Toyota officially entered the field of pure electric vehicles, and its battery system has a set of safety.

Although Toyota announced this year that it will officially develop pure electric vehicles, the car giants in the country are actually very good at research on lithium batteries, and they should be very effective and worth learning.

Since its first production of its hybrid Prius in 1997, Toyota has been an absolute leader in the hybrid vehicle market. In 2003 and 2009, it released the second and third generations of the Prius, but they all used NiMH batteries. Until the Prius Alpha in 2011, lithium batteries were used. At this time, the lithium battery was a generation of lithium batteries. In 2016, the 4th generation Prius, Toyota began using the latest second-generation lithium battery.

In the research and development of lithium batteries, Toyota's idea is: the first generation of lithium batteries to solve the safety and reliability problems, especially the emphasis on the safety of the batteries; the second generation of lithium batteries, emphasizing better performance, high energy density, High power.

Affecting the risk factor of lithium battery, Toyota analysis includes: overcharge, external short circuit, collision, internal short circuit.

For overcharge, system level, dual detection system is used, and the voltage of the battery and module is detected at the same time; for external short circuit, the system level mainly adopts the current shutdown system and the main circuit fuse scheme.

The main idea of ​​dealing with overcharge and external short circuit at the cell level is that when a certain temperature is reached, the current can be automatically cut off, which is mainly achieved by materials, electrodes and structures.

For the collision, the general idea is to protect the body strength of the body and the battery pack itself. At the level of the battery core, Toyota has made a lot of research and research, using the "Heat Resistant Layer" (HRL) design. . HRL is also used to deal with the risk of internal short circuit of the battery, because the internal short circuit of the battery, there is no solution at the current system level.

The main idea of ​​the HRL is to place the HRL between the positive and negative electrodes, which can prevent the separator from collapsing under extreme conditions, thus ensuring a certain resistance of the cell even in the case of a sharp temperature rise. On the first generation lithium battery, the HRL was applied to the positive electrode of the battery.

Toyota's first generation lithium battery schematic

Tests and verifications show that this design can better deal with internal short circuits.

Test Method (Improved JISC8714)

Test Results

In order to verify the safety and reliability of the 1st generation lithium battery, Toyota launched 150 demonstration vehicles to run in 2006-2009, and the Prius was officially used for mass production in 2011.

Alpha. Through the collection and analysis of the battery data of these vehicles, the design scheme of the first generation battery was basically demonstrated. Based on the 1st generation battery, we have further developed a 2nd generation lithium battery that meets various high performance requirements.

For electric vehicles, safety is always the number one. From the various policies, norms and standards of last year, the state is also such a way of thinking, first of all to ensure security, on this basis, will further provide indicators for other related performance, such as energy density.