Why does Samsung mobile phone battery explode

　　 Last week, the General Administration of Quality Supervision, Inspection and Quarantine issued a notice stating that Samsung recalled some Galaxy Note7. It is reported that the phone batteries within the scope of this recall have a partial thinning of the anode and cathode separators, and the insulation tape does not completely cover the electrode plate coating, a short circuit occurs, resulting in abnormal heating of the battery, and burning may occur in extreme cases ,There are security risks.

　　Why does the battery separator become thinner, and what safety hazards will the thinning cause?

The following is a scientific interpretation by researcher Chen Liwei from the Suzhou Institute of Nanotechnology and Nano-Bionics, Chinese Academy of Sciences.

　　 Why does the battery diaphragm become thinner and burn?

　　Chen Liwei introduced that the lithium-ion battery used in mobile phone batteries realizes the charging and discharging function of the battery through the movement of lithium ions back and forth between the positive electrode and the negative electrode. When charging, the current of the charger drives out the lithium ions in the positive electrode. These lithium ions 'swim' into the negative electrode through the electrolyte between the positive electrode and the negative electrode; and when discharging, these lithium ions pass through the electrolysis from the negative electrode. The liquid 'swims' back into the positive electrode, providing electricity for the mobile phone to work. In this process, the positive electrode and the negative electrode must not be in direct contact, otherwise a short circuit will occur, causing abnormal heating of the battery, or even fire and explosion.

　　How to ensure that the positive and negative electrodes inside the battery are not in contact with each other and there is sufficient electrolyte between them for the lithium ions to 'swim' back and forth? This is achieved through a key material in lithium-ion batteries-diaphragm.

　　 So, is the thinning of the diaphragm a production design error or is it another hidden story?

　　Chen Liwei speculates that this may be because mobile phone manufacturers have adopted thinner diaphragm materials in order to increase the volumetric energy density of batteries and extend the battery life of mobile phones. However, due to the lack of strict quality control of the diaphragm materials or Process defects caused partial thinning of the separator, which could not effectively isolate the positive electrode and the negative electrode, thus causing safety problems for the battery.

　　Chen Liwei said that mobile phone manufacturers are very concerned about the volumetric energy density of batteries. 'Almost all manufacturers are pursuing to pack more electrical energy into a limited volume to extend battery life.'

　　 However, the industry consensus, the improvement of battery energy density requires a long-term process. Chen Liwei explained to reporters: 'The development rules of the energy storage industry and the electronics industry are very different: the latter is the well-known Moore's Law, and the number of transistors that can be accommodated in an integrated circuit chip increases exponentially, about every 18 months. The improvement process of battery performance is stepped. On the basis of existing battery materials, it is quite good that the energy density can increase by 2%-3% per year.” Therefore, the performance improvement of electronic products and battery energy There is a scissors difference between the density increase, and it keeps expanding over time.

　　 Chen Liwei said frankly that the energy density of mobile phone batteries is approaching the 'limit'. In order to provide more energy in a smaller volume, manufacturers can only find ways to squeeze the space occupied by auxiliary materials. , 'Slim down' the battery.

　　 However, it is difficult to have both 'slimming' and 'safety' in mobile phone lithium batteries.

　　' For the same battery, if the separator becomes thinner, reducing the volume of this part, you can install a little more positive and negative materials, which can improve the battery energy density and the battery life of the mobile phone. However, the more The thinner diaphragm has stricter requirements on the process, and a slight quality defect or battery process error may cause diaphragm defects, which may lead to short circuits of the battery.' Chen Liwei expressed the risk.