A novel hybrid positive electrode with liquid-solid redox couples having high-capacity for lithium battery

We demonstrate a novel rechargeable energy storage system having a metallic lithium negative electrode and a liquid–solid hybrid positive electrode of Fe 3+ /Fe 2+ /Fe in N,N-Dimethylformamide, which are separated by an impermeable NASICON–type Li 1.4 Al 0.4 Ge 0.2 Ti 1.4 (PO 4 ) 3 –epoxy resin composite film with a lithium ion conductivity of ca. 5.0 × 10 −4  S cm −1 . The discharge curve for the battery shows two plateaus. The first plateau corresponds to Li + FeCl 3 = LiCl + FeCl 2 , while the second one is associated with 2 Li + FeCl 2  = 2 LiCl + Fe. In the process of reduction of Fe 3+ to Fe 2+ , it delivers a stable discharge capacity of ca. 110 mAh g FeCl3 −1 with a Coulombic efficiency higher than 95% and is capable of enduring over 60 circles at a high current density of 1.0 mA cm −2 without any catalyst. Furthermore, a stable discharge capacity up to ca. 455 mAh g FeCl3 −1 is achieved for conversion of FeCl 3 /FeCl 2 /Fe with a three–electron reaction. This work demonstrates a proof of feasibility of hybrid liquid–solid hybrid positive electrode, since these reactions are reversible confirmed by x–ray diffraction patterns and EDX mapping test.