Advanced Nanoclay-based Nanocomposite Solid Polymer Electrolyte

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Advanced Nanoclay-based Nanocomposite Solid Polymer Electrolyte for Lithium Iron Phosphate Batteries Qinyu Zhu, Xuming Wang, and Jan D Miller ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b13735 • Publication Date (Web): 06 Feb 2019 Downloaded from http://pubs.acs.org on February 6, 2019

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ACS Applied Materials & Interfaces

Advanced Nanoclay-based Nanocomposite Solid Polymer Electrolyte for Lithium Iron Phosphate Batteries

Qinyu Zhu, Xuming Wang and Jan D. Miller*

Department of Metallurgical Engineering, College of Mines and Earth Sciences, University of Utah, 135 S 1460 E, Room 412, Salt Lake City, UT 84112-0114, USA

Author e-mail addresses: Qinyu Zhu: [email protected] Xuming Wang: [email protected] Jan D. Miller: [email protected]

*Corresponding author: Jan D. Miller Department of Metallurgical Engineering, College of Mines and Earth Sciences, University of Utah, 135 S 1460 E, Room 412, Salt Lake City, UT 84112-0114, USA Email: [email protected]

Declarations of Interest: None

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-2ABSTRACT: High performance solid polymer electrolytes (SPEs) have long been desired for the next generation of lithium batteries. One of the most promising ways to improve the morphological and electrochemical properties of SPEs is the addition of fillers with specific nanostructures. However, the production of such fillers is generally expensive and requires complicated preparation procedures. Halloysite nanotubes (HNTs), with their tubular structure, resemble carbon nanotubes in terms of geometric features, and can be obtained at relatively low cost. Previously we reported that the HNT poly(ethylene oxide) (PEO) composite SPE possesses excellent electrochemical and mechanical properties, and outstanding cycling performance for allsolid-state lithium sulfur batteries. However, the HNT/SPE was not effective for lithium iron phosphate (LFP) batteries. The compatibility between the electrodes and electrolyte sharply decreased, and no decent cycling performance was achieved. Therefore, a modification was studied which involves a minor addition of LFP during the preparation procedure. With this modification, good ionic conductivity (9.23 × 10−5 S cm−1 at 25°C) is achieved and compatibility between the electrodes and electrolyte is enhanced. At the same time, an electrochemical stability window of 5.14 V, and lithium ion transference number of 0.46 are found. All-solid-state LFP batteries possessing excellent cycling performance are further demonstrated. KEYWORDS: Solid polymer electrolyte, Lithium iron phosphate, Halloysite nanotube, Poly (ethylene oxide), Lithium ion conductivity, Coin cell battery testing


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-31. Introduction In 1992, Sony first introduced lithium-ion batteries (LIBs) into the market 1. LIB technology has been applied to both flexible portable electronic devices, and more recently, for transportation systems, including hybrid and electric vehicles. Most of the research on commercial cathode materials for rechargeable LIBs involves lithium insertion compounds with layered, spinel, or olivine structures 2. Lithium iron phosphate (LiFePO4, LFP), first reported by the Goodenough group in 1997 3, appears to be a good cathode material due to its olivine structure. These ironbased compounds are relatively inexpensive and less toxic than Co, Ni, and Mn. LFP batteries provide good electrochemical performance with low resistance4. They are now common rechargeable batteries in the market and have found a number of roles in vehicle use and backup power. The global market for LFP batteries was valued at $4.76 billion in 2016, and is projected to grow to $25.47 billion by 2025, due to demand from the electric and hybrid electric vehicle industry (57.6%), and consumer electronics (21.2%) which include cameras, mobile phones, computers, and laptops 5. With the development of electric vehicle technology, enhanced safety characteristics for power batteries are urgently needed. Separators and liquid electrolytes currently used for LFP batteries have become major bottlenecks to further development. Solid polymer electrolytes (SPEs) can be used as electrolytic materials with many advantages at both ends of the spectrum. SPEbased batteries could be used as high density power sources in large applications such as electric vehicles or portable electronic devices in which size and weight are so significant6,7. The use of an SPE, such as a poly(ethylene oxide) (PEO) based SPE, instead of the conventional liquid or gel electrolyte can significantly improve the safety aspects of LIBs 8–11. However, existing PEO-based solid electrolytes do not meet functional performance requirements. At low temperatures the ionic



