Seeing that many friends at the bottom of the original video comment said that the video could not be understood, this article divided the knowledge points into the following parts:
1, Introduction of National Standard Test Method for Battery Safety
2. Introduction of different battery types
3. Review blade battery parameters
4. Interpretation of acupuncture experimental results.
5. Engineers' views on lithium iron phosphate batteries and ternary lithium batteries.
6. Summary
Introduction of current national standard test methods for battery safety.
In the national battery safety requirements, the hazards caused by battery cells, battery packs or systems of electric vehicles refer to:
-Electric leakage may lead to high voltage and insulation failure of the battery system, and indirectly lead to electric shock and fire of the battery system;
-Fire, direct burn to human body;
—— Explosion directly harms human body, including high-temperature burns, shock wave injuries and explosion debris injuries;
-Electric shock, injury caused by electric current flowing through human body.
Therefore, the Ministry of Industry and Information Technology specially designed the national standard test method for battery safety according to these dangerous situations. Is the battery safety test of electric vehicles still used in China? 20 15? Version of the national standard, and based on? GB/T？ 3 1485—20 15? What are the safety requirements and test methods of power batteries for electric vehicles? GB/T？ 3 1467.3—20 15 "Lithium-ion batteries and systems for electric vehicles?" 3? Part: safety requirements and test methods, and the standard formulation plan for upgrading is in? 20 16? Year? 9? Officially issued in June, plan number? 20 160967-? Q-339 .
The existing national standard battery safety test items are mainly divided into: vibration test, mechanical shock, simulated collision, extrusion, temperature shock, damp-heat cycle, seawater immersion, external fire, salt spray, high altitude, overcurrent protection, overtemperature protection, short circuit protection, overcharge protection and overdischarge protection. In the case that the new national standard has not been formally implemented, new energy automobile enterprises can selectively implement the overcharge and thermal diffusion tests specified in the new national standard 20 15. The acupuncture test required by the national standard version is now selectively implemented by enterprises as an optional project.
Test conditions: What is the required temperature range of ambient temperature in the latest standard? 22℃ 5℃, what is the relative humidity? 10% ~ 90%, atmospheric pressure is defined as? 86 kpa ~ 106 kpa, state of charge? SOC？ By who? 100%? Change it to 50%
Introduction of different battery types
After understanding the national standard test method of battery safety, we also need to understand different battery types. At present, the power batteries used in pure electric vehicles are mostly lithium-ion batteries, such as lithium iron phosphate battery, ternary lithium battery, lithium manganate battery, lithium cobaltate battery and lithium titanate battery. The basic structure of lithium ion battery is mainly composed of positive electrode, negative electrode, electrolyte, diaphragm, current collector, electrode lead and shell.
What ordinary consumers hear most are mainly lithium iron phosphate batteries and ternary lithium batteries. What do ternary lithium batteries mainly include? NCM？ Proportional square battery (common contemporary Anpu Technology Co., Ltd.? NCM8 1 1？ Battery), cylindrical NCA battery (generally provided by Panasonic to Tesla? 2 1700? Battery) and? Lithium iron phosphate battery, these names are actually taken according to the different materials of the battery anode.
The cathode materials of power battery can be divided into lithium cobaltate (LCO), lithium manganate (LMO), lithium ferrous phosphate (LFP), ternary lithium battery (lithium nickel cobalt manganate NCM, lithium nickel cobalt aluminate NCA) and other technical routes. The negative electrode usually consists of carbon-based negative electrodes such as graphite and graphene, titanium-based negative electrodes such as lithium titanate or alloy-based negative electrodes such as silicon and tin. Electrolyte is an organic solution containing lithium salt, which is the carrier to realize the flow of lithium ions (Li+). LiPF6？ Mixed solvent system. The separator is usually made of polyethylene or polypropylene film, which separates the positive and negative electrodes and provides a barrier for free electrons to pass through. Li+Shuttle Channel. The current collector has a positive electrode and a negative electrode, the positive electrode current collector is usually aluminum, and the negative electrode current collector is usually copper or nickel.
Review blade battery parameters
After reading the above explanation, friends who are not familiar with battery technology have doubts again. What is BYD's blade battery? In fact, the cathode material of the blade battery is also lithium ferrous phosphate, but it is much more on the blade battery? CTP？ Technology, design of single cell. Therefore, in the experimental video of the comparative test, the blade battery looks very different from the lithium iron phosphate battery.
