Ultrastrong and Heat-Resistant Poly(ether ether ketone) Separator for

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Ultra-strong and Heat-resistant Poly(ether ether ketone) Separator for Dendrite-proof and Heat-resistant Lithium-ion Batteries Junchen Liu, Yudi Mo, Shuanjin Wang, Shan Ren, Dongmei Han, Min Xiao, Luyi Sun, and Yuezhong Meng ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00568 • Publication Date (Web): 30 Apr 2019 Downloaded from http://pubs.acs.org on May 5, 2019

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ACS Applied Energy Materials

Ultra-strong and Heat-resistant Poly(ether ether ketone) Separator for Dendrite-proof and Heat-resistant Lithiumion Batteries Junchen Liua, Yudi Moa, Shuanjin Wanga, Shan Rena, Dongmei Hana, Min Xiaoa*, Luyi Sunb, Yuezhong Menga*

a. The Key Laboratory of Low-carbon Chemistry & Energy Conservation of Guangdong Province, State Key Laboratory of Optoelectronic Materials Technologies, School of Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510275, P.R. China b. Polymer Program, Institute of Materials Science and Department of Chemical & Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269, United States.

Abstract Separators are a pivotal component of lithium-ion batteries (LIBs) due to their vital role in maintaining a good ionic flow and preventing internal short circuit. The separators with superior thermal stability, ultra-high mechanical strength and excellent electrolyte wettability are essential for ensuring the safety and energy density of LIBs. Herein, an ultra-strong poly(ether ether ketone) (PEEK) separator is fabricated via thermally induced phase separation using a binary diluent for the first time, which maintains the intrinsic outstanding properties of a PEEK resin. Computational

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simulation and experimental verification are carried out to optimize fabrication conditions. The as-prepared PEEK separator with high porosity (70.3%) shows a tortuous and three-dimensional porous structure; furthermore, the abundant polar groups on PEEK endow the separator with excellent electrolyte wettability (contact angle of 19° and electrolyte uptake of 387%). Notably, the PEEK separator exhibits excellent thermal stability (almost no shrinkage at 300 ℃), flame resistance and ultrastrong mechanical strength (tensile strength of 124 MPa, Young’s modulus of 7.84 GPa and puncture strength of 10.5 MPa), which can avoid short circuit and greatly guarantee the safety of LIBs. In particular, the PEEK separator presents excellent interfacial compatibility and both a higher ionic conductivity (1.57 mS cm-1) and lithium-ion transference number (0.55). Significantly, the PEEK-based LiFePO4/Li cell displays a very stable cycle performance and better rate capability. In addition, the PEEK-based lithium-sulfur cell also shows better battery performance than a commercial polyethylene-based cell. Consequently, the specially fabricated PEEK separator is a promising separator candidate for enhanced safety and electrical performance of lithium-ion and lithium-sulfur batteries.

Keywords: Separator; Poly(ether ether ketone); Thermally induced phase separation; Lithium-ion batteries; Lithium-sulfur batteries.

1. Introduction Rechargeable lithium-ion batteries (LIBs) have been a ubiquitous power source


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for portable and consumable electronic devices due to their outstanding performance.1,2 Currently, their application in electric vehicles, grids and other large-scale electrical energy storage promotes intense interest in high safety and high power density LIBs.3,4 Safety issues, such as fire and explosions, are closely associated with internal short circuit, caused by poor dimensional thermal stability at elevated temperature, dendrite growth and the flammability of separators.5,6 In addition, to act as a barrier and avoid contact between anode and cathode electrodes, the separators can also permit ion transport, which means the role of the separators in improving safety and electrical performance of batteries is pivotal and could not be undervalued.7 Therefore, the separators with excellent electrolyte wettability, robust mechanical strength, superior thermal stability and flame retardancy are an urgent requirement for advanced LIBs.8 So far, polyolefin separators are the most commercially used ones for LIBs due to their favorable electrochemical and acceptable mechanical properties. However, they exhibit a low heat resistibility and inferior electrolyte wettability, which limit their application in high safety and high energy density LIBs.9 Although some strategies of modification (coating, grafting and blending) of the polyolefin-based separators could improve the performance of LIBs to some extent, the existence of polyethylene (PE) or polypropylene (PP) is always closely accompanied by hidden safety hazards.10,11 In addition, modification methods also generate inevitable negative effects, such as remarkably increased thickness and cost.12 Thus, considerable efforts have been undertaken to construct separators based on heat-resistant, tough strength and hydrophilic polymer substrates,13,14 such as cellulose-based,15,16 poly (vinylidene



fluoride-co-hexafluoropropylene) (PVDF-HFP),17,18 polyimide (PI),19 poly (ethylene terephthalate) (PET)20 and poly (m-phenylene isophthalamide) (PMIA).21 Poly(ether ether ketone) (PEEK), a semi-crystalline thermoplastic with high performance, possesses outstanding intrinsic characteristics, such as excellent chemical, thermal, fire and mechanical resistance ascribed to the aromatic structures of PEEK, which enable it to be a candidate separator material for LIBs.22 Meanwhile, the polar carboxyl (C=O) and oxy-ether bonds (—O—) in the PEEK backbone chains are supposed to enhance the affinity of the PEEK separator with high polar electrolyte.23 However, the fabrication of a PEEK porous separator is hampered by its poor solubility. One possible solution is the chemical modification of PEEK to increase its solubility, such as sulfonation,24 hydroxylation25 and fluorination.23 Nevertheless, these ways are accompanied by a decrease in crystallinity of PEEK and a sacrifice of its mechanical strength and thermal stability, which reduces the future safety of the batteries. The thermally induced phase separation method has been studied widely for manufacturing membranes, especially for fabricating microporous semi-crystalline membranes.26 A membrane fabricated by the TIPS method normally shows a morphology with high porosity, more uniformity and good mechanical stability. Meanwhile, the main challenge confronting the TIPS method is the selection of appropriate diluents for blending with polymers, which makes an important difference in the performance of the fabricated membrane.27 Here, we report on the fabrication of the PEEK separator via TIPS using a binary diluent for the first time (Figure 1). As a probing study of the method, we carry out


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molecular dynamics (MD)28 and mesoscopic dissipative particle dynamics (DPD)

29

simulations, which predict that the porous PEEK separator can be fabricated by proper proportions of the primary and second diluents. The as-fabricated PEEK separator not only holds the intrinsic advantages, such as thermal stability, flame retardancy, superior electrolyte wettability and mechanical performance, but also shows a porous structure with high porosity and a uniform pore size. Furthermore, the PEEK separator shows higher lithium-ion conductivity, a greater lithium-ion transference number and better interfacial stability than a commercial PE separator; hence, the PEEK separator-based lithium-ion and lithium-sulfur batteries display more excellent cycle and rate performance.

