Winding method for improving expansion and deformation of battery cells during high-temperature charging and discharging, and lithium battery preparation method

Abstract

A winding method and lithium battery preparation method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging, the winding method comprising: presetting winding parameters: the number of turns of the positive electrode sheet, the negative electrode sheet, and the separator is defined as N=1, 2, 3...(i-4), (i-3), (i-2), (i-1), i; wherein i is a positive integer; the tension applied to the positive electrode sheet, the negative electrode sheet, and the separator during the winding process is defined as F; and the rotational speed of the elliptical winding needle during the winding process is defined as R. The steps of preparing the electrode sheet and the separator, winding at a constant tension, winding at a variable tension, winding at a variable rotational speed, and removing the elliptical winding needle are sequentially performed to prepare a winding core. The winding method can greatly optimize the winding tape path, can simultaneously solve the problem of improving the deformation of the battery cell after winding, and can improve the expansion and deformation of the battery cell during high-temperature charging and discharging, thereby ensuring the safety and reliability of the battery cell, and can also achieve a higher degree of alignment between the electrode sheet and the separator.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery cell winding, and in particular to a winding method for improving expansion and deformation of a cell during high-temperature charging and discharging, and a method for preparing a lithium battery. Background Art

[0002] Winding is a crucial step in lithium-ion battery production. With technological advancements, the winding process is becoming increasingly automated. During the automated winding process, significant tension must be applied to the electrode sheets and separators to ensure alignment between the positive and negative electrode sheets and the separators.

[0003] However, the tension during the winding process will cause the isolation film to be extended in the mechanical direction (MD). After the winding is completed, the isolation film will shrink to a certain extent in the MD direction due to the release of the tension. This is because the isolation film has a certain ductility.

[0004] It should be noted that the length of the electrode sheets in the MD direction changes very little before and after winding. This is due to the poor ductility of the electrode sheets (positive and negative). It is precisely because the separator of the battery cell severely squeezes the electrode sheets after winding that the wound battery cell will deform during the static process. The deformed battery cell structure after winding, that is, the separator severely squeezes the positive and negative electrode sheets. The deformed battery cell not only has a poor appearance, but also has quality problems such as low capacity, poor cycle performance, and rapid self-discharge.

[0005] In response to the above problems, the existing method in the industry to improve the deformation of the battery cell after winding is mainly to bake the isolation film before winding so that it can fully shrink before winding, but this method is mainly used in manual winding production. Since the automated continuous winding uses a rolled isolation film, it is extremely difficult to shrink the rolled isolation film, and even if the isolation film shrinks to a certain extent, the isolation film will be extended again due to the large tension during automatic winding. Therefore, this method is difficult to apply to automated continuous winding production and the effect it can achieve is general. In this regard, Chinese patent CN201210057716.6 discloses a battery cell winding method, which can fully release the stress of the electrode sheet by heating the positive and negative electrode sheets before winding. During winding, the electrode sheet will be extended to a certain extent under the action of tension. After the winding is completed, the electrode sheet can shrink together with the isolation film during the cooling process, thereby improving the deformation of the battery cell.

[0006] However, this method has the following defects: this method can only ensure that the electrode can shrink together with the isolation membrane after cooling, and overcome the deformation caused by the inconsistent shrinkage of the electrode and the isolation membrane, but it cannot solve the expansion and deformation problem of the finished battery cell during the charge and discharge cycle. This is because the expansion of the electrode causes the finished battery cell to become too thick and deformed. The problem is particularly obvious during the charge and discharge cycle at high temperature. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a winding method and a lithium battery preparation method that can simultaneously solve the problem of improving the deformation of the battery cell after winding and improving the expansion deformation of the battery cell during high-temperature charging and discharging. The method is particularly suitable for lithium batteries with thicker thickness and lithium batteries containing silicon negative electrodes.

