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Cause analysis of lithium ion battery explosion

Jan 04, 2019   Pageview:658

Firstly, lithium ion battery features

Lithium is the most active metal with minimum diameter on the chemical periodic table. It has small volume and high capacity density, so it is very popular for consumers and engineers. However, too lively chemical properties will bring a high risk. If lithium metal is exposed to the air, it can produce intense oxidation reaction with oxygen and lead to explosion. In order to improve its safety and voltage, the scientists invented the graphite and cobalt acid lithium materials to store lithium atoms. The molecular structures of these materials form the nanometer grade tiny storage grids, and they can be used to store lithium atoms. As a result, even the battery shell bursts and oxygen get into the battery, but the oxygen molecule is too large to get into these small stores. The lithium atoms will not react with the oxygen so that it won't lead to explosion.

The principle of lithium ion batteries, make people for its high capacity density at the same time, also achieve the goal of security. Lithium ion batteries, the anode of lithium atom lose electrons, oxidation for lithium ion. Lithium ions via the electrolyte to the anode get into the cathode storage, and access to an electron, reduction of lithium atom. Discharge, the whole program upside down. In order to prevent negative direct touch and short circuit, the batteries are inside the battery will be combined with a diaphragm paper have many pores, to prevent short circuit. Good diaphragm paper can also be at high temperature, the battery automatically closed pores, let lithium-ion impenetrable, from waste fighting skill, prevent danger happening.

Protection measures: The lithium battery after batteries into the voltage higher than 4.2 V, will start to produce side effects. Of charging the higher the pressure, the higher the risk also follow. Lithium batteries voltage higher than 4.2 V, the anode materials within less than half the number of lithium atoms left, store usually break down at this time, let the battery capacity to produce permanent decline. If continue to charge, due to the storage of the cathode has been full of lithium atoms, subsequent anode materials of lithium metal accumulation in the surface. These lithium atoms from lithium ion to the cathode surface to grow in the direction of the dendritic crystal. The lithium metal crystal through the diaphragm paper makes is negative short circuit. Sometimes in short circuit batteries before the first explosion, this is because in the process of overcharge, electrolyte materials can produce gas cracking, such as making the battery shell or blow up pressure valve is broken, and let oxygen in and accumulation in the lithium atoms on the surface of the cathode reaction, then exploded. Therefore, lithium batteries, be sure to set the upper limit of voltage, can simultaneously to the battery life, capacity, and security. The ideal maximum charging voltage of 4.2 V. lithium batteries discharge voltage will be lower limit. The batteries voltage below 2.4 V, part of the material will begin to be destroyed. And because the battery self-discharge, put the more the longer the voltage is low, therefore, discharge when had better not to 2.4 V. Lithium battery discharge from 3.0 V to 2.4 V during this period, the release of energy accounted for only about 3% of the battery capacity. Therefore, is an ideal discharge cut-off voltage of 3.0 V. Charge and discharge, in addition to the limit of voltage and current limits can also be necessary. When the current is too large, lithium ions to enter the store, would gather in the material surface. After these lithium ion for electronic, can produce lithium atoms in the material surface crystallization, this has to do with the overcharge, will cause the risk. One thousand battery shells are broken, and would explode. Therefore, the protection of lithium ion batteries, to include at least: charging voltage upper limit, lower limit discharge voltage, and current limit. general lithium battery pack Inside, in addition to the lithium battery core, there will be a piece of protection board, the protection board is mainly to provide all three. Protection board, however, these three protections are obviously not enough, lithium battery explosion or disengaged from around the world.

To ensure the safety of the battery system, the battery must be the cause of the explosion, a more careful analysis.

Second, the battery explosion reasons:

1, internal polarization is larger;

2, water absorption, react with the electrolyte gas drum;

3, electrolyte itself, the quality of the performance issues;

4, when liquid injection liquid quantity cannot meet the technical requirements;

5, preparation process of laser welding sealing performance is poor, leak. Measuring air leak test;

6, dust, dust sheet first can cause micro short circuit, for reasons unknown;

7, is a process from the cathode scope thick, hard into the shell;

8, filler sealing problem, steel ball seal performance is bad to cause gas drum;

9, the incoming exist shell wall thick, shell thickness deformation effect;

Three, explosion type analysis

Battery core explosion type can be summarized as external short circuit, internal short circuit and overcharge 3 kinds.

The external refers to the batteries of the external, contains a battery pack and poor internal insulation design caused by short circuit. When external short-circuited batteries, electronic components and failed to cut off the circuit, batteries inside will produce heat, caused part of the electrolyte vaporization, the battery shell support. When high battery internal temperature to 135 degrees Celsius, good quality paper, diaphragm will close pores, electrochemical reaction termination or near end, current, temperature is falling slowly, then avoid the explosion occurred. But the pores close rate is poor, or pores do not close the diaphragm paper, can let the battery temperature continues to rise, more electrolyte vaporization, finally the battery shell burst, and even to increase the battery temperature to make the material combustion and explosion.

Internal short circuit is mainly because of the copper foil and aluminum foil burr in the diaphragm, or lithium atoms of dendritic crystal worn out by the diaphragm. These tiny acicular metals can cause micro short circuit. Because, the needle is very fine and have certain resistance, therefore, current will not very big. Copper foil burr is caused in the production process. The observable phenomena is battery leakage quickly, most can be screening out batteries factory or assembly plant. And, due to the burr tiny, sometimes burn out, and make the battery back to normal again. Therefore, due to the burr micro short-circuit explosion probability is not high. Such, can from the batteries inside the factory are very shortly after charging, voltage on the low side of bad battery, but rarely bombings, supported by statistically. Therefore, internal short circuit caused by the explosion, mostly because the overcharge. Because, after filling is everywhere on the pole piece needle lithium metal crystallization, Pierce point is everywhere, everywhere, in the event of a micro short circuit. As a result, the battery temperature rise gradually, and finally high-temperature electrolyte gas. This kind of situation, whether high temperature materials burning explosion, or the shell was broken, the air inside with lithium oxide, are explosive.

However, explosion caused by internal short circuit for overcharge, does not necessarily occur during charging. Maybe when the battery temperature is not so high to make gas combustion, and material is not enough to break the battery case, consumers will stop charging and go out with mobile phones. At this time, the heat produced in the micro short circuit increases the battery temperature slowly. After a period of time, the explosion happens. Consumer common description is that they pick up the phone, and find that mobile phone is very hot. It explodes after they throw away the phone. We can make an explosion-proof solution focused on preventing the overcharge, external short circuit, prevent, and security improvement. Preventing the overcharge and external short circuit belong to electronic protection, which are related to battery system design and the battery pack assembly. The key point to improve battery security are chemical and mechanical protection, which have great relationship with core battery factory.

The page contains the contents of the machine translation.

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