2. Experimental Section

2.1 Materials Poly(ether ether ketone) (PEEK, 330UPF) was purchased from Jilin Zhongyan High Performance Plastic Co., Ltd. (Changchun, China). Polyether sulfone (PES, 3600G, Mn = 30,000) was obtained from Sumitomo Chemical (Japan). Diphenyl sulfone (DPS) was supplied from Aladdin Co. Ltd. (Shanghai, China). The liquid electrolyte for lithium-ion batteries (LIBs) was supplied by DoDoChem (Suzhou, China) and consisted of 1 mol L-1 LiPF6 in a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) (1:1:1, volume ratio), referred to as “electrolyte” in the following unless specified otherwise. The liquid electrolyte for



lithium-sulfur batteries (LSBs) was supplied by DoDoChem (Suzhou, China) and consisted of 1 mol L-1 lithium bis (trifluoromethanesulfony) imide (LiTFSI) dissolved in mixture solvents of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1:1, volume ratio) with 2 wt.% LiNO3 as an additive. Li anode used in this paper is a disk with diameter of 15.6 mm and thickness of 450 m (Mass: 130 g). The commercial PE separator prepared by the wet-method was provided by Asahi Kasei E-materials (Japan) as a comparison in this study. All the chemical reagents were purchased commercially and used as received.

2.2 Fabrication of PEEK Separator The PEEK separators were fabricated via TIPS using a binary diluent, where DPS was chosen as the primary diluent and PES as the second diluent. The weight of PEEK was kept at 25 wt. %, while the weight ratio of the second diluent and primary diluent (PES/DPS) varied (1/0, 1/1, 1/2, 1/3, 1/5, 1/8, 1/10, 0/1). PEEK, PES and DPS were mixed at 300 ℃ with continuous stirring under nitrogen for 20 min to make a homogeneous solution and then the mixture was quenched into solid in liquid nitrogen quickly. The solidified sample was chopped into powders and hot calendered in a mold with a vulcanizing press at 300 ℃, 10 MPa to form a uniform film. Subsequently, the blending film was immersed in dimethyl sulfoxide (DMSO) for 12 h at 100 ℃ to extract the binary diluent (DPS and PES). The final PEEK porous separators were obtained after drying at 60 ℃ in an oven for 12 h. On the basis of the different weight ratios of PES and DPS in the binary diluent, the PEEK separators are named PEEK-10, PEEK-


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11, PEEK-12, PEEK-13, PEEK-15, PEEK-18, PEEK-110 and PEEK-01, respectively, just as described in Table S2 (Supporting Information, SI).

2.3 Physical Characterization of PEEK Separator The morphology of the separators was observed by a field emission scanning electron microscope (SEM, FEI Quanta 400, Netherlands). The porosity and pore size distribution of the separators were measured by mercury intrusion porosimetry (AutoPore IV9500 model, Micromeritics Inc., USA). The gas permeability of the separators was measured with a Gurley densometer (BTY-B2P, Labthink, China) by recording the time for air to pass through a determined volume (100 cc). The contact angle of the electrolyte against the separators was determined by a contact angle goniometer (SL200B, China). The tensile strength of the separators (70 mm × 4 mm) was measured by a universal tensile tester (QJ2118, China) with a strain rate of 2 mm min-1. The puncture strength of the separators was carried out on a universal tension tester (HY-0508, China) with a puncture rate of 50 mm min-1 (the section area of the needle was 0.785 mm2). The thermal stability of the separators was performed by a thermogravimetric analyzer (PerkinElmer Pyris TGA, USA) from 30 ℃ to 900 ℃ and different scanning calorimetry (DSC 200 PC, Netzsch, Germany) from 50 ℃ to 450 ℃ at a heating rate of 10 ℃ min-1 under nitrogen atmosphere. The electrolyte uptake of the separators was determined by measuring the weight of the dry separator and electrolyte-saturated separator, which was calculated according to Eq. (1):



Electrolyte Uptake (%) 

We - W0  100% W0

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(1)

where W0 and We are the weight of separator before and after immersing in the electrolyte for 4 h, respectively. The thermal shrinkage of the separators was evaluated by measuring the dimensional change before and after placing the separator in an oven at different temperatures for 1 h, which was calculated according to Eq. (2): Thermal Shrinkage (%) 

A0 - A1  100% A0

(2)

where A0 and A1 separately represent the area of the separator before and after being treated at varying temperatures.

2.4 Electrochemical Measurements Electrochemical performances of the separators were characterized by assembling coin cells in a glovebox filled with Ar. The ionic conductivity of the separators was investigated by assembling cells with liquid electrolyte impregnated separators sandwiched between stainless steel electrodes (SS/separator-electrolyte/SS). The bulk resistance (Rb) was measured by electrochemical impedance spectroscopy with an electrochemical workstation (EIS, Solartron 1287, England) over a frequency range of 0.1-105 Hz under AC amplitude of 5 mV. Then, the ionic conductivity could be calculated from Eq. (3):

 

h Rb  S

(3)


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where σ represents the ionic conductivity, Rb is the bulk resistance, h is the thickness of the separator, and S is the surface area of the stainless steel. The lithium-ion transference number of the separators was evaluated using the method of EIS combined with chronoamperometry (CA). The cell assembled by lithium/separator-electrolyte/lithium (Li/separator-electrolyte/Li) was subjected to a DC polarization potential (10 mV) for enough time to get a steady-state current. The interfacial resistances of the cell were measured by AC impedance before and after polarization. Then, the lithium-ion transference number (tLi+) was calculated from Eq. (4):30 t Li  

I s (V  I 0 R0 ) I 0 (V  I s Rs )

(4)

where ∆V represents the polarization potential. R0, Rs, I0 and Is are the initial and steadystate interfacial resistances and currents, in turn. The electrochemical stability of the separators was investigated by linear sweep voltammetry (LSV, Solartron 1287, England), ranging over 0–6 V (vs. Li+/Li) with a scan rate of 5 mV s-1. The cell was assembled by sandwiching the separator between the metallic lithium and the stainless steel (Li/separator-electrolyte/SS). The interfacial stability of the lithium/electrolyte interface employing the separator was evaluated by impedance measurements in the frequency range from 105 to 0.1 Hz at 10 mV amplitude, with a Li/separator-electrolyte/Li cell at different storage times. The effect of the separator

on

lithium

dendrite

suppression

was

evaluated

by

continuous

stripping/plating tests on a symmetrical Li/separator-electrolyte/Li cell with a current of 1 mA cm-2 and a stripping/plating of 1 h, by means of the battery test system (LAND-



