The battery for new energy vehicles is main component of new energy vehicles, and can be called heart of new energy vehicles. The quality of daily maintenance of power battery directly affects technical condition and service life of car. Among modern commercial batteries, lithium-ion batteries have advantages of high energy density, long service life, low self-discharge rate, wide temperature range, no memory effect and no environmental pollution. market.
1 Car lithium-ion battery and lithium-ion battery
A lithium-ion battery is a rechargeable battery that mainly uses movement of lithium ions between positive and negative electrodes through electrolyte to charge and discharge. According to 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 latter is replaced by solid polymers. electrolytes Solid polymer electrolytes are available in both "dry" and "colloidal" forms. In addition to different electrolytes used in these two types of lithium-ion batteries, materials of positive and negative electrodes and operating principles they use are basically same. Currently, lithium-ion batteries use lithium-containing compounds as positive electrodes and carbon materials as negative electrodes. There is no metallic lithium in materials of positive and negative electrodes, only lithium ions. Positive electrode materials include lithium cobaltate, lithium manganese oxide, ternary materials, and lithium iron phosphate, and negative electrode is usually 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 separator is made of a porous insulating material, which mainly plays role of insulating positive and negative electrodes of battery, preventing electrons from moving between positive and negative electrodes of battery, but allowing lithium ions (Li+) to move between positive and negative electrodes through micropores on separator. When charging a lithium-ion battery, Li+ is deintercalated from gap of positive electrode by force of electric field and is introduced into negative electrode through electrolyte through diaphragm, while negative electrode is in a rich state, and positive electrode is in a lithium-poor state; Li+, on contrary, is deintercalated from gap of negative electrode and intercalated into positive electrode through electrolyte. At this time, positive electrode is in a high lithium state and negative electrode is in a low lithium state. Therefore, during charge and discharge cycle, Li+ undergoes "intercalation and deintercalation" reactions at positive and negative electrodes respectively, Li+ moves back and forth between positive and negative electrodes, and electrons move between positive and negative battery electrodes through external battery wires to form current. charge and discharge. Therefore, in people, lithium-ion batteries are figuratively called "rocking chair batteries." The operating voltage of a lithium ion battery depends on lithium ion intercalation compound itself and concentration of lithium ions that make up the electrode.
Because voltage and capacity of single lithium-ion batteries are small, they cannot meet requirements of vehicles. It is necessary to connect n individual lithium-ion batteries to form a battery pack (commonly known as a "battery pack"). before it can be used as a car battery. Typically, a car battery is assembled from dozens or even hundreds of individual cells. In a battery pack, there must be individual differences in parameters such as capacity and voltage of individual batteries, making it difficult for each individual battery to remain constant when charging and discharging. Over-discharging, overcharging or internally shorting a single battery will cause it to heat up, which will not only affect battery life but also create a safety hazard. Therefore, in order to ensure safety and service life of battery pack, collection lines such as voltage, temperature and current are usually installed in lithium-ion battery pack, so that battery management system (BMS) can collect battery parameters and realize real-time monitoring, to make sure battery is in normal working condition.
2 Precautions when using automotive lithium-ion batteries
(1) When using and cleaning vehicle, care must be taken to avoid impact and water on lithium-ion battery pack.
(2) When meter shows that power is low, lithium-ion battery pack should be charged in time, so as not to affect normal use of battery due to power loss of battery pack, and even shorten service life. battery life.
(3) When battery over temperature alarm is triggered while vehicle is driving, stop vehicle to cool battery, and continue driving after over temperature warning light goes out; Non-professionals are strictly prohibited from disassembling and assembling battery pack by themselves to avoid injury.
(4) In event of a battery fire, use dry sand or a nitrogen fire extinguisher to extinguish fire.
(5) If vehicle is stopped for a long time, in order to avoid affecting battery life due to power loss, negative pole of battery should be removed and power battery should be charged regularly once a month.
3 Car lithium-ion battery maintenance
(1) Check appearance of battery. The cover of battery pack and electrode column must be clean, they should be free of dust, metal filings, and other contaminants; and other anomalies; The battery cover and tray must be closed, and connection between battery and housing must be tight.
(2) Check battery connection status. The connection of battery terminal connector must be strong and secure, and there must be no corrosion; contact of each connection point of an individual battery and conductive belt of battery, terminals for measuring voltage, temperature and other nodes must be reliable. , and there should be no play, falling off, rust or deformation, charging plug should fit snugly into outlet.
(3) Battery leakage detection. In order to reduce operating current of electrical equipment in electric vehicles, operating voltage of lithium-ion battery packs is generally within DC voltage specification of 300V or more, so automotive lithium-ion battery packs have high insulation requirements. The insulation performance of electric vehicles is measured by insulation resistance of positive and negative DC busbars of battery to ground. According to national standard GB/T18384.1-2001 for electric vehicles, insulation resistance of battery to ground is separated by electric vehicle. The rated voltage U of DC system is greater than 100 V, which meets safety requirements.
4 Replacing battery
When battery reaches end of its service life, it must be replaced. Battery replacement must be carried out by a qualified electrician. The battery replacement place should be ventilated and dry, without water and oil stains on ground, near high-voltage equipment, operators should wear dielectric gloves (with a withstand voltage of 600V or more), protective masks, etc. insulating rubber shoes and cannot carry any metal objects.
When removing battery from vehicle, first turn off vehicle's power switch and disconnect all connections between battery and battery's external electrical equipment. If electric vehicle is equipped with an emergency switch, it is only necessary to turn emergency switch knob to power off position. Then remove connection between power battery and battery management system (BMS), high voltage junction box, etc. (Special reminder: after removing high voltage wiring, exposed metal parts should be wrapped with electrical tape). Finally, use special plifting equipment to remove battery smoothly, and collisions are strictly prohibited.
When installing battery, first check tightness of battery and battery box tray, after installing battery on vehicle body, visually check tightness of connection between battery and vehicle body; then carry out a leak test on battery. After test meets specifications, properly install voltage, temperature and current measurement lines and high-voltage wiring according to specifications; Finally, check battery connection points and connect battery to external electrical equipment, making sure it is correct so as not to damage battery and electrical equipment.