In fact, soft-pack batteries are not a brand-new thing. The reasons why
cylindrical and prismatic batteries have become mainstream are related to cost,
research and development cycle, etc. As early as 2010, Qiantu Motor established
a technical route based on standard boxes of soft-packed batteries. Zhai Sheng
mentioned: "As a vehicle developer, the safety and consistency of batteries are
our first core issues to consider." For this reason, Qiantu Motor abandoned the
cylindrical and square single cells used in the mainstream market at that time,
and proactively adopted soft-pack batteries with higher safety and obvious
advantages in energy buffering and release.
Compared with cylindrical and square batteries with fixed shapes, due to
the aluminum-plastic film packaging, soft-pack batteries will undergo a
slow-release process when the internal energy is gathered and reaches the
explosion point, rather than a sudden explosion. Simply put, it is the internal
energy of the soft-pack battery. A short circuit will not explode immediately,
but will expand and release energy first, thereby providing passengers with more
ample time to react and escape after the vehicle alarms. Higher safety
advantages make soft-pack batteries the research and development foundation for
Qiantu Motor's entire power battery technology path.
From the perspective of OEMs, soft-pack batteries have gradually gained
favor from more first-tier manufacturers after their development in recent
years. General Motors, Nissan, Mercedes-Benz, and Audi have all invested in the
research and development and adaptation of soft-pack power batteries. .
Currently, the world's best-selling affordable electric vehicle, the Nissan
Leaf, is also equipped with soft-pack batteries. From the supplier level,
suppliers led by large-scale battery cell manufacturers such as CATL and LG are
increasingly participating in the research and development and manufacturing of
soft-pack batteries.
Innovative standard battery box
A few days ago, a series of spontaneous combustion incidents of electric
vehicles caused some psychological distress to the public. Taking cylindrical
batteries as an example, since the main heat source of the battery is located at
the pole ears, and the cooling circuit laid under the battery pack is difficult
to balance the temperature difference between the upper and lower parts of the
battery, the cylindrical battery pack has the inherent disadvantage of having
difficulty in BMS thermal management. Coupled with the aging of the battery
after years of use, the diaphragm of a battery is punctured under the influence
of lithium dendrites, resulting in an internal short circuit, which is prone to
a domino-like thermal runaway, causing a chain reaction of the battery pack.
Now, in order to ensure the energy density of the battery pack, the cells are
arranged very closely, which once again increases the risk of thermal runaway.
From this we know that in addition to the safety of individual batteries, the
safety measures between batteries, that is, the overall battery pack, are also
particularly important.
Standard battery box designed by Qiantu Motor
Faced with this problem, Qiantu Motor adopts a standard battery box design.
Since the battery cells will undergo slight volume changes during charging and
discharging, we call it the "breathing effect." Inside the Qiantu standard
battery box, a buffer design is used between the cells to absorb the size
changes caused by the breathing effect of the cells. And form an internal buffer
in the event of collisions, bumps, etc.
The exterior of the battery box is made of a high-strength composite
material casing, which makes its crash performance test score 30% higher than
the national standard and meets the IP67 protection level requirements. It is
worth mentioning that the sealed shell of the standard battery box can also
efficiently cooperate with the battery thermal management system to ensure the
consistency of battery cell temperature.
Taking the Qiantu K50 as an example, its power battery pack is composed of
10 standard boxes connected in series, with a total energy of 78.84kWh. This is
also a modular design idea. With the standard box, the battery packs of the
vehicle can be arranged and combined relatively freely. Qiantu K50 is positioned
as a high-performance sports car, so it uses this T-shaped combination to take
into account the vehicle's endurance, control and space utilization. In
addition, a great advantage of standard battery boxes in terms of safety is that
each single standard battery box is equipped with an independent thermal
management system and an independent battery management system, which not only
provides the standard battery box with more efficient heat dissipation
performance and structural strength, but also Effectively realize intelligent
management of battery cells and monitor the battery status of each battery box
throughout its life cycle in real time.
RESS rechargeable energy storage system
Relying on high-security standard battery box packs, Qiantu Motor is
matched with an efficient thermal management system and a sophisticated and
intelligent battery management system to form a comprehensive safety performance
solution for the vehicle's RESS rechargeable energy storage system. The RESS
system uses an active liquid cooling/liquid heating thermal management system to
ensure that each standard box can receive sufficient heat exchange, minimize the
temperature difference between cells, effectively improve temperature
consistency, and ensure the full temperature of the vehicle (-30 ℃ ~ 55 ℃) safe
driving range.
Qiantu Motor RESS rechargeable energy storage system
This BMS thermal management idea is like a 10-core CPU. Each core is
responsible for its own standard box and independently controls its cooling or
PTC heating. Compared with the traditional "one-size-fits-all" management method
of highly integrated battery packs, this decentralized management can extend the
service life of the battery to a certain extent while providing better safety.
Even if something goes wrong with a certain standard box, the BMS slave control
module can independently cut off its work; if the situation is extremely serious
and still cannot be controlled, the main control module will immediately shut
down all standard boxes. It can be said that Qiantu Motor defends against
thermal runaway from three dimensions: battery cells, battery packs, and thermal
management.
Production ideas in self-built factories
Maybe you don't know much about it, but the supply of battery cells is
sometimes like going to a restaurant to eat food, it also depends on the
"season". The same dish may taste different when eaten in different seasons. The
same is true for the supply of battery cells. Due to the processing of raw
materials, there may be slight differences in telecommunications products of the
same model from the same manufacturer in different batches and in different
months. If mixed, it will affect the status of the battery pack.
In order to ensure the consistency of battery products, Qiantu Motor built
its own factory and designed its own assembly lines to develop and produce the
entire battery system. At the same time, Qiantu also extended its supervision
system to raw material suppliers, and proposed that the electrolyte and positive
and negative electrode materials required for the battery cells in the same
standard box system must be assembled from the same manufacturer and the same
batch to avoid small differences in raw materials. If the battery performance
difference occurs, try to improve the internal consistency of the battery
standard box.
Summarize
This Qiantu Living Room lecture is more like an objective response to the
previous spontaneous combustion incident of electric vehicles. In fact, we are
always used to facing electric vehicles with a one-size-fits-all attitude, and
if one car burns, others will burn. After in-depth understanding, you will find
that there are so many ways to use batteries. Although the process difficulty
and cost of soft-pack batteries are slightly higher, many manufacturers choose
ready-made cylindrical/square battery pack solutions, but the safety of
soft-pack batteries The advantages in performance and service life are also
obvious. I believe that in the future, everyone can calm down and not blindly
pursue higher energy density, but choose a more reasonable cruising range while
ensuring safety. By then, soft-pack batteries will become the technical solution
chosen by more car manufacturers.
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