Non-Uniform Circumferential Expansion of Cylindrical Li-Ion Cells—The Potato Effect

Abstract

This paper presents the non-uniform change in cell thickness of cylindrical Lithium (Li)-ion cells due to the change of State of Charge (SoC). Using optical measurement methods, with the aid of a laser light band micrometer, the expansion and contraction are determined over a complete charge and discharge cycle. The cell is rotated around its own axis by an angle of α=10° in each step, so that the different positions can be compared with each other over the circumference. The experimental data show that, contrary to the assumption based on the physical properties of electrode growth due to lithium intercalation in the graphite, the cell does not expand uniformly. Depending on the position and orientation of the cell coil, there are different zones of expansion and contraction. In order to confirm the non-uniform expansion around the circumference of the cell in 3D, X-ray computed tomography (CT) scans of the cells are performed at low and at high SoC. Comparison of the high resolution 3D reconstructed volumes clearly visualizes a sinusoidal pattern for non-uniform expansion. From the 3D volume, it can be confirmed that the thickness variation does not vary significantly over the height of the battery cell due to the observed mechanisms. However, a slight decrease in the volume change towards the poles of the battery cells due to the higher stiffness can be monitored.

Aging‐Driven Composition and Distribution Changes of Electrolyte and Graphite Anode in 18650‐Type Li‐Ion Batteries

“…At the end of the CC charging process, characterized by the maximum expansion of the cell housing and, correspondingly, the jellyroll, the electrolyte is pressed out of the jellyroll either toward the cell housing or empty electrode‐free spaces at the cell top and bottom. [ 39 ] During the times of the CV phase and the relaxation in the rest phase, the electrolyte flows down, what shows the relevance of the cell cycling position and gravitational forces for battery characterization. [ 40 ] Here, cell charge forms a metastable state supplemented by relaxation of voltage, pressure and lithium concentration in electrodes along with the relaxation of electrolyte distribution in the battery jellyroll.…”

Radial Thermal Conductivity Measurements of Cylindrical Lithium-Ion Batteries—An Uncertainty Study of the Pipe Method

“…The degree of lithiation for the anode is highest at SOC 100%, meaning a fully charged cell. This is where prismatic LIB cells usually show their greatest thickness [23,24] or cylindrical cells show their greatest diameter [25]. In cylindrical cells this also leads to surface strain [26] caused by the mechanical force arising from the bulk materials.…”

Piezoresistive Free‐standing Microfiber Strain Sensor for High‐resolution Battery Thickness Monitoring

“…The state-of-the-art lithium-ion (Li-ion) battery is a widely used rechargeable energy storage device in application areas ranging of the Li-ion battery is a critical domain for improving its lifetime and performance. [4,5] Battery health diagnostic through the characterization of volume or thickness changes has been investigated by numerous studies using different methods: neutron imaging, [6] in situ X-ray diffraction, [7,8] in situ atomic force microscopy, [9] 3D digital image correlation, [10,11] mechanical measurement methods, [1,2,[12][13][14][15] thickness gauges, [3,16] ultrasonic probing, [17,18] and optical sensors. [19][20][21][22] However, all the measurement methods and sensors either require complicated laboratory setups, cannot be seamlessly integrated for in situ monitoring, and are not cost-efficient.…”

“…[30,[36][37][38] However, for most typical Li-ion battery expansion monitoring, a strain detection with an accuracy below 1 µm dimension change is required, which has not been achieved so far. [1,8,14,20] In this work, we implemented an innovative strategy to realize a microfiber-based strain sensor for battery expansion monitoring. We utilized silver-coated glass microspheres as conductive fillers in an ethylene-vinyl-acetate copolymer (EVA) matrix to obtain freestanding stretchable conductive microfiber via the upscalable wet-spinning method.…”

“…[ 30,36–38 ] However, for most typical Li‐ion battery expansion monitoring, a strain detection with an accuracy below 1 µm dimension change is required, which has not been achieved so far. [ 1,8,14,20 ]…”