BYD blade battery “cut” who’s neck?

In January 2020, by the 100th China Electric Vehicle Conference, BYD announced that it would launch a “blade battery” in March that will increase its energy density by 50% compared to conventional lithium-ion batteries and apply it to the new CAR BYD’s Han model, which will last more than 600 kilometers (NEDC). After BYD’s share price rose for days, triggering a lot of internet discussion, but did not cause much of a sensation, especially the author, did not feel anything special.

At the end of March 2020, BYD held a “blade battery” online launch, said that the traditional battery pack space utilization rate of only 40%, “blade battery” battery pack space utilization rate can reach more than 60%, can greatly improve battery life.

And because of the increased space utilization rate, so that the single cell energy density of 180Wh /kg of “blade battery”, assembled into a battery pack after the system energy density of 140Wh /kg, thus meeting BYD “Han” modelcant on the 549 kg weight of 77kWh battery pack, to achieve 605 km battery life (NEDC).

However, these, compared with the current large number of three-yuan lithium battery, is not a good advantage, because at this stage of the three-yuan lithium battery single cell density of up to 200-300Wh/kg, assembled into a battery pack system in 160-200Wh/kg or so.

What really makes netizens boil and the Internet is the next three video clips played by BYD, namely: a three-yuan lithium battery needle test, a lithium iron phosphate lithium battery needle test, “blade battery” needle test.

After playing the video, the results are clear: “Blade battery” passed the “power battery’s most demanding needle test”, in contrast to a three-dollar lithium battery burning violently, a lithium iron phosphate battery leakage high-pressure high-temperature gas.

The light and dark of the “blade battery”

BYD ‘blade battery’ needle test video, caused people to iron phosphate lithium battery and triple lithium battery debate, from the beginning of the technical principle analysis all the way into a melee, which triggered the author’s curiosity, decided to study a.

In any case, a few established facts need to be clarified, otherwise it would be meaningless.

First, the “blade battery” is a lithium iron phosphate (LFP, LiFePo4), first invented by Gudinav (one of the 2019 Nobel Laureates in Chemistry), and in 1996 the University of Texas filed a patent in the United States on behalf of Gudinav Laboratories (WO1997040541). But before Japan’s NTT sent a researcher, Okada, to assist Gudinaf’s research, and then registered a patent in Japan in 2015, there are many stories to tell about the subsequent patent battle.

Note: lithium-ion batteries, to be precise, lithium-ion batteries, because a variety of lithium-ion battery negative materials are mostly similar, so are by positive materials as a way to name. That is, the lithium iron phosphate lithium battery is extremely iron-phosphate lithium compound.

Second, lithium phosphate has the advantage of “natural”.

Lithium phosphate has good cycling performance, i.e. long cycle life. There are many reasons for the decline of lithium battery power, but the main thing related to positive material is the “crystal collapse” of the positive material structure during charge and discharge, resulting in structural damage, which causes some positive material sincarcity. The iron-phosphate compound is stable from the molecular structure compared with the nickel cobalt manganese compound, the NCM molecule is similar to the “thousand-layer cake” shape, the lithium ion flows from between the two layers, and the LFP molecule is the “olivine” shape, lithium ion swims in the three-dimensional structure gap. That is, even if the lithium ion “leaves” in the LFP molecular structure, the remaining FePo4-like structure is relatively stable, while the NCM is relatively unstable. (Three-way lithium battery cycle life of about 1500 to 2000 times, lithium phosphate can be about 4000 times)

(NCM is similar to NCA structure)

In addition, the high safety, iron phosphate lithium compound itself decomposition temperature in 700 to 800 degrees, far higher than the three-cell lithium compound 200 to 300 degrees, so the theoretical safety is much higher;

Crucially, although the early lithium iron phosphate batteries are less efficient due to their structural reasons (image is that the freedom of lithium-ion activity is not high due to structural stability), but with the clitoris technology (France’s world-class lithium-ion scientist Michel Armand invented, and later patented with Gudinav, MichelArmand), and nanochemical material sprocess technology, the current lithium-metal lithium phosphate charge discharge performance (i.e. power) is no worse than the triple lithium battery.

Finally, lithium iron phosphate also has “congenital” disadvantages.

The energy density of lithium iron phosphate battery is low, and the top of the single cell is just touching the general level of the lithium battery of three yuan. The reason is that compared to the triple lithium for low capacity (how much ah), and low voltage (three yuan is mostly more than 4V, lithium phosphate is about 3.4V), energy is the capacity multiplied by the voltage (how many Wh).

