[Dry goods] lipo battery 5s danger and safety technology

Today, the lithium battery manufacturer CNHL will introduce the danger of lipo battery 5s and its safety technology. The article will analyze the source of the danger of lipo battery 5s and give relevant technologies to ensure the safety of lipo battery 5s products.
Regarding the safety of lithium batteries, I also introduced it in the previous article cnhl 6s lipo battery safety problems and preventive measures. Interested partners can click to view.

The danger of lipo battery 5s

From its own chemical characteristics and system composition, lipo battery 5s determines that it is a potentially dangerous chemical power source.
1 High chemical activity
Lithium is an element of the main group I of the second period of the periodic table and has extremely active chemical properties.
2 High energy density 
The specific energy of lipo battery 5s is extremely high (≥140 Wh/kg), which is several times that of nickel-cadmium, nickel-metal hydride and other secondary batteries. If thermal runaway reaction occurs, it will release high heat and easily lead to unsafe behavior.
3 Using an organic electrolyte system
The organic solvent of the organic electrolyte system is hydrocarbon, which has a low decomposition voltage and is prone to oxidation, and the solvent is flammable; if there is leakage, it will cause the lipo battery 5s to catch fire, or even burn and explode.
4 High probability of side reactions
In the process of normal use, the lipo battery 5s undergoes a chemical positive reaction in which electrical energy and chemical energy are converted into each other. But under certain conditions, such as overcharging and overdischarging it or overcurrent work, it is easy to cause chemical side reactions inside the lipo battery 5s; after the side reaction is intensified, it will seriously affect the performance and service life of the lipo battery 5s, and may generate a large amount of gas, causing The pressure inside the lipo battery 5s increased rapidly and then exploded and caught fire, causing safety problems.
5 Structural instability of electrode materials
The 5s overcharge reaction of the lipo battery will change the structure of the positive electrode material and make the material have a strong oxidizing effect, making the solvent in the electrolyte strongly oxidize; and this effect is irreversible, and the heat caused by the reaction will accumulate if it accumulates. There is a danger of thermal runaway.

Lipo battery 5s product safety problem analysis

After 30 years of industrial development, lipo battery 5s products have made great progress in safety technology, effectively controlling the occurrence of side reactions in the battery and ensuring the safety of the battery. However, with the increasing use of lipo battery 5s and the increasing energy density, in recent years, incidents such as explosions and injuries or product recalls due to safety hazards have occurred frequently. We conclude that the main reasons for the safety problems of lipo battery 5s products are as follows:

1 lipo battery 5s battery core material problem

The materials used in the battery include: lipo battery 5s positive active material, negative active material, separator, electrolyte and shell, etc. The selection of materials and the matching of the composed system determine the safety performance of the battery. When choosing lipo battery 5s positive and negative active materials and diaphragm materials, the manufacturer did not conduct a certain assessment on the characteristics and matching of raw materials, resulting in a congenital shortage of cell safety.

2 lipo battery 5s production process problems

The raw materials of the battery cells are not tested strictly and the production environment is poor, resulting in impurities mixed in the production, which not only has a great adverse effect on the capacity of the battery, but also has a great impact on the safety of the battery;
In addition, if too much water is mixed into the electrolyte of lipo battery 5s, side reactions may occur and the internal pressure of the battery may increase, which will affect safety;
Due to the limitation of the production technology level, in the production process of the lipo battery 5s cell, the product cannot achieve good consistency, such as poor flatness of the electrode substrate, shedding of the electrode active material, mixing of other impurities in the active material, poor welding of the tabs Firmness, unstable welding temperature, burrs on the edge of the pole piece, and no insulating tape in key parts may adversely affect the safety of lipo battery 5s cells.

3 lipo battery 5s battery cell design defects, reduced safety performance

In terms of structural design, many key points that have an impact on safety have not been paid attention to by manufacturers. For example, there is no insulating tape in key parts, there is no margin or insufficient margin in the diaphragm design, and the capacity ratio of positive and negative electrodes of lipo battery 5s (What is the capacity of 11.1v lipo battery?) Unreasonable design, unreasonable design of the area ratio of positive and negative active materials, unreasonable design of the length of the tabs, etc., these may bury hidden dangers to the safety of the lipo battery 5s. In addition, in the production process of battery cells, in order to save costs and improve performance, some battery cell manufacturers try to save and compress raw materials, such as reducing the area of ​​diaphragms, thinning copper foil, aluminum foil, and not using pressure relief valves and insulating tapes, etc. , which will reduce the safety of the battery.

