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© 2019 IJRAR February 2019, Volume 6, Issue 1 www.ijrar.org (E-ISSN 2348-1269, P- ISSN 2349-5138)

IJRAR19J2078 International Journal of Research and Analytical Reviews (IJRAR) www.ijrar.org 903

Characterization of Microporous Separators for

Prismatic Lithium-ion batteries

Rekha L*, Narayan R, Venkateswarlu M, Jagadish M

R & D, Technology Centre, Amara Raja Batteries Ltd. Karakambadi – 517 520, Andhra Pradesh, India.

Abstract: The present paper focus on understanding the separator materials that are used in Lithium Ion prismatic type batteries. In

recent years, there have been intensive efforts to improve the overall performance of lithium-ion batteries where separator is the

key component of battery which isolates the electrodes and prevent electrical short-circuits of the battery. Also it is used as an

electrolyte reservoir which is used as a medium for ions to transfer between electrodes during charge and discharge process. Performance of the batteries are highly dependent on the physical, chemical, thermal properties and structure of the separator. Hence

our study focussed on separator material to understand its thermal properties, micro-structure, wettability and dimensional change

(area based) by adopting Differential scanning colorimetry (DSC), Scanning Electron Microscope (SEM), acid drop technique and

thermal shrinkage respectively. A comparative study was made on various types of Li-Ion spent batteries and the test results reveals

that the majority of the battery separator’s contains polyolefin type predominantly polyethylene, polypropylene and tri-layer based

separator. Further, it is observed that these separators are manufactured in different process such as dry, wet & coated surface types.

The observed results of the study are presented and discussed in detailed.

Key words: Polyolefin Separator, Scanning Electron Microscope (SEM), Differential Scanning Colorimetry (DSC), Wettability,

Thermal Shrinkage

1. Introduction:

Lithium ion batteries are playing the predominant role in rechargeable battery market. A strong demand for portable electronic and

electrical devices in recent years has led to corresponding demand for high –performance batteries. Due to the large amount of

energy can be stored per unit of weight and volume, lithium-ion batteries have become an apt choice of power source for many

portable electronic devices such as mobile phones, laptops, power tools, etc. Stimulatingly these cells are also being used for large

capacity applications including Electric Vehicles (EV) and Energy Storage Solutions (ESS) as well. The Li-Ion cell manufacturers

commonly provide data sheets that contain technical product information including parameters such as physical dimensions, weight,

capacity, voltage profile and cycle life. But while choosing batteries for any particular application, there are wide characteristics of

a battery that need to be considered. Thus there is a scope for understanding the insight into the state-of-the –art of commercial cells

[1].

Like any other battery, Li-Ion cell technology also consists of cathode, anode, separator, either in cut-stacked or wound in a circular

(jelly –roll) structure of the cell which is enclosed in a metallic can (Li-Ion prismatic) or aluminium/polymer pouch laminated (Li-

Ion polymer-LIP). The cathode and anode are electrically isolated by polyolefin based membrane. An organic electrolyte provides

ionic conducting medium for Li-ions to shuttle between anode and cathode during charging and discharging [2]. The pores in the

separator are filled with an ionically conductive liquid electrolyte –a solution of lithium salt in non-aqueous solvents. Any closure

of pores will directly impede the movement of ions in electrolyte, resulting in the battery performance degradation [3].

According to S.S Zhang [4], in most of the commercialized Li-Ion batteries, polyolefin porous membranes specifically polyethylene

(PE) and polypropylene (PP) are commonly used. The function of the separator is to prevent physical contact between positive and

negative electrodes while permitting ionic transport within the cell and the ions that are contained in the liquid electrolyte

unrestricted passage between the electrodes of the cell [4, 5, 6]. Thus, the separators should be chemically, electrochemically and

mechanically stable in the battery even at high temperature operations or else the anode and cathode would contact each other which leads to thermal runaway even causes combustion or explosion, especially under abused operating conditions [7]. Separators are

made up of different materials and methods for liquid electrolyte lithium ion batteries and it is broadly classified into microporous

membranes, non-woven mats and Inorganic composite membranes [3].

