Technical point of view: Samsung Note7 battery explosion reasons

　　The recent explosion of Samsung Note7 once again brought the "life safety of using mobile phones" back to the public's view. Although there are mobile phone explosions on average every year, such high-density explosions of Samsung Note7 are unprecedented in history, and I believe there will be no future. At the same time, this incident also brought the safety of lithium batteries to a boiling point by the way. I cannot help but ask whether the current smart phones are really going to be portable bombs?

　　The recent explosion of Samsung Note7 once again brought the "life safety of using mobile phones" back to the public's view. Although there are mobile phone explosions on average every year, such high-density explosions of Samsung Note7 are unprecedented in history, and I believe there will be no future. At the same time, this incident also brought the safety of lithium batteries to a boiling point by the way. I cannot help but ask whether the current smart phones are really going to be portable bombs?　　 Let’s take a look at the working principle of lithium batteries: 　　 How much do you know about mobile phone batteries? When charging, under the influence of an external electric field, the lithium element in the positive electrode material LiCoO2 molecules separates and becomes positively charged lithium ions (Li+). The carbon atoms undergo a chemical reaction to form LiC6, so the lithium ions that escape from the positive electrode are "stably" embedded in the graphite layered structure of the negative electrode. The more lithium ions run out of the positive electrode and transferred to the negative electrode, the more energy the battery can store.　　When discharging, the opposite is true. The internal electric field turns, and lithium ions (Li+) separate from the negative electrode, follow the direction of the electric field, and run back to the positive electrode, turning into lithium cobalt oxide molecules (LiCoO2) again. The more lithium ions run out of the negative electrode and transferred to the positive electrode, the more energy the battery can release. During each charge and discharge cycle, lithium ion (Li+) acts as a carrier for electric energy, moving back and forth from the positive electrode → the negative electrode → the positive electrode, and chemically reacts with the positive and negative materials to convert chemical energy and electrical energy. The transfer of charge is realized, which is the basic principle of the "lithium-ion battery". Since electrolytes, isolation membranes, etc. are all electronic insulators, there are no electrons moving back and forth between the positive and negative electrodes during this cycle. They only participate in the chemical reaction of the electrode.　　 After understanding the basic working principle of lithium batteries, we are going back to see why the Samsung Note7 battery exploded this time.　　 How much do you know about cell phone batteries?　　 After the explosion of Samsung Note7, an authoritative expert (Chen Liwei) analyzed the explosive battery and said that the battery explosion was not accidental, but inevitable, but Samsung Note7 sounded the alarm in advance. He also pointed out that under the dual effect of the current design of smart phones with ultra-thin bodies as the mainstream design and the dual effect of smart phone battery life becoming the biggest constraint, most manufacturers will violently increase battery life and force the battery to increase while the battery volume remains unchanged. The volumetric energy density, which leads to the result that has to use a thinner diaphragm material.　　 For the same battery, if the separator becomes thinner and the volume of this part is reduced, a little more positive and negative materials can be installed, which can increase the energy density of the battery and the battery life of the mobile phone. However, the thinner the diaphragm, the stricter the process requirements. A slight quality defect or battery process error may cause the diaphragm defect, which in turn leads to the short circuit of the battery.　　 How much do you know about cell phone batteries?　　At the same time, experts also said that mobile phone manufacturers are very concerned about the volumetric energy density of batteries. "Almost all manufacturers are pursuing to pack more electric energy into a limited volume to extend battery life." 　　 However, there is a consensus in the industry that the improvement of battery energy density requires a long-term process. Experts explain: "The development laws of the energy storage industry and the electronics industry are very different: the latter is the well-known Moore's Law, the number of transistors that can be accommodated in an integrated circuit chip increases exponentially, doubling about every 18 months; and The improvement process of battery performance is stepped. Based on the existing battery materials, it is quite good that the energy density can increase by 2%-3% per year.” Therefore, the improvement of the performance of electronic products and the increase of the energy density of the battery are quite good. There is a scissors gap, and it keeps expanding over time.　　Experts frankly said 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 and "slim down" the battery. However, it is difficult to have both "slimming" and "safety" in mobile phone lithium batteries.　　 So the question is, what the hell is the density of the lithium battery mentioned above? How big is the impact on the battery industry?　　 How much do you know about cell phone batteries?　　Battery density is actually the electric energy released by the average unit volume or mass of the battery. Battery energy density=battery capacity×discharge platform/battery thickness/battery width/battery length.　　 It can be said that energy density is the biggest bottleneck restricting the development of current lithium-ion batteries. Whether it is a mobile phone or an electric car, people expect the energy density of the battery to reach a whole new order of magnitude, so that the battery life or range of the product will no longer be the main factor that troubles the product.　　 In response to the current situation where energy density has become a bottleneck, countries around the world have formulated relevant battery industry policy goals, hoping to lead the battery industry to achieve significant breakthroughs in energy density. The 2020 goals set by governments or industry organizations in China, the United States, Japan and other countries basically point to a value of 300Wh/kg, which is equivalent to an increase of nearly double the current basis. The long-term goal in 2030 is to reach 500Wh/kg or even 700Wh/kg. The battery industry must have a major breakthrough in the chemical system to achieve this goal.