Development status and prospect of electric vehicle battery

0 Preface

According to a recent "World Electric Vehicle" report, it is predicted that by 2007, the annual sales of electric vehicles in the world will reach more than one million (see Table 1), accounting for about 1.5% of the total global car sales. Although such a small share is insufficient This shows that electric vehicles have been commercialized, but it also shows that after decades of global efforts, especially in the past 10 years, electric vehicles have made great achievements in technology. The main basis for predicting the sales of electric vehicles is still people's concern about environmental pollution, especially in central cities. Some central cities in developed countries such as the United States and Europe are restricting the use of fuel-powered vehicles. The Chinese government also pays more and more attention to environmental protection, and regards environmental protection as an important part of implementing sustainable development strategies. China's environmental monitoring data shows that vehicle exhaust emissions are one of the main sources of urban air pollution. Beijing's motor vehicle exhaust emissions share the air pollutants CO, HC, and NOx at 63.4%, 73.5%, and 46%, respectively, and this share is higher during the non-heating period, at 80.3% , 79.1% and 54.8%. Shanghai is more serious, with 86%, 96% and 56% respectively; Guangzhou, Tianjin, Chongqing and many other large and medium-sized cities have a similar situation. Therefore, the relevant ministries and commissions of the State Council recently organized a "Clean Vehicle Action" conference to promote the cleanliness of fuel-fueled vehicles in China, the promotion and application of new gas vehicles and the implementation of major national electric vehicle technology industrialization projects.

Table 1 Electric vehicle sales forecast (thousands)

Table 1 Electric vehicle sales forecast (thousands)

At present, various types of electric vehicles, including battery-driven BEVs, HEVs driven by internal combustion engines and batteries, and FCEVs driven by fuel cells are facing the market for improved fuel-fueled vehicles and low-pollution vehicles that use various alternative fuels. competition. Electric vehicles must be further improved in performance and price in order to be able to stand firm in market competition.

See Table 2 for a comparison of various main electric vehicle batteries. At present, only lead batteries and nickel-cadmium batteries can be produced and supplied in large quantities. Because the performance-price ratio of nickel-cadmium batteries is not as good as lead batteries and there is cadmium pollution, MH2Ni batteries with excellent performance may enter the market soon. This article will focus on the progress of lead batteries, MH2Ni, lithium ion and sodium nickel chloride batteries. Proton exchange membrane fuel cell (PEMFC) is the only battery that can compete with fuel-powered vehicles in performance. This article will introduce its recent development.

Table 2 Comparison of various main electric vehicle batteries

Table 2 Comparison of various main electric vehicle batteries

1 Development of electric vehicle batteries

1. 1 lead storage battery

Lead storage batteries are currently the only electric vehicle batteries that can be mass-produced and supplied. It can be seen from Table 2 that its advantages are low price, shortcomings are low specific energy, and a short mileage (about 100km) on a single charge. A survey of private car daily trips in North America shows that 90% of daily trips under 160km account for 90%, and the remaining 10% of daily trips exceed 240km or even higher. Therefore, it has been suggested that if the specific energy of lead batteries can be appropriately increased to achieve a single charging journey of 160km, and rapid charging research is carried out, it is possible to make low-cost lead batteries meet the needs of most urban short-distance transportation and transportation electric vehicles Claim. To this end, the "Advanced Lead Storage Battery Consortium (ALABC)" established by the International Lead and Zinc Organization in conjunction with the world lead storage battery manufacturers in 1992 set the development goals for advanced lead storage batteries as:

Specific energy 50W · hkg- 1 (160km for one charge)

Specific power 150Wkg- 1

Price "150 USD / kW · h

Cycle life 500 times

Fast charging performance:

50% 5min

80% 15min

Among the above five indicators, the price and specific power are already possessed by general lead storage batteries, so the main forces for improvement are concentrated on the three indicators of specific energy, cycle life and fast charging performance.

(1) The increase of specific energy mainly starts from reducing the weight of the grid and improving the utilization rate of the positive electrode active material. Studies have shown that increasing the tin content in the lead-calcium alloy can enhance the corrosion resistance and creep strength of the grid, thereby reducing the weight of the grid (Sn content 0.5% ~ 1%). Adding additives with strong acid absorption ability (such as foamed polypropylene) to the positive electrode active material can improve the positive electrode active material utilization rate by about 10%.