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-4conductivity is low, since PEO exists in crystalline form, which restricts the lithium ion mobility12. In addition, PEO-based all-solid-state batteries rarely exhibit decent performance when cycled at relatively high current densities. Therefore, the useful operating temperature for Li-ion polymer batteries is usually between 70°C and 100°C 13, a condition which excludes the use of such solidpolymer-based batteries in room temperature applications. The addition of nano-fillers such as ceramic and inert nano-particles is found to improve both the morphological properties and the electrochemical performance of solid polymer electrolytes 8,14–18. However, the production of such fillers is generally expensive and requires complicated preparation procedures. Numerous naturally occurring resources with unique nanostructures have been found, among which halloysite nanotubes (HNTs) are of particular interest, due to their tubular structure, which resembles carbon nanotubes in terms of geometric features. HNTs were first described as a 1:1 aluminosilicate clay mineral in 1826 19. They are composed of bilayers of alumina octahedral and silica tetrahedral sheets. Multilayer tubes are formed through neighboring alumina and silica layers, and their waters of hydration. According to the state of hydration, HNTs are generally classified into two groups: hydrated HNTs with a crystalline structure having 1.0 nm d001 spacing, and dehydrated HNTs with 0.7 nm d001 spacing 20. In general, the length of the ultra-tiny hollow tubes varies from the submicron scale to several microns 21, their external diameter ranges from approximately 30 to 190 nm, and the internal diameter from 10 to 100 nm

22.

Chemically, the

siloxane external surface of HNT has properties similar to certain SiO2 structures while the internal alumina core behaves like gibbsite. Thus, the zeta potential of HNT particles can be roughly described by a negatively charged outer layer of SiO2, with a small contribution from the positive Al2O3 inner surface, which accounts for the overall negative surface charge of HNT particles. Due to their unique structure, HNTs have different applications, such as for controlled or sustained


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-5release 23,24, for use in nanoreactors or nanotemplates 25–27, and as sorbents for contaminants and pollutants 28–30 etc. They can also be used as the filler in either naturally-existing or modified forms in nanocomposites. Through direct melt blending, HNTs are expected to be relatively uniformly dispersed in thermoplastics due to their easy dispersibilities 20. HNTs have gained wide interest in the preparation of complex structures as an economically available and environmentally friendly nanotube raw material. The development of advanced LFP polymer batteries requires maximization of the ionic conductivity of the solid polymer electrolyte, and integration and compatibility of the solid polymer electrolyte with the electrodes. In this study, HNT was used as filler in the solid polymer electrolyte to provide enhanced electrochemical properties, and thus help to improve the battery cycling performance. With a minor addition of LFP, improved compatibility between electrolyte and electrodes has been achieved, which has been a major challenge for SPE-based lithium batteries.

2. Experimental 2.1 Materials Poly(ethylene oxide) ((CH2CH2O)n, PEO, Molecular Weight=4×106) was obtained from Xiamen

TOB

New

Energy

Technology

Company,

China.

Lithium

bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2, LiTFSI, 99.5%) and halloysite nanotubes (HNT, 99.5%) were purchased from Sigma-Aldrich, USA. Lithium iron phosphate (LiFePO4, LFP) was acquired from Hydro-Québec, Canada. Analytical grade acetonitrile was used without further purification. All powder materials were dried before use.



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-62.2 Preparation of Flexible SPE The composition of the PEO+LiTFSI+HNT+LFP SPE (HNT-LFP/SPE) was EO: Li+ = 15:1 molar ratio, PEO: HNT = 10:1 weight ratio

31

and 1% LFP weight ratio. During the

preparation of each sample, HNT, LiTFSI and LFP were weighed and dispersed with acetonitrile in a glass bottle. After 5 minutes of ultrasonic treatment, the solution was mixed using a Teflon impeller. PEO was then added to the solution under vigorous stirring. The mixture was stirred for 4 hours, and then transferred to a vibrating ball mill for 20 minutes of ball milling to get a homogeneous electrolyte suspension. The suspension was cast on a clean plastic surface using a syringe, and dried into a thin film. The PEO+LiTFSI+HNT solid polymer electrolyte (HNT/SPE) and PEO+LiTFSI+LFP solid polymer electrolyte (LFP/SPE) were prepared using the same method. 2.3 Characterization of Flexible SPE The electrochemical properties of the HNT-LFP/SPEs were characterized via a Gamry PCI4/750 Potentiostat (Gamry Instrument, USA). The ionic conductivities of the HNT-LFP/SPE films were measured in a symmetrical stainless steel/electrolyte/stainless steel cell using electrochemical impedance spectroscopy (EIS). The conductivity was calculated using the following equation: σ=

l 𝑆𝑅𝑏

where l is the thickness of the electrolyte, 𝑅𝑏 is the resistance from EIS measurements, and S is the area of the blocking stainless steel electrodes. A symmetrical cell (Li/SPE/Li) was used to determine the lithium ion transference number (t+). A constant polarization voltage of 10 mV was applied to the cell and the currents from the initial to the steady state were measured. The lithium ion transference number is calculated from:


