Analysis of charging technology of lead-acid batteries and AG13 battery for electric vehicles

　　Power battery is one of the key technologies of electric vehicles. When Gustave Trouve built the world's first electric tricycle in 1881, he used lead-acid batteries. At present, there are still many hybrid vehicles and pure electric vehicles using new generation lead-acid batteries. In the past decade or so, lithium-ion power batteries have been used in the production of electric vehicles and have increasingly demonstrated their superiority.

　　American scholar J.A. Mas proposed the acceptable current theorem for battery charging through a large number of experiments: 1) For any given discharge current, the charging acceptance current of the battery is proportional to the square root of the discharge capacity; 2) For any discharge depth, a battery The charge acceptance ratio is proportional to the logarithm of the discharge current, and the charge acceptance ratio can be increased by increasing the discharge current; 3) A battery is discharged at several discharge rates, and its accepted current is the sum of the accepted currents at each discharge rate. In other words, the charging current of the battery can be increased by discharging. When the battery's charge acceptance capacity decreases, discharge can be added to the charging process to improve the capacity.

　　The performance and life of automobile power batteries are related to many factors. In addition to its own parameters, such as battery plate quality, electrolyte concentration, etc., there are also external factors, such as battery charging and discharging parameters, including charging methods and charging end voltage. , charge and discharge current, discharge depth, etc. This brings a lot of difficulties to the battery management system BMS to estimate the actual capacity and SOC of the battery, and many variables need to be taken into consideration. The battery management system of WG6120HD hybrid electric vehicle is based on the management of SOC values. SOC (state of charge) refers to the changing state of the charge parameters participating in the reaction inside the battery, reflecting the remaining capacity of the battery. This has formed a unified understanding at home and abroad.

　　1. Lead-acid battery

　　Lead-acid battery is a very complex chemical reaction system. External factors such as the size of the charge and discharge current and its operating temperature will affect the performance of the battery. Calculating the SOC value of the battery and determining the car's operating mode based on the car's operating status and other parameters is a key technology for electric vehicles.

　　Lead-acid batteries have the longest application history, are also the most mature and cheapest batteries, and have been mass-produced. But it has low specific energy, high self-discharge rate and low cycle life. The main problem currently is its short range on a single charge. The recently developed third-generation cylindrical sealed lead-acid batteries and fourth-generation TMF (foil rolled electrode) sealed lead-acid batteries have been used in EV and HEV electric vehicles. In particular, the low impedance advantage of the third-generation VRLA battery can control ohmic heat during fast charging and extend the battery life.

　　The pulse staged constant current fast charging method can well adapt to the requirements of hybrid electric vehicle lead-acid batteries under variable current discharge state and short charging time, so that the battery state of charge SOC can always be maintained in the range of 50%-80%. Tests show that it only takes 196 seconds to charge the battery from 50%C to 80%C. This charging method basically meets the acceptance curve of the battery. The battery has a small temperature rise, produces less gas, has little pressure effect, and has a short charging time.

　　The optimal charging method is that the charging current always follows the inherent charge acceptance curve. During the charging process, the charge acceptance rate remains unchanged. As time increases, the charging current decreases according to the inherent charge acceptance curve (exponential curve decreases), so that the charging time Shortest. The pulse depolarization charging method can achieve fast and high-efficiency charging, but the equipment is expensive and is not suitable for some batteries.

　　The new VRLA battery developed by a Japanese company for electric vehicles has voltage specifications of 2V and 4V per unit, and adopts a lean liquid type and a horizontal plate design. The distance between the rice plates is very small, so there will be no stratification of the electrolyte. The falling materials will be blocked by the plates when moving downward, and there will be no accumulation of fallen materials at the bottom of the battery.

　　Ectreosorce's 12Vl12A·h horizontal battery for electric vehicles has a 3-hour discharge mass specific energy of 50W·11/kg, and a cycle life of 80% IX)D (discharge depth) of more than 900 times.

