Lithium ion battery and manufacturing method thereof

Abstract

The invention relates to the technical field of lithium ion battery manufacturing, in particular to a lithium ion battery and a manufacturing method thereof. According to the battery disclosed by the invention, the positive electrode material is flatly paved on the front and back surfaces of the aluminum foil, and the positive electrode material is flatly paved at intervals after being empty, and the interval positions correspond to the front and back surfaces of the aluminum foil. During winding, the interval between the positive plates is just located on the two side edges of the winding core, the positive material laying length of the positive plates in the winding core on the first layer is the size obtained by subtracting the width of a positive lug from the width of a winding needle, and the interval width of the positive plates wound on the side edges of the winding core for the first time is the thickness of the winding needle from the second layer. According to the invention, the positive plate is subjected to design optimization, the front and back surfaces of the positive plate are subjected to blank leaving at intervals, and the blank leaving positions correspond to the two side edges of the roll core during winding, so that an expansion space is provided for the negative plate after subsequent battery formation and capacity grading, and arching after capacity grading of the finished battery cell is avoided; and the influence on the appearance and the thickness size of the battery is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery manufacturing, and in particular to a lithium ion battery and a manufacturing method thereof. Background Art

[0002] Polymer soft-pack lithium-ion batteries are widely used in 3C products due to their high energy density and flexible shape. At present, the negative electrode material system used in lithium-ion batteries is mainly graphite or silicon negative electrode. The embedding of lithium ions will cause the negative electrode material to expand. For thicker lithium-ion batteries, there are more layers, and the internal thickness space is smaller after the core is formed. After high temperature or charging, the material expands, which can easily cause the battery cell to bulge and deform. The thickness difference between the positive and negative ears is the main reason for the subsequent formation and capacity separation.

[0003] At present, the problem of cell arching and deformation is mainly improved by reducing the winding tension of the diaphragm and increasing the winding inserts to increase the deformation space of the winding core. However, the above method has a complicated process and low production efficiency.

[0004] As the energy density requirements of battery cells increase year by year, the automation level of equipment continues to improve, and the size of battery cells is getting larger and larger, battery cells produced by the battery cell winding process will experience abnormal arching and deformation. This abnormality can easily interfere with the installation size of the battery cell, affect the performance of the battery cell, and even cause safety accidents.

[0005] At present, the semi-automatic winding production process inserts special-shaped insulating sheets during the winding process and manually pulls them out after winding. Depending on the actual situation, 1-5 special-shaped insulating sheets are inserted. This process can solve the arching and deformation of the battery cell, but it results in a large void in the part where the special-shaped insulating sheet is pulled out. This void is generally manifested at the turning point of the battery cell, where the positive and negative electrodes are not in close contact and there is an abnormal phenomenon of insufficient electrolyte. Lithium deposition is likely to occur at this point during the recycling process, posing a serious safety hazard.

[0006] However, from the actual production observation of lithium-ion batteries, it can be seen that the main reason for the battery arching and deformation is that the negative electrode has a relatively large expansion degree after a series of manufacturing processes, especially after chemical division and capacity division. From the public paper "Study on the Thickness Expansion of Negative Electrodes in Each Process of Battery Manufacturing" published in the May 2019 issue of "Popular Science", it can be seen that after the wound battery cell is baked, imbibed and fully charged, the expansion rate of the negative electrode gradually increases, especially in the fully charged state, the expansion rate of the graphite negative electrode sheet is as high as about 33%. The core of the soft-pack lithium-ion battery has the greatest tension at both ends of the core, that is, the two side positions of the core length. After the battery is formed and shaped, the battery is relatively flat, but after charging by capacity division, the negative electrode sheet expands greatly. Taking the 852844 model soft-pack lithium-ion large battery as an example, according to the 33% expansion of the electrode after the negative electrode capacity division, the initial design thickness of the electrode is 0.13±0.02mm, and the electrode expands to 0.173±0.02mm. The expansion thickness difference of a single layer is 0.043mm. The number of layers of this model of battery is 24, which means that the entire battery must have 1.03mm of expansion space in the width direction. Otherwise, it will be squeezed and deformed under the tension of the diaphragm and the tension of the electrode itself, causing the battery surface to bulge.

