Investigation of the Effects of Physical Changes on Li-ion Battery

With the advances in battery technologies, the li-ion battery’s amount of energy storage per unit volume and weight increases and significant improvements occur in their control systems. Besides, the usage rate of li-ion batteries increases due to the decrease in prices of li-ion batteries in many areas from electric vehicles to user electronics. However, for high-performance use of these batteries, continuous monitor and control of their states of health and charge are needed. This control is commonly performed by using the voltage, current and temperature of the cells. In contrast, swelling and physical deformations of the cells should be used as function inputs in the monitoring of the state of safety condition. Especially for devices such as mobile phones and portable computers which directly touch to person, causes serious safety problems. In addition, the user's various usage habits which are using different battery chargers, fast charging and using in the charging process, lead to safety problems. In addition, in the electric vehicles, the series/parallel packaged cells swell and thus increase the pressure on the neighboring cells. In this study, a system with a high precision strain gauge, temperature sensor and Z-Wave communication module has been designed to observe the effects of strain changes and to investigate their effects. Aging tests have been performed on one single battery used in the market and a 4.58 mm swelling has been achieved. The behavior of the new battery and aged battery which has physical deformation is applied to the same charge/discharge cycles and the effects of the swelling are presented. Measurements of temperature, swelling amount, open circuit voltage and charge/discharge time of the amount of change are stated in detail. It has been shown that dangers occur for the user due to the high temperatures on the surface caused by the amount of swelling of the battery exposed to swelling during charge and discharge. This situation reveals the necessity of continuous monitoring of the swelling as a safety factor in mobile phones and portable computers