The Effect on the Reaction Rate By the Binder Contact with the Cathode Active Material for 2V Class Water Based Lithium Ion Battery

Abstract

Introduction Batteries with high electromotive force using aqueous electrolyte solution have been developed by the control of the Hydrogen and Oxygen overvoltage. Leclanche in 1866, manganese dioxide cathode active material, zinc anode active material, and ammonium chloride aqueous solution were applied as a Leclanche battery since zinc is well known as the suitable material of which having high hydrogen overvoltage to overcome the 1.23 V restriction of the water decomposition. Further break through on higher output voltage was achieved by applying PbO2 as the cathode material of lead-acid battery due to its high oxygen overvoltage. Similar point of view may be taken into account as a key point in the development on water-based lithium batteries. The binders commonly used in the conventional lithium ion batteries are polyvinylidene fluoride and polyacrylonitrile, they may work fine as the water based lithium batteries with similar functions. Thus we examined them from the view point of the overvoltage. Experimental The two electrode cells for testing cathode active material of 2V-class water based lithium-ion battery were prepared by the following procedure. Cathode active material of LiNi1/3Mn1/3Co1/3O2 (NMC), PVDF as the binder, and acetylene black conducting reagent were mixed to be as the cathode slurry. Aluminum or titanium were used as the current collector, and zinc was used as an anode. Charging/discharging performance in 6M LiNO3 aqueous electrolyte solution was evaluated by cyclic voltammetry at a sweep rate of 0.5 mV/s. To elucidate the effect of binder, the gold wire only and NMC implanted on gold wire were prepared by coated with and without PVDF, butyral resin, SBR binders, and used as the working electrode. The counter electrode of SUS and Ag/AgCl reference electrode were used for three-electrode cell with 6M LiNO3 aqueous electrolyte solution, and the electrochemical reaction was evaluated by cyclic voltammetry at a sweep rate of 5 mV/s. Results and Discussions For the case of Al current collector, the open circuit voltage of about 2.0 V was observed after charging. However, the gas evolution, probably oxygen evolution, from the electrode surface is observed, and the reaction current became unstable due to come unstuck of active material composites from Al current collector. The pH of electrolyte solution increased from 6 to 12 during the discharging, and this may be decreased the stability of Al. During the discharging, white precipitate was observed on zinc anode and this may be attributed to Zn(OH)2. To prevent these unstable situation, the current collector was changed from Al to Ti, and the results were fine as i) oxygen evolution was suppressed, ii) unstuck of active material composites was suppressed, iii) reaction current became stable. Clearly, it was concluded that the use of Ti was the promising current collector for the 2V class water based lithium-ion battery. According to the three-electrode cell measurement, only the case of PVDF binder showed clear charging/discharging current, whereas the other case did not show any charging/discharging current. As a conclusion, the choice of Ti as the current collector and the PVDF as the binder was suitable for 2V class water based lithium-ion battery.