BYD has mainly done the following aspects to improve the safety of batteries.
1, battery pack selection-hard shell square battery
As we all know, there are three main types of power batteries at present: cylindrical batteries, soft-package batteries and hard-shell square batteries. The selection of battery pack is very important, which determines the design layout of battery pack accessories and the control ability of battery safety in the later stage. After comparative analysis, BYD finally chose the hard-shell square battery for the following reasons.
(1) Although the energy density of a single flexible battery can be higher than that of a hard shell, the whole battery system needs a battery thermal management module to heat and cool the battery to control the temperature range of the battery. The thermal management module of flexible battery is more complicated than that of hard-shell battery, so the energy density of grouped flexible battery is lower than that of hard-shell battery.
(2) Due to the application of high energy density materials, the safety of the flexible battery is uncontrollable, because the flexible battery is sealed by two layers of polymers; Hard-shell square batteries are sealed with welded aluminum plates, so the sealing performance of hard-shell square batteries is higher than that of soft-bag batteries.
(3) Thermal runaway is a very important risk factor in battery safety. When thermal runaway occurs, the soft battery can't directionally release energy, but the hard-shell square battery can directionally design some specific exhaust and fire-fighting exhaust channels in the module. Ensure that even if one monomer is out of control, the energy of the monomer can be released along the fire escape channel, and the heat insulation and fireproof materials between monomers can protect other monomers from being affected, thus ensuring the safety of the whole system.
2.CID overcharge protection
In order to prevent overcharging, BYD has multiple protections: First, accurately detect the battery voltage and monitor the battery status in real time. The second level is BMS layered protection, which executes different commands when charging to different voltages, and controls the charging state by limiting current and cutting off relays. If these two stages fail, it is the third layer of protection-CID (Current Interrupt Device) technology. CID has designed a flip chip on the battery. When the battery is overcharged, the internal pressure of the battery rises. CID uses the high voltage inside the battery to flip the flip chip, thus breaking the circuit. The battery cells in the battery pack are connected in series. If only one battery is disconnected, the whole circuit will be cut off. As a pure hardware protection device, CID is BYD's patented technology.
3. Design of 3.FPC
The connection between battery modules of BYD adopts flexible printed circuit board, which saves many connectors and wires, which can make the layout of battery modules more concise and the layout of products more reasonable. Byd FPC (flexible printed circuit board) has a built-in fuse, which can avoid the risk of short circuit caused by accidental damage of the control circuit and further improve the battery safety.
Nowadays, new energy vehicles are developing rapidly, and the cruising range and safety can not be fully taken into account at present. BYD put the core of battery research and development on safety and won the support of many netizens!