The power battery is the core component of new energy vehicles, and it can be called the heart of new energy vehicles. The daily maintenance quality of the power battery will directly affect the technical condition and service life of the car. Among the current commercial power batteries, lithium-ion batteries have the advantages of high specific energy, long cycle life, low self-discharge rate, wide temperature range, no memory effect, and no pollution to the environment, and are most favored by the market.
1 Lithium-ion battery and lithium-ion battery pack
Lithium-ion battery is a rechargeable battery, which mainly relies on the movement of lithium ions between the positive and negative electrodes through the electrolyte to achieve charging and discharging. According to the different electrolyte materials used in lithium-ion batteries, lithium-ion batteries can be divided into two categories: liquid lithium-ion batteries and polymer lithium-ion batteries. The former uses liquid electrolytes, while the latter is replaced by solid polymer electrolytes. Solid polymer electrolytes have Available in both “dry” and “colloidal” forms. In addition to the different electrolytes used in these two types of lithium-ion batteries, the positive and negative electrode materials and working principles they use are basically the same. At present, lithium-ion batteries use lithium-containing compounds as positive electrodes and carbon materials as negative electrodes. There is no metal lithium in the positive and negative electrode materials, only lithium ions. The positive electrode materials include lithium cobaltate, lithium manganese oxide, ternary materials, and lithium iron phosphate, and the negative electrode is generally graphite.see more:12v 500ah lithium battery
As shown in Figure 1, a lithium-ion battery is mainly composed of a positive electrode, a negative electrode, an electrolyte, a separator, and a battery case. The separator is made of porous insulating material, which mainly plays the role of isolating the positive and negative electrodes of the battery, preventing electrons from moving between the positive and negative electrodes of the battery, but allowing lithium ions (Li+) to move between the positive and negative electrodes through the micropores on the separator. When the lithium-ion battery is being charged, Li+ is deintercalated from the gap of the positive electrode under the action of the electric field force, and embedded into the negative electrode through the electrolyte through the diaphragm. At this time, the negative electrode is in a rich state and the positive electrode is in a lithium-poor state; On the contrary, Li+ is deintercalated from the gap of the negative electrode and intercalated into the positive electrode through the electrolyte. At this time, the positive electrode is in a lithium-rich state, and the negative electrode is in a lithium-poor state. Therefore, during the charge and discharge cycle, Li+ undergoes “intercalation and deintercalation” reactions on the positive and negative electrodes respectively, Li+ moves back and forth between the positive and negative electrodes, and electrons move between the positive and negative electrodes of the battery through the external wires of the battery to form charge and discharge current. Therefore, people vividly call lithium-ion batteries “rocking chair batteries”. The working voltage of a lithium ion battery depends on the lithium ion intercalation compound itself and the concentration of lithium ions that make up the electrode.
Due to the small voltage and capacity of the single lithium-ion battery, it cannot meet the requirements of the car. It is necessary to combine and connect n single lithium-ion batteries to form a battery pack (commonly known as “battery pack”) before it can be used as a power battery for the car. . Usually, an automotive power battery pack is assembled from dozens or even hundreds of single cells. In a battery pack, there are bound to be individual differences in parameters such as capacity and voltage of individual batteries, making it difficult for each individual battery to be consistent when charging and discharging.
The over-discharge, over-charge or internal short circuit of the single battery will cause the battery to heat up, which will not only affect the service life of the battery, but also pose a safety hazard. Therefore, in order to ensure the safety and service life of the battery pack, collection lines such as voltage, temperature and current are generally set in the lithium-ion battery pack, so that the battery management system (BMS) can collect the parameters of the battery pack and implement real-time monitoring , to ensure that the battery pack is in normal working condition.
2 Precautions for the use of automotive lithium-ion power battery packs
(1) When using and cleaning the car, care should be taken to avoid impact and water ingress on the lithium-ion power battery pack.
(2) When the meter shows that the power is low, the lithium-ion power battery should be charged in time to avoid affecting the normal use of the battery due to power loss of the power battery, and even shortening the service life of the power battery.
(3) When the battery overheating alarm occurs while the car is running, stop the car to cool down the battery, and continue driving after the overheating warning light goes out; It is strictly forbidden for non-professionals to disassemble and assemble the battery pack by themselves to avoid personal injury.
(4) When the battery catches fire, dry sand or nitrogen fire extinguisher should be used to extinguish the fire.
(5) If the vehicle is stopped for a long time, in order to avoid the impact on the service life of the battery pack due to power loss, the negative pole of the battery pack should be removed, and the power battery should be charged once a month regularly.
3 Routine maintenance of lithium-ion power battery pack
(1) Check the appearance of the battery pack. The battery pack cover and electrode column should be clean, and there should be no dust, metal filings and other dirt. If there is, use compressed air to clean it; the battery pack shell should not have cracks, swelling, deformation, loose poles and other abnormalities; The battery cover and the tray should be kept sealed, and the junction between the battery and the body should be tightly fitted.
(2) Check the battery connection status. The connection of the battery pole connector should be firm and reliable, and there should be no corrosion; the contact of each connection point of the single battery and the conductive belt of the battery pack, voltage, temperature acquisition terminals and other nodes should be reliable, and there should be no looseness, falling off, or rust. Or deformation; the charging plug should be in good contact with the socket.
(3) Battery leakage detection. In order to reduce the working current of electrical equipment in electric vehicles, the working voltage of lithium-ion battery packs generally adopts a DC voltage specification of 300 V or more, so automotive lithium-ion power battery packs have high insulation requirements. The insulation performance of electric vehicles is measured by the insulation resistance of the DC positive and negative busbars of the battery pack to the ground. According to the national standard GB/T18384.1-2001 for electric vehicles, the insulation resistance of the battery pack to the ground is divided by the electric vehicle The nominal voltage U of the DC system is greater than 100 ON, which meets the safety requirements.
4 Replacement of the battery pack
When the battery pack reaches the end of its useful life, it needs to be replaced. The replacement of the battery pack must be operated by professionals with electrician qualifications. The battery pack replacement site should be ventilated and dry, with no water and oil stains on the ground, and no high-voltage equipment around; operators must wear insulating gloves (with a withstand voltage of 600 V or more), protective masks, and insulating rubber shoes, and cannot carry any metal objects with them.
When removing the battery pack from the car, first cut off the power switch of the car, and cut off all connections between the battery pack and the external electrical equipment of the battery. If the electric vehicle is provided with an emergency maintenance switch, it is only necessary to turn the handle of the emergency maintenance switch to the power-off position. Then remove the connection between the power battery and the battery management system (BMS), high-voltage distribution box, etc. (Special reminder: After the high-voltage wiring is removed, the exposed metal parts should be wrapped with insulating tape). Finally, use special lifting equipment to remove the battery pack smoothly, and collision is strictly prohibited.see more:what is the difference between lithium and alkaline batteries
When installing the battery pack, first check the tightness of the battery pack and the battery box tray; after the battery pack is installed on the vehicle body, visually check whether the joint between the battery pack and the vehicle body is tight; then conduct a leakage test on the battery pack, and the test meets the technical After the requirements, properly install the voltage, temperature and current acquisition lines and high-voltage wiring according to the specifications; finally, check the connection points of the battery pack, and only after confirming that they are correct can the battery pack be connected to its external electrical equipment to avoid damage Batteries and electrical equipment.