Pole piece preparation method for improving lithium precipitation at circular arc position of winding type battery cell and battery cell prepared by pole piece preparation method

Abstract

The invention discloses a preparation method of a pole piece for improving lithium precipitation at an arc position of a winding type battery cell and the battery cell, and relates to the technical field of winding type lithium ion batteries, the preparation method of the pole piece comprises the following steps: setting a rolling program according to a selected winding battery cell model, and setting the rolling pressure of an arc area to be smaller than that of a non-arc area; and rolling the current collector coiled material coated with the active substance according to a rolling procedure, and cutting to obtain the pole piece. According to the method, the roller pressure at the arc is reduced, so that the arc is thicker and lower in compaction, and the positive and negative plates are thicker and lower in compaction at the arc, so that under the action of the winding force, the fitting degree between the positive and negative electrodes of the winding type arc and the diaphragm is obviously improved. And at the corner and the position with relatively small compaction density of the pole piece, the migration kinetics of lithium ions is guaranteed, and lithium separation can be avoided under high magnification.

Description

Technical Field

[0001] The invention relates to a wound lithium-ion battery, and in particular to a method for preparing an electrode sheet for improving lithium deposition at an arc of a wound battery cell and a battery cell. Background Art

[0002] Lithium-ion batteries are now widely used in electronic products and mobile devices, and have gradually become an indispensable part of people's lives. At present, there are two main ways to package lithium-ion batteries: stacked and wound. Among them, the winding type is widely used because of its simple operation and easier control of process and product quality. However, the wound battery cell, especially the corner area, has poor adhesion between the poles during the formation stage, and continuous expansion and extrusion occur during the cycle, resulting in greater ion transmission resistance. Therefore, lithium plating is more likely to occur in the later stage of the cycle, which seriously affects the cycle life of the battery cell and even causes safety problems.

[0003] Therefore, the current lithium-ion battery production and manufacturing process needs to be further improved. In order to improve the lithium deposition problem in the turning area, a variety of strategies have been invented. For example, by optimizing the surface coating structure of the pole piece and rationally designing the N / P ratio of the positive and negative pole piece areas, the risk of lithium deposition in the corners can be reduced; by coating the anode active slurry with strong adhesion on the bending area of ​​the winding core, the adhesion between the anode active slurry and the anode pole piece in the bending area is strengthened to prevent the anode current collector in the bending area from being exposed; by designing a new type of rolling equipment and precisely designing the roller, the thickness of the electrode is controlled in sections, thereby improving the lithium deposition problem. However, these strategies often require sacrificing the energy density of the battery cell or making major changes to the current production process, so the application process is relatively slow.

[0004] In the prior art, a rolling device with corner grooves is provided to roll the pole piece, so that the active coating at the corner area of ​​the pole piece has a larger porosity, which solves the problem of poor electrolyte infiltration at the corner of the lithium battery pole piece and easy shedding of active materials at the corner, thereby improving the lithium precipitation problem. However, this solution requires a refined design of the rolling equipment, and can only manufacture pole pieces of a specific length. It is not universal for different battery cell sizes, so the design investment cost is relatively high. In addition, the slurry has a certain fluidity and viscosity, and the multi-groove design is easy to hang the slurry, affecting the subsequent coating.

[0005] In the prior art, there is also a method of extrusion coating to first coat the corner compensation area of ​​the electrode, and then perform a second layer of continuous coating. The two layers of coating slurry are consistent and there is no gap between the coated electrode. This method carefully designs the N / P ratio of the positive and negative electrode areas, which not only reduces the risk of lithium deposition in the corners, but also improves the energy density loss caused by the coating of the "yin and yang sides". This scheme suppresses lithium deposition at the corners by designing the N / P ratio. However, the use of a two-step coating method increases the difficulty of the process. Moreover, during the continuous rolling process of electrodes of different thicknesses, it is easy for the compaction density of thicker areas to be too high, which increases the risk of lithium deposition from another aspect.

