Sensorless Temperature Estimation for Lithium-ion Batteries via Online Impedance Acquisition

Temperature plays a significant role in the safety, performance, and lifespan of lithium-ion (Li-ion) batteries. To guarantee the safe, efficient, and long-lasting operations of batteries, one of the fundamental tasks of the battery management system (BMS) is to monitor battery temperature during operations. Nevertheless, subject to limited onboard temperature sensors, it becomes challenging for the BMS to obtain the temperature information of each cell in a battery system. To this end, this paper proposes a novel method to estimate the state of temperature (SOT) of batteries in real time based on the electrochemical impedance of batteries without the need for temperature sensors. By taking advantage of the smart battery architecture, the battery impedance at 5 Hz, which exhibit dependency on battery temperature while independency on the state of charge (SOC), can be obtained online via the bypass action. During battery operations, the impedance of the battery can be obtained through periodic bypass action and a designed filter. A simple impedance-temperature relationship that is calibrated offline, can be used to estimate and track the cell temperature. Experiments on charging show that the online calculated battery impedance has strong correlations to battery temperature, indicating its effectiveness in SOT estimation

Development of an in-vehicle power line communication network with in-situ instrumented smart cells

Instrumented cells, equipped with miniature sensors, are proposed to aid the next stage of electrification in the automotive and aerospace industries. To optimize the energy density available within a lithium ion (li-ion) pack we demonstrate how a power line communication (PLC) network can be formed at an individual cell level. This reduces the need for complex communication cables within a vehicle wiring loom. Here we show a unique prototype smart cell (instrumented cell equipped with interface circuitry and processing capability) can be connected via a PLC network, to enable monitoring of vital parameters (temperature, voltage, current), regardless of cell state of charge (2.5 V to 4.2 V DC operating voltage). In this proof-of-concept study, we show the reliable system (0 errors detected over ∼24 hr experiment, acquired data (logged at 10 Hz) from cells (in a parallel configuration), and comparative data for cell internal and external temperature was recorded. During a prolonged discharge (1C, 5A discharge) a peak core temperature >3 °C hotter than surface temperature was observed, highlighting the need to understand cell operation in cooling system design

Embedded distributed temperature sensing enabled multi-state joint observation of smart lithium-ion battery

Accurate monitoring of the internal statuses are highly valuable for the management of lithium-ion battery (LIB). This paper proposes a thermal model-based method for multi-state joint observation, enabled by a novel smart battery design with embedded and distributed temperature sensor. In particular, a novel smart battery is designed by implanting the distributed fiber optical sensor (DFOS) internally and externally. This promises a real-time distributed measurement of LIB internal and surface temperature with a high space resolution. Following this endeavor, a low-order joint observer is proposed to co-estimate the thermal parameters, heat generation rate, state of charge, and maximum capacity. Experimental results disclose that the smart battery has space-resolved self-monitoring capability with high reproducibility. With the new sensing data, the heat generation rate, state of charge, and maximum capacity of LIB can be observed precisely in real time. The proposed method validates to outperform the commonly-used electrical model-based method regarding the accuracy and the robustness to battery aging

Distributed internal thermal monitoring of lithium ion batteries with fibre sensors

Real-time monitoring of the thermal characteristics of a lithium ion battery under electrical excitation, is a key requirement that underpins the safe operation of the battery; its reliability and life. Further, it facilitates the design of many supporting elements of the battery system, including the thermal management strategy and the algorithms that comprise the battery management system. The novelty of this study is advanced distributed thermal monitoring from external to embedded measurement for future smart battery and management. Rayleigh scattering based optical fibre sensors are known to be robust and able to operate when immersed in electrolyte, they have a small physical size and are able to provide a measurement of temperature with a spatial resolution of circa 2.6 mm. The spatial distribution of the temperature profile, arising from the complexity and variations within the cell is investigated. The results show that the peak temperature between the cell core and surface, along the cell length can be as high as 9.7 °C for 1C discharge. This paper provides a detailed explanation of the cell modification method, instrumentation process and the fundamental principles of in-cell optical measurement. Results are presented and discussed within the context of enhanced battery thermal management and improved system safety that are applicable to the application of lithium ion batteries across a number of domains including automotive and aerospace

Development of smart battery cell monitoring system and characterization on a small-module through in-vehicle power line communication

Current generation battery electric vehicles lack sufficient systems to monitor battery degradation and aging; consumers demand longer range, faster charging and longer vehicle lifetime. Smart cells, incorporating sensors (e.g. temperature, voltage, and current) offer manufacturers a means to develop longer lasting packs, enabling faster charging and extending range. In this work, instrumented cells (cylindrical, 21700) have been developed. Our novel data logging solution (using power line communication, PLC) permits a comprehensive range of sensors to be installed on each cell. Utilizing the cell bus bars, this reduces the necessary wiring harness size and complexity to instrument packs, which can enable higher density energy storage per volume and weight within the vehicle. In this initial feasibility study, a module (4S2P cells) was tested using two diverse cycles (stepped current, 200 mins x10 cycles, and transient drive, 50 min) in a laboratory climate chamber. The interface system enables research-prototype or traditional sensors to be connected via the PLC network. Miniature sensors (6 temperature, 1 current, 1 voltage) were installed externally on each cell. Excellent performance was observed from the communication system; maximum 0.003% bit error rate, 50ms message receive time (compared to dedicated wired link). Variation in the measured parameters (originally identical cells, temperature 1.0 °C, voltage 5% state-of-charge, current ~10%) support the need for improved cell instrumentation to understand cell manufacturing tolerances and aging. This work shows a proof-of-concept study using PLC with instrumented cells, and leads to future work to further reduce the cost and physical size of smart cells

In-situ instrumentation of cells and power line communication data acquisition towards smart cell development

The internal core temperature of cells is required to create accurate cell models and understand cell performance within a module. Pack cooling concepts often trade off temperature uniformity, vs cost/weight and complexity. Poor thermal management systems can lead to accelerated cell degradation, and unbalanced ageing. To provide core temperature an internal array of 7 thermistors was constructed; these in conjunction with cell current, via bus bar mounted sensors, and voltage sensor measurements, we have developed instrumented cells. These cells are also equipped with power line communication (PLC) circuitry, forming smart cells. We report upon data from these miniature sensors during cell cycling, demonstrating successful operation of the PLC system (zero errors compared to a reference wired connection) during typical cell cycling (C/2 discharge, C/3 charge) and the application of automotive drive cycle, providing a transient current test profile. Temperature variation within the cell of approximately 1.2 °C gradients, and variation of >2.8 °C during just 30 min of 2C discharging demonstrate the need for internal sensing and monitoring throughout the lifetime of a cell. Our cycling experimental data, along with thorough cell performance tracking, where typically <0.5% degradation was found following instrumentation process, demonstrate the success of our novel prototype smart cells