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.
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.
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.
● Higher energy density
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.
● More stable internal structure
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.
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
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.
● Longer life span
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.
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.
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● 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.
If you have ever worked with batteries you have probably come across the terms series, parallel, and series-parallel, but what exactly do these terms mean?
Series, Series-Parallel, and Parallel is the act of connecting two batteries together, but why would you want to connect two or more batteries together in the first place?
By connecting two or more batteries in either series, series-parallel, or parallel, you can increase the voltage or amp-hour capacity, or even both; allowing for higher voltage applications or power hungry applications.
Connecting a battery in series is when you connect two or more batteries together to increase the battery systems overall voltage, connecting batteries in series does not increase the capacity only the voltage.
For example if you connect four 12Volt 26Ah batteries you will have a battery voltage of 48Volts and battery capacity of 26Ah.
To configure batteries with a series connection each battery must have the same voltage and capacity rating, or you can potentially damage the batteries. For example you can connect two 6Volt 10Ah batteries together in series but you cannot connect one 6V 10Ah battery with one 12V 20Ah battery.
To connect a group of batteries in series you connect the negative terminal of one battery to the positive terminal of another and so on until all batteries are connected. You would then connect a link/cable to the negative terminal of the first battery in your string of batteries to your application, then another cable to the positive terminal of the last battery in your string to your application.
When charging batteries in series, you need to use a charger that matches the battery system voltage. We recommend you charge each battery individually to avoid battery imbalance.
Sealed lead acid batteries have been the battery of choice for long string, high voltage battery systems for many years, although lithium batteries can be configured in series, it requires attention to the BMS or PCM.
Connecting a battery in parallel is when you connect two or more batteries together to increase the amp-hour capacity. With a parallel battery connection the capacity will increase, however the battery voltage will remain the same.
Batteries connected in parallel must be of the same voltage, i.e. a 12V battery can not be connected in parallel with a 6V battery. It is best to also use batteries of the same capacity when using parallel connections.
For example, if you connect four 12V 100Ah batteries in parallel, you would get a 12V 400Ah battery system.
When connecting batteries in parallel, the negative terminal of one battery is connected to the negative terminal of the next and so on through the string of batteries. The same is done with positive terminals, i.e. the positive terminal of one battery to the positive terminal of the next.
For example, let’s say you needed a 12V 300Ah battery system. You will need to connect three 12V 100Ah batteries together in parallel.
Parallel battery configuration helps increase the duration in which batteries can power equipment, but due to the increased amp-hour capacity they can take longer to charge than series connected batteries. This time can safely be reduced, without damaging the batteries, by charging faster. Now that the battery is larger, a higher current charge is still the same percentage of the total capacity, and each battery ‘feels’ a smaller current.
While it is often debated what the best way to connect in parallel is, the above method is common for low current applications. For high current applications, talk to one of our experts as your situation may need a special configuration to ensure all of the batteries age at as similar as possible rates.
Last but not least! There is series-parallel connected batteries. Series-parallel connection is when you connect a string of batteries to increase both the voltage and capacity of the battery system.
For example, you can connect six 6V 100Ah batteries together to give you a 12V 300Ah battery, this is achieved by configuring three strings of two batteries.
In this connection you will have two or more sets of batteries which will be configured in both series and parallel to increase the system capacity.
If you need any help with configuring batteries in series, parallel or series parallel please get in contact with one of our battery experts.
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