Fast and slow ion diffusion processes in lithium ion pouch cells during cycling observed with fiber optic strain sensors

Abstract

h i g h l i g h t sBetter cell utilization and life key to encourage broader Li-ion battery adoption. Residual electrode strain build-up is critical cell issue for performance and life. Cell strain overshoot at high SOC, rest recovery observed with fiber-optic sensors. Correlation of the cell strain overshoot/relaxation to SOC and temperature is characterized. Origins, implications of issue for longer cell life, utilization also discussed. a b s t r a c tCell monitoring for safe capacity utilization while maximizing pack life and performance is a key requirement for effective battery management and encouraging their adoption for clean-energy technologies. A key cell failure mode is the build-up of residual electrode strain over time, which affects both cell performance and life. Our team has been exploring the use of fiber optic (FO) sensors as a new alternative for cell state monitoring. In this present study, various charge-cycling experiments were performed on Lithium-ion pouch cells with a particular class of FO sensors, fiber Bragg gratings (FBGs), that were externally attached to the cells. An overshooting of the volume change at high SOC that recovers during rest can be observed. This phenomenon originates from the interplay between a fast and a slow Li ion diffusion process, which leads to non-homogeneous intercalation of Li ions. This paper focuses on the strain relaxation processes that occur after switching from charge to no-load phases. The correlation of the excess volume and subsequent relaxation to SOC as well as temperature is discussed. The implications of being able to monitor this phenomenon to control battery utilization for long life are also discussed.

Monitoring the Strain Evolution of Lithium‐Ion Battery Electrodes using an Optical Fiber Bragg Grating Sensor

“…We have developed at echnique that uses fiber optic (FO) sensors embedded within lithium-ion batteries to measure the parameters indicative of the cell state (in conjunction with our low-cost, compactw avelength-shiftd etection technology and intelligent algorithms) to enable effective realtime performance management and optimized battery design. [12] In this study,w ef ocus on an approachd istinct from what we explored previously where the fiber optic sensor was embedded between electrodes (referred to herein as the "attached" approach). [13] Here the fiber Bragg grating (FBG)s ensors are directlyi ntegrated within the electrode material itself by bonding them ontot he current collector prior to electrode slurry deposition( referred to herein as the "implanted" approach).…”

Non-Destructive Detection of Local Aging in Lithium-Ion Pouch Cells by Multi-Directional Laser Scanning

“…This information may provide a more profound data basis for explaining displacement overshoots near the end of the charging process under constant current which were described in detail in several previous works 1,7,16 and were ascribed to failure mechanisms.…”

“…z E-mail: johannes.sturm@tum.de to be a reliable method for determining intercalation stages in the electrodes 7,26,27 and the corresponding electrode specific SOC, to monitor irreversible swelling effects during aging 4 and to detect lithium plating.…”

“…These are largely caused by electrode swelling, [5][6][7][8] polymer deformation 5,9 and film growth. 10,11 Estimating the cell's SOH by a single point measurement implies a homogeneous stress and strain distribution over the housing of the cell.…”

A review on various temperature-indication methods for Li-ion batteries

“…After using FBG sensors to measure diffusion processes [252] and intercalation stages [253] through strain, the team of Raghavan et al [254] embedded FBG sensors for accurate internal monitoring battery states. The results have been published in a twofold paper [254,255].…”