An assessment of pyrite thin film cathode characteristics for thermal batteries by the doctor blade coating method (đánh giá đặc điểm của catốt màng mỏng pirit sắt cho pin nhiệt

Original ArticleAn assessment of pyrite thin-film cathode characteristics for thermal batteries by the doctor blade coating method Trang-Le Thi Thua, Thuy-Le Thi Thub, Tran Dinh Manhc,**

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Original Article

An assessment of pyrite thin-film cathode

characteristics for thermal batteries by the doctor

blade coating method

Trang-Le Thi Thua, Thuy-Le Thi Thub, Tran Dinh Manhc,**,

Trung-Truong Tanb, Jeng-Kuei Changd,*

aInstitute of Materials Science and Engineering, National Central University, Taoyuan, 32001, Taiwan

bInstitute of Research and Applied Technological Science, Dong Nai Technology University, Dong Nai, 810000,

Viet Nam

cInstitute of Applied Technology, Thu Dau Mot University, 6 Tran Van on Street, Phu Hoa Ward, Thu Dau Mot City,

Binh Duong, 820000, Viet Nam

dDepartment of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010, Taiwan

a r t i c l e i n f o

Article history:

Received 27 January 2021

Accepted 10 May 2021

Available online 21 May 2021

Keywords:

Pyrite thin-film

Thermal batteries

Blade coating

Adhesion test

Cathodes

a b s t r a c t Using FeS2(pyrite) as an active material for cathodes in the thermal battery has received much more attention due to its abundant natural resources, cheapness, and excellent ef-ficiency Nevertheless, scientists take a large internal resistance issue of the FeS2cathodes into urgent consideration, decreasing the electrochemical efficiency of typical LieSi/FeS2 thermal batteries In this study, we surveyed the effect of binders, thin-film thicknesses, and the addition of conductive carbonaceous additives such as carbon black (CB), super P (SP) and activated carbon (AC) on the FeS2thin film cathode fabrication by applying the blade coating method To obtain the FeS2homogeneous slurry, we utilized the ball-milling process to reduce the FeS2particle size from 8.7mm to 0.9 mm Subsequently, the FeS2thin film with different thicknesses, expected to elevate mass loading causing higher capacity

of thermal batteries, by means of the doctor blade was successfully fabricated from the homogeneous slurry comprising ball-milled FeS2active material, polyvinylidene fluoride (PVDF) binder or sodium silicate (Na2SiO3) binder, accompanied with conductive carbo-naceous additive; even without conductive carbocarbo-naceous additive, thin films were still capable of being produced Among these samples, the thin-film type, mass loading from 1.4

to 3.6 mg/cm2(corresponding to the doctor blade thicknesses in a range of 150e300 mm), manufactured from the slurry consisting of 80 wt% of ball-milled FeS2, 15 wt% of conductive carbonaceous additive (CB/SP/AC), and 5 wt% of PVDF binder will promisingly contribute to increasing electrochemical efficiency of thermal batteries, possibly on ac-count of high mechanical durability

BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

* Corresponding author

** Corresponding author

E-mail addresses:manhtd@tdmu.edu.vn(T.D Manh),jkchang@nctu.edu.tw(J.-K Chang)

