Depth: BYD blade battery safety and vehicle platform comprehensive judgment

On March 29th, 2020, BYD officially released the blade battery. Previously, the New Energy Information Analysis Network has published many articles on the comprehensive judgment of blade battery system. In my opinion, BYD's blade battery is longer (the longest dimension is more than 2000mm), and the power battery assembly with higher volume density is formed by module-free packaging process.

In fact, the blade battery has led the global power battery safety to a new height, which is not only the overall improvement of BYD's battery processing technology, cathode material ratio and packaging technology, but also a solution combined with the in-vehicle platform being developed.

1 and the safety of BYD blade battery;

Combined with the video (screenshot) of ternary lithium battery, block lithium iron phosphate battery and blade battery, the whole process and results of acupuncture test are compared.

The above picture shows a close-up of the video screenshot of the acupuncture experiment of ternary lithium battery. Puncture the battery cell with steel with a diameter of 5mm, resulting in a large area short circuit inside the battery cell. The temperature of ternary lithium battery changed sharply at the moment of acupuncture, and the surface temperature quickly exceeded 500℃, which caused extreme thermal runaway-violent combustion, and the eggs on the battery surface were blown up.

The above picture shows a close-up of the video screenshot of the acupuncture experiment of the lithium iron phosphate battery core.

Remarks: As a cathode material, lithium iron phosphate battery (LFP) was used as the power battery of BYD F3e electric vehicle as early as 2006.

After the traditional lithium iron phosphate battery was punctured, there was no open flame and smoke, the surface temperature reached 200℃-400℃, and the eggs on the battery surface were burnt at high temperature.

The above picture shows a close-up of the video screenshot of the blade battery acupuncture experiment.

Remarks: Blade battery and power battery components formed by module-free packaging process will be used for "Han" model;

After the blade battery is broken down, there is no open flame and smoke, the surface temperature of the battery is only about 30-60℃, and the eggs on the battery surface are still in a mobile liquid state. The safety of blade batteries is better than that of bulk lithium iron phosphate batteries commonly used in commercial vehicles and ternary lithium batteries commonly used in passenger cars. Comparing the process and results of acupuncture test of ternary lithium battery, lithium iron phosphate battery and blade battery, the blade battery won completely, not only using the improved lithium iron phosphate material as the positive electrode, but also using safer materials and designs as the negative electrode. Although BYD has not announced whether the formula of electrolyte has changed, BYD has changed the formula of positive electrode, negative electrode and the first two parts of electrolyte that determine safety.

2. BYD insists on lithium iron phosphate battery core, battery system and vehicle application;

In 2020, the e6 series EV models manufactured by BYD (with cruising range of 400km and 500km) will not only be used for taxi operation in many cities in China, but also exported to Brazil for police patrol. Qin, manufactured by BYD, keeps the original powertrain and lithium iron phosphate battery assembly, and participated in 20 14, 20 15, 20 16, 20 18 and 20 19 CRC events.

At the same time, BYD's bases in China, the United States and the United Kingdom made K-series electric buses with hub motors, aluminum bodies and lithium iron phosphate batteries based on different levels of liquid thermal management systems, and undertook bus operation tasks in the United States, Britain, Europe, South Asia, South America and other markets in a "competitor-free" state. Even the K-series electric buses exported to Japan were tested and used by adding vehicle driverless systems.

/kloc-in the past 0/0 years, the lithium iron phosphate battery developed and mass-produced by BYD itself has been continuously improved and put into use, both in monomer and density. The power density and discharge efficiency of lithium iron phosphate batteries for electric vehicles and PHEV are constantly improving.

3. Modular packaging process for blade batteries:

The traditional ternary lithium battery or lithium iron phosphate battery pack is based on batteries, with n batteries forming a module and n modules forming 1 power battery pack. In 1 power battery assembly, there are not only modules composed of batteries, but also cooling pipes (air ducts), high-voltage cables, BMS modules and low-voltage cables for servo. The energy density of power battery assembly depends not only on the battery cells, but also on these auxiliary systems. If these accessory systems are too many and too heavy, the energy density of the power battery assembly will decrease. In order to improve the energy density of power battery assembly, it is the simplest method to increase the energy density of battery cells, but in exchange for the decrease of stability, more complicated auxiliary systems are needed to suppress it.

The technical idea of BYD's blade battery is to use the blade battery with larger single volume and module-free packaging technology in exchange for better active safety and volume density improvement. The safety of lithium iron phosphate battery was proved by acupuncture experiment. The cross beam and longitudinal beam in the supporting shell are removed, which simplifies the structure, reduces the weight of the auxiliary system and indirectly improves the energy density of the system.

The above picture shows the schematic diagram of the internal structure of the power battery assembly composed of BYD blade battery and module-free packaging technology-1.

Large monomer is horizontally laid in the shell, and side plates and end plates are added at the front and rear ends; A bottom plate and a heat insulation layer are installed at the bottom, and a top plate and a water cooling plate for thermal management are installed at the top.

The above picture shows the internal structure of the power battery assembly composed of BYD blade battery and modular packaging technology -2.