Although the PP, PE separators are reliable for portable electronic applications, two major limitations should be overcome for

vehicular storage utilization. First, shrinkage or melting of polyolefin separators may happen at elevated temperature when the

battery is used for a long time under a high current density, which often causes the occurrence of internal short circuit and explosion

of batteries. Secondly, the hydrophobic surface and low surface energy of polyolefin separators result in their poor wettability with

liquid polar electrolytes such as ethylene carbonate (EC), dimethyl carbonate (DMC) and propylene carbonate (PC) [8, 9].

Several surface modification processes have been tried to improve the wettability and shrinkage characteristics of polyolefin separators. New developments in the “ceramic separators”, in which either the ceramic is applied with polymeric binders (e.g.

PVDF) [4, 5, 16] or in form of coated particles on a nonwoven substrate [2]. The separators made up of inorganic sub-micron

particles have been studied due to their excellent thermal stability and wettability with organic electrolytes. These particles require

a substrate on to which they can be coated. The inorganic separator could have the advantages of “absolutely” thermal stability,

strong electrolyte absorption and no dendrite puncturing problems [4, 10].

From the microporous structure viewpoint, the membrane made with dry process seems to be more suitable for a high power density

battery due to its open and straight porous structure, while those separator which are made by the wet process are more stable which

enhances the cycle life battery because of their tortuous and interconnected porous structure that is helpful in suppressing the growth

of dendritic lithium on the graphite anode during fast charging or low temperature charging [4].

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In this study, the separator samples are collected from the post mortem of various types of spent Li-Ion prismatic batteries which

are collected over a period of time to understand the types of separators and its manufacturing processes which are used in mobile

batteries. Here it is observed that the importance of microstructural characterization of the materials has a strong influence on the

battery performance. To get more insight understanding of the underlying properties of the separator, Differential Scanning

Colorimetry (DSC) studies have carried out to observe the melting temperature and the morphological studies by Scanning Electron

Microscopy (SEM) to know the microstructure and its parameters such as shape, size and uniformity of the pores. Further, the acid

drop and dimensional change studies were carried out to estimate the absorption of the electrolyte and shrinkage of the membranes

respectively.

2. Experimental:

2.1 Test matrix

In this study, we have identified and collected separators from various types of Li-Ion spent batteries over a period of time and they

have been further classified in to different groups which are referred as B1 to B14. From B1 to B7 (0.8-1.4Ah); B8 M1 to M7 (1.1-

3.0Ah); B9 M1 to M4 (1.05-2.0Ah); B10 M1 to M4 (0.68-2.0Ah); B11 M1 to M3 (1.0-2.1Ah); B12 M1 to M7 (0.9-2.4Ah); B13

M1 to M6 (0.9-2.0Ah) and B14 M1 to M2 (1.45-2.1Ah). Here B indicates Batch, M indicates Model, where Model A, AA denotes

as similar capacity and * indicates as pouch type Li-Ion battery.

2.2 Batteries dissection procedure and separation of components

The selected models are dissected for further analysis in order to understand the chemistry, design and engineering. Prior to

dissection, these batteries were fully discharged to 0% SOC and the test was carried out using Bitrode tester (Model: MCV) at

ambient environment. In order to overcome the short circuit of the cell while dissection, care need to be taken while cell opening.

The internal short circuits are most likely to be happened during cutting either due to penetration or deformation of the electrode

stack to jelly roll due to mechanical stress.

Therefore necessary precautions were well taken while carrying out the teardown process and Non-conductive ceramic tools are

used in the entire process for better safety. A cutting tool is used to cut at one end of the cell and the remaining case should be

isolated by peelers. In the entire process no excessive force should be applied while removing the jelly roll to avoid the internal

damage of the electrodes.