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-7-

𝑡+ =

𝐼𝑠(𝑉 ― 𝐼0𝑅0) 𝐼0(𝑉 ― 𝐼𝑠𝑅𝑠)

where V is the DC voltage applied, 𝐼0 and 𝐼𝑠 are the initial and steady-state currents, while 𝑅0 and 𝑅𝑠 are the initial and steady-state resistances, respectively. Linear sweep voltammetry was used to measure the electrochemical windows (EWs) of the SPE films in a Li/SPE/SS cell, with a scan range from 3-6.5V, at a scan rate of 10 mV s-1. Cyclic voltammograms of the battery at 25 °C were carried out at a voltage range of 2.53.8 V at a scan rate of 0.1 mV s−1. The fourier transform infrared spectroscopy (FTIR) measurement of the HNT-LFP/SPE was performed using a Nicolet iS50 FTIR (Thermo Fisher Scientific, USA). The spectra was collected from 0 to 4000 cm-1 on a glass substrate. Scanning electron microscopy (SEM) imaging was performed using an Apreo SEM (Thermo Fisher Scientific, USA). The secondary electron (SE) images were taken at a voltage of 2.0 kV and a current of 0.1 nA. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed on an SDT Q600 instrument to observe the thermal stability of the HNT-LFP/SPE. The experiment was conducted in an argon atmosphere (flow rate 200 ml/min) at a heating rate of 10 °C/min. The HNT-LFP/SPE based lithium iron phosphate polymer batteries were assembled by arranging, in sequence, a lithium anode, the HNT-LFP/SPE thin film and an LFP cathode disk. The LFP cathode slurry was prepared by grinding and dispersing the LFP, conductive carbon, and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) solvent at a weight ratio of 8 : 1 : 1. The slurry was cast on aluminum foil using a surgical blade to form a uniform cathode layer. The aluminum foil was dried on a hot plate at 100 °C overnight prior to coin cell assembly. A 2025



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-8coin cell was used to house the complete Li/SPE/LFP battery. Galvanostatic charge/discharge cycling was performed in a LAND CT2001A battery test system (Wuhan LAND Electronics Co., Ltd., China).

3. Results and Discussion 3.1 FTIR Spectra and SEM Images Figure 1 (a) shows the FTIR spectra of the HNT-LFP/SPE. The peaks in between 1100 cm-1 and 1500 cm-1 are attributed to the stretching of -SO2- and -CF3 in LiTFSI32,33, and the wagging and twisting of the -CH2- group in the PEO34. Peaks in between 400 cm-1 to 1000 cm-1 correspond to the asymmetric stretching mode, doublets and triplets of PO4 3, 35, which indicate the presence of LiFePO4. Figure 1 (b) shows the SEM image of HNT particles in the solid polymer electrolyte. The tubular structure of the HNT particles can be observed. The dimension of the HNT agglomerate was about 2 microns. Other HNT particles are dispersed as individual particles in the polymer matrix. 3.2 Ionic Conductivity Previous studies indicate that the ionic conductivity of the PEO based solid polymer electrolyte is sensitive to the degree of PEO crystallinity, the ionic conductivity being greater in the amorphous state due to the higher degree of freedom 12. Therefore, ionic conductivities from 25 °C to 100 °C were measured to determine the phase transition temperature of the HNT-LFP/SPE, as presented in Figure 1 (c). The ionic conductivities of the electrolyte were found to be 9.23105

S/cm and 1.7910-3 S/cm at 25 °C and 100 °C, respectively. The low temperature data are fitted

by the Arrhenius equation 36 and the high temperature data by the Vogel-Tamman-Fulcher (VTF)


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-9equation 37. So, the phase transition temperature at the crossing point of the two fitted lines was found to be 41.5 °C. The ionic conductivity of SPE prepared without HNT was also measured and is plotted in Figure 1 (c). The ionic conductivities of the electrolyte are 2.4210-5 S/cm and 9.5410-4 S/cm at 25 °C and 100 °C, respectively. The phase transition temperature is determined to be 47.3 °C. Thus, the addition of HNT helps enhance the ionic conductivity, and decrease the crystallization temperature of the SPE.



