Safety of Rechargeable Lithium Metal Cells

We have developed a prototype AA-size cell which consists of an amorphous (a-) 

V2O5-P2O5 (95 5, molar ratio) cathode and a lithium anode (Li/a-V2O5 cell) [1]. In this section, we describe safety test results for AA Li/a- V2O5 cells. The AA cell we fabricated has a pressure vent, a Polyswitch (PS, Raychem Co., thermal and current fuse) and is composed of a spirally wound cathode sheet, a metallic Li-based anode sheet and a polyethylene (PE) separator [87]. 

The basic considerations regarding the cell safety and the test results are described briefly below. 

Idota et al. have demonstrated [85] that amorphous material based on tin oxide has capacities of 800 mAh g l and 3200 mAh cm 3, which are respectively two and four times higher than those of carbon. An 18 650-size cell with an LiCo02 cathode has a capacity of 1850 mAh, which is higher than the value of 1350 mAh for the commercial cells. 

Sigaia et al. [86] also examined LiA.MV04 (M = Zn, Co, Ni, Cd) as anode materials. The best compounds (M = Zn, Ni) deliver capacities of about 700 mAh g 1 after 200 cycles. The search for new anode compounds will prove to be a fruitful area in the future. 

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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. 

Sony dubbed the new cell, lithium-ion, as only lithium-ions and not lithium metal are involved in the electrode reactions. The lithiated carbon had a voltage of about 0.05 V vs. lithium metal and avoided the safety issues of mossy and dendritic lithium metal deposits. The lithium-ion rechargeable battery system has replaced the heavier, bulkier, Ni-Cd and Ni-MH cells in most applications,... 

Fig. 2. Configuration for spirally wound rechargeable lithium cell. A, Cap B, cathode tab C, insulating disk (2) D, mandrel E, can F, ball G, safety vent H, glass-to-metal seal (with center pin) I, anode tab J, cathode K, separator L, anode. Courtesy of Moli Energy Ltd.

Lithium Metal. The search for high-energy-density batteries has inevitably led to the use of lithium, as the electrochemical characteristics of this metal are unique. A number of batteries, both primary and rechargeable, using a lithium anode in conjunction with intercalation cathodes, were developed which had attractive energy densities, excellent storage characteristics, and, for rechargeable cells, a reasonable cycle life. Commercial success has eluded all but the primary batteries due to persistent safety problems. 

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