Thermistors, as an important temperature sensing device, play a crucial role in new energy vehicles and energy storage systems. With the rapid development of new energy technology, the demand for the safety, stability, and efficient operation of battery systems is increasing. Thermistors, with their high precision and fast response characteristics, effectively monitor and control temperature changes within the system, ensuring that the battery pack operates within the optimal working range, thereby extending battery life and improving the overall reliability of the system. This article will explore the importance of thermistors in new energy vehicles and energy storage applications, as well as the product characteristics of thermistors introduced by Murata.
The growth of new energy vehicles drives the rapid increase in lithium-ion battery production
New energy vehicles (NEVs) have become the driving force in the current automotive industry, leading production and sales momentum worldwide. In China, for instance, the green and low-carbon transition is steadily progressing, and the structure of energy production and consumption is continuously being optimized. The rapid growth of China's new energy industry is driven by ongoing technological innovation and a well-developed industrial chain system. Among these, the production of NEVs has seen rapid year-on-year growth, with related products such as charging stations and automotive lithium-ion power batteries also experiencing fast growth. Furthermore, the photovoltaic industry chain is showing strong growth, with significant increases in the production of key materials like polysilicon, monocrystalline silicon, and ultra-clear glass for solar energy applications.
According to statistics, the annual total demand for lithium-ion battery packs for electric vehicles is expected to increase from around 600 GWh in 2023 to approximately 1,000 GWh in 2025, and about 1,600 GWh by 2029. China, which is leading the market, is rapidly increasing its battery manufacturing capacity. In 2023, China's battery production capacity was around 1,200 GWh, and according to announcements, this capacity is expected to exceed 3,000 GWh by 2025 and over 4,500 GWh by 2030.
This situation has several significant impacts, including the possibility of lower prices for manufacturers due to increased battery capacity. By 2023, the average price of battery packs had already decreased by 10-15%, and CATL plans to sell batteries at less than $60 per kWh this year, with expectations that battery prices will continue to decline. Additionally, Chinese companies like BYD and CATL are heavily investing in research and development and launching new and improved products, making it more challenging for new entrants to the battery industry.
The demand for thermistors is driven by new energy vehicles and energy storage applications
The demand for thermistors in photovoltaic and energy storage systems is quite high. Thermistors are essential for temperature sensing and control in battery management systems (BMS), power conversion systems, photovoltaic optimizers, and photovoltaic inverters. The quantity of thermistors required in the entire energy storage system depends on the scale of the equipment, with up to 5,000 units needed per 5MWh cabin. On the other hand, the demand for thermistors in new energy vehicles (NEVs) is also significant. An NEV typically requires around 150 thermistors, with the battery pack being the primary application point for thermistors. The AFE (Analog Front End) side usually reserves NTC (Negative Temperature Coefficient) thermistor interfaces for temperature measurement on the battery cells.
Taking the temperature sensing requirements for automotive BMS board IC protection as an example, thermistors can be used to detect the temperature of shunt resistors. When current detection in a battery module adopts a shunt resistor scheme, a thermistor is needed to monitor the shunt resistor temperature to correct the impact of ambient temperature on current detection. Additionally, thermistors are used to monitor the temperature of balancing resistors. In passive balancing, the balancing resistors dissipate excess energy from the battery to balance the charge and voltage across battery modules or cells. In addition, the thermistor plays a very critical role in detecting the temperature of the car battery cell. Its purpose is to detect the occurrence of thermal runaway by monitoring the temperature changes of the cell. It can also be used to calculate the battery life of SOH and battery power of SOC.
In energy storage system (ESS) applications, particularly in ESS battery packs, the mainstream market will utilize a combination of flexible printed circuits (FPC) or flexible die-cut circuits (FDC) with SMD (Surface-Mount Device) NTC thermistors to measure temperature. The function of NTC thermistors in these systems is temperature monitoring and compensation. On the BMS board, thermistors can monitor the temperature of the ECU, MOSFET, electrical connections, and ambient environment. In the battery cells, NTC thermistors are used to monitor cell temperature to prevent overheating or to provide temperature compensation to adjust efficiency. Typically, several NTC thermistors are used on the BMS board, and the ratio of NTC thermistors to battery cells ranges from 1:1 to 1:4, with 1:2 being the most common. ESS BMS battery packs usually integrate about 100 battery cells, so approximately 50 NTC thermistors are used in an ESS BMS battery pack.
