Passing the needle puncture test, BYD's lithium iron phosphate blade battery "fights back" against ternary lithium batteries?

New energy vehicles, which have been "feeling their way across the river", seem to be at a new crossroads.

Should we continue to focus on endurance?

Or after ensuring a certain battery life, will the shortcomings around the "barrel" be filled one by one, such as the safety of the power battery?

Of course, this is not to say that all power batteries on the market are unsafe. It is just that some safety accidents caused by power batteries have touched everyone's nerves and may have affected the acceptance of new energy vehicles in the market, so they are highlighted.

For this reason, I think new energy vehicles may need to make some choices that respect the market, and the safety of power batteries is an unavoidable topic. And this topic has also attracted more attention because of a "needle puncture test" in the past.

01 How should we view the “acupuncture test”?

Recently, I had the honor of visiting the battery factory of BYD's Fudi Battery in Bishan, Chongqing, where I witnessed a "needle penetration test" comparing lithium iron phosphate blade batteries and ternary lithium batteries.

When punctured by a high-temperature resistant steel needle with a needle tip taper of 45°, a diameter of 5mm, and a penetration speed of 25mm/s, the test results were consistent with the previously disclosed "needle penetration test" results, that is, the lithium iron phosphate blade battery being tested did not catch fire or smoke, while the tested ternary lithium battery instantly smoked and then caught fire, and the obvious heat wave could be quickly felt through the glass.

At the same time, data from on-site monitoring showed that the voltage of the tested lithium iron phosphate blade battery gradually decreased, the puncture point temperature was around 36°C, and the safety valve temperature was stable at a little over 23°C. On the other hand, the voltage of the tested ternary lithium battery dropped to zero instantly, the puncture point temperature reached 628°C, and the safety valve temperature rose accordingly.

The conclusion of the comparative test is obvious. Under the above test conditions, the heating of the lithium iron phosphate blade battery is controllable and the safety is better.

Despite this, some people still question whether the ability to withstand the "needle puncture test" necessarily means that the power battery is safe, and whether ternary lithium batteries are definitely unsafe.

To answer this question, we need to further understand the basic principles of the "needle penetration test" and the respective characteristics of lithium iron phosphate blade batteries and ternary lithium batteries.

First of all, the starting point of the "needle penetration test" is to simulate whether the battery will run away due to the heat caused by the short circuit, and then catch fire or even explode. For power batteries, the "needle penetration test" is undoubtedly a very demanding test. In fact, it also simulates the scenes of internal and external short circuits; and the thicker the needle used in the test, the more difficult the test is (for example, the International Electrotechnical Commission uses a needle with a diameter of 1mm/3mm, and this test uses a 5mm needle).

Secondly, the lithium iron phosphate blade battery is as its name suggests, thin and long, which is very beneficial for heat conduction, and the decomposition temperature of its positive electrode material lithium iron phosphate is about 600°C. Although the energy of lithium iron phosphate is lower, the design of the blade battery has made its volume energy density comparable to that of ternary lithium after removing some structural designs. In the comparative test, the block-shaped ternary lithium battery is not conducive to heat conduction, and the decomposition temperature of its positive electrode material ternary lithium is only about 200°C, which is relatively easy to release active oxygen, causing fire or even explosion; of course, the energy density of ternary lithium is advantageous.

Thirdly, for the whole vehicle, the safety of the power battery is affected not only by the battery cells, but also by factors such as the design of the battery pack after packaging, the thermal management system, and the safety structure design of the whole vehicle.

So overall, the "needle penetration test" simulates an accident scenario under harsh conditions. The fact that the BYD lithium iron phosphate blade battery under test withstood the test shows its high safety. However, the tested ternary lithium battery is not as safe under such conditions due to its own characteristics. In the future, it may be necessary to integrate the use scenarios of the power battery and make efforts in the thermal conduction design of the battery cell, the battery pack design, etc.

02 What is the significance of lithium iron phosphate blade battery?

The mass production of lithium iron phosphate blade batteries does have positive significance for the entire new energy vehicle market.

Prior to this, lithium iron phosphate batteries encountered some obstacles in practical applications due to their lower weight energy density than ternary lithium batteries. This was mainly reflected in the fact that when a power battery of limited weight (volume, not equivalent) was placed in a limited body space, the vehicle's range was not ideal. Especially in the context of the incentive policy oriented towards range and the current charging and other supporting facilities to be improved, the weaknesses of lithium iron phosphate battery models were magnified.

Today, lithium iron phosphate blade batteries are first used in the BYD Han EV, which is about to be launched. Public information shows that the new car has a maximum range of 605km, and it only takes 25 minutes to fast charge from 30% to 80%. It can be charged and discharged more than 3,000 times, and the cumulative mileage exceeds 1.2 million km.

From the above information, the application of lithium iron phosphate batteries has obviously improved significantly. The main performance is that the cruising range exceeds 600km, which is a height that lithium iron phosphate batteries could hardly reach before, reflecting BYD's outstanding efforts in this regard. In this regard, BYD explained that the volume energy density ratio of lithium iron phosphate blade batteries has increased by 50%, which is comparable to mainstream ternary lithium batteries. In addition, it is worth noting that its fast charging performance is also very attractive.

At this point, some people may think, whether the lithium iron phosphate blade battery, which has an advantage in safety, will launch a counterattack against the ternary lithium battery and replace it?

In this regard, the author believes that the lithium iron phosphate blade battery currently produced by BYD has a high level of endurance performance and improved safety, which is undoubtedly more suitable for the current market. However, objectively speaking, the technology of power batteries is also constantly evolving. At the same time as BYD's lithium iron phosphate blade battery was launched, the technology of ternary lithium batteries with high energy density also has room for improvement, such as further strengthening the safety design of battery packs and vehicle structure.

Therefore, it can be said that for the current new energy vehicle market, the significance of BYD's lithium iron phosphate blade battery may be that it provides a timely choice.

In conclusion: BYD, which started out as a battery manufacturer, has accumulated enough experience in the upstream and downstream battery industry chain to stand out from the crowd. The breakthrough lithium iron phosphate blade battery puts safety first, which can be said to be a reflection of respect for the market and deserves recognition. We look forward to the performance of the Han EV and its power battery after it is launched on the market.