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Page 2 of 27 Wang et al. Soft Sci 2024;4:32 https://dx.doi.org/10.20517/ss.2024.15

and future development trends, aiming to provide a reference for designing optimal BTMS. In the end, we point out
that it is crucial to select appropriate cooling technologies according to user requirements and to combine multiple
cooling technologies for meeting thermal management needs in different application scenarios.

Keywords: Thermoelectric cooler, battery thermal management system, air cooling, liquid cooling, phase change
material, hybrid cooling

INTRODUCTION
Thermoelectric technology based on the thermoelectric effect enables direct conversion between heat and
electricity. The discovery of the Seebeck effect in 1821, the Peltier effect in 1834, and the Thomson effect in
1855 together form a complete system of thermoelectric effects, providing the theoretical basis for the
[1,2]
application of thermoelectric generators (TEG) and thermoelectric coolers (TEC) . The Seebeck effect
enables the generation of electricity from a temperature difference, while the Peltier effect enables
[3]
thermoelectric cooling . Thermoelectric modules are arranged in series electrically and in parallel
thermally, consisting of N-type and P-type semiconductors inserted between ceramic plates [Figure 1A].
These ceramic plates maintain mechanical integrity and simultaneously act as electrical insulators for the
[4]
cooling and heating surfaces, ensuring the stability and safety of the thermoelectric modules .
Figure 1B shows a schematic TEC, which is based on the Peltier effect. In such a TEC, P-type and N-type
semiconductors are connected in series via metal plates. When a voltage is applied across the conductors,
one side of the TEC exhibits a cooling effect, while the other side shows a heating phenomenon, thereby
[5-7]
achieving directional heat transfer . Semiconductor-based TEC operates on direct current (DC) and
connects the cold side of the device to the object requiring cooling, while the hot side is connected to a heat
sink . By adjusting the voltage and current, precise control of cooling capacity and temperature can be
[5-7]
achieved continuously. Within the same system and without altering the structural conditions, simply
changing the direction of the current allows for the transition between cooling and heating modes.
[4]
Therefore, TECs can serve as efficient temperature controllers . In addition, flexible TECs are solid-state or
flexible thermoelectric modules designed to operate on flexible substrates . Their flexibility makes them
[7]
suitable for various applications requiring flexible thermal management solutions, such as wearable devices,
medical instruments, and electronic products. Flexible TECs typically consist of flexible substrates,
thermoelectric materials, and electrodes. The design and manufacturing of these TECs need to consider the
characteristics of flexible materials and the balance between cooling efficiency and cooling power.

TEC boasts high precision control and rapid response. Unlike conventional mechanical refrigeration, it does
not require moving parts such as compressors or refrigerants, eliminating emissions and environmental
pollution. It stands as an ideal solid-state, high-efficiency cooling and thermal management technology .
[8]
TEC, with its irreplaceable advantages and characteristics such as flexibility, diversity, and reliability, has
become a key technology supporting numerous modern industries [9-15] , and has provided significant
economic value in areas such as semiconductor refrigeration and bidirectional precise temperature
control . It finds wide applications across various sectors including consumer electronics,
[2]
telecommunications, medical experiments, aerospace defense, industrial processes, and automotive
industries. In consumer electronics, its typical applications include precise temperature control in confined
spaces or achieving cooling and heating effects, such as in constant-temperature wine cabinets, electronic
refrigerators, hot and cold water dispensers, electronic air conditioners, beer dispensers, constant-
temperature mattress pads, dehumidifiers, smartphone cooling clips, and water-ion hair dryers . In the
[16]
field of telecommunications, employing TEC for precise active temperature control of optical modules,