2.3 Physical Observations

During this process, majority of electrolyte evaporates and this is evidenced by sensing sweet odour smell from the moment of the

slit at the top of the can. Once the can is completely peeled, the electrode roll is taken out and we can observe these electrodes were

wrapped in flattened stack and were held together with a piece of adhesive tape on the outer side of the roll. Later to this cathode,

anode, separator and other inactive components are separated from the electrode roll and the extracted separator is used for further

analysis.

While removing the membranes from batteries, a noticeable changes were observed in the samples. It was found to be light brown

colour on the side in contact with negative electrode and the upper surface of separator is still in white colour where these changes

in the separator colour are assessed by visual inspection. The electrodes and the separators are still wetted by the electrolyte at the

movement of dismantling.

2.4 Sample preparation

2.4.1 Cleaning of separator samples:

After separation of the separator from the electrode roll in order to remove the surface residue of deposited lithium salts, the

separator was cleaned by adopting the rinsing procedure and it is followed by immersing each separator sample in DMC (Dimethyl

carbonate) at room temperature for three days and then replaced with fresh DMC. The samples are dried under vacuum for at least

30 minutes at room temperature and further considered for the analysis.

2.4.2 Thickness measurement

A Digimatic micrometer (Mitutoyo, 25mm) is used to measure the thickness of the separator for all samples. The measurements are

recorded at three points and the average of three measurements is considered as the thickness of the separator.

2.5 Material characterization

2.5.1 Differential Scanning Calorimetry (DSC)

The thermal properties of the membranes were determined by Differential Scanning Calorimetry (DSC 214 Polyma, NETZSCH).

The samples were heated at the rate of 25°C/10.0(K/min) up to 210°C under nitrogen purge which was used to determine the melting

points of the separator. The samples of approximately 8-9 mg, while two repeated heating /cooling cycles were applied at the

ramping rate at 10°C min-1 and the second heating scan was taken as the data in this experiment.




2.5.2 Scanning Electron Microscope (SEM)

The surface morphology of the separator was observed by Scanning Electron Microscope (SEM, JSM6010PLUS, and JEOL,

JAPAN). The samples are platinum coated using sputter coater (JEOL,JEC-3000FC The SEM images were recorded with an

accelerating voltage of 5.0KV, 10KV; coated type at 20KV and are captured at 20X magnification.

2.5.3 Wettability

The test was conducted by dropping a drop of electrolyte on the separator sample using ink pillar and observed the uniform spread

of the electrolyte for a minute time on the surface of each separator.

2.5.4 Thermal shrinkage of separator

The thermal shrinkage of separators is determined by measuring the dimensional changes of the sample (area based). The samples

are prepared by cutting it into 30mm x 30mm dimension. The samples were placed in an oven and were monitored at various

temperatures such as 120°C for one and four hours, 150°C for one hour and 180°C for one hour. Thermal shrinkage of the separator

sample is calculated using the following equation.

Thermal Shrinkage (%) = S0-S/S0×100

Here S0 and S indicates the area of the samples before and after the temperature storage.

3. Results and discussions:

3.1 Differential Scanning Calorimetry (DSC)

The DSC thermogram were carried out to understand the thermal analysis of the separator samples and are observed as

Polypropylene (PP), Polyethylene (PE) and bi-layer / tri-layer and are shown in Fig.1 and data is presented in Table.1. From the

figure it is evidence that the PE separator samples peaks are observed in between 133°C to136°C. The PP separator shows the

melting peak temperature around 162°C to168°C. It is also observed that the bi/tri -layer material shows two thermogram peaks,

one near the polyethylene melt temperature of around 133°C and the other one polypropylene around 164°C melt temperature. From

melting temperature results by DSC, it indicates that the separators are either polyethylene (PE) or Polypropylene (PP) or tri layer and observed the trend as polyethylene, polypropylene and bi/tri-layer.

