Three Bond Technical News
Issued July 1, 2002

59

Sealants for Lithium-Ion Batteries
Introduction ________________________________________________As portable electronic devices become increasingly compact, their parts must be made ever smaller.
In addition, there is increasing demand for technological innovations in batteries for such devices; forexample, a small, long lasting battery is a requisite for cellular phones. To increase the performance ofbatteries under such circumstances, improvement in the sealants used in their assembly is expected.
This issue introduces the battery market and discusses the development of battery sealants that canbe expected to flourish in the market.

Contents
Introduction ................................................1
1. Brief Description of Lithium-Ion
Batteries ...............................................2
2. Primary and Secondary Batteries ..........2
3. Energy Density of Lithium-Ion
Batteries.................................................3
4. Introduction of Three Bond's
Sealants .................................................4

4-1 Introduction of Lithium-Ion
Battery Sealants, ThreeBond1170B and 1171 ............................. 4
4-2 Introduction of Battery-Pack
Sealants, ThreeBond 1530D.......... 6
5. Conclusion............................................. 81

1.

Brief Description of Lithium-Ion
Batteries

Various batteries are now on the market, and arebroadly classified into two types: chemical batteries
and physical batteries. Chemical batteries utilize
chemical reactions (electrolytic reactions) togenerate electricity, while physical batteries induce
cell reaction in response to specific external
stimulation (with solar batteries being a
representative example). Lithium-ion batteries areclassified as chemical batteries and feature thehighest power among those currently availablebatteries, and their capacity increases year afteryear.
A battery generates electricity by transporting
electrons between electrodes. In a lithium-ion
battery, the positive electrode is made of carbon andthe negative electrode is made of lithium. Battery
manufacturers have extensive know-how withrespect to the crystalline structure of carbon used as
the material of the positive electrode. The mostsignificant difference between lithium-ion and otherbatteries is that the former uses organic solvent as
its electrolytic solution. This is due to the fact thatthe electrolyte is easily dissolved into the organic
solvent during the electrolytic reaction. As thiselectrolyte is very sensitive to water, it is made ofnon-aqueous material. The reason for it being very
sensitive to water is as follows:
From the position of Lithium in the periodic table,i.e., just below hydrogen, it is understood that
Lithium belongs to the same group as the elementsthat constitute water, which means that it has a highaffinity with water. It is for this reason that
Lithium-ionbatteries
areconsideredwater-sensitive.
Shown below are the materials that compose
lithium-ion batteries.
- Electrode
Positive electrode: Carbon + binder resin
Negative electrode: Lithium compound + binderresin- Electrolytic solution
Organic solution- Electrolyte
Halogenated lithium salt
- Separator
Nonwoven fabric
It is clear from the components listed above thatthe lithium-ion battery is an aggregation of organiccompounds. The components of the lithium-ion

2battery are different significantly among its types
and manufacturers. For example, the composition ofelectrodes and electrolytes differs between primaryand secondary batteries. In addition, individual
battery manufacturers employ unique combinationsof materials to configure a battery. Each
manufacturer pursues unique battery designs withthe goal of creating batteries with more power than
any that have come before them.
We believe that electrolytic solution andelectrolyte are vital materials of lithium-ion
batteries, and that finding the optimum combinationof the two materials is a key point in developing
high performance batteries. It is not an exaggeration
to say that the combination of electrolytic solution
and electrolyte determines the performance oflithium-ion batteries. As the safety and recyclabilityof batteries have been the focus of a great deal ofattention in recent years, the minimization ofenvironmental load of the electrolytic solution andthe dehalogenation of the electrolyte have become
important issues. However, there has always been
the inherent contradiction that the solution of theseissues represents an obstacle to the creation of highpower batteries. The battery manufacturing industry
is making efforts to resolve this contradiction.

2.

