Introduction of a Test Bench – Localized pressure analysis to optimize lithium-ion battery lifetime

Summary:

The pressure acting on a lithium-ion battery cell is an important parameter in battery design. Analyzing the local pressure distributions support the understanding of spatially resolved increases in pressure due to an inhomogenous cell degradation. These investigations aim to homogenize the cell degradation by developing pressure patterns which lead towards a uniformly distributed current and therefore a homogenized cell degradation. To analyse the local pressure distribution over lifetime, a rigid plate structure using resistive pressure sensors and a cushioning pad is presented.
The experimental setup consists of seven essential components. The lithium-ion pouch cell to be analyzed is centered between two rigid aluminum plates. Two cushioning pads are placed between the aluminum plates and the pouch cell acting as buffer layers. A designed electronics for sampling of resistive pressure sensors’ signals is attached to the test bench [1]. Pressure sensors are embedded into lower aluminum plate due to low compressibility of sensor‘s material to avoid pressure peaks on cell. The sensors are distributed over the area of interest to measure pressure distribution of the cell during operation. This aims at a localized pressure analysis to investigate pressure patterns regarding homogenized cell degradation.
The initial pressure studied with this setup was chosen in the medium pressure range as this is reported to improve cell performance [2]. In consideration of cell’s expected irreversible cell swelling until end of life, starting from the initial pressure the cushioning pad’s pressure deflection characteristic is close to a linerar increase in pressure over strain. While cycling the pouch cell its reversible expansion leads to a moderate change in pressure based on the cushioning pad’s stress-strain characteristics. This change in pressure causes a reasonable variation of the resistive pressure sensor’s signal.
This test bench is designed for localized pressure analysis using embedded resistive pressure sensors enabling detection of pressure change during cell cycling and cell‘s irreversible expansion. The cushioning pads used as buffer layers provide a spatially resolved pressure deflection characteristic and a semi-linear behavior over cell‘s expected irreversible expansion.
[1] S. Berg, H. Laufen, et al.; Session 3C-3; Advanced Battery Power Conference; 2022
[2] S. Hahn et al.; Journal of Energy Storage (2021); doi: 10.1016/j.est.2021.102517