Power battery not only provides a continuous and stable power source for vehicles, but also is the core element that determines key indicators such as performance, endurance, and safety of new energy vehicles. Unlike traditional fuel vehicles that rely on engines to burn fossil fuels to generate power, the power of new energy vehicles is completely dependent on the electrical energy stored in power batteries. To some extent, the development level of power battery technology directly restricts the development height of the new energy vehicle industry.
Working principle of power battery
The working principle of power battery is based on the chemical reaction between cathode and negative electrode materials and electrolyte. Taking the most widely used lithium ion battery materials as an example, when the battery is in a charging state, the electric energy provided by the external power supply prompts a chemical reaction inside the battery. At the cathode electrode, the lithium atom (Li) loses an electron and becomes a lithium ion (Li⁺). This process is called an oxidation reaction. The lost electron flows to the negative electrode through the external circuit, while the lithium ion is deintercalated from the cathode electrode and migrates to the negative electrode through the electrolyte. At the negative electrode, the lithium ion is embedded in the lattice of the negative electrode material (usually graphite), and at the same time receives electrons flowing from the external circuit to form a lithium carbon compound. This process is a reduction reaction. At this time, the electrical energy is converted into chemical energy and stored in the battery.
When the battery is in a discharge state, the chemical reaction proceeds in the reverse direction. The lithium ions in the lithium carbon compound of the negative electrode are deintercalated and migrate to the cathode electrode through the electrolyte, and the electrons flow from the negative electrode to the cathode electrode through the external circuit, forming a current to power the vehicle’s electric motor and other equipment. At the cathode electrode, lithium ions recombined with electrons flowing from the external circuit and turned back into lithium atoms, and chemical energy was converted into electrical energy and released.
Types and characteristics of power batteries
Types and characteristics of power batteries
At present, there are many types of power batteries on the market, each with its own unique performance and applicable scenarios. The mainstream power batteries and material types include ternary materials, lithium iron phosphate materials, and some batteries in research and development or specific application fields, such as nickel-hydrogen batteries, hydrogen fuel cells, lithium-sulfur batteries, etc.
Ternary lithium battery
The cathode electrode material of ternary lithium battery is mainly composed of metal oxides of three elements: nickel (Ni), cobalt (Co), manganese (Mn) or aluminum (Al). According to the different ratios of the three elements, there are different models, and the common ones are NCM523 (nickel, cobalt and manganese ratio is 5:2:3), NCM622, NCM811, etc. Among them, nickel can improve the energy density and endurance of the battery; cobalt can improve the stability and charge and discharge performance of the battery, but the price of cobalt is high and the resources are relatively scarce; manganese helps to reduce costs and improve safety.
The biggest advantage of ternary lithium battery is its high energy density, which enables it to store more electricity in a relatively small volume and weight, providing electric vehicles with a longer range. Taking Tesla Model 3 as an example, the ternary lithium battery used in some models has an energy density of 160-180Wh/kg, which helps the vehicle achieve a longer range. In addition, the cycle performance of ternary lithium batteries is also relatively good, generally reaching 1000-2000 charge and discharge cycles, which means that the battery can maintain a good performance state during the service life of the vehicle. Its charge and discharge speed is also relatively fast, which can meet the needs of rapid acceleration and charging of the vehicle.
However, ternary lithium batteries are not perfect. Its high temperature safety is poor. When the battery temperature is too high, especially when it exceeds 150℃, violent chemical reactions are likely to occur inside the battery, leading to thermal runaway, which in turn causes serious safety accidents such as combustion or even explosion. In order to ensure its safety, vehicles usually need to be equipped with complex and costly battery thermal management systems, which undoubtedly increases the cost and complexity of the entire vehicle.
Lithium iron phosphate battery
As the name implies, the cathode battery materials of lithium iron phosphate battery is lithium iron phosphate (LiFePO₄). During the charging and discharging process, lithium ions are embedded and de-embedded between the lithium iron phosphate cathode electrode and the graphite negative electrode to achieve the mutual conversion of electrical energy and chemical energy.
