The high intensity ultrasonication treatment allows the formation of FeSn 2 nanoparticles encapsulated in an organic matrix of polyacrylonitrile. The polymeric matrix stabilizes the intermetallic particles and improves the electrochemical cycling behavior in lithium batteries. For FeSn 2 @PAN, a capacity of 360 mAh/g (referred to the mass of iron and tin atoms or 418 mAh/g refereed to the mass of tin) is observed after 60 cycles, with a capacity loss of 12.8% from the cycle 10 to 60, while for PAN-free FeSn 2 the capacity drop from cycle 20 to 30 is 20%.Tin-transition metal-carbon alloys can be used as negative electrode for lithium ion batteries. 1 The carbonaceous phase buffers the volume changes of the metallic particles during lithiation and improves the electrical contact.Polymers such as polyacrylonitrile (PAN) can be used in solid electrolyte batteries. 2 In addition, it is worth noting that PAN molecules have great ability to interact with metallic surfaces (chemisorption), 3,4 the Li þ ions can migrate through the PAN chains by interaction with the CN groups 2 and PAN thin films can be electrical conductors by electron hopping. 3 Having all this in mind, PAN may be used in tin-containing composite electrodes. Thus, tin-transition metal-PAN composites have been explored as electrode materials and the encapsulation of CoSn 2 nanoparticles in a PAN matrix has been reported. 5,6 The reduction of Co(II) and Sn(II) with NaBH 4 in PAN-dimethylformamide solutions leads to CoSn 2 nanoparticles embedded in a PAN matrix (represented like CoSn 2 @PAN). The addition of PAN hinders the grain growth of the metallic phase, resulting in an improved electrochemical behavior. In contrast, the reduction of Fe(II) and Sn(II) leads to crystalline Sn. 6 This can be related to the easier Co/Sn alloying. Due to cost and environmental factors, the use of iron instead of cobalt would be advantageous, but it seems to be difficult to achieve good cycling behavior with cobalt-free tin alloys. 7 The sonochemical method can be used to prepare metallic nanoparticles, such as tin nanorods, 8 electrode materials for batteries 9 and to perform coating treatments. 10 Herein we describe a new strategy for the fabrication of FeSn 2 and FeSn 2 -PAN by using a sonochemical method.
ExperimentalFeSn 2 was obtained by using a combination of polyol and sonochemical methods (method A). The method involves the reduction of metal salts by NaBH 4 in tetraethylene glycol (TEG) medium. The ultrasonic radiation provided by a Sonics Vibra-cell Ultrasonic Processor VCX750 provided with a Ti horn was used. First, anhydrous SnCl 2 and FeCl 3 .6H 2 O were dissolved in 45 ml of TEG. Then, NaBH 4 dissolved in TEG was added drop-wise into the solution under continuous ultrasonication. Finally, the resulting FeSn 2 powders were separated by centrifugation, washed and dried.For the preparation of the FeSn 2 -PAN composite (method B), SnCl 2 .2H 2 O, FeCl 2 .4H 2 O and PAN (molecular weight ¼ 150.000) were added into n-dimethylformamide and ultrasound irradiation wa...