Image from: car home
In essence, BYD's blade battery still belongs to the category of lithium iron phosphate battery. It's just that the length of BYD blade battery developed by ourselves is greater than? 0.6? Battery cells are also evolving to large capacity, but the shape of the cells is flatter and narrower (the long side can be customized, and the maximum stable length of the cells can be achieved? 2 100mm), the batteries are stacked like "blades" and inserted in the battery pack, which is why it is called "blade battery". This is the latest "blade battery" to be carried by BYD Korea, with an increase in volume compared with energy? 50%, cost reduction? 30%, cruising range reached? 605 kilometers.
In addition, we also briefly introduce here? CTP？ What do you mean? In fact, at present, the battery packs carried by general electric vehicles are all assembled into modules by batteries, and then the modules are installed in the battery packs, forming a three-level assembly mode of "batteries-modules-battery packs". And then what? CTP, right? Cells? Where to? PACK, the battery cells are directly integrated into a battery pack, thus eliminating the intermediate module link. Because the module is directly integrated into the battery pack, the volume utilization rate of BYD blade battery has been greatly improved compared with the old ternary lithium battery, and the energy density of the system can also be indirectly improved.
Interpretation of acupuncture experiment of leaf battery
The dynamic thermal characteristics of power battery under the condition of internal short circuit are the research fields that many power battery manufacturers pay close attention to. The size of internal short-circuit area is an important factor affecting the short-circuit behavior in batteries. The larger the radius of the internal short-circuit area of the battery, the higher the heat released by the reaction and the higher the maximum temperature reached by the internal short-circuit. According to the heating mechanism of battery, the side reaction heat generated under abuse condition is the extreme condition of battery heating, and acupuncture experiment is the extreme test method based on this background.
The process of acupuncture experiment is not complicated. According to the national standard of acupuncture test method, it is necessary to set the diameter as? 6- 10mm？ High temperature resistant steel needle (tip cone angle 45 ~? 60), at the speed of (25 5) mm/s, from the direction perpendicular to the battery plate, the penetration position should be close to the geometric center of the penetration surface, and the steel needle should stay in the battery for observation 1 hour, and it is qualified that it does not catch fire or explode.
In the video released by BYD, the battery samples of the comparative acupuncture test are all automotive batteries produced by BYD, and the three experimental samples are ordinary lithium iron phosphate battery, NCM622 ternary lithium ion battery and blade battery. Due to the fire in the video and the high surface temperature of ternary lithium battery after the experiment, it caused a hot discussion among netizens.
Experimental results:
NCM622？ Ternary lithium-ion battery: At the moment when the steel needle pierces the battery, the battery shell expands rapidly, the pressure relief valve of the battery opens, the internal high-pressure electrolyte is sprayed out, the battery catches fire, and the surface temperature of the battery shell exceeds 500℃.
Ordinary lithium iron phosphate battery: After the thermal runaway, the internal temperature and pressure of the battery rose rapidly, the battery shell expanded to a certain extent, the battery pressure relief valve opened, the battery did not catch fire and explode, and the surface temperature of the battery shell? 200℃-400℃。
Blade battery: After the steel needle pierces the battery, the battery voltage drops, no spark, smoke or electrolyte is ejected at the piercing position, and the battery case does not expand. The surface temperature of the battery shell is 30℃-60℃.
Why are the experimental results so different? First of all, we need to know what thermal runaway and thermal diffusion mean respectively. Thermal runaway (thermal? Out of control) refers to the phenomenon that the battery temperature rises uncontrollably due to the exothermic chain reaction of the battery monomer. Thermal diffusion? (hot? Propagation) refers to the phenomenon that the thermal runaway of other battery cells in the battery pack or system is caused by the thermal runaway of one battery cell. Simulation of internal short circuit of lithium ion battery by acupuncture experiment. When the metal needle is slowly inserted into the lithium-ion battery at a certain speed, it causes a short circuit inside the battery. At this time, the electricity of the battery is released through the short circuit point, and this part of heat is finally converted into heat energy. Because the generated heat cannot be diffused in time, can the instantaneous temperature of the short circuit point reach? 1000? ℃? Above, resulting in thermal runaway.
Mathematical model of reaction heat
From a chemical point of view, the electrolyte of lithium-ion batteries usually contains carbonate. Carbonate will decompose at high temperature to produce hydrogen and hydrogen radicals, which will react with oxygen to produce hydroxyl radicals and oxygen radicals, and oxygen radicals will react with hydrogen to produce more hydrogen radicals, and so on. So once the thermal runaway happens, the consequence is a very serious spontaneous combustion accident.