[0008] The object of the present invention is achieved through the following technical solutions:

[0009] A winding method for improving expansion and deformation of a battery cell during high-temperature charging and discharging, wherein winding parameters are pre-set: the number of turns of the positive electrode sheet, the negative electrode sheet, and the separator is defined as N=1, 2, 3...(i-4), (i-3), (i-2), (i-1), i; wherein i is a positive integer; the tension applied to the positive electrode sheet, the negative electrode sheet, and the separator during the winding process is defined as F; the rotation speed of the elliptical winding needle during the winding process is defined as R;

[0010] The steps include:

[0011] S110: Steps for preparing the electrode and isolation film:

[0012] Install the positive electrode sheet on the positive electrode feeding mechanism, install the negative electrode sheet on the negative electrode feeding mechanism, install the separator on the separator feeding mechanism, and fix the initial ends of the positive electrode sheet, the negative electrode sheet, and the separator on the elliptical winding needle respectively;

[0013] S120: Constant tension winding steps:

[0014] When the number of winding turns N is the first and second turns, the winding operation is performed with constant tension, F1 = F2;

[0015] S130: Variable tension winding steps:

[0016] When the number of winding turns N is from the 3rd to the (i-4th), the winding operation is performed using variable tension, F3>...>F(i-4);

[0017] S140: Variable speed winding step:

[0018] When the number of winding turns N is (i-3), (i-2), (i-1) and i, a variable speed winding step is adopted, R(i-3)<R(i-2)<R(i-1)<Ri;

[0019] S150: Pull out the oval winding needle to prepare a winding core.

[0020] In one embodiment, in step S120 and step S130, F3>F2.

[0021] In one embodiment, in step S140, when the number of winding turns N is (i-3), (i-2), (i-1) and i, the corresponding positive electrode sheet and / or the negative electrode sheet is an empty foil area.

[0022] In one embodiment, in step S140, F(i-3)<F(i-2)<F(i-1)<Fi.

[0023] In one embodiment, in step S130 and step S140, F(i-3)>F(i-4).

[0024] In one embodiment, the pulling force range of F1 is 30-50 kg.

[0025] In one embodiment, the winding core is a square battery lithium-ion battery winding core. In the step S130, when the number of winding turns N is 3, a first partition is inserted at the end corner of the winding core, and in the step S150, the first partition is pulled out first, and then the elliptical winding needle is pulled out.

[0026] In one embodiment, the core is a square battery lithium-ion battery core. In the step S140, when the number of winding turns N is (i-3), a second partition is inserted at the end corner of the core, and in the step S150, the second partition is pulled out first, and then the elliptical winding needle is pulled out.

[0027] A method for preparing a lithium battery includes the winding method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging as described in any of the above embodiments, and after step S150, the winding core is further hot-pressed and shaped.

[0028] In one embodiment, the number of turns N of the winding core is greater than 10, the thickness of the winding core is greater than 5 mm, and the slurry layer of the negative electrode plate contains silicon.

[0029] Compared with the prior art, the present invention has at least the following advantages:

[0030] The above-mentioned winding method for improving the expansion and deformation of the battery cell during high-temperature charging and discharging sequentially uses the winding operation steps of constant tension, variable tension and variable speed, which greatly optimizes the winding tape mode. It can simultaneously solve the problem of improving the deformation of the battery cell after winding and improve the expansion and deformation of the battery cell during high-temperature charging and discharging, ensuring the safety and reliability of the battery cell, and at the same time can make the alignment of the electrode and the isolation membrane higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a flowchart of the steps of a winding method for improving expansion and deformation of a battery cell during high-temperature charging and discharging according to one embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of a polished cross-section of a comparative example core according to one embodiment of the present invention, after being discharged to 3.0V after 300 cycles in a high-temperature environment at 45°C;

[0034] Figure 3 This is a schematic diagram of a polished cross-section of a battery cell discharged to 3.0V after 300 cycles in a 45°C high-temperature environment according to an embodiment of the present invention;

[0035] Figure 4 This is a comparison curve of the charge and discharge capacity retention rate of the comparative example (conventional example) core and the example (inventive example) core at 1C high temperature 45°C according to one embodiment of the present invention. DETAILED DESCRIPTION

