In the history of hybrid and pure electric vehicles, lithium iron phosphate batteries were once considered by manufacturers to be the most suitable choice.
But nowadays in household new energy vehicles, the term is hardly mentioned anymore. The reason is that another technological route is gradually gaining the upper hand, that is, the ternary lithium battery that people now hear most.
"The industry's over-reliance on ternary lithium batteries has led consumers to question the safety of new energy vehicles." BYD Chairman and President Wang Chuanfu said.
This time, BYD launched the "Blade Battery" to address the pain points in the field of vehicle power batteries, which is a step forward in battery innovation.
What is Blade Battery? Generally, a battery pack of an electric vehicle is composed of a module composed of a plurality of battery cells. For example, Tesla's battery cells are cylindrical 18650 batteries.
In order to keep the battery module stable in the car, it needs to be fixed with bolts, cross beams, longitudinal beams, etc.
The difference of the Blade Battery is that it eliminates the module step and directly inserts the battery cells into the battery pack in an array manner, thereby improving the internal space utilization.
The more innovative point than the structure is that Blade Battery has regained people's attention to the lithium iron phosphate battery that has been forgotten by home electric cars.
Batteries make a comeback
In the field of new energy passenger vehicles, ternary lithium batteries are almost "dominating the world."
According to statistics from the Research Department of the Power Battery Application Branch, the installed capacity of ternary lithium batteries and lithium iron phosphate batteries in the first half of 2019 accounted for 71.14% and 26.97%, respectively, and the gap continued to widen compared with the same period in 2018.
New Energy Vehicle Power Battery Installed Capacity in the First Half of 2018 and 2019 | Research Department of Power Battery Application Branch
But this does not mean that ternary lithium batteries can become the only choice. If you lengthen the timeline, you will find that there is no so-called "winner" in the technical route of the battery.
Battery technology is leading the development of electric vehicles to a certain extent. In the late 19th century, electric vehicles developed rapidly. People use electric cars for exactly the same reasons as they are today: noiseless, odorless, and inexpensive.
From the end of the 19th century to the beginning of the 20th century, the automobile market even formed a "three minutes of the world" situation: steam, electric and internal combustion engines. However, with the fastest development of internal combustion engines, the remaining two eventually withdrew from the automotive market.
Due to the pollution of the atmospheric environment and the rise of battery technology, electric cars have been renewed attention. The early electric car market was in a state of "a hundred schools of thought", and various battery technologies were installed on the car.
In 1990, GM showed the Impact electric concept car for the first time at the Los Angeles Auto Show, and the industry had a huge impact. GM then developed a pure electric car EV1 based on Impact's core technology and design, which was regarded as the pioneering work of modern electric vehicles.
As a result, major auto manufacturers have invested a lot of resources in developing electric vehicles. The only difference is that the batteries inside the vehicles are not uniform.
The EV1 is equipped with a lead-acid battery. In 1992, Ford launched the Ecostar with calcium-sulfur batteries. In 1996, Toyota used a nickel-metal hydride battery hybrid vehicle RAV4LEV. In 1997, Toyota launched the hybrid sedan Prius Prius (also equipped with nickel-hydrogen batteries) ).
Nissan also launched the world's first lithium-ion battery electric car Prairie Joy EV in the same year ...
The speed of commercialization is one of the most important factors in the development of inspection technology. After the commercialization of lithium-ion batteries by Sony in 1992, it happened to meet the development of the telecommunications and information markets. Because of the highest volume specific energy and mass specific energy, lithium-ion batteries have become the best choice for electric vehicles in terms of commercialization progress.
Among them, the most representative are lithium iron phosphate batteries and ternary lithium batteries.
The battle for technology
After the rise of lithium-ion batteries, there are currently only three types that can be used as power batteries in new energy vehicles: lithium iron phosphate batteries, ternary lithium batteries, and lithium titanate batteries. The last one is out of the scope of discussion for the time being because there is too little popularity.
Lithium iron phosphate batteries use lithium iron phosphate as the positive electrode material, while ternary lithium batteries use lithium nickel cobalt manganate as the positive electrode material, and the negative electrode material is graphite. Regarding the advantages and disadvantages of the two, here are a few points:
In terms of cost, the cost of lithium iron phosphate battery is much lower than that of ternary lithium battery. The former is characterized by the absence of precious metal elements, so the cost of raw materials can be relatively low.
Cobalt in ternary lithium batteries is a precious metal element, and the price of cobalt is rising rapidly. With the emergence of new things such as 5G, the supply and demand gap for cobalt will further expand.
In terms of energy density, lithium iron phosphate batteries are far inferior to ternary lithium batteries. The weight energy density of lithium iron phosphate battery is only 120Wh / kg.
If you calculate the energy density of the entire stack, including battery management systems, heat dissipation and other components, the energy density of ternary lithium batteries can reach 200Wh / kg.
In terms of safety, lithium iron phosphate batteries are even better. Lithium iron phosphate has stable chemical properties and good high-temperature stability. Decomposition will only occur at 700 ° C-800 ° C. It will not produce severe combustion when facing impact, acupuncture, short circuit, etc., and has high safety performance.