4 lipo battery 5s energy density is too high

At present, the market is pursuing higher-capacity battery products. In order to increase the competitiveness of products, manufacturers continue to improve the volume specific energy of lipo battery 5s, which increases the danger of batteries to a large extent.

Lipo battery 5s safety technology

Although lipo battery 5s has many hidden dangers, under specific conditions of use and taking certain measures, the occurrence of side reactions and violent reactions in the battery can be effectively controlled to ensure its safe use. The following is a brief introduction to several commonly used safety technologies for lipo battery 5s.

1 Use lipo battery 5s raw materials with higher safety factor:

Use lipo battery 5s positive and negative active materials, diaphragm materials and electrolytes with a higher safety factor.
About the positive and negative active materials, diaphragm materials and electrolytes of lipo battery, the following article has a detailed introduction. Interested partners can click to view:
Four key materials for lipo battery 3s dry goods!
a) Selection of positive electrode material for lipo battery 5s
The safety of cathode materials is mainly based on the following three aspects:
1 Thermodynamic stability of the material;
2 the chemical stability of the material;
3 Physical properties of the material.
b) Selection of diaphragm material for lipo battery 5s

The main function of the separator is to separate the positive and negative electrodes of the battery, to prevent the positive and negative electrodes from contacting and short-circuit, and at the same time, it has the ability to pass electrolyte ions, that is, electronic insulation and ionic conductivity. When choosing a diaphragm for lipo battery 5s, you should pay attention to the following points:
1 It has electronic insulation to ensure the mechanical isolation of positive and negative electrodes;
2 has a certain pore size and porosity to ensure low resistance and high ionic conductivity;
3 The diaphragm material has sufficient chemical stability and must be resistant to electrolyte corrosion;
4 The diaphragm must have the function of automatic shutdown protection;
5 The thermal shrinkage and deformability of the diaphragm should be as small as possible;
6 The diaphragm should have a certain thickness;
7 The diaphragm should have strong physical strength and sufficient puncture resistance.
c) Choice of lipo battery 5s electrolyte
The electrolyte is an important part of the lipo battery 5s, which plays the role of transporting and conducting current between the positive and negative electrodes of the battery. The electrolyte used in the lipo battery 5s is an electrolyte solution formed by dissolving a suitable lithium salt in an organic aprotic mixed solvent. It should generally meet the following requirements:
1 Good chemical stability, no chemical reaction with electrode active material, current collector and diaphragm;
2. Good electrochemical stability and wide electrochemical window;
3 Lithium ion conductivity is high, electron conductivity is low;
4 Wide liquid temperature range;
5 Safe, non-toxic and environmentally friendly.

2 Strengthen the overall safety design of lipo battery 5s cells:

The battery cell is the link that combines various substances of the battery. It is the integration of the positive electrode, negative electrode, diaphragm, tab and packaging film of the lipo battery 5s. The structural design of the battery cell not only affects the performance of various materials, but also affects the The overall electrochemical performance and safety performance of lipo battery 5s have an important impact. The selection of materials and the design of the cell structure are exactly the relationship between the part and the whole. In the design of the cell, a reasonable structural model should be formulated in combination with the material properties.
In addition, some additional protection devices can also be considered on the structure of lipo battery 5s. Common protection mechanism designs are as follows:
1 Using switching elements, when the temperature of the lipo battery rises within 5s, its resistance will rise, and when the temperature is too high, it will automatically stop power supply;
2 Set the safety valve (that is, the vent hole on the top of the lipo battery 5s). When the internal pressure of the battery rises to a certain value, the safety valve will automatically open to ensure the safety of the lipo battery 5s.
The following are some examples of the safety design of the cell structure:
a) Positive and negative capacity ratio and design size
Choose the appropriate positive and negative capacity ratio according to the characteristics of the positive and negative materials. The ratio of the positive and negative capacity of the battery is an important link related to the safety of the lipo battery 5s. If the positive capacity is too large, metal lithium will appear on the surface of the negative electrode. If the negative electrode is too large, the capacity of the battery will be greatly lost. Generally speaking, N/P=1.05～1.15, and make an appropriate choice according to the actual battery capacity and safety requirements. Design large and small pieces so that the position of the negative electrode paste (active material) covers (greater than) the position of the positive electrode paste. Generally, the width should be 1-5 mm larger and the length should be 5-10 mm larger.
b) There is a margin for the width of the diaphragm
The general principle of the diaphragm width design is to prevent the positive and negative plates from directly contacting and causing internal short circuit. Due to the lipo battery 5s in the process of charging and discharging and in the environment of thermal shock, the thermal shrinkage of the diaphragm causes the diaphragm to deform in the length and width directions. 

