Analysis of lead-acid battery and lithium-ion battery charging technology for electric vehicles

Power batteries are one of the key technologies in electric vehicles. When GustaveTrouve built the world's first electric tricycle in 1881, it was powered by lead-acid batteries. At present, there are still a lot of hybrid electric vehicles and pure electric vehicles using a new generation of lead-acid batteries. Over the past decade, lithium ion power batteries have been applied in the production of electric vehicles, and more and more show its advantages.

American scholar j.a.mcas proposed the acceptable current theorem of battery charging through a large number of experiments: 1) for any given discharge current, the accepted current of battery charging is proportional to the square root of the released capacity; 2) for any discharge depth, the charge acceptance ratio of a battery is proportional to the logarithm of the discharge current, which can be increased by increasing the discharge current; 3) a battery is discharged by several discharge rates, and its receiving current is the sum of the receiving current of each discharge rate. That is to say, the charge acceptable current of the battery can be improved by discharging. When the acceptability of battery charging decreases, discharge can be added in the process of charging to improve the acceptability.

The performance and life of automobile power battery is related to many factors, besides its own parameters, such as the quality of the battery plate, the concentration of electrolyte, etc. There are also external factors, such as the charge and discharge parameters of the battery, including charging mode, voltage at the end of charging, current of charge and discharge, discharge depth and so on. This makes it difficult for BMS to estimate the actual capacity of battery and SOC, and many variables need to be considered. The WG6120HD hybrid electric vehicle battery management system is based on the management of SOC values. SOC(stateofcharge) refers to the change stateof the charge parameter that takes part in the reaction inside the battery, which reflects the residual capacity of the battery. This has formed a unified understanding at home and abroad.

Lead acid batteries

Lead-acid battery is a very complex chemical reaction system. External factors such as the size of charge and discharge current and its operating temperature will affect the performance of the battery. It is a key technology to calculate the SOC value of the battery and determine the running mode of the car according to the running state of the car and other parameters.

Lead-acid battery has the longest application history, and is also the most mature and low-cost battery, which has achieved mass production. But it has low specific energy, high self-discharge rate and low cycle life. At present, the main problem is the short stroke of one charge. Recently developed third-generation cylindrical sealed lead-acid batteries and fourth-generation TMF(foil coil 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 the ohmic heat in the rapid charging process and extend the battery life.

Pulse phased constant current fast charging method can be well adapted to the hybrid electric vehicle lead-acid battery in the substation exile state, charging time is short, so that the battery SOC charged state is always maintained in the range of 50-80% requirements. Tests have shown that it only takes 196 seconds to charge a battery from 50% C to 80% C. This charging method basically meets the acceptance curve of the battery. The temperature rise of the battery is small, resulting in less gas, little pressure effect and short charging time.

The optimal charging method is that the charging current always follows the inherent charging acceptance curve. In the process of charging, the charging acceptance rate remains unchanged. With the increase of time, the charging current decreases according to the inherent charging acceptance curve (exponential curve), so that the charging time is the shortest. Pulse depolarizing charging method can achieve rapid and efficient charging, but the equipment is expensive and is not suitable for some batteries.

A new VRLA battery for electric vehicles developed by a Japanese company, whose voltage specifications are monomer 2V and 4V, adopts lean liquid type and horizontal plate design. The spacing between the rice plates is very small, and there will be no electrolyte layering. The slabbed material moves downward and is blocked by the electrode plate, and there is no slabbed material accumulation at the bottom of the battery.

Ectreosorce company 12 vl12a h. battery electric vehicles use level, the rate of discharge in 3 hours quality than the energy for the 50 w · 11 / kg, 80% Ⅸ) D (depth of discharge) the cycle life of more than 900 times.

Lead-acid batteries for electric vehicles of German sunshine company are designed with colloidal electrolyte, and the life expectancy of 6V and 160A·h batteries can reach 4 years after detection, with the advantages of large heat capacity and small temperature rise.

In 1994, American Arias company launched the bipolar lead-acid battery for electric vehicles, whose structure technology is unique. The cell's operating current is only perpendicular to the electrode plane and passes through a thin double electrode, so it has very little ohmic resistance. The technical parameters of the bipolar lead-acid battery for electric vehicles developed by BPC company in the United States are as follows: the combined voltage is 180V, the battery capacity is 60A·h, the discharge rate specific energy is 50W·h/kg, and the cycle life can reach 1000 times.

Sweden OPTLMA roll electric vehicle lead-acid battery, product capacity of 56A·h, the starting power can reach 95kW, than the ordinary 195A·h VRLA battery starting power is even larger, and the volume of a quarter smaller.

Lithium-ion batteries

The characteristics and price of lithium ion battery are closely related to its positive electrode materials, in general, positive electrode materials should meet: ? in the required range of charge and discharge potential, with electrolyte solution electrochemical compatibility; The moderate electrode process kinetics; (3) high reversibility; Of all lithium state in the air stability is good. With the development of lithium ion battery, the research of high performance and low cost anode materials is continuously carried out. At present, the research mainly focused on the lithium cobalt oxide, lithium nickel oxide, lithium and lithium manganese oxide of transition metal oxide, lithium cobalt oxide (LiCoO2) belong to - NaFeO2 type structure, with a 2 d layer structure, suitable for lithium ion embedded. Its preparation technology is simple, stable performance, high specific capacity and good cycle performance, its synthetic methods are mainly in high temperature solid method and in low temperature solid method, and oxalic acid precipitation method, sol-gel method, the method of cold and hot, soft chemical method such as organic hybrid method. lithium manganese oxide is a modification of traditional anode materials. Currently, spinel LixMn2O4 is widely used. It has a three-dimensional tunnel structure, which is more suitable for the delocking of lithium ions. Rich in raw materials, low cost, no pollution, overcharge resistance and better thermal safety, the safety of the battery protection device requirements are relatively low, is considered to have the most potential development of lithium ion battery anode material.

