Batteries are being seen as a key technology for battling CO2 emissions from the transport, power, and industry sectors. However, to reach the sustainability goals, they must exhibit ultrahigh performance beyond their capabilities today. So, it is becoming crucial to develop advanced diagnostic/prognostic tools injected into the battery that could nonintrusively track in time and space its physical and chemical parameters, for ensuring a greater lifetime and therefore lower its CO2 footprint. In this context, a smart battery sensing system with high performance and easy implementation is critically needed for the vital importance of safety and reliability in all batteries. Parameters like temperature (heat flow), strain, pressure, electrochemical events from electrode lithiation to gassing production, refractive index, and SoX battery indicators are of high importance to monitor. Recently, optical fiber sensors (OFS) have shown to be a feasible, accurate, and useful tool to perform this sensing, due to their intrinsic advantages and capabilities (lower invasiveness, multipoint and multiparameter detection, capability of multiplexing being embedded in harsh environments, and fast response). This chapter presents and discusses the studies published regarding the different types of OFS, which were developed to track several critical key parameters in Li-ion batteries, since the first study was reported in 2013. 

Tracking Li-Ion Batteries Using Fiber Optic Sensors

In this paper, we present a solution for sensor data communication within an electric vehicle battery module, which is based on an optical transmission channel without any optical fibers. Instead, the communication is implemented via a transparent plastic component integrated in the battery package. The development of such a light guide body is discussed. Using this physical layer, the concept of the dedicated sensor network follows the idea of a decentralized signal processing. Thereby, parallel operating cell controllers at each cell are implemented. The solution is compared to the state-of-the-art wired communication as well as to alternative methods. Besides the functional demonstration, the implementation of a double-stack communication protocol is also discussed. This ensures a flexible and scalable integration with different sensors and battery setups in the future. 

Sensor Data Communication via Light Guide Body for Monitoring Vehicle Batteries

In this paper, we present a solution for sensor data communication within an electric vehicle battery module, which is based on an optical transmission channel without any optical fibers. Instead, the communication is implemented via a transparent plastic component integrated in the battery package. The development of such a light guide body is discussed. Using this physical layer, the concept of the dedicated sensor network follows the idea of a decentralized signal processing. Thereby, parallel operating cell controllers at each cell are implemented. The solution is compared to the state-of-the-art wired communication as well as to alternative methods. Besides the functional demonstration, the implementation of a double-stack communication protocol is also discussed. This ensures a flexible and scalable integration with different sensors and battery setups in the future.

In this paper, we discuss some major obstacles and solutions towards an industrialization of optical fiber sensors for cell state monitoring of lithium-ion batteries. We present measurement results based on transmitted light intensities through the optical fiber as indicator for the state of charge. Cells are built with commercial electrodes in a pouch cell setup. To compensate for cross influences and stabilize the measuring signal against manufacturing tolerances, a referencing method is introduced. Thus, ratios of transmitted light intensities at different wavelengths are evaluated to avoid the use of absolute values. The obtained transmission ratios are in good agreement with the state of charge for various C-rates. Finally, possibilities towards an industrial implementation with inexpensive LEDs and phototransistors are discussed.

Philipp Schiepel

Papers

Self-Compensation of Cross Influences using Spectral Transmission Ratios for Optical Fiber Sensors in Lithium-Ion Batteries