 in Li
x
Si), the average modulus was gradually recovered. The Li
x
Si moduli obtained from this study are consistent with the values from the first-principles calculations, showing the sensitivity and reliability of the technique6. The demonstrated technique can be implemented for a wide range of battery materials for both solid-state and liquid-electrolyte lithium battery systems.

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