Lithium-ion power battery use and maintenance
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 currently commercialized power batteries, lithium-ion batteries have the advantages of high specific energy, long cycle life, low self-discharge rate, wide operating 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 kind of rechargeable battery, which mainly relies on lithium ions to move between the positive electrode and the negative electrode 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 uses solid polymer electrolytes instead. There are two forms of "dry state" and "colloid state". In addition to the different electrolytes used in these two types of lithium-ion batteries, the positive and negative materials and working principles they use are basically the same. At present, lithium-ion batteries use lithium-containing compounds as the positive electrode and carbon materials as the negative electrode. There is no metal lithium in the positive and negative materials, only lithium ions. The positive electrode materials include lithium sulphate, lithium manganate, ternary materials and lithium iron phosphate, and the negative electrode is generally graphite.
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 diaphragm adopts porous insulating material, which mainly functions to isolate the positive and negative electrodes of the battery, blocking electrons from moving between the positive and negative electrodes of the battery, but allows lithium ions (Li+) to move between the positive and negative electrodes through the micropores on the diaphragm. When a lithium ion battery is charged, Li+ is released from the gap of the positive electrode under the action of the electric field force, and inserted into the negative electrode through the electrolyte through the separator. 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 extracted from the gap of the negative electrode and inserted into the positive electrode through the electrolyte. At this time, the positive electrode is in the lithium-rich state and the negative electrode is in the lithium-depleted state. Therefore, during the charge and discharge cycle, Li+ undergoes "embedding and deintercalation" reactions on the positive and negative electrodes, respectively, Li+ moves back and forth between the positive and negative electrodes, and electrons are formed by moving between the positive and negative electrodes of the battery through the external wires of the battery. Charge and discharge current. Therefore, people vividly refer to lithium-ion batteries as "rocking chair batteries." The operating voltage of a lithium ion battery depends on the lithium ion intercalation compound itself and the concentration of lithium ions constituting the electrode.
Due to the small voltage and capacity of single lithium ion batteries, it cannot meet the requirements of the use of automobiles. It is necessary to combine 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 automobiles . Usually, the automobile power battery pack is assembled by dozens or even hundreds of single cells. In a battery pack, there are bound to be individual differences in the capacity, voltage and other parameters of the single cells, which makes it difficult for each single cell to be consistent during charging and discharging. The overdischarge, overcharge 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 have safety risks. Therefore, in order to ensure the safety and service life of the battery pack, the voltage, temperature and current collection lines 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 of 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 the loss of power from the power battery and affect the normal use of the battery, or even shorten the service life of the power battery.
(3) When a battery overheating alarm occurs while the car is running, stop to cool the battery and continue driving after the overheating warning light goes out; if there are frequent battery overheating alarms or the battery failure warning light is always on, the fault should be promptly performed by professionals Excluded, 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, use dry sand or nitrogen fire extinguisher to extinguish the fire.
(5) If the vehicle is stopped for a long time, in order to prevent the battery pack from losing power and affecting its service life, the negative electrode of the battery pack should be removed, and the power battery should be charged regularly once a month.
3 Daily 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 shavings and other dirt. If there is, compressed air should be used for cleaning; the battery pack casing should not have cracks, swelling, deformation, loose poles and other abnormal conditions; The battery cover and tray should be kept airtight, and the joint between the battery and the vehicle body should fit tightly.
(2) Check the battery connection status. The connection of the battery pole connector should be firm and reliable, and there should be no corrosion; each connection point of the single battery and the contact of the battery pack conductive belt, voltage, temperature collection terminal 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) Leakage detection of battery pack. In order to reduce the working current of the electrical equipment of electric vehicles, the working voltage of the lithium-ion battery pack generally adopts a voltage specification above 300 V DC, so the automobile lithium-ion power battery pack has a high insulation requirement. The insulation performance of an electric vehicle is measured by the insulation resistance of the battery pack’s DC positive and negative bus bars to the ground. According to the national standard for electric vehicles GB/T18384.1-2001, 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 service life, it needs to be replaced. The replacement of the battery pack must be performed by a professional qualified as an electrician. The battery pack replacement site should be ventilated and dry, and there should be no water or oil traces on the ground, and no high-voltage equipment around; operators must wear insulated gloves (withstand voltage above 600 V), protective masks, and insulated rubber shoes. They cannot carry any metal objects.
When disassembling the battery pack in the car, you should first cut off the power switch of the car, and cut off all the connections between the battery pack and the external electrical equipment of the battery. If the electric vehicle is equipped with an emergency maintenance switch, simply pull 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 a special lifting device to remove the battery pack steadily, and no impact is allowed.
When installing the battery pack, you should first check the tightness of the battery pack and the battery box tray; after the battery pack is installed on the car body, you should visually check whether the joint between the battery pack and the car body fits tightly; then conduct a leakage test on the battery pack, and the test conforms to the technology After requesting, properly install the voltage, temperature and current collection lines and high-voltage wiring according to the specifications; finally, check the connection points of the battery pack, and then connect the battery pack to the external electrical equipment to avoid damage Batteries and electrical equipment.