Combined with this experimental video, when the ternary lithium battery is short-circuited in the battery, the decomposition temperature of the cathode material is at? 200℃? Left and right, the heat generated after thermal runaway can't spread in time, so it is an irreversible process after thermal runaway. Blade battery belongs to lithium iron phosphate battery, and the decomposition temperature of cathode material is at? 500℃? Most importantly, the temperature of thermal runaway is higher than that of ternary lithium ion battery, and the single cell of blade battery is very thin, so the heat release caused by short circuit inside the battery is not obvious, and there will be no strong thermal runaway. Moreover, compared with the common lithium iron phosphate battery, the blade battery shell has a large heat dissipation area, and the generated heat can be diffused in time, so the surface temperature of the battery shell has been kept at? 30℃-60℃. During the experiment, even the eggs placed on the surface of the blade battery shell were not cooked.
After the video was released, careful netizens found in Weibo's comments that in the video paragraph of the blade battery, the eggs placed on the surface of the blade battery shell were not always placed on the battery. The manufacturer did not reply to this question, but judging from the temperature change data of the blade battery case, it may be just an editing problem. Because the experimental duration of puncture test needs to be observed for one hour, it is impossible for this video to record the whole process. For blade batteries without serious thermal runaway, engineers may put eggs on the battery surface in the second half of the waiting period. If you have any questions about this place, we will go to BYD factory to shoot the whole acupuncture test video for you later.
The passing rate of acupuncture examination is extremely low.
In fact, it is not surprising that such experimental results appear. In the previous data, the passing rate of acupuncture examination was extremely low. Why? 20 17? Year? 1? Month? 17? In the "Regulations on the Administration of New Energy Vehicle Manufacturers and Products Access" issued in June, GB/T? 3 1485—20 15? The acupuncture test in is not implemented for the time being. Drafting group study? IEC？ 62660-2，IEC？ 62660-? 3? And other standards have not been adopted to evaluate battery safety.
Future Prospect of Lithium Ferrophosphate and Lithium Ternary
In this year's promotion catalogue of new energy vehicles, we found that BYD batteries are ideal. Contemporary Amperex Technology Co., Ltd. and BAIC New Energy use limited lithium iron phosphate batteries. Will Tesla be made in China in the future? Models? 3? Lithium iron phosphate batteries will also be used. It seems that there are signs that lithium iron phosphate batteries are likely to make a comeback, so will ternary lithium batteries be replaced?
Contemporary Ampere Technology Co., Ltd. lithium iron phosphate battery used in BAIC new energy?
Actually, I don't think so. Because the energy density of lithium iron phosphate battery can not be greatly improved under the existing material structure and R&D technology, it is difficult to meet the growing cruising range demand of electric vehicles in the future and the development planning requirements of power batteries proposed by the state. 2020? What is the annual battery energy density? 300Wh/kg，2025？ Reached in 2008? 400? Wh/kg，2030？ Reached in 2008? 500 WHr/kg.
20 19 major manufacturers install lithium batteries of different materials (picture from: cars and accessories)
In the field of passenger cars for ordinary users, especially pure electric vehicles with long battery life, ternary lithium batteries with high energy density have obvious advantages in improving the driving range of electric vehicles. However, compared with lithium iron phosphate battery, ternary lithium battery has poor thermal safety and is prone to thermal runaway under extreme abuse conditions, which is a severe test for its further application and promotion in electric vehicles.
Recommended car catalog ratio of lithium iron phosphate battery for passenger cars (image from: cars and accessories)
Especially after the introduction of blade battery, the volume energy density is improved, and the overall weight is close to that of ternary lithium battery, and the energy density is enough to meet the needs of most family cars. Coupled with the thin and light design, it can meet the layout requirements of different types of pure electric vehicles.
Views of engineers in new energy automobile enterprises
Based on the selection of battery wires, we also interviewed BAIC New Energy? Beijing? Several questions of the brand engineer, the engineer specifically answered as follows.
1. Some car companies began to reuse lithium iron phosphate batteries. Will lithium iron phosphate battery become the mainstream in the future?