[0006] Therefore, in order to solve the shortcomings of poor universality and complex process of lithium deposition methods in the prior art, it is necessary to develop an electrode preparation method and a battery cell that improves lithium deposition at the arc of a wound battery cell. The processed electrode sheet can be adapted to any battery cell size, and the process is simple and the reliability is high. Summary of the invention

[0007] The purpose of the present invention is to solve the shortcomings of the above-mentioned background technology and provide a method for preparing an electrode sheet and a battery cell for improving lithium deposition at the arc of a wound battery cell. The processed electrode sheet can be adapted to any battery cell size, and the process is simple and the reliability is high.

[0008] The technical solution of the present invention is:

[0009] In the first aspect, the present application provides a method for improving lithium deposition in the arc portion of a wound battery cell, comprising: setting a rolling program according to a selected wound battery cell model, setting the rolling pressure in the arc region to be smaller than the rolling pressure in the non-arc region; rolling a current collector coil coated with an active material according to the rolling program, and cutting to obtain pole pieces.

[0010] In the above scheme, by intermittently reducing the roller pressure, the thickness at the arc is ensured to be thicker and the compaction is lower, so that the produced electrode sheet can be adapted to any battery cell size. Therefore, there is no need to change the surface structure of the roller, avoiding the investment cost and high maintenance cost of the high-precision design of the roller press; there is no need to add a coating process, and the thickness change at the arc can be achieved simultaneously during the rolling process.

[0011] Preferably, the method for improving lithium deposition at the arc of a wound battery cell comprises:

[0012] S1. According to the selected winding cell model, determine the full length of the pole piece of the selected cell and the respective lengths of all non-arc areas on the pole piece, and the respective lengths of all non-arc areas. Set the rolling device to perform a periodic rolling program with the full length of the pole piece as a rolling length cycle. Set the rolling pressure of the arc area in each rolling cycle to P S , the roller pressure in the non-arc area is P L , the P S , PL Between P S <P L ;

[0013] S2, placing the current collector coil coated with active material into a rolling device for rolling according to the rolling program set in step S1, and cutting it according to the rolling length cycle to obtain a pole piece with a thickness in the arc area greater than that in the non-arc area.

[0014] Furthermore, it is determined that the non-arc areas and the arc areas on the electrode sheets of the selected battery cells are arranged alternately in sequence.

[0015] Furthermore, in step S1, in each rolling cycle, the roller pressure P of all arc regions is S The same, the roller pressure P of all non-arc areas L same.

[0016] Furthermore, in step S1, in each rolling cycle, the roller pressure P of the arc area S Roller pressure P relative to the non-arc area L Reduce by 5-20%.

[0017] That is, (P L -P S ) / P L *100% = 5-20%, control P S P L The reduction range is 5-20% because if the roller pressure difference is too small, the effect of suppressing lithium precipitation is not obvious, and if the roller pressure difference is too large, it may cause local electrolyte enrichment of the electrode and even affect the overall conductivity of the electrode.

[0018] Preferably, the obtained pole piece satisfies: the compaction density of the arc region is reduced by 3-12% relative to the compaction density of the non-arc region. The compaction density reduction range of the arc region is controlled to be 3-12% because the compaction density of the pole piece is directly related to the roller pressure. If the compaction density is reduced too little, it will not inhibit lithium dendrites. If the compaction density is too different, it may lead to poor consistency of the pole piece, which may cause the pole piece to bulge or fall off during the cycle.

[0019] Preferably, the obtained pole piece satisfies: the thickness of the arc region is increased by 5-15% relative to the thickness of the non-arc region.

[0020] Preferably, at least one side of the current collector coil is coated with an active material.

[0021] Furthermore, both sides of the current collector coil are coated with active materials.