[0007] Therefore, in order to eliminate the problem of arching and deformation of the pole piece after capacity division, adjustments can be made in the battery design. That is, if the battery design capacity allows, this difficult problem can be solved from the perspective of battery design. Summary of the invention

[0008] The object of the present invention is to provide a lithium-ion battery and a method for manufacturing the same in view of the above-mentioned problems, mainly by optimizing the design of the positive electrode sheet, leaving blank spaces on the front and back sides of the positive electrode sheet at intervals, and making the blank spaces correspond to the two sides of the winding core when winding, so that after the subsequent battery is divided into different capacities, the negative electrode sheet will have enough expansion space after expansion, thereby preventing the electrode sheets from being squeezed and deformed due to insufficient expansion space, avoiding the arching of the finished battery cell after the capacity is divided, and preventing the appearance of the battery and the thickness of the battery from being affected.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A lithium-ion battery comprises a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet is composed of a negative electrode tab, a copper foil and a negative electrode material, and except for the negative electrode tab, the other parts are paved with negative electrode material on the front and back sides of the copper foil; the positive electrode sheet is composed of a positive electrode tab, an aluminum foil and a positive electrode material, and the positive electrode material is paved on the front and back sides of the aluminum foil, and the positive electrode material is paved for a section and then left blank for a section to form an interval, wherein the position of the interval corresponds to the front and back sides of the aluminum foil.

[0011] Furthermore, the positive electrode material of the present invention is laid flat on the front and back surfaces of the aluminum foil, with at least 6 intervals therebetween.

[0012] The present invention provides a method for manufacturing a lithium ion battery. During winding, the spacing of the positive electrode sheets is just located on both sides of the winding core. The flat length of the positive electrode material of the positive electrode sheet in the first layer of the winding core is the width of the winding needle minus the width of the positive electrode ear. Starting from the second layer, the flat length of the positive electrode material in the positive electrode sheet is the width of the winding needle plus the thickness of two layers of positive and negative electrode sheets. The flat length of the positive electrode material of each subsequent layer is the flat length of the positive electrode sheet at the corresponding position of the previous layer plus the thickness of two layers of positive and negative electrode sheets. The spacing width on the positive electrode sheet on the side of the winding core during the first winding is the thickness of the winding needle, and the spacing width on the positive electrode sheet on the side of the winding core during the second winding is the thickness of the winding needle plus the thickness of two layers of negative electrode sheets.

[0013] Furthermore, the active material contained in the negative electrode material of the present invention is graphite, and the graphite accounts for no less than 93%.

[0014] Furthermore, the thickness of the winding core of the present invention is not less than 5.0 mm.

[0015] Furthermore, in the present invention, during winding, the side edge of the middle pole ear of the positive electrode sheet and the side edge of the middle pole ear of the negative electrode sheet are both at a distance of not less than 1 mm from the side sheet of the winding needle when placed in the winding needle.

[0016] In summary, due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0017] 1. The present invention provides a lithium-ion battery and a method for manufacturing the same, which mainly optimizes the design of the positive electrode sheet, leaves blank spaces on the front and back sides of the positive electrode sheet at intervals, and makes the blank spaces correspond to the two sides of the winding core when winding, so that after the battery is subsequently divided into different capacities, the negative electrode sheet has enough expansion space after expansion, thereby preventing the electrodes from being squeezed and deformed due to insufficient expansion space, avoiding the appearance of arching of the finished battery cell after the capacity is divided, and preventing the appearance of the battery and the thickness of the battery from being affected.

[0018] 2. The method of the present invention is mainly suitable for lithium-ion batteries with a core thickness greater than 5.0 mm. According to production time statistics, the core is more than 5.0 mm, and the actual thickness of the battery cell will reach more than 6.5 mm after capacity division. Due to the large number of winding layers, the relative risk of arching and deformation of the battery cell increases with the increase in thickness.

[0019] 3. The side edges of the tabs in the positive electrode sheet and the negative electrode sheet of the present invention are at least 1 mm away from the side sheets of the winding needle when placed in the winding needle. This allows the negative electrode sheet to expand without exerting pressure on the tabs close to the inner side of the winding core, thereby avoiding the risk of arching and deformation caused by the placement of the tabs.