Available online at www.sciencedirect.com

https://doi.org/10.1016/j.jmrt.2021.05.014

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1 Introduction

Thermal batteries (TBs) or molten salt batteries are power

sources that use solid electrolytes and operated at a high

temperature (between around 350 and 500C) [1] Similar to

other batteries, the single-cell structure of the thermal battery

consists of an electrolyte placed between an anode (LieSi) and

a cathode (FeS2) [2e5] Specifically, the use of the heat source is

to allow the thermal battery to reach operating temperatures

TBs are mainly employed as energy sources for major military

applications (guided missiles, rockets, guided bombs, and

mines) [6,7], radar and electronic guidance, emergency backup

power, etc due to their excellent mechanical robustness,

longevity, short activation time, high reliability along with high

energy density and power density [3e5,8e10] Besides, TBs are

often used in safe and urgent cases Several of the largest TBs

are mainly incorporated into the hydraulic systems as backup

power sources in the scope of military aircraft

Potential of the Li and Li-alloy/FeS2 couple was

demon-strated in the past [11e13] instead of the previously Ca/CaCrO4

system, since the Li and Li-alloy/FeS2 system possessed a

powerful combination with well-characterized and

foresee-able chemical reactions as well as being eco-friendly than Ca/

CaCrO4system, no presence of Cr(VI) as a carcinogen and FeS2

being available in nature Some scientists reported FeS2,

having electrical conductivities in a range between 0.03 and

333 S/cm [14] and an energy band gap approximately 0.92 eV

[15,16] at ambient temperature, as a good material for both

n-type and p-n-type semiconductor [17e19] More importantly, its

electrical conductivity will increase with increasing

temper-ature, which promotes it be perfect for TBs

However, the FeS2cathode still exists some minor issues

such as medium thermal stability, voltage transients on

acti-vating the battery, and the remarkable ability to dissolve in

the molten-salt electrolytes This phenomenon is willingly

resolved by lithiation [20] Li2O and Li2S are popular lithiation

voltage transients In addition, notable solubility of FeS2in

molten-salt electrolytes turns into a problem when the battery

in the state of the open circuit for prolonging time or a very

small load as < 20 mA/cm2

is applied to the battery The diffusion of dissolved FeS2 into the separator can have

re-actions with anodic species to produce Fe and Li2S, which may

cause battery capacity loss [21]

Electrochemical efficiency of LieSi/FeS2thermal batteries

was reduced due to high internal resistance of the pyrite

cathodes [6] Almost all the efforts of researchers in recently

years have reported that reducing of the internal resistance of

lithium and Ni-MH batteries was conducted by adding

conductive carbonaceous materials, such as carbon blacks

(CBs) and carbon nanotubes (CNTs) [11,12,22e24] but

improving the electrochemical efficiency of LieSi/FeS2

ther-mal batteries has not yet been reported Recently, Choi et al

[25] have demonstrated that adding conductive carbonaceous

materials to pyrite electrode enhanced electrochemical

per-formance of LieSi/FeS2 thermal batteries In addition, the

effectiveness of binders in the electrolyte (e.g ceramic

mate-rials) has been studied [10] As a result, fumed silicas was

considered to be more effective because it was in need of less

material, around 9 w/o than the previous electrolyte material required a large concentration around 35e50 w/o

Most of the previous methods in thermal battery manufacturing generated thicker electrodes resulting in reducing electrode usages, consequently reducing energy density of the thermal battery Therefore, thinning of the cathode electrode must ensure mechanical strength and optimal electrochemical efficiency of the electrode is essential and can be carried out by tape casting process with doctor blade method which is expressed via previous study [8,26,27]

In this study, we assessed the effect of binders, the addition of conductive carbonaceous additives such as carbon black (CB), super P (SP) and activated carbon (AC), and thin-film thick-nesses of the fabricated FeS2thin film cathodes via assess-ment of forming material characterization

2 Materials and methods

2.1 Preparation of active materials

ballemilling process attachment with Zirconium (Zr) ball (3 mm diameter) and anhydrous EtOH (99.5%) operated at a constant velocity of 250 revolutions per minute (rpm) during

24 h for particle size reduction Finally, the smaller-particle FeS2was obtained after drying the milled FeS2collected by filtration with general meshwork

2.2 Slurry preparation

The slurry was prepared by mixing the compositions of the above-milled FeS2as an active material, carbonaceous material (SP/CB/AC, 99.9%, SigmaeAldrich) as an additive material, and a binder The binder used is Polyvinylidene fluoride (PVDF)

or liquid sodium silicate (Na2SiO3) with sodium tripolyphos-phate (STP)/lignosulfonic acids (LSAS)/sodium hexametaphos-phate (SHMP) as a dispersant in a weight ratio in N-Methyl-2-pyrrolidone (NMP) or deionized (DI) water as a solvent, respec-tively PVDF was absolutely dissolved in NMP under stirring, or

DI water and STP/LSAS/SHMP and Na2SiO3were stirred till all solid dissolved, then gradually added FeS2and SP/CB/AC The as-prepared mixture in the sealed container was stirred at

