The solubility and ultra solubility of borax decahydrate both in pure and impure solutions have been determined in the temperature range from (0 to 30) °C by means of the conventional polythermal method using the laser technique. The metastable zone width and the apparent nucleation order of borax were calculated. The effects and the action mechanism of KCl on metastable zone property of borax were studied. It was found that the presence of KCl made an increase in the solubility and a decrease in the metastable zones of borax. However, the trends in the changes of metastable zone width at low impurity concentrations were different from high concentrations because of the adsorption equilibria on the crystals.

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In this paper, the overcharge tests of 25 Ah LiFePO 4 /graphite batteries are conducted in an open environment and the overcharge-to-thermal-runaway characteristics are studied. The effects of current rates (C-rates: 2C, 1C, 0.5C, and 0.3C) and states of health (SOHs: 100%, 80%, 70%, and 60%) on thermal runaway features are discussed in detail. The overcharge process can be summarized into five stages based on the experimental phenomena (C-rate ≥ 1 and SOH ≥ 80%): expansion, fast venting after safety valve rupture, slow venting, intense jet smoke, and explosion, while the battery cannot explode at lower Crates and SOHs. The maximum pressure increases with the increase in C-rate or SOH. There are five obvious inflection points in the voltage curve during overcharge process. The V 1 (point B) of aged battery, corresponding to lithium plating on the anode, changes little with C-rates. It is slightly lower than that of the new battery. A sharp drop in voltage (point E) is probably due to the internal short circuit (ISC), caused by the local melting and rupture of the separator. It takes more than 2 minutes from the moment of ISC to thermal runaway regardless of the SOH, indicating that there are a few minutes to take safety measures if the voltage is an indication parameter. The onset temperature of thermal runaway decreases first and then increases as the SOH decreases from 100% to 60% during 1C constant overcharge tests. These results can provide guidance for the thermal management of the whole battery life cycle and the reuse of retired batteries. K E Y W O R D Sageing, lithium-ion battery safety, overcharge, SOH, thermal runaway

The conventional heating materials of thermal battery have the disadvantages of low combustion rate and less heat release, so it is necessary to develop new heating materials. Al/Ni Reactive Multilayer Foils (RMFs) is an ideal heat source due to its high heat release, fast burning speed and no gas generated during combustion. Al/Ni RMFs were prepared by magnetron sputtering, and the heat transfer process of thermal battery using Al/Ni RMFs as heating material was simulated by the COMSOL MULTIPHYSICS simulation. The Al/Ni RMFs combustion reaction mechanism with different Al/Ni ratios was proposed according to DSC and XRD results. The effects of Al/Ni atomic ratio of RMFs on the melting time of electrolyte were investigated, and the temperature distribution during the activation was obtained, indicating the rapid activation process of the thermal battery.