Primary and Secondary Batteries

In the industry, there are various technical termswith respect to batteries, including lithium-ionbatteries. Such terms are summarized herein.
Batteries are broadly classified into two
categories: primary batteries and secondary
batteries. However, with the introduction of solar
batteries and fuel cells, batteries have recently
begun to be categorized as either chemical or
physical batteries. Primary batteries are so-called"disposable batteries" that can be used only once.
Dry batteries are typical primary batteries, and arecycling campaign for disposable batteries has
recently been actively organized. Cylindrical andsquare shapes are the most popular. The button
batteries used in cameras and portable gamemachines are typically shaped primary batteries.
Secondary batteries are rechargeable batteries. As
secondary batteries are used primarily as a powersource for specialized equipment (in the form of abattery pack), unlike primary batteries, they are
generically referred to as "batteries." The word
makes most people think of storage batteries.
Storage batteries are rechargeable and are thusclassified as secondary batteries as well. Fuel cells
haveattracted
considerable
attentionasnext-generation batteries. As the designs of fuelcells differ completely from those of the batteriesdiscussed above, primary and secondary batteries
are not an appropriate categorization approach forfuel cells. Fuel cells are secondary batteries in a
broad sense but, taking into consideration theirdesigns and applications, it can be said that fuelcells are an energy system.

3.

Energy Density of Lithium-Ion
Batteries

Among batteries for which there is increasing
demand that they be made "lighter, thinner, andsmaller," the greatest demand is placed onlithium-ion batteries due to their excellent
capabilities, particularly their high energy density.
Nickel metal hydride (NiMH) and lithium-ion
batteries feature the highest performance among
batteries currently on the market. While the former
are popularly thought of as "clean" batteries, theirshapes are limited and many difficult technologies
are required to make them compact and lightweightin design. On the other hand, the latter utilizes ionsto induce electrolytic reaction, making it is possible
to generate electricity as long as there is sufficientspace to allow ionic conduction. Fig. 1 compares
the battery potentials (i.e., energy densities)
necessary for the generation of electricity. The
per-weight energy density of the NiMH battery is ashigh as 100 Wh/kg due to the fact that a metallic
material is used as the main power-generating
component. The per-weight energy density of thelithium-ion battery shows the highest value, at 150
Wh/kg. As the energy density can be directly
converted into energy efficiency, it can be said thata higher energy density will result in greater
electromotive force, i.e., increased power. The
current target energy densities of lithium-ion
secondary batteries are 300 Wh/L (per-volumeenergy density) and 150 Wh/kg (per-weight energydensity). Now, even inorganic and polymer batteries,
both of which have heretofore not been considered
R&D items, in addition to new hybrid batteries, areunder study using these figures as development
goals. Fig. 2 shows trends in the overall weights ofportable electronic devices on a year-by-year basis.
It can be seen that the overall weights of portableelectronic devices have remained at nearly the samelevel, despite the fact that their performance hasimproved steadily. It is estimated that lightweightbatteries, together with lightweight peripheral parts,
contribute to the constant device weights.

Lithium-ionbatteries

Energy density per weight, Wh/kg

400

NiMH batteries

350300NiCdbatteries

250200

Leadbatteries

150100500

Lithium-ion batteries generate the highest power.
Fig. 1 Comparison - Energy Densities of Secondary Batteries310000The mass of each portable electronic
device remains nearly constantregardless of an increase in volume.

Mass, g1000

100

Mass reduction on the part-by-part basis
PDADigital camera

10Notebook PC
Cellular phone

1708090100300

500 1000 2000 3000 5000

Volume, cm3
The battery is the heaviest part of a portable electronic device.

Fig. 2 Volume vs. Weight - Portable Electronic Devices (Survey in FY2000)

4.

Introduction of Three Bond'sSealants

Due to its unique structure, each lithium-ion
battery consists of various materials. As lithium-ion
batteries are being developed continuously, battery
manufacturers are setting the highest development
goals and working to develop extremely high powerand high efficiency batteries. The components oflithium-ion battery have been briefly explained inprevious sections; this section primarily discusses
the future prospects for and Three Bond's
contributions to the development of lithium-ionbatteries.
4-1

Introduction of Lithium-Ion Battery
Sealants, ThreeBond 1170B and 1171
ThreeBond (hereinafter referred to as "TB")
1170B and 1171 are sealants developed forlithium-ion batteries (see Table 1). Their major
component is olefin hydrocarbon. As the polymericprincipal chain structure of this olefin hydrocarbon

is neutral, each sealant strongly withstands
electrolytic solution. Previously caulked sections
and packing entrances, where sealing is required,
are sealed with asphalt pitch or other materials. The
problem has been pointed out that since the asphalt
contains chains composed of relatively low
molecules, areas adjacent to or exposed to theelectrolytic solution suffer from decreased sealing
performance. With the recent trend toward "lighter,thinner, and smaller" and high power batteries,
battery manufacturers are forced to reduce thesealing area. For this reason, they are making every
effort to continue using the asphalt pitch by
improving the battery design. Due to their excellent
sealing performance, TB1170B and TB1171 allow
to seal batteries satisfactorily without changes to thestructural design of a battery. In addition, webelieve that higher sealing performance can reduce
the sealing area without reducing the batterycapacity.