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- 10 -

Figure 1. Characterization of SPEs (a) FTIR Spectra of HNT-LFP/SPE (b) SEM Image of HNT in the Solid Polymer Electrolyte (c) Ionic Conductivity Results for HNT-LFP/SPE and LFP/SPE.


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- 11 3.3 Lithium Ion Transference Number (t+) In addition to the high ionic conductivity, the HNT-LFP/SPE also exhibits a higher lithium ion transference number (t+), as shown in Figure 2. The t+ was measured using a combination of electrochemical impedance spectroscopy and potential polarization. Before polarization, the movement of both cations and anions between the electrodes contributes to the current, however, at steady state, only lithium ion transport exists between the electrodes

38.

The t+ at room

temperature for the HNT-LFP/SPE was found to be 0.46, which is much greater than that of pure PEO at room temperature, the value of which is usually in the range of 0.1–0.25 23.

Figure 2 Chronoamperometry of the Li/ SPE /Li Cell for the HNT-LFP/SPE at a Potential of 10 mV at 25 °C Inset: The EIS of the Same Cell before and after Polarization.

3.4 Electrochemical Stability Using linear sweep voltammetry, the electrochemical stabilities of the HNT-LFP/SPE and LFP/SPE at room temperature were measured within the range of 3.0 V to 6.5 V (potential vs. Li+/Li), as shown in Figure 3. It was found that the HNT-LFP/SPE is stable up to 5.14 V at 25 °C. In contrast, the SPE prepared without HNT is only stable up to 4.32 V. The decomposition voltage



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- 12 of commercial liquid organic electrolytes (~4.2 V) 31 is still lower than both values. Therefore, the HNT-LFP/SPE should be suitable for high voltage applications.

Figure 3. Linear Sweep Voltammetry Results at 25 °C at a Rate of 10 mV s-1.

3.5 Battery Cycling Performance Since multiple tests of HNT/SPE-based and LFP/SPE-based LFP polymer batteries did not achieve decent cycling performance results (average specific capacity below 30 mAh g−1 at 0.1 C and 25 °C), this section focuses on the battery performance tests of HNT-LFP/SPE-based LFP polymer batteries, and other results are not presented. The assembly of the HNT-LFP/SPE-based LFP polymer battery is shown in Figure 4 (a). The LFP cathode, HNT-LFP/SPE, and the lithium anode were contacted sequentially and were sealed in CR2025 shells. The open circuit potential of all testing cells was in the range of 3.21±0.3 V, which indicates that the minor addition of LFP in the SPE does not cause short-circuiting of the batteries. Figure 4 (b) shows the potential vs. capacity profiles at 0.1 C and 25 °C (1 C= 172 mAh g−1) for the 1st, 10th, and 100th cycles, respectively. The voltage plateaus representing the cell


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- 13 reactions are clearly observed. The plateaus are maintained even after 100 cycles. The initial discharge capacity is 171.6 mAh g−1, and the initial charge capacity is 170.4 mAh g−1, which is close to the theoretical capacity. The capacity is maintained at 156 mAh g−1 after 100 cycles, with 90.9 % retention compared to the first discharge capacity. The cyclic voltammetry profile is provided in Figure 4 (c). The oxidation and reduction peaks of the first three cycles almost overlap with each other, except for slight deviation due to polarization during the charge/discharge process, indicating the stable performance of the HNTLFP/SPE-based LFP polymer battery. In addition, the positions of the oxidation and reduction peaks correspond well with the charge/discharge behavior shown in Figure 4 (b). The results for battery cycling performance tests of HNT-LFP/SPE-based LFP polymer batteries are presented in Figure 5. The battery presents stable discharge capacities at room temperatures from 0.1 C to 0.5 C, with an averaged value of 152 ± 3 mAh g−1 at 0.1 C, 130 ± 4 mAh g−1 at 0.3 C, and 120 ± 3 mAh g−1 at 0.5 C after 300 discharge/charge cycles. The coulombic efficiency is almost 100% for each and every cycle. High temperature testing at 60 °C and 1 C was also performed, and an average capacity of 102 ± 6 mAh g−1 is maintained after 100 cycles. It should be noted that the LFP polymer batteries can not be cycled at room temperature when just HNT/SPE is used in the battery, which indicates that the addition of LFP to the HNT/SPE is necessary to have improved battery cycling performance for the LFP polymer battery.