In the 1990s, the Japanese company SONY first developed the lithium battery for electric vehicles, which was made of lithium cobalt oxide material at that time, with the disadvantage of inflammable and explosive. At present, China's shin-guo unita guli power supply co., ltd. has developed a 100Ah lithium battery with lithium manganate as the positive electrode material, which solves the shortage of lithium cobalt battery.

As of October 2006, there are more than 20 automotive companies in the world for lithium ion battery research and development. For example, Fuji heavy industries cooperated with NEC to develop a cheap single Cell (Cell) manganese lithium ion battery (i.e. Toshiba developed a rapid rechargeable lithium-ion battery pack, in addition to the small, large capacity characteristics, the use of nano-particle homogenization fixation technology, can make the lithium ion adsorption evenly on the battery cathode, can be charged to 80% of its capacity in one minute, and then after six minutes can be fully charged. The main battery plant JohnsonControls for electric car demand characteristics of lithium ion battery in September 2005 set up r&d sites in Milwaukee, Wisconsin, in January 2006, another funding 50% and the French factory Saft JohnsonControls - created SaftAdvancedPowerSolution (JCS). JCS in August 2006, dominated by the U.S. department of energy (DOE) 2 years USABC (UnitedStatesAdvancedBatteryConsortium) pure electric vehicle research and development of lithium ion battery project contract, provide high power lithium ion battery. The research level of lithium ion battery in China has exceeded the long-term target set by USABC in 2010. Since 1997 suzhou star constant as the national industrialization test lithium ion power battery industrialization demonstration project base, its research and development of power battery has passed the American UL and European independent organization ExtraEnergy test certification, and in suzhou to build the first power lithium ion battery production line and trial-produce smoothly, has to realize batch production.

During the 2008 Beijing Olympic Games, 50 12-meter-long lithium-ion electric buses were in service in the central area of the Olympic Games, marking the first large-scale use of lithium-ion battery electric buses in the world. Electric bus charging time long, it is to ensure that the electric car run don't disconnect: electric cars into the charging station, two robots to take out the battery pack in the automobile chassis, stay in the channel, and then taking it from has filled channel fully charged battery, it in electric vehicle chassis, the entire process takes only 8 minutes.

France's Citroen, Renault and Peugeot have completed user testing of their electric commercial vehicles powered by lithium-ion batteries. Bordeaux is one of the demonstration and application cities of electric cars in France, with 500 electric cars of various types, mainly used in municipal vehicles and electric minibuses, and 20 parking lots with supporting charging facilities for electric cars, 16 of which are equipped with fast charging devices. The charging process of lithium battery is different from that of lead-acid battery. The Lipo charger has a very small chip with very few external components, and because the chip itself is very small (2mm 3mm), the whole charger is very small. Lipo's battery is charged when the battery voltage is very low (0. When 5V), charge with a small current, and the typical value of this current is less than 0. 1C, if the voltage is high enough but below 4. At 2V, the battery is charged with a constant current. Most manufacturers specify a current of 1C during this process, and the voltage on the battery will not exceed 4. At 2V, during a constant voltage period, the current passing through the battery will slowly drop, while the battery charging continues. Battery voltage up to 4. At 2V, the charging current drops to zero. At 1C, the battery is charged to about 80~90%, and then transformed into a trickle charge. Two parameters can be adjusted in the charger: normal charging current and trickle charging current (when the battery is "full"). It should be noted that the charging current should be carefully selected, and the charging current should be kept lower than the maximum recommended by the manufacturer.

At present, lead-acid batteries are mainly used in the power batteries of electric cars in France, and the second-generation lithium-ion electric cars have been put into test operation. The charging device of its electric vehicle adopts conduction charging mode. Conduction charging mode includes conventional charging device and rapid charging device. Conventional charging is provided with standard civil ac power interface by charging facilities, with simple leakage protection function. It takes 6 ~ 7 hours to complete charging for electric cars with on-board charger, which has many applications. Quick charging is provided by the dc output of the charger for quick charging of electric cars. An electric car with a residual power of 25% can be charged in 25 minutes. There are few quick charging applications.

Charging facilities have a unified charging interface, and the standard ac power interface is one of the important technical directions. Using ordinary household socket and a special charging cable with a special plug, it can provide ac power for electric cars equipped with on-board charger.

Further development of lithium-ion battery technology is needed. (1) at present, most of the lithium ion batteries of pure electric vehicles published by various enterprises are laboratory test data, such as acceleration performance, charging time, continuous mileage, etc., which must be further verified for reliability and mass production quality control under the actual operation in a complex external environment. (2) the diaphragm material required by lithium ion battery has not made a substantial breakthrough, and its price is expensive, accounting for more than 30% of the cost of power battery. If the scale production technology is realized on this material, the cost can be greatly reduced

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