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 i s responsible for the poor cycle performance of lithium alloy anodes. Pulve rization effects may be reduced by using, (i) smaller active particles; (ii ) active particle composites with different potentials for the onset of lit hium 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 spectrosco py (EIS) to determine their electrochemical kinetics and intrinsic resistan ce during initial Lithium insertion-extraction. The electrodes were prepare d by sandwiching a disk of active powder between two nickel screens, so tha t the contact resistance may be determined by EIS and from a d.c. voltage d ifference 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 t he initial charge. This result suggest that the matrix materials should hav e a small coefficient of elasticity to give low stress on expansion of the active alloy, together with a large elastic deformation to compensate for v olume reduction. This is contrary to generally accepted argument that the m atrix should have a high ductility. EIS results for measurement of intrinsi c resistance and reaction kinetics during initial lithium insertion into na no-Sn and AlSi0.1 alloys show that both solid electrolyte interphase (SEI) films formed on particle surfaces, together with particle pulverization, ar e 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 reserve d.