CT2001A, China). To study the performance of the separator in lithium-ion batteries (LIBs), a LiFePO4/separator-electrolyte/Li half-cell was assembled, and the cycling stability and rate capability were analyzed, which was conducted on a LAND-CT2001A multichannel battery tester within a potential ranging over 2.5–4.2 V. The LiFePO4 cathode was obtained by coating the mixed slurry of LiFePO4, super P and polyvinylidene fluoride (8:1:1, weight ratio) in N-methyl-2-prrplidinone (NMP) onto carbon coated aluminum foil (the mass loading of LiFePO4 was approximately 2 mg cm-2). The separators were also applied to assemble lithium-sulfur batteries (LSBs), which were tested in galvanostatic mode within a voltage range of 1.7–2.8 V at different C-rates. The sulfur cathode was prepared according to our previous work (the mass loading of sulfur was approximately 1.8 g cm-2).31 Unless otherwise noted, all experiments were performed at ambient temperature (around 25 ℃).


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Figure 1. Schematic illustration of the fabrication of PEEK porous separator. The insets represent the mesoscopic morphology from DPD simulation and the transportation of lithium-ion in the separator.

3. Results and Discussion

3.1 Computational Simulation of Fabricating PEEK Separator The specially designed PEEK porous separator was fabricated via an unordinary thermally induced phase separation (TIPS) method using a binary diluent, where diphenyl sulfone (DPS) was employed as the primary diluent and polyether sulfone (PES) as the second diluent. DPS was chosen as the primary diluent due to its good mobility upon melt point and high boiling point, while PES was applied as the second diluent to make it easier to regulate the interaction between the diluent and PEEK.32 It was confirmed that the PEEK separator prepared using DPS as a unary diluent shows a nonporous structure because of its good fluidity above the melting point and ease of loss, as shown in Figure S1. In addition, the PEEK-PES blended membrane is wrecked after removing the unary diluent PES by immersing it in an extracting agent (shown in Figure S2), which is consistent with the relatively poor compatibility of PES as the second diluent with a PEEK polymer but the good compatibility with DPS. On the contrary, the PEEK separators fabricated using appropriate components of a binary diluent exhibit a stable and porous microstructure. As a future probing study, molecular dynamics (MD) and mesoscopic dissipative



particle dynamics (DPD) simulations were performed to investigate the miscibility between the binary diluent and PEEK. The details of the simulation and calculation processes are described in the supporting information, as shown in Tables S1 and S2. The compatibility is evaluated by the Flory-Huggins interaction parameter () and the future confirmed by the mesoscopic morphology from DPD simulation, as shown in Figure 2 (a). It can be clearly found that the  values of PEEK and the unary diluent (DPS or PES) blend systems are considerably greater than the critical value ( > critical), which illustrates that PEEK and the unary diluent are immiscible, i.e., the PEEK and unary diluent (DPS or PES) separate into two phases.33 On the other hand, PEEK and the binary diluent blend systems are miscible when the weight ratios of PES to DPS range from 1/3 to 1/10 ( < critical), implying that a stable and uniform porous PEEK separator can be obtained after extracting the diluent. Moreover, the simulation result can also forecast that the most compatible system of PEEK with a binary diluent is at the weight ratio of PES to DPS of approximately 1/8, suggesting that these are the best conditions to fabricate a porous PEEK separator.


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Figure 2. (a) The Flory-Huggins interaction parameter versus the weight ratios of PES/DPS, and the insets are the mesoscopic morphologies from the DPD simulation of the PEEK-10, PEEK-18 and PEEK-01 systems; (b) pore size distribution and (c) surface and (d) cross-section SEM images of the PEES-18 separator.

3.2 Morphology and Structure The surface and cross-section SEM images of the PEEK-18 separator are displayed in Figures 2 (c) and (d), which shows a highly porous, interconnected and three dimensional network microstructure which could provide high lithium-ion transport and good electrochemical performance. It should be noted that the small aggregation on the separator surface results from the strong interaction between the polymer chains, and this phenomenon has little effect on ion transport,34 as shown at high magnifications (Figures 1 and 2 (d)). The PEEK-18 separator not only possesses



a tortuous, submicron pore structure with an average pore size of around 580 nm (shown in Figure 2 (b)), but it also exhibits a narrower pore size distribution, which can provide uniform ion channels and prevent lithium dendrites growth. It is believed that the uniform ion channel can play a meaningful role in preventing an internal short circuit and the future enhancement of battery safety and avoidance of self-discharge, especially at high rates.35 Besides, the surface and cross-section microstructures of PEEK separators prepared using other binary diluents are shown in Figure S3, where porous and interconnected morphologies can be clearly seen on the PEEK-13, PEEK-15 and PEEK-110 separators. The aggregation degree of the surface of the PEEK separators can be affected by the composition of the binary, which is consistent with the conclusion of the simulation that the composition of the binary diluent can impact the compatibility with PEEK. The thickness, porosity and gas permeability of PEEK and commercial PE separators are listed in Table 1. The thickness of the as-prepared PEEK separators is approximately 28 m, which is suitable for LIBs, especially for power batteries. Therefore, we can conclude that the PEEK separators with different can be fabricated by different weight ratio of the primary and the second diluent. All as-prepared PEEK separators show higher porosity and air permeability than PE separators, which will then contribute to sufficient liquid electrolyte holding. Among them, the PEEK-18 separator possesses the highest porosity (70.3%) and lowest Gurley value (142 s) due to its well-developed pore structure, which can guarantee a fast migration of lithiumions. Besides, the variation of the porosity and Gurley values of the PEEK separators


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prepared under different conditions is consistent with their microstructures and previous simulation predictions.

Table 1 Physical properties of the PE and PEEK separators.

