Studies of tin-transition metal-carbon alloys prepared by mechanical milling for lithium-ion battery negative electrodes

Mechanical milling and co-sputtering were used to prepare various Sn-Co-C alloys as negative electrodes materials for Li-ion batteries. By varying milling conditions, it was possible to obtain nanostructured materials by mechanical methods whose x-ray diffraction patterns mimicked the diffraction patterns of co-sputtered materials. Electrochemical testing of L/Sn30 Co30C40 cells showed stable charge-discharge capacity for at least 100 cycles, and stable differential capacity versus potential profiles. Although the materials appeared to have similar nanostructures, the sputtered material showed a reversible capacity near the theoretical capacity of Sn30Co30C40, while the materials prepared by mechanical methods showed lower capacity.;In an attempt to replace cobalt with a cheaper transition metal, iron, several compositions of Sn30(Co1-xFe x)30C40 were prepared by attritor milling. XRD and Mossbauer studies showed evidence of a nanostructured phase, most prominent near x = 0, and nanocrystalline FeSn 2, most prominent near x = 1. Mossbauer studies showed an increase in the amount of Fe-carbides as the Fe content increased. Both the x = 0 and x = 0.5 samples showed excellent capacity retention with a specific capacity of 450 mAh/g for at least 100 cycles. The x = 1 sample showed the highest reversible capacity for the cells tested at approximately 500 mAh/g but its capacity retention was poor.;Structural and electrochemical experiments were reported for numerous Sn30TM30C40 and Sn30Co15 TM15C40 alloys, prepared by attritor milling, with TM = 3d transition metals. Sn30TM30C40 samples with TM = Co and TM = Ni showed stable differential capacity versus potential plots, and stable cycling for at least 100 cycles with reversible capacities of 425 and 250 mAh/g, respectively. All samples prepared with 15 at.% Co show good capacity retention for at least 100 cycles ranging from 270 mAh/g (TM = Ni) to 500 mAh/g (TM = Ti).;From small angle neutron scattering results, it was found that milled materials had grain sizes on the order of 60 A, while those of sputter deposited materials had grain sizes on the order of 10 A or were truly amorphous. These results were used to understand why mechanically alloyed Sn-Co-C alloys do not reach their expected theoretical specific capacity.