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Threebond.co.jpThree Bond Technical News Issued July 1, 2002 Sealants for Lithium-Ion Batteries 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; for example, a small, long lasting battery is a requisite for cellular phones. To increase the performance of batteries 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 can be expected to flourish in the market. 4-1 Introduction of Lithium-Ion 1. Brief Description of Lithium-Ion Battery Sealants, ThreeBond 1170B and 1171 . 4 2. Primary and Secondary Batteries .2 4-2 Introduction of Battery-Pack 3. Energy Density of Lithium-Ion Sealants, ThreeBond 1530D. 6 4. Introduction of Three Bond's Brief Description of Lithium-Ion battery are different significantly among its types and manufacturers. For example, the composition of Various batteries are now on the market, and are electrodes and electrolytes differs between primary broadly classified into two types: chemical batteries and secondary batteries. In addition, individual and physical batteries. Chemical batteries utilize battery manufacturers employ unique combinations chemical reactions (electrolytic reactions) to of materials to configure a battery. Each generate electricity, while physical batteries induce manufacturer pursues unique battery designs with cell reaction in response to specific external the goal of creating batteries with more power than stimulation (with solar batteries being a any that have come before them. representative example). Lithium-ion batteries are We believe that electrolytic solution and classified as chemical batteries and feature the electrolyte are vital materials of lithium-ion highest power among those currently available batteries, and that finding the optimum combination batteries, and their capacity increases year after of the two materials is a key point in developing high performance batteries. It is not an exaggeration A battery generates electricity by transporting to say that the combination of electrolytic solution electrons between electrodes. In a lithium-ion and electrolyte determines the performance of battery, the positive electrode is made of carbon and lithium-ion batteries. As the safety and recyclability the negative electrode is made of lithium. Battery of batteries have been the focus of a great deal of manufacturers have extensive know-how with attention in recent years, the minimization of respect to the crystalline structure of carbon used as environmental load of the electrolytic solution and the material of the positive electrode. The most the dehalogenation of the electrolyte have become significant difference between lithium-ion and other important issues. However, there has always been batteries is that the former uses organic solvent as the inherent contradiction that the solution of these its electrolytic solution. This is due to the fact that issues represents an obstacle to the creation of high the electrolyte is easily dissolved into the organic power batteries. The battery manufacturing industry solvent during the electrolytic reaction. As this is making efforts to resolve this contradiction. electrolyte is very sensitive to water, it is made of non-aqueous material. The reason for it being very Primary and Secondary Batteries sensitive to water is as follows: In the industry, there are various technical terms From the position of Lithium in the periodic table, with respect to batteries, including lithium-ion i.e., just below hydrogen, it is understood that batteries. Such terms are summarized herein. Lithium belongs to the same group as the elements Batteries are broadly classified into two that constitute water, which means that it has a high categories: primary batteries and secondary affinity with water. It is for this reason that batteries. However, with the introduction of solar Lithium-ion batteries are considered batteries and fuel cells, batteries have recently water-sensitive. begun to be categorized as either chemical or Shown below are the materials that compose physical batteries. Primary batteries are so-called lithium-ion batteries. "disposable batteries" that can be used only once. Dry batteries are typical primary batteries, and a Positive electrode: Carbon + binder resin recycling campaign for disposable batteries has Negative electrode: Lithium compound + binder recently been actively organized. Cylindrical and square shapes are the most popular. The button - Electrolytic solution batteries used in cameras and portable game Organic solution machines are typically shaped primary batteries. Secondary batteries are rechargeable batteries. As Halogenated lithium salt secondary batteries are used primarily as a power source for specialized equipment (in the form of a battery pack), unlike primary batteries, they are It is clear from the components listed above that generically referred to as "batteries." The word the lithium-ion battery is an aggregation of organic makes most people think of storage batteries. compounds. The components of the lithium-ion Storage batteries are rechargeable and are thus classified as secondary batteries as well. Fuel cells space to allow ionic conduction. Fig. 1 compares have attracted considerable attention as the battery potentials (i.e., energy densities) next-generation batteries. As the designs of fuel necessary for the generation of electricity. The cells differ completely from those of the batteries per-weight energy density of the NiMH battery is as discussed above, primary and secondary batteries high as 100 Wh/kg due to the fact that a metallic are not an appropriate categorization approach for material is used as the main power-generating fuel cells. Fuel cells are secondary batteries in a component. The per-weight energy density of the broad sense but, taking into consideration their lithium-ion battery shows the highest value, at 150 designs and applications, it can be said that fuel Wh/kg. As the energy density can be directly cells are an energy system. converted into energy efficiency, it can be said that a higher energy density will result in greater Energy Density of Lithium-Ion electromotive force, i.e., increased power. The current target energy densities of lithium-ion Among batteries for which there is increasing secondary batteries are 300 Wh/L (per-volume demand that they be made "lighter, thinner, and energy density) and 150 Wh/kg (per-weight energy smaller," the greatest demand is placed on density). Now, even inorganic and polymer batteries, lithium-ion batteries due to their excellent both of which have heretofore not been considered capabilities, particularly their high energy density. R&D items, in addition to new hybrid batteries, are Nickel metal hydride (NiMH) and lithium-ion under study using these figures as development batteries feature the highest performance among goals. Fig. 2 shows trends in the overall weights of batteries currently on the market. While the former portable electronic devices on a year-by-year basis. are popularly thought of as "clean" batteries, their It can be seen that the overall weights of portable shapes are limited and many difficult technologies electronic devices have remained at nearly the same are required to make them compact and lightweight level, despite the fact that their performance has in design. On the other hand, the latter utilizes ions improved steadily. It is estimated that lightweight to induce electrolytic reaction, making it is possible batteries, together with lightweight peripheral parts, to generate electricity as long as there is sufficient contribute to the constant device weights. Energy density per weight, Wh/kg Lithium-ion batteries generate the highest power.
