Why do batteries bulge and explode?

The analysis reasons of battery bulge and explosion:

A,Lithium ion batteries features

Lithium is a chemical on the periodic table minimum diameter is also the most active metal.Small volume so high capacity density, popular with consumers and engineers.However, chemical properties too lively, bring a high risk.Lithium metal is exposed to air, can produce intense oxidation reaction with oxygen and explosion.In order to improve safety and voltage, the scientists invented the graphite and cobalt acid lithium materials such as to store lithium atoms.The molecular structure of these materials to form the nanometer grade tiny storage grid, can be used to store lithium atoms.In this way, even if the battery shell is broken, and oxygen to, also because of too much oxygen, into these small store, making lithium atoms will not avoid contact with the oxygen blast.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, 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 batteryCore overcharge voltage higher than 4.After 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.After 2 v, the anode material in 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 most ideal charging voltage upper limit of 4.2 v.

Lithium batteries discharge voltage will be lower limit.When the batteries voltage is less than 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 in 2.4 v.Lithium batteries from 3.Discharge to 2 0 v.4 v during this period, the release of energy accounted for only about 3% of the battery capacity.Therefore, 3.0 v is as an ideal discharge voltage.

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 shell is 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 protection is 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 bigger!

2: a piece of absorbent, react with the electrolyte gas drum.

3: the electrolyte itself, the quality of the performance problems.

4: when liquid injection fluid quantity can not meet the technical requirements.

5: pack preparation process of laser welding welding sealing performance is poor, leak and air leak test.

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

7: is a process from the cathode partial thickness range, into the shell.

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

9: shell material exists partial shell wall thickness, thickness of shell deformation effects.

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 metal, can cause micro short circuit.Because, the needle is very fine 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, 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.

But charge cause internal short circuit caused by the explosion, does not necessarily occur in charge at the time.Possible battery temperature is not high to make a gas combustion, material is not enough to be broken when the battery case, consumers will stop charging, with mobile phones to go out.At this time many of the heat produced in the micro short circuit, the battery temperature increase slowly, after a period of time, the explosion occurred.Consumer common description is pick up the phone, it found that mobile phone is very hot, throw away after the explosion.

We will see how all of the type of explosive, explosion-proof focused on preventing the overcharge, external short circuit, prevent, and to promote cell security three aspects.Preventing the overcharge and external short circuit belongs to the electronic protection, and battery system design and the battery pack is equipped with larger relationship.Batteries security key for chemical and mechanical protection of ascension, and core battery factory has great relationship.

Four, the design specification

Because there are hundreds of millions of global mobile phone, only to achieve safety, security protection failure rate must be less than one over one hundred million.Because of circuit board fault rate is generally much higher than one over one hundred million.Therefore, battery system design, must have at least two security defense.Common mistake is designed with the charger (adaptor) directly to the battery.This will be overcharge protection role, completely to the battery protection board.Although the protective plate failure rate is not high, but, even if the failure rate is low to one over one million, everyday probability on a global or explosion.

Battery systems, such as to over charge and discharge, over current are providing security for two respectively, each protection failure if it is one over ten thousand, two protection failure rate can be dropped to one over one hundred million.Common battery charging system block diagram is as follows, including the charger and battery pack.The charger and adapter (Adaptor) and charge control two parts.Adapter will alternating current into direct current, charging controller limit maximum current and high voltage direct current (dc).The battery pack consists of two parts, and battery protection board core and a PTC to limit maximum current.

Text box: adapter ac variable dc text box: charging controller current limiting pressure limiting text box: charger text box: protective plate overcharge, pass flow such as protective text box: battery text box: current limiting text box: battery core with mobile phone battery system as an example, the overcharge protection system using the charger output voltage is set in 4.Around 2 v, to achieve the first layer of protection, so that even in the battery protection board failure, the battery will not be overcharge and dangerous.Second protection is to protect the overcharge protection function on the plate, generally set to 4.3 v.In this way, the protection plate usually don't have to be responsible to cut off the charging current, only when the charger, the abnormal high voltage only need action.Overcurrent protection is the protection board and current limit to be responsible for, this also is two protection, protection from over current and external short circuit.Due to the over discharge occurs only in the process of electronic products have been used.Therefore, the general design is provided by the circuit board of the electronic products first to protection, battery protection board is provide the second protection.When the electronic products to detect the voltage is less than 3.0 v, the should automatically power off.If the product design is not the function design, low voltage protection board will in to 2.4 v, close the discharge circuit.

All in all, battery system design, it must be right, etc. To top it off with over-current provides two electronic protection, respectively.The protection plate is the name of the second protection.Take off after charging the protection plate, if the battery will explode is poorly designed.

This method provides two protection, but due to the consumer after the charger is broken, can buy the original charger to recharge batteries and the charger, based on cost considerations, often take out the charging controller, to reduce the cost.As a result, the good money after bad COINS, appear on the market a lot of bad charger.This makes the overcharge protection lost the first and most important line of defence.And overcharge the battery explosion is the most important factors, therefore, inferior charger is battery explosion.

Of course, not all of the battery system using the above scheme.In some cases, the battery pack will have a charge controller design.For example: many laptop computer and battery, there is charge controller.This is because the laptop will generally charge controller inside a computer, only an adapter to consumers.Therefore, laptop computer and battery pack, you must have a charge controller, in order to ensure the safety of the plus when using the adapter charging the battery pack.In addition, the use of car cigarette lighter charging products, sometimes will do within the battery charge controller.

The last line of defense

If the protective measures have failed, the last line of defense, will be provided by the batteries.Safe levels of batteries, and can be on the basis of batteries can be roughly distinguish by external short circuit and overcharge.Because, before the battery explosion, if internal accumulation of lithium atom in material surface, explosive power will be bigger.And the overcharge protection often only line of defense for consumers to use inferior charger, therefore, batteries, resistance to overcharge ability is more important than the ability to resist external short circuit.

Aluminum shell batteries compared with steel shell batteries safety shell relative to steel shell has the very high security advantages.

The page contains the contents of the machine translation.