[0022] In the present invention, the coil can be coated with active substances on one side or both sides. When the coil is coated with active substances on one side, the rolling device adopts a single-sided rolling device, and when the coil is coated with active substances on both sides, the rolling device adopts a double-sided rolling device.

[0023] Furthermore, both sides of the current collector coil are coated with active materials.

[0024] In the second aspect, the present application provides a positive electrode sheet for a wound battery cell, which is prepared by the electrode sheet preparation method for improving lithium deposition at the arc of a wound battery cell as described in any of the above items, wherein the current collector coil coated with an active material is a positive current collector coil coated with a positive electrode active material. The positive current collector material and the positive electrode active material are consistent with the selected wound battery cell model. Generally, the positive current collector material can be selected from any one of aluminum foil, carbon-coated aluminum foil, and composite aluminum foil. The positive electrode active material can be selected from any one of lithium iron phosphate, ternary positive electrode (low nickel, medium nickel, high nickel), lithium cobalt oxide, lithium-rich manganese-based materials, lithium manganate, and lithium iron manganese phosphate.

[0025] In the third aspect, the present application provides a negative electrode sheet for a wound battery cell, which is prepared by using any of the above methods for preparing an electrode sheet for improving lithium deposition at the arc of a wound battery cell, wherein the current collector coil coated with an active material is a negative current collector coil coated with a negative electrode active material. The negative current collector material and the negative electrode active material are consistent with the selected wound battery cell model. Generally, the negative current collector material can be selected from any one of copper foil, carbon-coated copper foil, and composite copper foil, and the negative electrode active material can be selected from any one of natural graphite, artificial graphite, hard carbon, silicon carbon, and lithium titanate.

[0026] In a fourth aspect, the present application provides a wound battery cell, comprising the above positive electrode sheet, the above negative electrode sheet and a separator, wherein the positive and negative electrode sheets are stacked and wound together with the separator to form a bare battery cell.

[0027] The beneficial effects of the present invention include:

[0028] 1. The present invention avoids the investment cost of high-precision design and high maintenance cost of the roller press by designing a periodic rolling mode without changing the surface structure of the roller. In addition, compared with the existing surface groove design of the roller press, which can only obtain electrode sheets of a specific size, the present invention only reduces the roller pressure intermittently to ensure that the thickness at the arc is thicker and the compaction is lower, so that the produced electrode sheets can adapt to any battery cell size.

[0029] 2. The present invention realizes the periodic change of the compaction density of the electrode surface by reducing the roller pressure at the arc, without designing different N / P ratios for coating different areas of the electrode as in the prior art. The method provided by the present invention has simple steps and higher reliability.

[0030] 3. The present invention optimizes the pole piece structure, and the thickness at the arc is thicker and the compaction is lower. Since the positive and negative pole pieces are thicker and the compaction is lower at the arc, under the action of the winding force, the fit between the positive and negative poles and the separator of the wound arc is significantly improved. At the corners, where the pole piece compaction density is relatively small, the lithium ion migration dynamics can be guaranteed, and lithium precipitation can be avoided at high rates. In addition, the porosity at the corners is relatively high, and the volume expansion is alleviated, avoiding problems such as cracking, powdering and falling off at the bends. In addition, the thicker arc also helps to absorb and retain liquid at the arc, further improving the cycle life of the battery. Therefore, not only can the occurrence of lithium precipitation at the arc of the battery cell be improved, but also the consistency of the overall internal stress of the battery cell is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0033] Figure 1 Schematic diagram of the roll-pressing of the current collector coil of the present invention

[0034] Figure 2 Thickness comparison of different areas of the prepared battery cell

[0035] Among them: 1-current collector coil 2-arc area 3-non-arc area. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0038] In view of the shortcomings of current lithium precipitation methods, such as poor universality and complex processes, for example, the use of a rolling device with corner grooves to roll the pole piece can only manufacture pole pieces of a specific length, which is costly and easy to be slurried, affecting subsequent coating; for example, the corner compensation area of ​​the pole piece is coated first, and then a second layer of continuous coating is performed, which increases the coating process.

