Examples of the safety, detection and solution of lithium-ion batteries

　　Author ：Iflowpower – Portable Power Station Supplier

In recent years, due to the accidents caused by battery safety, there are many problems caused by the consequences of the problem, such as the shocked industry Boeing 787 fantasy passenger plane lithium-ion battery fire event, and Samsunggalaxynote7 large-scale battery bootsticks, to lithium ion batteries Security problem sounds again. I. Composition and working principle of lithium ion batteries are important from the positive electrode, the negative electrode, the electrolyte, the diaphragm, and the external connection, and the packaging member.

Among them, the positive electrode, the negative electrode includes an active electrode material, a conductive agent, a binder, or the like, uniformly applied to the copper foil and the aluminum foil concentration fluid. The positive electrode potential of the lithium-ion battery is high, often an inconed lithium transition metal oxide, or a polyanionic compound such as lithium cobaltate, lithium manganate, three yuan, lithium iron phosphate, etc., the lithium ion battery is usually carbon material.

Such as graphite and non-graphitized carbon, etc.; the lithium ion battery electrolyte is important for non-aqueous solution, consisting of organic mixed solvents and lithium salts, wherein the solvent is mostly carbonated organic solvent, and the lithium salt is mostly a unit price polyanionic salt, such as Lithium hexafluorophosphate, etc .; the lithium ion battery diaphragm is mostly polyethylene, polypropine thin microporous membrane, which functions to isolate positive, negative electrode, preventing electrons from causing short circuit while allowing electrolyte ions to pass.

During the charging process, the inside of the battery is removed from the positive electrode in ionic form, and is transmitted from the electrolyte to the negative electrode; the outside of the battery is migrated from the external circuit to the negative electrode. During the discharge process: The internal lithium ions in the battery are detached from the negative electrode, through the diaphragm, embedded into the positive electrode; the outside of the battery, the electron is migrated from the outer circuit to the positive electrode. As charging, discharge, migration is lithium ions, rather than lithium, so battery is called lithium ion batteries.

Second, the safety hazard of lithium-ion battery is generally, and the safety problems in lithium-ion batteries appear as combustion or even explosion. The root cause of these problems is the thermal out of control inside the battery, in addition to this, some external factors, such as overtilight, fire Source, extrusion, puncture, short circuit, etc. also lead to safety issues.

The lithium-ion battery will heat during charge and discharge. If the heat exceeds the heat dissipation capacity of the battery heat, the lithium-ion battery will overheat, the battery material will occur, the decomposition of the SEI film, the electrolyte decomposition, the positive decomposition, the negative electrode EtOAc EtOAc. 1.

At the same time, these two reactions can occur in a large amount of heat, resulting in further increase in battery temperature. Different de-lithium states have a difference in the transformation of the active material lattice, decomposition temperature, and battery thermostability. 2.

The lithium lithium compound can effectively prevent the occurrence of lithium dendrites, greatly improve the safety of lithium-ion batteries. As the temperature increases, the carbon negative electrode in the lithium state is first reflective with the electrolyte. Under the same charge and discharge conditions, the exothermic rate of the electrolyte and the antidemic lithium artificial graphite reaction is much larger than the reaction heat transfer rate of the intermediate phase carbon microspheres, carbon fibers, cokes, etc.

of the intercallium. 3. The electrolyte of the separator and electrolytic solution is a mixed solution of the lithium salt and an organic solvent in which the commercial lithium salt is lithium hexafluorophosphate which is prone to thermal decomposition in high temperature, and with trace water and organic Heat chemical reaction between the solvent, reducing the thermal stability of the electrolyte.

The electrolyte organic solvent is carbonate, such a solvent boiling point, low flash point, easy to release PF5 in high temperatures, easy to oxidize. 4. Safety hidden dangers in manufacturing processes, lithium-ion batteries, electrode manufacturing, battery assembly, etc.

, affect the safety of batteries. Such as positive and negative electrode mixes, coating, rolling, tabs or punching, assembly, filling electrolyte, sealing, etc., the quality control, etc.

The uniformity of the slurry determines the uniformity of the active substance distribution on the electrode, thereby affecting the safety of the battery. The slurry is too large, and the expansion of the negative electrode material and the contraction of the negative electrode material are large, and the precipitation of metal lithium may occur; the slurry fineness will cause the battery to block the battery. The coating heating temperature is too low or the drying time will leave the solvent residue, the binder portion is dissolved, resulting in a portion of the active material to be easily peeled off; the temperature is too high may cause the binder carbonization, the active material falls off causes the internal short circuit of the battery.

