Short communicationLi(Mn1/3Ni1/3Fe1/3)O2–Polyaniline hybrids as cathode active material with ultra-fast charge–discharge capability for lithium batteries
Graphical abstract
Highlights
► Ultra-fast charge–discharge capability is achieved for Fe based layered composites with polyaniline. ► Li(Mn1/3Ni1/3Fe1/3)O2–polyaniline composite delivered reversible capacity of ∼110 mAh g−1 at 40 C rate. ► Extraordinary performance is mainly due to drastic improvement of electronic conductivity.
Introduction
Of late immense research focus is directed toward the development of high capacity, high voltage, low cost and eco-friendly cathode for Li-ion batteries (LIB) typically containing layered structure [1], [2], [3], [4], [5], [6]. Since the commercialization of LIBs by Sony Inc. in 1991, layered type LiCoO2 and graphite were dominated as cathode and anode materials, respectively [7]. In such combination, graphitic anode essentially serves as buffer medium during Li-insertion/extraction; hence any advancement in LIB technology relies on the development of high performance cathodes [8], [9], [10]. Although the theoretical capacity of LixCoO2 is 274 mAh g−1, complete removal of 1 mol lithium is found difficult due to the structural transformation from hexagonal to cubic which results in severe fade during cycling. Hence, the practical capacity is restricted to ∼140 mAh g−1. Apart from the capacity, LiCoO2 displayed poor high current performance, toxicity of cobalt and its expensiveness is another important concern, therefore search for alternate high performance cathodes is warranted. In this line, other layered type cathodes such as LiMnO2, LiNiO2, LiFeO2 and Li2MnO3 were proposed, however practical application of such candidates are too limited due to their own setbacks [10], [11], [12]. Eco-friendly, spinel LiMn2O4 and olivine LiFePO4 were also proposed as potential alternatives, nevertheless former one suffers Mn3+ dissolution issue and later compound lacks of conductivity and limited operating potential problems, respectively [13]. Latter, Yabuuchi and Ohzuku [14] reported the performance of layered LiCo1/3Ni1/3Mn1/3O2 cathode with reversible capacity over 200 mAh g−1 which is higher capacity than reported elsewhere on layered compounds. On the other hand, aforementioned cathode still contains Co and also suffers high rate operations, which is one of the pre-requisite to power zero emission vehicles such as hybrid electric vehicles (HEV) and electric vehicles (EV). Recently, a series of “cobalt-free” Fe based layered type cathodes were reported by Tabuchi et al. [15], [16] and delivered the reversible capacity over 200 mAh g−1 in the initial cycles. However, severe capacity fading is encountered for said layered type compounds and also complex synthetic process was employed to yield single phase material and inherent electronic conductivity issues as well. Very recently, we reported Fe based layered type Li1.2(Mn0.32Ni0.32Fe0.16)O2 cathodes by a simple sol–gel technique in the presence of adipic acid with good electrochemical properties [17]. As expected, in general Fe based materials are generally experiencing poor electrochemical behavior at high current operations due to the intrinsic nature such compounds [18]. In this line, we made an attempt to synthesize LiFe1/3Ni1/3Mn1/3O2 cathodes by simple co-precipitation technique and followed by annealing. To alleviate the inherent properties of said compound, the concept of making composite cathode was developed by using a conducting polymer, polyaniline (PANI) to form composite inorganic-organic hybrids [19], [20]. Among the conducting polymers reported, PANI has certain advantageous likely, higher chemical stability, high electrical conductivity in its oxidized/protonated form, better acid–base properties and stable electrochemical behavior [19]. In addition, few reports based on PANI based composites cathodes were already reported to promote the conducting nature of cathodes, for example LiFePO4–PANI [20], [21], [22] and LiNi0.8Co0.2O2–PANI [23]. In the present work, a novel organic–inorganic hybrid LiFe1/3Ni1/3Mn1/3O2–PANI cathode was prepared first time by co-precipitation and followed by sonication with two different concentration of polymer (0.1 and 0.2 mol). Li-insertion properties were evaluated in half-cell configuration with ultra-high rate of 40 C (mass loading of active material 10 mg cm−2) and described in detail.
Section snippets
Experimental
The Li(Mn1/3Ni1/3Fe1/3)O2 was prepared using a mixed hydroxide method. Analytical grade LiOH (95%), Fe(NO3)3·9H2O (98%), and Ni(NO3)3·6H2O (97%) were procured from Junsei chemicals, Japan and MnCl2·4H2O (99.9%) was obtained from Wako Japan and used as such. In the typical synthesis procedure, stoichiometric amounts of transition metal salts were dissolved in distilled water separately and mixed together to enable solution phase reaction. Later, aqueous solution containing LiOH was added by drop
Results and discussion
Fig. 1a represents the powder-XRD patterns of pristine Li(Mn1/3Ni1/3Fe1/3)O2, Li(Mn1/3Ni1/3Fe1/3)O2–PANI-0.1 mol (hereafter abbreviated as Li(Mn1/3Ni1/3Fe1/3)O2–P1) and Li(Mn1/3Ni1/3Fe1/3)O2–PANI-0.2 mol (hereafter abbreviated as Li(Mn1/3Ni1/3Fe1/3)O2–P2). The observed XRD reflections are indexed according to the α-NaFeO2 structure with space group. Apparent to notice the formation of phase pure layered structure without any impurity traces, more importantly the absence secondary peaks
Conclusion
A novel eco-friendly organic–inorganic hybrid composite with excellent electrochemical performance was demonstrated in half-cell configuration under harsh conditions. The TEM pictures revealed the formation of sub-micron size Li(Mn1/3Ni1/3Fe1/3)O2 particles and composite formation with two different concentration of PANI. Among them, Li(Mn1/3Ni1/3Fe1/3)O2–PANI (0.2 mol) was exhibiting better battery characteristics and retained 86% of initial discharge capacity after 40 cycles. The composite
Acknowledgement
This work was supported by the IT R&D program of MKE/KEIT [KI002176, Development of 3.6 Ah Class Cylindrical Type Lithium Secondary Battery].
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