[0039] The present application intends to provide a method for preparing an electrode sheet that can adapt to any battery cell size, has a simple process and high reliability, and improves lithium deposition at the arc of a wound battery cell. The electrode sheet produced can be adapted to any battery cell size by simply reducing the roller pressure at the arc when rolling the electrode sheet, making the thickness at the arc thicker and the compaction lower.

[0040] The method for preparing a pole piece for improving lithium deposition at an arc of a wound-type battery cell of the present invention comprises:

[0041] S1. According to the selected winding cell model, determine the total length of the pole piece of the selected cell and the lengths of all non-arc areas on the pole piece, and the lengths of all non-arc areas. The lengths of the non-arc areas and arc areas are set alternately. The rolling device is set to perform a periodic rolling program with the total length of the pole piece as a rolling length cycle. The rolling pressure of the arc area in each rolling cycle is set to P S , the roller pressure in the non-arc area is P L , the P S , P L Between P S <P L ;

[0042] S2, placing the current collector coil coated with active material into a rolling device for rolling according to the rolling program set in step S1, and cutting it according to the rolling length cycle to obtain a pole piece with a thickness in the arc area greater than that in the non-arc area.

[0043] In some embodiments, in each rolling cycle, the roller pressures of all arc regions are the same, and the roller pressures of all non-arc regions are the same. The roller pressure P of the arc region is S Roller pressure P relative to the non-arc area L Reduce by 5-20%.

[0044] In some embodiments, the pole piece obtained after rolling satisfies: the compaction density of the arc region is reduced by 3-10% relative to the compaction density of the non-arc region.

[0045] In some embodiments, the pole piece obtained after rolling satisfies: the thickness of the arc region is increased by 5-15% relative to the thickness of the non-arc region.

[0046] In the present invention, the electrode sheet coil can be coated with active material on one side or on both sides. When the active material is coated on one side, the rolling device adopts a single-sided rolling device, and the active material contacts the roller. When the active material is coated on both sides, the rolling device adopts a double-sided rolling device, and the active material on both sides contacts the roller. Figure 1 As shown, the current collector coil is rolled on both sides, and the roller pressure P in the arc area 2 is S Roller pressure P in non-arc area 3 L , so the thickness of the arc area 2 is greater than the thickness of the non-arc area 3.

[0047] Based on a general inventive concept, the embodiment of the present application also provides a positive electrode sheet for a battery cell, that is, the above preparation method is used to roll and cut the positive current collector coil coated with the positive active material to obtain a positive electrode sheet that is compatible with the selected winding battery cell model. The positive current collector material and the positive active material are consistent with the selected winding battery cell model. Generally, the positive current collector material can be selected from any one of aluminum foil, carbon-coated aluminum foil, and composite aluminum foil. The positive active material can be selected from any one of lithium iron phosphate, ternary positive electrode (low nickel, medium nickel, high nickel), lithium cobalt oxide, lithium-rich manganese-based materials, lithium manganate, and lithium iron manganese phosphate.

[0048] Based on a general inventive concept, the embodiment of the present application also provides a negative electrode sheet for a battery cell, that is, the above preparation method is used to roll and cut the positive current collector coil coated with the positive active material to obtain a positive electrode sheet that is compatible with the selected wound battery cell model. The negative current collector material and the negative active material are consistent with the selected wound battery cell model. Generally, the negative current collector material can be selected from any one of copper foil, carbon-coated copper foil, and composite copper foil, and the negative active material can be selected from any one of natural graphite, artificial graphite, hard carbon, silicon carbon, and lithium titanate.

