Electrochemical study on nano-Sn, Li4.4Sn and AlSi0.1 powders used as secondary lithium battery anodes

It is believed that particle cracking resulting from phase transformation is responsible for the poor cycle performance of lithium alloy anodes. Pulverization effects may be reduced by using, (i) smaller active particles; (ii) active particle composites with different potentials for the onset of lithium ahoy formation; and (iii) expanded alloys which have undergone a major increase during initial charging. Three alloys of the above types (nano-Sn, AlSi0.1 and Li4.4Sn) were studied by electrochemical impedance spectroscopy (EIS) to determine their electrochemical kinetics and intrinsic resistance during initial Lithium insertion-extraction. The electrodes were prepared by sandwiching a disk of active powder between two nickel screens, so that the contact resistance may be determined by EIS and from a d.c. voltage difference across the electrode (trans-electrode voltage). A large increase in contact resistance was found during lithium discharge (extraction) from nano-LixSn and LixAlSi0.1 alloys, compared with the small increase during the initial charge. This result suggest that the matrix materials should have a small coefficient of elasticity to give low stress on expansion of the active alloy, together with a large elastic deformation to compensate for volume reduction. This is contrary to generally accepted argument that the matrix should have a high ductility. EIS results for measurement of intrinsic resistance and reaction kinetics during initial lithium insertion into nano-Sn and AlSi0.1 alloys show that both solid electrolyte interphase (SEI) films formed on particle surfaces, together with particle pulverization, are responsible for the high contact resistance. The electrochemical kinetics of both lithium charge and discharge are controlled by contact resistance at high states of charge. (C) 2001 Elsevier Science B.V. All rights reserved.