500 rpm by using a magnetic stirrer for 1 h to obtain the ho-mogeneous slurry All of samples were conducted with different procedures as described inTable 1and done in triplicate

2.3 Electrode coating

The as-prepared electrode homogeneous slurry was cast onto the ethanol-washed aluminum foil to remove oxide on the surface The wet coated thin film was obtained after the auto-coating machine flattened the slurry with 150e300 mm thick-ness of the doctor blade with the size of 10 cm 15 cm Finally, this samples was then dried under vacuum at 100C for 3 h

2.4 Assessment of materials characterization

To assess characterization of tested materials, the measure-ments of the particle sizes and the structure of material of

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FeS2powder before and after the ballemilling process by

dy-namic light scattering (DLS) and X-ray diffraction (XRD),

respectively were carried out The PVDF or Na2SiO3binder,

raw FeS2 powder, ball-milled FeS2 powder, and ball-milled

FeS2 film using PVDF or Na2SiO3 binder (shaved the active

thin-film layer off the copper foil substrate) were subjected to

thermal-gravimetric analysis (TGA), to determine thermal

stability properties The durability of the formed thin films

after coated using PVDF or Na2SiO3binder was assessed by the

adhesion test Electrochemical efficiency was also predicted

by mass loading

2.4.1 Dynamic light scattering (DLS)

In this research, the method of DLS, one of the most pop-ular measurement technique for measuring small particles

in solution, was used to determine the particle size distri-bution profile of the raw FeS2and ball-milled FeS2powder DLS measurements were carried out using a Malvern Zetasizer software, version 7.12 We used ethanol 99.5% as

a dispersant because the FeS2samples well dispersed in it Each sample would be repeated three times across the scanning session, corresponding to recognition of a regular rhythm

Table 1e All of the conducted samples with different procedures

material

process

Ratio (wt%)

Blade thickness (mm)

Result

15 FeS2 None Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 91:4:5 150 Exfoliated

24 FeS2 None Na2SiO3 LSAS DI water Al Foil 100ºCe3 hrs 90:5:5 150 Exfoliated

27 FeS2 None Na2SiO3 SHMP DI water Al Foil 100ºCe3 hrs 90:5:5 150 Exfoliated

30 FeS2 None Na2SiO3 STP DI water Al Foil 50C (30 min)

¼> 75C (1 h)

¼> 85C (30 min)

¼> 100C (1 h)

85:10:5 150 Exfoliated

35 FeS2 CB Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 30:60:5:5 150 Good

36 FeS2 SP Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 30:60:5:5 150 Good

37 FeS2 AC Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 30:60:5:5 150 Good

40 FeS2 AC Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 45:45:5:5 150 Good

41 FeS2 SP Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 60:30:5 5 150 Good

42 FeS2 AC Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 60:30:5 5 150 Good

45 FeS2 AC Na2SiO3 STP DI water Al Foil 100ºCe3 hrs 70:20:5:5 150 Good FeS2: pyrite, CB: carbon black, SP: super P, AC: activated carbon, PVDF: polyvinylidene fluoride, Na2SiO3: sodium silicate, STP: sodium tripoly-phosphate, LSAS: lignosulfonic acids, SHMP: sodium hexametatripoly-phosphate, NMP: N-Methyl-2-pyrrolidone and DI water: deionized water

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2.4.2 Thermo-gravimetric analyzer (TGA)

Because thermal batteries must be operated at high

temper-ature, FeS2 powder before and after ball milling process,

binders, and the powder scraped off from the cathode thin

films were treated with TGA analysis, PerkinElmer TGA7

se-ries, in order to prove their thermal stability The heating

range was set from 40 to 600C at 10C/min rate operated

under nitrogen

below: (1) Liquid sample: original Na2SiO3binder; (2) Powder

sample: liquid Na2SiO3binder was dried in the oven at 100C

for 5 h to become solid binder, then heated up to around 300C

for approximately 10 min to become powder binder after

grinding by mortar and pestle

2.4.3 X-ray diffractometer (XRD)

The structural changes of FeS2active materials after the

ball-milling process will be recognized by X-ray diffraction (XRD)