Heat insulation layers are arranged between horizontally placed large-size monomers for external heat (cold) exchange of the battery cells. All explosion-proof valves at the side end of the monomer are "built-in" with exhaust channels and are physically isolated. In order to ensure the rigidity of the battery assembly shell, a variety of aluminum alloy welding processes and high-strength structural adhesives are adopted.

The non-modular packaging process of BYD blade battery assembly is not only the guarantee of structural strength after removing the reinforcing beam. The method also comprise that following step: setting the control capability of cold and heat exchange of the water cooling plate on the top of the macromonomer, and keep the temperature difference between all battery cells within 3 DEG C; Balance of strength, torsion resistance and self-weight of battery cells; The high voltage distribution system is arranged inside and outside the battery box.

BYD blade battery greatly improved the volume utilization rate, and finally achieved the design goal of loading more batteries in the same space. Compared with the traditional modular battery pack, the volume utilization rate of "blade battery" has increased by more than 50%. Modular packaging technology is no longer a simple means to improve the bulk density, but also includes the passive safety of the battery itself, the expansibility of vehicle platform integration, and the forecasting ability based on the development of global new energy industry, which are easily overlooked.

4. Safety-oriented application of BYD blade battery system in automobiles;

2065438+In August, 2009, BYD made public the "Standard Packaging Design Concept under E Platform | Platform Strategy". In the "Standard Package Design Concept under Platform E | Platform Strategy", in addition to the interpretation of the electric drive technology of "Platform E", some data of the new standardized power battery assembly are also published.

As shown in the above figure, this standardized power battery assembly has two standardized heights (1 10mm and 140mm) and two standardized widths (11300mm and1300mm). And it has the ability of flattening, highly integrated subsystems, single-layer arrangement of batteries and volume grouping rate > 65%. Obviously, these functional descriptions are very close to the upcoming blade battery system, which is composed of module-free packaging technology.

Or the BYD "Han" model listed after June 2020 will first be equipped with blade battery systems with different attributes. The vehicle platform developed in the forward direction is adopted, and the EV version and DM version of "Han" car are adopted.

By studying the details of Korean EV propaganda film released by BYD, it is found that the blade battery system is completely integrated into the car body welding, located at the bottom of the cockpit, with a wheelbase close to 3000 mm The front, rear, left and right edges of the "blade" battery system do not protrude from the bottom of the car body welding, and the size of the large single battery of the blade battery system has been preliminarily set.

BYD, as a new energy industry chain that independently develops and manufactures batteries, electric drives and complete vehicles, combines with the complete vehicle platform being developed, and finally obtains multiple passive safety settings for the shell of the blade battery system by welding the front power cabin, the rear floor and the two side beams.

Combining with the vehicle platform is an aspect of strengthening the structural safety of blade batteries. The inherent stability and safety of blade battery are directly related to the 3.9-second acceleration performance of EV0- 100.

In the 28-minute breakdown test of the blade battery mentioned above, there was no fire or burning caused by thermal runaway after internal short circuit, and even the shell was not deformed, and the highest temperature did not exceed 33 degrees Celsius. This means that during the whole life cycle of "Han" car, even under the conditions of habitual rapid acceleration (large rate discharge) and large rate charging of 600V high-voltage platform, the blade battery can still give the whole car inherent safety and low attenuation efficiency.

It is precisely because the blade battery system is "insensitive" to temperature, so the cruising range and charging and discharging efficiency when used in high temperature and cold environment will completely exceed any similar model based on ternary lithium battery system which is mass-produced at the same time.

The author has something to say:

Comparing ternary lithium battery, lithium iron phosphate battery and blade battery, the most intuitive result is that they show different safety performance at different times. During the 28-minute puncture, the maximum temperature of the blade battery did not exceed 33 degrees Celsius, and there was no physical phenomenon involving safety such as fire or even smoke. It reflects the absolute active safety advantage of blade battery.

Blade battery and non-modular packaging technology to balance structural strength, thermal management system and power distribution system increase the passive safety advantage of the shell for the active safety advantage of the battery core.

The appearance of BYD blade battery system is the continuation of lithium iron phosphate battery technology that Wang Chuanfu insisted on. However, during the period of 20 16 -2020, BYD changed from lithium iron phosphate battery to ternary lithium battery with more dominant energy density due to the industrial policy of linking battery energy density with subsidy amount.

BYD, which spans the markets of passenger cars, commercial vehicles and special vehicles, continues to mass-produce lithium iron phosphate battery e6 electric vehicles with a cruising range of 500 kilometers (mainly in the rental market) while replacing passenger cars with ternary lithium batteries and thermal management strategies under different technical conditions. On the other hand, K-series electric buses sold all over the world were equipped with standard modular lithium iron phosphate power battery modules and standard thermal management strategies with energy density exceeding 160Wh/kg in 20 17 years.

In 2020, the development of China's new energy industry will change rapidly from "policy-driven" to "market-driven", the amount of subsidies will decrease, and the policy guidance will be weakened. Safer lithium iron phosphate batteries will return to the market, and at this time, blade batteries will sweep the market with the powerful advantages of super safety and long battery life.

Text/New Energy Information Analysis Network Song?

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.