The Performance of Polymer Binders in Lithium Ion Batteries

High-energy-density lithium-ion batteries (LIBs) with a long cycle life are in tremendous demand for use inportable electronics and electric vehicles [1]. Unfortunately, the practical application of high capacity anode materialsin LIBs is still quite challenging. Large variation in volume occurs during charge–discharge cycling, which causesfracturing and pulverization of the anode materials and breaks the electrical contacts between active materials andconductive additives, resulting in a rapid capacity fading and a short cycle life [2]. One of the main approaches isusing binders to stabilize the structure of the electrode [3]. The traditional PVDF binder, which interacts withelectrode materials via weak Van der Waals forces and consequently lacks the necessary capabilities (e.g., thesuppression of significant volume variations, the interface maintenance etc.), could not fulfill the high demands ofbatteries with high energy density. Besides, extensive usage of the PVDF binder in the lithium ion battery is costineffectiveand may raise environmental concerns as its handling often needs the assistance of organic solvents [4]. Atraditional binder system is dual-component based, essentially with two components for two different functionalities.Polymer binders, such as polyvinylidene fluoride (PVDF), mechanically hold the active materials and additivestogether. Electronically conductive additives, such as acetylene black (AB), are necessary to ensure electricalconductivity of the entire electrode. In a porous composite electrode, the nonconductive polymer binder combineswith AB conductive additives to maintain the electronic connection. In addition to the mechanical adhesion andelectronic connection, the polymer covers the active material surfaces, so the polymer should swell in electrolyte toprovide enough ionic conductivity. Although such classic dual-component binder design is popular in the current Liionbatteries, it does not work well for the high-capacity electrodes with large volume change. Mechanically, highcapacityelectrode materials tend to generate more than an order of magnitude higher stress in the electrode thanthose of graphite during lithiation. The stress disrupts the mechanical integrity, leading to electrode fracture anddelamination. More seriously, the electronic integrity of electrodes relies on the connections between thenonadhesive conductive additives and active materials. Even with extensive amounts of conductive additive, thisconnection will break after extended cycles of large volume change. The dilemma of employing high-capacitybattery materials and maintaining the electronic and mechanical integrity of electrodes demands novel designs ofbinder systems [5]. In this study the goal is to show that electrochemical performance of the MOF anode with CMCbinder and polyaniline binder will significantly improve compared to that of a MOF anode with a PVDF binder.