Improving the energy density of batteries (limited to capacity batteries) is the top priority in designing batteries.


The capacity is not enough, no matter how low the unit price, how good the cycle is, and how high the safety is, the battery produced may still be unpopular. So how can we improve the energy density of batteries? There are several main aspects to consider:


1. Enhance 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 manufacturing process conditions and conduct stricter production monitoring;


5. Optimize miscellaneous items that affect capacity;


Below, we will discuss the categories separately:


1. Increasing the performance of materials that contribute to battery capacity: This is mainly the most direct way to improve capacity density for positive and negative electrode active materials. The main directions include:


① Use materials with greater performance, such as lithium rich materials for positive electrodes, high-voltage ternary materials, high-voltage lithium cobalt oxide materials, binary materials, etc; Soft carbon, hard carbon, silicon tin based compounds, etc. for the negative electrode.


② Use positive and negative electrode materials with higher compaction density.


③ Using active substances with better adhesion and conductivity: This can reduce the content of binders and conductive agents in the dressing, thereby increasing the capacity of the dressing per unit mass; In addition, reducing the amount of binders and conductive agents can also improve the compaction and other processing properties of active materials.


④ Using materials with smaller thickness rebound: After cycling, lithium-ion batteries will experience a certain rebound in thickness; During design, it is necessary to reserve the rebound thickness after cycling; When materials with smaller thickness rebound are used (based on current observations, these materials also have good cycling performance), the saved thickness rebound reserve space can be transferred to the design thickness of the battery cell, thereby increasing the design capacity of the battery cell.


⑤ Choosing a material system with better performance: Combining a single "good positive electrode", "good negative electrode", and "good electrolyte" does not guarantee the production of a "good battery". Combining materials with poor compatibility not only reduces the cycling performance of the battery, but may also affect the rate performance and even the performance of the positive and negative electrodes; Similarly, when the material matching is better, performance such as performance, cycling, and expansion rate may be improved.


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


2. Reduce the volume of materials that do not contribute to battery capacity: This is a complex task, mainly including: using thinner aluminum-plastic films, thinner battery separators, thinner electrode lugs, thinner copper and aluminum foils, thinner transparent adhesive tape, etc.


It can be seen that improvements in this area are mostly attributed to "thinness". In a limited volume, the reduction in volume of aluminum-plastic films, separators, etc. that do not directly contribute to capacity means an increase in the amount of chemicals that can provide capacity, thereby improving the capacity of the battery cell.


But when these materials are thinner, their mechanical strength and safety performance will be affected; On the one hand, auxiliary material manufacturers need to be able to reduce the volume without significantly reducing material performance. On the other hand, battery cell manufacturers need to change their processes, manufacturing parameters, and even equipment (for example, thinner aluminum foil means a higher elongation coefficient under rod pressure and increases the probability of breakage during coating and rod pressure; thinner separators have a higher risk of short circuit; thinner aluminum-plastic films are more prone to foot damage; thinner electrode lugs will reduce the rate performance of batteries, etc.).


Replacing these thinner materials requires a lot of certification from the battery factory. If the trial production quantity is too small, accurate statistical data cannot be obtained. If the problem is too big, it will cause waste. Compared with improving the performance of active substances, reducing the content of inactive substances seems to have more ideas and involves equally broad aspects.


3. Use more advanced production equipment: Advanced equipment is mainly used to improve the consistency of production, reduce production fluctuations, and achieve the minimum value that can be improved without changing the mean value. The quality of a batch of battery cells is precisely determined by the minimum value that is improved. Here are two examples:


① When the coating tolerance of the coating machine is smaller, the minimum capacity/design capacity can be increased. If the customer has a requirement for the minimum capacity, it is equivalent to increasing the minimum capacity while keeping the design capacity unchanged, which means increasing the capacity of the battery cells evaluated to the customer; At the same time, the coating deviation of the positive and negative electrodes is reduced. After considering factors such as initial efficiency and capacity degradation after cycling, designing an excess of negative electrodes can moderately reduce it, resulting in more positive electrode materials for the battery, which is equivalent to having more capacity.


② When the accuracy of the rolling machine is improved, due to the reduction of errors during actual rolling, the design compaction can be closer to the maximum compaction of the material, thereby increasing the design capacity and the capacity of the produced battery cells; The thickness of the rolled out polarizer is more consistent, which is equivalent to increasing the consistency of the thickness of the battery cell. Therefore, smaller maxTHK designTHK can be selected during design to improve the design capacity (similar to the width of the slitting blade, tape measure, and the accuracy of the slitting cabinet, which will not be repeated).


4. Improve manufacturing conditions and conduct stricter production monitoring. There is a lot of knowledge in production control, listed below:


① Reduce the transition time from rolling to winding: This can reduce the thickness rebound of the polarizer and better control the thickness of the battery cell. If the thickness of the battery cell is significantly lower than the maximum thickness, the design thickness can be appropriately increased to increase the battery cell design capacity.


② Stable temperature distribution room: Temperature has a significant impact on the capacity of battery cells for capacity distribution. Low temperatures may cause qualified batteries to be converted to secondary capacity distribution as low capacity, wasting resources. High temperatures may result in inferior capacity batteries being shipped as qualified products.


Just like the principle of short board, the capacity of a batch of battery cells is calculated based on the lowest value of the shipped battery cells, and the thickness of a batch of battery cells is calculated based on the maximum thickness of the shipped battery cells. The human operation has a particularly important impact on the quality of products in labor-intensive industries in China. In production, if operators and quality personnel can minimize human error and reduce fluctuations during production, it is equivalent to increasing the length of the shortest board in the wooden barrel, thereby increasing the capacity of the battery and reducing its thickness.


5. Optimize miscellaneous items that affect cell capacity.


When the fully charged core is disassembled, the negative electrode body should be uniformly and perfectly golden yellow. However, when there are problems with human operation, materials, equipment, and even design, various minor issues such as lithium deposition in the first circle of the negative electrode, lithium deposition at the wrinkled part of the separator, and uneven lithium deposition at the tail of the positive and negative electrodes during coating can occur. From a capacity perspective, lithium deposition is likely to result in a lower capacity; If similar situations can be eliminated, it is equivalent to increasing the capacity of the battery cells; If such situations cannot be eliminated, it is necessary to predict the probability of their occurrence and the magnitude of the potential impact more accurately from a design perspective, in order to avoid some battery cells being scrapped due to problems that could have been predicted.


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