Talk about the development trend of AG13 battery

It is understood that 18650 is the originator of lithium-ion batteries - a standard lithium-ion battery model set by Japan's SONY company in order to save costs. 18 represents a diameter of 18mm, 65 represents a length of 65mm, and 0 represents a cylindrical battery.

The well-known Tesla Model S uses 18650 cylindrical batteries. Although it is very powerful in the field of pure electric vehicles, its battery safety is the most dangerous and the least durable among the types of batteries currently used in pure electric vehicles. Its cycle number is only about 700 times, while domestic soft-pack and hard-shell square lithium-ion batteries can reach 2,000 times.

Not only is the cycle number low, but there are also problems with the discharge power of the battery. Tesla Model S is a product that focuses on performance and has high requirements for the discharge power of the battery. The power of the front motor of Tesla Model S is 193 kilowatts. For example, the capacity of its power lithium battery is 10 degrees. If you want this motor to perform well, the discharge power of its battery will reach 19.3C, which is a very scary number. In order to reduce the discharge rate, Tesla solves this safety problem by adding battery capacity. When the battery power reaches 100 degrees, the discharge rate is reduced to 1.9C, which is why the power lithium battery capacity of higher-performance Tesla is higher, which is a necessary approach.

Another disadvantage is the attenuation of 18650 cylindrical batteries from single cells to battery systems. The attenuation of the battery single cell to the battery system of the common Tesla Model S in our country is 57%. It is precisely because of its various shortcomings that mainstream pure electric vehicles in China do not use 18650 batteries.

Although Tesla uses the latest 21700 battery with a single cell energy density of 280Wh/kg, the system energy density is only 150Wh/kg, and this attenuation has reached as much as 53.5%. However, soft-pack and hard-shell square lithium-ion batteries have huge advantages in this process. Domestic companies with good PACK can control the attenuation to less than 20%.

In addition to the problem of structural limitations, its safety is also worse than that of soft-pack and hard-shell square lithium-ion batteries. Recently, accidents caused by electric vehicle safety issues have emerged in an endless stream, most of which are 18650. Therefore, the future development trend of power lithium batteries will be towards square hard-shell and square soft-pack batteries with a capacity of more than 100Ah.

Power lithium battery safety

Wang Zidong said: This is a sensitive topic and a topic that cannot be avoided. It should be said that after ten years of accumulation, my country's power lithium battery industry has made great progress, especially in the understanding and recognition of power lithium batteries, and is competent for the use of current pure electric vehicles.

After ten years of accumulation and exploration, the current new energy vehicles should meet the current promotion requirements, but problems have also begun to emerge, that is, the technology has not made significant progress in recent years. In fact, everyone should understand these problems. One is that the progress of technology is not like electronic products, which are completely overturned in two years after six months of iteration. The automotive industry does not have such a fast update speed. If there is no obvious technological breakthrough in the material of the current power lithium battery, it will be difficult to make further breakthroughs after the energy has developed to a certain level. At the same time, the negative impact on safety will become greater and greater.

Because we have found a strange circle while pursuing energy density. That is, the higher the energy density, the worse the safety. Some people say that it is possible to ensure safety while ensuring high energy density? In fact, this is a contradiction. In this contradiction, we can only try our best to pursue a balance.

Many people have asked why no one pays attention to the fire of fuel vehicles, but the fire of electric vehicles is so important? This is because we are currently unable to master the law of power lithium battery fire. Now no one in the world can find the real cause of a fire accident. Therefore, before we master the law of lithium-ion battery fire, we cannot ignore the balance between energy density and safety and long life. We cannot blindly pursue a certain goal.

The power lithium battery of Qiantu K50 has found this balance point. It does not blindly pursue higher energy density. Instead, it chooses to find the best balance between energy density, safety, high efficiency and durability. It ensures the high safety, long life, high performance, light weight and low energy consumption of the power lithium battery pack.

We all know that the Qiantu K50 is a sports car that focuses on performance, but it does not abandon safety and long life.