Sample

Thickness

Porosity

Gurley value

Electrolyte uptake

Tensile strength

Puncture strength

(m)

(%)

(s 100mL-1)

(%)

(MPa)

(MPa)

PE

25.0

45.0

330

115

85.7

5.65

PEEK-13

29.0

46.4

228

274

120

9.84

PEEK-15

29.0

56.2

180

336

118

9.57

PEEK-18

28.0

70.3

142

387

124

10.5

PEEK-

28.0

68.9

158

374

121

10.4

110

3.3 Electrolyte Wettability Uniform and fast wetting of an electrolyte through the whole separator is definitely necessary for quick migration of lithium-ions, which leads to excellent electrochemical performance in the future.36 Therefore, the electrolyte wettability of the PEEK and PE separators is characterized by a contact angle measurement and spreading test of the liquid electrolyte, as shown in Figure 3. It can be clearly found that the contact angle of the PE separator is up to 58° and that the electrolyte on the PE separator maintains droplet-like after 2 h. The inferior electrolyte wettability of the PE separator can be



ascribed to its intrinsically hydrophobic character and low surface energy.37 Contrastingly, the PEEK separator contains lots of polar groups (Figure 1), such as carboxyl and oxy-ether bonds,22 endowing it with an intrinsic physicochemical affinity to polar electrolytes. Thus, the PEEK separator exhibits superior electrolyte wettability with a contact angle lower than 20° and a quicker electrolyte spreading rate. The electrolyte uptake test was conducted to quantitatively confirm the wettability of the separator, as listed in Table 1. As expected, the electrolyte uptake of the asprepared PEEK separator is two times higher than that of the PE separator. The superior electrolyte wettability of the PEEK separator not only results from the abundant polar groups but is also attributed to its highly porous structure. Based on the above results, it can be concluded that the superior electrolyte wettability of the PEEK separator may promote the rapid migration of lithium ions and is supposed to have satisfactory lithium-ion conductivity.38

Figure 3. (a) Electrolyte contact angles and (b) wetting test of PE and PEEK separators.


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3.4 Mechanical Properties The mechanical strength of a separator must be high enough to avoid rupture, which is significant for the safety of batteries. The separator acting as a physical barrier between the electrodes should not only withstand industrial-scale processing but also should mechanically inhibit the lithium dendrite growth to prevent internal short circuit. Figure 4 illustrates the mechanical properties of the PEEK and PE separators. It is clearly demonstrated that the as-prepared PEEK separator exhibits an impressive tensile strength of 124 MPa and a puncture strength of 10.5 MPa, which is significantly stronger than that of the commercial PE separator, as listed in Table 1. Moreover, the PEEK separator also shows a obviously higher Young’s modulus (7.84 GPa) than that of the commercial PE separator (0.352 GPa), which is sufficient to prevent lithium dendrite growth based on Newman’s and Balsara’s predictions.39,40 The robust strength of the PEEK separator can be owe to the intrinsic ultra-strong performance of PEEK and the special fabrication process in this study. It is noteworthy that the mechanical strength of the as-fabricated PEEK separator is much stronger than previously reported similar PEEK-based separators, as summarized in Table 2. That is, the PEEK separator with an ultra-high mechanical strength shows the advantage of retaining its mechanical integrity during internal or external mechanical stress and could ensure the future safety performance of batteries.



Figure 4. (a) Tensile strength and (b) puncture strength of PE and PEEK separators; the inset is the schematic illustration of mechanical suppression preventing lithium dendrite formation with PE and PEEK separators.

3.5 Thermal Stability and Flame Resistance The heat resistance of the separator is another vital consideration for battery safety characteristics because it plays a prominent role in avoiding internal short circuit and avoiding thermal runaway, fire and even explosions when exposed to elevated temperature, especially for high energy density batteries.41,42 The heat deterioration test of the PEEK and PE separators was characterized by observing the area-based dimensional changes during different temperatures for 1 h, as shown in Figure S4. The PE separator displays a severe heat distortion at 120 ℃ and exhibits total thermal shrinkage (> 80%, Figure S5 (a)) at 150 ℃, which is a critical drawback for reliable battery safety. However, the PEEK separator exhibits an excellent thermal stability with a negligible dimensional shrinkage even up to 300 ℃, which can then effectively avoid internal short circuit at extreme temperatures. Moreover, the DSC and TGA


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measurements were conducted to quantitatively analysis the thermal properties of the separators, as shown in Figure S5. It can be clearly seen that the PEEK separator displays an endothermic peak at 343 ℃ for melting and that the decomposition temperature is as high as 572 ℃; however, the PE separator melts at 135 ℃, and thermal degradation occurs at around 450 ℃. These results illustrate the superior thermal stability of the PEEK separator and imply that it is a promising candidate for enhancing the safety of batteries even at extreme temperatures. As well known, the thermal shutdown property of a separator at a high temperature is also significant for preventing battery thermal runaway in case of overheating or internal short circuit.43 The PEEK separator has high thermal stability to maintain the dimensional stability of multilayer separator. The microscopic morphology of PEEK separator after high temperature storage has been investigated, as shown in Figure S6. It can be seen obviously that a number of the pores in the PEEK separator are held after heat treatment at 250 ℃, while they almost collapse to form a nonporous film at 300 ℃. More importantly, the dimension of PEEK separator can remain stable after the collapse of the pore structure, which can further enhance the battery safety effectively. The flame retardancy of the separator is also necessary as it could terminate further fire and retain its physical integrity in abuse conditions. As shown in Figure S7, the PE separator immediately catches on fire and is completely engulfed in flames, which can be attributed to the limiting oxygen index (LOI) value (as low as 17.4%) of the PE separator. However, the PEEK separator exhibits perfect fire resistance and flame selfextinguishing, which could be ascribed to its intrinsically high LOI (37%, UL940



grade).44 Combining the above results, the PEEK separator with excellent thermal stability and the flame retardancy should be beneficial for avoiding thermal runaway and enhancing the safety characteristics of the battery.

3.6 Electrochemical Properties in LIBs A PEEK separator with highly porous structure and superior electrolyte wettability is supposed to have an advantage in lithium-ion conductivity, which is a very important parameter determining the electrochemical performance of a battery. As shown in Figure 5 (a), the bulk resistances (Rb) of the electrolyte-soaked PE and PEEK-13, PEEK-15, PEEK-18 and PEEK-110 separators are 1.75, 1.81, 1.42, 0.95, and 1.02 Ω, respectively. The ionic conductivity of the PEEK-13, PEEK-15, PEEK-18 and PEEK110 separators can be calculated to be 0.85, 1.08, 1.57 and 1.46 mS cm-1, in turn, which are much higher than that of the commercial PE separator (0.76 mS cm-1). Meanwhile, the PEEK separators also exhibit higher lithium-ion transference numbers than the PE separator, as shown in Figure 5 (b). The PEEK-18 separator displays the highest lithium-ion conductivity and lithium-ion transference number (tLi+ = 0.55), which is not only due to its highly porous structure providing more diffusion paths for lithium-ions but also results from the abundant polar groups in its structure accelerating the transference of lithium-ions. The electrochemical stability window of the separator is crucial for a battery and was investigated by conducting the linear sweep stability (LSV) preformed on a Li/separator-electrolyte/SS cell, as shown in Figure 5 (c). There is no obvious oxidation


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current below 5 V (vs. Li/Li+) both for the PEEK and PE separators. The result suggests that the PEEK separator is available for LIBs electrochemical window of LIBs.