[0020] 4. The battery capacity retention rate produced by the method of the present invention is relatively better, and the internal resistance increases less after cycling, which further promotes the improvement of the battery cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a schematic diagram of a lithium-ion battery and a method for manufacturing the same.

[0022] Figure 2 The present invention is a schematic diagram of the positive and negative electrode states of a lithium ion battery and a manufacturing method thereof.

[0023] Figure 3 It is a cycle comparison curve of this scheme and the comparative example in the embodiment and verification example of the present invention.

[0024] In the figure: 1. positive electrode sheet; 11. positive electrode tab; 12. positive electrode material; 13. aluminum foil; 2. negative electrode sheet; 21. negative electrode tab; 22. negative electrode material; 23. copper foil; 3. spacer. DETAILED DESCRIPTION

[0025] In order to express the present invention more clearly, the present invention is further described below through specific examples.

[0026] 1. Implementation

[0027] like Figure 2 As shown, a lithium-ion battery in this scheme includes a positive electrode sheet 1 and a negative electrode sheet 2, wherein the negative electrode sheet 2 is composed of a negative electrode tab 21, a copper foil 23 and a negative electrode material 22, wherein the active material of the negative electrode material 22 is graphite, which accounts for no less than 93% of the negative electrode material 22, and the negative electrode material 22 is stirred according to a normal batching process and then coated on the copper foil 23, and except for the negative electrode tab 21, the negative electrode material 22 is flatly coated on the front and back sides of the copper foil 23; the positive electrode sheet 1 is composed of a positive electrode tab 11, an aluminum The positive electrode material 12 is composed of an aluminum foil 13 and a positive electrode material 12, and the positive electrode material 12 is spread flat on the front and back sides of the aluminum foil 13. In order to prevent the battery from arching and deforming, during the coating process of the positive electrode sheet 1, the positive electrode material 12 needs to be spread flat on the aluminum foil 13 for a section, and then a part of the aluminum foil 13 is left empty, and then a section is continued to be spread flat on the aluminum foil 13, and then another section is left empty to form a gap 3. The position of the gap 3 on the front and back sides of the positive electrode sheet 1 corresponds one by one to the front and back sides of the aluminum foil 13.

[0028] Generally, the pit depth of the aluminum-plastic film of lithium-ion batteries is about 5mm. If it is too deep, it is easy to be damaged. Therefore, the corresponding core will generally not exceed 8.5mm, that is, the number of layers of the corresponding core is about 30. The thickness of the electrode sheet of a general consumer lithium-ion battery is about 0.13mm after the rolling process. According to the expansion degree of 30%, the total thickness of the negative electrode sheet 2 after the lithium-ion battery capacity is divided is about 1.1mm, and the thickness of the positive electrode sheet 1 after rolling is about 0.125mm. Corresponding to the aluminum foil 13 after removing 0.01mm, the material thickness of the negative electrode sheet 2 is 0.115mm. The positive electrode material 12 of the present invention is flat on the front and back sides of the aluminum foil 13. The thickness of the negative electrode sheet 2 is 0.07 mm, and the space 3 is not less than 6. That is, at least 0.07 mm of space is expected to be vacated for the expansion of the thickness of the negative electrode sheet 2. In addition, according to statistics from production practice, after capacity division, the thickness of the positive electrode sheet 1 will also expand by about 10%, that is, the space 3 between the positive electrode sheet 1 and the negative electrode can vacate a total of about 0.77 mm of thickness space for the negative electrode. For the expansion of the thickness of the negative electrode sheet 2 minus the space vacated by the space 3 between the positive electrode and the negative electrode, only about 0.3 mm of thickness space needs to be expanded. Such a small size is not enough to cause the battery to bulge and deform. Therefore, this design can prevent the lithium-ion battery with a thickness of more than 6 mm from bulging and deforming.