[0036] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0037] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly attached to the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] The present application provides a winding method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging, comprising: an outer shell and a flip cover, the outer shell comprising a rod body, a raised portion and a suction nozzle, the raised portion being arranged at the end position of the rod body, the raised portion being provided with an inclined chamfered structure, the suction nozzle being arranged on the chamfered structure, and two rotation fulcrum grooves being provided at the connection position between the raised portion and the rod body; the flip cover comprising a shielding cover and two rotating shafts, the shielding cover being connected to the two rotating shafts respectively, the two rotating shafts being inserted into the two rotating fulcrum grooves one by one, so that the flip cover can be rotated relative to the raised portion with the line connecting the two rotating fulcrum grooves as the rotation axis, and the shielding cover is used to shield the suction nozzle on the chamfered structure.

[0040] In order to better understand the technical concept of the winding method for improving the expansion and deformation of the battery cell during high-temperature charging and discharging, the winding method for improving the expansion and deformation of the battery cell during high-temperature charging and discharging is further explained below:

[0041] One embodiment of a winding method for improving the expansion and deformation of battery cells during high-temperature charging and discharging requires pre-setting of winding parameters. It can be understood that when adopting an automated winding solution, in order to improve the quality of the finished core and the stability and consistency of product performance, the winding parameters need to be pre-set, and the automated winding equipment performs winding operations according to the preset winding parameters.

[0042] The number of turns of the positive electrode sheet, the negative electrode sheet, and the separator is defined as N = 1, 2, 3...(i-4), (i-3), (i-2), (i-1), i, where i is a positive integer. Since the positive electrode sheet, the negative electrode sheet, and the separator are stacked sequentially, i.e., the same turn structure of the battery core, i.e., the cross-sectional structure includes sequentially stacked positive electrode sheets, separators, and negative electrode sheets, the number of turns of the negative electrode sheet, the positive electrode sheet, and the separator is consistent throughout the entire battery core. The number of turns of the positive electrode sheet, the negative electrode sheet, and the separator affects many parameters and performance of the lithium battery core, such as the thickness, deformation, and battery capacity of the lithium battery. It should be noted that, for example, when the number of turns of the positive electrode sheet, the negative electrode sheet and the separator is 10, that is, the number of turns of the winding core is 10, that is, i=10, then N=1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

[0043] The tension applied to the positive electrode sheet, the negative electrode sheet, and the separator during the winding process is defined as F. During the winding process, tension needs to be applied to the positive electrode sheet, the negative electrode sheet, and the separator. This is used to adjust the tightness inside the winding core and to ensure alignment between the positive electrode sheet, the negative electrode sheet, and the separator, preventing them from deviating during the winding process. Of course, tension can also be used to manipulate many other parameters, depending on the actual situation. The tension of the positive electrode sheet, the negative electrode sheet, and the separator is determined by the tensioning roller assembly on the winding needle and the feeding mechanism. That is, the positive electrode sheet, the negative electrode sheet, and the separator are pulled by the tensioning roller assembly on the winding needle and the feeding mechanism, which together apply tension to the positive electrode sheet, the negative electrode sheet, and the separator.

[0044] The rotational speed of the elliptical winding needle during the winding process is defined as R; during the winding process of the core, the positive electrode sheet, the negative electrode sheet and the isolation membrane are subjected to tension. Since the winding process is a continuous and dynamic feeding and continuous winding operation, that is, the tensioning roller group of the feeding mechanism rotates continuously, the elliptical winding needle will also rotate continuously. When the tensioning roller group of the feeding mechanism is maintained at a consistent speed, by adjusting the rotational speed of the elliptical winding needle, firstly, it can greatly affect the conveying speed of the positive electrode sheet, the negative electrode sheet and the isolation membrane, and has a greater impact on the neatness between the positive electrode sheet, the negative electrode sheet and the isolation membrane. Secondly, the rotational speed of the elliptical winding needle is proportional to the tension F to a certain extent. Of course, it is also affected by the rotational speed of the tensioning roller group of the feeding mechanism.