Figure 5. (a) Nyquist plots of the SS/separator-electrolyte/SS cells, (b) chronoamperometry (insets are EIS before and after polarization) of the Li/separatorelectrolyte/Li cells and (c) liner sweep voltammetry (LSV) curves of the SS/separatorelectrolyte/Li cells assembled with PE and PEEK separators.

The aforementioned results demonstrate that the PEEK separator efficiently permits lithium-ion transportation. Moreover, the interfacial compatibility between lithium

metal

with

the

separator

is

also

necessary

for

a

stable

intercalation/deintercalation of lithium-ions, which plays an important role in reducing polarization and enhancing the cycle and rate performance of a battery.45 Figure S8 depicts the electrochemical impedance spectra variations of the symmetric lithium/separator-electrolyte/lithium cells with PE and PEEK separators over different storage times. The semicircle in the impedance spectra usually represents the value of the interfacial resistance (Rint), which is relevant to the charge transfer reaction on the electrode and the SEI layer, as listed in Figure S8 (f). The interfacial resistance of the cells with PEEK separators is much lower than that of the cell with the commercial PE



separator, especially when using the PEEK-18-based cell. It is believed that this is due to the enhanced intimate contact and compatibility between the PEEK separators with the lithium electrode. The interfacial resistance of those cells increases continuously with increasing storage time due to the formation and growth of the SEI layer on the lithium electrode surface, which results from the reaction with the electrolyte components. In contrast, the PEEK-based cells exhibit a lower speed of increase in the interfacial resistance with the storage time, indicating a more compatible interface with the lithium electrode. This can be interpreted as the better electrolyte wettability and electrolyte retention of the PEEK separators. Moreover, the excellent compatibility between the PEEK separators with the electrodes usually results in a smaller polarization during the lithium plating/striping electrochemical cycling.46 Figure S9 shows the time-dependent voltage curves of lithium symmetric cells with PE and PEEK separators at the current density of 1 mA cm-2. The voltage value of the PE-based cell shows more erratic shifts and suffers soft short circuit when the PE separator is slowly pierced by lithium dendrites. However, the PEEK-based cells deliver a smooth and stable voltage plateau even after 2000 h, indicating very stable reversibility and effective lithium-dendrite inhibition. Notably, the PEEK-18-based cell exhibits the lowest polarization and is the most stable over voltage (29 mV for 2000 h) due to its fast and uniform lithium-ion transport. As mentioned above, the PEEK separator displays obvious advantages in pore structure, electrolyte uptake, mechanical and thermal properties, as well as lithium-ion conductivity, lithium-ion transference number and interface impedance, especially for


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the PEEK-18 separator. The practicality of the PEEK as a separator was evaluated by assembling a LiFePO4/Li half-cell. As shown in Figure 6 (b), both the PEEK- and PEbased LIBs exhibit typical charge-discharge curves with initial discharge capacities of around 160 mAh g-1. However, the PEEK-based cells demonstrate better long-term stability compared with the PE-based cell at 2C as displayed in Figure 6 (a). The PEEK18-based cell retains the highest capacity with 104.8 mAh g-1 after 580 cycles (0.060% capacity fading per cycle), while the capacity of the PE-based cell drops quickly to 79.4 mAh g-1 (0.087% capacity fading per cycle). The enhanced cycle performance of the PEEK-based cells result from a more stable interface and lower polarization. Figure 6 (b) reports the battery performance with PE and PEEK separators by plotting the charge and discharge polarization in the 1st and 200th at 2C. It is apparent that the 200th discharge capacities of the PE-, PEEK-13-, PEEK-15-, PEEK-18- and PEEK-110based LIBs are 112.1, 121.4, 123.2, 135.7 and 127.9 mAh g-1, respectively. In addition, the differences between the charge and discharge platform of the PEEK-based cells are very small, less than 0.1 V, which is much smaller than that of the PE-based cell (at least 0.3 V).

Table 2 Summary of the mechanical strength, thermal stability and electrochemical performance based on PEEK separators. Separator

FPEEK 23

Thermal

Mechanical

Discharge /

Initial capacity

Capacity fading

shrinkage *

strength (MPa)

charge rates (C)

(mA h g−1)

per cycle

150 ℃ / 0%

27.7 T

0.5

151 LFP

0.024%



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PEEK 22

150 ℃ / 38%

11.99 T

0.5

147 LFP

0.030%

OHPEEK 25

260 ℃ / 10%

0.39 P

1.0

168 NCM

0.110%

PEEK 47

150 ℃ / 0%

—

0.5

146 LFP

0.105%

CEPEEK 44

160 ℃ / 1%

—

1.0

162 NCM

0.083%

PEEK-18 This work

300 ℃ / 1%

124 T / 10.5 P

2.0

161 LFP

0.060%

Thermal shrinkage * represents the dimension shrinkage of the separators at a given temperature. T

represents the tensile strength of the separators.

LFP

represents the LiFePO4-Li half-cell.

NCM

P

represents the puncture strength of the separators.

represents the LiNi0.5CoMn0.3O2-Li half-cell.

A rate step-progressive test was also measured to validate the reliability of the PEEK-based battery for high power density LIBs. The measurement was performed by applying different current densities from 0.05C to 5C and subsequently back to 0.05C for 5 cycles each step as illustrated in Figure 6 (c). It can be clearly found that the discharge capacities of the PEEK-based cells are much higher than those of the PEbased cell at high current densities, and they also show better cycle performance than other PEEK-based LIBs in previous studies (as shown in Table 2). Notably, the PEEK18-based cell shows the best rate performance, and its discharge capacities are 0.73, 0.81, 1.01, 2.31, 4.89, 7.54, and 13.34% higher than those of the PE-based cell at the rates of 0.05, 0.1, 0.2, 0.5, 1, 2, and 5C, respectively. The superior cycle and rate performance of the PEEK-based LIBs result from the following four reasons. First, the highly porous PEEK separator with an interconnected and tortuous pore structure provides an abundant channel for transporting lithium-ions.48 Second, the PEEK


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separator with abundant polar groups can absorb more electrolytes and lead to higher lithium-ion conductivity and transference numbers. Third, the excellent interfacial compatibility between the separators with electrodes can result in a lower interfacial resistance and more stable interface. Moreover, the PEEK with an ultra-high mechanical strength can inhibit the growth of lithium dendrites and effectively avoid soft short circuit and self-discharge.49 To further demonstrate the safe operation of the PEEK separator in a real cell system at a high temperature, the open circuit voltages (OCVs) of fully charged LiFePO4/Li cells with PE and PEEK separators were monitored in response to the temperature,50 as shown in Figure 6 (d). The PE-based cell fails at about 120 ℃ as internal short circuit which caused by the severe thermal shrinkage of the PE separator. By contraries, the PEEK-18-based cell shows only a slow voltage drop and continues to work until a higher temperature of 180 ℃. At this temperature, the electrolyte begins to decompose. These results indicate that the PEEK separator is thermally stable at high temperatures and contributes to ensuring the safety of LIBs.



