Electrolyte loaded hexagonal boron nitride/polyacrylonitrile nanofibers for lithium ion battery application

doi:10.1016/j.ssi.2017.07.004

Solid State Ionics

Volume 309, 15 October 2017, Pages 71-76

https://doi.org/10.1016/j.ssi.2017.07.004 Get rights and content

Highlights

•
hBN/polyacrylonitrile composite nanofibers were produced via electrospinning approach
•
Electrospun hBN/PAN composite nanofiber filled with liquid electrolyte to form polymer electrolyte (PE)
•
Li/PE /LiCoO₂ cell systems were assembled for charge and discharge cycling measurements.

Abstract

In the present work, Novel hBN/polyacrylonitrile composite nanofibers were produced via electrospinning approach and loaded with electrolyte for rechargeable lithium-ion battery applications. The electrospun nanofibers comprising various hBN contents were characterized by using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The influence of hBN/PAN ratios onto the properties of the porous composite system, such as fiber diameter, porosity and the liquid electrolyte uptake capability were systematically studied. Ionic conductivities and electrochemical characterizations were evaluated after loading electrospun hBN/PAN composite nanofiber with liquid electrolyte, i.e., 1 M lithium hexafluorophosphate (LiPF₆) in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (1:1 vol). The electrolyte loaded nanofiber has a highest ionic conductivity of 10^− 3 S cm^− 1 at room temperature. According to cyclic voltammetry (CV) results it exhibited a high electrochemical stability window up to 4.7 V versus Li⁺/Li. Li//10 wt% hBN/PAN//LiCO₂ cell was produced which delivered high discharge capacity of 144 mAhg^− 1 and capacity retention of 92.4%. Considering high safety and low cost properties of the resulting hBN/PAN fiber electrolytes, these materials can be suggested as potential separator materials for lithium ion batteries.

Introduction

Li-ion batteries have become important in the field of electronic industry due to their advantages like compactness, lightweight, high operational voltage and providing highest energy density [1], [2], [3]. Typical Li-ion battery has a cathode (LiCoO₂, LiMnO₂, LiFePO₄ etc.), an anode (graphite, graphene, carbon nanotubes, carbon nanofibres, lithium titanium oxides etc.) and a separator [1], [3].

The separator provides an electrical insulation between anode and cathode and allow ion transfer during operation. It also plays a significant role in determining battery performance [4], [5]. The performance of the Li-ion battery separator is determined by several factors such as permeability, porosity, electrolyte uptake capacity, mechanical, thermal and chemical stability [1], [3], [6]. Several commercially available polymers have been used as separators and the most common polymers are poly(ethylene) [7], poly(propylene) [8], poly(ethylene oxide) [9], poly(acrylonitrile) [10], [11], [12], poly(methyl methacrylate) [13] and poly(vinylidene fluoride) (PVDF) [14], [15], [16]. During the preparation of the battery separator several types of Li-salts (LiClO₄, LiPF₆, CF₃SO₃Li etc.) and fillers (SiO₂, TiO₂, etc.) [9], [11], [17], [18], molecular sieves and clays [19], [20], ferroelectric materials [21] and carbon based fillers can be mixed with the polymer matrix. Although Li-salts participate in the conduction process, fillers are not directly contributing to the conduction process. They enhance of morphological, mechanical, thermal, electrochemical properties and interfacial stability of the separators [4], [5].

Hexagonal boron nitride (hBN) is physically analogous to graphite with comprising hexagonal layers of 0.33 nm distance and is the most examined polymorph among other systems [22]. It is white powder and has a melting point of 3000 °C. hBN has important physical and chemical properties such as high corrosion resistance, good lubrication property, high thermal conductivity, high temperature stability, good resistance to oxidation and chemical inertness. It has several applications such as coatings, electrical insulation, optical storage, optoelectronic devices, medical treatment, and lubricant [23], [24], [25], [26]. The blending of hBN in polymers is mostly due to its thermal conductivity property [24]. The usage of hBN in fuel cell polymer electrolyte was previously investigated by our group and contribution of hBN to the electrolyte stability as well as proton conduction was reported [27], [28]. Another important innovative part of this work is that the presence of high thermal conducting separator may positively contribute to the thermal management in lithium ion batteries.

