Materials Today Energy
Volume 18, December 2020, 100494
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Lithium-ion battery separator membranes based on poly(L-lactic acid) biopolymer

https://doi.org/10.1016/j.mtener.2020.100494Get rights and content

Highlights

  • Different PLLA membranes have been developed for battery separator applications by varying polymer concentration.

  • The best ionic conductivity of 1.6 mS/cm has been obtained for the PLLA separator membranes.

  • The membranes show excellent properties for environmentally friendly Li-ion battery separators.

Abstract

Sustainable materials are increasingly needed in lithium ion batteries in order to reduce their environmental impact and improve their recyclability. This work reports on the production of separators using poly (L-lactic acid) (PLLA) for lithium ion battery applications. PLLA separators were obtained by solvent casting technique, by varying polymer concentration in solution between 8 wt% and 12 wt% in order to evaluate their morphology, thermal, electrical and electrochemical properties. It is verified that morphology and porosity can be tuned by varying polymer concentration and that the separators are thermally stable up to 250 °C. The best ionic conductivity of 1.6 mS/cm was obtained for the PLLA separator prepared from 10 wt% polymer concentration in solution, due to the synergistic effect of the morphology and electrolyte uptake. For this membrane, a high discharge capacity value of 93 mAh/g was obtained at the rate of 1C. In this work, it is demonstrated that PLLA is a good candidate for the development of separator membranes, in order to produce greener and environmentally friendly batteries in a circular economy context.

Introduction

Energy storage systems are necessary to supply energy and power in portable electronic devices and electrical vehicles, among others. In particular, considering the advances in electronic miniaturization, there is a demand for smaller and lighter batteries with enhanced performance [1]. Lithium-ion batteries are energy storage systems that meet the above specifications, with a global battery market of 75% which is expected to grow by around 7% annually until 2024 [2]. Lithium-ion batteries present specific advantages when compared to other battery types, such as high energy density, low self-discharge, no memory effect and higher number of charge/discharge cycles [3,4].

To improve battery performance in lithium-ion batteries, key issues such as specific energy, power, safety and reliability must be addressed. These issues depend on the characteristics of the materials for the different battery components [5]. A lithium-ion battery consists of a negative electrode (anode) and a positive electrode (cathode), which are separated by a porous membrane called a separator [6,7]. The separator is essential to improve battery performance. It can be based on different types of porous materials, including microporous membranes, nonwoven membranes, electrospun membranes, membranes with external surface modification, composites or polymer blend membranes [8]. The main functions of the separator are to promote a medium for ions to transfer between the electrodes, prevent physical contact between the anode and the cathode, regulate cell kinetics and improve safety in the charge and discharge mechanism, as well as to warrant battery mechanical stability [4,9]. Separator properties mainly depend on its physical-chemical characteristics including thickness, permeability, overall porosity, pore size and interconnectivity, wettability, electrolyte absorption and retention, and chemical, thermal and mechanical stability [10]. Regardless of the separator type, they are mostly based on porous membranes [8]. The incorporation of the lithium solution is usually achieved by uptake, through the immersion of the polymer membrane directly within the lithium-ion solution until the weight remains unchanged [11].

Different processing techniques can be used to obtain porous materials, such as thermal induced phase separation, template synthesis, self-assembly or even electrospinning [12].

Different polymer materials including poly (ethylene), PE [13], poly (propylene), PP [14], poly (methyl methacrylate), PMMA [15], poly (ether-ether-ketone) (PEEK) [16], poly (acrylonitrile), PAN [17], polyimide (PI) [18], Nylon 6.6 [19], poly (vinylidene fluoride), PVDF [20], poly (vinylidene fluoride-co-hexafluoropropene), PVDF-HFP [21] and poly (vinylidene fluoride-co-trifluoroethylene, PVDF-TrFE [20] are being explored for battery separator applications [7].