According to that, XRD analysis was performed to identify the

phases, composition, and structure of the raw and ball-milled

FeS2powder sample for comparison

The sample was put on the sample holder which works as a

substrate and then pressed flatly by using the measure glass

to perform a better baseline and clearer peaks in the XRD

result graph, followed by placing inside the XRD (Bruker)

chamber operated with Cu Ka radiation (l ¼ 0.15418 nm) at

40 kV and 40 mA Data was recorded between 20and 70at a

scan rate of around 2.4/min

2.4.4 Adhesion test

The adhesion test was conducted to check the

substrate-active material connection as follow two methods Method

one: The thin films were punched to produce the

circle-shaped electrodes (1.2 cm in diameter) Examining adhesion

by seeing through the edge of the circle whether the active

material layer was still glued smoothly to the substrate or

exfoliated from the substrate Method two:

Rectangular-shaped pieces (3 cm 2 cm) were cut from the thin films

Dimensions of these pieces depend on the tape sizes used to

do the test We pasted the tapes to the rectangular-shaped

pieces’ surfaces and applied the same pressing force to all

the pieces from the surfaces, then peeling the tapes off The

distributions of amounts of material over the tapes reflect the

adhesion

3 Results and discussion

3.1 Particle sizes of active material

The FeS2particle size was controlled by the ball-milled

pro-cess and diminishes when the ball-milled time increases

According to previous studies, the ball-milling process was

conducted to the raw FeS2 powder for 24 h Fig 1a and b

present the results of DLS analysis, the raw FeS2particle size is

8.7mm and 0.9 mm for the ball-milled FeS2particle size The

ball-milled FeS2size is around 8 times smaller than the raw

FeS2particle size Since different particle sizes of FeS2own

different thermal decomposition rates at the high operating

temperature of the thermal battery, the electrochemical

performance of the thermal battery differs from the particle sizes of the FeS2active material There is a certain size range for FeS2particle, where thermal stability and electrochemical efficiency are maintained As the FeS2 particle size is too small, the discharge capacity of the thermal battery becomes lower due to the higher thermal decomposition rate of the FeS2active electrode material However, if the particle size of FeS2is too large, the homogeneous slurry as prepared for the electrode coating process can not be obtained and a large number of pores in the electrode will also exist, causing a rise

in internal resistance [8

3.2 TGA analysis

In order to investigate the thermal stability of the electrode material used in this research, which is related thermal decomposition temperatures, the thermal-gravimetric anal-ysis of the PVDF binder, raw FeS2powder, ball-milled FeS2 powder, and ball-milled FeS2film using PVDF binder (shaved the active thin-film layer off the copper foil substrate) was conducted The TGA data shows inFig 2that PVDF binder has excellent thermal stability due to a low mass reduction rate Fig 1e Intensity distribution analysis of (a) raw FeS2 powder and (b) ball-milled FeS2powder

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under 1% at 450C In addition, thermal stability of ball-milled

FeS2powder and ball-milled FeS2film with a mass reduction

rate under 10% at 450C are acceptable, compared to that of

raw FeS2powder which possesses the low mass reduction rate

under 2% at 450C Basically, the discharge capacity of

ther-mal batteries increases when internal resistance decreases,

which results from the good connection between the active

material particles in the electrode as lowering the active

ma-terial particle size [28] On the other side, the thermal battery

will be operated at the high temperature (350C - 500C), thus

electrochemical efficiency greatly increases if the electrode

material has high thermal decomposition temperature As

mentioned before, in case the FeS2particle size is too small,

out of the certain size range, electrochemical efficiency of

thermal batteries using FeS2as an active electrode material

will be declined because of high thermal decomposition rate

of FeS2active electrode material

The thermal-gravimetric analysis results of the Na2SiO3

sample are shown inFig 3 The TGA data of liquid Na2SiO3

confirmed its poor thermal stability due to the high mass

reduction rate of approximately 60% at 500C In comparison,

the excellent thermal stability of solid Na2SiO3with a mass reduction rate around 4% at 500C was indicated by TGA data

of solid Na2SiO3 A large amount of solvent contains in liquid

Na2SiO3due to the obvious disparity between two states of

Na2SiO3 This was observed as an explanation of the poor FeS2 active material layer-copper foil substrate contact when using

