Identifying Defects in Li-Ion Cells Using Ultrasound Acoustic Measurements

Abstract

Identification of the state-of-health (SoH) of Li-ion cells is a vital tool to protect operating battery packs against accelerated degradation and failure. This is becoming increasingly important as the energy and power densities demanded by batteries and the economic costs of packs increase. Here, ultrasonic time-of-flight analysis is performed to demonstrate the technique as a tool for the identification of a range of defects and SoH in Li-ion cells. Analysis of large, purpose-built defects across multiple length scales is performed in pouch cells. The technique is then demonstrated to detect a microscale defect in a commercial cell, which is validated by examining the acoustic transmission signal through the cell. The location and scale of the defects are confirmed using X-ray computed tomography, which also provides information pertaining to the layered structure of the cells. The demonstration of this technique as a methodology for obtaining direct, non-destructive, depth-resolved measurements of the condition of electrode layers highlights the potential application of acoustic methods in real-time diagnostics for SoH monitoring and manufacturing processes.

Future Material Developments for Electric Vehicle Battery Cells Answering Growing Demands from an End-User Perspective

“…Pressure sensors and gas detection are quite similar, since they are activated by gas emissions from the cells, whereas the pressure sensor is monitoring the forces between cells and how these are affected by cell swelling, and the strain gauge measures cell deformation and excessive swelling. There are also examples of more advanced detection principles based on acoustic signals, e.g., ultrasonic methods, and predictive models incorporated into the BMS, which use data from the battery, e.g., cell voltages, temperatures and currents, to detect inconsistencies [213,214]. Commercial systems based on these principles are appearing on the market.…”

Challenges and needs for system-level electrochemical lithium-ion battery management and diagnostics

“…Common conditions include Li plating due to fast or lowtemperature charging or path-dependent aging; mild overcharge and overdischarge due to faulty or less-resilient sensors and management; nonuniform aging due to aggressive use or inadequate or faulty management; internal and external shorts due to latent manufacturing defects or incorrect use, inappropriate fixturing, or cell damage and aging; and divergent aging due to cell-to-cell variability. 17,[25][26][27][28][29][30][31][32][33][34][35][36][37][38] Literature surveys indicate the existence of a diverse set of diagnostics for LiB cells-diagnosing Li plating, [39][40][41][42][43][44] overcharge, [45][46][47] overdischarge, 45,48,49 internal shorts, [50][51][52][53] external shorts, [54][55][56] and electrode-and cell-level inhomogeneities 28,[57][58][59][60][61][62] -employing various thermal, electrochemical, acoustic, and entropy-based methods, often combined with different modeling-based approaches. Most of these methods are still in development; therefore, they have not been extended to module, string, or pack levels.…”

In-Situ Li-Ion Pouch Cell Diagnostics Utilising Plasmonic Based Optical Fibre Sensors

“…Thermistors can be used to measure temperature, which can provide important information about battery operating limits and safety, but do not correlate to SOC or State-of-Health (SOH) [22,23]. X-ray computed tomography has been demonstrated as a technique that can be utilised to detect microscale defects in cells [24], while ultrasonic techniques have been shown to correlate signal wave height with battery cell SoC [25]. Externally applied strain gauges have been used to monitor expansion of a cell and correlate it to cell degradation [26] and a variation on this setup has been shown to measure the volumetric expansion of a cell associated with SEI layer growth [27].…”