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Lead-acid Battery and its charging technology
Lithium-ion battery and its charging technology
Abstract: The electric vehicle power battery has been developed from lead-acid batteries, hydrogen-nickel batteries and fuel cells to lithium-ion batteries. Shortening the charging time of the power battery and increasing the charging capacity of the power battery are the key technologies for charging.
Power batteries are one of the key technologies of electric vehicles. In 1881, Gustave Trouve used the lead-acid battery when he built the world's first electric tricycle. At present, there are still many hybrid and pure electric vehicles that use a new generation of lead-acid batteries. In the past ten years, lithium-ion power batteries have been used in the production of electric vehicles, and they have increasingly shown their superiority.
American scholar Max MAMas proposed a current theorem acceptable for battery charging through a large number of experiments: 1) For any given discharge current, the charging current of the battery is proportional to the square root of the discharge capacity; 2) for any depth of discharge, 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) one battery is discharged through several discharge rates, and the acceptance current is the sum of the discharge currents of the respective discharge rates. That is to say, it is possible to increase the charge acceptable current of the battery by discharging. When the battery charge acceptance capability is reduced, a discharge can be added during the charging process to improve the acceptability.
The performance and life of an automotive power battery are related to many factors, in addition to its own parameters, such as battery plate quality, electrolyte concentration, etc. There are external factors, such as battery charge and discharge parameters, including charging mode, charging end voltage. , charge and discharge current, depth of discharge, and so on. This gives the battery management system BMS a lot of difficulty in estimating the actual capacity and SOC of the battery, and many variables need to be considered. The battery management system of the WG6120HD hybrid electric vehicle is based on the management of SOC values. SOC (state of charge) refers to the state of change 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.
Lead-acid batteries are a very complex chemical reaction system. External factors such as the magnitude of the charge and discharge current and its operating temperature can affect the performance of the battery. Calculating the SOC value of the battery and determining the operating mode of the car according to the running state of the car and other parameters is a key technology of the electric vehicle.
Lead-acid batteries have the longest application history and are the most mature and lowest-cost batteries, which have been mass-produced. However, it is lower than energy, has a high self-discharge rate, and has a low cycle life. The main problem currently exists is that the journey of one charge is short. 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 the ohmic heat during fast charging and prolong the life of the battery.
The pulse phased constant current fast charging method can well adapt to the requirement that the charging time of the lead-acid battery of the hybrid vehicle is short in the state of variable current discharge, so that the SOC of the battery state of charge is always maintained within the range of 50%-80%. Tests have shown that it takes only 196 seconds to charge the battery from 50% C to 80% C. This charging method basically satisfies the acceptance curve of the battery, the temperature rise of the battery is small, the gas generation is small, the pressure effect is not large, and the charging time is short.
The optimal charging method is that the charging current always follows the inherent charging acceptance curve. During the charging process, the charging acceptance rate remains unchanged. As time increases, the charging current decreases according to the inherent charging acceptance curve (the exponential curve decreases), so that the charging time The shortest. The pulse depolarization charging method enables fast, high-efficiency charging, but the equipment is expensive and not suitable for some batteries.
The new VRLA battery for electric vehicles developed by Japanese companies has a voltage specification of 2V and 4V. It is designed with lean liquid and plate. The spacing between the rice plates is small, and there is no stratification of the electrolyte. The lower movement is blocked by the plates, and there is no accumulation of debris at the bottom of the battery.
Ectreosorce's 12V l12A·h electric vehicle horizontal battery uses a 3-hour rate discharge mass ratio of 50W·11/kg and 80% IX)D (discharge depth) with a cycle life of more than 900 cycles.
German Sunshine's lead-acid battery for electric vehicles adopts colloidal electrolyte design. After testing, the expected life of 6V, 160A·h battery can reach 4 years, with the advantages of large heat capacity and small temperature rise.
In 1994, Arias of the United States introduced a lead-acid battery for bipolar electric vehicles, which has a unique structure and technology. The operating current of this battery is only perpendicular to the plane of the electrode and passes through the thin two electrodes, so it has an extremely small ohmic resistance. The technical parameters of the lead-acid battery for bipolar electric vehicles developed by American BPC Company are: 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.
The lead-acid battery for rolling electric vehicles introduced by OPTLMA of Sweden has a product capacity of 56A·h and a starting power of 95kW, which is larger than the normal 195A·h VRLA battery starting power and a small one-fourth.
2 lithium ion battery
The characteristics and price of a lithium-ion battery are closely related to its positive electrode material. In general, the positive electrode material should satisfy: (1) electrochemical compatibility with the electrolyte solution in the required charge and discharge potential range; (2) mild Electrode process kinetics; (3) highly reversible; (4) good stability in air in full lithium state. With the development of lithium-ion batteries, research work on high-performance, low-cost cathode materials is constantly underway. At present, the research focuses on lithium transition metal oxide lithium cobalt oxide (LiCoO2) such as lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide, which belongs to the -NaFeO2 type structure and has a two-dimensional layered structure suitable for lithium ion. The preparation process is simple, stable in performance, high in specific capacity and good in cycle performance. The synthesis methods mainly include high-temperature solid phase synthesis and low-temperature solid phase synthesis, as well as oxalic acid precipitation, sol-gel method and cold. Soft chemical methods such as thermal methods and organic mixing methods. Lithium manganese oxide is a modification of the traditional positive electrode material. At present, spinel type LixMn2O4 is widely used, which has a three-dimensional tunnel structure and is more suitable for deintercalation of lithium ions. Lithium manganese oxide is rich in raw materials, low in cost, non-polluting, overcharge-resistant and heat-safe. It has relatively low requirements for battery safety protection devices and is considered to be the most promising cathode material for lithium-ion batteries.
