How to design the capacity density of the battery core?

Increasing the energy density of the battery(limited to volumetric batteries) is the first priority for designing batteries.

The capacity is not enough, the unit price is low again, the cycle is good, the safety is high again, the battery that makes also may no one cares. So how can you increase the energy density of the battery? It can mainly be considered in several ways:

1. Increase the performance of materials that contribute to battery capacity;

2. Reduce the volume of materials that do not contribute to battery capacity;

3. Use more advanced production equipment;

4. Improve the process conditions and conduct stricter production monitoring;

5. Optimize miscellaneous items that affect capacity;

The following categories are discussed separately:

1. Increase the performance of materials that contribute to battery capacity: This is mainly for positive and negative polar active substances, which is the most direct way to increase capacity density. The main directions include:

(1) Use of larger materials: such as positive lithium-rich materials, high voltage ternary materials, high voltage cobalt acid materials, binary materials, etc.; Negative soft carbon hard carbon, Silicon tin based compound, etc.

(2 )Use more compaction density of positive and negative materials.

(3) The use of binders, better conductivity active substances: This can reduce the content of binders, conductors in the dressing, thereby improving the capacity of unit mass dressing; In addition, the reduction of the amount of binder and conductive agent can also improve the compaction of the active material and other processing properties.

(4) Using materials with a smaller rebound thickness: After the lithium ion battery cycle, the thickness will rebound; The design needs to reserve the rebound thickness after the cycle; When using materials with a smaller thickness rebound(according to current observations, these materials are also materials with good cycling performance), the reserved space for the saved thickness rebound can be transferred to the design thickness of the core. Thus increasing the design capacity of the core.

(5) Choose a material system that matches better performance: a single "good pole", "good negative pole" and "good electrolyte" are paired together, and there is no guarantee that a "good battery" will be made. The combination of poorly matched materials will not only reduce the cycle performance of the battery, but also affect the doubling performance and even the positive and negative grams. Similarly, when the material matches better, the performance of grams, cycles, and expansion rates may all be improved.

With the increasing maturity of lithium-ion battery material technology, the potential of common lithium cobalt and graphite has reached its limit. In the future, if mature other systems can be produced, the energy density of lithium-ion batteries will have a revolutionary impact!

2. Reduce the volume of materials that do not contribute to battery capacity: This is more complicated. Mainly include: use thinner aluminum plastic film, use thinner battery diaphragm, use thinner ears, use thinner copper foil and aluminum foil, use thinner transparent adhesive paper and so on.

It can be seen that the improvement in this area is basically based on the adjective "thin". In a limited volume, the reduction of the volume of aluminum plastic membranes, diaphragm, etc. that have no direct contribution to capacity means that the volume of chemical substances can be provided, thereby increasing the core capacity.

However, when these materials are thinner, their mechanical strength and safety performance will be affected; This requires that the auxiliary material manufacturing plant be able to reduce the volume without basically reducing the material performance. On the one hand, it requires the core manufacturing plant to change the process, parameters, and even equipment(for example,, Thinner aluminum foil means higher extension coefficient of the stick pressure and increase the probability of fragmentation when coating and stick pressure; Thinner diaphragm has a higher short-circuit risk; Thinner aluminum plastic film is more likely to produce foot damage; A thinner polar ear will reduce the doubling performance of the battery and so on.)

The replacement of these thinner materials requires a large number of certifications by the battery factory. If the number of trials is too small, statistics can not be accurately obtained. If the problem is too large, it will cause waste. Compared with improving the properties of active substances, reducing the content of inactive substances appears to have more ideas and involves the same broad aspects.

3. Use more advanced production equipment: Advanced equipment is mainly designed to improve the consistency of production, reduce the fluctuations in production, and then achieve a minimum value without changing the average, and determine the quality of a batch of cores. It is precisely the minimum value that is raised here. Take the following two examples:

(1)When the coating tolerance of the coating machine is smaller, the minimum volume/design capacity can be increased. If the customer has a minimum capacity requirement, it is equivalent to increasing the minimum capacity when the design capacity is unchanged. In other words, the capacity of the core evaluated to the customer is increased; At the same time, the bias of the positive and negative poles is reduced. After considering factors such as the first efficiency and the attenuation of the capacity after the cycle, the design of the negative pole excess can be moderately reduced, so that the battery has more positive electrode materials, which is equivalent to more capacity..

(2)When the accuracy of the roller is improved, due to the reduction of the actual rolling error, the design compaction can be closer to the maximum compaction of the material, thereby increasing the design capacity and the core capacity. The thickness of the roll out electrode is more consistent, which is equivalent to increasing the consistency of the core thickness, and can then select a smaller maxTHK-design THK at the time of design. Therefore, the design capacity is increased(the width of the cutter, the width of the tape measure, the accuracy of the container, etc. are similar, and are not repeated).

4. Improve manufacturing conditions and conduct stricter production monitoring. There is a lot of knowledge in production control, citing one or two:

(1) reduce the sequence time after rolling pressure to before winding: This can reduce the thickness of the electrode rebound, so as to better control the thickness of the core. If the thickness of the core is significantly lower than the maximum thickness, the design thickness can be appropriately increased, thereby increasing the design capacity of the core.

(2) The temperature of the stable capacity room: The temperature has a large impact on the capacity of the core. The low temperature may cause the qualified core of the capacity to be transferred to the secondary capacity as a low capacity to waste resources. At high temperatures, the capacity may be poor. The core is shipped as a qualified product.

Like the principle of short plates, the capacity of a batch of electric cores is measured by the lowest value of the shipping core, the thickness of a batch of electric cores, and the maximum thickness of the shipping core. Human operation is very important to the quality of products in this labor-intensive industry. In production, if the operator and quality personnel can reduce the error of human operation as low as possible and reduce the fluctuation of production, it will be equivalent to increasing the length of the shortest plate in the barrel. This increases the capacity of the battery and reduces the thickness of the battery.

5. Optimize the miscellaneous that affects the core capacity.

Full charge core open, negative body should be uniform perfect golden yellow. However, when there are problems with human operations, materials, equipment, and even design, various types of small hair diseases such as: lithium in the first circle of the core negative electrode, lithium in the diaphragm wrinkle, and lithium in the positive and negative tail membrane density when coated. Lithium and other problems will appear. From the perspective of capacity, lithium analysis is likely to cause low capacity; If similar conditions can be eliminated, it is equivalent to increasing the capacity of the core; If such cases can not be eliminated, the probability of their occurrence and the magnitude of possible impacts need to be more accurately predicted from the design, so as to prevent some cores from being scrapped due to problems that could have been predicted.

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