The low temperature performance is poor, compared to the triple lithium at -20 degrees has about 70% capacity, iron phosphate is only about 50%. The main reason is still the structure of its positive material, although the lithium ion freedom under the structure is increased by technology such as carbon encapsulation and nanomaterials mentioned earlier. However, at low temperatures, the problem is still not possible.

Measuring power (SoC, State of Charge) is more difficult, because the voltage of lithium iron phosphate batteries is more stable during discharge, so if the BMS (Battery Management System) does not do well, it is likely to show that there is still 10% of the charge, instantly become 0%. The resulting problem is not only the inconvenience of the use end, more is that if the core data can not be detected well, it is more impossible to manage the charge and discharge strategy, so that the battery life is reduced or even the phenomenon of lithium zhilist caused by short circuit.

However, whether it is lithium phosphate or triple lithium, its “natural” advantages and disadvantages are the industry consensus, but also all researchers know the part. It is clear that the biggest threshold in the open-door market for electric vehicles has always been “life-long anxiety”, and if this pass is not passed, then all the other “advantages” will disappear. So, relatively safe but low-capacity lithium iron phosphate batteries have long been used by public transport and urban special vehicles (and, of course, many portable appliances), while passenger cars are getting further and further away from lithium phosphate.

But there are two major factors in the market “promising” the return of lithium phosphate: first, the core material cost of three-way lithium batteries is getting higher and higher, resulting in further reduction in battery costs, and second, people’s safety requirements are increasing, such as the impact of China Insurance Research on the purchase of cars.

The key point to solve this problem lies in how to make up for the “disadvantage” of lithium phosphate and break the threshold of “life-long anxiety”.

BYD’s answer

The first problem for lithium phosphate is energy density, but the energy density of a single cell is limited by the material itself, and it is not impossible to break through further, but to achieve it in a short time;

Electric vehicles require voltages of up to several hundred volts, so lithium batteries are basically combined in series and parallel with a number of cells, forming modules and then packing them into the battery pack. However, combined with wiring arrangement, temperature control system, battery pack protection materials, battery pack frame structure, and even the BMS system included, resulting in a significant reduction in the energy density of the system, which is assembled into a battery pack that can be used by a vehicle, although the core energy density is high. (Cell-module-battery pack)

BYD’s strategy is:

1. Improve the total amount of monomer energy by “flattening and elongating” the battery to reduce the waste of space caused by placing multiple batteries in the unit volume.

2. “Flat long” type battery because of the contact area is large, temperature control system can be slightly simpler can also be satisfied, further reduce the use of space.

3. By laying the electrodes of the battery at both ends, reduce the trouble of wiring and the waste of Z-axis space, and further improve the use of space.

This set of strategies down, so that the single core energy density is not high “blade battery”, through the CTP (cell-battery pack, Cell-To-Pack) way, thereby increasing the energy density of the system, only dare to triple lithium battery package “call board”.

Although essentially, “blade battery” does not have a breakthrough in the battery material itself, but in the current direction of the development of the entire industry, this structure upgrade is not only the overall trend, but also the current optimal solution to improve the density of the system. For example, the Nindh-era CTP structure, Tesla went from the Model S’s 11 module battery packs to the Model 3’s 4 module battery packs.

At this stage, however, the “blade battery” solves only the “innate” energy density problem and does not explain the solution to the two other “innate” problems of lithium phosphate.

So there is the author to visit BYD battery factory.

Unexpected, reasonable

BYD ‘Blade Battery’ was produced by Chongqing Bishan Fudi Battery Co., Chongqing (renamed BYD Battery in March 2020), which was established in 1998.

The first thing to visit the factory was to experience the three battery needle tests mentioned earlier; of course, the results were still the same, but with a slight difference, the author was able to see the whole process with my own eyes, and in accordance with the requirements of the national standard, the needle after the injection to retain the battery status after an hour.

The highlights that followed focused on the challenges overcome by the “stacking” process in “blade” production: the long-size double-sided coating process and the fast-stacking technology (which may involve secrets and not being shown).

Here to add a little knowledge, cylindrical battery is a winding process, square-shaped batteries will use winding and stacking process, wherein the difficulty of stacking process is cutting, rapid stacking and late packaging, so from a production perspective is more difficult and cost is not low, especially such a long size of the core.

This, to give BYD technical affirmation, especially related production equipment are self-produced.

Then although BYD spent a lot of time and chapter on the safety of the “blade battery”, but the lithium iron phosphate itself has the “innate” advantages, enough to support it to complete the three-way lithium battery can pass the test (squeezing, high temperature, overcharge, battery pack thermal diffusion).