Table 1 Properties of Lithium-Ion Battery Sealants

4TB1170B

TB1171

Test method

Remarks

Appearance

Colorless

Colorless

3TS-201-01

VisualViscosity, mPa•s

2400

400

3TS-210-01 or -02

BL/BH rotational viscometer

Specific gravity

0.87

0.87

3TS-213-02

Specific-gravity cup method

Nonvolatile content, %15

4.5

3TS-217-01

Weight-change ratio after heating at 160°C

pitch. This is the result of the unique molecular
structure of TB1171 and TB1170B, i.e., their neutral
chain structure and low permeability design, aspreviously discussed.
Fig. 5 compares the thermal viscoelasticities ofTB1171 and asphalt pitch. Many sealants now
feature solder reflow resistance in response tomarket needs; therefore, we measured the storage
elastic modulus under heat as one of the features ofthese sealants. It was proven that when stress wasgradually applied to the asphalt pitch at 260°C, its
storage elastic modulus dropped at low stress levels.
On the other hand, the storage elastic modulus ofTB1171 did not fall at the test temperature. This test
result shows that TB1171 is not destroyed by thestress accumulated in the battery (i.e., the pressure
increase due to the evaporation of electrolyticsolution) even under high temperature conditions,and that the resin maintains its elasticity even after
the stress increase.

Fig. 3 compares TB1170B, TB1171, and asphalt
pitch with respect to their resistance againstelectrolytic solution. General electrolytic solutions,dimethoxy ether (DME), propylene carbonate (PC),and ϒ-butyrolactone (ϒ-BL) were used in this test.
Our sealants are designed to offer a higher
molecular weight and smaller amount of low
molecules compared to the asphalt pitch. As a result,
our sealants have less component elution from highpolarity electrolytic solutions compared to pitches.
This fact can be clearly seen in the test result shownin Fig. 3. It has been proven that our sealants havehigher electrolytic-solution resistance than asphalt
pitch, and that components are not eluted into
electrolytic solutions even under high temperature
conditions.
Fig. 4 shows a comparison of permeability tested
under various conditions. It is clear from this figurethat TB1171 has the lowest permeability among thetest materials, and that this characteristic is
substantially improved compared to the asphalt
Test method and conditions:
Apply 0.1 g of each resin to a glass plate so that the coated area will be 15 mm
across and 100 µm in thickness. Immerse the coated glass plate in thespecified electrolytic solution for 10 days at 60°C, and calculate theweight-change ratio using the weights measured before and after the test.

Test method and conditions:
In accordance with JIS K7129 "Test method for thewater-vapor transmission rate of plastic film and sheeting,"
measure the permeability of resin 100 µm in thickness.
1210TB1170Bg/m2

8TB1171

642Asphaltpitch-100-80-60-40-20020040

TB1170B

Weight-change ratio, %Fig. 3 Comparison of Three Bond Battery Sealants and Asphalt Pitch

Storage elastic modulus, Pa

5TB1171

Asphalt pitch

Fig. 4 Comparison of Sealants - Permeability

Possibility of degradation

432Tar pitch

1TB1171
Slide when shear stress applied

00102030405060

Shear stress, PaFig. 5 Comparison of Sealants - Thermal Elastic Modulus (Heating Temperature: 260°C; Frequency: 1 Hz)