Fig. 1 Comparison - Energy Densities of Secondary Batteries The mass of each portable electronic device remains nearly constant regardless of an increase in volume.
Mass reduction on the part-by-part basis Digital camera Notebook PC Cellular phone 100 300 500 1000 2000 3000 5000 The battery is the heaviest part of a portable electronic device.
Fig. 2 Volume vs. Weight - Portable Electronic Devices (Survey in FY2000) is neutral, each sealant strongly withstands electrolytic solution. Previously caulked sections Due to its unique structure, each lithium-ion and packing entrances, where sealing is required, battery consists of various materials. As lithium-ion are sealed with asphalt pitch or other materials. The batteries are being developed continuously, battery problem has been pointed out that since the asphalt manufacturers are setting the highest development contains chains composed of relatively low goals and working to develop extremely high power molecules, areas adjacent to or exposed to the and high efficiency batteries. The components of electrolytic solution suffer from decreased sealing lithium-ion battery have been briefly explained in performance. With the recent trend toward "lighter, previous sections; this section primarily discusses thinner, and smaller" and high power batteries, the future prospects for and Three Bond's battery manufacturers are forced to reduce the contributions to the development of lithium-ion sealing area. For this reason, they are making every effort to continue using the asphalt pitch by improving the battery design. Due to their excellent 4-1 Introduction of Lithium-Ion Battery sealing performance, TB1170B and TB1171 allow Sealants, ThreeBond 1170B and 1171 to seal batteries satisfactorily without changes to the ThreeBond (hereinafter referred to as "TB") structural design of a battery. In addition, we 1170B and 1171 are sealants developed for believe that higher sealing performance can reduce lithium-ion batteries (see Table 1). Their major the sealing area without reducing the battery component is olefin hydrocarbon. As the polymeric principal chain structure of this olefin hydrocarbon Table 1 Properties of Lithium-Ion Battery Sealants Appearance Colorless Viscosity, mPa•s 3TS-210-01 or -02 BL/BH rotational viscometer Specific gravity Specific-gravity cup method Nonvolatile content, % Weight-change ratio after heating at 160°C Fig. 3 compares TB1170B, TB1171, and asphalt pitch. This is the result of the unique molecular pitch with respect to their resistance against structure of TB1171 and TB1170B, i.e., their neutral electrolytic solution. General electrolytic solutions, chain structure and low permeability design, as dimethoxy ether (DME), propylene carbonate (PC), previously discussed. and ϒ-butyrolactone (ϒ-BL) were used in this test. Fig. 5 compares the thermal viscoelasticities of Our sealants are designed to offer a higher TB1171 and asphalt pitch. Many sealants now molecular weight and smaller amount of low feature solder reflow resistance in response to molecules compared to the asphalt pitch. As a result, market needs; therefore, we measured the storage our sealants have less component elution from high elastic modulus under heat as one of the features of polarity electrolytic solutions compared to pitches. these sealants. It was proven that when stress was This fact can be clearly seen in the test result shown gradually applied to the asphalt pitch at 260°C, its in Fig. 3. It has been proven that our sealants have storage elastic modulus dropped at low stress levels. higher electrolytic-solution resistance than asphalt On the other hand, the storage elastic modulus of pitch, and that components are not eluted into TB1171 did not fall at the test temperature. This test electrolytic solutions even under high temperature result shows that TB1171 is not destroyed by the stress accumulated in the battery (i.e., the pressure Fig. 4 shows a comparison of permeability tested increase due to the evaporation of electrolytic under various conditions. It is clear from this figure solution) even under high temperature conditions, that TB1171 has the lowest permeability among the and that the resin maintains its elasticity even after test materials, and that this characteristic is the stress increase. substantially improved compared to the asphalt Test method and conditions: Test method and conditions: Apply 0.1 g of each resin to a glass plate so that the coated area will be 15 mm In accordance with JIS K7129 "Test method for the across and 100 µm in thickness. Immerse the coated glass plate in the water-vapor transmission rate of plastic film and sheeting," specified electrolytic solution for 10 days at 60°C, and calculate the measure the permeability of resin 100 µm in thickness. weight-change ratio using the weights measured before and after the test. Weight-change ratio, % Fig. 3 Comparison of Three Bond Battery Sealants and Asphalt Pitch Fig. 4 Comparison of Sealants - Permeability Possibility of degradation Storage elastic modulus, Pa 1 Slide when shear