[0045] See also Figure 1 A winding method for improving expansion and deformation of a battery cell during high-temperature charging and discharging, according to one embodiment, comprises the following steps:

[0046] S110: Steps for preparing the electrode and isolation film:

[0047] The positive electrode sheet is installed on the positive electrode feeding mechanism, the negative electrode sheet is installed on the negative electrode feeding mechanism, and the isolation membrane is installed on the isolation membrane feeding mechanism. The initial ends of the positive electrode sheet, the negative electrode sheet and the isolation membrane are fixed on the elliptical winding needle respectively to smoothly carry out the subsequent core winding operation.

[0048] S120: Constant tension winding steps:

[0049] When the number of winding turns N is the first and second turns, the winding operation is performed with constant tension, F1 = F2.

[0050] It should be noted that by providing a constant tension winding step at the beginning of the winding operation, the alignment consistency of the first two turns of the winding core can be improved, that is, the pre-winding operation of the battery winding core can be prevented from deviating.

[0051] In one embodiment, F1=F2, and the pulling force range of F1 and F2 is 30-50 kg.

[0052] S130: Variable tension winding steps:

[0053] When the number of winding turns N is from the 3rd to the (i-4th) turn, the winding operation is performed using variable tension, F3>...>F(i-4).

[0054] It should be noted that the cell deformation caused by the shrinkage of the isolation film of the cell after winding and the expansion of the negative electrode during high-temperature charging and discharging of the cell is different. The stresses experienced by the winding turns N from the 3rd to the (i-4th) are different. The internal stress and the release space required for deformation compensation increase layer by layer from the inside of the cell to the outside of the cell. The variable tension winding step of S130 can more reasonably take the actual situation into consideration, so that sufficient expansion space can be reserved for different deformation conditions of the core after winding and after charging and discharging, which can greatly improve the deformation problem.

[0055] In one embodiment, in step S120 and step S130, F3>F2. By optimizing the transition direction between the constant tension winding step and the variable tension winding step, the tension of the first turn of the variable tension winding step (i.e., i=3, the third turn of the entire core) is greater than the tension of the constant tension winding step. It can be understood that since the two turns in the constant tension winding step are attached to the elliptical winding needle, the elliptical winding needle may not be in firm contact. By ensuring that the tension of the first turn of the variable tension winding step is greater than the tension of the constant tension winding step, the first two turns of the winding layers in the constant tension winding step can be compacted during the transition, further suppressing slippage and misalignment of the positive electrode sheet, the negative electrode sheet, and the separator due to excessive tension in the transition area of the core end angle. In addition, after the elliptical winding needle is withdrawn, the first two turns of the winding layers in the constant tension winding step have a larger internal stress release space, which can compensate for the defect of large deformation of the separator caused by the sudden increase in tension in the first turn of the variable tension winding step.

[0056] In one embodiment, the core is a square battery lithium-ion battery core. In the step S130, when the number of winding turns N is the third, the first partition is inserted at the end corner of the core of the square battery, and in the step S150, the first partition is pulled out first, and then the elliptical winding needle is pulled out. By inserting the first partition at the end corner of the core of the square battery, a larger compensation space can be further provided for the inward release of stress of each winding layer in the variable tension winding step. Since the number of winding turns N is from the third to the (i-4), the winding operation is performed using variable tension, F3>...>F(i-4). When winding, the tension of each winding layer decreases successively, and the compensable space of each winding layer from the inside to the outside increases successively, avoiding excessive stress release into the compensation space formed at the withdrawal of the first partition, making the overall deformation compensation more reasonable, and avoiding the obvious deformation problem between the layers.

[0057] Furthermore, the winding core is a prismatic lithium-ion battery winding core. In step S130, when the number of winding turns N is from the third to the (i-4th) winding turns, a first separator is inserted at the end corners of the prismatic battery winding core at each winding turn. Furthermore, in step S150, the first separator is first removed, followed by the elliptical winding needle. This allows for better adaptation to the required deformation compensation for lithium batteries with large deformation and thickness, as well as for lithium batteries containing silicon negative electrodes (the expansion rate of silicon-containing negative electrode active materials during charge and discharge is much greater than the expansion rate of graphite negative electrode active materials during charge and discharge). Furthermore, when the number of winding turns N is from the third to the (i-4th) winding turns, a first separator is inserted at the end corners of the prismatic battery winding core at each winding turn, and the thickness of the first separator increases with each winding turn. This allows for better and simultaneous improvement of the problem of cell deformation after winding.