Figure 6. Electrochemical properties of the PE- and PEEK-based LiFePO4/separatorelectrolyte/Li cells: (a) cycle performance of the cells at 2C from 2.5 to 4.2 V; (b) charge and discharge voltage curves of the cells at the 1st and 200th cycle; (c) C-rate performance of the cells; (d) open circuit voltage (OCV) change in the cells from 20 ℃ to 165 ℃.

3.7 Electrochemical Properties in LSBs Furthermore, the effect of the lithium dendrite-proof PEEK separator in LSBs was also investigated.51 According to the Nyquist plots of the cells (SS /separator/SS, as shown in Figure S10) with PE and PEEK-18 separators, the lithium-ion conductivity of the PE and PEEK-18 separators soaked with a common electrolyte for LSBs (LiTFSI


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in DOL and DME) are 0.72 and 1.33 mS cm-1, in turn. The PEEK-18 separator shows higher ionic conductivity due to its highly porous structure and good interaction with the ether electrolyte. Figure 7 (a) presents the cycling stability of LSBs containing PE and PEEK-18 separators at a current density of 1C after 500 cycles. The initial discharge capacities of the LSBs with PE and PEEK-18 separators are 1113.1 and 1179.9 mAh g-1, respectively, while the discharge capacities and Coulombic efficiencies of a LSB with a PEEK-18 separator are much more stable than those of a LSB with a PE separator in the following cycles. After 500 cycles, the discharge capacity of a LSB with a PEEK-18 separator remains at 563.4 mAh g-1 (0.22% capacity fading per cycle), which is much higher than that of the cell with a PE separator (420.8 mAh g-1, 0.33% capacity fading per cycle). Meanwhile, the rate performances of the LSBs with PE and PEEK-18 separators are compared in Figure 7 (b). The discharge capacity continued decreases when increasing the current rate from 0.1 to 5C for both LSBs. It can be observed that more stable capacities of 1165.2, 955.4, 792.4, 617.8, 492.6, and 356.2 mAh g-1 are observed for the LSB with a PEEK-18 separator at 0.1, 0.2, 0.5, 1, 2, and 5C rates, while 1148.9, 893.1, 732.0, 518.6, 338.9, and 199.9 mAh g-1, respectively, are observed for the LSB with a PE separator. According to the above results, it can be concluded that the LSB with a PEEK-18 separator exhibits a more enhanced cycling and rate performance than that of the LSB with a PE separator. This not only can be attributed to the lithium dendrite suppression by the robust mechanical strength of the PEEK-18 separator but is also due to the restriction of polysulfides to the cathode side by physical barriers created by the PEEK-18 separator.



Figure 7. Electrochemical characterization of the Lithium-sulfur cells with PE and PEEK-18 separators. (a) cycle performance of the cells at 1 C from 1.7 to 2.8 V; (b) C-rate performance of the cells.

To understand the suppression of lithium dendrites by the PEEK separator, the LSB cells were disassembled after 500 cycles (at a current density of 1C) in an argonfilled glovebox, and the morphologies of the lithium anodes were investigated, as shown in Figure 8. It can be clearly seen that a number of lithium dendrites cover the lithium anode disassembled from the PE-based LSB, while a relatively smooth surface without notable growth of lithium dendrites can be observed on the lithium anode from the PEEK-based LSB. The direct evidence well proves that the PEEK separator is capable of suppressing lithium dendrites and enhancing the battery performance.


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Figure 8. Surface morphologies of the lithium-metal anode disassembled from lithiumsulfur cells (a) before and after 500th cycles employing (b) PE separator and (c) PEEK18 separator

4. Conclusions In summary, we successfully fabricated a PEEK separator with a bicontinuous pore structure via TIPS using a binary diluent for the first time. The effects of the composition of binary diluents on the structure of the PEEK separator were first investigated by computational simulation. The results correlate well with the experimental results. The as-fabricated PEEK separator shows high porosity (70.3%) with a uniform, tortuous and interconnected pore structure. It exhibits excellent electrolyte wettability with a contact angle of 17° and electrolyte uptake of 387%, further resulting in a high ionic conductivity (1.57 mS cm-1) and lithium-ion transference number (0.55). Meanwhile, the PEEK separator can effectively prevent thermal runaway with excellent thermal resistance (without dimensional shrinkage up to 300 ℃) and flame retardancy (LOI of 37%). Moreover, the PEEK shows ultra-high mechanical strength (tensile strength of 124 MPa, puncture strength of 10.5 MPa and Young’s modulus of 7.84 GPa) and an outstanding interfacial compatibility with the



lithium electrode, which can effectively suppress the growth of lithium dendrites. More importantly, the lithium-ion and lithium-sulfur batteries with a PEEK separator show good cycle stability and rate performance due to the lower ion transfer resistance, interfacial resistance and polarization. Basically, the as-fabricated PEEK separator can enhance the safety and electrochemical performance of lithium-ion and lithium-sulfur batteries. Finally, the fabrication methodology of the PEEK separator in this work is suitable for preparing other high-performance polymer-based separators, which is crucial for high power energy storage batteries.

Associated Content

Supporting Information Supplemental information includes Computer simulation details and Supplemental experimental results, ten figures and two tables.

Author Information

*Corresponding Authors

E-mail: [email protected] (Yuezhong Meng) E-mail: [email protected] (Min Xiao)

Author Contributions


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Y.M. proposed the concept and led the team. M.X. and S.W. designed and supervised the project. J. L. preformed the experiments ad wrote the paper. Y.M., D.H., R. S. and L. S. conducted part of the characterizations. All authors discussed the results and commented on the manuscript. All authors have approved the final version of the manuscript. Notes The authors declare no competing interests.

Acknowledgements The authors would like to thank Li Gong for the support of PFM measurements. The authors would also like to thank the Link Project of the National Natural Science Foundation of China and Guangdong Province (Grant No. U1301244); National Natural Science Foundation of China (Grant No. 51573215, 21506260, 21706294); Guangdong Natural Science Foundation (Grant No. 2016A030313354); the National key research and development program （ Japan-China joint research program ） , 2017YFGH001753. Guangdong Province Sci & Tech Bureau (2017B090901003, 2016B010114004, 2016A050503001); Guangzhou Scientific and Technological Planning

Project

(201607010042,

201707010424

and

201804020025);

the

Fundamental Research Funds for the Central Universities (Grant No.171gjc37) for financial support of this work.



