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The effect of polyaniline on TiO2 nanoparticles as anode materials for lithium ion batteries
© Zheng et al. 2016
Received: 30 May 2015
Accepted: 17 February 2016
Published: 17 May 2016
Polyaniline (PANI) additives have been shown to have a significant effect on titanium dioxide (TiO2) nanoparticles as lithium ion battery anode materials. TiO2/PANI composites were prepared using a solid coating method with different ratios of PANI and then characterized using XRD and SEM. These composites have shown increased reversible capacity compared with pure TiO2. At the current rate of 20 and 200 mAg−1, maximum capacities were also found on 15 % PANI incorporated TiO2 composite with 281 mAh g−1 and 168.2 mAh g−1, respectively, and 230 and 99.6 mAh g−1 were obtained in the case of pure TiO2. Among all the composite materials, 10 % PANI incorporated TiO2 composite exhibited the highest reversible capacity with cycle stability after 100 cycles at the current rate of 200 mAg−1, suggestive that the optimal ratio is 10 % PANI of TiO2/polyaniline. The cycle stability showed swift fade when the ratio of PANI in the composites exceeded 10 % though the highest initial capacity was achieved on 15 % PANI in the composites. These results suggest that PANI has effectively enhanced the reversible capacity of commercial TiO2, and may be a promising polymer matrix materials for lithium ion batteries.
Titanium based oxides have attracted tremendous attention from researchers as the potential next generation anode materials in lithium ion batteries. They are currently being investigated as potential graphite substitutes. The theoretical capacity of titanium dioxide (TiO2) is 330 mAhg−1 which is slightly lower than that of graphite at 372 mAhg−1. TiO2 also offers better properties over graphite owing to its high lithium insertion/de-insertion potential, higher reversible capacity and lower volume expansion during lithium ion insertion/de-insertion. This leads to enhanced structural stability and a longer cycle stability (Wang et al. 2007; Nuspl et al. 1997; Su et al. 2012). However, the practical attainable capacity of TiO2 is only half the theoretical value due to the blocking of further li-ion insertion of TiO2 resulting from the strong repulsive force between Li ions. This reportedly limits the application and development of TiO2 as anode materials for LIBs (Kavan et al. 1995; Kavan et al. 2000; Tang et al. 2009). Furthermore, its low conductivity is hampered for application of LIBs. Fortunately, it has been predicted by theoretical simulations with experimental results that the capacity and cycling stability of the TiO2 electrode can be improved dramatically when the nanoscale of TiO2 was explored (Sudant et al. 2005; Jiang et al. 2007; Fattakhova Rohlfing et al. 2007; Yang and Zeng 2004). The TiO2 performance of anode materials can be improved by combining TiO2 with other materials such as carbon (Yang et al. 2012; Wang et al. 2013).
Conducting polymers have drawn considerable attention due to their good environmental stability and electronic properties as well as their optical performance. The polymers have been studied as active matrices to improve the capacity, cycling stability and rate of performance of electrodes for LIBs because the polymer can provide a conducting backbone for the active materials amongst their many properties (Chen et al. 2012; Chew et al. 2007; Dong et al. 2013; Huang and Goodenough 2008; Jeong et al. 2013). Furthermore, with regard to electrochemical activity towards Li, the relatively inert matrix of polymeric composites would accommodate the mechanical stresses/strains resulting from the active phase which would maintain the structural integrity of the composite during lithium intercalation/de-intercalation. Polyaniline (PANI) is one of the more important conducting polymers because of its relatively facile processability, electrical conductivity and environmental stability. PANI has been studied extensively for energy storage systems because of its good redox reversibility and high stability (Novák et al. 1997; Karthikeyan et al. 2013; Liang et al. 2011). Mesoporous PANI/TiO2 microspheres were reported as anode materials with a significantly improved capacity (Lai et al. 2011; Lai et al. 2010). The material was calcined at 500 °C for 3 h in air. However, PANI begins to decompose around 300 °C and completely decomposes at 500 °C in air (Zeng and Ko 1998). We have repeated the same methods to prepare PANI/TiO2 composites without air treatment. In this work, we have prepared PANI/TiO2 composite materials using a mechanical method with a different ratio of PANI to TiO2 as anodes for lithium- ion batteries (Yang et al. 2008).