(2) The results of cycle life research indicate that there are four methods to improve the cycle life of lead storage batteries: (i) The grid alloy uses lead-calcium alloy with high tin content, which can overcome the early failure caused by the grid creep. (Ii) In order to prevent the expansion of the polar plate, the normal pressure of the polar plate is increased. The test proves that increasing the normal pressure from 8kpa to 40kpa can increase the cycle life from 200 times to 700 times. To this end, the diaphragm material needs to be improved to avoid loosening under pressure. (Iii) Adopt a reasonable charging system, especially to accurately grasp the charging amount and charging rate in the later stage of charging to ensure full charge. (Iv) Improve the negative electrode expansion agent to avoid the hardening of the negative electrode active material sponge lead after prolonging the charge and discharge cycle life.

(3) Fast charging Due to the recent development of fast charging technology, the concept of poor fast charging performance of traditional lead storage batteries has changed. Experiments show that most valve-regulated lead-acid batteries can withstand the fast charging system (50% soc, 5min; 80% soc, 15min). Moreover, a reasonable fast charging system and method are not only harmless but also beneficial to prolong battery life. Abroad, the rapid charging method has been extended from a single battery to the entire battery, and tested in the vehicle. The ALABC report published in 1998 shows that through research and improvement, the specific energy of valve-regulated lead-acid batteries is expected to increase to twice that before the improvement, the cycle life may be increased to 10 times the original, and the charging time is shortened by an order of magnitude. At present, ALABC is vigorously supporting the research and improvement of all relevant parties. If the above research improvement goals can be achieved in the production of lead storage batteries, then lead storage batteries will play an important role in the recent industrialization of electric vehicles.

During the “Eighth Five-Year Plan” period in China, the State Science and Technology Commission and the State Planning Commission supported the research and development of lead storage batteries for electric vehicles as a key project. Many units engaged in the design and development of electric vehicles believe that although lead batteries have lower energy than that, but in the case where China expects to place buses and taxis as the top priority for the use of electric vehicles, lead batteries can be mass-produced because of their low prices. The advantage of supply is still feasible in the recent electric vehicle industrialization project plan.

Table 3 lists the recent research and development goals of sealed lead-acid batteries for electric vehicles in China. The first phase emphasizes the improvement of overall battery performance, and the second phase focuses on the improvement of battery cycle life and uniformity of battery performance.

Table 3 Development goals of sealed lead-acid batteries for electric vehicles in China

Table 3 Development goals of sealed lead-acid batteries for electric vehicles in China

From 1991 to 1995, Baoding Jinfengfan Battery Co., Ltd., Light Industry Chemical Power Research Institute and other units participated in the development of sealed lead-acid batteries for electric vehicles. Among them, Fengfan Battery Factory adopts positive and negative electrode paste flat electrode, Light Industry Chemical Power Research Institute adopts its patented elliptical tube electrode plate, and the negative electrode is still paste electrode. The results of the trial production show that the lead-acid batteries for electric vehicles in China can achieve the first stage of development goals except for the cycle life.

At present, the sealed lead-acid batteries of Fengfan Company and Zhenjiang Battery Factory have been tried on modified cars in China. Among them, 20 12V · 150A · h batteries are used in the van, the maximum speed is 80km / h, and the driving distance is 100km at a time. · 150A · h battery pack, the vehicle speed can reach 80km / h, and it can drive 100km on one charge. The biggest problem is poor uniformity. Individual batteries need to be replaced if the accumulated mileage is less than 1 000km.

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A D-sub connector is a form of connector commonly found in electronic and computer systems. It consists of a D shaped metal band and two or more parallel rows of either pin contacts (male) or socket contacts (female). D-sub connector contacts can vary in size, material, current rating, length and resistance.

The most common type of connector is the crimp contact. These are assembled by inserting a stripped wire end into the cavity at the rear of the contact. The cavity is then crushed using a crimp tool, gripping the contact to the wire.

What are D-sub connector contacts used for?
The D-sub connector contacts carry the signal from the source to the destination across the D–sub connection.

Types of D-sub connector contacts
Most D-sub connectors are supplied with contacts ready in place. Contacts can be replaced if damaged or if the application of the D-sub connector is to be changed from the original design specification.

High-current, high-voltage, or co-axial inserts require larger contacts. The material of the D-sub connector contact can be changed if the robustness or quality of the connection needs to be improved.

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