Digital data transmission system with capacitive coupling for in-situ temperature sensing in lithium ion cells

Precise temperature measurement within a narrow time frame is crucial for the safe operation of Li-Ion battery cells. This paper proposes a digital approach for in-situ cell temperature measurement, relying on capacitive coupled data transmission between the controller in a cell and an external controller. In contrast to purely analog solutions, the digital approach satisfies all requirements in terms of electrochemical, space and transmission quality. For this purpose, analog and digital conceptual hardware setups were implemented for comparison and extensive measurements were carried out. The experimental results for the digital implementation show the influence of capacitor sizes and baud rates, providing a guideline for transmission rates for different sizes of cells. The paper also discusses in detail integration aspects for the digital approach. From the digital concept setup, valuable information is deduced regarding the communication latency, achievable energy consumption and miniaturization potential: Depending on the employed sampling rate, the transmission duration for one message with five temperature values can be reduced to as little as 65 μs with a power consumption in the μW range. The proposed miniaturization enables an efficient, low cost, fully integrated logic circuit for data collection and transmission with a size not bigger than 2 mm × 3 mm.