Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-019-01730-1 PEDOT:PSS coating on pristine and carbon coated LiFePO 4 by one‑step process: the study of electrochemical performance Hari Raj 1  · Anjan Sil 1 Received: 8 April 2019 / Accepted: 19 June 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract The carbon coating on lithium iron phosphate (LiFePO 4 ) is well known process to improve the electrical conductivity of non-conductive LiFePO 4 (LFP). But due to complex process of carbon coating at high temperature, herein, we report study on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) water soluble conducting polymer coated pris- tine LFP as well as carbon coated LFP (LFP/C) prepared by simple one step process. PEDOT:PSS coating has played very important role in enhancing the electrochemical performance of Li-ion battery as well as electrical conductivity of LFP and LFP/C samples. The electrical conductivity of PEDOT:PSS coated LiFePO 4 samples is increased by many folds (10 4 −10 8 ) as compared to pristine and carbon coated LFP. The study reveals that diferent optimum amount of PEDOT:PSS say 10 wt% and 5 wt% is required for best electrochemical performance of pristine LFP and LFP/C, and samples are designated as LFP-10P and LFP/C-5P respectively. Sample LFP-10P has shown discharge capacity of 140.8 mAh g −1 whereas LFP/C-5P shown 154.6 mAh g −1 at current rate of 0.1C. The same samples have shown highest capacity retention of 92% and 96% respectively after 200 cycles, in their group. 1 Introduction Lithium ion (Li-ion) battery is one of the most reliable sources of energy for portable electronics [1]. However, there are various cathode materials for Li-ion batteries but LiFePO 4 has got adequate attention from scientifc com- munity due to its good life cycle, high energy density, low cost and environmentally benign nature [2, 3]. The theo- retical capacity of LiFePO 4 is 170 mAh g −1 and discharge potential is 3.45 V versus Li/Li + of half cell [4, 5]. How- ever, LiFePO 4 sufers from poor electrical conductivity (10 −8 –10 −10  S cm −1 ) as well as with lower Li + ion difusion (10 −10 –10 −16  cm 2  s −1 ). Therefore, use of LiFePO 4 in high power applications is very difcult [6–8]. There are various processes that have been applied to overcome the limitation of poor electrical conductivity of LiFePO 4 . Some of the suc- cessful methods reported are using nano particle LiFePO 4 [9], coating of LiFePO 4 particles with conductive agents [10–12], and doping with other elements [13, 14]. Carbon coating with optimized thickness of 3–8 nm is considered most benefcial due to low cost, easy to use and chemically stable [15, 16]. Moreover, coating of conducting polymers such as poly- aniline, polypyrrole, polythiophene and their derivatives have shown improvement in the electrochemical perfor- mance of LiFePO 4 [17–19]. Among the various conducting polymers, poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) conducting polymer has attracted adequate attention of researchers due to its relatively low cost, water solubility, excellent electrochemical stability, good thermal as well as mechanical properties, and most importantly adjustable conductivity from 0.1 to 3000 S cm −1 [20–22] on doping. Various studies have been reported in which PEDOT:PSS polymer is used as coating as well as binder material [23–29]. In addition, PEDOT:PSS is a water soluble conducting polymer. In the present work, PEDOT:PSS coating on pristine LiFePO 4 (LFP) and carbon coated LiFePO 4 (LFP/C) was done by direct mixing (a simple one-step process) with varying polymer content. The weight ratios of active materials (LFP or LFP/C) to the PEDOT:PSS are considered as 100:0, 95:5 and 90:10. The study reveals the positive efect of synergy * Anjan Sil asil1fmt@iitr.ac.in; anj_si1@yahoo.co.uk Hari Raj harirajphy@gmail.com 1 Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Roorkee-247667, Roorkee, Uttarakhand, India