The combination of electrochemistry with mass spectrometry led to the development of a large number of techniques, only a few of which are the subject of this report. We will not discuss the methods that originated from different ionization approaches (e.g., chemical ionization, desorption electrospray ionization, fast atom bombardment, etc.),1 but only those deployed for the direct investigation of gaseous or volatile reaction products of lithium ion batteries [The term “lithium ion battery” is used for any kind of batteries, in which the main charge carriers are lithium ions (also for cells containing a lithium metal anode, like in lithium-sulfur (Li–S) or lithium–air/lithium–oxygen (Li–O2) batteries, or so-called half-cells).] (LIBs). Differential electrochemical mass spectrometry (DEMS) has been extensively used in other fields of electrochemistry, especially in electrocatalysis2,3; however these applications are also beyond the scope of this report. After a short historical review of DEMS, we will show the different development periods relevant to battery research and the implementations used recently, demonstrating the versati ... mehrlity and strengths of this technique. Lastly, we discuss the typical gases observed with DEMS and their formation patterns based on the literature data.