In overcharging mode, there are also some rigid requirements for the car end. From the perspective of vehicle components, the vehicle battery voltage has increased from 450V to 950V or higher, and the charging and distribution system, electric drive system, battery system and thermal management system have all undergone significant changes. High voltage will increase the cost of compressors, PTCs and motor drive MCUs. Compared with the more mature 2C and 400V fast charging systems, the cost of the 950V voltage platform increases by about 6,500 yuan compared to the 450V voltage platform. In the future, domestic and foreign OEMs will prioritize the application of 800V and above high-voltage platforms in mid- to high-end models to create differentiated competitiveness. In the long term, as the cost of core components such as SiC and fast-charging batteries decreases, mid- to low-end models also have demand for fast charging, and there is a long-term trend for upgrading electrical architectures to 800V and above.
Compared with the 450V voltage platform, under the premise of the same pack power, the 950V platform is achieved by increasing the number of battery cells in series and reducing the capacity of a single battery cell. The number of batteries in series increases. If there are differences between batteries, the battery life will be shortened. Affected by this, the 800V battery system has increased its requirements for cell production technology and consistency. As the number of cell strings increases, the difficulty of battery consistency management increases. Components and connectors such as the main chip of the BMS (battery management system) on the vehicle end, the sampling chip, and the communication isolation chip between the high and low voltage circuits need to be reselected. At the same time, Due to the large amount of heat generated during fast charging, the risk of thermal runaway increases, so effective monitoring and early warning are required.
In slow charging technology, because the current in the external circuit is small, the corresponding electron migration speed is slower. At this time, the reaction of ions and electrons in the internal circuit is adapted to the electron speed in the external circuit. In this environment, the potential of the two poles The difference is basically the same as the equilibrium potential. In fast charging applications, lithium ions quickly fall off the positive electrode, resulting in an extremely high lithium ion concentration inside the battery. The sudden increase in lithium ion concentration causes a stress mismatch between the active particles inside the battery. When this occurs After the stress reaches the threshold, it will cause the active particles to break and be damaged, which not only reduces the life of the power battery, but also increases its internal resistance. Due to the increase in internal resistance of the battery, the migration speed of ions and electrons in the internal circuit slows down. At the same time, the neutralization speed between the two cannot keep up with the migration speed of electrons in the external circuit. In this 'fast on the outside but slow on the inside' Under the action of , electrons begin to accumulate at the electrode, which causes the electrode potential to deviate from the equilibrium potential, which is commonly known as polarization.
The accumulation of polarization phenomena causes problems such as lithium precipitation, capacity loss, and heat generation in the negative electrode, which limits the development of fast charging. Currently, there are three targeted solutions: secondary granulation, surface carbon coating, and silicon-carbon negative electrodes.
The function of conductive additives is to collect microcurrents between active materials and between active materials and current collectors to reduce the contact resistance of electrodes and accelerate the movement speed of electrons. At present, carbon-based conductive agents can be divided into five types: conductive graphite, conductive carbon black, chopped carbon fiber, carbon nanotubes and graphene. The conductive additive compounded with carbon black and carbon nanotubes is the most ideal form of use. According to GGII data, in 2021, conductive carbon black accounts for up to 60% of my country's power battery conductive agents, carbon nanotubes account for 27%, graphene and conductive graphite account for 8% and 4% respectively.
According to GGII calculations, the addition amount of traditional carbon black conductive agents such as conductive carbon black is about 3% of the weight of the cathode material, while the addition amount of new conductive agents such as carbon nanotubes and graphene is reduced to 0.8%-1.5%. The role of the conductive agent in the electrode is to provide a channel for electrons to move. If the content of the conductive agent is appropriate, a higher discharge capacity and better cycle performance can be obtained. If the content is too low, there will be few conductive channels for electrons, which is not conducive to large current charging and discharging; if it is too high, Then the relative content of active materials is reduced and the battery capacity is reduced. As the charging rate increases, conductive carbon black materials with higher conductivity need to be used. In order to meet the fast charging performance, the proportion of conductive agent added to the positive and negative electrodes will be further increased. Under 4C, the demand for 1GWh conductive carbon black will increase by about 35% compared to 2C. Carbon coating of current collectors will also increase the demand for conductive carbon black.
Most of the existing power devices are based on silicon semiconductor materials. Due to the limitations of the physical properties of silicon materials, the energy efficiency and performance of the devices have gradually approached their limits, making it difficult to meet the rapidly growing and changing new demands for electrical energy applications. With its excellent high voltage resistance, high temperature resistance, low loss and other properties, silicon carbide power devices can effectively meet the high efficiency, miniaturization and lightweight requirements of power electronic systems. Compared with silicon-based MOSFETs of the same specifications, silicon carbide-based MOSFETs have Its size can be significantly reduced to 1/10 of the original, and the on-resistance can be reduced to at least 1/100 of the original. The total energy loss of silicon carbide-based MOSFETs with the same specifications can be greatly reduced by 70% compared with silicon-based IGBTs. SiC's high efficiency and small size accurately solve the needs of electric vehicles' cruising range, fast charging, and lightweight.
The value of power semiconductors in traditional fuel vehicles is US$88 per vehicle, while the value of power semiconductors in pure electric vehicles is as high as US$350 per vehicle, or even higher. The subsequent deepening of electric intelligence is expected to drive the continued increase in semiconductor content; from an economic perspective, with the large-scale application of SiC, the price of SiC devices is expected to be about 2 times that of IGBTs. If it is assumed that 70% of power semiconductors are completely replaced by SiC, the value of a bicycle will increase from 2450 Yuan increased to about 4,000 Yuan. On the other hand, SiC at the vehicle level drives NEDC efficiency to increase by 3%. For a 100kwh model, the configured power is equivalently reduced by 2-3kwh, saving about 2,000 Yuan in partial hedging costs. In the future, the dilution will be fixed with the expansion of production capacity. Cost and technological progress have improved yields, and costs will continue to decline rapidly, driving the inflection point of SiC vehicle cost parity, accelerating the extension of SiC high-voltage models to economical models, and increasing the penetration rate of 800V.
