چكيده به لاتين
Lithium-ion batteries are one of the most important and popular batteries in the market, and due to their recharging capability, charging speed, high energy density, low self-discharge, light weight, and relatively long lifespan, Their popularity is increasing day by day. In this type of battery, the separator is usually a porous polymer membrane that is made in different ways and allows the ionic current to be established between the two electrodes (anode and cathode), while the physical contact between It prevents both. The commercial separators available in the market are mostly made of polyolefins (polypropylene and polyethylene), which are widely used due to their high mechanical strength and good chemical stability. But these types of separators have disadvantages such as low wettability compared to the liquid electrolyte in the battery and high dimensional shrinkage at high temperatures. These two features are very influential factors in battery performance. Therefore, by introducing non-polyolefinic polymer, we are trying to solve these two problems. In this project, according to the phase separation method with antisolvent induction in order to make the separator, we first examined four different antisolvents and selected one of them as the suitable option, and started making composite separators containing silica nanoparticles. By making several samples (both the change in the mass percentage of polyvinyl alcohol and the change in the mass percentage of silica nanoparticles), the influence of silica nanoparticles on the resulting separators was investigated. According to the electron microscope images as well as the calculation of the average diameter of the holes, the presence and increase in the mass percentage of silica nanoparticles caused the average diameter of the holes to decrease and the porosity of the resulting separators to decrease. This amount of reduction in the diameter of holes, porosity and electrolyte absorption is still within the standard range of those parameters. Therefore, in the presence of silica nanoparticles, by observing the decrease in the diameter of the holes (reducing the possibility of internal short circuit in the battery), increasing the percentage of remaining electrolyte, improving wettability and, as a result, improving the ionic conductivity (charge and discharge curves of the battery resulting from this separator) composite) these separators can be used more.
It was also observed that all the manufactured samples have higher ionic conductivity and conductivity than the commercial separator, and some composite samples showed a higher electrolyte retention percentage than the commercial separator.
Key words: lithium-ion battery, composite separator based on polyvinyl alcohol, phase transfer method with antisolvent induction, silica nanoparticles