[0058] In one embodiment, the first partition is a half-moon partition, and the half-moon partition has a semicircular cross-section, the outer wide side of the semicircular cross-section fits the outer circle of the core, and the inner narrow side of the semicircular cross-section fits the inner circle of the core. Compared with traditional square partitions and cylindrical partitions, since the number of winding circles N of the technical solution is from the 3rd circle to the (i-4th), variable tension is used for winding operation, F3>...>F(i-4), and the tension decreases with each circle. If traditional square partitions or cylindrical partitions are used, space will inevitably be left between the core circles and the partitions, and the tension itself is decreasing. The space left will make the winding process The tension is locally too loose at the partition, that is, the tension is prone to get out of control at the end corners, and the pole piece and the isolation membrane are locally misaligned, which will affect the quality of the entire core. By setting a half-moon partition, because it fits more closely with the inner and outer rings of the core and leaves less space, this problem can be better solved. Moreover, since the number of winding turns N is from the 3rd to the (i-4th), variable tension is used for winding operation, F3>...>F(i-4), and the tension decreases turn by turn. When the needle is pulled out later, there is no need to worry about the static friction between the half-moon partition and the diaphragm being large and the diaphragm being pulled out. This is why the traditional full-process constant tension winding process must use cylindrical or square partitions.

[0059] S140: Variable speed winding step:

[0060] When the number of winding turns N is (i-3), (i-2), (i-1) and i, a variable speed winding step is adopted, R(i-3)<R(i-2)<R(i-1)<Ri.

[0061] It should be emphasized that when the number of winding turns N is (i-3), (i-2), (i-1) and i, that is, when the last four turns are completed, it is an empty foil area of the square lithium battery core. For example, in the step S140, when the number of winding turns N is (i-3), (i-2), (i-1) and i, the corresponding positive electrode sheet and / or the negative electrode sheet is an empty foil area, and the thickness will drop sharply compared to the negative electrode sheet and the positive electrode sheet in the coil layer in the variable tension winding step. If the electrode is double-sided roller coated, the thickness will drop more sharply. If constant tension or decreasing tension is used, it is easy to cause the problem of deviation of the winding end electrode or isolation film. By using the variable speed winding steps when the number of winding turns N is (i-3), (i-2), (i-1) and i, R(i-3)<R(i-2)<R(i-1)<Ri, the problem of deviation of the winding end electrode or isolation film can be avoided. At the same time, due to the four empty foil circles at the end of the core, Processing, the negative electrode sheet is not coated with active material, and the expansion rate of the negative electrode sheet in the four turns at the end of the winding core will not change much. Furthermore, in the step S140, F(i-3)<F(i-2)<F(i-1)<Fi, through gradually increasing tension, the tension is usually proportional to the rotation speed of the elliptical winding needle, but not absolutely. For example, although the rotation speed of the elliptical winding needle is increased, the rotation speed of the tensioning roller group of the feeding mechanism is simultaneously increased, which may cause the tension to drop. However, simply increasing the tension cannot effectively avoid the alignment problem caused by the thickness difference of the empty foil. This is because the thickness difference will cause the transition area with active material and inactive material to be simply tightened. This time difference is likely to cause more problems, and instead cause local wrinkling problems. However, through the variable speed winding step and R(i-3)<R(i-2)<R(i-1)<Ri, the winding operation can be completed quickly. This is because the transition area will fit with the inner ring and share the internal stress caused by the tension, without having to worry about the above problems.

[0062] In one embodiment, the core is a square battery lithium-ion battery core. In the steps S130 and S140, R(i-3)>R(i-4). This can better solve the problem of alignment between the electrode and the isolation film in the last four turns of the core.

[0063] In one embodiment, in step S130 and step S140, F(i-3)>F(i-4), so that the problem of aligning the electrode and the isolation film in the last four turns of the winding core can be better solved.

