Evaluating the Effect of Binder for Sulfurized Polyacrylonitrile Cathode via Optical Fiber Sensors

Sulfurized polyacrylonitrile (SPAN) is a very stable and promising sulfur‐based cathode material for high energy density lithium–sulfur (Li–S) batteries, which can circumvent the polysulfides dissolution issue. However, the stress concentration caused by volume change in SPAN cathodes is relatively significant but is rarely focused on. It is widely reckoned that the binder plays a key role in buffering the stress induced by electrode materials and hence maintains the integrity of electrodes. Nevertheless, the understanding of the actual effect of binders to SPAN cathodes from the aspect of mechanics remains to be deepened. Here, the optical fiber Bragg grating (FBG) is implanted into SPAN cathode films to in situ evaluate the electrochemo‐mechanical behaviors by using four different binders. The internal strain evolution of SPAN cathodes is affected by multiple factors of adhesion and mechanical properties of different binders. It is found that the SPAN cathode using poly(acrylic acid) (PAA) binder with outstanding mechanical properties experiences the largest strain change but the electrochemical performance is even better under high sulfur loading. Furthermore, the strain evolution is monitored under high sulfur loading condition and how the sulfur loading affects the signals of the built‐in FBG sensors is tried to figure out. The actual mechanical effect of different binders on sulfurized polyacrylonitrile (SPAN) cathodes is in situ evaluated via built‐in optical fiber Bragg grating sensors. The internal strain evolution of SPAN cathodes is affected by mechanical properties of different binders as well as the sulfur loading. The SPAN cathode using poly(acrylic acid) binder with best mechanical properties experiences the largest strain change.