Short communicationPorous NiO/poly(3,4-ethylenedioxythiophene) films as anode materials for lithium ion batteries
Introduction
3d transition-metal oxide (MO, M = Fe, Co, Ni, and Cu) films are widely investigated as anode materials for film lithium ion batteries since they were proposed by Tarascon's team [1], [2], [3], [4], [5], [6]. These films exhibit high capacities over 700 mAh g−1 even at high charge–discharge current density. However, for many bare films, their capacities reduce very quickly during the repeated discharge–charge cycling. The main reason for this is that these 3d transition-metal oxides are a kind of semiconductor with poor conductivity. To overcome this problem, forming composite with other highly conductive materials such as silver, nickel, carbon, and some conducting polymers is an effective method [7], [8], [9], [10], [11], [12], [13].
Poly(3,4-ethylenedioxythiophene) (PEDOT) is a conductive polymer and it can be used to improve the electrochemical performances of electrode materials for lithium ion batteries [14]. In this present work, porous NiO/PEDOT composite films were deposited on the nickel foam substrate. The nickel foam substrate has much larger surface area than the metal-foil flat substrate and much more active materials can be obtained [15], [16]. The porous films were constructed by many interconnected NiO nanoflakes and the PEDOT covered on the surfaces of each flake. This porous structure offers a larger electrode/electrolyte contact area and a shorter diffusion length of lithium ions. The PEDOT facilitated the electron transfer between the film, the current collector, and the electrolyte and thus improved the electrochemical properties.
Section snippets
Experimental
NiO/PEDOT films were deposited by two steps. Firstly, NiO films were deposited on the nickel foam substrate using chemical bath deposition method as reported in Refs. [17], [18]. The solution for chemical bath deposition contained 40 mL of 1 mol L−1 NiSO4, 30 mL of 0.25 mol L−1 K2S2O8, 10 mL of concentrated aqueous ammonia, and 20 mL of deionized water. After depositing for 1 h at room temperature, the films were calcined in a tube furnace at 350 °C for 2 h in flowing argon. Secondly, PEDOT was deposited
Results and discussion
Fig. 1 shows the SEM images of the bare NiO film and the NiO/PEDOT films deposited after 1, 2 and 3 CV cycles, respectively. The bare NiO film is porous, and it is constructed by many interconnected NiO nanoflakes, whose thicknesses are about 20 nm. These nanoflakes grow vertically on the substrate, forming a net-like structure and the pores among the flakes are about 200 nm (Fig. 1a). Obviously, this porous film has a large electrode/electrolyte contact area, and during the electrode reaction,
Conclusions
Porous NiO/PEDOT composite films were prepared by chemical bath deposition and electrodeposition techniques. These films have a porous net-like morphology, which was constructed by NiO nanoflakes coated by PEDOT. Electrochemical tests showed that the composite film prepared after 2 CV cycles exhibited the best cycling performance and its capacity after 50 cycles at 2 C was 520 mAh g−1. Compared to the bare NiO film, this NiO/PEDOT film exhibited weaker polarization and better cycling performance.
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