PE Separators are used as secondary safety mechanisms which helps to limit cell temperatures by melting which closes pores, stops

mass transfer between electrodes and there by increases cell resistance [4]. High temperatures may occur during thermal runaway

reactions induced by short circuit or overcharge. The PP separators have too high of a melt temperature to work in this way because

either venting or mechanical disconnect which will generally occur first [17]. Besides the material differences, the separators had

important differences, which indicated that they were produced by a manufacturing method. However, most commercial batteries

use separators with a lower shutdown temperature between 130°C and 140°C [5].

While in tri layer separator where PE layer is sandwiched between two porous PP layers [5], the PE layer offers lower shutdown

temperature while PP provides the mechanical stability at and above the shutdown temperature. These multi-ply separators are expected to provide a wider shutdown window and may be safer than single layer separator for some applications and is commonly

used as a fail-safe device in commercial cells [5, 2]. In additional to this, the multilayer separators offer advantages by combining

the lower melting temperature of PE (~130°C) with the high temperature strength of PP. The porosity in the separator collapses, so

that the cells fail as the ion conduction is cut off. But if the temperature continues to increasing above the melting point of PP

(~160°C), the separator could fail in separating the electrodes, there by result in internal in shorting of the cell potentially [8].




Fig.1.DSC Thermograms of Polyolefin Separators, B1 to B14

3.2 Surface Morphology by SEM

The microstructural data would be helpful to the likelihood of battery failure through Lithium dendrite growth and changes in

separator structure through pore closure by mechanical stress and chemical degradation [11, 12, 13]. In our previous work, SEM

results of commercial polyolefin separator for optima sample preparation, image recording conditions are reported elsewhere [14].

The surface morphologies of the separators were monitored by Scanning Electron Microscope (SEM) and images are shown in

Fig.2 to Fig.9. Here, Table.1 shows a distinct difference in the orientation of the pore structure for microporous polyolefin

membranes made by the dry and wet process respectively. However, the separators made by either dry process or wet process have

slightly different surface morphologies which may be dependent on process conditions to control the thickness.

The separator was inspected for clogging & degradation by SEM and it was found that the separator retain the oriented porous

structure with some minor imprints likely caused by compression. In contrast, where the separator was exposed to plated lithium

on the negative side of the separator exhibit thick string –like aggregates. Plated lithium and the damaged separator influence the safety of lithium-ion cells in thermal and mechanical abuse scenarios [15]. The typical morphology of the commercial PP separator

indicates needle like nanoscaled pores distributed along the dry-stretching direction whereas PE membrane has a uniformly

interconnected highly porous structure which is responsible for free dendrite growth and penetration. [20,21]. X. Huang J et al.

reported the porous membranes produced through this dry process usually show characteristic slit-like structure where as in wet

process, the pores are round like structure [3].




From the summary of Table. 1 and Fig.2 to Fig.9, the pores in separators were produced either by dry process or wet process. In

dry process it is observed a fibrils to well-defined oriented micro pores with slit like characteristics oriented in the same direction

and in the wet process pores are observed interconnected spherical or elliptical pores with different pore diameter. However some

of these samples have found pore closing and swollen fibres. Also the lithium deposition is observed which is may be due to

electrolyte decomposition products/stack pressure during manufacturing mechanical stress /chemical degradation/ mechanical

effect caused by a smearing of the upper layer onto the pores. In some cases it is observed that even after rinsing, the lithium salt

traces haven’t been completely washed out from the separator and in such condition it is furthermore important to rinse yet again

in the same way to get comparable results.