In the 1990s, Sony Corporation of Japan first developed a Lithium Battery for electric vehicles. At that time, it used lithium cobalt oxide material, which had the disadvantage of being flammable and explosive. At present, China Xinguo Anmeng Guli Power Co., Ltd. has developed a 100Ah power lithium battery with lithium manganate as a positive electrode material, which solves the shortage of lithium cobalt oxide battery.
As of October 2006, more than 20 automotive companies around the world have been developing lithium-ion batteries. For example, Fuji Heavy Industries and NEC have jointly developed an inexpensive single-cell (Cell) manganese-based lithium-ion battery (ie, lithium manganate battery), which has a lifespan of 12 years and 100,000 kilometers in an in-vehicle environment, which is equivalent to the life of a pure electric vehicle. . Toshiba developed a fast-charging lithium-ion battery pack. In addition to the small-sized and large-capacity battery, it adopts a technology that enables nano-scale particles to be uniformized and fixed, so that lithium ions can be uniformly adsorbed on the negative electrode of the battery, which can be used in one minute. Charge it to 80% of its capacity and fully charge it in 6 minutes. Johnson Controls, a major battery manufacturer in the United States, set up a research and development facility for electric vehicle demand in Milwaukee, Wis., in September 2005. In January 2006, it also invested 50% to establish Johnson Controls-Saft Advanced Power with French battery plant Saft. Solution (JCS). In August 2006, JCS undertook a two-year USBC (United States Advanced Battery Consortium) lithium-ion battery research and development program contract led by the US Department of Energy (DOE) to provide high-power lithium-ion batteries. China's research level in lithium-ion batteries has a number of indicators that exceed the targets set by the USABC's 2010 long-term indicators. Suzhou Xingheng, which began industrial testing in 1997, is the national lithium ion power battery industrialization demonstration project base. Its power battery pack has passed the test certification of UL and the European independent organization Extra Energy, and built the first in Suzhou. The production line of the power lithium-ion battery has been successfully trial-produced, and mass production has been realized.
During the 2008 Beijing Olympic Games, 50 lithium-ion electric buses with a length of 12 meters were served in the Olympic Center. This is the first large-scale use of lithium-ion battery electric buses in the world. The electric bus has a long charging time, which ensures that the electric car runs without dislocation: the electric car enters the charging station, and the two robots take out the battery pack in the car chassis, put it into the charging channel, and then take it off from the charged channel. The electric battery pack is replaced by the electric vehicle's chassis, and the whole process takes only about 8 minutes.
French Citroen, Renault, and Peugeot Motors have completed user test operations for electric commercial vehicles using lithium-ion power batteries. Bordeaux is one of the French demonstration cities for electric vehicles. There are 500 electric vehicles of various types, mainly used in municipal vehicles and electric minibuses, and there are 20 parking lots with electric vehicle charging facilities, including 16 configurations. A fast charging device. The charging process of a lithium battery is different from that of a lead-acid battery. The lithium polymer (Lipo) charger's integrated block has very few external components. Since the manifold itself is extremely small (2mm x 3mm), the entire charger is also very small. Lipo battery charging process is: when the battery voltage is very low (0.5V), charge 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 low At 4.2V, the battery is charged with a constant current. Most manufacturers will specify the current of 1C in this process. The voltage on the battery will not exceed 4.2V. During the constant voltage, the current through the battery will slowly drop, and the battery will slowly drop. The charging continues. When the battery voltage reaches 4.2V and the charging current drops to 0.1C, the battery is charged to 80~90%, and then converted to trickle charge 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 charge is "full"). It should be noted that the charging current should be carefully selected and the charging current should be kept below the maximum recommended by the manufacturer.
The current use of French electric vehicle power batteries is mainly lead-acid batteries, and the second-generation lithium-ion electric vehicles have been put into test operation. Its electric vehicle charging device adopts a conductive charging method. Conductive charging methods include two types of conventional charging devices and fast charging devices. Conventional charging is provided by the charging facility with a standard civilian AC power interface. It has a simple leakage protection function. It charges the electric vehicle with the car charger, and it takes 6-7 hours to complete the charging. Fast charging is provided by the charger with DC output for fast charging of electric vehicles.
An electric car with 25% residual power can be recharged in 25 minutes, with less rapid charging applications, mainly for industry users and street emergency.
The charging facility has a uniform charging interface, and the standard AC power interface is one of the important technical directions. AC power can be supplied to an electric vehicle equipped with a car charger by using an ordinary household socket and a charging dedicated cable with a dedicated plug.
Lithium-ion power battery technology has yet to be further developed. (1) Most of the pure electric vehicle lithium-ion batteries announced by various enterprises are laboratory test data, such as acceleration performance, charging time, continuous mileage, etc., and must be further verified under the actual operation of complex external environment. Sex, as well as production batch quality control. (2) The diaphragm material required for lithium ion batteries has not been substantially broken, and the price is expensive, accounting for more than 30% of the cost of the power battery. If large-scale production technology is realized on this material, the cost can be greatly reduced.
The PV Charge Controller works as a voltage regulator, its primary function is to prevent the battery from being overcharged by the P.V array, being overly discharged by the load, or both.
Controller types:
• Single Stage controllers:
This type of controllers prevents battery overcharging by switching the PV array off when the battery voltage reaches the state of charge set point. The array and battery are automatically reconnected when the battery voltage reaches a lower value called the charge resumption.
• Pulse Width Modulation (PWM) controllers:
PWM controllers are the most common controller on the market today. These charge the battery by rapidly switching the full charging current on and off when the battery reaches a fully charged state. The length of the charging current pulse gradually decreases as battery voltage rises, reducing the average current into the battery.
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