The vehicle was tested for ultra-large current discharge performance during the R&D stage: the discharge performance test was simulated in the vehicle BOOST mode, the vehicle BOOST mode was 5C discharge, and the laboratory used 5.5C discharge conditions. The results showed that 5.5C discharge did not cause battery life decay after 20,000 cycles; 5.5C discharge caused battery life decay after 30,000 cycles. Under 5.5C discharge, it can support the driver's use for 10 years (calculated as 10 times a day and 300 days of driving per year). 5C discharge can greatly extend the life of the battery.

From this we can see that in order to ensure the battery life, K50 does not use the more extreme 5.5C discharge, but makes the strongest performance under the premise of ensuring the long life of the power lithium battery.

Now many companies are pursuing higher single and system energy density. In order to ensure more energy supply, both positive and negative electrolytes are indispensable, and the thickness of the diaphragm can only be squeezed. The thickness of the lithium-ion battery diaphragm used to be 40 microns, but now it is only about 12 microns. Once this film is damaged, the consequences are very serious. The battery fire of Samsung Note7 in 2016 was caused by the diaphragm being too thin.

At present, the theoretical energy density limit of ternary lithium-ion batteries is about 350Wh/kg-400Wh/kg, and there are still many engineering problems to be solved here. Therefore, if there is no breakthrough in new materials, the battery specific energy may hover between 300Wh/kg-400Wh/kg. Only on the premise of achieving engineering technology breakthroughs can it be possible to increase the energy density of single cells to 500Wh/kg and the energy density of battery packs to more than 260Wh/kg.

However, the development and application of various materials will take 1-2 years, or even longer. The current practice of the country to adjust the system specific energy density once a year is inconsistent with the development cycle of the power lithium battery system, resulting in the inability to fully verify, leading to frequent fire accidents.

EV Century also interviewed Mr. Wang Zidong about his views on the current use of NCM811 batteries by many car companies. Mr. Wang Zidong said: In the case of insufficient verification of the battery system and inadequate thermal management system technology, these models are the walking time bombs he mentioned before, and I hope that car companies can pay attention to it.

Power lithium battery safety issues

1. During the manufacturing process of the battery cell. The safety requirements in the manufacturing process are very high. There are no lithium-ion battery factories that have not had accidents, including LG and Samsung.

2. During the battery pack integration process. The battery cells are exposed outside and problems occur when they are assembled into battery packs.

3. Storage process. Why do batteries need to be stored after they are produced, but cannot be directly used by users. Because the manufacturing process of lithium-ion batteries is too demanding, the current domestic level, including the international level, these big companies are difficult to control foolproof. Only in the process of shelving will the bad things appear. Good companies take 10-15 days. During this period, the small flaw is that the battery voltage decays faster, and the big one is catching fire.

4. During transportation. An accident occurred when the battery-carrying vehicle went down a long slope, 10-20 kilometers, and the temperature of the brake system was too high and the battery ignited.

5. Use process. This is directly related to charging. The principle of all chargers on the market is wrong. This principle is a bit like me taking the subway this morning, which is pushed in by the back. When it was invented in 1970, it was called a rocking chair battery, and the ions moved back and forth between the positive and negative electrodes. Now there is no rocking reduction method in the charging process. The traction charging method should be used, and it should not be charged by pushing. Lithium is very active in the periodic table, just like squeezing in the subway, everyone is blocked at the door, the more crowded, the more people are blocked at the door, and it will become a problem. You can see many photos online, all of which are on fire when charging.

6. The recycling process is more problematic because it will pollute the environment. The organic solvents in the battery are difficult to control during the recycling process. If they are accidentally released into the environment, they will cause great pollution. When the electrolyte meets cement, the cement will be corroded, and even the glass will be corroded.

Electrolyte leakage also includes battery combustion. At present, we have no way to deal with electrolytes that leak into the environment. The best way is to let it burn out. The electrolyte contains uranium, which is a highly toxic chemical substance. There is no life where it passes.

7. In the process of refining the materials required for the battery, there will also be a great threat to environmental safety. This is a problem that needs to be solved as soon as possible.

Safety advantages of Qiantu K50

As we all know, the power lithium battery pack on electric vehicles is a very complex energy system, involving a wide range of aspects. In addition to the chemistry, materials, structure, production process, and production equipment of the battery itself, the energy storage battery system also involves the battery box frame layout structure, energy management system, heat dissipation system, system integration matching, various sensors, safety protection system, system integration design, system reliability, testing technology, testing and family, daily maintenance adjustment, cost, recycling and many other aspects, which are typical multidisciplinary coordinated research projects.

