High-Performance Snsb Nanostructured Electrode Assembly for Lithium-Ion Batteries
Authors: Jiang Qianlei , Jia Mengqiu , Hu Daozhong , Jin Yuhong , Zhao Yujuan , Ji Changwei 
Published: February 2020

Lithium-ion batteries as a new clean energy with high specific energy and excellent cycle performance and long life serve widely as the power source for many portable electronic devices. However, their power and energy densities need to be further increased particularly for the application in electric vehicles. It is important to develop high capacity anode materials to increase the energy density of lithium-ion batteries as the anode material is one of the key factors affect the performance of lithium-ion batteries. SnSb intermetallic alloys are attractive materials as a potential substitute for the conventional graphite anode because their theoretical capacity of SnSb alloys has been estimated to be superior to that of graphite. However, its practical use is hampered by their large volume change during alloying and de-alloying reaction with Li+, as the continuous volume change during cycling will cause the mechanical pulverization resulting in poor cyclability and cracking of the electrode. Various strategies have been brought forward to improve the cycling stability, for example, preparing thin film materials or nanostructured materials. nanostructured alloy anodes have shown an improved cycle lifetime because nanostructured alloy anodes can accommodate the large volume change and maintain the structural integrity of the electrode during the lithiation/de-lithiation process.

In this paper, a nanostructured SnSb anode for Li-ion battery has been prepared by a two-step electrode design consisting of the electrochemically assisted template growth of Cu nanopillars onto a current collector followed by electrochemical plating of SnSb, there among, Cu nanopillars current collector was obtained by P. Simon's method. We try to take advantage of the nanostructuration of our electrodes to buffer the mechanical strains occurring during the cycling of tin and antimony with Li+, thanks to larger free space available for alloy–dealloying reactions, delivers a high cycle life and good power performance.

Firstly, Cu nanopillars current collectors were obtained using previously reported procedure. Briefly, arrays of copper nanorods on copper disk substrate were prepared by pulsed cathodic electrodeposition through an alumina oxide membrane. The electrolytic cell assembly has been described in P. Simon's work. Secondly, Copper nanopillars were covered with SnSb by means of an electro-co-deposition process from an aqueous solution consisting of SnSO4, KSbOC4H4O6∙1/2H2O, K4P207∙l0H2O and gelatin. The SnSb coating was produced at a constant cathode current density using a two-electrode glass cell at room temperature. Cu substrate containing copper nanopillars acted as the working electrode, whereas a Pt foil served as the counter electrode. The electrodeposits were carried out for a certain deposition time in a galvanostatic mode. After SnSb electro-co-deposition, the obtained SnSb nanostructured anodes were washed with distilled water and acetone successively and then placed under argon atmosphere to avoid oxidation. The morphology, structure and composition of these anode materials were characterized by XRD, SEM and EDS, respectively. The electrochemical reaction mechanism, charge/discharge capacity and cycle performance were analyzed by various electrochemical measurements. And on this basis, we investigated the correlations between material properties and electrochemical performance of the electrode.

The scanning electron microscopy (SEM) image clearly shows SnSb nanoparticles are uniformly deposited on the surface of the Cu nanopillars without any coalescence between them. This particular nanostructure is expected to be able to accommodate volume variations occurring during cycling in a lithium cell and thus result in excellent capacity retention. EDS analysis of the deposits of SnSb on Cu nanopillars current collectors gave a Sn:Sb atomic ratio of about 1: 1. The peaks of X-ray diffraction (XRD) pattern are attributed to the SnSb phase and show a rather amorphous feature. Electrochemical measurements showed that the SnSb nanostructured anodes show a relatively smooth voltage curve and a high initial coulombic efficiency of 95.7%,Quite different the curves with distinct voltage plateaus of the SnSb film electrode which SnSb deposited on a flat surface. And more importantly, the SnSb nanostructured electrode exhibited a high initial reversible storage capacity of about 738.9mAh/g and excellent capacity retention with only 10.6% decay over 30 cycles. The reversible capacity and capacity retention is high compared with the similar materials reported by other literatures.

 Obviously, the SnSb alloy deposited on the Cu nanopillars experiences the same internal stress as that of the SnSb alloy deposited on a flat Cu surface. In the case of the nanostructured electrode, however, the volume variations upon cycling are effectively buffered by the large free volume between the pillars, thus giving to the electrode the observed excellent capacity retention. It is anticipated that the AAO template-assisted method could also be applied to synthesize other promising nanostructured electrode materials by electrodeposition.

Figure 1