ИСТИНА

Li-O2 batteries have the highest theoretical energy density among electrochemical energy sources. Unfortunately, these batteries maintain poor cyclability, as the main discharge product – Li2O2, is an insulator. Introducing redox mediators (RM) into electrolyte may solve this problem: electrochemically oxidized form of RM chemically oxidizes lithium peroxide during the charge process. In order to investigate possible candidates for RM and their behavior at the positive electrode, it is necessary to understand the side reactions and their effect on discharge/charge curves. For instance, processes that occur on the Li-electrode lead to degradation of the Li-O2, furthermore severe corrosion may affect electric conductivity and RM stability. This study is attributed to investigation of side reactions in Li-O2 batteries. To facilitate the interpretation of GCPL metallic Li anode could be replaced by lithium-iron phosphate (LFP) electrode – commercially available material with low-energy density yet with high stability. Since LFP has a two-phase intercalation-deintercalation mechanism, the potential remains unchanged during both lithiation and delithiation [1]. Commercially available LFP is deposited onto thin aluminum foil (LFP@Al), which exhibits corrosion during cycling in 1M LiTFSI/DMSO. To prevent degradation preliminary cycling of LFP-Li half-cell in LiPF6/EC:DMC (1:1) is necessary. This procedure results in enhanced stability towards corrosion and therefore longer battery life, which is shown in Figure 1a. Cycling of Li-O2 cell revealed that the shape of discharge curve depend on the charge voltage limit: increasing the limit leads to enlarging “step” at the beginning of the discharge. We believe that this region is a reverse process to side oxidation reactions that occur at the positive electrode surface upon charge. The charging curve include two regions at lower and higher potentials, the capacity of discharging “step” correlates to capacity of the higher-potential charging region which is demonstrated at Figure 1b. In this work, we have applied passivation technique on LFP@Al electrode that prevents current collector corrosion. Relationship between the shape of the discharge and charge curves has been investigated, and influence of voltage upper-limit on discharge plateau is emphasized. Overall, the way is paved for further RM investigation by GCPL technique in Li-O2 batteries. References: 1. Bergner, B.J.; Busche, M.R.; Pinedo, R.; Berkes, B.B.; Schröder, D.; Janek, J.// ACS applied materials & interfaces 2016, 8(12), 7756-7765.