As known, the leakage of lithium battery (LIB) electrolyte is an important cause for runaway failure of LIB, so it has great significance to develop an approach for electrolyte leakage detection with low detection limit and fast response. In this work, we developed a Pd-doped WO3 gas sensor, taking the main component of electrolyte Ethyl Methyl Carbonate (EMC) as the target gas. The sensor has a hollow microsphere structure assembled by nano-particles, and the sensor with Pd doping ratio of 1.5% has the best gas sensing performance. At 275 ℃, the response to 10 ppm EMC is 17.8, and still 45% to EMC as low as 100 ppb. Furthermore, the response time is fast as 19 s to 10 ppm EMC. In addition, the sensor also shows novel stability and gas selectivity, the fluctuations of baseline resistance and response just were 0.77% and 4.6%, respectively. The results show that the sensor can detect extremely low concentration of EMC gas with fast response, and has great application potential in the field of lithium battery safety. Display omitted