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- 14 -

Figure 4. All-solid-state LFP Battery Performance. (a) Assembly of the HNT-LFP/SPE-based LFP Polymer Battery. (b) Typical Potential vs. Capacity Profiles at 0.1 C and 25 °C for HNT-LFP/SPE-based LFP Polymer Battery. (c) Cyclic Voltammograms of the HNT-LFP/SPE-based LFP Polymer Battery in the Voltage Range of 2.5-3.8 V at 25 °C and a scan rate of 0.1 mV s−1.


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- 15 -

Figure 5 HNT-LFP/SPE-based LFP Polymer Battery Performance at (a) 0.1 C and 25 °C, (b) 0.3 C and 25 °C, (c) 0.5 C and 25 °C, and (d) 1 C and 60 °C.

3.6 Thermal Stability Figure 6 shows the TGA and DSC results of HNT-LFP/SPE from 60 to 800 °C in an argon atmosphere at a heating rate of 10 °C min−1. The evaporation of absorbed atmospheric water led to a weight loss of about 1.5 % below 118 °C. The removal of the structural water resulted in the 1.1 % weight loss between 118 and 333 °C39,40. The main weight loss of the SPE from about 333 to 458 °C and the corresponding exothermic peak in the DSC curve at 458 °C are ascribed to the decomposition of the polymer and the lithium salt. The residual for the HNT-LFP/SPE is 9.5 %,



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- 16 which is higher than the 6 % residue of the PEO+LiTFSI solid polymer electrolyte reported in our previous study 31. Thus, the HNT-LFP/SPE should be available for applications under ~300 °C.

Figure 6. TGA and DSC Results of HNT-LFP/SPE in an Ar Atmosphere at a Heating Rate of 10 °C/min.

3.7 Interfacial Compatibility between SPEs and LFP Electrode Since SPEs have similar ionic conductivities and lithium ion transference numbers with and without LFP, the reasons why SPE with LFP gives much better cycling performance remain to be studied. In order to further investigate the interfacial compatibility of SPEs and the electrodes on cycling performance, the EIS spectra of LFP polymer batteries with different SPEs were analyzed. The impedance spectra of the HNT-LFP/SPE based LFP polymer battery were measured before and after 30 charge-discharge cycles at 0.1 C and 25 °C and the analyzed results are presented in Figure 7 (a). The intercept of the spectra with the real axis in the high-frequency area represents the bulk resistance (Rbulk) of the battery, while the charge transfer resistance at the LFP/SPE interface (R1) and the solid electrolyte interface resistance at the Li-SPE interface (R2)


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- 17 are represented by the semicircle in the mid-frequency region. As shown in Figure 7 (a), the bulk resistance increases slightly from 214 Ω to 251 Ω, indicating stable ionic conductivity of HNTLFP/SPE is maintained during the charge/discharge cycles. For the interfacial resistance, the value is 13.8 kΩ before cycling and 15.1 kΩ after cycling, with an increase of only 10 % after 30 cycles. The relatively stable interfacial resistance accounts for the capacity retention for repeated charging and discharging after 30 cycles, which correspond well with the cycling performance data, see Figure 5. The stable interfacial properties are attributed mainly to 1) the addition of LFP, since it adds to the compatibility between the electrode and electrolyte, and 2) the addition of HNT, since it facilitates the charge transfer between the electrode and the electrolyte 31.

Figure 7. EIS spectra of LFP Cells. (a) HNT-LFP/SPE-based Cell before and after 30 Cycles. Inset: Equivalent Circuit of the HNT-LFP/SPE-based Cell, and (b) Comparison of EIS spectra of LFP Cells with different SPEs.

Figure 7 (b) presents the comparison of the EIS spectra of LFP cells using different SPEs. It is evident that the interfacial resistances of the HNT/SPE-based cell and the LFP/SPE-based cell are significantly greater than those of the HNT-LFP/SPE-based cell for initial behavior and after cycling, which explains why the SPEs without addition of LFP are not suitable for room temperature LFP polymer batteries.



