External short safety test

We experienced no safety problems during the external short tests because of the Polyswitch inside the cell. We confirmed that even if the Polyswitch fails to operate, the short-circuit current stops flowing before thermal runaway occurs because the micropores are closed by the polyethylene separator, which melts at 125 °C ("separator shutdown"). 

Safety tests at the battery level should, as a minimum, include overcharge, overdischarge and external short tests. It has been well established through years of testing at NASA-JSC that cell-level controls do not translate into battery-level controls. Controls, especially those internal to the cells, have shown to not protect or themselves be the cause for hazardous events due to their limitations (previously discussed in Section 3). Safety tests should also be carried out in the relevant environment. NASA-JSC test programs have indicated that safety tests under ambient pressure conditions display results contrary to that in a vacuum environment [22]. A cell or battery s safety tolerance up to the settings of the safety controls shall be verified by test. 

Underwriters Laboratories (UL) requires that consumer batteries pass a number of safety tests [3]. UL requires that a battery withstand a short circuit without fire or explosion. A positive temperature coefficient (PTC) device [4] is used for external short-circuit protection. The resistance of a PTC placed in series with the cell increases by orders of magnitude at high currents and resulting high temperatures. However, in the case of an internal short, e.g., if the positive tab comes lose and contacts the interior of the negative metal can, the separator could act as a fuse. That is, the impedance of the separator increases by two to three orders of magnitude due to an increase in cell temperature. 

Battery safety is so important for mobile and vehicle apphcations. Especially for vehicles, on the road, accident likely becomes heavy, and the crash accident should not bring more danger by release of the energy stored in the cells. And various tests are usually conducted. In ZEBRA battery case, test results were reported. Crash of an operative battery against a pole with 50 km/h, overcharge test, overdischarge test, short circuit test, vibration test, external fire test, and submersion of the battery in water have been specified and performed [6]. The ZEBRA battery did pass all these tests owing to its four-barrier safety concept [7, 8] chemical aspects, cell case, thermal structure, and battery controller. 

Nociception pain perception can be measured in rodents by a variety of procedures whereby aversive stimulation is applied externally either by heat or electrical stimulation to the tail or paws (tail flick, hot plate, plantar test) or internally by injection into the peritoneum of chemicals (acetic acid, phenylbenzoquinone). Inflammation pain can also be induced by injecting chemicals (carrageenan, formalin) into the paws. More complex approaches induce neuropathic pain by surgical lesions, usually to the sciatic or spinal nerve. For safety pharmacology purposes, usually only the simpler procedures are used. For example, with the hot plate test [18] the animal is placed onto a heated metal plate (54°C) within a vertical cylinder, and the latency to licking its front paws is measured over a short period. 

There is therefore a need to use plastics parts with a higher level of fire safety meeting the requirements of UL94 Vertical tests so as to ensure adequate consumer protection. External fire sources, inadequate design, manufacturing faults or defects due to simple wear and tear, plus consumer misuse may lead to flashover and fully developed fires in a very short time if housings and backplates are not flame retarded to meet the vertical test criteria. 

Underwriters Laboratories (UL) requires that consumer batteries pass a number of safety tests (UL 1642 [119] and UL-2054 [120]). There are similar recommendations from UN for transport of dangerous goods, [121] the International Electrotechnical Commission (lEC), and the Japan Battery Association [122]. An abnormal increase in ceU temperature can occur from internal heating caused by either electrical abuse - overcharge or short circuit - or mechanical abuse - nail penetration or crush. Higher ceU temperature could also be a result of external... 

The fact that cells involved in field-failures generally have passed all standardized safety tests is the first clue that these incidents should be given special craisider-ation. Internal shorts — not external abuses — cause field-failures far more frequently than is generally appreciated. Such shorts are a major focus of this chapter. 

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