Comparison between winding process and lamination process

At present, what restricts the development of pure electric vehicles is the mileage and the efficiency of supplementary energy , The core component that limits these two points is the power battery technology . At present, the mainstream power battery cells in the industry are divided according to the manufacturing process , It can be divided into winding process and lamination process . Different manufacturing processes will directly affect the core indicators of the battery, thus affecting some performance characteristics of pure electric vehicles .

As an important part of lithium battery manufacturing , Lamination and winding technology has been widely concerned by academic and commercial circles . Coating the positive and negative electrode sheets 、 dry 、 Striping 、 After slitting , The assembly process of electrode sheets will be carried out , The unpacked cell can be divided into lamination and winding processing .

▲  Schematic diagram of comparison between winding process and lamination process

Lamination process It is to divide the coated positive and negative agent layer into initial sizes , Then, the positive bonding agent layer is deposited in sequence 、 The diaphragm 、 The negative bonding agent layer is bonded , There will be more “ Sandwich ” The structural layers are overlapped in parallel , An electrode chip core that can be encapsulated is formed . The continuity of gasket process depends on the diaphragm “Z” Zigzag bend , Put the positive and negative electrodes on the diaphragm continuously , The diaphragm “Z” The glyph goes through it , Separate the poles , Finally, wrap the shell .

One ． Summary of advantages and disadvantages of lamination process

// advantage

I.  High capacity density ： The internal space of lithium battery is fully utilized , Therefore, compared with the winding process , Volume is higher than capacity ;

II.  High energy density ： The discharge platform and volume specific capacity are both higher than those of the winding lithium battery , So the energy density is relatively high ;

III.  Flexible size ： The size of each pole piece can be designed according to the size of lithium battery , Thus, the lithium battery can be made into any shape .

// Inferiority

I.  Easy to solder ： All pole pieces shall be spot welded to one spot , Difficult to operate and easy to solder ;

II.  Equipment efficiency is slow ： At present, the efficiency of domestic laminating machine is mostly 0.8s/ The rate of the slice , Imported laminating machine 0.17s/ There is a big difference in the efficiency of the chips .

Winding process It is winding by fixing the winding needle , The positive pole piece treated in the early stage 、 The diaphragm 、 The negative pole pieces are wound and extruded in sequence . The specific process is to press the raw material as the negative electrode 、 The diaphragm 、 Positive pole 、 The order of the diaphragms is stacked together , It is directly rolled into a cylindrical or elliptic cylinder by the winding method , Then put it in the metal shell of square shell or cylinder .

Two ． Summary of advantages and disadvantages of winding process

// advantage

I.  High internal resistance ： Normally, the positive and negative electrodes have only a single lug ;

II.  Easy electric welding ： Each lithium battery only needs to be welded at two places , Easy to control ;

III.  Production control is relatively simple ： A lithium battery has two poles , Easy to control .

// Inferiority

I.  Single shape ： It can only be made into cuboid lithium battery ;

II.  Poor heat dissipation effect ： It is difficult to take thermal isolation measures between cells , It is easy to cause local overheating , This causes the heat to spread out of control .

It is mainly explained from two aspects of the electrical performance and processing technology of the electric core ：

// Electrochemical performance

1.  Internal resistance difference

Batteries manufactured by the lamination process have low internal resistance , The battery made by winding process has high internal resistance . Because the winding process of the cell usually uses a monopole ear to output current , The lamination process is a parallel welding of multiple pole lugs , This method greatly reduces the lithium ion migration path in the charge and discharge process . The lower internal resistance improves the heating condition of the cell in use , Thus, the attenuation rate of the initial energy density of the cell is optimized , Therefore, the battery capacity of the lamination process decays more slowly .

2.  Cycle life difference

With the normal use of the battery, the charging and discharging process accumulates , After heat generation in the cell, the working temperature of the cell is affected . For cells manufactured by lamination process , The internal structure is uniform , It can also distribute heat evenly , Including good heat dissipation capacity ; And the winding process makes the electric core , The internal structure and mechanical performance show gradient changes , The heat dissipation direction between the pole piece and the diaphragm is uneven , This results in the temperature gradient distribution , It is easy to cause slow heat dissipation in the inner circle 、 Fast heat dissipation in the outer ring . The concentrated high temperature will also affect the phase structure and electrochemical performance of battery active materials , Resistance to lithium ion deinterlacing caused by long-term use , It also makes the battery show the phenomenon of rapid capacity decay , That is, the battery cycle is short .

3.  Difference in mechanical stress of electrode piece

Two kinds of electrode sheet treatment process lead to different internal mechanical stress performance of the battery . The stress areas between the electrode sheets manufactured by the lamination process are the same , There is no obvious stress concentration point , In addition, it is not easy to damage the electrode material layer in the process of charging and discharging . The winding process produces stress concentration at the bend of the cell . According to the experience of battery analysis , The bending part of the winding is more prone to structural damage under the stimulation of electrical signals , And cause short circuit and lithium metal precipitation . The stress concentration point is the initial position that mainly causes battery failure , It also leads to short cycle life of the winding process .

4.  The battery magnification performance is different

Lamination process is equivalent to multi pole pieces connected in parallel , It is easier to complete large current discharge in a short time , It is beneficial to the battery's magnification performance . The winding process is just the opposite , A single polar lug leads to slightly poor magnification performance .

5. Energy density design differences

The battery made by lamination process can support higher energy density , The main reason is that the lamination processing method can make better use of the packaging space , Increase the filling of effective materials ; And the battery made by the winding process , The electrode piece has a curved circular structure , And the double diaphragm structure used occupies a certain space , Failed to achieve higher space utilization , This will result in a lower energy effect .

// Treatment process

1.  Electrode sheet manufacturing difference

Compared with the production method of laminations , The mode of winding production, the degree of automation and the suppliers of supporting equipment are in the mature stage , And at present, most of the cell manufacturers use the winding production process . However, the equipment and supporting links of the lamination process are slightly complicated , The requirements for the qualified rate of pole piece cutting are extremely strict . generally speaking , The cutting of winding mode is mainly at the two nodes of starting and ending winding of the electric core , The lamination cutting needs long-term and accurate control , Each pole piece has to undergo four knife cutting , And the cross section of the pole piece 、 Powder drop 、 Burr and other conditions need to be controlled , The requirements for pole piece consistency are quite high .

2.  Battery manufacturing differences

The operation of manufacturing battery by winding process is relatively simple , Both semi-automatic equipment and full-automatic equipment can efficiently complete the assembly and packaging of electric cells . It is complicated to manufacture batteries by lamination process , A higher proportion of manual operation is required , And because the equipment industry chain is not mature , Automated production is difficult to replicate on a large scale .

in addition , In terms of battery quality control , The type of winding process is easier to control , Lamination process manufacturing is difficult to obtain good consistency because of complex process links .

In general , Battery manufacturers need to design the production process according to battery quality requirements and cost control , Before and after the optimization of electrode sheet treatment process , About pole piece cutting and welding 、 There will be great changes in the assembly process .