In the lithium-ion battery cell assembly process, there are two main technologies: winding and stacking.
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These two technologies set up are always related to the below key technical points: Battery cell space utilization, battery cell cycle life, cell manufacturing efficiency and manufacturing investment. Overview 1. What is Winding Technology? 2. What is Stacking Technology? 3. What technology was used in the lithium-ion battery cell you saw on the market? 4. What are the benefits of lithium-ion battery cell that formed by stacking process? 5. What is the development direction of cylindrical cell, prismatic cell and pouch cell from current scene? 6. How do you comment on these two technical routes if by manufacturing efficiency and yield efficiency? 1. What is Winding Technology? After slitting the cathode roll, separator and anode roll, the winding process is to winding them by a fixed winding needle in sequence and extruding them into a cylindrical or square shape, then placing them inside a square or cylindrical metal shell. The size of the slitted rolls, the number of coils and other parameters are determined according to the design capacity of the battery cell. 2. What is Stacking Technology? The stacking process is to cut the cathode and anode sheets into the required size, then stack the cathode sheets, separator and anode sheets into small cell unit, and then stack the small cell unit to form the final single cell. Pouch cell: Two technology are both adopted, it depends on the cell manufacturer. 4. What are the benefits of lithium-ion battery cell that formed by stacking process? Lithium-ion cell products formed by stacking have a higher energy density, a more stable internal structure, a higher level of safety, and a longer life span. Goto Energyland to know more. ● Higher energy density ● More stable internal structure Although the stacking process will expand during the repeated use of the battery, in general, the expansion force of each layer is similar, so the interface can be kept flat. ● Higher level of safety ● Longer life span 5. What is the development direction of cylindrical cell, prismatic cell and pouch cell from current scene? ● Cylindrical: 4680 big cylindrical is more and more popular, standardized winding process. The manufacturing speed of a single cell needs to be improved, so can widen the use scenario. ● Pouch cell: Adopting stacking process is becoming a trend and overwhelming. ● Prismatic cell: If the existing size is maintained, continuing to use winding (coiling) is a reasonable option; but after developing into a square shell stacking transition size, and becoming a short blade and a long blade, the stacking process will naturally be adopted. For consumer batteries, compared with battery capacity and performance, manufacturers pay more attention to the improvement of efficiency, so there is a large demand for winding technology; but for power batteries, large modules and large cells will be the trend in the future. The stacking process can better play the advantages of large-scale batteries, and it has advantages over winding in terms of safety, energy density, and process control. 6. How do you comment on these two technical routes if by manufacturing efficiency and yield efficiency? ● The most potential is winding large cylindrical. The most important process is to introduce dry electrodes around mature processes. We could expect a lot in near future. ● Stacking is the fastest growing: With the continuous innovation of tier-1 cell manufacturer stacking technology and the continuous follow-up of power battery companies, Chinese battery companies are all moving towards the super stacking + blade battery solution design, this section has the greatest potential. ● Winding is in the direction of stable development: Square shell winding maintains the status, and we have also seen that this route was the largest capacity construction in terms of the original production. 3. What technology was used in the lithium-ion battery cell you saw on the market?
Blade cell: Designed and produced by stacking process.
Prismatic cell: Both stacking and winding processes can be used. At present, the main technology direction in China is mainly winding and is transiting to stacking.
Cylindrical cell: As a mature product, it always with the winding process.
From the inside of the cell, the winding corner of the winding process has radians, and the space utilization rate is lower. The stacking process can make full use of the battery space, and the energy density of the cell formed under the same volume of cell design is higher.
During the use of the battery, the insertion of lithium ions will cause both the cathode and anode plates to expand, and the internal stress of the inner and outer layers at the corners of the winding will be inconsistent, and the winding battery will undergo wavy deformation, which will cause the interface of the battery to deteriorate and the current distribution unevenness accelerates the instability of the internal structure of the battery.
The plates at both ends of the winding are bent, the coating material will be greatly bent and deformed, and powder dropping and burrs will easily occur at the bending place. The tension on the plates piece and the separator is prone to unevenness and wrinkles. The expansion and contraction of the plates piece and the stretching of the separator will cause the deformation of the battery cell. The stacking battery cell is evenly stressed, and from this perspective, the battery safety is higher.
The stacked battery cell has more tabs, the shorter the electron transmission distance, and the smaller the resistance, so the internal resistance of the stacked battery cell can be reduced, and the heat generated by the battery cell is small. The winding is prone to deformation, expansion and other problems, which affect the attenuation performance of the battery.
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You can do this, but be aware that as a lithium-ion battery ages its internal resistance increases.
When you wire an old and new cell in parallel the new cell will initially supply more of the load current. This causes it to discharge faster until both cells share the load equally. When load current is reduced the old cell will charge the new cell for a while until they equalize again. When charging a similar effect occurs.
How much the old cell's resistance increases depends on how it is used. For lowest degradation it should be maintained at ~50% charge and the temperature should be kept below 25 °C. Charge/discharge cycles should be shallow, eg. 80% to 20% rather than 100% to 0%. If these rules are followed the resistance should not increase much in 6 months to 1 year.
So long as the cell resistances are similar, the current is not too high (ie. less than the charge/discharge ratings of a single cell), and the battery is not discharged too far (eg. no less than 3.5 V), this temporary imbalance should not be a problem. However it could be a problem if you intend to draw more current from the larger battery.
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