The folded area of ​​the diaphragm increases the polarization due to the increase of the distance between the positive and negative electrodes; the stretched area of ​​the diaphragm increases the possibility of micro-short circuit due to the thinning of the diaphragm; the shrinkage of the edge area of ​​the diaphragm may cause the positive and negative Internal short circuit occurs due to direct contact, which will make the battery dangerous due to thermal runaway.

Therefore, when designing the lipo battery 5s, the shrinkage characteristics of the separator must be considered in the use of the area and width, and the separator is larger than the anode and cathode. Considering the process error, the isolation film must be at least 0.1mm longer than the outer edge of the pole piece.
c) Insulation treatment
Internal short circuit is an important factor for lipo battery 5s to have potential safety hazards. There are many potentially dangerous parts that cause internal short circuit in the structural design of the battery cell. Therefore, necessary measures or insulation should be set in these key positions to prevent abnormal conditions. In the event of a short circuit in the battery, for example: maintain the necessary distance between the positive and negative ears of the lipo battery 5s; place insulating tape on the middle of the single side without paste at the end, and cover all the exposed parts; stick insulation between the positive aluminum foil and the negative active material Tape; use insulating tape to cover all the welding parts of the tabs; use insulating tape on the top of the cell.

d) Set safety valve (pressure relief device)
The danger of lipo battery 5s is often caused by an explosion or fire due to excessive internal temperature or pressure; a reasonable pressure relief device can be set up to quickly release the pressure and heat inside the battery when danger occurs, reducing the risk of explosion. Reasonable pressure relief device requirements can not only meet the internal pressure of lipo battery 5s during normal operation, but also automatically open to relieve the pressure when the internal pressure reaches the dangerous limit. The location of the pressure relief device needs to consider the increase in internal pressure of the battery case The characteristics of the resulting deformation are designed; the design of the safety valve can be achieved by means of lamellae, edges, seams and nicks, etc.

3 Improve the level of craftsmanship:

Although lipo battery 5s has many hidden dangers, under specific conditions of use and taking certain measures, the occurrence of side reactions and violent reactions in the battery can be effectively controlled to ensure its safe use. The following is a brief introduction to several commonly used safety technologies for lipo battery 5s.
1 Use lipo battery 5s raw materials with higher safety factor
Use lipo battery 5s positive and negative active materials, diaphragm materials and electrolytes with a higher safety factor.
a) Selection of positive electrode material for lipo battery 5s
The safety of cathode materials is mainly based on the following three aspects:
1 Thermodynamic stability of the material;
2 the chemical stability of the material;
3 Physical properties of the material.
b) Selection of diaphragm material for lipo battery 5s
The main function of the separator is to separate the positive and negative electrodes of the battery, to prevent the positive and negative electrodes from contacting and short-circuit, and at the same time, it has the ability to pass electrolyte ions, that is, electronic insulation and ionic conductivity. When choosing a diaphragm for lipo battery 5s, you should pay attention to the following points:
1 It has electronic insulation to ensure the mechanical isolation of positive and negative electrodes;
2 has a certain pore size and porosity to ensure low resistance and high ionic conductivity;
3 The diaphragm material has sufficient chemical stability and must be resistant to electrolyte corrosion;
4 The diaphragm must have the function of automatic shutdown protection;
5 The thermal shrinkage and deformability of the diaphragm should be as small as possible;
6 The diaphragm should have a certain thickness;
7 The diaphragm should have strong physical strength and sufficient puncture resistance.
c) Choice of lipo battery 5s electrolyte
The electrolyte is an important part of the lipo battery 5s, which plays the role of transporting and conducting current between the positive and negative electrodes of the battery. The electrolyte used in the lipo battery 5s is an electrolyte solution formed by dissolving a suitable lithium salt in an organic aprotic mixed solvent. It should generally meet the following requirements:
1 Good chemical stability, no chemical reaction with electrode active material, current collector and diaphragm;
2. Good electrochemical stability and wide electrochemical window;
3 Lithium ion conductivity is high, electron conductivity is low;
4 Wide liquid temperature range;
5 Safe, non-toxic and environmentally friendly.
2 Strengthen the overall safety design of lipo battery 5s cells
The battery cell is the link that combines various substances of the battery. It is the integration of the positive electrode, negative electrode, diaphragm, tab and packaging film of the lipo battery 5s. The structural design of the battery cell not only affects the performance of various materials, but also affects the The overall electrochemical performance and safety performance of lipo battery 5s have an important impact. The selection of materials and the design of the cell structure are exactly the relationship between the part and the whole. In the design of the cell, a reasonable structural model should be formulated in combination with the material properties.