Here the SEM images are taken on both the sides S1 and S2 due to its coated surface in the models which are represented in Fig.2

(B7 S1, B7 S2), Fig.6 (B11 M3 S1, B11 M3 S2), Fig.7 (B12 M6 S1, B12 M6 S2). Comparatively from these images, the porous PE separator with ceramic coated in B7 S2, B11 M3 S2, B12 M6 S2, Al2O3 particles (evidenced by EDAX) are homogeneously

distributed in the surface layer without agglomeration. According to C. Shi et al, the surface coating layer on the separator is

expected to protect from shrinkage owing to the existence of heat resistant, which are expected to play a key role in improving the

electrolyte wettability, uptake of liquid electrolyte and ionic conduction of the membranes with electrolyte [7]. W.K. Shin et.al

Ceramic –coated separators, the coating of ceramic particles has been effective in improving the mechanical, thermal and electrical

properties of separators only due to physical actions without directly contributing to the lithium ion transport process [16].

Fig.2.SEM Micrographs of the separator from B1 to B7




Fig.3. SEM Micrographs of the separator from B8, M1 to M7





Table .1 Summary of membrane from DSC & SEM

Batch (B) /

Model (M)

Capacity

(Ah)

Thickness

(µm) Melt Temp.

(0C ) by DSC

Nature of

Polymer

Mfg.

Process Observations (SEM)

B1 0.8 14 136.6 PE Wet

Uniformly interconnected spherical pores, medium

size pore configuration

B2 1 15 132.4 167.3

Bi/Tri

layer Dry

Slit like characteristics, pores are closed may be due to

mechanical stress /chemical degradation

B3 1 20 166.7 PP Dry

Oriented micro pores with slit like characteristics,

pores are clogged at some areas due to stress and

swallowed fibrils

B4 1 15 135.5 PE Wet

Uniformly interconnected spherical /elliptical pores,

medium size pore dia configuration and thick tree branch like polymer phases

B5 1.07 13 132.9 163.9

Bi/Tri

layer Dry

Slit like pores, clogs the pores by the electrolyte

decomposition products /mechanical stress /chemical

degradation, small pore dia configuration

B6 1.1 16 136.2 PE Wet

Uniformly interconnected spherical pores, many thick

tree like branch polymer phases, medium pore dia

configuration

B7 1.4 30 135.3 PE

Wet-

Single

side

coated

Clogs the pores by the electrolyte decomposition

products, Thick tree like branch polymer phases,

Uniformly coated Inorganic particles on surface

B8 M1 1.1 10 136.6 PE Wet

Spherical shape pores, small pore dia configuration,

surface covered with Li deposition

B8 M2 1.2 16 133.0 PE Wet

Spherical shape pores, small pore dia configuration,

thick tree like branch polymer phases, surface covered

with Li deposition

B8 M3 1.4 20 133.5 164.2

Bi/Tri

layer Dry

Oriented micro pores with slit like characteristics, pores are compressed may be due to mechanical stress

/chemical degradation, Li dendrites are visible

B8 M4 1.5 20 163.1 PP Wet

Interconnected spherical shape pores, small pore dia

configuration, thick tree branch like polymer phases,

Li dendrite are visible

B8 M4A 1.5 18 136.0 PE Wet

Interconnected spherical pores, small pore dia

configuration, Li dendrites are visible

B8 M5 2 17 135.7 PE Wet

Interconnected spherical pores, medium pore dia

configuration, thick tree branch like polymer phases

B8 M5A 2 17 133.0 PE Wet

Interconnected spherical pores, small pore dia

configuration

B8 M6 2.1 15 136.2 PE Wet

Interconnected elliptical pores, thick tree branch like

polymer phases, large pore dia configuration

B8 M7* 3 13 133.5 PE Wet


products/ mechanical stress

B9 M1 1.05 14 135.7 PE Wet

Interconnected Spherical shape pores, small pore dia

configuration, some area surface covered by

electrolyte decomposition products

B9 M2 1.45 15 167.2 PP Dry Oriented micro pores with slit like characteristics, pore area are crushed may be stress

