What is the main source of energy for electric vehicles

The main source of energy for electric vehicles must be high-voltage power batteries. The biggest difference between an electric car and a traditional fuel car is the energy source. The energy source of a fuel car is gasoline, which is ignited and exploded to do work through spark plugs, and exhaust gases are discharged into the atmosphere through feedback control and emission treatment of the engine.

With the increase in the number of cars, environmental pollution and energy consumption is becoming more and more serious. With the development of the times, zero-emission electric vehicles have begun to develop. It can be said that every country is vigorously developing new energy vehicles. China's development of new energy vehicles is "bend the road to overtake the car", focusing on the development of pure electric vehicles, especially in some cities with better economic development, electric vehicles can be seen everywhere. Then, let's analyze the energy of electric vehicles - high-voltage power battery.

Analysis of the structure of electric vehicles

Electric vehicles are mainly composed of electric drive system, mechanical transmission system, battery system and charging system, in which the electric drive system is the core of the entire electric vehicle to achieve energy conversion, such as the battery's electrical energy output to the motor, the mechanical transmission device will be transmitted in the form of mechanical energy transmission of electrical energy to the drive wheels.

Let's take the pure electric vehicle structure as an example, as shown in the figure below. When the car is traveling, the electrical energy output from the battery is calculated by the control system, the rotation of the motor is controlled by the controller (inverter), and the torque output from the motor is the wheel forward or backward through the transmission system.

The control system can convert energy according to the speed of the vehicle in various road conditions, the opening signal of the gas pedal position sensor and acceleration. The motor has a different inverter and a different controller. The controller converts DC power from the power battery to AC power to drive the AC motor.

Analysis of power batteries for EVs

There are actually two types of power batteries on the market: nickel-metal hydride (NiMH) batteries and lithium iron phosphate (Li-FePO4) batteries. For example, Toyota's most fuel-efficient hybrid system, THS-II, uses Toyota Corolla, Lexus and Prius, Buick Grand Ville and Honda CRV and other brands, and the foreign Tesla Pure Electric Vehicle uses ternary lithium batteries, or lithium cobalt acid batteries.

Nickel-metal hydride batteries

Currently, most hybrid cars use nickel-metal hydride batteries. This type of battery has a nickel hydroxide positive electrode, a metal oxide negative electrode, and an electrolyte of 30% potassium hydroxide. The metal oxide works by the movement of hydrogen ions in an aqueous solution to produce an electric current, and then the hydrogen is gradually consumed at the negative electrode. The working principle is shown in the diagram below.

There is no problem of heavy metal pollution with NiMH batteries. NiMH batteries have high specific energy, which can be more than 70WH/kg, and specific power is 200W/kg. The rated voltage of a single cell is 1.2V, and usually 10 single cells form a 12V battery pack, and there are also 7 cells forming a 7.4V battery pack, such as the Prius, which has a capacitance of 6.5AH, and an overall battery voltage of 201.6V

Nickel-metal hydride batteries have a very strong charging and discharging capability . During operation, the anode releases oxygen and the cathode releases hydrogen. These two gases can easily combine into water inside the battery, keeping the internal pressure constant and basically eliminating the need to adjust the density of the electrolyte.

Lithium iron phosphate

The positive pole of lithium iron phosphate battery is lithium iron ferrite phosphate structure, the negative pole is graphite, the middle partition is polyethylene, the battery is equipped with organic electrolyte in the middle of the upper and lower sides. When the battery temperature is abnormal, the middle partition can block the passage of lithium ions, preventing the battery internal current short circuit.

When the battery is discharged, lithium ions precipitate from the negative graphite plate and reach the positive plate through the middle spacer, thus generating current; during charging, lithium ions precipitate from the positive electrode to the negative electrode under the action of electric potential.

LiFePO4 batteries have a cell voltage of 3.2V, a maximum voltage of 3.6V, and a maximum boiling point voltage of 2.0V V. These batteries have a winding structure in the shape of "18650". The battery has a diameter of 18 millimeters, a height of 65 millimeters, and a maximum capacity of 3100 mAh.

LiFePO4 batteries do not have a battery memory response, that is, in the process of using the car if you find that there is very little power left, you can find a nearby charging station for charging, will not affect the performance of the battery, and do not need to use up the last bit of power before charging. NiMH batteries are different. If used in plug-in hybrids, they need to be used after the battery has been fully charged for the first time. This is because the two types of batteries have different battery memory effects.

Summary

The main source of energy for electric vehicles is the power battery, which is divided into nickel-metal hydride (NiMH) batteries and lithium iron phosphate (LiFePO4) batteries, which are suitable for hybrid and pure electric vehicles respectively. After a long time of use, the performance of the original single battery will appear some differences, such as the voltage can not reach the original level, the range can not reach the required mileage and so on. Therefore, the battery must be tested in time after the fault is found.