Power cell design technology
Regardless of the shape, the cell contains at least five parts. The inner four parts: cathode sheet, anode sheet, isolation membrane, electrolyte; the outer part is the outer shell, the outer shell has output electrodes, and may also be equipped with safety devices such as anti-riot valves.
The complete cell design should cover material design and cell parameters (cathode, anode, separator, electrolyte) design.
Cathode material surface coating technology, anode material artificial graphite and nanotechnology, electrolyte cathode surface protection, conductivity improvement technology, and isolation membrane coating technology are all commonly used technologies. The technologies used in the design process include quantum dynamics simulation, material development and characterization, cell parameter design and characterization, simulation simulation, safety design, reliability design, life prediction, cell test verification, equipment technology and other technologies.
The main points of the overall design of the battery: comprehensive balance. According to the needs of the application, a balance is achieved in terms of safety, life, reliability, energy density, power density, cost, and process difficulty.
Example 1: The balance of energy density and power density. When designing coating thickness and compaction density, the larger the parameter, the more lithium ion quantity and higher energy density can be obtained. However, the movement speed of lithium ions is limited, which affects the power density, so the coating thickness and compaction density should be determined according to the application requirements. If it is a pure electric vehicle application, to pursue the driving range of a single charge, a high compaction density is required to achieve a higher energy density; on the contrary, if it is a hybrid vehicle that requires battery power performance, a lower compaction density is required, leaving a faster path for lithium ions.
Example 2: The balance between safety and power and energy density. A thicker cell isolation film helps prevent internal short circuits and improves safety; however, a thinner isolation film is beneficial to improve power characteristics, as well as to assemble larger-area pole pieces and increase energy density.
Parameter balance is centered on safety, and several other parameters are balanced. The technology used and related control points are shown in Figure 1.
Advanced power battery technology development
Power battery is the power source of electric vehicles and the key core part of electric vehicles. The performance of the battery determines the cost and driving range of electric vehicles. These two aspects are the key to the competition between electric vehicles and traditional fuel vehicles. Therefore, the development of high-performance power batteries is critical to the future development of electric vehicles. The power battery is different from the general battery in that it is mainly discharged by a medium current for a long time, and discharged by a large current occasionally (when starting and accelerating), and is mainly used in a deep cycle. In order to meet the power performance, safety performance and economic index requirements of electric vehicles, power batteries should generally have the following characteristics: high specific energy, high specific power, long cycle life, good safety, good uniformity, good high and low temperature performance, low self-discharge rate, low price, and environmental protection. For any kind of power battery at present, it is obvious that there are certain difficulties in fully satisfying all the above requirements. At present, the main requirements for power batteries developed at home and abroad are: the specific energy of the single battery is ≥300W·h/kg or even ≥400W·h/kg, the cycle life is ≥500 times (100%DOD) or even ≥2000 times (100%DOD), and the safety meets the requirements of the national standard. In view of the above situation, the following article mainly introduces 4 kinds of advanced power batteries: high-stability lithium titanate batteries, high-safety all-solid-state batteries, high-specific energy lithium-sulfur batteries, and environmentally friendly lithium-air batteries.