Rechargeable safety

Sulphur annulus thickness this is determined by the energy/ power output required, the desired cell resistance and the time available for recharge. Safety considerations are also important. 

Coin and Button Cell Commercial Systems. Initial commercialization of rechargeable lithium technology has been through the introduction of coin or button cells. The eadiest of these systems was the Li—C system commercialized by Matsushita Electric Industries (MEI) in 1985 (26,27). The negative electrode consists of a lithium alloy and the positive electrode consists of activated carbon [7440-44-0J, carbon black, and binder. The discharge curve is not flat, but rather slopes from about 3 V to 1.5 V in a manner similar to a capacitor. Use of lithium alloy circumvents problems with cycle life, dendrite formation, and safety. However, the system suffers from generally low energy density. 

Fig. 2. Configuration for spirally wound rechargeable lithium ceU. A, Cap B, cathode tab C, insulating disk (2) D, mandrel E, can F, bak G, safety vent ...

Efforts to commercialize larger versions of rechargeable lithium cells have been fmstrated by concerns over product safety. MoH Energy Ltd. briefly introduced "AA" Li—M0S2 cells for OEM use in laptop computers and cellular phones. However, safety issues resulted in a product recall and a halt to commercialization of this product. 

The lithium-ion-polymer battery, which uses a cathode that contains lithium instead of cobalt, is likely to eventually replace lithium-ion. Lithium-ion-polymer batteries boast a longer life expectancy (over 500 charge-and-discharge cycles as opposed to around 400), much more versatility (they are flat and flexible and can be cut to fit almost any shape), and better safety (far less likely to vent flames while recharging). 

Secondary lithium-metal batteries which have a lithium-metal anode are attractive because their energy density is theoretically higher than that of lithium-ion batteries. Lithium-molybdenum disulfide batteries were the world s first secondary cylindrical lithium—metal batteries. However, the batteries were recalled in 1989 because of an overheating defect. Lithium-manganese dioxide batteries are the only secondary cylindrical lithium—metal batteries which are manufactured at present. Lithium-vanadium oxide batteries are being researched and developed. Furthermore, electrolytes, electrolyte additives and lithium surface treatments are being studied to improve safety and recharge-ability. 

Many studies have been undertaken with a view to improving lithium anode performance to obtain a practical cell. This section will describe recent progress in the study of lithium-metal anodes and the cells. Sections 3.2 to 3.7 describe studies on the surface of uncycled lithium and of lithium coupled with electrolytes, methods for measuring the cycling efficiency of lithium, the morphology of deposited lithium, the mechanism of lithium deposition and dissolution, the amount of dead lithium, the improvement of cycling efficiency, and alternatives to the lithium-metal anode. Section 3.8 describes the safety of rechargeable lithium-metal cells. 

The basic problem in regard to the safety of rechargeable metal cells is how to manage the heat generated in a cell when it is abused. The temperature of a cell is determined by the balance between the amount of heat generated in the cell and the heat dissipated outside the cell. Heat is generated in a cell by thermal decomposition and /or the reaction of materials in the cell, as listed below ... 

It is worthwhile attempting to develop a rechargeable lithium metal anode. This anode should have a high lithium cycling efficiency and be very safe. These properties can be realized by reducing the dead lithium. Practical levels of lithium cycling efficiency and safety could be achieved... 

Electrical failures are by far the most common. The most important safety measure is the installation of emergency lights, w hich will go on as soon as the power fails. Their batteries will automatically be recharged after the pow er comes back. They should be installed even in laboratories where w ork is normally performed only during the day. Such units are fairly expensive, but smaller ones made for home use are now available in hard-W are stores. A check should be made with local authorities as to whether these are permissible for industrial use. 

Sony s Introduction of the rechargeable lithium-ion battery in the early 1990s precipitated a need for new separators that provided not only good mechanical and electrical properties but also added safety through a thermal shutdown mechanism. Although a variety of separators (e.g., cellulose, nonwoven fabric, etc.) have been used in different type of batteries, various studies on separators for lithium-ion batteries have been pursued in past few years as separators for lithium-ion batteries require different characteristics than separators used in conventional batteries. 

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