Monitoring the battery temperature with electrothermal heaters based on graphene nanoplatelets

Environmental temperature is a critical parameter that affects battery performance, for example low temperature causes sluggish charge transfer process at electrode-electrolyte interphase. In this work, we have developed a graphene-based electrothermal heater coating to maintain the temperature of a battery at its best working condition. Composites of graphene nanoplatelets (GNPs) and poly(styrene-isoprene-styrene) (SIS) were fabricated as free-standing films. Various particle sizes of GNPs were tested in the electrothermal heaters to achieve optimal performance. It was revealed that the composite films with 10 μm particle size and 50% concentration of GNPs delivered the best electrothermal performance achieving high and stable heating up to 160 °C above room temperature at just 18 V driving voltage and delivered the high electric to heat conversion efficiency (ɳ) of ~97.4 °C·cm 2 /W. The stability of the film was recorded at two different voltages (10 V and 12 V) for 8 h and demonstrated that the films maintain their structure without physical damage. The films also demonstrated excellent repeatability upon testing for ON-OFF cycles with 30 min interval times. The electrochemical performance of a commercial 18,650 cylindrical cell degraded to 54 mAh g −1 at lower temperature (10 °C) from 95 mAhg −1 at room temperature. The electrothermal coating successfully improved cell performance to 90 mAhg −1 at low environmental temperatures. These results suggest that such electrothermal coating can enhance battery performance, offering a potential solution to the issue of reduced electric vehicles (EVs) mileage in cold climates. • Flexible graphene nanoplatelet (GNP)/SIS composite films were developed as efficient electrothermal heaters for battery temperature monitoring. • A systematic study of GNP particle sizes (5–50 μm) revealed that 10 μm particles offer the best balance of conductivity and heat distribution. • The optimized 10 μm GNP film (50 wt%) achieved rapid and uniform heating up to 160 °C at only 18 V. • The electrothermal films demonstrated excellent stability and repeatability during prolonged and cyclic operation. • The GNP-based coating restored Li-ion battery capacity at 10 °C, significantly improving performance in cold conditions.