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Suppressing Sodium Dendrites by Multifunctional Polyvinylidene Fluoride (PVDF) Interlayers with Nonthrough Pores and High Flux/Affinity of Sodium Ions toward Long Cycle Life Sodium Oxygen-Batteries

Advanced Functional Materials

March 2018
28(13):1703931

DOI:10.1002/adfm.201703931

Authors:

Ma Jin Ling

Chongqing University

Show all 6 authorsHide

Rechargeable sodium–oxygen (Na–O2) batteries are of interest due to their high specific capacity, high equilibrium potential output, and the abundance of sodium resources; however, their cycle life is still very poor due to instability of electrolytes and especially the uncontrollable growth of Na dendrites. Herein, as a proof-of-concept experiment, a facile and low-cost strategy is first proposed and demonstrated to effectively suppress growth of Na dendrites by using a fibrillar polyvinylidene fluoride film (f-PVDF) with nonthrough pore as a multifunctional blocking interlayer. Unexpectedly, the f-PVDF interlayer endows Na–O2 battery with superior electrochemical performances, including high rate capability and long cycle life (up to 87 cycles), which is superior to those of the compact PVDF (c-PVDF), PVDF with through pores (p-PVDF), polyethylene oxide (PEO), and conventional polytetrafluoroethylene (PTFE) counterparts due to the following combined advantages: (1) the stronger CF polar function groups provide a better affinity to Na ions, thus enabling a more homogeneous Na deposition than that of CO function groups in PEO interlayer; (2) compared with c-PVDF and p-PVDF interlayers, f-PVDF holds more electrolyte uptake for higher ion conductivity; (3) the good wettability of the f-PVDF interlayer with electrolyte benefits Na dendrite suppression compared with PTFE interlayer.

SEM image of a) c‐PVDF, b) p‐PVDF, c) f‐PVDF, d) PEO film, e) PTFE film, and f) ion conductivity of these films in 0.5 m NaCF3SO3/TEGDME electrolyte.

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a) Schematics of the symmetrical battery design, schematics showing Na deposition behavior and top‐view SEM images of b) c‐PVDF, c) p‐PVDF, d) f‐PVDF, e) PEO, and f) PTFE blocking interlayer after depositing 3 mA h Na at current density of 0.5 mA cm⁻².

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a) CV profiles at a voltage sweep rate of 0.1 mV s⁻¹ under different atmospheres for Na–O2 batteries with and without f‐PVDF blocking interlayer, b) rate capability, c) voltage of the terminal discharge versus the cycle number curves of Na–O2 batteries with the five blocking interlayers, and d) cycle life for Na–O2 batteries with and without f‐PVDF blocking interlayer at different current densities.

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SEM image of the anodes after the a) 1st charge (1C), b) 20C, c) 40C, d) 80C with PVDF blocking interlayer and i) the corresponding XRD results; SEM image of the anodes after the e) 1C, f) 10C, g) 20C, h) 40C without PVDF blocking interlayer and j) the corresponding XRD results.

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SEM image of CNTs cathode a) before 1st discharge, after b) 1st, c) 40th, d) 80th charge, e) XRD patterns of CNTs cathode during cycling, and f) 1H‐NMR spectra of CNTs cathode after 40 cycles.

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1703931 (1 of 7)