Polyacrylonitrile (PAN) is a semicrystalline thermoplastic polymer used in many industrial areas. It provides several improvements with easy modification of its morphology and physical properties [10], [11], [17].

Electrospinning of polymer solutions to prepare thin fibers provides high porosity, better morphology and high surface area resulting high electrolyte uptake and easy ion transport [14]. If the processing parameters are controlled it is possible to obtain electrospun fibrous materials with 30–90% porosity and μm range pore sizes [15]. It is preferred in recent years for the production of polymer nanocomposites due to the elimination of homogeneity problems observed in normal casting methods.

The present work includes the preparation of new hBN/PAN composite nanofibers by electrospinning. The nanofibers were characterized with different spectroscopic techniques. The morphological properties and the electrochemical performance of the liquid electrolyte loaded hBN/PAN composite nanofibers were investigated.

The Li ion conductivity of electrolyte loaded nanofibers were measured via dielectric-impedance analyzer. A battery cell, Li//10 wt% hBN/PAN//LiCO₂ was constructed and its capacity as well as cycling stability results are discussed.

Section snippets

Materials

PAN (average Mw = 150.000 g mol^− 1) and N,N-Dimethylformamide(DMF) were obtained from Sigma-Aldrich. Liquid electrolyte, 1 M lithium hexafluorophosphate (LiPF₆) in ethylene carbonate and ethyl methyl carbonate (EC + DEC, 1:1 by volume), was delivered from Sigma Aldrich. Hexagonal boron nitride (hBN, particle size = ~ 70 nm) was supplied from Lower Friction. LiCoO₂, Lithium chip and CR2032 cells were purchased from MTI Corporation. All chemicals were used without further purification. Lithium chip and

FT-IR spectra

The FI-IR spectra of pure PAN fibers and hBN/PAN nanocomposite fibers are illustrated in Fig. 1. At around 2935 cm^− 1 a peak is observed which is due to the methylene ( single bond CH₂) group, the peaks at 2246 cm^− 1 and 1449 cm^− 1 can be attributed to stretching vibration of nitrile groups (CN) and the bending vibration of methylene (CH₂), respectively [29]. The FT-IR spectra of all the samples after spinning are showing the presence of characteristic peak of single bond C triple bond N at 2243 cm^− 1.

Huang et al. previously studied the

Conclusion

Novel hBN/PAN electrospun fibers were produced by using electrospinning method to apply as thermally stable Li-ion battery separator and the host of a gel polymer electrolyte. SEM analysis verified the presence of greatly porous nanofibrous structure. Experimental results indicated that the electrospun 10 wt% hBN/PAN composite fibers has better thermal stability (280 °C), largest electrolyte uptake (1250%), highest ionic conductivity (1.0 × 10^− 3 Scm^− 1), and best electrochemical stability (4,7 V). The

Acknowledgements

This study is partially supported by TÜBİTAK#112M488.

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Electrolyte loaded hexagonal boron nitride/polyacrylonitrile nanofibers for lithium ion battery application

Highlights

Abstract

Introduction

Section snippets

Materials

FT-IR spectra

Conclusion

Acknowledgements

J. Power Sources

J. Solid State Electrochem.

J. Power Sources

Eur. Polym. J.

J. Membr. Sci.

Ceram. Int.

J. Power Sources

Electrochim. Acta

Electrochim. Acta

Mater. Chem. Phys.

Electrochim. Acta

J. Power Sources

Solid State Ionics

Int. J. Electrochem. Sci.

Electrochim. Acta

J. Solid State Chem.

Thermochim. Acta

J. Eur. Ceram. Soc.

J. Power Sources