Cross-Sectional In Situ Optical Microscopy with Simultaneous Electrochemical Measurements for Lithium-Ion Full Cells

Abstract

A new in situ optical microscopy set-up is introduced which allows direct observation of cross-sections of Li-ion full cells in combination with simultaneous recording of electrochemical data. The method is validated by comparison of electrochemical data from coin full cells. Color changes give insights into processes on the electrode and particle level, such as lithiation behavior and electrode thickness changes. Our observations allow the evaluation of (i) the speed of lithiation fronts for LiC12 and LiC6 through anode coatings, (ii) estimation of apparent diffusion coefficients from analysis of the color distribution in single graphite particles, as well as (iii) electrical de-contacting and re-contacting of single graphite particles in connection with (iv) electrode thickness changes. Furthermore, our direct observations from the inside of full cells give indirect insights into aging phenomena such as Li plating and SEI growth.

Multistep Improvement of Pilot-Scale 21700 Cells for Increased Fast-Charging Capability: Combining Optimized Electrolyte, Cell Design and Fast-Charging Protocol

“…4,47 Another difference between the 21700 and the PAT-cells is the overhang area. As discussed previously, 13,48 changing the areal ratio between anode to cathode results in different capacities. In order to avoid issues due to the electrode alignment, the same electrode area for both anode and cathode was chosen in the PAT-cells.…”

“…The in situ cell set-up and preparation of the cross-sectional cell were developed in our group and are described in detail in our previous publications. 13,14 For these measurements, the anode and cathode had identical dimensions (diameter: 16 mm), and two layers of Celgard 2325 separator (diameter: 18 mm) were used. The electrodes were dried overnight under vacuum conditions at 130 °C, and the separator was dried at 70 °C.…”

“…[10][11][12] Especially at higher charging rates, the transport properties can cause a depletion of Li + in the electrolyte within the parts of the electrode close to the current collector. 8,9 This causes an inhomogeneous lithiation distribution within the electrodes 13,14 which can ultimately lead to faster aging at the electrode surface. 15 Changing the conductive salt concentration 8,16 or the conductive salt itself 17 can improve the mass transport properties and allow higher charging rates.…”

Failure Mechanisms at the Interfaces between Lithium Metal Electrodes and a Single-Ion Conducting Polymer Gel Electrolyte

“…Nondestructive characterization techniques are particularly relevant for answering these questions . Examples of advanced characterization methods include in situ optical microscopy, , in situ XPS, and TOF-SIMS, as well as cryogenic electron microscopy. , In contrast to the limited resolution of optical methods and partly tedious sample preparation, X-ray microtomography allows for reconstruction of optical images of the whole sample without prior disassembly of the cells. In principle, a sealed pouch cell is illuminated with monochromatic X-rays and a corresponding optical image is reconstructed from the radiogram using a scintillator and an optical microscope .…”

Operando Color-Coding of Reversible Lithiation and Cycle Life in Batteries Using Photonic Crystal Materials

“…36 Cross-sectional optical microscopy images of lithiumion full cells have been used to provide in situ insights into lithiation-linked color changes and electrode thickness evolution. 37 In-situ UV-vis spectroscopy has been shown to provide useful supplementary characterisation to electrochemical processes by z E-mail: c.odwyer@ucc.ie ECS Sensors Plus, 2023 2 045401 determining charge storage mechanisms and tracking of changes in material oxidation states. 38 Adopting optical probes provides many opportunities to evaluate mechanical/volumetric changes, interfacial species changes, electrolyte composition and absorption characteristics related to electronic processes with materials, to name a few possibilities.…”