B9 M3 1.8 19 136.3 PE Wet

Interconnected ,Spherical shape pores, medium pore

dia configuration, thick tree branches

B9 M3A 1.8 15 136.9 PE Dry

Spherical shape pores, surface covered by electrolyte

decomposition products and Li dendrites

B9 M3AA 1.8 12 133.8 PE Wet


configuration, thick tree branch like polymer phases

B9 M4 2 15 165.4 PP Wet

thick tree branch like polymer phases covered by

electrolyte decomposition products

B10 M1 0.68 18 162.0 PP Wet

Spherical shape pores, thick tree branch like polymer

phases

B10 M2 1 20 136.1 PE Wet

Spherical shape pores, small pore dia configuration

surface covered by electrolyte decomposition products




Here “A&AA” indicates same Capacity (Ah) with different models and “*” indicates pouch case sample

3.3 Wettability:

The wettability of the separator plays an important role in battery performance because a separator with good wettability can

effectively retain the electrolyte solution and facilitate ion transport between electrodes. Further it also affects the overall electrolyte

filling time of a battery. Beside this it plays a critical role in the battery performance that can be effectively retain the electrolyte

and facilitate its diffusion well into the cell. Commercial separators are normally chemically treated and /or coated with surfactants

in an additional step for improved wettability. Polyolefin is an inherently hydrophobic polymer, thus untreated commercial

separators made of polyolefin do not usually provide good electrolyte wettability [2, 4, 18, 19].

The observed wettability test results of both sides were show in Fig.10 and are indicated as Side1 and Side2. From this it is clear

that the electrolyte remained as a drop even after a minute duration on the PE & PP separator even though the visible grey region indicates that the electrolyte has penetrated through the separator. However, the B7, B11 M3, B12 M6 samples where the inorganic

Batch (B) / Model (M)

Capacity (Ah)

Thickness (µm)

Melt Temp. (0C ) by DSC

Nature of Polymer

Mfg. Process

Observations SEM

B10 M3 1.5 19 164.8 PP Wet


configuration with thick tree branch like polymer

phases, Li dendrites are visible

B10 M4 2 17 136.1 PE Wet

Uniformly interconnected spherical pores, small pore

dia configuration with thick branches

B11 M1 1 20 133.6 164.7

Bi/Tri

layer Dry


electrolyte decomposition products /mechanical stress,

Li dendrites are visible

B11 M2 1.65 21 133.5 164.3

Bi/Tri

layer Dry


pores are not visible may be mechanical stress

B11 M3 2.1 13 137.4 PE

Wet –

Single

side

coated

Interconnected spherical pores, medium pore dia

configuration with thick tree branch like polymer

phases, Uniformly coated Inorganic particles on

surface

B12 M1 0.9 15 166 PP Wet

Interconnected elliptical pores with honey comb like

structure with thick branches

B12 M2 1 17 135.4 PE Wet Clogs the pores by the electrolyte decomposition products /mechanical stress /chemical degradation

B12 M3 1.4 15 167.0 PP Dry

Slit like pores, clogs the pores by the electrolyte

decomposition products /mechanical stress /chemical

degradation

B12 M3A 1.4 21 167.4 PP Dry

Oriented micro pores with slit like characteristics, few

fibrils are damaged may be stress

B12 M4 1.5 15 - - Dry


products /mechanical stress /chemical degradation

B12 M5 1.75 22 167.4 PP Dry

Oriented micro pores with slit like characteristics, Li

deposition are visible

B12 M6 2.1 14 136.4 PE

Wet -

Single

side

coated


dia configuration with thick branches, Uniformly

coated Inorganic particles on surface

B12 M7 2.4 20 133.8 164.7

Bi/Tri

layer Dry


pores are not visible may be mechanical stress

B13 M1 0.9 18 135 PE Wet

Uniformly interconnected spherical pores, large pore

dia configuration with thick branches

B13 M2 1.4 21 167.9 PP Dry Oriented micro pores with slit like characteristics

B13 M3 1.75 17 132.9 PE Wet Spherical pores, clogs the pores by the electrolyte decomposition products small pore dia configuration

