Synthesis and electrochemical properties of polyradical cathode material for lithium second batteries

Abstract

A stable polyradical, poly (2,2,6,6-tetramethylpiperidinyloxy methacrylate)(PTMA), was synthesized, and its structure was determined by infrared, ultraviolet-visible, and ESR spectroscopy. Cyclic voltammograms of the PTMA polyradical electrodes were obtained by using a three-electrode cell at a scan rate of 5 mV/s within a potential range of 3.2–4.0 V. The results show that the shape of oxidation peak is very similar to that of reduction peak, and oxidation peak current is equal to the corresponding reduction peak current, which suggest that PTMA possesses an excellent reversibility. The difference of the anodic peak potential (E _a,p=3.66 V, vs Li/Li⁺) and cathodic peak potential(E _c,p=3.58 V, vs Li/Li⁺) is estimated at 80 mV, which is extremely less than that of the other organic positive materials in lithium second batteries such as organosulfide compounds, leading to a capability for high current capability in the charging and discharging process of the battery. The maximum discharge specific capacity of PTMA is 78.4 mA · h/g at the constant discharge current of 0.3 mA (0.2 C rate), the coulombic efficiency is about 95%, and the charging and discharging curves of the batteries have an obvious plateau at 3.65 V and 3.56 V, respectively. The discharging specific capacity of the battery decreased is about 2% after 100 cycles. The PTMA/Li button batteries exhibite an excellent stability.