Commercial separators basically rely on polyolefin polymers based on their mechanical stability and chemical stability, good electrochemical performance and low cost [22]. The drawbacks of these separators are their hydrophobic behavior, high flammability and, considering environmental issues, their difficult recyclability, not being in agreement with the circular economy and sustainability paradigms [10]. Considering those issues, new types of separators based on natural polymers, including cellulose derivatives, eggshell membranes or poly (vinyl alcohol), have been proposed due to the low production cost, good physical and chemical properties and suitable performance as separators [[23], [24], [25]]. In this context, it is interesting to explore the suitability of poly-l-lactic acid (PLLA) for battery separator applications. PLLA is a biocompatible and biodegradable enantiomeric polyester produced from lactic acid synthesis [26]. Further, PLLA presents a broad spectra of processing morphologies, including films [27,28], electrospun fibers [29,30] and membranes [31], as well as electroactive characteristics, with a piezoelectric constant of about 6–10 pC.N−1 [32], enabling the possibility to integrate smart and responsive materials in battery applications [33]. The suitable characteristics of PLLA have been demonstrated in its applications in the field of tissue and biomedical engineering [34], agriculture [35], aquaculture [36], sensors [37] and electronics [37].

It is important to note that the interest in PLLA as a recyclable polymer has grown due to environmental concerns with conventional plastics [38]. The biodegradability of PLLA makes easier its recyclability, when compared with the most widely used polymers [39]. The life cycle assessment with respect to recycling of PLLA has proven the economic and environmental benefits of reusing the polymer instead of disposing or incinerating it [40].

PLLA has been recently investigated as gel polymer electrolytes (GPE) through the production of cellulose acetate (CA)/poly-l-lactic acid (PLLA)/Halloysite nanotube composite nanofibers. These CA/PLLA/HNT composite nanofiber membranes have been used as green skeleton materials in GPEs for lithium-ion batteries in search for high performance and environmental sustainability [41]. Also, PLLA was successfully used as a coating in a GPE, in order to suppress the growth of lithium dendrites in the battery, allowing high electrolyte uptake and retention, thermal stability, electrochemical stability and Li+ transference number [42]. Nevertheless, to our knowledge, there are still no applications of this polymer directly as separator membranes for lithium ion batteries or in the electrochemistry field. In the present work, porous membranes based on PLLA were developed by thermal induced phase separation by varying polymer concentration in solution. The effect of processing conditions on the physical-chemical properties of the membranes and on the performance of the fabricated batteries was investigated.

Section snippets

Materials

Poly (L-lactic acid) (PLLA) with an average molecular weight of 217.000–225.000 g/mol (Purasorb PL18) was supplied by Purasorb. N, N-dimethylformamide (DMF), dichloromethane (MC), N-methylpyrrolidinone (NMP) and 1 M LiPF6 in a mixture of ethyl carbonate (EC) and dimethyl carbonate (DMC) (1:1 in vol. ratio) were obtained from Merck. The materials were used as provided. Lithium iron phosphate, C–LiFePO4 (LFP), carbon black, and poly (vinylidene fluoride), PVDF (Solef 5130) were supplied by

Morphology, polymer phase and thermal stability

Surface SEM images in two magnifications of the different PLLA separators are shown in Fig. 1. Regardless of the polymer concentration in the original solution, all membranes are characterized by a porous morphology with interconnected pores homogenously distributed along the membrane. The obtained morphology is explained by the polymer-solvent interaction and evaporation temperature, which results in both liquid–liquid (Solvent (S)–Solvent (S)) and solid–liquid (Polymer (P)–S) demixing during

Conclusions

Lithium-ion battery separator membranes based on poly (l-lactic acid) (PLLA) are presented in order to address the environmental impact of the polymers used in energy storage systems.

PLLA separators were developed varying the polymer concentration between 8 wt% to 12 wt% in a mixture of DMC/DMF solvent and produced by solvent casting technique with thermal induced phase separation.

It is shown that the polymer concentration affects the microstructure and morphology of the membranes, being

Author contribution

João C. Barbosa: Methodology; Validation; Formal analysis; Investigation; Writing - Original Draft; Writing -Review & Editing. Ander Reizabal: Investigation; Validation; Methodology; Writing - Original Draft. Daniela M. Correia: Methodology; Validation; Formal analysis; Investigation; Writing - Original Draft; Writing - Review & Editing. Arkaitz Fidaldo-Marijuan: Methodology; Validation; Formal analysis; Investigation; Writing - Original Draft; Writing - Review & Editing. Renato Gonçalves:

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Work supported by the Portuguese Foundation for Science and Technology (FCT) under strategic funding UID/FIS/04650/2020 and UID/QUI/0686/2020, project PTDC/FIS-MAC/28157/2017, and Grants SFRH/BD/140842/2018 (J.C.B.), SFRH/BPD/121526/2016 (D.M.C), CEECIND/00833/2017 (R.G.) and SFRH/BPD/112547/2015 (C.M.C.). Financial support from the Basque Government Industry Department under the ELKARTEK and HAZITEK programs is also acknowledged. Technical and human support provided by SGIker (UPV/EHU, MICINN,

References (67)

  • I. Kuribayashi

    Characterization of composite cellulosic separators for rechargeable lithium-ion batteries

    J. Power Sources

    (1996)
  • V.H. Nguyen et al.

    Recycling different eggshell membranes for lithium-ion battery

    Mater. Lett.

    (2018)
  • D. Boriboon et al.

    Cellulose ultrafine fibers embedded with titania particles as a high performance and eco-friendly separator for lithium-ion batteries

    Carbohydr. Polym.

    (2018)
  • W. Xiao et al.

    Preparation and performance of poly(vinyl alcohol) porous separator for lithium-ion batteries

    J. Membr. Sci.

    (2015)
  • L. Pellegrino et al.

    Taurine grafting and collagen adsorption on PLLA films improve human primary chondrocyte adhesion and growth

    Colloids Surf. B Biointerfaces

    (2017)
  • J.M. Corey et al.

    The design of electrospun PLLA nanofiber scaffolds compatible with serum-free growth of primary motor and sensory neurons

    Acta Biomater.

    (2008)
  • P. Ladpli et al.

    Multifunctional energy storage composite structures with embedded lithium-ion batteries

    J. Power Sources

    (2019)
  • M. Shah Mohammadi et al.

    11 - polylactic acid (PLA) biomedical foams for tissue engineering

  • R.E. Conn et al.

    Safety assessment of polylactide (PLA) for use as a food-contact polymer

    Food Chem. Toxicology

    (1995)
  • D. Maga et al.

    Life cycle assessment of recycling options for polylactic acid

    Resour. Conserv. Recycl.

    (2019)
  • E. Al Tawil et al.

    Microarchitecture of poly(lactic acid) membranes with an interconnected network of macropores and micropores influences cell behavior

    Eur. Polym. J.

    (2018)
  • L.D. Kock et al.

    Solid state vibrational spectroscopy of anhydrous lithium hexafluorophosphate (LiPF6)

    J. Mol. Struct.

    (2012)
  • I.A. Neumann et al.

    Biodegradable poly (l-lactic acid) (PLLA) and PLLA-3-arm blend membranes: The Use Of Plla-3-Arm As A Plasticizer

    Polymer Testing

    (2017)
  • H. Liu et al.

    Effect of silica nanoparticles/poly(vinylidene fluoride-hexafluoropropylene) coated layers on the performance of polypropylene separator for lithium-ion batteries

    J. Energy Chem.

    (2014)
  • J. Hassoun et al.

    A lithium ion battery using nanostructured Sn–C anode, LiFePO4 cathode and polyethylene oxide-based electrolyte

    Solid State Ionics

    (2011)
  • D. Djian et al.

    Lithium-ion batteries with high charge rate capacity: influence of the porous separator

    J. Power Sources

    (2007)
  • J. Cao et al.

    La0.6Sr0.4CoO3−δ modified LiFePO4/C composite cathodes with improved electrochemical performances

    Electrochim. Acta

    (2012)
  • J. Guo et al.

    Cyclability study of silicon–carbon composite anodes for lithium-ion batteries using electrochemical impedance spectroscopy

    Electrochim. Acta

    (2011)
  • R. Pan et al.

    Mesoporous Cladophora cellulose separators for lithium-ion batteries

    J. Power Sources

    (2016)
  • A. Reizabal et al.

    Tailoring silk fibroin separator membranes pore size for improving performance of lithium ion batteries

    J. Membr. Sci.

    (2020)
  • P. Harrop et al.

    Batteries, Supercapacitors, Alternative Storage for Portable Devices 2009-2019

    (2010)
  • H.S. Choi et al.
  • P.B. Balbuena et al.

    Lithium-Ion Batteries: Solid-Electrolyte Interphase

    (2004)
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