Na2SiO3as a binder

3.3 XRD analysis

Any changes in the crystal structure of FeS2will be verified by XRD analysis because chemical and physical damage may occur during the ballemilling process The XRD patterns of raw FeS2powder and ballemilled FeS2film using PVDF binder (shaved the active thin-film layer off the copper foil substrate) are presented in Fig 4a and b, respectively As shown, the reflections of the ball-milled FeS2film are sharper and stron-ger in comparison with the raw FeS2powder, proving that it possesses higher crystallinity A comparison of the XRD peaks

of raw FeS2 powder and ballemilled FeS2 film proved that there is no change in the crystal structure before and after the ball milling process, demonstrating the 24 h ballemilling process did not change the phase of the FeS2active material

3.4 FeS2thin film coating and adhesion test

Ball-milled FeS2was used as an active material for the thin-film coating process (blade coating method) after having characteristic test results to ensure its ability There were 2 types of binders applied to produce FeS2homogeneous slurry

3.4.1 With PVDF binder

The first coating process was performed from the slurry con-sisting of FeS2active material, small amounts of binder and no additive to maximize an amount of active material in an electrode The slurry was prepared by following formulations

as shown inTable 1(e.g number 1 to 2) with different ratios of PVDF binder and their appearances after coated and vacuum dried present inFig 5 It is clearly seen that their surfaces are uniformly smooth The adhesion test result illustrated inFig 6

2 (degree)

(a) (b)

Fig 4e XRD patterns of (a) raw FeS2powder and (b) ball-milled FeS film

25

50

75

100

PVDF

Temperature (°C)

Fig 2e TGA traces of PVDF binder, raw FeS2powder,

ball-milled FeS2powder, and ball-milled FeS2film

50

75

100

Temperature (°C)

Fig 3e TGA traces of NaSiO

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was conducted on these samples to make sure that the FeS2

electrode thin films are durable enough for cutting into the

coin cell shape and during the electrochemical test As a

result, the sample with 1.5% of PVDF binder has better

adhe-sion This PVDF binder ratio will be applied for the next

experiments

The second coating process was performed from the

slurry composed of FeS2 active material, 1.5 wt% of PVDF

binder, and a carbonaceous additive (SP/CB/AC) in order

to increase discharge capacities The slurry was prepared

number 3 to 5) with the different additives added and their appearances after coating and drying under vacuum

the previous samples fabricated in the first coating pro-cess was obtained, which means good adhesion and smooth surface Moreover, the charge transfer resistance

of samples added carbonaceous additives is reduced when the amount of a carbonaceous additive increases As a consequence of the formation of conductive networks

Fig 6e The adhesion test result of the FeS2electrode thin films produced from the slurry with the different PVDF binder ratios and no additive

Fig 7e The adhesion test result of the FeS2electrode thin film produced from the slurry with the different PVDF binder ratios and CB added

Fig 5e The appearances of the FeS2electrode thin films produced from the slurry with the different PVDF binder ratios and

no additive

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between FeS2 particles and their high electrical

conduc-tivity, high charge transfer rate and conductivity density

can be relieved [25]

The next process is to improve the adhesion and the

adhesion test results are shown inFig 8 After punching to

manufacture the coin cell shapes, the FeS2thin film with 5 wt

% of PVDF binder had better visual appearance than the

sample with 1.5 wt% of PVDF binder which was cracked on the

edges of the circles Because of that, coming samples were

prepared by following 5 wt% of PVDF binder ratio

The last coating process was conducted to upgrade the

mass loading of the electrode which may affect

electro-chemical efficiency due to increasing the amount of active

material of an electrode Different thicknesses of FeS2 thin films were fabricated by using the doctor blade with the thickness range from 150mm to 300 mm as describable inTable

1(e.g number 6 to 14) The slurry containing 80 wt% of FeS2,

15 wt% of a carbonaceous additive (CB/SP/AC), and 5 wt% of PVDF binder was coated on the ethanol-washed copper foil with the different doctor blade thicknesses and the real thickness results show inTable 2