[0049] Based on a general inventive concept, the embodiment of the present application also provides a wound battery cell, comprising a positive electrode sheet prepared by the above method, a negative electrode sheet prepared by the above method and a separator, wherein the positive and negative electrode sheets and the separator are stacked and wound together to form a bare battery cell, and the battery cell is wound in an arc region. Figure 2 As shown, the thickness of the non-arc region of the positive electrode sheet d1 is less than the thickness of the arc region d2, and the thickness of the non-arc region of the negative electrode sheet d2 is less than the thickness of the arc region d4.

[0050] Since both the positive and negative electrode sheets are thicker and have lower compaction at the arc, the fit between the positive and negative electrodes and the separator of the battery cell at the wound arc is significantly improved under the action of the winding force. At the corners, where the compaction density of the electrode sheets is relatively small, the kinetics of lithium ion migration is guaranteed, and lithium plating can be avoided at high rates. In addition, the porosity at the corners is relatively high, and the volume expansion is alleviated, avoiding problems such as cracking, powdering and falling at the bends. In addition, the thicker arc also helps to absorb and retain liquid at the arc, further improving the cycle life of the battery. Therefore, not only can the occurrence of lithium plating at the arc of the battery cell be improved, but also the consistency of the overall internal stress of the battery cell is improved.

[0051] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0052] Example 1

[0053] like Figure 1 As shown, this embodiment provides a method for preparing an electrode sheet to improve lithium deposition at the arc of a wound battery cell:

[0054] S1. Perform dimensional analysis on the selected wound cell model (166Ah iron lithium wound cell). The dimensions of the electrode in the cell after winding are: length 295.9±1mm, width 105.5±1mm, thickness 37±2mm. Spread out the wound cell after injection and aging to determine the total length of the electrode and the lengths of all non-arc areas on the electrode, and the lengths of all non-arc areas on the electrode are alternately set.

[0055] The double-sided rolling device is set to perform a periodic rolling program with the full length of the pole piece as one rolling length cycle. The roller pressure of the arc area is set to P in each rolling cycle. S , the roller pressure in the non-arc area is P L , the P S , P L Between P S <P L In this embodiment, P S P L Reduce by 5%;

[0056] S2, placing the current collector coil coated with active material into a rolling device for rolling according to the rolling program set in step S1, and cutting it according to the rolling length cycle to obtain a pole piece with a thickness in the arc area greater than that in the non-arc area.

[0057] The positive current collector coil coated with positive active material (the positive current collector material and the positive active material are consistent with the selected wound battery cell model) is rolled and cut according to the above method to obtain a positive electrode sheet adapted to the selected wound battery cell model. The compaction density of the non-circular area on the positive electrode sheet is 2.50g / cm 3 The compaction density of the arc area is 2.35g / cm 3 .

[0058] The negative current collector coil coated with negative active material on both sides (the negative current collector material and negative active material can be consistent with the selected wound battery model) is rolled and cut according to the above method to obtain a negative electrode sheet that is compatible with the selected wound battery model. The compaction density of the non-arc area on the negative electrode sheet is 1.58g / cm 3 The compacted density of the arc area is 1.42g / cm 3 .

[0059] In this embodiment, the positive electrode sheet and the negative electrode sheet in the selected wound battery cell model have the same overall length, and all arc regions and all non-arc regions are also configured the same way. Therefore, the same rolling procedure is set to roll the positive current collector coil coated with the positive electrode active material and the negative current collector coil coated with the negative electrode active material.

[0060] In this embodiment, the prepared negative electrode sheet, positive electrode sheet and separator are stacked and wound together to form a bare battery cell. The material and size of the separator can be consistent with the selected wound battery cell model.

[0061] Example 2

[0062] like Figure 1 As shown, this embodiment provides a method for preparing an electrode sheet to improve lithium deposition at the arc of a wound battery cell:

[0063] S1. Perform dimensional analysis on the selected wound cell model (173Ah iron lithium wound cell). The dimensions of the electrode in the cell after winding are: length 295.9±1mm, width 105.5±1mm, thickness 37±2mm. Spread out the wound cell after injection and aging to determine the total length of the electrode and the lengths of all non-arc areas on the electrode, and the lengths of all non-arc areas on the electrode are alternately set.

