The new energy vehicle power battery is the core component of the new energy vehicle, and it can be called the heart of the new energy vehicle. The daily maintenance quality of power battery will directly affect the technical condition and service life of automobile. In the current commercial application of power batteries, lithium ion batteries have the advantages of high specific energy, long cycle life, low self release rate, wide use of temperature range, no memory effect, no pollution to the environment and so on, which are most favored by the market. 1 the lithium ion battery and lithium ion battery group lithium ion battery is a kind of rechargeable battery. It mainly relies on the lithium ion to move between the cathode and the negative electrode through the electrolyte to realize the charge and discharge. 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, the latter is replaced by solid polymer electrolytes, and solid polymer electrolytes have two forms of "dry state" and "colloidal". These two kinds of lithium-ion batteries use the same positive and negative materials as well as their working principles in addition to the different electrolytes used. At present, lithium-ion batteries take lithium compounds as positive electrodes, carbon materials as negative electrodes, and lithium and lithium exist in positive and negative pole materials. The cathode materials include lithium chloride, lithium manganate, three element material and lithium iron phosphate. As shown in Fig. 1, lithium ion batteries are mainly composed of positive electrode, negative electrode, electrolyte, separator and battery shell. The diaphragm uses porous insulating material, which mainly plays the role of isolating the positive and negative electrodes of the battery. The barrier electrons move between the positive and negative poles of the battery, but the lithium ion (Li+) is allowed to move between the positive and negative poles through the micropores on the diaphragm. When the lithium ion battery is charged, Li + is inlaid from the gap of the positive pole under the action of the electric field force, and the electrolyte is embedded into the negative electrode through the diaphragm through the electrolyte. At this time, the anode is in the Beaver State and the positive pole is in the poor lithium state. When the discharge is disconnected, the Li+ is embed from the gap of the negative electrode and embed through the electrolysis to the positive pole, and the positive pole is rich at this time. The lithium state, the negative electrode is in the poor lithium state. Therefore, in the charging and discharging cycle, the "embedded" reaction occurs on the positive and negative poles of the Li +, and the Li + moves back and forth between the positive and negative poles, and the electrons move between the positive and negative electrodes of the battery to form the charge and discharge currents. Therefore, people visually call lithium ion battery "rocking chair battery". The working voltage of lithium ion battery depends on the lithium ion intercalation compound and lithium ion concentration. Because the voltage and capacity of the single lithium ion battery can not meet the requirements of the vehicle, it is necessary to combine n single lithium ion batteries to form a battery group (commonly called "battery pack"), which can be used as a power battery for automobiles. Usually, the automobile power battery pack is made up of dozens or even hundreds of single cell batteries. In the battery pack, there are individual differences in the capacity and voltage of a single cell, making it difficult for each single cell to reach a uniform charge and discharge. The overdischarge, overcharge or internal short circuit of the single cell will cause the heating up of the battery, which not only affects the service life of the battery, but also has the potential of safety. Therefore, in order to ensure the safety and service life of the battery pack, the collection lines of voltage, temperature and current are usually set in the lithium ion battery group, so that the battery management system (BMS) can collect the parameters of the battery group and implement the real-time monitoring to ensure the normal working state of the battery group. 2 attention should be paid to automotive lithium ion battery pack (1) attention should be paid to avoid lithium ion battery pack being hit and flooded when using and cleaning cars. (2) when the meter shows low power, it should be charged to lithium ion power battery in time, so as to avoid the battery's normal use because of power battery loss, and even shorten the life of power battery. (3) when the battery is overheated, the battery should be stopped to cool the battery and continue to drive after the overheating warning lamp is extinguished. If the battery overheating alarm or the battery fault warning lamp is frequently lighted, the professional personnel should be eliminated in time, and the non professional personnel should be strictly prohibited to disassemble and disassemble the battery group. Cause personal injury. (4) when the battery is on fire, dry sand or nitrogen fire extinguishers are used to extinguish the fire. (5) if the vehicle is discontinued for a long time, the negative electrode of the battery group should be removed to avoid the loss of battery power, and the battery charge should be charged 1 times a month. 3 daily maintenance of automotive lithium ion battery pack (1) check battery appearance. Battery cover and electrode column should be clean, there should be no dust, metal debris and other dirt. If there is, use compressed air to clean up; battery pack should not have cracks, bulging, deformation, pole loosening and other abnormal conditions; battery cover and tray should be sealed, the battery and car body should be close close. (2) check the condition of battery connection. The connection of the battery pole joint should be firm and reliable, and there should be no corrosion. The contact points of the single cell and the contact of the battery pack, voltage and temperature collecting terminal should be reliable, and should not be loose, exfoliated, rusty or deformed; the charging plug should be in good contact with the socket. (3) electric leakage detection in battery group. In order to reduce the working current of electric vehicle electrical equipment, the operating voltage of lithium ion battery pack usually adopts voltage specification over 300 V DC, so the lithium ion battery pack has high insulation requirement. The insulation performance of the electric vehicle is measured by the DC positive and negative busbar insulation resistance of the battery group. According to the national standard GB/T18384.1-2001 of the electric vehicle, the insulation resistance of the battery group is divided by the nominal voltage U of the electric vehicle DC system, and the result is more than 100 ON, which is in line with the safety requirements. 4 the replacement of the battery pack needs to be replaced after the battery pack reaches its service life. The replacement of battery pack must be operated by professionals with electrician qualification. The replacement of battery group should be ventilated, dry, no water trace and oil trace on the ground, no high pressure equipment in the surrounding area; the operator must wear insulating gloves (pressure 600 V above), protective mask, insulating rubber shoes, and can not carry any metal items with them. When disassembling the battery pack, the car power switch should be cut off first and all connections between the battery pack and the battery external electrical equipment should be cut off. If the electric vehicle is equipped with an emergency maintenance switch, it is necessary to pull the handle of the emergency maintenance switch to the power cut position. Then dismantling the connection between the power battery and the battery management system (BMS), the high voltage distribution box, etc. (special reminder: after the high pressure wiring is removed, the insulating tape will be used to wrap the exposed metal part). Finally, the battery pack is removed smoothly with special lifting equipment, and no impact is strictly prohibited. When the battery pack is installed, first check the seal of the battery pack and the battery box tray. After the battery pack is installed to the body, it should be able to see whether the combination of the battery group and the body is close close; then the battery pack is tested for leakage. After the test meets the technical requirements, the voltage, temperature and current are used to match the line and high pressure according to the specification. The line is properly installed; finally, each connection point of the battery group is checked to confirm that the battery group can be connected with the external electric equipment without error, so as to avoid damage to the battery and the electrical equipment.