Received: 9 November 2007, Revised: 27 June 2008, Accepted: 29 June 2008, Published online in Wiley InterScience: 28 January 2009 Ionic conductivity in poly (L-leucine)1,3-diamino propane–lithium iodide solid polymer electrolyte N. H. Kaus a , N. Lahazan a and A. H. Ahmad a * The pelletized Poly(L-Leucine)-1,3-diamino propane–lithium iodide (LiI) samples have been prepared by using a low temperature sintering method. Results from impedance spectroscopy have proven this mixture to be a superionic material with maximum conductivity obtained in the range of 10 S3 S/cm for the samples containing 50 wt% LiI. The high ionic conductivity achieved was due to the increased number of charge carrier from LiI. Improved conductivity could also be due to hopping of lithium ion through the side chain of polymer. Infrared spectroscopy showed that both LiI and poly amino acid may co-exist together. From the spectra it is revealed that the C – –O band at 1643 cm S1 shifted to higher wave number indicating that chelation of Li R may have occurred at oxygen atom. Results from X-ray diffraction show that the prepared samples were partially crystalline in nature. Some of the peaks have disappeared and this confirmed that some complexation has occurred within the sample. Copyright ß 2009 John Wiley & Sons, Ltd. Keywords: PLL-Lil INTRODUCTION Lithium ion conducting dry polymer electrolytes have attracted a lot of interest due to their safety feature when compared to liquid electrolyte. The advantages of solid electrolyte over the liquid electrolyte as safer alternatives to liquid electrolyte or gel polymer electrolytes in lithium secondary batteries have been discussed and can be found in the literature [1–3] . High dissociative property, high electrochemical stability, and good thermal stability are necessary for lithium salts in polymer electrolytes. However, the ionic conductivity of polymer elec- trolytes is still too low for general practical application. In another work, [4] ionic conductivity was greatly affected in zwitterionic polymer due to structural modification during the preparation of the sample. Zwitterion polymer blend material is shown to be a material with many applications. It may be employed as medical and electrochemical devices because of its unique physical and mechanical properties. Salt impurities can be held by zwitterions and studies on thermal, viscometry, and electrical conductivity have been carried out. [5–7] The addition of zwitterions to a composite and gel polymer electrolyte helped to increase the mobility of the lithium ion and led to improved conductivity. According to Takada et al., [8] any composition containing Lithium iodide (LiI) are called superionic conductors and these compounds showed highest conductivity. In other works, [9,10] they reported that the solid electrolyte system containing LiI has showed high conductivities of about 10 3 Scm 1 at room temperature. Creating a new material that is useful, easily reproducible and is a sustainable source of energy that is environmental friendly due to its biodegradable properties is our objective in this work. The material that is of current interest is poly amino acid that is poly-L-Leucine (PLL) and LiI. Amino acid chosen in this research is made up of a long chain of leucine monomer. Poly amino acid is non-toxic, biodegradable and the use of this material helps to prevent world environmental degradation. This organic polymer is chosen as the host material due to its molecular structure which can be complexed with lithium salts such as LiI to produce superionic lithium based solid polymer electrolyte. Its plastic characteristic helped to rubberize molten salt systems or the hygroscopic nature of most lithium salt systems. This gives the advantage of the newly developed solid electrolyte which is stable in air. In this work, a new PLL and LiI as a solid electrolyte is prepared and characterized by using impedance spectroscopy, Fourier transform infrared, X-ray diffraction (XRD), and transfer- ence number measurement. METHODOLOGY Sample preparation The two mixtures of PLL and LiI were mixed in appropriate weight ratio and ground in agate mortar. The powdered mixtures were then pelletized and sintered at 908C for 3 days. The temperature of 908C was chosen because LiI liberates free I 2 at temperatures above 1338C. [11] Sintering in the vacuum oven also helps to remove the influence of residual water in the samples. The choice of 3 days has been determined by optimizing the conductivity of the samples with fixed amount of LiI with sintering time. (www.interscience.wiley.com) DOI: 10.1002/pat.1246 Special issue: Research Article * Correspondence to: A. H. Ahmad, Institute of Science, Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia E-mail: azizahanom@salam.uitm.edu.my a N. H. Kaus, N. Lahazan, A. H. Ahmad Institute of Science, Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia Contract/grant sponsor: Scientific Advancement Grant Allocation (SAGA); contract/grant number: 100-IRDC/SAGA. Polym. Adv. Technol. 2009, 20 156–160 Copyright ß 2009 John Wiley & Sons, Ltd. 156