[0064] The double-sided rolling device is set to perform a periodic rolling program with the full length of the pole piece as one rolling length cycle. The roller pressure of the arc area is set to P in each rolling cycle. S , the roller pressure in the non-arc area is P L , the P S , P L Between P S <P L In this embodiment, P SP L Reduced by 8%;

[0065] S2, placing the current collector coil coated with active material into a rolling device for rolling according to the rolling program set in step S1, and cutting it according to the rolling length cycle to obtain a pole piece with a thickness in the arc area greater than that in the non-arc area.

[0066] The positive current collector coil coated with positive electrode active material (the positive current collector material and the positive electrode active material are consistent with the selected wound battery cell model) is rolled and cut according to the above method to obtain a positive electrode sheet adapted to the selected wound battery cell model. The compaction density of the non-circular area on the positive electrode sheet is 2.56 g / cm 3 The compacted density of the arc area is 2.42g / cm 3 .

[0067] The negative current collector coil coated with negative active material on both sides (the negative current collector material and negative active material can be consistent with the selected wound battery model) is rolled and cut according to the above method to obtain a negative electrode sheet that is compatible with the selected wound battery model. The compaction density of the non-circular area on the negative electrode sheet is 1.62g / cm 3 The compaction density of the arc area is 1.48g / cm 3 .

[0068] In this embodiment, the positive electrode sheet and the negative electrode sheet in the selected wound battery cell model have the same overall length, and all arc regions and all non-arc regions are also configured the same way. Therefore, the same rolling procedure is set to roll the positive current collector coil coated with the positive electrode active material and the negative current collector coil coated with the negative electrode active material.

[0069] In this embodiment, the prepared negative electrode sheet, positive electrode sheet and separator are stacked and wound together to form a bare battery cell. The material and size of the separator can be consistent with the selected wound battery cell model.

[0070] Example 3

[0071] like Figure 1 As shown, this embodiment provides a method for preparing an electrode sheet to improve lithium deposition at the arc of a wound battery cell:

[0072] S1. Perform dimensional analysis on the selected wound cell model (173Ah iron lithium wound cell). The dimensions of the electrode in the cell after winding are: length 295.9±1mm, width 105.5±1mm, thickness 37±2mm. Spread out the wound cell after injection and aging to determine the total length of the electrode and the lengths of all non-arc areas on the electrode, and the lengths of all non-arc areas on the electrode are alternately set.

[0073] The double-sided rolling device is set to perform a periodic rolling program with the full length of the pole piece as one rolling length cycle. The roller pressure of the arc area is set to P in each rolling cycle. S , the roller pressure in the non-arc area is P L , the P S , P L Between P S <P L In this embodiment, P S P L Reduce by 5%;

[0074] S2, the current collector coil coated with active materials on both sides is put into a rolling device for rolling according to the rolling program set in step S1, and cut according to the rolling length cycle to obtain a pole piece with a thickness in the arc area greater than that in the non-arc area.

[0075] The positive current collector coil coated with positive electrode active material (the positive current collector material and the positive electrode active material are consistent with the selected wound battery cell model) is rolled and cut according to the above method to obtain a positive electrode sheet adapted to the selected wound battery cell model. The compaction density of the non-circular area on the positive electrode sheet is 2.58g / cm 3 The compacted density of the arc area is 2.45g / cm 3 .

[0076] The negative current collector coil coated with negative active material (the negative current collector material and negative active material can be consistent with the selected wound battery model) is rolled and cut according to the above method to obtain a negative electrode sheet that is compatible with the selected wound battery model. The compaction density of the non-circular area on the negative electrode sheet is 1.62g / cm 3 The compaction density of the arc area is 1.48g / cm 3 .

