The first part of battery cell technology
The power battery system is the energy storage device of the energy storage car, which is a complex engineering system integrating mechanical, electrochemical and thermodynamic disciplines. Structurally speaking, it includes battery cells, battery modules, battery packs, battery management control systems, thermal management systems, high and low voltage plug-ins and wiring harness connections, and high voltage control boxes. Figure 1 BMW ix3 battery system.
Figure 1 BMW ix3 battery system
In terms of cost, as shown in Figure 2, the cost distribution map of the battery system.
Figure 2 Cost distribution of battery systems for pure electric vehicles
(Data from the Internet)
The three key technologies of the power battery system include the key technologies as shown in Figure 1. The plan is to carry out a series of articles around the key technologies of this pure electric vehicle power battery system, with the purpose of sorting out some of the current technical bottlenecks and discussing the response plan in the current market, hoping to be able to help everyone.
Figure 3 Key technologies of battery systems for pure electric vehicles
According to the cost distribution chart of the battery cell, the cost of the battery cell accounts for the largest in the battery system. Power battery structures typically include positive electrode, negative electrode, diaphragm, electrolyte and aluminum-plastic film, etc.
The development of high-energy batteries first began with the search for electrode materials with high specific energies. Among all the metallic elements, lithium has the smallest relative atomic mass, the smallest density, and the most negative electrode potential, so the battery with lithium metal as the negative electrode has the highest operating voltage and the largest specific energy. Coupled with the invention of lithium polymer battery, the use of polymer electrolyte not only has no leakage problem, but also because lithium-ion batteries have excellent electrical properties and safety, pollution-free, shape has a high degree of plasticity and other characteristics, in line with the requirements of electronic products light, thin, short, small, so lithium-ion batteries are widely used in the field of power battery production. As shown in Figure 4.
Figure 4 Internal structure diagram of lithium-ion battery
●Cell selection comparison
According to the appearance shape of the battery, it can be divided into three categories: cylindrical battery, square shell battery, and soft pack battery. Lithium-ion batteries, according to the different cathode materials, can be divided into the following five kinds of lithium iron phosphate, ternary (nickel cobalt manganese NCM), lithium manganese oxide, lithium manganese iron phosphate, lithium titanate.
Table 1 Comparison of different cathode battery performance
Note: Because of the materials and processes of different manufacturers, the assembly forms are different, and the parameters in the table are for reference only.
In 2021, benefiting from the complete layout of the lithium iron phosphate industry chain and deep technical reserves, major battery companies have increased the production capacity planning of lithium iron phosphate battery production, making the market demand for lithium iron phosphate batteries grow rapidly. From January to December 2021, China's power battery production accumulated 219.7GWh, an increase of 163.4% year-on-year. Among them, the production of ternary batteries accumulated 93.9GWh, accounting for 42.7% of the total output, an increase of 93.6% year-on-year; the cumulative output of lithium iron phosphate batteries was 125.4GWh, accounting for 57.1% of the total output, an increase of 262.9% year-on-year. The installed capacity of lithium iron phosphate batteries in the Chinese market has exceeded the installed capacity of ternary batteries.
●Cell structure comparison
The composition of the battery cell directly determines the design of the module and battery pack, as shown in Figure 3. The structure of the battery determines the characteristics of the battery, such as Table 2, which compares the soft pack cell with the cylindrical cell and the square shell cell.
Figure 5 Different cell structures make up the module and battery pack
Table 2 Different batteries are compared into battery packs
●Comparison of assembly processes of batteries
Lithium-ion battery core manufacturing process is divided into lamination process and winding process, at present, major battery manufacturers are based on their own product characteristics to design the corresponding production process, and gradually form their own core competitiveness.
Figure 6 Lamination process flow chart
Fig. 7 Winding process flow diagram
summary:
◎ In the future, with the increase in the demand for electric vehicle mileage, improving the energy density and power density of power batteries will be an important trend, and related to it is the improvement of the lightweight design of the whole vehicle.
◎ Whether it is a ternary battery or a lithium iron phosphate battery, in the face of the continuous heating of the new energy market, how to overcome the problem of capacity climbing is the bottleneck problem faced by major OEMs and battery factories. Strengthening in-depth cooperation with equipment suppliers, further improving the overall comprehensive efficiency of equipment, and ensuring the one-time pass rate of products, ensuring the stable output of production capacity will also be an effective guarantee of production capacity.
◎ The development of new battery varieties still needs further in-depth research, accompanied by the in-depth research and development of solid-state batteries and lithium-sulfur batteries, technology developers, equipment suppliers, battery manufacturers and automakers need to work together to further strengthen technical support and fill the gap in the supply chain.
About the Author: Nuts
Senior engineer of luxury car companies,
Move from engine test to battery test.
At present, he focuses on the research of battery testing technology.
I hope to work with you to "electrify, to the future"!