References (1) Goodenough, J.B.; Park, K.S. The Li-ion rechargeable battery: a perspective. J. Am. Chem. Soc. 2013, 135, 1167–1176. (2) Scrosati, B.; Hassoun, J.; Sun, Y.K. Lithium-ion batteries. A look into the future. Energ. Environ. Sci. 2011, 4, 3287–3295. (3) Choi, J.W.; Aurbach, D. Promise and reality of post-lithium-ion batteries with high energy densities. Nat. Rev. Mater. 2016, 1, 16013–16028. (4) Dunn, B.; Kamath, H.; Tarascon, J.M. Electrical energy storage for the grid: a battery of choices. Science 2011, 334, 928–935. (5) Balakrishnan, P.G.; Ramesh, R.; Prem Kumar, T. Safety mechanisms in lithium-ion batteries. J. Power Sources 2006, 155, 401–414. (6) Chen, Y.; Yue, M.; Liu, C.; Zhang, H.; Yu, Y.; Li, X.; Zhang, H. Long cycle life lithium metal batteries enabled with upright lithium anode. Adv. Funct. Mater. 2019, 29, 1806752–1806760. (7) Zhang, S.S. A review on the separators of liquid electrolyte Li-ion batteries. J. Power Sources 2007, 164, 351–364. (8) Lee, H.; Yanilmaz, M.; Toprakci, O.; Fu, K.; Zhang, X. A review of recent developments in membrane separators for rechargeable lithium-ion batteries. Energ. Environ. Sci. 2014, 7, 3857– 3886. (9) Huang, X. Separator technologies for lithium-ion batteries. J. Solid State Electr. 2010, 15, 649– 662. (10) Long, L.; Wang, S.; Xiao, M.; Meng, Y. Polymer electrolyte for lithium polymer batteries. J. Mater. Chem. A 2016, 4, 10038–10069.


Page 32 of 39

Page 33 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(11) Pan, L.; Wang, H.; Wu, C.; Liao, C.; Li, L. Tannic-acid-coated polypropylene membrane as a separator for lithium-ion batteries. ACS Appl. Mater. Inter. 2015, 7, 16003–16010. (12) Bates, D.J.; Elliott, C.M.; Prieto, A.L. Synthesis and characterization of diazonium salts with polyethylene glycol appendages and resulting films afforded by electrodeposition for use as a battery separator material. Chem. Mater. 2014, 26, 5514–5522. (13) Xiang, Y.; Li, J.; Lei, J.; Liu, D.; Xie, Z.; Qu, D.; Li, K.; Deng, T.; Tang, H. Advanced separators for lithium-ion and lithium-sulfur batteries: a review of recent progress. ChemSusChem 2016, 9, 3023–3039. (14) Orendorff, C.J.; Lambert, T.N.; Chavez, C.A.; Bencomo, M.; Fenton, K.R. Polyester separators for lithium-ion cells: improving thermal stability and abuse tolerance. Adv. Energ. Mater. 2013, 3, 314–320. (15) Zhang, J.; Liu, Z.; Kong, Q.; Zhang, C.; Pang, S.; Yue, L.; Wang, X.; Yao, J.; Cui, G. Renewable and superior thermal-resistant cellulose-based composite nonwoven as lithium-ion battery separator. ACS Appl. Mater. Inter. 2013, 5, 128–134. (16) Sheng, J.; Tong, S.; He, Z.; Yang, R. Recent developments of cellulose materials for lithiumion battery separators. Cellulose 2017, 24, 4103–4122. (17) Seidel, S.M.; Jeschke, S.; Vettikuzha, P.; Wiemhofer, H.D. PVDF-HFP/ether-modified polysiloxane membranes obtained via airbrush spraying as active separators for application in lithium ion batteries. Chem. Commun. 2015, 51, 12048–12051. (18) Ali, S.; Tan, C.; Waqas, M.; Lv, W.; Wei, Z.; Wu, S.; Boateng, B.; Liu, J.; Ahmed, J.; Xiong, J.; Goodenough, J.B.; He, W. Highly efficient PVDF-HFP/colloidal alumina composite separator for high-temperature lithium-ion batteries. Adv. Mater. Interfaces 2018, 5, 1701147–1701156.



(19) Shi, J.; Hu, H.; Xia, Y.; Liu, Y.; Liu, Z. Polyimide matrix-enhanced cross-linked gel separator with three-dimensional heat-resistance skeleton for high-safety and high-power lithium ion batteries. J. Mater. Chem. A 2014, 2, 9134–9141. (20) Hao, J.; Lei, G.; Li, Z.; Wu, L.; Xiao, Q.; Wang, L. A novel polyethylene terephthalate nonwoven separator based on electrospinning technique for lithium ion battery. J. Membrane Sci. 2013, 428, 11–16. (21) Zhang, H.; Zhang, Y.; Xu, T.; John, A.E.; Li, Y.; Li, W.; Zhu, B. Poly( m -phenylene isophthalamide) separator for improving the heat resistance and power density of lithium-ion batteries. J. Power Sources 2016, 329, 8–16. (22) Li, D.; Shi, D.; Feng, K.; Li, X.; Zhang, H. Poly (ether ether ketone) (PEEK) porous membranes with super high thermal stability and high rate capability for lithium-ion batteries. J. Membrane Sci. 2017, 530, 125–131. (23) Li, H.; Zhang, B.; Liu, W.; Lin, B.; Ou, Q.; Wang, H.; Fang, M.; Liu, D.; Neelakandan, S.; Wang, L. Effects of an electrospun fluorinated poly(ether ether ketone) separator on the enhanced safety and electrochemical properties of lithium ion batteries. Electrochim. Acta 2018, 290, 150– 164. (24) Babu, D.B.; Giribabu, K.; Ramesha, K. Permselective SPEEK/Nafion composite-coated separator as a potential polysulfide crossover barrier layer for Li-S batteries. ACS Appl. Mater. Inter. 2018, 10, 19721–19729. (25) Li, Z.; Cao, T.; Zhang, Y.; Han, Y.; Xu, S.; Xu, Z. Novel lithium ion battery separator based on hydroxymethyl functionalized poly(ether ether ketone). J. Membrane Sci. 2017, 540, 422–429. (26) Wu, Q.Y.; Liang, H.Q.; Gu, L.; Yu, Y.; Huang, Y.Q.; Xu, Z.K. PVDF/PAN blend separators