[0077] In this embodiment, the positive electrode sheet and the negative electrode sheet in the selected wound battery cell model have the same overall length, and all arc regions and all non-arc regions are also configured the same way. Therefore, the same rolling procedure is set to roll the positive current collector coil coated with the positive electrode active material and the negative current collector coil coated with the negative electrode active material.

[0078] In this embodiment, the prepared negative electrode sheet, positive electrode sheet and separator are stacked and wound together to form a bare battery cell. The material and size of the separator can be consistent with the selected wound battery cell model.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing a pole piece:

[0081] S1. Perform dimensional analysis on the selected wound cell model (173Ah iron-lithium wound cell). The dimensions of the electrode sheet in the cell after winding are: length 295.9±1mm, width 105.5±1mm, thickness 37±2mm. Unroll the wound cell after injection and aging, determine the full length of the electrode sheet, and set a constant roller pressure on the double-sided roller pressing device.

[0082] S2, the current collector coil coated with active materials on both sides is put into the rolling device for rolling according to the roller pressure set in step S1, and cut according to the full length of the pole piece of the selected model to obtain a pole piece with uniform thickness over the entire length.

[0083] The positive current collector coil coated with positive electrode active material (the positive current collector material and the positive electrode active material are consistent with the selected wound battery model) is rolled and cut according to the above method to obtain a positive electrode sheet adapted to the selected wound battery model, and the compaction density on the positive electrode sheet is 2.56g / cm 3 .

[0084] The negative current collector coil coated with negative active material (the negative current collector material and negative active material can be consistent with the selected wound battery cell model) is rolled and cut according to the above method to obtain a negative electrode sheet that is compatible with the selected wound battery cell model. The compaction density on the negative electrode sheet is 1.62g / cm 3 .

[0085] In this embodiment, the prepared negative electrode sheet, positive electrode sheet and separator are stacked and wound together to form a bare battery cell. The material and size of the separator can be consistent with the selected wound battery cell model.

[0086] Comparative Example 2

[0087] This comparative example provides a method for preparing a pole piece:

[0088] S1. Perform dimensional analysis on the selected wound cell model (166Ah iron-lithium wound cell). The dimensions of the electrode sheet in the cell after winding are: length 295.9±1mm, width 105.5±1mm, thickness 37±2mm. Unroll the wound cell after injection and aging, determine the full length of the electrode sheet, and set a constant roller pressure on the double-sided roller pressing device.

[0089] S2, the current collector coil coated with active materials on both sides is put into the rolling device for rolling according to the roller pressure set in step S1, and cut according to the full length of the pole piece of the selected model to obtain a pole piece with uniform thickness over the entire length.

[0090] The positive current collector coil coated with positive active material (the positive current collector material and the positive active material are consistent with the selected wound battery model) is rolled and cut according to the above method to obtain a positive electrode sheet adapted to the selected wound battery model, and the compaction density on the positive electrode sheet is 2.50g / cm 3 .

[0091] The negative current collector coil coated with negative active material (the negative current collector material and negative active material can be consistent with the selected wound battery model) is rolled and cut according to the above method to obtain a negative electrode sheet that is compatible with the selected wound battery model. The compaction density on the negative electrode sheet is 1.58g / cm 3 .

[0092] In this embodiment, the prepared negative electrode sheet, positive electrode sheet and separator are stacked and wound together to form a bare battery cell. The material and size of the separator can be consistent with the selected wound battery cell model.

[0093] Performance Testing

[0094] The battery cells prepared in the above embodiments and comparative examples were tested for single-cell energy density under the conditions of 0.33°C and room temperature. The battery cells were disassembled after 500 cycles under the conditions of 1°C and room temperature. Finally, the battery cells were disassembled in a dry room (dew point temperature ≤ -45°C) in a fully charged state. The results are shown in Table 1 below.