Moreover, before the birth of the power lithium battery, it is necessary to consider: the assemblability design of the battery module, the installability design of the battery module, the maintainability design of the battery module, the adjustability design of the battery module, and the recycling and convenient disassembly design of the battery module. These designs are very important. Don't make all the batteries and then solve these performances.

Qiantu Automobile has done very well in this aspect. First of all, its battery system is composed of 10 standard boxes in series, and each standard box is a separate individual. The structure and quantity are standardized and designed, and can be assembled according to customer requirements, suitable for different models.

The cells are connected by flexible materials, which can not only compress the cells, but also absorb the deformation caused by the breathing effect (about 1.8%). The modules are combined with metal belts, which have appropriate compression force and flexibility. The modules are connected without bolts to prevent screw failure.

The standard box is fixed by a suspension device, which effectively absorbs road vibration and is double-fastened with flexible metal belts to effectively buffer collision energy.

Another benefit of using a standard box is that when the vehicle power lithium battery fails, only the standard box with the problem can be replaced. It greatly reduces costs and is also more conducive to later recycling. Its adjustable line, maintainability, installability and later recycling are all excellent.

In terms of battery system temperature control, Qiantu K50 adopts active liquid cooling/liquid heating temperature control system: the water system adopts parallel circuit design to ensure that each standard box can get sufficient heat exchange, minimize the temperature difference between the cells, and improve temperature consistency. The system temperature difference is less than 3°C when the ambient temperature is 0~45°C, and the system temperature difference is less than 5°C when the ambient temperature is -30~55°C; in a -30°C environment, standing for 24 hours, thermal management is turned on for 20 minutes, and the acceleration time from 0 to 100 kilometers is increased by 50%; in a 45°C environment, standing for 12 hours, thermal management is turned on for 20 minutes, and the acceleration time from 0 to 100 kilometers is optimal; the water chamber design has been optimized by CFD and bench testing, and has excellent performance; according to the different temperature states of the cells, it can intelligently select strong and economic thermal management modes to optimize energy consumption; it has advanced charging and heat preservation management functions to prepare for the operation of the vehicle in advance.

Mr. Wang Zidong had previously visited Walter Electric (a high-tech company integrating the R&D, production and sales of electric vehicle power systems and important components) under the Qiantu system and commented that Qiantu Automobile is the safest power lithium battery design in my country's electric vehicle industry. As the director of the Power Lithium Battery Laboratory of the Northern Vehicle Research Institute of my country and the director of the Power Lithium Battery Testing Center of the National 863 Electric Vehicle Major Project. The fact that he can give such an evaluation to Qiantu Automobile is enough to prove its leading position in the new energy field. A phrase we often say now is to stay true to our original aspiration. Looking back at our strategic planning for power lithium batteries a few years ago, our goal at that time was to reduce the cost to 1.5 yuan per watt-hour and the energy density to 300 watt-hours/kilogram in 2020. Now looking at this goal, we have definitely achieved it ahead of schedule in terms of cost, but we have delayed in terms of energy density.

At present, most of the power lithium battery industry feels very struggling or difficult. Now the industry has a hard indicator for the energy density of power lithium batteries: if it does not reach 140 watt-hours/kilogram, the car manufacturer will most likely not want your battery. Because only when it reaches 140 watt-hours/kilogram can you get a subsidy multiplied by a coefficient of 1.1. Therefore, everyone pursues energy density as a hard indicator. Because of this, many things happen. Why? Because if you simply pursue energy density, it is a very risky thing, which will inevitably sacrifice the safety and service life (cycle life) of power lithium batteries.

Improving the energy density of power lithium batteries is meaningful only when safety is guaranteed and the cost and life are acceptable. If you simply pursue energy density, the probability of vehicle accidents will be very high. The car burning incident this summer proves this! So I think safety cannot be compromised.

As a listed company with more than 30 years of experience in battery manufacturing, Mengshi Technology has started to deploy high-end lithium batteries since 2015, and has developed an industrial chain layout around power lithium batteries.

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