[0029] like Figure 1As shown, in the present invention, a method for manufacturing a lithium-ion battery is provided. During winding, the interval 3 of the positive electrode sheet 1 is located just on both sides of the winding core. Because the tension of the diaphragm on both sides of the winding core is the largest, the negative electrode sheet 2 can be extended on both sides of the winding core when the thickness of the negative electrode sheet 2 expands, thereby reducing the compression of the positive electrode sheet 1 on the negative electrode sheet 2 corresponding to the interval 3. The electrode sheet is wound into a winding core by a winding machine. In the winding core, the flat length of the positive electrode material 12 of the first layer of the positive electrode sheet 1 is the width of the winding needle minus the width of the positive electrode ear. In actual production, in order to prevent the positive electrode sheet 1 from falling off near the positive electrode ear, a certain length of space is generally left between the positive electrode ear and the positive electrode ear when the positive electrode material 12 is coated, so as to ensure that the positive electrode sheet 1 is not easy to fall off at this location during subsequent processing. The core becomes thicker as the electrode sheet is rolled around the winding needle. Starting from the second layer, the flat length of the positive electrode material 12 in the positive electrode sheet 1 is the width of the winding needle plus the thickness of two layers of positive and negative electrode sheets 2. The flat length of each subsequent layer of positive electrode material 12 is the flat length of the positive electrode sheet 1 at the corresponding position of the previous layer plus the thickness of two layers of positive and negative electrode sheets 2. The width of the gap 3 on the positive electrode sheet 1 on the side of the core for the first winding is the thickness of the winding needle. The width of the gap 3 on the positive electrode sheet 1 on the side of the core for the second winding is the thickness of the winding needle plus the thickness of two layers of negative electrode sheets 2. The other winding layers are all based on the size of the gap 3 of the second layer. This solution is suitable for batteries with a core thickness of not less than 5.0 mm. Because the core is 5.0 mm, the corresponding battery cell thickness after capacity division is about 6.5 mm. Therefore, for a core thickness exceeding 5.0 mm, at least 6 intervals 3 are set, and as the core thickness continues to increase, the number of intervals 3 increases, and increases by 2 each time; the intervals 3 are set sequentially from the pole ear position of the pole piece to the tail of the pole piece.

[0030] This solution is optimized. During winding, the side edges of the pole ears of the positive electrode sheet 1 and the two side edges of the pole ears of the negative electrode sheet are at least 1 mm away from the side sheets of the winding needle when placed in the winding needle. This ensures that the position of the pole ears of the electrode sheet will not press against the two sides of the winding core, which may cause arching and deformation in the future.

[0031] 2. Verification Example

[0032] 1. Thickness comparison analysis

[0033] The 862844 model soft-pack lithium-ion battery was made into batteries using the existing normal production method and the method of this scheme. The specification requires the thickness to be less than 8.6 mm. The other process steps are exactly the same. The batteries are produced on the same production line. They are first formed and then sealed. The thickness of each battery is measured. After the capacity is divided and the batteries are left to stand for 72 hours, the thickness of each battery is measured again for comparison, as shown in Table 1 below:

[0034] Table 1 Comparison of the thickness of the battery before and after capacity division between this solution and the comparative solution

[0035]

[0036]

[0037] It can be seen from Table 1 that the thickness expansion rate of the battery of this solution is only about 6.5%, while the thickness expansion rate of the comparison is as high as about 13.5%, which is more than twice the thickness expansion rate of this solution. This shows that the expansion rate of the comparison is caused by abnormal expansion of the pole piece and the arching deformation of the battery. It can also be judged from the appearance of the battery itself that the battery of the comparison has undergone relatively serious arching deformation. In addition, most of the batteries in the comparison have a thickness exceeding the 8.6mm thickness range required by the specification due to arching deformation. The batteries made by this solution are not too thick after capacity division, and are more than 0.2mm away from the thickness required by the specification. In summary, the thickness of the battery using this solution can be effectively controlled, and the problem of battery arching deformation is also solved more thoroughly.

[0038] 2. Performance test of two batteries

[0039] (1) Internal resistance test: The battery of the comparative example and the battery of the present solution were subjected to a 500-cycle performance test at a current of 1.0C. The internal resistance of the battery was measured before the test, and the internal resistance of the battery was measured again after 500 cycles of charge and discharge, as shown in Table 2 below.

