The history of the battery can be traced back to a century and a half ago. The lead-acid battery invented by French scientist Plante in 1859 was the world’s first rechargeable battery. From 1889 to 1901, Jungner of Sweden and Edison of the United States successively developed nickel-iron batteries and nickel-cadmium batteries. These batteries have undergone several structural, technological, and material improvements in practical applications, and their performance has been greatly improved. With the advent of nickel-metal hydride batteries (all called metal hydride nickel batteries) in the 1980s and the emergence of lithium-ion batteries in the 1990s, the performance and life of the batteries have been greatly improved. At the same time, the cycle from the successful development of the battery to the large-scale production is also greatly shortened. So far, the batteries commonly used in electric vehicles include lead-acid batteries, nickel-metal hydride batteries, and lithium-ion batteries.
Because of its safety, durability and low price, lead-acid batteries have been the first choice for power supply for electric vehicles for nearly a century after they were invented. The nickel-iron battery has a solid structure and a long service life. It has also been successfully applied to electric vehicles such as forklifts and milk delivery vehicles. However, due to the low energy density and power density of the two batteries, the weight and volume of the battery pack are too large, and the use of electric vehicles is decreasing. The performance of nickel-cadmium batteries is significantly better than that of lead-acid batteries. They have been used in large quantities in electric vehicles, but due to heavy metal pot pollution, production has been stopped.
Sodium nickel chloride (ZEBRA) batteries have high energy density. The application of ZEBRA batteries in electric vehicles has been studied since the 1970s. However, the biggest disadvantage of ZEBRA batteries is that the operating temperature is above 270°C, which limits their use. Application on electric vehicles.
The energy density and power density of nickel-metal hydride batteries are better than lead-acid batteries and nickel-cadmium batteries, and are increasingly being used in pure electric vehicles and hybrid vehicles.
Lithium-ion batteries have better performance than nickel-metal hydride batteries and ZEBRA batteries, and have attracted more and more attention in recent years, and their applications in electric vehicles have also increased.
As the power source of automobiles, all these batteries, although new varieties continue to appear, their performance continues to improve, and technology continues to advance, they still cannot fully meet the requirements of electric vehicles. The existing problems can be summarized as follows.
(1) Low energy density
The mass energy density and volume energy density of the battery are very low. The mass energy density of lead-acid batteries is 35~40W·h/kg, the mass energy density of lithium-ion batteries can reach 150W·h/kg, and the gasoline is 10000~12000W· h/kg. A car with 50kg of gasoline can travel more than 600km, while the same type of electric car with a 400kg lead-acid battery can only travel about 100km on a single charge.
Due to the low energy density of batteries, cars have to carry a large number of batteries. For example, the pure electric car EV-1 developed by General Motors in the United States has a weight of 998kg and a lead-acid battery pack of 395kg. The ratio of the weight of the vehicle to the weight of the battery is about 5: 2. Part of the electric energy stored in the battery is consumed by the weight of the battery, which reduces the operating efficiency of the car; at the same time, it also reduces the performance of the car, such as acceleration, maximum speed, maximum gradeability, and braking performance. In addition, this also adds great difficulty to the vehicle design.
(2) The ability to accept fast charging is poor, and the charging time is long
Judging from the current battery charge acceptance capabilities and smart charging equipment, it is still difficult to charge electric vehicle battery packs as quickly as refueling internal combustion engine vehicles. At present, for safety and guarantee of battery life, it is recommended to use C/3 current charging for lithium-ion batteries, so it takes at least 3h to fully charge a fully discharged battery. According to the current charging acceptance capacity of lithium-ion batteries, it usually takes 3~5h. Even if a relatively fast 1C constant current charge is used, it takes more than 1h. Long charging time is another problem in the promotion and application of electric vehicles.
(3) The battery is expensive
If relatively cheap lead-acid batteries are used, the price of a battery pack for a light-duty electric bus is nearly 20,000 yuan, but it can only travel less than 100km on a single charge. For electric vehicles using lithium-ion batteries, although the driving range on a single charge is greatly improved than that of lead-acid batteries, the current price is several times or even ten times higher than that of lead-acid batteries.
(4) The use of car accessories is restricted
Due to the limited amount of electric energy that batteries can carry in electric vehicles, the use of electric energy has to be caressed about. The selection of electric auxiliary systems for vehicles (such as air conditioning, power steering, braking systems, etc.) must take full account of the impact on the electric energy consumption of electric vehicles.
With the development of technology, the performance of batteries has made great progress, and the above-mentioned problems have continuously reduced the degree of restriction on the development of electric vehicles. Figure 1 shows the performance comparison of current power batteries commonly used in electric vehicles. Driven by the pressure of energy and environmental protection, battery technology will continue to advance and develop, and related problems are expected to be fundamentally resolved.