　　German Sunshine Company's lead-acid batteries for electric vehicles use a colloidal electrolyte design. It has been tested that the expected life of its 6V, 160A·h battery can reach 4 years. It has the advantages of large heat capacity and low temperature rise.

　　The American company Arias launched bipolar lead-acid batteries for electric vehicles in 1994 with unique structural technology. The operating current of this kind of battery only passes through the thin double electrodes perpendicular to the electrode plane, so it has extremely small ohmic resistance. The technical parameters of the bipolar lead-acid battery for electric vehicles developed by the American BPC company are: combined voltage is 180V, battery capacity is 60A·h, discharge rate specific energy is 50W·h/kg, and cycle life can reach 1,000 times.

　　The roll-type lead-acid battery for electric vehicles launched by Sweden's OPTLMA has a product capacity of 56A·h and a starting power of 95kW, which is greater than the ordinary 195A·h VRLA battery and is a quarter smaller in size.

　　2.Lithium-ion battery

　　The characteristics and price of lithium-ion batteries are closely related to its cathode material. Generally speaking, the cathode material should meet: ⑴ Have electrochemical compatibility with the electrolyte solution within the required charge and discharge potential range; ⑵ Mild Electrode process kinetics; (3) High reversibility; (4) Good stability in air in full lithium state. With the development of lithium-ion batteries, research on high-performance, low-cost cathode materials is continuously carried out. At present, research mainly focuses on lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide. Lithium cobalt oxide (LiCoO2) belongs to the -NaFeO2 type structure, has a two-dimensional layered structure, and is suitable for lithium ions. Deintercalation. Its preparation process is relatively simple, its performance is stable, its specific capacity is high, and its cycle performance is good. Its synthesis methods mainly include high-temperature solid-phase synthesis and low-temperature solid-phase synthesis, as well as oxalic acid precipitation, sol-gel, and cold Soft chemical methods such as thermal method and organic mixing method. Lithium manganese oxide is a modification of traditional cathode materials. Currently, spinel-type LixMn2O4 is widely used. It has a three-dimensional tunnel structure and is more suitable for the deintercalation of lithium ions. Lithium manganese oxide has abundant raw materials, low cost, no pollution, better overcharge resistance and thermal safety, and has relatively low requirements for battery safety protection devices. It is considered to be the most promising lithium-ion battery cathode material.

　　In the 1990s, Japan's Sony Corporation first successfully developed AG13 battery for electric vehicles. At that time, it used lithium cobalt oxide material, which had the disadvantage of being flammable and explosive. At present, companies such as China Xinguoanmeng Guli Power Supply and other companies have developed 100Ah power AG13 battery using lithium manganate as the cathode material, which solves the shortcomings of lithium cobalt oxide batteries.

　　As of October 2006, more than 20 automobile companies around the world have conducted research and development of lithium-ion batteries. For example, Fuji Heavy Industries and NEC have cooperated to develop cheap single-unit (Cell) manganese-based lithium-ion batteries (lithium manganate batteries), which have a lifespan of up to 12 years and 100,000 kilometers in a vehicle environment, which is equivalent to the entire vehicle life of pure electric vehicles. . The fast-chargeable lithium-ion battery pack developed by Toshiba, in addition to its small size and large capacity, adopts a technology that can uniformize and fix nano-scale particles, allowing lithium ions to be evenly adsorbed on the negative electrode of the battery. It can be charged to 80% of its capacity within 6 minutes and can be fully charged in 6 minutes. Johnson Controls, a major battery factory in the United States, established a research and development site in Milwaukee, Wisconsin, in September 2005 for lithium-ion batteries with characteristics required for electric vehicles. In January 2006, it invested 50% to jointly establish Johnson Controls-Saft Advanced Power Solution (JCS) with French battery factory Saft. In August 2006, JCS undertook the 2-year USABC (United States Advanced Battery Consortium) pure electric vehicle lithium-ion battery research and development project contract led by the U.S. Department of Energy (DOE) to provide high-power lithium-ion batteries. my country's research level in lithium-ion batteries has many indicators exceeding the goals set by the 2010 long-term indicators proposed by USABC. Suzhou Phylion, which started industrialization testing in 1997, serves as the base for the national lithium-ion power battery industrialization demonstration project. The power battery packs it develops have passed the test certifications of UL in the United States and ExtraEnergy, an independent organization of the European Union, and built the first battery pack in Suzhou. The production line of power lithium-ion batteries has been successfully trial-produced and has now achieved mass production.