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- 18 3.8 Ionic Transport Mechanism in the HNT-LFP/SPE-based LFP Polymer Battery In our previous study, a 3D-channel theory was proposed to explain the lithium ion transport in the HNT based SPE 31. As stated in the previous section, the halloysite nanotubes have two oppositely charged surfaces. The difference in surface charges guarantees selective association of charged species, which means the negatively charged species, in this case the TFSI- anions, will preferably adsorb on the inner surface, while the positively charged species, Li+ cations, will more likely be accommodated on the silica surface

41,42.

The lone-pair electrons in the EO units,

interacting with the lithium cation adsorbed on the silica surface of HNT, enable the polymer to conform regularly to the HNT particles. The interactions among HNT, LiTFSI and PEO result in the ordered 3D structure for lithium ion transport. It is proposed that the 3D channels significantly facilitate the dissociation of the lithium salt and transport of the free Li+ ion. Furthermore, the HNT reduces the temperature for crystallization of the PEO. The reduced phase transition temperature promotes lithium transport and significantly increases the lithium ionic conductivity. In addition, as discussed in the previous section, after the addition of a minor amount of LFP, the interfacial resistance drops dramatically compared to the HNT/SPE-based and LFP/SPEbased LFP cells (from ~220 kΩ to ~14 kΩ). Thus, the increased interfacial compatibilities between the electrodes and electrolyte also further promote the charge transfer between the electrodes and electrolyte.

4. Conclusions The results from our research suggest that the comprehensive performance for the lithium iron phosphate battery is improved due to the use of a new solid polymer electrolyte, HNTLFP/SPE. It can be concluded from the data that the addition of both HNT and LFP account for


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- 19 the improved ionic conductivity and electrochemical stability of the new SPE. The addition of LFP also increases the compatibility between the electrode and electrolyte. The new solid polymer electrolyte, HNT-LFP/SPE, should be easy to integrate into current commercial lithium iron phosphate battery production.

Acknowledgements This work was supported by a Utah Science Technology and Research Initiative (USTAR)/University Technology Acceleration Grant (UTAG), Salt Lake City, UT [Grant Number 172171]. The funding source had no involvement in the design of the study; in the collection, analysis and interpretation of data; in the writing of the manuscript; or in the decision to submit the manuscript for publication. Appreciation is extended to Ms. Dorrie Spurlock for her assistance in the preparation of the manuscript, and to Applied Minerals for discussion of halloysite characteristics.

References (1)

Ozawa, K. Lithium-Ion Rechargeable Batteries with LiCoO2 and Carbon Electrodes: The LiCoO2/C System. Solid State Ionics 1994, 69 (3–4), 212–221.

(2)

Whittingham, M. S. Lithium Batteries and Cathode Materials. Chem. Rev. 2004, 104 (10), 4271–4301.

(3)

Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B. Phospho-Olivines as PositiveElectrode Materials for Rechargeable Lithium Batteries. J. Electrochem. Soc. 1997, 144 (4), 1188–1194.



Page 20 of 25

- 20 (4)

Xu, H.; Liu, W.; Su, Y.; Yang, X. Study on Microwave Synthesis and Properties of LiFeP04/C Cathode Materials. Mater. Rev. 2001, 25 (6), 148–150.

(5)

Grand View Research Inc. Lithium Iron Phosphate (LiFePO4) Material and Battery Market Analysis By Raw Material (Graphite, Lithium Iron Phosphate, Lithium Fluoride), By Application, By Region, And Segment Forecasts, 2014 - 2025; 2017.

(6)

Sequeira, C. A. C.; Santos, D. M. F. Polymer Electrolytes: Fundamentals and Applications; Woodhead Publishing: Cambridge, UK, 2010.

(7)

Zhang, L.; Liu, Z.; Cui, G.; Chen, L. Biomass-Derived Materials for Electrochemical Energy Storages. Prog. Polym. Sci. 2015, 43, 136–164.

(8)

Lin, D.; Liu, W.; Liu, Y.; Lee, H. R.; Hsu, P. C.; Liu, K.; Cui, Y. High Ionic Conductivity of Composite Solid Polymer Electrolyte via in Situ Synthesis of Monodispersed SiO2 Nanospheres in Poly(Ethylene Oxide). Nano Lett. 2016, 16 (1), 459–465.

(9)

Long, L.; Wang, S.; Xiao, M.; Meng, Y. Polymer Electrolytes for Lithium Polymer Batteries. J. Mater. Chem. A 2016, 4 (26), 10038–10069.

(10)

Ogawa, M.; Yoshida, K.; Harada, K. All-Solid-State Lithium Batteries with Wide Operating Temperature Range. SEI Tech. Rev. 2012, No. 74, 88–90.

