Why are lithium batteries so dangerous?

Lithium is a kind of special metal that is easy to react. It is silvery white, very soft, scalable, and flammable. Lithium metal will release flammable gas under the influence of water.

A metallic lithium properties:

(1) the water or damp air will release of flammable gas;

(2) the solid state, when the temperature exceeds its melting point 180 ℃, can burn;

(3) a powder, can burn in room temperature;

(4) can cause serious burns and corrosion.

The lithium battery core or lithium battery belong to 9 kind of dangerous goods, the risk depends on the content of lithium.

1) highly flammable lithium-ion batteries;

(2) the short circuit and overcharge, extreme temperature, error operation or other errors can be on fire;

(3) whether because the internal or external heating or physical impact, it can generate enough heat to make thermal runaway adjacent to the battery. Lithium batteries release of electrolytes mixed melting of lithium metal, accompanied by a large pressure pulse. Flammable electrolytes and molten lithium metal can produce explosive mixture;

(4) in grade C cargo agent halon 1301 (three fluorine methyl bromide extinguishing agent), cannot effectively control ignition of lithium battery.

First, the classification of lithium battery

Generally divided into a battery (not recharged) and secondary battery (can be repeated charge).The lithium battery is a kind of by lithium metal or lithium alloy as the cathode material, using nonaqueous electrolyte battery, generally fall into two categories: battery and lithium metal lithium ion batteries(including lithium ion polymer battery), the main difference is that a lithium battery is a battery, lithium containing metallic state, such as the button battery; And lithium ion batteries are secondary batteries, do not contain lithium metal state, such as mobile phone battery.

The lithium-ion polymer battery, as the representative of the secondary battery is widely used in mobile phones, tablets and other portable electronic products. The reason is that using polymer tandem cells structure, make its need only a small amount of liquid electrolyte, so the battery does not need to do protect hard shell, there is no limit to the shape, the packaging volume can be greatly reduced. Based on these characteristics, lithium-ion polymer battery replaces traditional the trend of the lithium ion battery.

Second, the working principle of lithium-ion batteries

Now called especially lithium-ion batteries, lithium batteries its positive and negative electrode is composed of different embedded lithium ion compound, is a kind of chemical energy and electric energy conversion device. Its structure is mainly composed of battery is negative, as shown below.

The anode structure

LiCoO2 (PVDF) + + conductive agent, binder set fluid (aluminum foil)

The cathode structure

Graphite + conductive agent, thickening agent (CMC) + binder (SBR) + fluid (copper foil)

When lithium-ion batteries in charging process, sent via charger current on lithium-ion (Li +) thrust, from the anode through the electrolyte to the negative electrode, stored in the form of electrochemical potential. When there is no more lithium ion flow from anode to cathode, explain the battery has been charged. In this process, the battery is between the cathode electrochemical driving force, called the terminal voltage. As shown in figure 3.

When lithium battery in the process of discharge, attached to the negative electrode of lithium ion began to migrate back to the positive electrode, the process of storage battery, continue to discharge terminal voltage continues to decline. Once all the lithium ions migrated from the positive terminal, the battery totally discharge, then you need to be recharged after use.

Fourth, factors affecting the safety of lithium-ion batteries

1) the internal factors

Electrode materials and electrolyte of lithium batteries are flammable, heated (internal or external) can cause fires, and decompose to produce gas, thus increase the possibility of a battery explosion. And now the high polymer separation membrane strength is relatively low, in the case of collision or overheat easily damage the membrane, causing the battery short circuit.

At the same time, manufacturing defects are easy to cause lithium battery safety problems. Such as batteries, extremely long ears, contact with the plate or shell cause short circuit; Ear pressure core winding, lead to negative short circuit; Between the poles leave pieces of metal powder, copper foil, aluminum foil, etc. may cause causing membrane perforation micro short circuit, etc.

2) external factors

External factors affecting the safety of the lithium battery is relatively complex, such as charging, short circuit, slammed into are likely to cause spontaneous combustion lithium-ion batteries.

The page contains the contents of the machine translation.