During the Thirteenth Five-Year Plan period, with the rapid development of ternary batteries, the energy density of lithium iron phosphate batteries has also been greatly improved. 20 15? About 2008? 125Wh/kg？ Promotion to closure? 170Wh/kg, and some batteries reached 180Wh/kg. Thanks to the energy density of lithium iron phosphate battery? 50%? Upgrade, as well as the upgrade of battery system integration technology, now under the same volume, 20 15? Can only run every year? 200 kilometers? Can your car run now? 300-350km, this mileage range has been able to meet part of the market demand, coupled with the cost advantage over ternary batteries, making lithium iron phosphate batteries stand firm in this market.
But according to the data released by China Information Data Center, 400km? The above cruising range is still the demand of most electric vehicle users. Based on this, high specific energy ternary battery will still be the mainstream demand in the market.
2. Predict the future development direction of lithium ferrous phosphate and ternary lithium battery solutions?
Facing the differentiated market demand, ternary lithium batteries with high energy density will still be used for vehicles with long driving range. Compared with some users who only need to meet the daily mileage demand and pursue cost performance, lithium iron phosphate battery is just a better choice. So I think both of them will occupy different market shares. In the future, ternary lithium batteries will give full play to the advantages of high energy density and focus on solving the problems of safety and instability of their own batteries, while lithium iron phosphate batteries will continue to improve energy density.
3. Beijing? Will the brand model be changed to lithium iron phosphate battery in the future?
BAIC New Energy provides users with a variety of product configurations, including the models of lithium iron phosphate batteries. Differentiated market demand brings differentiated product configuration and creates different product matrices for different user groups.
Engineers of SAIC passenger cars also expressed their opinions on the selection of power battery lines. The engineer's opinion is as follows:
In the early stage of electric vehicle development, the energy density of battery pack was < 140 Wh/kg, so what about the whole vehicle? NEDC？ The cruising range is mostly lower than? 300 kilometers. At that time, the bottleneck affecting the development of electric vehicles was cruising range, and with the support of national subsidy policy, it could make up for the lack of economy, so ternary lithium batteries were the first choice. With the decline of the national new energy subsidy policy, everyone is facing great pressure to reduce costs. At the same time, the energy density and charging shortcomings of lithium iron phosphate battery, which has been criticized by people, have also been improved with the development of technology.
In terms of energy density, CTP (cell? Where to? PACK), that is, the technology of directly integrating the battery into the battery pack has matured, the battery pack integration is more efficient, and the energy consumption of the whole vehicle is lower. What is the endurance of lithium ferrous phosphate model? 400km？ Even? 500 kilometers? Above.
In terms of charging, with the development of battery fast charging, thermal management and charging pile technology, lithium iron phosphate batteries used in passenger cars can basically reach the same fast charging rate as the existing mainstream ternary batteries.
In terms of cost, the national subsidy policy has declined, with NCM8 1 1? Although the cobalt content of the battery is reduced and the cost is reduced, the process is complicated and the production cost is relatively low at this stage. NCM523？ No obvious advantage. At this time, lithium iron phosphate batteries with lower cost and longer service life are naturally selected by more car companies and become the mainstream trend. Or the sales ratio will be high.
Generally speaking, these two battery materials will coexist in the future. According to the market demand positioning planning, it provides more choices for users to buy cars, and there is no substitute for anyone.
1)? Lithium iron phosphate battery gives full play to the advantages of cost, life and safety, focusing on low-end models and operating vehicles, with cruising range? ≥400km, can it be realized? 500? Even? 600 kilometers.
2)? With its high energy density, faster charging speed and longer cruising range, Sanyuan focuses on mid-to high-end private sales models and driving range. ≥500km, what can be achieved? 600? Even? 700 kilometers.
Weilai's engineers also gave their own opinions based on this problem.
If iron and lithium are popularized, it may mean that the subsidy policy based on energy density will no longer be the goal of car companies. Ternary and lithium iron have their own advantages and disadvantages. It cannot be simply said that lithium iron is the only direction in the future.
Edit the summary? /
A video has warmed up the topic of line dispute between lithium iron phosphate battery and ternary lithium battery. After communicating with professional engineers, I will also talk about my views. I think these two lithium batteries with different cathode materials can be regarded as complementary. Just like turbocharging and mechanical supercharging, it is also to improve the power of the engine. These two technologies with different structures can be applied to cars with different personalities. The same is true for new energy vehicles. Lithium iron phosphate battery and ternary lithium battery have their own advantages. For new energy vehicles with different design and positioning, the most suitable power battery can also be selected. With the continuous improvement of battery technology, the battery life, charging speed and battery life of pure electric vehicles will also enter a new level.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.