The core technology of new energy vehicles mainly refers to the battery, motor and electronic control, which is often referred to as the “three electric” system. Battery, that is, the power battery of new energy vehicles, which mainly affects the range and charging speed of new energy vehicles.

1, new energy vehicle power battery overview

The power battery is the power source of electric vehicles, is the energy storage device, but also the key factor restricting the development of electric vehicles. To enable electric vehicles to compete with fuel vehicles, the key is to develop power batteries with high specific energy, high specific power, long service life and low cost.

(1) Commonly used words and common performance indicators of power battery for electric vehicles

State Of Charge (SOC): the percentage of remaining battery capacity and total capacity.

State Of Health (SOH): Provides information on the health status of the battery.

Battery Management System (BMS): real-time monitoring of power battery operating parameters, fault diagnosis, SOC estimation, mileage estimation, short-circuit protection, leakage monitoring, display alarm, charging and discharging mode selection, etc., so as to ensure the efficient, reliable and safe operation of electric vehicles.

Specific energy (Wh/kg): the size of electric energy discharged per unit mass of electrode material, which marks the range capability of electric vehicles in pure electric mode.

Specific power (W/kg): the power that can be provided by the battery per unit mass, which is used to judge the acceleration performance and maximum speed of electric vehicles, and directly affects the power performance of electric vehicles.

Cycle life: the number of times a battery is charged and discharged for 1 week is an important indicator of power battery life. The more cycles, the longer the use of the power battery. The rate of battery discharge, i.e., a quantity of how fast or slow the discharge is.

Battery discharge C (times) rate: indicates the rate of battery discharge, i.e., a measure of how fast or slow the discharge is. The full capacity of the battery is discharged in 1h, known as 1C discharge.

Depth of discharge (DOD): the ratio of the capacity discharged by the battery to the rated capacity of the battery.

(2) Power Battery Performance Requirements for Electric Vehicles

As the energy storage device of the vehicle, the electric vehicle battery requires enough energy to meet a certain driving cycle and mileage, and also to provide the maximum power needed to achieve the specified acceleration performance of the vehicle. That is, the power battery is required to have good charging and discharging performance, high specific power and specific energy, low price, easy to use and maintain.

Power battery performance requirements

(3) Types of power batteries for electric vehicles

There are three types of power batteries commonly used in electric vehicles:

Chemical batteries: devices that utilize chemical energy to transform electrical energy, and there are two main types of batteries and fuel cells from the structural point of view.

Physical batteries: devices that rely on physical changes to provide and store electrical energy, such as supercapacitors, flywheel batteries and solar cells.

Biological batteries: the use of biochemical reactions to generate electricity devices, such as microbial batteries is the use of the anode of the battery to replace the oxygen or nitrate and other natural electron acceptors, through the continuous transfer of electrons to generate electricity.

Power battery classification

2、Storage Battery

Storage battery is a kind of chemical battery, its work is characterized by the battery discharge, can use the charging method to make the internal active material regeneration, that is, the electrical energy is stored as chemical energy, need to be discharged when the chemical energy is converted to electrical energy.

Batteries can be divided into lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries and so on according to the different materials of positive and negative electrodes.

(1) Lead-acid battery

Lead-acid batteries use metallic lead as the negative electrode, lead dioxide as the positive electrode, and sulfuric acid as the electrolyte, when discharging, lead and lead dioxide react with the electrolyte to generate lead sulfate. When charging, the reaction process is just the opposite.

Lead-acid batteries can be divided into traditional maintenance-free lead-acid batteries and valve-regulated sealed lead-acid batteries according to the electrolyte and battery tank structure.

Lead-acid battery structure

(2) Nickel-metal hydride battery

Nickel-metal hydride batteries use hydrogen storage alloy as the negative electrode, nickel oxide as the positive electrode, potassium hydroxide aqueous solution as the electrolyte, when the battery is charged, hydrogen from the positive electrode enters into the negative electrode in the hydrogen storage alloy, and the reaction process is just the opposite when the battery is discharged.

Nickel-metal hydride batteries have become another important energy source used in electric vehicles because of their high specific energy, high power, high rate discharge, fast charging capability and no obvious memory effect.

The main components of sealed nickel-metal hydride batteries include positive plate, negative plate, diaphragm paper (spacer), insulating ring, sealing ring, lugs, caps and steel case.

(3) Lithium-ion batteries

Lithium-ion battery is in 1990 by Japan’s Sony announced the development of successful, and in a year to the market. Lithium-ion battery positive electrode using lithium compounds, negative electrode lithium – carbon interlayer compounds, electrolyte for the organic solution, in the process of charging and discharging, lithium ions in the battery between the positive electrode and the negative electrode back and forth flow.

Lithium-ion battery has high voltage, high specific energy and other outstanding performance, mainly by the positive and negative electrode, electrolyte, diaphragm and shell and other components.

Lithium-ion battery structure

3、Key technologies of power battery

The power battery used in China’s new energy vehicles mainly includes two kinds of lithium iron phosphate batteries and lithium ternary batteries.Since 2018, China’s new energy passenger cars have basically started to use higher energy density lithium ternary batteries, and the driving range of electric vehicles has moved from 300 kilometers to 500 kilometers. The four key technologies of new energy electric vehicles include battery and management technology, motor and its control technology, vehicle control technology, and vehicle lightweight technology.

Power battery is the power source of electric vehicles, electric energy storage to power the drive system, battery selection will be directly related to the performance of the vehicle. The main performance indicators of electric vehicle power battery are energy density, power density and cycle life.

The key technologies of automotive power battery include battery chemistry technology, such as lithium-ion and solid-state batteries; advanced application of battery management system (BMS); fast charging and wireless charging technology; energy density enhancement and research of sustainable materials; improve cycle life and safety, while reducing manufacturing costs, and promote the performance and sustainability of electric vehicles.

(1) Battery electrochemical technology

Battery electrochemical technologies involve chemical reactions and electron flow within the battery, including factors such as energy density, charging speed, life, safety and cost, which are critical to the performance and characteristics of the battery.

(2) Battery Management System (BMS)

The BMS is the key component that manages the battery, monitoring the state of the battery, equalizing charge and temperature between battery cells, and ensuring that the battery operates within safe limits. Advanced BMS technologies can improve battery performance, extend life and increase safety.

(3) Charging technologies

Fast charging technology: such as fast DC charging (DC fast charging), which can charge the battery in a short period of time and improve the availability of EVs.

Wireless charging technology: through wireless electromagnetic induction or resonance, wireless charging of electric vehicles is realized, which improves the convenience of charging.

(4) Energy Density Improvement

Increasing the energy density of batteries can increase the range of EVs, which is usually achieved by improving battery materials and structure.

(5) Cycle life and safety

Improving the cycle life of batteries extends the service life of batteries and reduces the cost of battery replacement. Enhance the safety of the battery to prevent problems such as overcharging, over-discharging and short-circuit.

The significance of the research on key technologies of power batteries for new energy vehicles is to promote a sustainable transportation revolution, reduce greenhouse gas emissions, mitigate climate change, improve air quality, and reduce dependence on limited fossil fuels. This research can improve the energy density, charging speed and life of batteries, reduce manufacturing costs, and increase the range and availability of electric vehicles, thereby promoting the large-scale adoption of clean-energy transportation and achieving environmental sustainability and energy security.