Lithium iron phosphate battery is known for its excellent safety. The crystal structure of its cathode electrode material is stable, and the probability of thermal runaway is extremely low under extreme conditions such as high temperature, overcharge, and short circuit. Even when it is severely damaged by external force puncture, it is not easy to catch fire, which makes vehicles equipped with lithium iron phosphate batteries safer and more reliable during use. For example, BYD’s “blade battery” is essentially a lithium iron phosphate battery. Through its unique structural design, it further improves the safety of the battery and performs well in safety tests such as needle puncture experiments. In addition, lithium iron phosphate batteries have a long service life, and the cycle life can usually reach 2000-3500 times, or even higher, which is of great significance for reducing the long-term use cost of vehicles. Moreover, its raw materials are abundant and relatively low in cost, which gives it a significant cost advantage in large-scale applications, especially in the cost-sensitive commercial vehicle and low-end passenger car markets.
However, lithium iron phosphate batteries also have some shortcomings. The most obvious one is the relatively low energy density, which is generally around 140-180Wh/kg, lower than ternary lithium batteries. This results in a larger volume and weight of the battery at the same power, thus affecting the vehicle’s range and space layout. In low temperature environments, its performance will also be greatly affected, the battery’s internal resistance will increase, and the discharge capacity will decrease, resulting in a significant reduction in the vehicle’s range, which is particularly evident in cold areas.
Other types of batteries
The cathode electrode of the nickel-hydrogen battery is nickel hydroxide, the negative electrode is a metal hydride hydrogen storage material, and the electrolyte is a potassium hydroxide solution. It has the advantages of good power performance, excellent low-temperature performance, fast charging and discharging, and no pollution, and is called a “green power source”. In some fields that require high battery power and low-temperature performance, such as the early application of hybrid vehicles, nickel-hydrogen batteries have played an important role. Toyota’s Prius used nickel-hydrogen batteries in the early days. However, the energy density of nickel-hydrogen batteries is relatively low, generally 50-70Wh/kg, which is much lower than that of lithium batteries. In addition, its material cost is high and its self-discharge is large. These factors limit its large-scale application in the field of new energy vehicles and are gradually replaced by lithium batteries.
Hydrogen fuel cells are a power generation device that directly converts the chemical energy of hydrogen and oxygen into electrical energy. The working principle is that through electrochemical reactions, hydrogen loses electrons at the anode to produce hydrogen ions and electrons. Electrons pass through the external circuit to form current, and hydrogen ions pass through the proton exchange membrane to the cathode to combine with oxygen to form water. Its energy conversion efficiency is high, theoretically up to 60% – 80%, and the only product is water, which is pollution-free to the environment. In the field of transportation, hydrogen fuel cell vehicles have the advantages of short hydrogenation time and long driving range. Hydrogen fuel cell vehicles such as Toyota’s Mirai and Honda’s Clarity have been launched on the market. However, hydrogen fuel cells face the problem of high cost. Its key materials and components, such as proton exchange membranes and catalysts (platinum), are expensive, and the production, storage and transportation costs of hydrogen are also high. The construction of hydrogenation infrastructure is seriously insufficient. These factors have greatly restricted the popularization and promotion of hydrogen fuel cell vehicles.
Lithium-sulfur batteries use sulfur as the cathode electrode and metallic lithium as the negative electrode. They have extremely high theoretical specific capacity and theoretical energy density. Their theoretical specific energy is as high as 2600Wh/kg, which is more than 6 times the theoretical energy density of lithium cobalt oxide batteries. From the perspective of practical application, lithium-sulfur batteries are most likely to be used in some specific fields that require high power and low mass but do not pursue cycle life, such as unmanned aerial vehicles, cargo planes, electric vehicles, especially heavy vehicles, submarines, aerospace and portable equipment. However, it also faces many challenges, such as low utilization of active materials, poor cycle stability, and low Coulombic efficiency, which seriously restrict its large-scale commercial application.
Performance indicators of power batteries
Specific energy and specific power
Specific energy and specific power are two key indicators to measure the performance of power batteries. Specific energy refers to the electrical energy that can be output per unit mass or unit volume of the battery, and the unit is usually Wh/kg or Wh/L. It reflects the battery’s ability to store energy. The higher the specific energy, the more electrical energy the battery can store under the same weight or volume, providing the vehicle with a longer range.