3.4.2 With Na2SiO3binder

The FeS2thin-film electrode using Na2SiO3binder could not fabricate without a carbonaceous additive since different binder ratios, different dispersants, and different heating process (Table 1, e.g number 15 to 34) was tried and the result was the loss connection between the active material layer and the copper foil causing by exfoliated after vacuum dried

in the oven as illustrated inFig 9 The thermal stability of carbonaceous material is low, so the amount of activated carbon was gradually reduced (60e20 wt%) to get the mini-mum amount of carbonaceous additive added, the slurry

When the amount of carbonaceous additive added was ex-pected to diminish to 10 wt%, the exfoliated film was collected as also illustrated inFig 9 The appearance results

of samples had CB added are illustrated in Fig 10 It can demonstrate that a good connection between the active material layer and the copper foil was obtained due to the utility of the matrix structure of carbonaceous material where FeS2particles can be better confined

Fig 8e The appearances of the FeS2electrode thin films produced from the slurry with 1.5 wt% of PVDF binder and different additives

Table 2e The real thickness results from the slurry with

5 wt% of PVDF binder and 15 wt% of a carbonaceous

additive added after coating by the different doctor blade

thicknesses

FeS2: CB/SP/AC: PVDF¼ 80 : 15: 5 (wt%)

Doctor blade

thickness (mm)

Real thickness (without Al foil) (mm)

FeS2: pyrite, CB: carbon black, SP: super P, AC: activated carbon,

PVDF: polyvinylidene fluoride

Fig 9e The appearance of the FeS thin film formed from the slurry using 5% NaSiO binder and no carbonaceous additive

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3.5 Comparison of adhesion between PVDF and

Na2SiO3binder

In order to compare mechanical durability between samples

using PVDF and Na2SiO3binder, the adhesion test would be

carried out.Fig 11indicated that the FeS2thin film using PVDF

as a binder is more durable than the FeS2 thin film using

Na2SiO3as a binder As a result, the FeS2thin film using PVDF

binder is suggested to investigate in further researches

3.6 Electrode size

As proved in the above part, the FeS2 thin film using a PVDF

binder was supposed to be undertaken in the further

detailed groundwork The sufficient size and mechanical

strength of electrodes are required to ensure the

perfor-mance of TBs In Fig 12, the PVDF-binder FeS2-active

ma-terial electrode with a thickness of 138 mm, cut into discs

from the prepared thin film, was objectively measured the

size (around 5 cm in diameter) (a) and mechanical strength (b) It was bent for durability testing, admittedly, the terial layer still adhered to the substrate, without any ma-terials peeling off In other words, great mechanical stability and flexibility of the electrode were visually demonstrated

We can confirm that it met the mandatory requirements of the thermal-battery manufacture

3.7 Mass loading

According to the previous session, there were some samples had been obtained successfully when using PVDF or Na2SiO3 binder for the slurry to produce FeS2thin films As following preferences [8,29,30], the thickness of the conventional pellet cathode is around several hundreds of micrometers and decreasing the thickness of the cathode to a certain level has several exceptional advantages such as better ion-diffusion across the electrode and lower electrode resistance That means a certain-level thickness of the cathode, in case too Fig 11e The adhesion test result of the FeS2electrode thin films with the PVDF and Na2SiO3binder

Fig 10e The appearance of the FeS2thin film formed from the slurry using Na2SiO3binder and CB added with different ratios (a) 60%, (b) 45%, (c) 30%, (d) 20%

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thin cathodes, it may cause reduce the electrochemical

effi-ciency due to the sharp decrease of active-material mass

loading Understandingly, some samples were achieved with

the best results on this research, which were thoroughly

measured the real thickness (without substrate) and the mass

loading, the data as showed inTable 3for PVDF-binder sam-ples and inTable 4for Na2SiO3-binder samples As a result, the mass loading increased with increasing the amount of FeS2 active material, more clearly proven in Na2SiO3-binder

possessed the mass loading from 1.7 to 7.4 mg/cm2 in the stable state of the real thickness around 108 mm (Fig 14) Moreover, the mass loading also increased with the increase

of the film thickness, it could be clearly seen in PVDF-binder

138 mm corresponding to the doctor blade thicknesses in a range of 150e300 mm (Fig 13), the mass loading was elevated from 1.4 to 3.6 mg/cm2 In comparison with Na2SiO3-binder, preparation of battery slurry using PVDF-binder provided a better connection between the active materials layer and the substrate (is more durable), along with a large-enough mass loading, which simply increased the mass of active materials and could lead to increase electrochemical efficiency (can in-crease electrochemical efficiency) of thermal batteries Therefore, the thin-film type with PVDF-binder will promis-ingly contribute to increasing electrochemical efficiency of thermal batteries