All of the author’s concerns are in low temperature performance and SoC measurement methods, but the answer is a bit “unexpected”.

The first is the low-temperature performance, BYD did not specify how to achieve the low-temperature performance of lithium iron phosphate, just said that “the performance of the material has improved, heat management heating”;

“Blade battery pack” in the 0 degrees and -10 degrees ambient temperature, charging speed is slightly slower than The NCM811 three-yuan lithium battery;

Most surprisingly, the “blade pack” can hold a battery pack capacity of 90% at -10 degrees and -20 degrees, and the discharge power is higher than the NCM811 at low temperatures and low power.

Of course, the charging power mentioned before, in the current package of carbon, nano-materials and other technical support, lithium phosphate charge and discharge speed is no longer a disadvantage.

But when I asked about the “SoC calculation and measurement method”, BYD said, “We have overcome the calculation of SoC in lithium iron phosphate BMS, and it is no longer a problem.”

The answer is “unexpected” because the insurmountable shortcomings of lithium phosphate have been overcome by BYD, but the specific technical explanation seditious is somewhat “reasonable”.

The author speculates that BYD may be unwilling to explain too many technical details to an editor, or is unwilling to publish “confidential” directly under such circumstances, but the true reason is unknown.

Lithium iron phosphate batteries want to improve low temperature performance, can not escape the application of nanochemical materials, positive materials to add conductive substances, the use of particle spherical technology, adjust the composition of electrolyte and other methods. As for whether the actual effect is in line with BYD’s test results, it will be clear when it is time for BYD’s “Han” mass production delivery.

Whether it’s sustainable or safe?

In fact, no matter how much waves BYD’s “blade battery” in public opinion, can not escape a consumer’s most direct torture: “to continue the air or safe.” “

Note that the safety here refers to is relatively safe, not absolutely safe, even if the lithium iron phosphate battery compared to the triple lithium battery are safe, but loaded into the electric vehicle, the final reflection of the safety by the battery package, BMS system, vehicle passive safety and many other factors. If anyone says “electric cars with lithium iron phosphate batteries are absolutely safe”, it is not bad or stupid.

The previous Ningde era and BYD’s air-to-air confrontation, it seems that the Ningde era “lost the wife and fold the soldiers”, not only did not let consumers understand, but made the Ningde era on the back of the “stupid public relations” charge;

Iron-phosphate lithium batteries are safer than lithium batteries, and triple lithium batteries have a higher energy density than lithium-ion phosphate batteries, and there is little room for debate between the two.

(A lithium iron phosphate needle test)

Iron-phosphate lithium battery can be used CTP way into a battery pack, three-way lithium battery can be the same; So no matter which aspect of the debate is too narrow and limited, the problem is in the current technical point of view on two aspects: “continued” and “safety”.

Three-way lithium battery is not unable to make “needle-proof”, but if you want to demand a single cell through the “needle” experiment, it is necessary to in the electrolyte, diaphragm, cell packaging and other aspects of the protective material, resulting in a decrease in energy density, increased costs. Military vehicles use these batteries (GJB4477), but for electric passenger cars, the loss of range is basically tantamount to loss of competitiveness, and additional costs will be added.

The same product, must be expanding its advantages, make up for its disadvantages, before it will gradually be accepted by the market.

For triple lithium batteries, to make up for the safety disadvantage, Kung Fu is best spent in the battery pack system safety, from BMS active safety control, to the battery pack internal structure and materials, to the entire battery package passive safety. The reason is very simple, for example, rather than painstakingly make people into Hulk, it is better to be safe in the overall owner of the car passive collision.

In turn, lithium iron phosphate batteries want to compensate for the energy density, with the current level of battery material development, preferably through the use of space optimized path, thereby increasing the overall system energy density.

Both are long and short, but the standard of measuring electric vehicles has changed. The biggest enemy of the previous obstacle to people’s choice of electric cars was “continued”, but today’s 500km and 600km range has led to a gradual easing of this worry and a focus on other areas.

That’s why, when “blade batteries” use safety performance as their core selling point, there are so many consumers “buying” the root cause.

But in summary, the use of lithium phosphate “blade battery” will certainly have a significant impact on the existing electric vehicle market, but not enough to eliminate the status of triple lithium batteries, because people’s demand for “continued” is different, and the current “safe” or not is in the comparative level, not the product qualification level. So, for a long time to come, the two will be co-existing.

In the final analysis, when there is various forms of competition and head-on collisions in the industry, it is the market that is developing rapidly, and only then will the ultimate beneficiaries be consumers.

As for by BYD Han, which is strongly connected to the “blade battery”, whether it will perform well in the market in the future will tell us everything.