(I) Main Types and Performance Parameters of Power Batteries
Currently, the power batteries used in new energy vehicles mainly fall into two categories: nickel-metal hydride batteries and lithium batteries.
(1) Lithium battery
1. Basic classification of lithium batteries
1) Ternary lithium batteries, also known as "ternary material batteries," generally refer to lithium batteries that use ternary cathode materials such as lithium nickel cobalt manganese oxide (Li(NiCoMn)O2, NCM) or lithium nickel cobalt aluminum oxide (NCA). The nickel, cobalt, and manganese salts are used as three different components in varying proportions, hence the name "ternary." This category encompasses many different battery types with varying proportions. In terms of shape, they can be divided into pouch batteries, cylindrical batteries, and prismatic hard-shell batteries. Their nominal voltage can reach 3.6–3.8V, with relatively high energy density, high voltage plateau, high tap density, long driving range, and high output power. They have poor high-temperature stability but excellent low-temperature performance, and are also relatively expensive.
2) Lithium iron phosphate batteries use lithium iron phosphate (LiFePO4) as the cathode material. Using iron as a battery raw material is inexpensive and does not contain heavy metals, resulting in less environmental pollution. The operating voltage is 3.2V. The PO bonds in the lithium iron phosphate crystal are stable, so there is no leakage when stored at zero voltage. It has very high safety under high temperature conditions or overcharge, can be charged quickly, has high discharge power, no memory effect, and long cycle life. The disadvantages are poor low-temperature performance, low tap density of the cathode material, low energy density, and the yield and consistency of the product are also questionable.
Japanese companies like Panasonic, South Korean companies like LG Chem, and Samsung SDI mostly use ternary lithium batteries. Tesla uses Panasonic's nickel-cobalt-aluminum ternary lithium batteries, also known as NCA. Domestic new energy vehicle companies mostly use lithium iron phosphate batteries.
The risks of leakage, deformation, combustion, and explosion of ternary lithium-ion batteries cannot be ignored. Currently, new energy companies are adding functions such as overcharge protection (OVP), over-discharge protection (UVP), over-temperature protection (OTP), and overcurrent protection (OCP) to their battery management systems. They have also adopted high-strength aluminum alloy protection structures and made remarkable achievements in technical routes such as adding silicon-titanium nanotubes, solvent-free PI binders, and solid electrolytes to cathode materials, which have greatly reduced risks and costs.
BYD has added manganese to lithium iron phosphate batteries to explore lithium iron manganese phosphate batteries, breaking through the original energy density limit and achieving excellent cost control, but posing new challenges to charging time.
(2) Nickel-metal hydride batteries
Nickel-metal hydride (NiMH) batteries are currently mainly used in hybrid vehicles. Compared with other types of batteries, NiMH batteries have the following specific advantages:
1) Nickel-metal hydride batteries are safe and reliable.
2) Nickel-metal hydride batteries have good fast-charging performance.
3) Nickel-metal hydride batteries have good low-temperature performance.
4) Nickel-metal hydride batteries have good environmental protection and recyclability.
(II) Battery Management System Operating Mode
(1) Power-off mode is a mode in which the low-voltage and high-voltage systems of the entire system are inactive. In power-off mode, all high-voltage contactors controlled by the power battery management system are in the open state, and the low-voltage control power supply is not supplying power. Power-off mode is a power-saving mode.
(2) In the preparation mode, all contactors in the system are in an unengaged state. In this mode, the system can receive hard-wired signals or low-voltage signals controlled by CAN messages from external components such as the ignition switch, vehicle controller, motor controller, and charging plug switch to drive and control the high-voltage contactors of each high voltage, thereby enabling the power battery management system to enter the required working mode.
