I. The role of power batteries
In new energy vehicles, the battery that provides the power source for the vehicle is called the power battery. The function of the power battery is to receive and store high-voltage direct current (DC) electricity provided by on-board chargers, generators, regenerative braking devices, or external charging devices, and to provide high-voltage DC electricity for electric vehicles.
The power battery is the core component of a pure electric vehicle and one of the most expensive components in a new energy vehicle. The performance of the power battery directly determines the actual value of the vehicle.
In pure electric vehicles, the power battery serves as the power source for the entire vehicle. It replaces the petroleum energy used in gasoline-powered vehicles and is equivalent to the "heart" of the pure electric vehicle, providing continuous and stable energy to drive the vehicle.
II. Classification of Power Batteries
There are various types of power batteries used in new energy vehicles. Through technological development and replacement, the main types currently used in new energy vehicles are: lead-acid batteries, nickel-metal hydride batteries, and lithium-ion batteries.
Lead-acid batteries, used as low-voltage auxiliary batteries in new energy vehicles, provide low-voltage operating power to the vehicle's ordinary low-voltage electrical system. Currently, lead-acid batteries are no longer used as power batteries.
Nickel-metal hydride (NiMH) batteries are mainly used in Toyota's hybrid and plug-in hybrid vehicles, such as the Toyota Camry Hybrid, Corolla Hybrid, and Levin Hybrid, while the Prius plug-in hybrid also uses NiMH batteries.
Lithium-ion batteries are widely used in pure electric vehicles, such as the BYD E6, BAIC EV200/160, Roewe E50, Changan Eado EV, and BMW i3. The characteristics of various types of power batteries are shown in the table below.
III. Applications of Nickel-Metal Hydride Batteries
1. Characteristics of nickel-metal hydride batteries
Nickel-metal hydride (NiMH) batteries are alkaline batteries and a new type of green battery developed in the 1990s. They were widely used in the 1990s with the large-scale adoption of electric vehicles, especially hybrid electric vehicles.
Nickel-metal hydride batteries exhibit almost no change in characteristics under the irregular charging and discharging conditions of hybrid vehicles, making them a suitable choice for hybrid vehicles.
The characteristics of nickel-metal hydride batteries are as follows:
Nickel-metal hydride (NiMH) batteries offer numerous advantages, including being pollution-free, having high specific energy, high power output, rapid charging and discharging, and durability. Compared to lead-acid batteries, NiMH batteries are characterized by higher specific energy, lighter weight, smaller size, and longer cycle life.
The basic unit of a nickel-metal hydride battery is a single cell with a voltage of 1.2V. They are combined into nickel-metal hydride battery assemblies with different voltages and charge amounts according to usage requirements.
2. Applications of nickel-metal hydride batteries
The Toyota Prius, Camry Hybrid, Corolla Hybrid, and Levin Hybrid models all utilize Toyota's THS-II hybrid drive system. The power battery is a nickel-metal hydride (NiMH) battery, installed in the trunk behind the rear seats. The power battery consists of 34 battery modules, each composed of six 1.2V NiMH cells, with a total voltage of 7.2V. The nominal voltage of the power battery is 244.8V. The composition and installation location of the power battery are shown below.
IV. Principles and Applications of Lithium-ion Power Batteries
1. Characteristics of lithium-ion power batteries
Lithium-ion batteries have advantages such as high energy density and strong high-power charge and discharge capabilities, and have gradually become the preferred choice for electric vehicles. Depending on the cathode material, lithium-ion batteries in electric vehicles can be classified into lithium manganese oxide batteries, lithium cobalt oxide batteries, lithium iron phosphate batteries, and ternary lithium batteries, among others.
BYD E6 electric vehicle, BAIC EV200/160, GAC New Energy AG, and Roewe E50 all use lithium iron phosphate batteries, while Tesla electric vehicles generally use ternary lithium batteries.
Lithium-ion batteries come in two shapes: square and cylindrical. A lithium-ion battery consists of a positive electrode, a negative electrode, a separator, an electrolyte, and a safety valve.
The charging temperature of lithium batteries should generally be limited to the range of 0–60°C. Excessive heat can damage the battery and may cause it to explode; while insufficient heat will not pose a safety risk, it will make it difficult to fully charge the battery.
2. Applications of lithium-ion batteries
Currently, lithium-ion batteries are widely used in various types of electric vehicles both domestically and internationally.
The BYD E6 uses a lithium iron phosphate (LFP) battery, which is a lithium-ion battery with lithium iron phosphate as the positive electrode material. The BYD E6's battery has a single cell voltage of 3.3V, and consists of 11 battery modules, totaling 96 cells, with a nominal voltage of 316.8V. The battery is installed at the bottom of the vehicle.
The Zotye Cloud 100S lithium-ion battery is installed at the bottom of the vehicle. The battery has a rated voltage of 108V, a maximum output current of 160A, a maximum input current of 120A, a maximum output power of 37.8kW, and a minimum output voltage of 90V.
The Zotye Taijie pure electric microbus uses a ternary lithium-ion battery with a rated voltage of 324V, a maximum output power of 64.8kW, and an operating temperature range of -20℃ to 60℃. The battery is installed at the bottom of the vehicle.
The Tesla Model S's battery pack is installed between the front and rear axles of the vehicle's chassis, occupying almost the entire chassis. The battery pack consists of over 7,000 18650 lithium-ion cells, with a capacity of 85 kWh and a DC power rating of 400V. The battery pack is composed of 16 battery groups connected in series, with each group containing 444 lithium-ion cells, arranged in parallel with 74 cells connected in each group. Therefore, the Tesla Model S battery pack consists of 7,104 18650 lithium-ion cells.
The BMW i8/i3 uses lithium-ion batteries supplied by Samsung SDI of South Korea. Each individual battery has a rated voltage of 3.7V, and 12 individual batteries make up a battery module. A total of 8 battery modules constitute a high-voltage power battery with a rated voltage of 360V.
