Analysis of the development of CR927 battery technology

It seems a bit "inappropriate" to discuss technology under the development trend of lithium-ion power batteries. Everyone is expanding production capacity, pulling the cart with their heads down, and working hard. Although they are in awe and fear of technology, this is not a big deal in the context of a frenzied market. But I still think that only by looking at the past technological changes historically, why and how they changed, maybe we can better think about whether the original intention of our actions is still "original", and everyone should just watch the story.

Let's first use the following four pictures to extend our topic-power battery technology is changing and developing in debate. Comparison chart of installed capacity changes of batteries of different systems, the range of battery capacity for mainstream vehicles, and the differences in battery shape of mainstream battery factories used by car manufacturers. It can be said that every debate is fierce, whether it is the drafter and maker of the standard, or the stakeholders involved (battery companies), and each change and corresponding adjustment is painful and may be repeated.

From the beginning of research on power batteries to the present, the following four aspects of discussion and debate have been inseparable.

First, the dispute over material systems

There has been a lot of discussion about this, especially about ternary and lithium iron phosphate (see: The dispute between ternary and lithium iron phosphate is necessary and cannot negate ternary materials). Dialectically speaking, there is no bad material. It is bad just because it has not found its best living space. Actual data shows that lithium iron phosphate is more suitable for use in buses, and ternary has obvious advantages in passenger cars (the decline in the share of ternary in passenger cars from January to April 2016 was affected by the "temporary suspension of ternary" policy). The rest is how to alleviate and solve the safety problem from multiple dimensions of materials, battery design, and pack design. It can be optimistically estimated that the suspension of ternary is temporary from a technical point of view, and the safety deficiencies of ternary can be made up through technological improvements.

In addition, for the negative electrode side, lithium titanate batteries (the negative electrode uses lithium titanate-LTO, not graphite) also have a place in certain specific fields (fast charging vehicles, energy storage) due to the safety and fast charging advantages brought by zero strain; hard carbon is also gradually paired with ternary materials in hybrid vehicles and other fields because of its ability to deintercalate Li better than graphite (the lattice interlayer spacing is larger than that of graphite materials).

Second, the capacity competition

At the beginning of the development of power batteries, it seems that the larger the capacity, the higher the level. Some claim to make 400Ah and 500Ah, which was very popular for a while and was advertised everywhere. Later, they slowly "lyed on the beach forever". From the current process control and technical level, this is unscientific and unreliable. It can only be used as a "gimmick" for publicity. Who dares to use it? The reasonable threshold of capacity should be based on the value under the comprehensive balance of material system, size design and process level. The following table lists some typical capacities of battery factories. In addition, is small capacity good? I remember that in an industry standard discussion meeting in 2009 (to avoid suspicion, no specific standards were mentioned), there was a discussion on the capacity range of batteries for electric vehicles. The CEO of one company said arrogantly that a capacity greater than 5Ah would be fine (someone proposed that it should be defined according to the function of energy conversion, that is, any battery that can convert chemical energy into kinetic energy, regardless of size, is classified as a power battery, but unfortunately it was rejected). I wonder what he would think when he saw the current mass application of 18650.

JBT11137-2001 recommended some capacities, but based on the special products of the battery factory at that time, it is basically not adopted by everyone at present, and there is no universally recognized standard to define the capacity range.

Then everyone can play their own role, but the space for play will be slowly defined for you, that is, size!

Third, the size dispute

Like capacity, it is a topic of "a hundred schools of thought". The same capacity, different sizes, bring different performance (especially rate and life). The following figure shows three different sizes of a 20Ah battery (without thickness). It is obvious that the power characteristics will be more different. Although there is a recommended standard in China at present: QCT840-2010 (Specifications and dimensions of power batteries for electric vehicles), it is basically not adopted due to insufficient representativeness or considerations that it needs to be improved; Europe has VDADIN-91252, and German car companies all require batteries to be provided according to this standard. At present, many domestic battery factories are also developing batteries according to the size requirements of this standard. The reason why domestic standards are shelved is that there is no participation from vehicle manufacturers, and at the same time, vehicle manufacturers do not have unified size requirements.

At present, the VDA standard is aimed at passenger cars. Given the size, the capacity is free to play. How much room there is depends on their own "efforts"; in the field of buses, they are still independent at present. The various sizes bring about a variety of capacity products. Unification requires a process, so take your time!

Fourth, the shape dispute

Which is more suitable, winding, hard shell square, or soft packaging? Small wound cells such as 18650 and 26650 have been used in large quantities as standard products. They have the characteristics of mature automated production equipment, stable process, good consistency, etc., and can achieve ppm or even ppb-level defective rate control; hard-shell square has the advantages of high dimensional accuracy and strong pressure resistance; soft-package batteries have the advantages of good safety control and high degree of flexible design, but which shape of battery to use needs to be considered not only from the perspective of battery, but also from the perspective of module design and grouping technology. It cannot be generalized.

Along with the debate, lithium-ion power battery technology has gone through a period of confusion. In this process, China has also made continuous progress from doing, learning, and changing to finalization.

At present, in these four aspects, the material system is basically divided into two parts; capacity and size are gradually moving from disorder to order; shape is divided into three parts. It is much simpler and more regular. The rest is to go deeper and deeper in this rule, and the better it is.

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