Overcharge, safety test

In the overcharge tests we carried out, there was no fire or explosion. The cell impedance increased suddenly in every test. This was due to the oxidation of the electrolyte with a low charging current, or to the separator melting with a high charging current. In practical applications, an electronic device should be used to provide overcharge protection and ensure complete safety. 

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. 

Standardization of tests is crucial to comparing safety and abuse response of batteries. For example, changes as simple as the magnitude of the current can affect the outcome of overcharge tests [17]. There are a number of standardized test procedures that evaluate the safety and abuse tolerance of cells and batteries. The test procedures are adapted to the intended applications. 

The safety of the ZEBRA battery has been proven extensively by abuse testing overheating, overcharging, short-circuiting of battery terminals and of cell groups, crash tests on the battery itself by dropping it at 50 km h 1 onto a pole or spike, and crash tests of cars with built-in ZEBRA batteries at 50 kmh-1 [10]. The results of abuse testing prove the ZEBRA battery to be a safe battery system. 

Zebra batteries have been subjected to a series of tests to demonstrate their ruggedness and safety. These include overcharge, short circuit, overheating and vibration and shock. Drop testing to simulate the effect of a... 

Safety has been the subject of study at Harwell and no incidents were observed when the cells were (i) overcharged and overdischarged (C/10, C and 10 C rates) (ii) short-circuited (iii) forced to discharge (iv) heated above 400°C, and (v) cut open. It must, however, be recognized that the evaluation was run on test cells and thus that the safety characteristics of large units may be still a matter to be ascertained. 

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... 

Abuse tests could include overcharge, overdischarge, short circuit, crush and high temperature tests to check cell safety. 

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. 

Due to their reactivity with electrolyte solutions, especially in the charged state, the most useful thermal behavior testing (e.g., DSC) of the candidate cathode materials occurs in the presence of electrolyte. Below, the results of a comprehensive study done by MacNeil et al. [9] have been used in preparation of graphs shown in Figs. 5.4, 5.5, 5.6, and 5.7, with several cathode/electrolyte system behavior trends identified and discussed common cathode name abbreviations used in the discussion are listed in Table 5.1. Similar studies are commonly done by the lithium-ion battery manufacturers on various cathode and/or electrolyte materials candidates and are usually treated as a basic introduction to the ARC testing and other safety-related experiments on larger cells (overcharge, nail penetration tests, etc.). 

An attractive feature of C/LiMn204 polymer Li-ion cells is their ability to sustain abuse. Safety and abuse tests passed by C/LiMn204 polymer Li-ion cells are listed in Table 35.25. In addition, C/LiMn204 polymer Li-ion cells can sustain nail penetration in the fully charged state or the overcharged state without explosion or Are. 

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