In addition, some additional protection devices can also be considered on the structure of lipo battery 5s. Common protection mechanism designs are as follows:
1 Using switching elements, when the temperature of the lipo battery rises within 5s, its resistance will rise, and when the temperature is too high, it will automatically stop power supply;
2 Set the safety valve (that is, the vent hole on the top of the lipo battery 5s). When the internal pressure of the battery rises to a certain value, the safety valve will automatically open to ensure the safety of the lipo battery 5s.
The following are some examples of the safety design of the cell structure:
a) Positive and negative capacity ratio and design size
Choose the appropriate positive and negative capacity ratio according to the characteristics of the positive and negative materials. The ratio of the positive and negative capacity of the battery is an important link related to the safety of the lipo battery 5s. If the positive capacity is too large, metal lithium will appear on the surface of the negative electrode. If the negative electrode is too large, the capacity of the battery will be greatly lost. Generally speaking, N/P=1.05～1.15, and make an appropriate choice according to the actual battery capacity and safety requirements. Design large and small pieces so that the position of the negative electrode paste (active material) covers (greater than) the position of the positive electrode paste. Generally, the width should be 1-5 mm larger and the length should be 5-10 mm larger.
b) There is a margin for the width of the diaphragm
The general principle of the diaphragm width design is to prevent the positive and negative plates from directly contacting and causing internal short circuit. Due to the lipo battery 5s in the process of charging and discharging and in the environment of thermal shock, the thermal shrinkage of the diaphragm causes the diaphragm to deform in the length and width directions. , the folded area of ​​the diaphragm increases the polarization due to the increase of the distance between the positive and negative electrodes; the stretched area of ​​the diaphragm increases the possibility of micro-short circuit due to the thinning of the diaphragm; the shrinkage of the edge area of ​​the diaphragm may cause the positive and negative Internal short circuit occurs due to direct contact, which will make the battery dangerous due to thermal runaway. Therefore, when designing the lipo battery 5s, the shrinkage characteristics of the separator must be considered in the use of the area and width, and the separator is larger than the anode and cathode. Considering the process error, the isolation film must be at least 0.1mm longer than the outer edge of the pole piece.
c) Insulation treatment
Internal short circuit is an important factor for lipo battery 5s to have potential safety hazards. There are many potentially dangerous parts that cause internal short circuit in the structural design of the battery cell. Therefore, necessary measures or insulation should be set in these key positions to prevent abnormal conditions. In the event of a short circuit in the battery, for example: maintain the necessary distance between the positive and negative ears of the lipo battery 5s; place insulating tape on the middle of the single side without paste at the end, and cover all the exposed parts; stick insulation between the positive aluminum foil and the negative active material Tape; use insulating tape to cover all the welding parts of the tabs; use insulating tape on the top of the cell.
d) Set safety valve (pressure relief device)
The danger of lipo battery 5s is often caused by an explosion or fire due to excessive internal temperature or pressure; a reasonable pressure relief device can be set up to quickly release the pressure and heat inside the battery when danger occurs, reducing the risk of explosion. Reasonable pressure relief device requirements can not only meet the internal pressure of lipo battery 5s during normal operation, but also automatically open to relieve the pressure when the internal pressure reaches the dangerous limit. The location of the pressure relief device needs to consider the increase in internal pressure of the battery case The characteristics of the resulting deformation are designed; the design of the safety valve can be achieved by means of lamellae, edges, seams and nicks, etc.
3 Improve the level of craftsmanship
Efforts are made to standardize and standardize the production process of lipo battery 5s cells. In the steps of mixing, coating, baking, compacting, slitting and winding, formulate standardization (such as diaphragm width, electrolyte injection volume, etc.), and improve process methods (such as low-pressure injection method, centrifugal Shell method, etc.), do a good job in process control, ensure process quality, and reduce the difference between products; set up special steps in key steps that have an impact on safety (such as deburring, powder sweeping, and different welding for different materials). methods, etc.), implement standardized quality monitoring, eliminate lipo battery 5s defective parts, and exclude defective products (such as pole piece deformation, diaphragm puncture, active material shedding and electrolyte leakage, etc.); keep the production site tidy and clean, implement 5S Management and 6-sigma quality control to prevent impurities and moisture from mixing in production and minimize the impact of unexpected situations in lipo battery 5s production on safety.
The above is the entire content of the safety issues of lipo battery 5s brought to you by CNHL, a professional lithium battery company today, hoping to help you understand the reasons for the safety problems of lipo battery 5s and take corresponding measures to improve the safety of lithium batteries.

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