stress applied Fig. 5 Comparison of Sealants - Thermal Elastic Modulus (Heating Temperature: 260°C; Frequency: 1 Hz) 4-2 Introduction of the Battery-Pack Sealant increase the weight of the battery, contrary to the current needs. Even if silicone resin is used, the Recently, many home electric appliances are structural design of the battery pack will be greatly being made smaller and lighter. As a result, batteries restricted and, for this reason, the material cannot are frequently used as the power source of these be used as a permanent measure. If the electrolytic devices, including a slew of lithium-ion secondary solution leaked inside the battery pack and the batteries, due to their large energy density. Despite sealant could not be dissolved into the electrolytic this trend, the leakage of electrolytic solution has solution or swelled, the solution would remain in been a serious problem, and the industry is making the battery pack, which would have negative every effort to develop technologies that will environmental effects. When a hard resin is used, it contribute to the secondary prevention of leakage. may come off from the battery during the drop test, Specifically, battery packs used in portable PCs are for example. If the resin comes off from the tab or being designed taking into consideration the other parts after curing, the electrolytic solution will possibility that surrounding electrodes, printed pass through the partition wall with the aid of circuits, and electronic parts will be damaged by the capillarity to corrode the electric circuit. electrolytic solution (or electrolyte) leaking from To solve this problem, Three Bond has developed battery packs. The most popular technique for a moisture-curing elastic sealant, TB1530D, which protecting printed boards and the like is to coat and is designed for use in battery packs. The major seal these electronic parts and battery packs with component of the resin used in TB1530D is a special polymer that contains a silyl group and Moisture-curing silicone resin is a conventional cures as a result of reaction with a small amount of material widely used as a coating sealant, but this moisture in the air. TB1530D offers excellent resin is dissolved into electrolytic solutions, losing adhesion and bonding capabilities for a wide variety the expected coating and sealing effect as a result. of materials, including metals, plastics, rubbers, and In addition, as a thin coat of the resin cannot inorganic materials, and features low viscosity. withstand electrolytic solutions, it is expected that it Therefore, this sealant is suitable for coating will be necessary to apply a thick coating of the applications. Table 2 lists the properties and resin. However, such a thick application will characteristics of TB1530D. Table 2 Properties and Characteristics of TB1530D Appearance 3TS-201-02 Viscosity (25°C) 3TS-210-02 BH, No.6, 20 rpm Specific gravity (25°C) 3TS-213-02 Dry-to-touch time Curing conditions: 25°C, 55 %RH, 7 days Hardness 3TS-215-01 Characteristics Peeling property Peeling shear adhesive strength As the cured TB1530D, unlike those of the coated on the electrodes to which the control circuit aforementioned TB1170B and TB1171, is swelled and battery units are connected, and on those by the electrolytic solution in a lithium-ion battery, portions from which it is most likely that the the electrolytic solution is gelled to lose fluidity, electrolytic solution will leak. If the electrolytic and consequently the electric circuit is protected solution leaks, the cured TB1530D will absorb the from contact with electrolytic solution. As solution to prevent flowing out. The cured TB1530D is also an elastic material, it will not be TB1530D swells with electrolytic solution, and, by separated from the battery parts even when the adhering the resin with the electrodes, protects battery pack is dropped onto a hard object. This electrolytic solution to penetrate into electric contributes to increasing product safety. circuits with capillarity. Fig. 7 shows an example of The leakage prevention system for lithium-ion batteries is illustrated in Fig. 6. TB1530D should be Lithium-ion battery unit Resin filler (TB1530D) Fig. 6 Lithium-Ion Battery Leakage Prevention System Fig. 7 Battery Pack (photograph provided by Sony Corporation) 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, and smaller" 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. Material Development Section Three Bond Co., Ltd. 1456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, JapanTel: 81-426-61-1333
International Journal of Food Microbiology 90 (2004) 1 – 8 Inhibition of pathogens on fresh produce by ultraviolet energy Brian R. Yaun*, Susan S. Sumner, Joseph D. Eifert, Joseph E. Marcy Department of Food Science and Technology, Virginia Tech., Blacksburg, VA 24061, USA Received 10 September 2002; received in revised form 20 February 2003; accepted 3 March 2003 Ultraviolet energy at a wavelength of 253.7 nm (UVC) was investigated for its bactericidal effects on the surface of Red