Development of a Novel Acoustic Based State-of-Charge Sensor (SOC) for Lithium-Ion Batteries

Our proposal aims to assess the feasibility of embedding novel, miniature acoustic sensors directly within the structure of a lithium ion battery (LIB) to provide a direct measure of retained energy or state of charge (SOC). The term SOC defines the level of stored energy in the battery relative to its rated capacity and is often expressed as a percentage (0-100%).

Context

The UK's vision for transport by 2050 must be net-zero at the point of use. This requirement mandates the electrification of multiple sectors and the use of battery technology to replace traditional fossil fuels. A complete battery system will often consist of many hundreds of lithium-ion batteries (LIBs) combined electrically.

Manufacturing variations, combined with the impact of interconnection resistance and temperature differences between individual batteries makes the measurement of SOC a highly challenging task and one where there is no current solution. SOC uncertainty underpins considerable complexity and cost when scaling-up battery components into complete systems, e.g., for electric vehicles (EVs).

The problem is more acute for future all-electric aircraft. Regulatory bodies mandate that because of this uncertainty, redundancy must be included, in the form of additional battery capacity, to ensure safe aircraft operation. UCL has pioneered the use of ultrasound imaging to LIBs, as it provides very fast (sub-second) data collection via a relatively low-cost platform.

Deploying the technique within a LIB is challenging and calls for a fundamentally different approach. This project will develop a new miniature acoustic sensor that can be embedded within the LIB as a single sensor or array to provide a non-electrochemical means of SOC measurement. Objective

To develop and validate a proof-of-concept demonstration for how a low-profile piezoelectric transducer can be used as a non-electrochemical SOC sensor. Methods of integrating the sensor within the internal structure of the LIB that do not adversely affect sensor and battery operation will be defined.

Applications

The significant scientific contribution of this research to both sensor and battery development, includes but is not constrained too:

- Sensor: Low-profile ultrasonic sensors capable of withstanding insertion within the harsh environment of a lithium-ion battery will highlight new opportunities in the development of acoustic transducers.

- Battery Monitoring: The inclusion of an acoustic sensor within the internal structure of a battery will underpin new methods of diagnostics and prognostics and will further support the creation of a battery circular economy.

- Battery Manufacturing: The ability to manufacture a battery with embedded instrumentation has the potential to create a new classification of 'smart battery' for high-value and safety-critical applications.

- Battery Safety: The ability to measure the microstructure and SOC of the battery as internal temperature and gas pressure evolves will highlight new innovations in battery design and the selection of materials that comprise the electrolyte, electrical separator and electrodes.