[0064] In one embodiment, the core is a square battery lithium-ion battery core. In the step S140, when the number of winding turns N is (i-3), a second separator is inserted at the end corner of the core, and in the step S150, the second separator is pulled out first, and then the elliptical winding needle is pulled out. In this way, although the empty foil area can slow down the expansion and deformation problem of the battery cell during high-temperature charging and discharging, the shrinkage of the isolation membrane after being stretched after winding will still cause deformation of the battery cell. Combined with the variable speed winding step of step S140 and the insertion of the second separator, this problem can be well alleviated, especially for the situation where the positive electrode sheet is empty foil but the negative electrode sheet is not completely empty foil. Furthermore, in the step S140, when the number of winding turns N is (i-3), (i-2), (i-1) and i, a second partition is inserted at the end corner of the winding core in each turn, and in the step S150, the second partition is pulled out first, and then the elliptical winding needle is pulled out.

[0065] S150: Pull out the oval winding needle to prepare a winding core.

[0066] When the three winding steps, namely constant tension, variable tension and variable speed, are completed, the needle is pulled out to obtain the core product.

[0067] The present invention also provides a method for preparing a lithium battery, comprising the winding method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging as described in any of the above embodiments, wherein after step S150, the winding core is further subjected to hot pressing and shaping.

[0068] In one embodiment, the core hot pressing and shaping operation specifically includes the following steps:

[0069] The coil core is packaged in aluminum plastic to prepare a battery cell;

[0070] Preheat the upper mold hot platen and the lower mold hot platen;

[0071] Place the battery cell between the upper and lower hot plates and apply pressure.

[0072] The heat transferred from the battery cell in the above operation is from the outside to the inside. Although there will be a temperature difference problem, the core prepared by this method can compensate for the space difference and can adapt to the temperature difference problem. It will not cause poor adhesion between the electrode and the isolation film of the bare battery cell (core). Similarly, the expansion and deformation problem can also be greatly improved.

[0073] In one embodiment, the number of turns N of the winding core is greater than 10, the thickness of the winding core is greater than 5 mm, and the slurry layer of the negative electrode plate contains silicon.

[0074] Compared with the prior art, the present invention has at least the following advantages:

[0075] The above-mentioned winding method for improving the expansion and deformation of the battery cell during high-temperature charging and discharging sequentially uses the winding operation steps of constant tension, variable tension and variable speed, which greatly optimizes the winding tape mode. It can simultaneously solve the problem of improving the deformation of the battery cell after winding and improve the expansion and deformation of the battery cell during high-temperature charging and discharging, ensuring the safety and reliability of the battery cell, and at the same time can make the alignment of the electrode and the isolation membrane higher.

[0076] The following are specific embodiments

[0077] Take the battery with thickness greater than 5mm and winding number greater than 10 turns for production;

[0078] Step 1: Preparation of electrode sheets and separators: Prepare the positive electrode sheet, negative electrode sheet and separator into continuous rolls and install them on the positive electrode sheet feeding mechanism, negative electrode sheet feeding mechanism and separator feeding mechanism respectively;

[0079] Step 2: Wind the positive electrode sheet, the negative electrode sheet and the separator into a core through an elliptical winding needle, where the number of winding core turns is N;

[0080] Step 3: Constant tension winding: The positive electrode sheet, negative electrode sheet and separator are wound into a battery cell through an elliptical winding needle. The initial tension of the electrode sheet and separator is set to F. When the winding N is the 1st-2nd turn, constant tension F1 and F2 are used for winding, where F2 = F1 = F.

[0081] Step 4: Insert partition A and perform variable tension winding. When N>2, < the last 4 turns, insert partition A for variable tension winding. The tensions of the 3rd to the last 4 turns are F3, F4, F5, F6, and FN-4, respectively, where F3>F4>F5>F6>FN-4.

[0082] Step 5: Insert partition B and change speed winding: When N is the last 4 turns, insert partition B and change speed R winding. The winding speeds of the last 4 turns are RN-3, RN-2, RN-1, and RN, where RN-3<RN-2<RN-1<RN;

[0083] Step 6. After winding, pull out the partition first, and then pull out the oval winding needle inside the battery cell.

