Piezoresistive-piezocapacitive hybrid pressure sensor based on synergetic MXene porous conducting and ion trapping effects for operando battery state-of-charge monitoring

Battery pressure evolution provides essential information for battery state diagnosis. However, challenges still exist for achieving suitable pressure sensors to realize precise operando battery pressure monitoring. Herein, we develop a flexible hybrid pressure sensor by sandwiching one ionic piezocapacitive layer between two piezoresistive electrode networks. By taking advantage of the synergistic resistance and capacitance variation effects of the sensor upon compression by the interwoven conductive MXene fibers and the ionic nanofibers with MXene ion trappers, a remarkably improved sensing performance is achieved with a low detection limit of 4 Pa, an excellent durability under both small and ultrahigh pressures for over 20 000 cycles, and high sensitivities over an ultrawide detection range of 0-1 MPa. Meanwhile, the developed sensor is soft and stretchable, ensuring a convenient and conformal attachment to batteries of various shapes without in-plane strain interference. Towards practical application, the hybrid sensor is used to monitor the pressure evolution of lithium-ion battery pouch cells under different constrained pressures, and highly sensitive response is gained, through which the state of charge (SoC) of the battery during normal operation can be precisely estimated. When the battery is slightly overcharged, an instant warning can be made upon the diagnosis of SoC of even a few percentages over 100 %. Its application can be expanded to other areas where high sensitivity across an ultrawide detection range is demanded.