The contradictory and opposite sides of the development of lithium batteries are accompanied by each other. Without one, the other will no longer exist. Among the lithium batteries, there are also many opposing parties similar to the zero-sum game, so we can't help but admire the contradictions in the difficult choice of losing the other.
1. The opposition between battery energy density and battery cell performance
Capacity is the first attribute of a battery, and energy density is the primary issue that must be considered when designing almost all batteries. When the designed energy density increases, the battery cell has to choose a thinner film, and the material also needs to be used under the ultimate compaction and areal density. On the one hand, such an extreme design will make it more difficult to suck and roll the cell, which will affect the cycle performance of the cell; on the other hand, thinner diaphragm aluminum plastic film and higher energy density materials also mean worse safety performance . Energy density and battery cell performance can be said to be a problem that any company has to encounter when designing batteries; a company often has a greater advantage in energy density, the cycle safety performance of the battery may have certain hidden dangers ; When its cycle safety performance is 100% correct, the energy density is often low and the product lacks strong competitiveness.
2. The injection volume of lithium batteries is opposite to the processing performance
In terms of cell performance, increasing the injection volume is beneficial and harmless; but when the injection volume is large, the processing performance of the cell will be significantly reduced. After injection, the vacuum adsorption is difficult, and the cell pressure during hot and cold pressing and fixture baking Questions such as explosion, degassing, and even unsealing of soft batteries will follow one after another. Strictly speaking, the amount of liquid injection in the process must not allow the battery cell to have batch abnormalities caused by excessive liquid injection during processing, otherwise the injection amount needs to be reduced (if the result is reduced, the result is Decrease of liquid retention and NG cycle, it means that the material needs to be replaced); of course, before confirming that there is a problem with the liquid injection, optimization from the perspective of the process is also essential, for example, can the capacity of the adsorption box be increased when the adsorption is difficult Efficiency, whether it is possible to reduce the pressure of the splint to reduce the ratio of pressure explosion during pressure explosion, etc. When the process optimization has reached the limit or it has reached its short-term no further optimization, then reduce the injection volume. When the fish and bear's paws are not available at the same time, the supreme leader decides that he wants that, then that is good.
3. Production efficiency and product yield
As far as production is concerned, increasing output or improving efficiency is the goal pursued in its core. Higher efficiency means shorter process cycle and shorter processing time in the production process, and the latter often results in products Performance degradation. It is interesting to say that many quality problems encountered in production can be improved by methods similar to "reducing production efficiency and increasing processing time"; for example, cracks encountered in the coating process can be improved by simultaneously reducing temperature and speed , Semi-automatic winding and easy deformation can be improved by variable speed winding with slow winding speed first and then fast winding speed. The poor effect of forming SEI film during formation can be improved by reducing the charging rate. After the fixture is baked, the battery core can be softened by extending the baking time. Extend the shelf time at room temperature before clamping the battery core to improve and so on. Statistically speaking, "time" here often acts as a "stability factor"; perceptually speaking, if an improvement can increase the yield while increasing efficiency, is the method used before too low? Up? When there is a conflict between efficiency and yield, the priority must be to ensure yield, but at the same time, it is necessary to understand that the production line loses efficiency in order to achieve yield. The increase in personnel, the addition of equipment, and the decrease in output are only thoughts. Think, your improvement plan will be accepted.
4. The gram capacity of lithium battery negative electrode is opposite to expansion
Silicon-based materials are a choice of anode materials in the future, and their ultra-high intercalation capacity is the biggest advantage; but at the same time, too much expansion during charging and discharging is also an important limitation for its failure to promote. When graphite is intercalated with lithium, lithium ions are embedded in the middle of the graphite layer. Its state is similar to that of a few small glass balls placed between two layers of quilts. The deformation must be small and the lithium intercalation capacity will not be too high. When lithium reacts with silicon, lithium is directly inserted between silicon and silicon atoms, which is similar to inserting more glass balls in the middle of a full and flat glass ball. Although more lithium can be inserted, it takes up more The volume must also be larger. On the surface, the seemingly related "level of lithium insertion capacity" and "intersection size after lithium insertion" are actually determined by the mechanism of lithium insertion. In other words, when a material has a larger capacity, its charge and discharge deformation tends to be larger, and its promotion is bound to be limited. Of course, excellent materials can be researched, and the expansion of materials can also be improved by coating or nano-processing, and there is no inevitable result of high capacity and large deformation (not so much a "result", Rather, it is a trend. With the advancement of science and technology, the development of new materials will become more and more important (it seems that one of the main reasons for Chinese engine NG is that the materials are not good).
5. Lithium battery anode energy and safety
The higher the energy of the material, the less safe it is. When a material has a higher energy, it means that the amount of debonding after charging is greater, and the structure change is also greater, so it is more unstable; for example, there will be more 4 The presence of valence increases the oxidability of the positive electrode, and the structure of Co02-1 (cobaltate?) as the skeleton of the cobalt acid bond is destroyed, which makes the positive electrode material easier to decompose and reduces safety. But when the energy of a material is low, it loses fewer bonds after charging, the structure of the material itself can be better retained, and the safety will be improved; after the iron phosphate bond is fully charged, it will act as a skeleton structure and occupy The phosphate root, which has a large molecular weight, is not destroyed, and the molecular structure is not destroyed, so its safety is naturally higher. The seemingly correlated performance and expansion of the negative electrode are actually determined by the material structure, and the seemingly negative correlation between the positive electrode performance and safety is actually determined by the structure of the material itself.
The battery's materials, design, manufacturing process, etc. are a unified whole, which are infinitely related to each other and are all derived from the most fundamental theoretical foundations. In the design of the battery cell, it is inevitable that there will be a time when both sides of the conflict can reach the best point at the same time. It is absolutely impossible to find the best balance point or choose the direction that you are more concerned about as the priority reference direction. Is the best move.