Are lithium batteries dangerous? What makes lithium batteries safe?

Are lithium batteries dangerous？

Why are lithium batteries dangerous?

1. High chemical activity

Lithium is the second period of the periodic table of elements, the main group I elements, with extremely active chemical properties.

2. High energy density

Lithium ion batteries are extremely high specific energy (≥ 140Wh/kg), which is several times more than nickel cadmium, nickel hydrogen, and other secondary batteries, if the thermal runaway reaction occurs, it will release a very high heat easily leading to unsafe behavior.

3. Using organic electrolyte system

The organic solvent of organic electrolyte system is hydrocarbon, with low decomposition voltage, easy to oxidize, and the solvent is flammable; if there is leakage, it will cause the battery to catch fire, or even burn and explode.

4. The probability of side reactions is large

Lithium ion battery in the process of normal use, its internal chemical positive reaction of electrical energy and chemical energy conversion. However, under certain conditions, such as overcharging, over discharging, or over current work, it will easily lead to chemical side reactions inside the battery; the side reactions will seriously affect the performance and service life of the battery after intensification and may produce a large amount of gas so that the internal pressure of the battery will rapidly increase and then explode and cause fire and lead to lithium batteries safe problems.

5. The structure of the electrode material is unstable

Lithium ion battery overcharge reaction will make the structure of the cathode material change and make the material have a strong oxidation effect, so that the solvent in the electrolyte is strongly oxidized; and this effect is irreversible, the heat caused by the reaction will be the risk of thermal runaway if accumulated.

Lithium ion battery product safety problem analysis

Lithium ion battery products after 30 years of industrial development, safety technology has made great progress, effectively controlling the occurrence of side reactions in the battery to ensure its safety of the battery. However, with the use of lithium ion batteries more and more widespread, energy density is getting higher and higher, in recent years, there are still repeated incidents of explosion injury or recall of products due to safety hazards. We summarize the causes of lithium batteries safe issues are mainly the following:

1. Lithium cells material problems

The materials used in the cell include positive active material, negative active material, diaphragm, electrolyte, shell, etc. The choice of materials and the matching of the system determines the safety performance of the cell. In the selection of positive and negative active materials and diaphragm materials, manufacturers do not make certain assessments on the characteristics and matching of raw materials, which causes the innate deficiency of the safety of electric cores.

2. Production process problems

Poor testing of raw materials and poor production environment lead to the mixing of impurities in the production, which is not only unfavorable to the capacity of the battery but also has a great impact on the lithium batteries safe issues; in addition, if the electrolyte is mixed with too much water, it may have a side reaction and increase the internal pressure of the battery, which has an impact on the safety; due to the limitation of the production process, the product cannot reach good consistency in the production process of the battery core. For example, the poor flatness of the electrode substrate, detachment of electrode active material, mixing of other impurities in the active material, poor welding of lug, unstable welding temperature, burr at the edge of the pole piece, and no insulating tape at the key part may adversely affect the safety of the battery cell.

3. Defective core design and reduced safety performance

In the structural design, many key points affecting safety are not paid attention to by manufacturers, such as no insulating tape in key parts, no or insufficient margin for diaphragm design, unreasonable design of positive and negative electrode capacity ratio, unreasonable design of positive and negative electrode active material area ratio, unreasonable design of electrode lug length, etc., which may lay hidden dangers on the safety of battery. In addition, in the production process of battery cells, some battery manufacturers try to save and compress raw materials in order to save cost and improve performance, such as reducing the area of diaphragm, thinning copper foil, aluminum foil and not using pressure relief valve, not using insulation tape, etc., which will reduce the safety of the battery.

4. Energy density is too high

At present, the market is in pursuit of higher capacity battery products, and manufacturers in order to increase the competitiveness of products, and constantly improve the volume of lithium ion battery specific energy, which largely increases the danger of the battery.

Are lithium batteries safe? Why does NPP have the safest lithium battery?

Although there are lithium batteries dangerous factors, under specific conditions of use, as well as the use of certain measures, can effectively control the occurrence of side reactions and violent reactions within the cell to ensure their safe use. The following is a brief introduction to several common safety techniques for lithium ion batteries.

1. Select raw materials with the higher lithium batteries safe factor

Select positive and negative electrode active materials, diaphragm materials, and electrolytes with higher safety factors.

(a) Selection of cathode materials

The safety of cathode materials is mainly based on the following 3 aspects:

1. Thermodynamic stability of the material;
2. The chemical stability of the material;
3. The physical properties of the material.

(b) Selection of diaphragm material

The main role of the diaphragm is to separate the positive and negative electrodes of the battery, to prevent the positive and negative electrodes from contacting and short circuiting, while having the ability to pass through the electrolyte ions, that is, with electronic insulation and ion conductivity. Lithium ion batteries should pay attention to the following points when choosing a diaphragm:

1. with electronic insulation, to ensure the mechanical isolation of the positive and negative electrodes;
2. have a certain pore size and porosity to ensure low resistance and high ionic conductivity;
3. adequate chemical stability of the diaphragm material, which must be resistant to electrolyte corrosion;
4. the diaphragm should have the function of automatic shutdown protection;
5. the thermal shrinkage and deformation of the diaphragm should be as small as possible;
6. the diaphragm should have a certain thickness;
7. The diaphragm should be physically strong and have a large enough resistance to punctures.