(11)

Yue, L.; Ma, J.; Zhang, J.; Zhao, J.; Dong, S.; Liu, Z.; Cui, G.; Chen, L. All Solid-State Polymer Electrolytes for High-Performance Lithium Ion Batteries. Energy Storage Materials. 2016, pp 139–164.

(12)

Kumar, B.; Rodrigues, S. J.; Koka, S. The Crystalline to Amorphous Transition in PEOBased Composite Electrolytes: Role of Lithium Salts. Electrochim. Acta 2002, 47 (25), 4125–4131.


Page 21 of 25 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


- 21 (13)

Mo, S.; Lu, P.; Ding, F.; Xu, Z.; Liu, J.; Liu, X.; Xu, Q. High-Temperature Performance of All-Solid-State Battery Assembled with 95(0.7Li2S-0.3P2S5)-5Li3PO4glass Electrolyte. Solid State Ionics 2016, 296, 37–41.

(14)

Liu, W.; Liu, N.; Sun, J.; Hsu, P. C.; Li, Y.; Lee, H. W.; Cui, Y. Ionic Conductivity Enhancement of Polymer Electrolytes with Ceramic Nanowire Fillers. Nano Lett. 2015, 15 (4), 2740–2745.

(15)

Chen, S.; Wang, J.; Zhang, Z.; Wu, L.; Yao, L.; Wei, Z.; Deng, Y.; Xie, D.; Yao, X.; Xu, X. In-Situ Preparation of Poly(Ethylene Oxide)/Li3PS4 Hybrid Polymer Electrolyte with Good Nanofiller Distribution for Rechargeable Solid-State Lithium Batteries. J. Power Sources 2018, 387, 72–80.

(16)

Saito, Y.; Stephan, A. M.; Kataoka, H. Ionic Conduction Mechanisms of Lithium Gel Polymer Electrolytes Investigated by the Conductivity and Diffusion Coefficient. Solid State Ionics 2003, 160 (1–2), 149–153.

(17)

Appetecchi, G. B.; Scaccia, S.; Passerini, S. Investigation on the Stability of the LithiumPolymer Electrolyte Interface. J. Electrochem. Soc. 2000, 147 (12), 4448–4452.

(18)

Weston, J. E.; Steele, B. C. H. Effects of Inert Fillers on the Mechanical and Electrochemical Properties of Lithium Salt-Poly(Ethylene Oxide) Polymer Electrolytes. Solid State Ionics 1982, 7 (1), 75–79.

(19)

Berthier, P. Analyse de l ’ Halloysite. Ann. Chim. Phys. 1826, 32, 332–335.

(20)

Du, M.; Guo, B.; Jia, D. Newly Emerging Applications of Halloysite Nanotubes: A Review. Polymer International. 2010, pp 574–582.

(21)

Joussein, E.; Petit, S.; Churchman, J.; Theng, B.; Righi, D.; Delvaux, B. Halloysite Clay Minerals – a Review. Clay Miner. 2005, 40 (4), 383–426.



Page 22 of 25

- 22 (22)

Yuan, P.; Southon, P. D.; Liu, Z.; Green, M. E. R.; Hook, J. M.; Antill, S. J.; Kepert, C. J. Functionalization

of

Halloysite

Clay

Nanotubes

by

Grafting

with

γ-

Aminopropyltriethoxysilane. J. Phys. Chem. C 2008, 112 (40), 15742–15751. (23)

Quartarone, E.; Mustarelli, P. Electrolytes for Solid-State Lithium Rechargeable Batteries: Recent Advances and Perspectives. Chem. Soc. Rev. 2011, 40 (5), 2525–2540.

(24)

Armand, M. The History of Polymer Electrolytes. Solid State Ionics 1994, 69 (3–4), 309– 319.

(25)

Luca, V.; Thomson, S. Intercalation and Polymerisation of Aniline within a Tubular Aluminosilicate. J. Mater. Chem. 2000, 10 (9), 2121–2126.

(26)

Fu, Y.; Zhang, L. Deposition Feature of Ni Nanoparticles on Halloysite Template and Magnetic Properties of the Composite. J. Nanosci. Nanotechnol. 2005, 5 (7), 1113–1119.

(27)

Fu, Y.; Zhang, L.; Zheng, J. In-Situ Deposition of Pd Nanoparticles on Tubular Halloysite Template for Initiation of Metallization. J. Nanosci. Nanotechnol. 2005, 5 (4), 558–564.