In contrast, the ternary lithium battery will decompose at 250-300 ° C. It will burn after encountering the flammable electrolyte and carbon materials in the battery. The heat generated will further aggravate the decomposition of the positive electrode, and it will deflagrate in a very short time.
Most of the spontaneous combustion of new energy vehicles in recent years is caused by ternary lithium batteries.
The reason that no major accidents occurred was that the vehicle's battery management system did relatively well. For vehicles equipped with ternary lithium batteries, the design of the battery management system and the heat dissipation system are both critical.
Based on safety considerations, new energy buses equipped with ternary lithium batteries cannot enter the new energy vehicle catalog of the Ministry of Industry and Information Technology, but China's policies on new energy vehicles also have strict regulations on energy density. The ternary lithium battery has become a new energy passenger vehicle. The mainstream choice for cars.
In terms of service life, lithium iron phosphate batteries have more advantages in cyclic utilization than ternary lithium batteries, but the low temperature performance of lithium iron phosphate batteries is poor, which is its "lethal injury".
Studies have shown that under low temperature conditions (air temperature below -10 ° C), the lithium phosphate battery will reduce the battery capacity to 20% of its initial capacity after less than 100 charge and discharge cycles. The ternary lithium battery has excellent low temperature performance, and can maintain normal battery capacity at -30 ° C. In low temperature areas in northern China, it is obvious that lithium iron phosphate cannot meet the service standards.
To sum up, the ternary lithium battery successfully relies on high energy density, and the direct expression of energy density is high mileage. It can be seen that the current mileage of several electric vehicles has exceeded 700km.
This is the pain point of car companies and consumers, so ternary lithium batteries have become the mainstream choice for electric car companies.
The lithium iron phosphate battery has temporarily died down, and has become the first choice for new energy buses due to its high safety.
However, when we analyze the pros and cons of the two batteries in detail, we will find that if the energy density of lithium iron phosphate batteries increases, the current market of ternary lithium batteries is likely to be affected. This is also an important reason for the widespread discussion of Blade Battery.
Can Blade Battery break through?
According to BYD, the volume energy density of the Blade Battery is the same as that of mainstream ternary lithium batteries, and the power stored in the same volume is almost the same.
As mentioned at the beginning of the article, Blade Battery omits the steps of the module compared with the traditional battery pack, and adopts the CTP (Cell to Pack, no module power battery pack) design idea, and installs the battery cell directly into the battery pack case.
This design can save accessories such as beams, stringers, and bolts while maintaining the strength of the battery pack, improve the internal space utilization of the battery pack, and increase the total capacity and energy density of the battery pack.
It is reported that BYD's CTP design has improved the space utilization rate inside the battery pack case from 40-50% of the traditional design method to 60-80%.
The increase in the total capacity of the battery pack directly leads to a significant increase in the battery life of electric vehicles.
The first BYD "Han" model equipped with Blade Battery has a range of 605km, which has basically reached the same level as that of models equipped with ternary lithium batteries.
But in terms of security, Blade Battery performs much better.
BYD Battery Lab conducted a needle-puncture experiment on lithium iron phosphate batteries, Blade Battery, and ternary lithium batteries, that is, the use of steel needles to pierce the battery plate, which instantly triggered an internal short-circuit of the battery, which led to battery thermal runaway.
The needling test is recognized by the industry as the harshest of all battery safety tests and can simulate extreme short-circuit conditions in the battery.
It is a mandatory test item for batteries of mass consumer digital products such as mobile phones and laptops, and it is not enforced as a mandatory standard for new energy vehicles.
According to the acupuncture video of three battery samples, NCM622 (the ratio of the three components of nickel, cobalt and manganese in the positive electrode material is 6: 2: 2) ternary lithium battery deflagration occurred at the moment of being punctured by the needle.
In comparison, the safety of lithium iron phosphate batteries is slightly better. At the moment of being punctured by a needle, lithium iron phosphate did not catch fire, but the surface temperature of the battery was as high as five or six hundred degrees Celsius.
When the Blade Battery was pierced, it did not behave abnormally, and its structure remained stable. The temperature sensor shows that the surface temperature of the battery is only 60 degrees Celsius.
Battery safety is indeed one of the issues that consumers are most concerned about. Blade Battery's solution reinforces this and also gives lithium iron phosphate batteries some right to speak.
In addition, Tesla is in talks with Contemporary Amperex Technology (CATL), China's largest automotive lithium-ion battery maker, and will use cobalt-free batteries produced by the latter in Tesla cars produced in China. lithium battery.
Tesla CEO Musk stated in June 2018 that he was committed to reducing the amount of cobalt. At that time, Tesla used about 3% of the cobalt in batteries. In the next generation of vehicles, cobalt was completely included in the list of raw materials. Get rid of.
Can lithium iron phosphate batteries surpass ternary lithium batteries and become the mainstream of automotive power batteries again? Before the results appeared, no one said badly. But in the field of battery innovation, the development of a cost-effective battery is indeed the key goal of all enterprises at the moment.
Blade Battery made a start. As the innovation of vehicle power batteries is becoming a bottleneck, the range of "climbing" speed is getting slower and slower. Blade Battery turns around and puts the type of batteries that will be forgotten on the stage.
If it is widely used in the future, it may be at the crossroads of power batteries, giving mainstream car companies another option.