Specific power refers to the maximum power that can be output per unit mass or unit volume per unit time, and the unit is W/kg or W/L. It reflects the battery’s ability to release energy quickly. A battery with a high specific power can output a large amount of power in a short time, allowing the vehicle to achieve better acceleration performance.
For example, for household electric vehicles that pursue long battery life, more emphasis may be placed on improving specific energy; while for sports cars or racing cars that pursue high performance, more attention may be paid to improving specific power.
Energy density comparison
The energy storage capacity of power batteries is compared with the energy density of traditional fuel — gasoline. Gasoline, as a traditional energy source that has been widely used for more than a hundred years, has a very high energy density. Its energy density is about 12000-13000Wh/kg, which means that 1 kg of gasoline contains huge energy and can provide strong and lasting power support for vehicles.
In contrast, the energy density of the current mainstream ternary lithium battery is generally between 150-300Wh/kg. Even for products with more advanced technology, it is difficult to break through 350Wh/kg. This data shows that under the same mass, the energy contained in gasoline is about 40-80 times that of ternary lithium batteries.
Although batteries are far less energy dense than gasoline, electric vehicles have advantages in energy conversion efficiency. Generally speaking, the energy conversion efficiency of fuel vehicles is around 30%, while that of electric vehicles can reach 80% – 90%, and the electrical energy stored in the battery can be more efficiently converted into the vehicle’s kinetic energy. Despite this, the energy density of the battery is still a shortcoming.
Lifespan
The service life of a battery is one of the important indicators for measuring the performance of a power battery, which directly determines the cost of use and long-term reliability of the vehicle. For new energy vehicles, battery consistency and the number of charge and discharge cycles are two key factors affecting the service life.
The cycle life of a lithium iron phosphate battery can usually reach 2000-3500 times, or even higher; while the cycle life of a ternary lithium battery is generally around 1000-2000 times. Therefore, when choosing a new energy vehicle, consumers can pay attention to the type of battery and the number of charge and discharge cycles to evaluate the long-term cost and performance of the vehicle.
The current status and future trends of power battery development
Development
Currently, the new energy vehicle market is showing a rapid development trend. By the end of 2024, China’s new energy vehicle ownership has reached 31.4 million, and the installed capacity of power batteries has been the world’s leading for many years. In December 2024, the installed capacity of power batteries was 75.4GWh, a month-on-month increase of 12.2% and a year-on-year increase of 57.3%. From January to December, the cumulative installed capacity of power batteries was 548.4GWh, a cumulative year-on-year increase of 41.5%. Among them, lithium iron phosphate batteries occupy a large share in the market due to their advantages such as high safety and low cost. From January to December 2024, the cumulative installed capacity was 409.0GWh, accounting for 74.6% of the total installed capacity, with a cumulative year-on-year growth of 56.7%; ternary lithium batteries are widely used in mid-to-high-end models with high energy density. From January to December, the cumulative installed capacity was 139.0GWh, accounting for 25.3% of the total installed capacity, with a cumulative year-on-year growth of 10.2%.
However, with the vigorous development of the new energy vehicle industry, power batteries are also facing some problems. Among them, the advent of the power battery retirement wave has attracted much attention.
For the treatment of retired power batteries, there are currently two main ways: cascade utilization and recycling. When the battery capacity is between 50% and 80%, the recycling company will dismantle and reorganize the retired power batteries, and then continue to serve as emergency power supplies, energy storage equipment, etc.
Future Trends
At the technical level, power batteries will develop towards higher energy density, faster charging speed, longer life and lower cost. Researchers are constantly exploring new materials and technologies, such as solid-state batteries and sodium-ion batteries, to break through the bottleneck of existing battery technology. Solid-state batteries use solid electrolytes instead of traditional liquid electrolytes, have higher energy density and safety, and are expected to become the mainstream technology of the next generation of power batteries. Sodium-ion batteries have the advantages of abundant raw material reserves and low cost, and have broad development prospects in some application scenarios with relatively low energy density requirements.