The development of new energy vehicles relies heavily on power batteries, which are the core and most expensive components. The structural technology of power batteries determines their performance, safety, lifespan, and cost, making it a hot research topic in the new energy vehicle field. This article will introduce the structural technology of power batteries for new energy vehicles from the following aspects:
Classification of power batteries
Structure of power batteries
Working principle of power battery
Main parameters of power batteries
A power battery is a secondary battery that provides driving energy for new energy vehicles. Based on the different cathode materials, it is mainly divided into the following types:
Lithium iron phosphate (LFP) batteries use lithium iron phosphate as the cathode material and have advantages such as good safety, long cycle life and abundant raw material resources, but they have disadvantages such as low energy density, poor low temperature performance and limited charge and discharge rate.
Lithium manganese oxide (LMO) batteries use lithium manganese oxide as the cathode material. They have advantages such as abundant resources, relatively low cost, and high specific capacity, but they have disadvantages such as poor high-temperature cycle performance and electrochemical stability, and easy generation of gas.
Lithium cobalt oxide (LCO) batteries: Using lithium cobalt oxide as the cathode material, they have advantages such as high specific capacity, high charge and discharge rate, and good low-temperature performance, but disadvantages such as poor safety, high cost, and short cycle life.
Ternary lithium batteries (NMC/NCA): Using nickel-cobalt-manganese (NMC) or nickel-cobalt-aluminum (NCA) as cathode materials, they have advantages such as high energy density, high power density, and low internal resistance, but disadvantages such as poor safety, scarcity of cobalt resources, and short cycle life.
Currently, the mainstream power battery types on the market are lithium iron phosphate and ternary lithium batteries. They each have their own advantages and disadvantages, and different choices are made for different application scenarios.
Power battery is actually a general term that includes three levels: cells, modules, and battery packs.
A battery cell is the basic unit of a power battery, containing positive and negative electrodes, a separator, and an electrolyte; it is the space where electrochemical reactions occur. Depending on the packaging method, they can be divided into three types: cylindrical, prismatic, and pouch cells.
A module is an assembly consisting of a number of battery cells connected together and housed in a frame to protect them from external shocks such as heat and vibration. Modules can improve the efficiency of the BMS in managing the battery cells, and enhance battery safety and maintainability.
Battery pack: This is the final form installed in a new energy vehicle. It is based on the module and includes components such as BMS (Battery Management System), TMS (Temperature Management System), wiring harness, and brackets. The BMS is responsible for collecting and controlling parameters such as voltage, temperature, and SOC to protect the battery from abnormal conditions such as overcharging and over-discharging; the TMS is responsible for cooling or heating the battery cells to ensure that they operate within the optimal temperature range.
In short, multiple cells form a module, and multiple modules form a battery pack.
The working principle of a power battery is to utilize the movement of lithium ions between the positive and negative electrodes to achieve the charging and discharging process.
During charging, external energy causes lithium ions in the positive electrode to deintercalate and move towards the negative electrode, where they intercalate to form lithium compounds. At this time, the positive electrode is in an oxidized state, and the negative electrode is in a reduced state.
As we all know, the power battery is the heart of an electric vehicle, and it must be resistant to high temperatures, water, and freezing. Currently, most electric vehicles in my country use lithium batteries as the main raw material for their power batteries. These include ternary lithium, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide. Ternary lithium batteries have higher energy density, smaller size, and lighter weight, making them a commonly used type in the market.
power battery
Why do electric vehicle lithium-ion battery packs need a cooling system? What is its function?
Because power batteries generate a lot of heat, and the battery pack is in a relatively enclosed environment, the battery temperature will rise. The battery module cooling system is a device used for heat dissipation in new energy vehicles. By cooling or heating the power battery, it maintains the power battery at an optimal operating temperature, thereby improving its operating efficiency and extending its life.
How to dissipate heat has always been a key focus of research in new energy vehicles. The thermal management of new energy vehicle power lithium battery pack systems can be broadly categorized into four types:
Natural cooling, air cooling, liquid cooling, and direct cooling are all types of heat management systems. Natural cooling is a passive heat management method, while air cooling, liquid cooling, and direct cooling are active methods. The key difference between these three lies in the heat exchange medium. Natural cooling does not require any additional heat exchange equipment.