[0040] Table 2 Comparison data of internal resistance test of comparative battery and battery of this solution before and after charge and discharge cycle test

[0041]

[0042] According to Table 2, after 500 cycles of charge and discharge at a current of 1.0C, the internal resistance of the battery of this scheme increases by about 4.5%, while the internal resistance of the battery of the comparative example increases by about 10.5% after 500 cycles of charge and discharge at a current of 1.0C, which is more than twice the internal resistance increase of this scheme. It can be concluded that setting a gap between the positive plates on both sides of the winding core can reduce the internal resistance of the battery during cyclic charge and discharge. Because the tension on both sides of the winding core is too large, the electrolyte is not easy to wet, resulting in dead lithium in subsequent charge and discharge cycles, thereby increasing the internal resistance of the battery.

[0043] (2) Cycle performance test: The battery of the comparative example and the battery of the present solution were subjected to a 1000-cycle cycle performance test at a current of 1.0C. After the cycle test, the capacity retention rate was calculated as shown in Table 3. The specific cycle curve comparison is as follows: Figure 3 shown.

[0044] Table 3 Capacity retention of the batteries of this solution and the comparative example after 1000 cycles at 1.0C current

[0045]

[0046] From Table 3, it can be concluded that after 1000 cycles of charge and discharge at 1.0C current, the capacity retention rate of the battery in the comparative example is about 81.5%; while after 1000 cycles of charge and discharge at 1.0C current, the capacity retention rate of the battery in the present solution is about 88%; the overall capacity retention rate is improved by 6.5%. Figure 3 It can also be seen.

[0047] In summary, it has been verified that the battery manufactured by the scheme of the present invention can effectively avoid the phenomenon of arching and deformation in batteries with thicker thickness, and effectively solve the problem of poor appearance caused by arching and deformation. After the battery is charged and discharged for 500 cycles at a current of 1.0C, the increase in internal resistance is smaller. At the same time, after 1000 cycles, the capacity retention rate is better.

Claims

1. A lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The negative electrode sheet is composed of a negative electrode tab, copper foil and negative electrode material. Except for the negative electrode tab, the other parts are spread with negative electrode material on the front and back sides of the copper foil. The positive electrode sheet is composed of a positive electrode tab, aluminum foil and positive electrode material. The positive electrode material is spread on the front and back sides of the aluminum foil, and the positive electrode material is spread for a section and then left empty for a section to form an interval, wherein the position of the interval corresponds to the front and back sides of the aluminum foil.

2. A lithium ion battery according to claim 1, characterized in that: The positive electrode material is laid flat on the front and back sides of the aluminum foil, with at least 6 intervals therebetween.

3. A method for manufacturing a lithium-ion battery according to claim 1, comprising winding, characterized in that: During winding, the spacing of the positive electrode sheets is just located on both sides of the winding core. The flat length of the positive electrode material of the positive electrode sheet in the first layer of the winding core is the width of the winding needle minus the width of the positive ear. Starting from the second layer, the flat length of the positive electrode material in the positive electrode sheet is the width of the winding needle plus the thickness of two layers of positive and negative electrode sheets. The flat length of each subsequent layer of positive electrode material is the flat length of the positive electrode sheet at the corresponding position of the previous layer plus the thickness of two layers of positive and negative electrode sheets; the spacing width on the positive electrode sheet on the side of the winding core for the first winding is the thickness of the winding needle, and the spacing width on the positive electrode sheet on the side of the winding core for the second winding is the thickness of the winding needle plus the thickness of two layers of negative electrode sheets.

4. The method for manufacturing a lithium-ion battery according to claim 2, characterized in that: The active material contained in the negative electrode material is graphite, and the graphite accounts for no less than 93%.

5. The method for manufacturing a lithium-ion battery according to claim 2, characterized in that: The thickness of the winding core is not less than 5.0 mm.

6. The method for manufacturing a lithium-ion battery according to claim 2, characterized in that: During winding, the side edge of the middle pole ear of the positive electrode sheet and the side edge of the middle pole ear of the negative electrode sheet are at least 1 mm away from the side sheet of the winding needle when they are placed in the winding needle.

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