54-2

Introduction of the Battery-Pack SealantThreeBond 1530D
Recently, many home electric appliances arebeing made smaller and lighter. As a result, batteries
are frequently used as the power source of thesedevices, including a slew of lithium-ion secondary
batteries, due to their large energy density. Despite
this trend, the leakage of electrolytic solution has
been a serious problem, and the industry is making
every effort to develop technologies that willcontribute to the secondary prevention of leakage.
Specifically, battery packs used in portable PCs arebeing designed taking into consideration thepossibility that surrounding electrodes, printed
circuits, and electronic parts will be damaged by theelectrolytic solution (or electrolyte) leaking frombattery packs. The most popular technique forprotecting printed boards and the like is to coat andseal these electronic parts and battery packs withresins.
Moisture-curing silicone resin is a conventional
material widely used as a coating sealant, but thisresin is dissolved into electrolytic solutions, losing
the expected coating and sealing effect as a result.
In addition, as a thin coat of the resin cannot
withstand electrolytic solutions, it is expected that it
will be necessary to apply a thick coating of theresin. However, such a thick application will

increase the weight of the battery, contrary to thecurrent needs. Even if silicone resin is used, thestructural design of the battery pack will be greatly
restricted and, for this reason, the material cannot
be used as a permanent measure. If the electrolyticsolution leaked inside the battery pack and thesealant could not be dissolved into the electrolytic
solution or swelled, the solution would remain in
the battery pack, which would have negativeenvironmental effects. When a hard resin is used, it
may come off from the battery during the drop test,for example. If the resin comes off from the tab orother parts after curing, the electrolytic solution willpass through the partition wall with the aid of
capillarity to corrode the electric circuit.
To solve this problem, Three Bond has developed
a moisture-curing elastic sealant, TB1530D, which
is designed for use in battery packs. The major
component of the resin used in TB1530D is aspecial polymer that contains a silyl group andcures as a result of reaction with a small amount ofmoisture in the air. TB1530D offers excellent
adhesion and bonding capabilities for a wide variety
of materials, including metals, plastics, rubbers, andinorganic materials, and features low viscosity.
Therefore, this sealant is suitable for coating
applications. Table 2 lists the properties andcharacteristics of TB1530D.

Table 2 Properties and Characteristics of TB1530D

Properties

Appearance

Unit

Measurement results

Appearance

3TS-201-02

-

Gray

Viscosity (25°C)

3TS-210-02

Pa•s

20

Specific gravity (25°C)

3TS-213-02-1.39

Dry-to-touch time

3TS-219-05

min5Remarks

BH, No.6, 20 rpm

Curing conditions: 25°C, 55 %RH, 7 days

Characteristics

6Hardness

3TS-215-01-A34

Peeling property

3TS-320-01

MPa

3.2

No. 5 dumbbell

Elongation

3TS-320-01%220

No. 5 dumbbell

Peeling shear adhesive strength

3TS-301-13

MPa

2.5

As the cured TB1530D, unlike those of theaforementioned TB1170B and TB1171, is swelledby the electrolytic solution in a lithium-ion battery,the electrolytic solution is gelled to lose fluidity,
and consequently the electric circuit is protectedfrom contact with electrolytic solution. As
TB1530D is also an elastic material, it will not be
separated from the battery parts even when thebattery pack is dropped onto a hard object. This
contributes to increasing product safety.
The leakage prevention system for lithium-ion
batteries is illustrated in Fig. 6. TB1530D should be

Shield wall

Battery housing

coated on the electrodes to which the control circuitand battery units are connected, and on thoseportions from which it is most likely that theelectrolytic solution will leak. If the electrolytic
solution leaks, the cured TB1530D will absorb thesolution to prevent flowing out. The cured
TB1530D swells with electrolytic solution, and, byadhering the resin with the electrodes, protects
electrolytic solution to penetrate into electric
circuits with capillarity. Fig. 7 shows an example ofa battery pack.

Resin filler (TB1530D)

Control circuit

Lithium-ion battery unit

Fig. 6 Lithium-Ion Battery Leakage Prevention SystemFig. 7 Battery Pack (photograph provided by Sony Corporation)

75.

Conclusion

Various resin materials are used in order to compose of batteries, and it is no exaggeration to say that individuals
are key materials to improve performance of batteries. It is forecasted that the trend toward "lighter, thinner, andsmaller" for portable electronic devices will be continued and heated. We are studying various plans to develop
not only sealants but other resins as well. We hope you continue to have interests on this trend and watch closely
our activities in the future.
Katsuhiko Kishi
Research Section
Research Department
Ho Kenkyo
Material Development Section
Development Department
Research Laboratory
Three Bond Co., Ltd.

1456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, Japan
Tel: 81-426-61-1333

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