4 Conclusions

In this research, using the blade coating method applied to the

uniform thin films has been possessed It is such a result of the

Table 3e FeS2mass loading of the successfully coated samples with PVDF binder

FeS2: pyrite, CB: carbon black, SP: super P, AC: activated carbon, PVDF: polyvinylidene fluoride

Table 4e FeS2mass loading of the successfully coated samples with Na2SiO3binder

(mg/Cm2)

FeS2: pyrite, CB: carbon black, SP: super P, AC: activated carbon, Na2SiO3: sodium silicate, STP: sodium tripolyphosphate

Fig 13e Image of the ratio of FeS2: CB: PVDF¼ 80 : 15: 5 wt% compositions with doctor blade thickness: a) 150 mm, b) 200 mm, c) 300mm

Fig 12e Image of the thermal-battery electrode: (a) Size

examination, and (b) Mechanical stability inspection

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ball-milling process to produce FeS2powder with the smaller

to 0.9mm particle size According to the XRD result, there is no

phase change after the ball-milling process of FeS2 The area

electrodes of thermal batteries

The FeS2 thin films fabricated using PVDF binder have

outstanding advantages such as higher mechanical durability,

binder Among the samples prepared with PVDF binder, the

FeS2 thin film samples manufactured from the slurry

con-sisting of 80 wt% of FeS2, 15 wt% of a carbonaceous additive

(CB/SP/AC) and 5 wt% of PVDF binder will be promising

elec-trodes for thermal batteries with high electrochemical

per-formance owing to the high electrical conductivity and good

trap networks of carbonaceous materials In addition, real

thicknesses of the tested sample from 108 to 138mm fabricated

from the doctor blade thicknesses in a range of 150e300 mm

have the mass loading which is elevated from 1.4 to 3.6 mg/

cm2 maybe resulting in increasing capacity of TBs These

samples reached the excellent coating results with smooth

and uniform surfaces

Declaration of Competing Interest

The authors declare that they have no known competing

financial interests or personal relationships that could have

appeared to influence the work reported in this paper

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[12] Bernardi D Mathematical modeling of lithium (alloy), iron sulfide cells and the electrochemical precipitation of nickel hydroxide Ph.D Thesis University of California; 1986

[13] Bernardi D, Newman J Mathematical modeling of lithium (alloy), iron disulfide cells University of California; 1986 [14] Sasaki A On the electrical conduction of pyrite Mineral J 1955;1(5):290e302

[15] Finklea SL, Cathey L, Amma EL Investigation of the bonding mechanism in pyrite using the M€ossbauer effect and X-ray crystallography Acta Crystallogr Sect A Cryst Phys Diffr Theor Gen Crystallogr 1976;32(4):529e37

FeS2 : AC : Na2SiO3 : STP = 30 : 60 : 5 : 5 FeS2 : AC : Na2SiO3 : STP = 45 : 45 : 5 : 5

FeS2 : AC : Na2SiO3 : STP = 60 : 30 : 5 : 5 FeS2 : AC : Na2SiO3 : STP = 70 : 20 : 5 : 5

Fig 14e Image of the ratio of different compositions with a 150 mm doctor blade thickness

Tiêu đề	An assessment of pyrite thin-film cathode characteristics for thermal batteries by the doctor blade coating method (đánh giá đặc điểm của catốt màng mỏng pirit sắt cho pin nhiệt
Tác giả	Trang-Le Thi Thu, Thuy-Le Thi Thu, Tran Dinh Manh, Trung-Truong Tan, Jeng-Kuei Chang
Trường học	Institute of Materials Science and Engineering, National Central University
Chuyên ngành	Materials Science and Engineering
Thể loại	Original Article
Năm xuất bản	2021
Thành phố	Taoyuan, Taiwan

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Số trang	11
Dung lượng	1,92 MB