Electric vehicles rely heavily on their power sources, with the battery being the most critical component. Currently, the main challenge limiting the growth of electric vehicles is the performance of power batteries. Key performance indicators for these batteries include specific energy, specific power, and cycle life. For electric vehicles to compete effectively with internal combustion engine vehicles, it is essential to develop batteries that offer higher energy density, greater power output, longer lifespan, and lower costs.
**Lead-Acid Batteries**
Lead-acid batteries have a long history and are commonly used as starting power sources in traditional vehicles. They are also one of the earliest and most established options for electric vehicles. These batteries are known for their reliability, low cost, and easy availability of materials. Their specific power is generally sufficient for basic Electric Vehicle applications. However, they suffer from two major drawbacks: low energy density, leading to limited range on a single charge, and a relatively short lifespan, which increases long-term maintenance costs.
**Nickel-Metal Hydride (NiMH) Batteries**
NiMH batteries are alkaline batteries with a long service life and no memory effect. While their initial cost is high, their overall lifetime cost is more competitive due to superior energy and cycle performance. Companies like Ovonie, Toyota, and Panasonic have developed NiMH batteries with specific energy up to 80 W·h/kg and cycle life exceeding 600 cycles. In China, similar technologies have been developed, with unit cells offering energy densities around 65 W·h/kg. Despite their advantages, high production costs have limited mass adoption.
**Lithium-Ion Batteries**
Lithium-ion batteries are a modern, high-energy-density option with excellent characteristics such as light weight, no memory effect, and long cycle life. Compared to NiMH and nickel-cadmium batteries, lithium-ion offers significantly higher energy storage capacity. With only about 20-30% of its theoretical capacity currently utilized, there is great potential for future development. As a green technology, lithium-ion batteries do not pollute the environment and are well-suited for electric vehicles. China has made significant progress in developing independent lithium-ion battery technologies.
**Nickel-Cadmium (NiCd) Batteries**
NiCd batteries come after lead-acid batteries and offer better specific energy (up to 55 W·h/kg) and specific power (over 190 W/kg). They can be quickly charged and have a long cycle life—more than 2,000 cycles. However, they are expensive, about four to five times the price of lead-acid batteries. A major disadvantage is the memory effect, which reduces battery capacity if not fully discharged and recharged regularly. Additionally, cadmium is toxic, requiring careful recycling to prevent environmental harm.
**Sodium-Sulfur (NaS) Batteries**
NaS batteries offer high energy density, with a theoretical specific energy of 760 W·h/kg and actual values over 100 W·h/kg—three to four times that of lead-acid batteries. They also support high-current discharge and efficient charge-discharge cycles. However, they require operation at high temperatures (300–350°C), making them less practical for everyday use. Advances in insulation technology have improved stability, and Japan has led in developing this technology for fixed applications. Some models, like ABB’s B240K, show promising performance for electric vehicles.
**Nickel-Zinc (NiZn) Batteries**
New sealed NiZn batteries provide high power output and fast charging capabilities, making them ideal for electric vehicles. They have a specific energy of over 50 W·h/kg, good cycle life (≥500 cycles), and fast charging times. These batteries are compatible with existing lead-acid systems, making them an attractive replacement. Although slightly more expensive now, their cost is expected to decrease with increased production. Their ability to replace lead-acid batteries easily makes them a strong contender for the future.
**Zinc-Air Batteries**
Zinc-air batteries, also known as zinc oxide batteries, have a theoretical specific energy of 1350 W·h/kg, far exceeding lead-acid batteries. Current models already achieve 230 W·h/kg, showing great potential. These batteries can be “recharged†by replacing the zinc electrode, a process that takes just minutes. This feature could eliminate the need for widespread charging stations, making them convenient for public use. Though still in early stages, zinc-air batteries are being tested in various countries for use in postal vehicles and buses.
**Flywheel Batteries**
Flywheel batteries store energy mechanically, using kinetic energy from a spinning wheel. Unlike chemical batteries, they operate without harmful substances. When charged, the flywheel spins at high speeds, and when discharging, it converts mechanical energy back into electricity. These batteries offer high specific power (5000–10000 W/kg) and a long lifespan of up to 25 years. Some models claim a range of 5 million kilometers, making them a promising alternative for future electric vehicles.
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