button cell battery cr1620.A brief discussion on the three contradictory relationships of power battery technology

　　In the direction of power batteries, two things that have had a big impact recently are the 8GWh production capacity requirement and the legend that new energy vehicles are subsidized based on energy density (115 Wh/kg is the watershed), so that everyone exchanges technology and talks about energy density when meeting. When talking about production capacity plans, people who make lithium iron phosphate materials and batteries are very dissatisfied. Why is it my turn to be injured?

　　Regardless of the route, the improvement of energy density is the direction and goal. After all, the target of 300Wh/kg in 2020 is already on paper (I personally think that the target of 350Wh/kg is excessive, and industrialization really cannot be achieved by hard work alone. ). However, under the argument of energy density theory alone, the following three contradictory relationships need to be dialectically analyzed:

　　1. Dialectical relationship between energy density and safety issues

　　Here is a simple Rogen plot. From it we can see that the energy density of the battery is determined by the cathode material. Battery factories of these materials can get samples or products, so in terms of energy density alone, everyone can do it. It doesn’t matter. Who is higher and who is lower can only be said to be more courageous. How much weight does security issue carry here? Whether it really comes first.

　　This proposition seems to echo the dispute over the ternary-LFP route at the beginning of the year. It was denied at the beginning and praised at the end of the year. The experience of ternary batteries can be described as ups and downs. But from a technical point of view, there is indeed a big revelation: the increase in energy density is based on safety issues, otherwise it will put you back in the cold.

　　Therefore, just talking about energy density has no practical significance and does not have certain prerequisites. This is not something new. Otherwise, we will easily become arrogant, and we can destroy countless enemies in an instant, and have the illusion of dominating the world.

　　2. Dialectical relationship between energy, life and charging rate

　　It is clear from the Rogen plot that high energy comes at the expense of power. In the context of many passenger cars currently promoting fast charging (basically 2C), energy density and lifespan need to be optimized and sacrificed a lot. The picture below shows the lifespan of a certain 18650 battery at different charging rates. It is obvious that it cannot support the 1C charging rate, which makes it difficult to talk about the so-called fast charging performance.

　　Personally, I think the application of high specific energy density batteries is targeted at certain customers: areas that are not sensitive to charging time and where long cruising range is more urgent.

　　In the field of fast charging, energy density will inevitably require some compromises and concessions to achieve a balance between energy, lifespan and power. This is actually a branch that can distinguish true technical capabilities.

　　3. Dialectical relationship between sample and product consistency

　　It can be said with certainty that currently domestic high-energy-density (>200 Wh/kg) batteries are basically in the sample and trial production stages, and few are truly mass-produced. The reason why I say this is because the well-known policy guidance at the beginning of the year caused many ternary battery companies to cease operations for a period of time, and it takes at least a year for a battery product to go from research and development to stable mass production. Based on this, this hasty conclusion was reached.

　　The consistency of high-specific-energy ternary batteries should be better controlled from a design perspective, and this is also true from the perspective of partial process control. However, in terms of sensitivity to temperature and humidity, the requirements are higher, 2-3 Temperature differences of degrees can lead to significant differences in capacity, which poses a great challenge to product consistency. And this is impossible to show without sample data of thousands of batteries.

　　Therefore, it is of little significance to talk about energy density alone, and it is easy to take the wrong approach. High-energy-density batteries must be safe, reliable, have a long lifespan, and have beneficial product consistency.

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