In ESS BMS battery packs, using leaded thermistors can offer additional structural support (cable type) with high waterproofing and vibration resistance. However, over years of use, the plastic components of the cables may degrade, becoming points of corrosion, and the unit cost and assembly labor cost are relatively high. If FPC combined with SMD-type thermistors is used, the design offers higher integration, lower costs (both in terms of assembly labor and the unit value of the NTC), and easier maintenance than the leaded type. However, it requires additional FPC laminating processes and quality control management.
In photovoltaic and ESS product applications, the equipment is often placed in harsh outdoor environments, subjected to day-night temperature shocks, and exposed to high concentrations of hydrogen sulfide (H2S) and coastal salt invasion. During maintenance or inspection, opening and closing the cabin doors can introduce external gases into the cabin, potentially corroding electronic devices, or causing condensation due to temperature changes. Given that product warranties typically last 5–10 years, with a design lifespan of 15–25 years, long-term reliability is essential. NTC thermistors, as critical temperature sensing devices, require corresponding high reliability. Among them, Murata’s NTC thermistors are suitable and widely recognized in the market as a reliable solution.
NTC thermistors are ideal temperature sensors
Murata's NCU series NTC thermistors are SMD type, suitable for temperature sensing, and offer high reliability. The NCU series is the main of Murata's thermistor lineup, capable of temperature sensing and temperature compensation functions over a wide temperature range, making it suitable for applications with high reliability requirements, such as in the automotive market.
The NCG series NTC thermistor SMD type is used for temperature sensing (compatible with conductive glue). The NCG series is an SMD type temperature sensor suitable for various temperature sensing and compensation applications. It is also suitable for automotive applications requiring high reliability. The NCG series is limited to conductive glue mounting and is not compatible with solder mounting.
PTC thermistors can achieve temperature sensing and circuit current limiting applications
Murata's PTC thermistors (POSISTOR) are elements whose resistance increases as the temperature rises, enabling applications such as temperature sensing and circuit current limiting. Murata's POSISTOR PTC thermistors are made from ceramic materials with excellent reliability and performance, and includes products designed for different applications such as overcurrent protection, and overheating protection.
The PRF series PTC thermistors, SMD type, can be used for overheating sensing. These SMD type PTC thermistors for temperature sensing utilize the characteristic of a sharp increase in resistance at a certain temperature, making them suitable for overheating sensing in FETs, power ICs, and other heat-generating components. The PRF series leverages the characteristic of rapid electrical impedance change, due to the rapid change in resistance, even in a simple circuit with multiple heat generation points connected in series with PTCs, accurate overheating sensing can be achieved. Therefore, the PRF series can reduce the number of IC ports and contribute to device miniaturization.
The PRG series PTC thermistors, SMD type, are suitable for overload current protection. These SMD type PTC thermistors for overcurrent protection quickly respond to overcurrent conditions, such as short circuits, eliminating the overload condition and automatically restoring the device to its initial state, repeatedly. Using ceramic materials, these thermistors offer high reliability, with a short response time from the occurrence of a short-circuit fault to the protective action, achieving mechanical maintenance-free operation and improved safety. Additionally, compared to organic PTCs and chip resistors with similar characteristics, their high voltage tolerance and large power capacity enable product miniaturization, contributing to the downsizing of machinery.
The PRG series can also serve as a resettable fuse after an abnormal condition is resolved. Its compact design saves installation space on the PCB, and once installed and powered on the PCB, it maintains stable characteristics. Due to its high-power capacity, it can be used as a small current-limiting resistor and complies with safety standards such as UL: E137188, VDE, and TUV.
Conclusion
Thermistors play an indispensable role in new energy vehicles and energy storage applications. They not only provide critical temperature monitoring and protection functions for battery management systems but also contribute to the enhancement of overall system safety and efficiency. As technology continues to advance, the accuracy and reliability of thermistors will further improve, providing strong support for the ongoing development of new energy technologies. Murata has introduced a comprehensive line of thermistor products that will meet the diverse safety needs of new energy vehicles and energy storage applications.