　　During the 2008 Beijing Olympics, 50 12-meter-long lithium-ion electric buses served in the central Olympic area. This was the first large-scale use of lithium-ion battery electric buses in the world. The electric bus takes a long time to charge. This is how to ensure that the electric car runs smoothly: the electric car drives into the charging station, and two manipulators take out the battery pack from the chassis of the car, put it into the channel to be charged, and then take it out from the charged channel to fully charge it. The electric battery pack is replaced into the chassis of the electric vehicle. The whole process only takes about 8 minutes.

　　French electric commercial vehicles powered by lithium-ion power batteries from Citroën, Renault and Peugeot have completed user testing. Bordeaux is one of the demonstration cities for electric vehicles in France. There are 500 electric vehicles of various types, mainly used in municipal vehicles and electric minibuses. It has also built 20 parking lots with supporting charging facilities for electric vehicles, 16 of which are configured A quick charging device is installed. The charging process of AG13 battery is different from that of lead-acid batteries. The integrated block of lithium polymer (Lipo) charger has very few external components. Since the integrated block itself is extremely small (2mm × 3mm), the entire charger is also very small. The charging process of Lipo battery is: when the battery voltage is very low (0.5V), it is charged with a small current. The typical value of this current is less than 0.1C (where C is the nominal battery capacity). If the voltage is high enough, But if it is lower than 4.2V, a constant current is used to charge the battery. Most manufacturers will specify a current of 1C during this process. The voltage on the battery will not exceed 4.2V. During the constant voltage period, the current flowing through the battery will be slow. drops while battery charging continues. When the battery voltage reaches 4.2V and the charging current drops to 0.1C, the battery is charged to about 80~90%, and then it changes to trickle charging of the battery. There are two parameters that can be adjusted in the charger, namely the normal charging current and the trickle charging current (when the battery is fully charged). It should be noted that the charging current should be selected carefully and the charging current should be kept below the maximum value recommended by the manufacturer.

　　French electric vehicle power batteries are currently mainly using lead-acid batteries, and second-generation lithium-ion electric vehicles have been put into test operation. Its electric vehicle charging device uses conductive charging. Conductive charging methods include conventional charging devices and fast charging devices. For conventional charging, the charging facility provides a standard civilian AC power interface with a simple leakage protection function. It takes 6 to 7 hours to charge an electric vehicle with an on-board charger and is widely used. Fast charging uses a charger to provide DC output to quickly charge electric vehicles. An electric car with 25% remaining power can be charged in 25 minutes. Fast charging applications are rare and are mainly used for industrial users and street emergencies.

　　Charging facilities have a unified charging interface, and the standard AC power interface is one of the important technical directions. Using an ordinary household socket and a special charging cable with a special plug, AC power can be provided for electric vehicles equipped with on-board chargers.

　　Lithium-ion power battery technology still needs further development. (1) Most of the lithium-ion batteries for pure electric vehicles currently announced by various companies are laboratory test data, such as acceleration performance, charging time, continuous mileage, etc., and their reliability must be further verified under actual operation in complex external environments. performance, and mass production quality control. (2) There has been no substantial breakthrough in the separator materials required for lithium-ion batteries, and they are expensive, accounting for more than 30% of the cost of power batteries. If large-scale production technology is implemented on this material, costs can be significantly reduced.

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