Page 34 of 39

Page 35 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


via thermally induced phase separation for lithium ion batteries. Polymer 2016, 107, 54–60. (27) Matsuyama, H.; Teramoto, M.; Kudari, S.; Kitamura, Y. Effect of diluents on membrane formation via thermally induced phase separation. J. Appl. Polym. Sci. 2001, 82, 169–177. (28) Perilla, J.R.; Goh, B.C.; Cassidy, C.K.; Liu, B.; Bernardi, R.C.; Rudack, T.; Yu, H.; Wu, Z.; Schulten, K. Molecular dynamics simulations of large macromolecular complexes. Curr. Opin. Struct. Biol. 2015, 31, 64–74. (29) Espanol, P.; Warren, P.B. Perspective: dissipative particle dynamics. J. Chem. Phys. 2017, 146, 150901–150914. (30) Evans, J.; Vincent, C.A.; Bruce, P.G. Electrochemical measurement of transference numbers in polymer electrolytes. Polymer 1987, 28, 2324–2328. (31) Yang, K.; Zhong, L.; Guan, R.; Xiao, M.; Han, D.; Wang, S.; Meng, Y. Carbon felt interlayer derived from rice paper and its synergistic encapsulation of polysulfides for lithium-sulfur batteries. Appl. Surf. Sci. 2018, 441, 914–922. (32) Tang, Y.H.; He, Y.D.; Wang, X.L.; Effect of adding a second diluent on the membrane formation of polymer/diluent system via thermally induced phase separation: dissipative particle dynamics simulation and its experimental verification. J. Membrane Sci. 2012, 409-410, 164–172. (33) Jeon, M.Y.; Kim, C.K. Phase behavior of polymer/diluent/diluent mixtures and their application to control microporous membrane structure. J. Membrane Sci. 2007, 300, 172–181. (34) Wang, M.; Chen, X.; Wang, H.; Wu, H.; Jin, X.; Huang, C. Improved performances of lithiumion batteries with a separator based on inorganic fibers. J. Mater. Chem. A 2017, 5, 311–318. (35) Zhang, B.; Wang, Q.; Zhang,J.; Ding, G.; Xu, G.; Liu, Z.; Cui, G. A superior thermostable and nonflammable composite membrane towards high power battery separator. Nano Energy 2014,



10, 277–287. (36) Li, H.; Wu, D.; Wu, J.; Dong, L.Y.; Zhu, Y.J.; Hu, X. Flexible, high-wettability and fireresistant separators based on hydroxyapatite nanowires for advanced lithium-ion batteries. Adv. Mater. 2017, 29, 1703548–1703558. (37) Xu, Q.; Kong, Q.; Liu, Z.; Wang, X.; Liu, R.; Zhang, J.; Yue, L.; Duan, Y.; Cui, G. Cellulose/polysulfonamide composite membrane as a high performance lithium-ion battery separator. ACS Sustain. Chem. Eng. 2013, 2, 194–199. (38) Li, B.; Li, Y.; Dai, D.; Chang, K.; Tang, H.; Chang, Z.; Wang, C.; Yuan, X.Z.; Wang, H. Facile and nonradiation pretreated membrane as a high conductive separator for Li-ion batteries. ACS Appl. Mater. Inter. 2015, 7, 20184–20189. (39) Monroe, C.; Newman, J. Dendrite growth in lithium/polymer systems. J. Electrochem. Soc. 2003, 150, A1377-A1384. (40) Zhang, W.; Tu, Z.; Qian, J.; Choudhury, S.; Archer, L.A.; Lu, Y. Design principles of functional polymer separators for high-energy, metal-based batteries. Small 2018, 14, 1703001– 1703021. (41) Zhao, R.; Liu, J.; Gu, J. Simulation and experimental study on lithium ion battery short circuit. Appl. Energ. 2016, 173, 29–39. (42) Wu, T.; Chen, H.; Wang, Q.; Sun, J. Comparison analysis on the thermal runaway of lithiumion battery under two heating modes. J. Hazard. Mater. 2018, 344, 733–741. (43) Baginska, M.; Blaiszik, B.J.; Merriman, R.J.; Sottos, N.R.; Moore, J.S.; White, S.R. Autonomic shutdown of lithium-ion batteries using thermoresponsive microspheres. Adv. Energy Mater. 2012, 2, 583–590.


Page 36 of 39

Page 37 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(44) Li, Z.; Wang, W.; Han, Y.; Zhang, L.; Li, S.; Tang, B.; Xu, S.; Xu, Z. Ether modified poly(ether ether ketone) nonwoven membrane with excellent wettability and stability as a lithium ion battery separator. J. Power Sources 2018, 378, 176–183. (45) Hao, X.; Zhu, J.; Jiang, X.; Wu, H.; Qiao, J.; Sun, W.; Wang, Z.; Sun, K. Ultrastrong polyoxyzole nanofiber membranes for dendrite-proof and heat-resistant battery separators. Nano Lett. 2016, 16, 2981–2987. (46) Lin, D.; Zhuo, D.; Liu, Y.; Cui, Y. All-integrated bifunctional separator for Li dendrite detection via novel solution synthesis of a thermostable polyimide separator. J. Am. Chem. Soc. 2016, 138, 11044–11050. (47) Li, H.; Zhang, B.; Lin, B.; Yang, Y.; Zhao, Y.; Wang, L. Electrospun poly (ether ether ketone) nanofibrous separator with superior performance for lithium-ion batteries. J. Electrochem. Soc. 2018, 165, A939–A946. (48) Shi, J.; Xia, Y.; Yuan, Z.; Hu, H.; Li, X.; Zhang, H.; Liu, Z. Porous membrane with high curvature, three-dimensional heat-resistance skeleton: a new and practical separator candidate for high safety lithium ion battery. Sci. Rep. 2015, 5, 8255–8263. (49) Kim, M.; Park, J.H. Multi-scale pore generation from controlled phase inversion: application to separators for Li-ion batteries. Adv. Energy Mater. 2013, 3, 1417–1420. (50) Dai, J. Shi, C. Li, C. Shen, X. Peng, L.; Wu, D.; Sun, D.; Zhang, P.; Zhao, J. A rational design of separator with substantially enhanced thermal features for lithium-ion batteries by the polydopamine–ceramic composite modification of polyolefin membranes. Energ. Environ. Sci. 2016, 9, 3252–3261. (51) Huang, S.; Guan, R.; Wang, S.; Xiao, M.; Han, D.; Sun, L.; Meng, Y.; Polymer for high



performance Li-S batteries: material selection and structure design. Prog. Polym. Sci. 2019, 89, 19– 60.


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99x59mm (300 x 300 DPI)


Ultrastrong and Heat-Resistant Poly(ether ether ketone) Separator for

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