[0084] The present invention divides the number of layers in the battery core winding process into turns and formulates appropriate winding methods for different numbers of turns. Constant tension winding can improve the alignment consistency of the first two turns of the core (so that it does not deviate during pre-winding). According to the tension stress and other stress conditions of the core at different turns, separators of different specifications are used to apply an additional force to allow the core to prepare expansion space. At the same time, due to the different core structures of the last four turns (mostly copper and aluminum foil endings, due to the thickness difference between the electrode and the foil material), a gradually increasing winding speed is used. Using the core winding end can overcome the winding deviation problem caused by the thickness difference.

[0085] See also Figure 2 and Figure 3 As can be seen from the figure, the first and middle coils of the winding core corresponding to the comparative example have obvious deformation problems, while the coils of the winding core of this embodiment do not have obvious deformation problems.

[0086] See also Figure 4 In the comparison of the charge and discharge capacity retention rate of the comparative example (traditional example) core and the embodiment (inventive example) core at 1C high temperature 45℃, it can be seen that the charge and discharge capacity retention rate of the embodiment (inventive example) core is significantly better than that of the comparative example (traditional example).

[0087] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A winding method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging, characterized in that: Preset winding parameters: the number of turns of positive electrode sheet, negative electrode sheet and separator is defined as N=1, 2, 3 …… (i-4), (i-3), (i-2), (i-1), i; wherein i is a positive integer; the tension of the positive electrode sheet, the negative electrode sheet and the separator during the winding process is defined as F; the rotation speed of the elliptical winding needle during the winding process is defined as R; The steps include: S110: Steps for preparing the electrode and isolation film: Install the positive electrode sheet on the positive electrode feeding mechanism, install the negative electrode sheet on the negative electrode feeding mechanism, install the separator on the separator feeding mechanism, and fix the initial ends of the positive electrode sheet, the negative electrode sheet, and the separator on the elliptical winding needle respectively; S120: Constant tension winding steps: When the number of winding turns N is the first and second turns, the winding operation is performed with constant tension, F1=F2; S130: Variable tension winding steps: When the number of winding turns N is from the 3rd to the (i-4th), the winding operation is performed using variable tension, F3> …… >F(i-4), F3>F2; S140: Variable speed winding step: When the number of winding turns N is (i-3), (i-2), (i-1) and i, a variable speed winding step is adopted, R(i-3)<R(i-2)<R(i-1)<R i; when the number of winding turns N is (i-3), (i-2), (i-1) and i, the corresponding positive electrode sheet and / or the negative electrode sheet is an empty foil area; F(i-3)<F(i-2)<F(i-1)<Fi, F(i-3)>F(i-4); S150: Pull out the oval winding needle to prepare a winding core.

2. The winding method for improving the expansion and deformation of the battery cell during high-temperature charging and discharging according to claim 1, characterized in that: The pulling force range of F1 is 30-50 kg.

3. The winding method for improving the expansion and deformation of the battery cell during high-temperature charging and discharging according to claim 1, characterized in that: The winding core is a square battery lithium-ion battery winding core. In the step S130, when the number of winding turns N is 3, a first separator is inserted at the end corner of the winding core, and in the step S150, the first separator is pulled out first, and then the elliptical winding needle is pulled out.

4. The winding method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging according to claim 1, characterized in that: The winding core is a square battery lithium-ion battery winding core. In the step S140, when the number of winding turns N is (i-3), a second separator is inserted at the end corner of the winding core, and in the step S150, the second separator is pulled out first, and then the elliptical winding needle is pulled out.

5. A method for preparing a lithium battery, characterized in that: The winding method for improving the expansion and deformation of a battery cell during high-temperature charging and discharging according to any one of claims 1 to 4 further comprises hot pressing and shaping the winding core after step S150.

6. The method for preparing a lithium battery according to claim 5, wherein: The number of turns N of the winding core is greater than 10, the thickness of the winding core is greater than 5 mm, and the slurry layer of the negative electrode plate contains silicon.

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