B13 M4 1.78 15 135.6 PE Wet


dia configuration

B13 M5 1.95 19 168.0 PP Dry


very few fibrils are mechanically stress

B13 M6 2 19 166.5 PP Wet

Uniformly interconnected spherical pores, many thick

tree branch like polymer phases medium pore dia

configuration

B14 M1 1.45 16 134.6 PE Wet

Uniformly interconnected spherical pores, few fibre

branches are swollen appearance, medium pore dia

configuration

B14 M2 2.1 11 133.4 162.8

Bi/Tri

layer Dry


Partially clogs the pores by the electrolyte

decomposition products




particles were coated on single side, here the electrolyte drops penetrated and spread across the separator surface quickly. Here it is

observed that the absorption has taken place on the coated side rather than the other one. The rapid absorption and spreading of the

electrolyte in the composite separators and on their surfaces is attributed to the high affinity of the liquid electrolyte to the ceramic

particles.

Fig.10 Comparison of the liquid electrolyte, wettability of separators with liquid electrolyte droplets




3.4 Thermal shrinkage

Thermal shrinkage of separators is another important property to be invstigated pertaining to not only battery performance but also

the safety aspects. A shrunk of separator caused by the heat generated during cell cycling could result in shorting of the electrodes

along the perimeter of the separator ultimately resulting in the thermal runaway of Lithium ion batteries accompanied by smoke,

flames and explosion. The thermal stability of the separator is evaluated by measuring the dimensional changes (area-based) of the

separators after exposure at high temperatures from 120°C to 180°C. The pictorial images of the seperators after exposure to

temperatuers 120°C for one hour and four hours, 150°C for one hour and 180°C for one hour images are shown in Fig.11 and Fig.12

respectively.

Initially the shrinkage is examined at the temperature 120°C for one hour and recorded the images and maintained the same till four hours. From the observation it is found that there is no significant changes occurred at 120°C for one hour and four hours, so

considered the values of four hours duration and the observed shrinkage results is given in detailed. From B1 to B7, the shrinkage

is observed as ~3.3 to 10%; B8 is ~3.3 to 16.7%; B9 is ~3.3 to 20%; B10 & B11 is ~3.3 to 10%; B12 is 0 to ~10%; B13 is ~3.3 to

10%; B14 is ~3.3 to 14%. Further study was made at 150°C at one hour and the images clearly show that the PE membrane was

found a high degree of shrinkage during exposure to the high temperature (150°C) and found all the samples of Polyethelene based

seperators shrinks at the range of ~63 to 83%. It is evidence from the DSC results, PE separator samples melt peaks is in between

133°C to 136°C. On the other hand, PP , bi/tri-layer and coated seperator undergoes the lowest degree of dimensional change

polypropylene is ~10 to 20%, where as bi/Tri-layer seperators is ~26 to 33%.

Also the study was performed at 180°C and the tests was carried out only on PP and bi/tri-layer. From the images it is clear that the

membrane has almost melted among all the models except B7, B11 M3 and B12 M6 and this is may due to the presence of ceramic coated layer (Al2O3) which is evident by SEM-EDAX. The ceramic coating layers are expected to prevent the separators from

thermal shrinkage, due to the existence of the heat resistant nano particles it states that all the coated separators have a reduced

thermal shrinkage than the uncoated polyolefin separator over a wider range of temperatures, which verifies that the introduction

of ceramic coating layers is effective in improving the thermal performance of separators.