[0095] Table 1 Test results of embodiments and comparative examples

[0096]

[0097]

[0098] From Table 1 above, it can be seen that the compaction density of the arc region of the positive electrode sheets of Examples 1-3 is reduced by 6.0%, 5.5%, and 5.0% respectively compared with the compaction density of the non-arc region, and the compaction density of the arc region of the negative electrode sheets of Examples 1-3 is reduced by 10.1%, 8.6%, and 8.9% respectively compared with the compaction density of the non-arc region. From the energy density data, it can be seen that the compaction reduction of the arc region does not affect the overall energy density of the battery cell. From the disassembly of the battery after 500 cycles, it can be seen that the disassembled electrode sheets of Examples 1-3 have no lithium deposition, no purple spots, and no powder loss. The arc region of the electrode sheets after the comparative example is disassembled has a small amount of lithium deposition, a small amount of purple spots, and a small amount of powder loss, indicating that the battery cell prepared by the present invention has the advantages of better electrode interface adhesion, smoother lithium ion transmission channels, and higher safety.

Claims

1. A method for preparing a pole piece for improving lithium deposition at the arc of a wound battery cell, characterized in that: include: Set the roller pressing program according to the selected winding cell model, and set the roller pressure in the arc area to be smaller than the roller pressure in the non-arc area; The current collector coil coated with the active material is rolled according to a rolling procedure and cut to obtain pole pieces.

2. The method for improving lithium deposition at the arc of a wound battery cell according to claim 1, characterized in that: include: S1. According to the selected winding cell model, determine the full length of the pole piece of the selected cell and the respective lengths of all non-arc areas on the pole piece, and the respective lengths of all non-arc areas. Set the rolling device to perform a periodic rolling program with the full length of the pole piece as a rolling length cycle. Set the rolling pressure of the arc area in each rolling cycle to P S , the roller pressure in the non-arc area is P L , the P S , P L Between P S <P L ; S2, placing the current collector coil coated with active material into a rolling device for rolling according to the rolling program set in step S1, and cutting it according to the rolling length cycle to obtain a pole piece with a thickness in the arc region greater than that in the non-arc region.

3. The method for improving lithium deposition at the arc of a wound battery cell according to claim 2, characterized in that: In step S1, in each rolling cycle, the roller pressures of all arc regions are the same, and the roller pressures of all non-arc regions are the same.

4. The method for improving lithium deposition at the arc of a wound battery cell according to claim 2, characterized in that: In step S1, in each rolling cycle, the roller pressure P in the arc area is S Roller pressure P relative to the non-arc area L Reduce by 5-20%.

5. The method for improving lithium deposition at the arc of a wound battery cell according to claim 1 or 2, characterized in that: The obtained pole piece satisfies: the compaction density of the arc region is reduced by 3-12% relative to the compaction density of the non-arc region.

6. The method for improving lithium deposition at the arc of a wound battery cell according to claim 1 or 2, characterized in that: At least one side of the current collector coil is coated with an active material.

7. The method for improving lithium deposition at the arc of a wound battery cell according to claim 6, characterized in that: Both sides of the current collector coil are coated with active materials.

8. A positive electrode sheet for a wound battery cell, characterized in that: The electrode sheet is prepared by the method for preparing an electrode sheet for improving lithium deposition at an arc of a wound-type battery cell as claimed in any one of claims 1 to 7, wherein the current collector coil coated with an active material is a positive current collector coil coated with a positive electrode active material.

9. A negative electrode sheet for a wound battery cell, characterized in that: The electrode sheet is prepared by the method for preparing an electrode sheet for improving lithium deposition at an arc of a wound-type battery cell according to any one of claims 1 to 7, wherein the current collector coil coated with an active material is a negative current collector coil coated with a negative electrode active material.

10. A wound battery cell, comprising the positive electrode sheet as claimed in claim 8, the negative electrode sheet as claimed in claim 9 and a separator, wherein the positive and negative electrode sheets and the separator are stacked and wound together to form a bare battery cell.

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