From：CTECHI GROUP Limited Release time：2018-12-03
Overview：Lithium is a particularly reactive metal with a silvery white appearance. It is very soft, extensible and flammable. Lithium metal belongs to the substance that releases flammable gases when exposed to water.
Lithium is a particularly reactive metal with a silvery white appearance. It is very soft, extensible and flammable. Lithium metal belongs to the substance that releases flammable gases when exposed to water.
Attributes of lithium:
(1) Flammable gases will be released in the presence of water or moist air;
(2) When it is in solid state, it can burn itself when the temperature exceeds its melting point of 180 degrees Celsius.
(3) When powder is present, it can be burned at room temperature.
(4) It can cause serious burns and corrosion.
Lithium batteries belong to the ninth category of dangerous goods. Their danger depends on the lithium contained in them.
(1) Lithium batteries are highly flammable.
(2) Short circuit, over charging, limit temperature, wrong operation or other wrong conditions can ignite;
(3) Whether it is due to internal or external heating or physical impact, it can generate enough heat to cause the adjacent batteries to heat out of control. The electrolytes released by lithium metal batteries are mixed with the melted lithium metal and accompanied by a large pressure pulse. Flammable electrolytes and molten lithium metals can produce explosive mixtures.
(4) Halon 1301 (trifluoromethyl bromide fire extinguishing agent) in Class C cargo hold can not effectively control the ignition of lithium metal batteries.
I. Classification of lithium batteries
Batteries are generally divided into primary (non-rechargeable) and secondary (rechargeable). Lithium battery is a kind of battery with lithium metal or lithium alloy as anode material and non-aqueous electrolyte. It is generally divided into two categories: lithium metal battery and lithium ion battery (including lithium ion polymer battery). The main difference is that lithium metal battery is primary battery, which contains metallic lithium, such as button battery. Ion batteries are secondary batteries and do not contain metallic lithium, such as cell phone batteries.
Lithium ion polymer batteries, as the representative of secondary batteries, are widely used in mobile phones, tablets and other portable electronic products. The reason lies in the use of polymer series battery structure, so that it only needs a small amount of liquid electrolyte, so this kind of battery does not need hard shell protection, the shape is not limited, and its packaging volume can be greatly reduced. Based on these characteristics, lithium-ion polymer batteries have a tendency to replace traditional lithium-ion batteries.
II. Working Principle of Lithium Batteries
At present, the commonly used lithium-ion batteries refer to lithium-ion batteries. The positive and negative electrodes of lithium-ion batteries are composed of different lithium-ion intercalation compounds. They are devices to realize the mutual conversion of chemical energy and electric energy. Its structure is mainly composed of positive and negative electrodes of batteries, as shown below.
LiCoO 2 + Conductive Agent + Adhesive (PVDF) + Collector (Aluminum Foil)
Negative pole structure
Graphite+Conductive Agent+Thickener(CMC)+Binder(SBR)+Collector(Copper Foil)
When the lithium battery is in the charging process, the current sent by the charger exerts a thrust on the lithium ion (Li+), which is stored in the form of electrochemical energy after passing through the electrolyte from the positive electrode to the negative electrode. When no more lithium ions flow from the positive to the negative, the battery is fully charged. In this process, the electrochemical driving force between the positive and negative electrodes of the battery is called the terminal voltage. As shown in Figure 3.
When the lithium battery is in the process of discharge, the lithium ions attached to the negative electrode begin to migrate back to the positive electrode, while the battery continues to discharge, and the terminal voltage continues to decline. Once all lithium ions are removed from the positive extremity and the battery is fully discharged, it needs to be recharged and used.
III. Factors Affecting the Safety of Lithium Batteries
1) Internal factors
Electrode materials and electrolytes of lithium batteries are flammable. When heated (internal or external), they can cause fire and decompose to produce gas, which increases the possibility of battery explosion. At present, the strength of polymer isolation film is relatively low, and it is easy to damage the film under collision or overheating conditions, resulting in short circuit of batteries.
At the same time, the faults of manufacturing process can easily lead to the safety problems of lithium batteries. For example, the electrode ear of the core is too long and short circuit is caused by contacting with the plate or shell; the core is compressed by the electrode ear, resulting in short circuit of the positive and negative poles; leaving metal powder, copper foil, aluminum foil fragments between the two poles may lead to the perforation of the diaphragm and then cause a series of problems such as micro-short circuit.
2) External factors
External factors affecting the safety of lithium batteries are relatively complex, such as overcharging, short circuit, violent impact and so on, which may cause lithium battery spontaneous combustion.
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