Studies on Capacity Loss and Capacity Fading of Nanosized SnSb Alloy Anode for Li-Ion Batteries

Abstract

Nanosized SnSb alloy exhibits much higher reversible capacity as an anode active material for Li-ion batteries. However, rather large capacity loss at the first charge and discharge cycle as well as capacity fading during cycling for pure nanosized alloy has been observed. These phenomena originate from the following factors: the decomposition reaction of surface oxide and the formation of solid electrolyte interphase on the surface of alloy, the irreversible trapping of Li ions by host atoms, serious aggregation of alloy particles during electrochemical cycling, and the existence of an impure phase. Several strategies have been proposed to overcome these drawbacks, including surface modification, addition of dispersant, and coating on stable frame cores, such as mesophase carbon microbeads, to form composite materials.Recently, much attention has been given to the exploration of novel electrode materials in order to enhance the energy density of Li-ion batteries. Compared with carbonaceous materials, tin-based composite oxides ͑TCO͒ and alloys show higher specific capacity as anode active materials. 1-10 However, for oxide anode materials, a large irreversible capacity loss was observed at the first charge and discharge cycle due to a reduction/replacement reaction. 2 As a result, the cathode has to provide an extra Li source to compensate for the lost capacity, leading to a decrease of the energy density of the battery. On the other hand, alloy particles with larger size always pulverize rapidly during discharge and charge cycles, due to drastic volume variation. Consequently, their reversible capacities faded significantly with cycling. 7,11,12 In order to overcome this problem, superfine intermetallic compounds and active/inactive composite alloy materials have been studied recently, such as Sn/SnSb x , Sn/SnAg x , and SnFe/SnFeC. [7][8][9][10] Although direct structural evidence has not been presented yet, two conclusions can be accepted. First, a nanosized metal or alloy electrode can keep a rather stable microstructure during cycling because it has high endurance to volume variation due to their superplasticity and high ductility. 7,9,13 Second, for intermetallic compounds and active/inactive composite materials, the active component is produced in situ and dispersed into the matrix of inactive component uniformly at an atomic or nanometer scale, as with the situation in oxide anodes. 10 As a result, the volume variation of the active element could be alleviated effectively. In addition, inactive elements with higher conductivity can also provide a better conductive environment. Owning to these beneficial factors, the cyclic performance of alloy anode materials with superfine particles has been improved impressively. Based on this idea, nano-Si/carbon black composite materials have been studied by us, and better cyclic performance and a reversible capacity of 1700 mAh/g have been achieved. 12 However, it has been noticed recently that the Coulombic efficiency of superfine alloys was not as high as that of ...

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