Suppressing Sodium Dendrites by Multifunctional

Polyvinylidene Fluoride (PVDF) Interlayers with

Nonthrough Pores and High Flux/Afﬁnity of Sodium Ions

toward Long Cycle Life Sodium Oxygen-Batteries

Jin-Ling Ma, Yan-Bin Yin, Tong Liu, Xin-Bo Zhang, Jun-Min Yan,* and Qing Jiang

Rechargeable sodium–oxygen (Na–O2) batteries are of interest due to their

high speciﬁc capacity, high equilibrium potential output, and the abun-

dance of sodium resources; however, their cycle life is still very poor due

to instability of electrolytes and especially the uncontrollable growth of Na

dendrites. Herein, as a proof-of-concept experiment, a facile and low-cost

strategy is ﬁrst proposed and demonstrated to effectively suppress growth

of Na dendrites by using a ﬁbrillar polyvinylidene ﬂuoride ﬁlm (f-PVDF) with

nonthrough pore as a multifunctional blocking interlayer. Unexpectedly,

the f-PVDF interlayer endows Na–O2 battery with superior electrochemical

performances, including high rate capability and long cycle life (up to

87 cycles), which is superior to those of the compact PVDF (c-PVDF), PVDF

with through pores (p-PVDF), polyethylene oxide (PEO), and conventional

polytetraﬂuoroethylene (PTFE) counterparts due to the following combined

advantages: (1) the stronger CF polar function groups provide a better

afﬁnity to Na ions, thus enabling a more homogeneous Na deposition than

that of CO function groups in PEO interlayer; (2) compared with c-PVDF

and p-PVDF interlayers, f-PVDF holds more electrolyte uptake for higher ion

conductivity; (3) the good wettability of the f-PVDF interlayer with electrolyte

beneﬁts Na dendrite suppression compared with PTFE interlayer.

DOI: 10.1002/adfm.201703931

J.-L. Ma, Dr. Y.-B. Yin, Prof. J.-M. Yan, Prof. Q. Jiang

Key Laboratory of Automobile Materials

Ministry of Education

Department of Materials Science and Engineering

Jilin University

Changchun 130022, China

E-mail: junminyan@jlu.edu.cn

J.-L. Ma, T. Liu, Prof. X.-B. Zhang

State Key Laboratory of Rare Earth Resource Utilization

Changchun Institute of Applied Chemistry

Chinese Academy of Sciences

Changchun 130022, Jilin, China

The ORCID identiﬁcation number(s) for the author(s) of this article

can be found under https://doi.org/10.1002/adfm.201703931.

lithium–oxygen (Li–O2) batteries hold high

speciﬁc capacity and equilibrium poten-

tial output (2.96 V), their cycling stability

is still very poor due to serious electrolyte

and carbon cathode decomposition caused

by high charging overpotential.[1] Further-

more, we shall always be prepared for

the limited and unbalanced distribution

of lithium resources forces. In response,

a promising alternative to Li–O2 battery

chemistry would be Na–O2 battery due to

its low charging overpotential (<200 mV)

and abundant natural resources of Na.[2,3]

Unfortunately, cycle life of Na–O2 battery is

also very poor due to electrolyte decomposi-

tion, crossover of O2 and moisture to anode,

and especially Na dendrite formation. To

improve the cycle life of Na–O2 battery,

many efforts are devoted to developing efﬁ-

cient catalysts,[4] novel cathode matrixes,[5]

and stable electrolytes.[6] Although signiﬁ-

cant achievements have been obtained, the

stability of Na metal anode and especially

the uncontrolled Na dendrites growth

during cycling are still rather unexplored.

Sodium dendrite growth mainly causes two serious prob-

lems: (1) the growing Na dendrites would pierce separator,

resulting in short circuit and subsequent thermal runaway of

the battery; (2) Na dendrites would break the solid electrolyte

interphase (SEI) and continuously generate cracks upon strip-

ping/plating processes. Consequently, the exposed fresh Na

would react with electrolyte to form SEI, and thus result in a

low Coulombic efﬁciency because of excessive Na and electro-

lyte consumption. In response, some novel methods have been

developed, such as coating Na metal by ceramic/solid polymer

electrolyte with high Young modulus,[6b,7,8] using liquid–metal

Na.[9] However, these strategies still hold more or less draw-

backs, including low ionic conductivities, high interfacial resist-

ance, and thermal management difﬁculty, thus resulting in

poor rate capability of Na–O2 batteries and safe issues. There-

fore, suppression of Na dendrites while not compromising the

electrochemical performances is a still a paramount challenge

for the development of Na–O2 batteries.

Theoretically, Na dendrites are induced by inhomogeneous

distribution of current density on the rough Na metal anode

Sodium-Oxygen Batteries

1. Introduction

Increasing attentions have been devoted to alkali metal–air

batteries to meet the challenges of cost-effective and high-

energy electrochemical storage devices. Although aprotic

Adv. Funct. Mater. 2018, 28, 1703931

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