5, the safety hazards in the battery use, lithium-free battery should minimize overcharge or over-discharge, specifically regarding a battery with high monomer capacity, may cause a series of exothermic side reactions due to heat disturbance, resulting in safety Sexual problem. Third, lithium-ion battery safety test indicator Lithium-ion battery production, one series of detection is carried out before reaching the consumer, try to ensure the safety of the battery and reduce safety hazards. 1.

Extrusion test: Place the charged battery in one plane, from the steel rod of 131KN, a steel rod plane extruded by a steel rod having a diameter of 32 mm, once the extrusion pressure reaches the maximum stop extrusion The battery does not afford fire, not exploding. 2, hit test: After the battery is fully charged, place the steel column of 15.8mm in diameter vertically on a plane, and the weight of 9.

1 kg from 610 mm is free to the steel column above the battery. The battery is not fire, not exploding. 3, over-recharge test: Fill the battery with 1C, press the overcharge test according to 3C overcharge 10V, when the battery over-charge voltage rises to a certain voltage, it is close to one time, the battery voltage rapidly increases, when rising At a certain limit, the battery high hat is broken, the voltage fell to 0V, the battery did not fire, exploded.

4. Short-circuit test: Powering the battery with a wire with a wire with a resistor not more than 50m, test the surface temperature of the battery, the upper temperature of the battery is 140 ¡ã C, the battery cap is opened, the battery does not affont fire, not exploding. 5.

Acupuncture test: Place the electric battery on a plane, pierce the battery in the radial direction with a steel needle with a diameter of 3mm. Test the battery does not afford fire, not exploding. 6.

Temperature cycle test: Lithium ion battery temperature cycle test is used to simulate lithium-ion batteries during transportation or storage, repeated exposure to low temperature and high temperature environments, the safety of lithium-ion batteries, the test is to utilize rapid and extreme temperatures Changing. After the test, the sample should not be fired, not exploded, no leakage. Fourth, lithium-ion battery safety solution For many safety hazards in materials, manufacturing, and use, how to improve the safety issues, is the problem to be solved by lithium-ion battery manufacturers.

1. By adding functional additives, using new lithium salts and using new solvents can effectively solve the safety hazard of electrolyte. Depending on the function of the additive function, it is important to be divided into the following: Safety protection additives, film formation additives, protect the positive electrode additive, stabilize the lithium salt additive, lithium precipitation additive, collective anticorrosive additive, enhanced wetting additives, etc.

In order to improve the performance of the commercial lithium salt, the researchers replaced them, got a number of derivatives, of which the compounds obtained with perfluoroalkyl substituted atoms have a high flash point, electrical conductivity approximation, water resistance, etc. It is a kind of lithium salt compound that is very useful. Further, with the anionic lithium salt obtained by cheating the oxygen foundation with a boron atom, it has high thermal stability.

With regard to solvent, many researchers have proposed a range of new organic solvents such as carboxylate, organic ether organic solvents. In addition, the ionic liquid also has a kind of safety high electrolyte, but relatively commonly used carbonate electrolyte, the viscosity of the ionic liquid is high, the electrical conductivity, the ion self-diffusion coefficient is low, and there are still many work from the practicalization. Have to do.

2. Improve the safety lithium iron phosphate and ternary composites of electrode materials and three-membered composites are considered to be a positive material material, excellent in safety, and it is possible to spread applications in electric vehicle industries. Regarding the positive material, improve the common method of improving its safety is coated, such as surface covering of the positive electrode material with a metal oxide, can prevent direct contact between the positive electrode material and the electrolyte, inhibiting the phase change of the positive electrode material, improves Its structural stability, reducing the disorder resistance of cation in lattice, to reduce the secondary reaction.

Regarding the negative electrode material, since its surface is often the most susceptibility to heat dissipation and exotherm in a lithium ion battery, the thermal stability of the SEI film is a key method for improving the safety of the negative electrode material. By weak oxidation, metal and metal oxide deposition, polymer or carbon coating, can improve the thermal stability of the negative electrode material. 3.

Improve the safety protection of the battery In addition to improving the safety of battery materials, many safety protection measures employed by commodity lithium-ion batteries, such as setting battery safety valves, thermo-soluble fuses, series with positive temperature coefficients, using hot sealing diaphragms, Load special protection circuits, dedicated battery management systems, etc., is also means of enhancing security.