(28)

Zhao, M.; Liu, P. Adsorption Behavior of Methylene Blue on Halloysite Nanotubes. Microporous Mesoporous Mater. 2008, 112 (1–3), 419–424.

(29)

Kilislioglu, A.; Bilgin, B. Adsorption of Uranium on Halloysite. Radiochim. Acta 2002, 90 (3), 155–160.

(30)

Abdullayev, E.; Joshi, A.; Wei, W.; Zhao, Y.; Lvov, Y. Enlargement of Halloysite Clay Nanotube Lumen by Selective Etching of Aluminum Oxide. ACS Nano 2012, 6 (8), 7216– 7226.

(31)

Lin, Y.; Wang, X.; Liu, J.; Miller, J. D. Natural Halloysite Nano-Clay Electrolyte for Advanced All-Solid-State Lithium-Sulfur Batteries. Nano Energy 2017, 31, 478–485.


Page 23 of 25 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


- 23 (32)

Wen, S. J.; Richardson, T. J.; Ghantous, D. I.; Striebel, K. a; Ross, P. N.; Cairns, E. J. FTIR Characterization of PEO+LiN(CF3SO2)(2) Electrolytes. J. Electroanal. Chem. 1996, 113118.

(33)

Hardwick, L. J.; Saint, J. A.; Lucas, I. T.; Doeff, M. M.; Kostecki, R. FTIR and Raman Study of the LixTiyMn1-yO2 (Y=0, 0.11) Cathodes in Methylpropyl Pyrrolidinium Bis(Fluoro-Sulfonyl)Imide, LiTFSI Electrolyte. J. Electrochem. Soc. 2009, A120-A127

(34)

Yang, S.; Liu, Z.; Liu, Y.; Jiao, Y. Effect of Molecular Weight on Conformational Changes of PEO: An Infrared Spectroscopic Analysis. J. Mater. Sci. 2015, 50 (4), 1544–1552.

(35)

Ait Salah, A.; Jozwiak, P.; Zaghib, K.; Garbarczyk, J.; Gendron, F.; Mauger, A.; Julien, C. M. FTIR Features of Lithium-Iron Phosphates as Electrode Materials for Rechargeable Lithium Batteries. Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 2006, 65 (5), 1007– 1013.

(36)

Li, Y. H.; Wu, X. L.; Kim, J. H.; Xin, S.; Su, J.; Yan, Y.; Lee, J. S.; Guo, Y. G. A Novel Polymer Electrolyte with Improved High-Temperaturetolerance up to 170 °C for HighTemperature Lithium-Ion Batteries. J. Power Sources 2013, 244, 234–239.

(37)

Ratner, M. A.; Johansson, P.; Shriver, D. F. Polymer Electrolytes: Ionic Transport Mechanisms and Relaxation Coupling. MRS Bull. 2000, 25 (3), 31–37.

(38)

Zugmann, S.; Fleischmann, M.; Amereller, M.; Gschwind, R. M.; Wiemhöfer, H. D.; Gores, H. J. Measurement of Transference Numbers for Lithium Ion Electrolytes via Four Different Methods, a Comparative Study. Electrochim. Acta 2011, 56 (11), 3926–3933.

(39)

Li, Y.; Zhang, Y.; Zhang, Y.; Sun, J.; Wang, Z. Thermal Behavior Analysis of Halloysite– Dimethylsulfoxide Intercalation Complex. J. Therm. Anal. Calorim. 2017, 129 (2), 985– 990.



Page 24 of 25

- 24 (40)

Theodosopoulos, G. V.; Zisis, C.; Charalambidis, G.; Nikolaou, V.; Coutsolelos, A. G.; Pitsikalis, M. Synthesis, Characterization and Thermal Properties of Poly(Ethylene Oxide), PEO, Polymacromonomers via Anionic and Ring Opening Metathesis Polymerization. Polymers (Basel). 2017, 9 (4).

(41)

Zhao, Y.; Abdullayev, E.; Vasiliev, A.; Lvov, Y. Halloysite Nanotubule Clay for Efficient

Water Purification. J. Colloid Interface Sci. 2013, 406, 121–129. (42)

Tully, J.; Yendluri, R.; Lvov, Y. Halloysite Clay Nanotubes for Enzyme Immobilization. Biomacromolecules 2016, 17 (2), 615–621.


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Advanced Nanoclay-based Nanocomposite Solid Polymer Electrolyte

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