(a) Thermal shrinkage at 120°C [1hr] (b) Thermal shrinkage at 120°C [4hrs] (c) Thermal shrinkage at 150°C [1hr]




Fig.11 Thermal Shrinkage of separators at 120°C (1 & 4 hrs), 150°C (1 hr)

Thermal shrinkage at 180°C [1hr]*

* Selected samples are PP & Coated type

Fig.12 Thermal Shrinkage of separators at 180°C (1 hr)




4.Summary:

From the studies it was observed that the PE and PP based separators are able to protect the batteries even at the 120°C temperature.

By the SEM results, the pores in separators were produced either by dry process or wet process where a fibrils to well-defined

oriented micro pores with slit like characteristics oriented in the same direction are observed in dry process and interconnected

spherical or elliptical pores are observed in the wet process. The EDAX results evidenced that the observed samples are ceramic

coated and shown better wettability and the average thickness of the separators are observed in the range of 12 – 30 µm. The results

indicates that the majority of the seperator samples in the portable application segments deployed the separator of PE with wet

process followed by PP with dry process, Bi/Tri layer, PP with wet process, PE with wet coated.

Acknowledgements

The authors would greatly acknowledge to the management of Amara Raja Batteries Ltd., for their support and encouragement.

Also we would like to thank Advanced Laboratory team, Technology Centre for their timely support.

References:

[1] Valentin Muenzel Et al Journal of The Electrochemical Society, 162 (8) A1592-A1600 (2015)

[2] P. Arora, Z. Zhang, Chem. Rev. 104 (2004) 4419-4462.

[3] X. Huang, J. Solid State Electrochem. 15, (2011) 649-662

[4] S.S. Zhang / Journal of Power Sources 164 (2007) 351–364

[5] G. Venugopal et al.Journal of Power Sources 77 (1999) 34–41

[6] J. L. Shi, L. F. Fang, H. Li, H. Zhang, B. K. Zhu and L. P. Zhu, J. Membr. Sci., 437 (2013) 160

[7] C. Shi et al. / Journal of Power Sources 270 (2014) 547-553

[8] S. Tobishima, J. Yamaki, J. Power Sources 81-82 (1999) 882-886.

[9] J. Fang, A. Kelarakis, Y. W. Lin, C. Y. Kang, M. H. Yang, C. L. Cheng, Y. Wang, E. P. Giannelis and L. D. Tsai, Phys.

Chem. Chem. Phys., 2011, 13, 14457.

[10] J. Li, C. Daniel, D. Wood, J. Power Sources 196 (2011) 2452-2460

[11] A. Jana, D. R. Ely, and R. E. Garcia, J. Power Sources, 275, 912 (2015).

[12] C. Peabody and C. B. Arnold, J. Power Sources, 196, 8147 (2011).

[13] J. Cannarella and C. B. Arnold, J. Power Sources, 245, 745 (2014).

[14] Rekha et.al International Journal of Science and Research DOI: 10.21275/ART2019518

[15] M. Fleischhammer, T. Waldmann, G. Bisle, B.-I. Hogg, M. Wohlfahrt-Mehrens, J. Power Sources 274 (2015), 432-439

[16] W.-K. Shin, D.-W. Kim / Journal of Power Sources 226 (2013) 54-60

[17] R. Spotnitz, M. Ferebee, R. Callahan, K. Nguyen, W.-C. Yu, M. Geiger, C. Dwiggins, H. Fisher and D. Hoffman,

Shutdown Battery separators, 12th Int. Seminar of Primary and Secondary Battery Technology and Application, 6-9 Mar.

1995, Deerfield Beach, FL, USA, Florida Educational Seminars, Boca Raton, FL

[18] Y.M. Lee, J.W. Kim, N.S. Choi, J.A. Lee, W.H. Seol, J.K. Park, J. Power Sources 139(2005) 235-241.

[19] J. Saunier, F. Alloin, J.Y. Sanchez, G. Caillon, J. Power Sources 119-121 (2003) 454-459.

[20] M. Xia et al., Journal of Power Sources 266 (2014) 2-35

[21] J. Kumar et al., Journal of Power Sources 301 (2016) 194-198


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