In the current era of new energy vehicles, battery safety and endurance
have always been the issues that everyone pays close attention to. As the leader
of domestic new energy vehicles, BYD's strength cannot be underestimated. In
1995, BYD was established and began to produce lithium batteries for mobile
phones. By 2005, BYD began to engage in the research and development of new
energy vehicle power batteries. The scary thing is that in the 15 years of power
battery research and development and more than 500,000 installed capacity, there
has not been a single battery safety incident.
How has BYD, which has always kept a low profile, never had a battery
safety incident in 15 years? Let us uncover the secrets of BYD’s power battery
safety technology. BYD's research direction of power batteries is mainly lithium
iron phosphate batteries and ternary lithium batteries. The safety of lithium
iron phosphate batteries is higher than that of ternary lithium batteries, so we
will explore the relatively unsafe ternary lithium batteries.
Ternary lithium batteries have the advantages of high energy density and
large output power. However, the shortcomings are also very prominent. The
deoxidation temperature of the ternary material is 200°C. It has poor
high-temperature stability and the exothermic energy exceeds 800J/g. It cannot
pass the needle stick test. If the ternary battery is internally
short-circuited, it is easy to cause serious damage. safety incident.
Regarding the safety issues of ternary lithium batteries, BYD conducted
in-depth research from a technical perspective to resolve the conflicts one by
one and seek solutions.
1. A well-thought-out choice - hard-shell prismatic battery
As we all know, the current selection of power battery packs mainly falls
into three categories: cylindrical batteries, soft-pack batteries and hard-shell
square batteries. The selection of battery pack is very important, as it
determines the design and ease of arrangement of later battery pack accessories
and the ability to control battery safety. After comparative analysis, BYD
finally chose hard-shell square batteries for the following reasons.
Although the energy density of a soft-pack battery cell can be higher than
that of a hard-shell rectangular battery, the entire battery system requires a
battery thermal management module to heat and cool the battery to control the
temperature range of the battery. The thermal management module of soft-pack
batteries is more complex than that of hard-shell prismatic batteries, so the
energy density of a group of soft-pack batteries is lower than that of
hard-shell prismatic batteries.
Due to the application of high energy density materials, the safety of
soft-pack batteries is uncontrollable, because soft-pack batteries are sealed by
two layers of polymers pasted together; while hard-shell square batteries are
sealed by welding of metal aluminum plates, so hard-shell square batteries The
sealing of batteries is higher than that of soft pack batteries.
Thermal runaway is a very important risk factor in battery safety. When
thermal runaway occurs, soft-pack batteries cannot release energy in a
directional manner, but hard-shell rectangular batteries can have some specific
exhaust and directional design in the module. Fire exhaust channel. This ensures
that even if a cell goes out of control, the energy of the cell can be released
along the fire exhaust channel, and the thermal insulation and fireproof
materials between cells can protect other cells from being affected, thereby
ensuring the safety of the entire system.
If you want to meet the vehicle's driving range of five to six hundred
kilometers, the number of cylindrical batteries required will be particularly
large. Tesla chose the cylindrical battery 18650. Model Large, it is difficult
to achieve a high level of battery safety.
Therefore, BYD, which has always been known for its safety and technology,
finally chose hard-shell prismatic batteries. The prerequisite for bringing
consumers the wonderful driving experience of electric vehicles is to ensure the
safety of passengers. This is BYD's consistent style.
2. Battery Thermal Management System BMS
Similar to the "bad temper" of the engine, the power battery is very
"delicate". Lithium batteries are not sensitive to the temperature range of
0°-40°. However, once the temperature exceeds this range, the life and capacity
will be greatly reduced. The low-temperature attenuation of lithium batteries is
more serious than that at high temperatures, so the problem of reduced cruising
range of electric vehicles in winter is more serious in northern my country. In
response to the adverse effects of temperature on batteries, battery
manufacturers have developed a battery management system. BYD's battery thermal
management system can effectively control the temperature of the battery and
control it within a suitable temperature range, improving the vehicle's charge
and discharge performance and delaying Battery degradation. The battery thermal
management system can achieve battery cooling and battery heating.
Battery cooling is a battery thermal management system that reduces the
temperature of the coolant in the battery water channel as needed by controlling
the opening of the electronic expansion valve and the speed of the electric
compressor, thereby taking away the heat generated during battery operation and
the heat in the environment. The cooling tubes of the internal cooling circuit
of the battery are arranged in an S-shape, which makes the contact area with the
battery cells larger and is more conducive to the heat dissipation of the
battery pack. Improve the charging and discharging performance of the vehicle
and delay battery decay.
Battery heating: When the vehicle is in a low-temperature environment and
the battery temperature is low, the battery thermal management system controls
the PTC water heater to heat the coolant in the water channel during the
charging process, and the high-temperature liquid in the water channel increases
the battery temperature to achieve low-temperature charging and discharging
functions.
3. “Technical means” to control security
Within BYD, battery safety is defined as the highest level, and no safety
issues are allowed. BYD considers battery safety from 7 dimensions and 4 levels,
and has corresponding protective measures in each dimension and level. From four
levels of cells, modules, battery packs and systems, to seven dimensions of
reliable connection, high voltage protection, collision, overcharge, short
circuit and thermal runaway, battery safety is effectively protected in all
aspects.
"Safety Guard" for CID overcharge protection
To prevent overcharging, BYD has multiple levels of protection: first, it
accurately detects the voltage of the battery and monitors the status of the
battery in real time. The second level is BMS layered protection. It charges to
different voltages and executes different commands. It controls the charging
status by limiting current and cutting off relays. If both levels fail, the
third layer of protection is CID (Current Interrupt Device) technology. CID
designs a flip piece on the battery cell. When the battery is overcharged, the
internal pressure of the battery increases. CID uses the internal pressure of
the battery to The high voltage turns over the flip piece to disconnect the
circuit. The battery cells of the battery pack are connected in series. As long
as one cell is disconnected, the entire circuit is cut off. As a pure hardware
protection device, CID is BYD's patented technology.
FPC (flexible circuit board) simplifies the "friendship bridge" between
modules
BYD uses flexible circuit boards to connect battery modules, which
eliminates many connectors and wires, making the battery module layout more
concise and the product layout more reasonable. BYD's FPC (flexible circuit
board) has built-in fuses to avoid risks such as short circuits caused by
accidental damage to the control circuit, further improving battery safety.
Explosion-proof valve-the "fireman" of battery safety
As a powerful line of defense at critical moments of battery safety, the
explosion-proof valve is a "firefighter" that ensures vehicle safety. When the
vehicle is in a fire or high-temperature environment, the high-temperature
environment of the battery core will cause the electrolyte to vaporize. The
vaporized electrolyte will cause excessive pressure inside the battery core. If
it is not relieved in time, excessive pressure in the battery core will cause
the conductive core to burst. The function of the explosion-proof valve is to
release the high-pressure gas inside the battery core when the pressure inside
the battery core exceeds the safe pressure to avoid battery core explosion and
more serious consequences.
No amount can be done too much on safety issues. Compared with the
profit-seeking behavior of American companies such as General Motors and Ford
that did not modify design defects for the sake of profit, causing safety
accidents and disregarding consumer safety, BYD is truly a conscientious
company. Always put safety issues first. BYD has not had any safety accidents
caused by battery problems in the past 15 years. In the field of electric
vehicles, the battery life and safety that consumers are most concerned about
have been initially solved by BYD. We look forward to BYD's further achievements
in electrification and intelligence in the future. Good performance, stay true
to your original intention and move forward.
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