Aniline, Ammonium peroxydisulfate and 37 % hydrochloric acid were purchased from Sigma-Aldrich. TiO2 and carbon black PRINTEX XE 2-B were procured from DUGASSA and used as received.
Synthesis of polyaniline (PANI)
Polyaniline was synthesized by chemical polymerization. Aniline monomer was dissolved in the 0.02 M HCl aqueous solution and stirred magnetically at 0–5 °C for 0.5 h. An aqueous solution of (NH4)2S2O8 that acts as an oxidant was added to the above solution. The mixture was then left to react over night at 0–5 °C. The precipitate was washed with deionized water followed by methanol, and then finally dried overnight at 70 °C in a vacuum.
Preparation of TiO2/polyaniline composite
TiO2/polyaniline composite was formed by the mechanical mixing method. The ratio of PANI/TO (w/w) was 0, 5, 10, 15 and 20 %, named as TO, TO5PA, TO10PA, TO15PA and TO20PA.
Electrochemical measurements were carried out between 1.0 and 3.0 V vs Li+/Li0 with CR2032 coin cells. The synthesized composites were mixed with Carbon black (PRINTEX XE 2-B) and PVDF (75:13:12 wt %) to fabricate the anode. In the coin-cell tests, metallic lithium foil was used as the counter and reference electrodes; the electrolyte was 1 M LiPF6 in 1:1 (v/v) solvent mixture of ethylene carbonate and diethyl carbonate (EC/DEC).
Results and discussion
The maximum number of inserted Li+ was evaluated to be 0.5 (Nuspl et al. 1997) that result in a theoretical capacity of 167.5 mAh g−1 (Lou and Archer 2008). The cathodic peaks at 1.6 V (TO15PA) and 1.3 V (TO) determines that two phase transitions happened on the structure from tetragonal anatase to orthothombic Li0.5TiO2 when the insertion coefficient X in reaction (Wang et al. 2007) has reached about 0.5 (Chen and Lou 2010; Sivakkumar and Kim 2007). There is a coupling of cathodic/anodic peaks around 2.8 V, especially on TO20PA which is associated with the doping/leaching processes of polyaniline (Kavan et al. 1996).
Summary of CV results (Fig. 3) on TO and TO/PANI composites at a scan rate of 1 mVs−1 for the first and second cycles
During the rate performance, the TO/PANI composites exhibited better capacity retention when the current rate eventually increased to 160 mAg−1. The capacities of pure TO reduced to 70.1 mAh g−1 at a current rate of 160 mAg−1 (at the end of tenth cycle), which is 30 % retention of this at the initial stage. The TO10PA, TO15PA and TO20PA showed the capacities of 83.1, 123.1 and 85.9 mAh g−1 respectively which are 42, 44 and 34 % of the capacities of the initial stage at a current rate of 20 mAg−1. This indicates the improved capacity rate of TO/PANI composites compared with pure TO.
Summary of specific capacity and capacity retention at a current rate of 200 mAg−1 with different cycle number (1th, 50th and 100th)
Capacity retention (%)
Capacity retention (%)
Discharge retention (mAg−1)
Capacity retention (%)
Capacity retention (%)
In this work, TO/polyaniline composites were prepared via the solid coating method. The results demonstrated that polyaniline has effectively enhanced the reversible capacity of commercial TO. At the current rate of 20 mAg−1, the TO15PA has showed the highest capacity of 281 mAh g−1, while the capacities TO10PA, TO20PA and TO were 198, 250, and 230 mAh g−1 respectively. In addition, TO, TO10PA, TO15PA and TO20PA showed the capacities of 99.6, 127.2, 168.2 and 125.4 mAh g−1 respectively at the current rate of 200 mAg−1. TO10PA retained the best capacity (83.7 mAh g−1) and cycle stability after 100 cycles. It is suggested that polyaniline is a potential matrix material for lithium ion batteries; however, the synthesis of polyaniline or polyaniline composites still need improvement to meet the requirements for lithium ion battery applications.
NN and NM were involved in the coating preparation and the assisted battery performance testing. HZ was involved in the synthesis and characterizations of PANI and TO/PANIs and battery performance testing as well as writing. KR and MM assisted writing. All authors read and approved the final manuscript.
The authors are thankful for the financial support from CSIR of South Africa (No. HTR046P).
The authors declare that they have no competing interests.
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