Binder Free Carbon Fiber-Based High-Voltage Cathode for Lithium-Ion Batteries

Abstract

Introduction With increasing demands of large-scale electronic applications such as electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium ion batteries (LIBs) with high energy density and power density are desired. To meet the performance requirements, an electrode design that enables to accommodate more active material loading while reducing additives, such as binders and conductive agents, is drawing much attention from researchers. Currently, Al foil is commonly used as the current collectors for cathodes of LIBs. However, corrosion of Al foil could become a serious issue, particularly for long-term cycling at high voltage, deteriorating battery performance [1]. On the contrary, carbon fibers (CFs) are thermally and electrochemically stable, and they can work as good electrical conductors with lightweight, thereby becoming a potential candidate for current collector application[2]. In the current study, we aim to combine nickel-manganese-chromium based cathode material and CFs to develop a composite electrode that can tolerate high-voltage operation. Experimental First, heat and acid treatments were carried out to remove resin from CFs surface. Then, electrodeposition of the pretreated CFs was performed in a solution containing nickel, manganese, and chromium ions, to obtain precursor fibers. After that, the precursor fibers went through hydrothermal reaction and calcination, forming a CF-based composite. The composite was further grinded, slurried, and filtrated on a carbon paper to complete the composite electrode. The electrodes were characterized through SEM, TEM, XRD, EDS, XPS and their electrochemical performance was evaluated through a coin cell (CR2032) with lithium metal foil as a counter electrode. In addition, 1 M LiPF6 in a mixture of ethylene carbonate : dimethyl carbonate (1:1 in volume ratio) was used as the electrolyte, and a polyolefin film was used as the separator. Results and Discussion From the experiment results, it is convinced that the electrode fabrication process is appropriate to prepare the CF-based composite electrodes. However, properties of the electrodes, including morphology, chemical composition, and crystallinity, vary depending on the fabrication conditions. More interestingly, it is found that Cr doping can stabilize the structure of the Li-Ni-Mn-Cr-O active material with increased crystallinity. The Li-Ni-Mn-Cr-O/CF cathode with proper Cr doping content demonstrates favorable electrochemical performance against high-voltage operation (3.0 ~ 4.9 V). It delivers discharge capacities of 143 and 104 mAh g-1 at 0.2 C and 1 C, respectively. In addition, the cathode possesses excellent cycling stability with a capacity retention over 95% after 100 cycles.