Battery cell and manufacturing method thereof
By setting a gradually decreasing depth groove on the positive electrode sheet of the lithium-ion battery pouch cell and optimizing the expansion rate, the problem of cell expansion caused by electrolyte decomposition is solved, achieving low expansion risk and long life of the cell.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-19
- Publication Date
- 2026-03-31
AI Technical Summary
Existing lithium-ion battery pouch cells suffer from reduced cycle life, increased internal resistance, and increased safety risks due to electrode expansion during cycling. In particular, the lithium deposition phenomenon caused by electrolyte decomposition reaction and excessive consumption cannot be effectively resolved.
Uniformly distributed grooves are set on the positive electrode sheet of the battery cell, with the groove depth gradually decreasing. The grooves adopt a 'deep inside and shallow outside' design. Electrolyte can be stored in the grooves to improve the problem of insufficient electrolyte. The expansion rate of each positive electrode sheet is optimized by data fitting. The center line of the grooves is arranged in an equilateral triangle to ensure uniform tension.
It effectively reduces the risk of cell expansion, improves cell lifespan, reduces costs, increases the energy density of the cell pack, and extends the lifespan of the cells.
Smart Images
Figure CN121768982A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery cell manufacturing technology, and more specifically, to battery cells and methods for manufacturing battery cells. Background Technology
[0002] In recent years, with the continuous development of science and technology and the economy, the demand for high-efficiency batteries has been increasing. Lithium-ion batteries, due to their advantages such as high operating voltage, long cycle life, and high energy density, have been widely used in mobile devices such as mobile phones and computers, as well as new modes of transportation such as electric vehicles and electric ships, and large-scale energy storage fields such as energy storage power stations. During cycling, the expansion of the electrode sheets in typical pouch cells leads to adverse phenomena such as reduced cycle life and increased internal resistance. After disassembling the cells, it is found that this results in wrinkled electrode sheets, poor wettability, black spots, and even lithium plating. Furthermore, as the electrode sheet areal density increases, not only does the electrode sheet expansion become more severe, but the electrode sheet thickness also increases, further deteriorating the liquid injection wetting effect. In addition, with the increase in the number of cell cycles, for example, conventional silicon anodes may experience expansion deterioration and even cracking and powdering in the later stages of cycling, significantly increasing the safety risks of the cell.
[0003] The swelling of pouch cells during use is a particularly critical issue, and the causes of lithium battery swelling can be attributed to two main categories. First, variations in the thickness of the battery electrodes can cause swelling. Second, the oxidation and decomposition of the electrolyte, producing gas, can also trigger swelling. Internal gas production is a significant cause of battery swelling, a phenomenon that occurs to varying degrees during normal temperature cycling, high-temperature cycling, or high-temperature storage. Research indicates that the root cause of cell swelling lies in the decomposition reaction of the electrolyte and the lithium deposition phenomenon caused by rapid electrolyte depletion.
[0004] Current solutions include: 1. Material side: adding film-forming agents to stabilize the SEI film and reduce side reaction gas production; positive electrode coating technology to reduce positive electrode oxygen release and reduce electrolyte oxidation risk; 2. Design side: reserving expansion gaps; 3. User side: avoiding overcharging / over-discharging to prevent positive electrode structure collapse and copper foil dissolution; strengthening heat dissipation during high-temperature storage to avoid SEI film decomposition and recombination accelerating gas production; however, these methods cannot completely solve the cell expansion problem and are costly.
[0005] In view of this, the present invention is proposed. Summary of the Invention
[0006] The purpose of this invention is to provide a battery cell and a method for manufacturing the battery cell, which aims to improve at least one of the problems mentioned in the background art.
[0007] This invention is implemented as follows: In a first aspect, the present invention provides a battery cell, which is a laminated or wound battery cell. One side of the positive electrode sheet of the battery cell is provided with uniformly distributed grooves. Along the direction from the center outward, the depth of the grooves of each positive electrode sheet gradually decreases. The bottom surface of each groove is arc-shaped with R being 1~3µm. The groove opening is circular with a diameter of 2R. The number of grooves η on each square centimeter of positive electrode sheet is 200~4000.
[0008] In an optional implementation, on each positive electrode, the center line connecting any three adjacent grooves forms an equilateral triangle.
[0009] In an optional implementation, the total number of positive electrode layers n is 10 to 40 layers.
[0010] In an optional implementation, the method for determining the groove depth of each positive electrode layer is as follows: The relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer after cycling of a normal battery cell is obtained by data fitting (1): E(i) = E mid +k*∣i i mid | 2 In the formula, E(i) represents the amount of residual electrolyte in the i-th layer after cell cycling, in mg. mid Let k be a constant, k be the electrolyte consumption attenuation coefficient, and i be the stratification number. mid = (n+1) / 2, where n is the total number of layers in the positive electrode; To obtain the curve symmetric to equation (1) about the y-axis on the coordinate plane, equation (2) is: E( H i )=K m -E(i), E( H i ) represents the amount of electrolyte stored in the i-th layer of positive electrode cell; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R))η; The positive electrode sheet of the pressure groove is assembled into a battery cell. The positive electrode sheet of the battery cell is multi-layered, and each layer has a pressure groove. The bottom of the pressure groove is an arc surface, and the groove depth is obtained according to formula (3). H i .
[0011] In an optional implementation, the number of cycles is x, where x is 0 to 3000.
[0012] In an optional implementation, the data fitting method is to take multiple cells from the same batch and cycle them for the same number of times, measure the amount of residual electrolyte in each layer of the positive electrode of each cell, and take the average value of the data from multiple cells for data fitting.
[0013] Secondly, the present invention provides a method for manufacturing a battery cell, wherein the battery cell is a laminated or wound battery cell, comprising: A positive electrode is provided, one side of which has uniformly distributed grooves, and the other side has protrusions corresponding to the grooves; The positive electrode is assembled into a cell. Along the direction from the center outward, the depth of the grooves of each positive electrode layer gradually decreases. The bottom surface of each groove is arc-shaped with R = 1~3µm. The groove opening is circular with a diameter of 2R. The number of grooves η on each square centimeter of positive electrode is 200~4000.
[0014] In an optional implementation, the groove depth of each positive electrode layer is obtained in the following manner: The relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer after cycling of a normal battery cell is obtained by data fitting (1): E(i) = E mid +k*∣i i mid | 2 In the formula, E(i) represents the amount of residual electrolyte in the i-th layer after cell cycling, in mg. mid Let k be a constant, k be the electrolyte consumption attenuation coefficient, and i be the stratification number. mid = (n+1) / 2, where n is the total number of layers in the positive electrode; To obtain the curve symmetric to equation (1) about the y-axis on the coordinate plane, equation (2) is: E( H i )=K m -E(i), E( H i ) represents the amount of electrolyte stored in the i-th layer of positive electrode cell; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R))η; The positive electrode sheet of the pressure groove is assembled into a battery cell. The positive electrode sheet of the battery cell is multi-layered, and each layer has a pressure groove. The bottom of the pressure groove is an arc surface, and the groove depth is obtained according to formula (3). H i .
[0015] In an optional implementation, the number of cycles is x, where x is 0 to 3000.
[0016] In an optional implementation, on each positive electrode, the line connecting the centers of any three adjacent grooves forms an equilateral triangle. Optionally, the total number of positive electrode layers n is 10 to 40 layers.
[0017] The present invention has the following beneficial effects: The battery cell provided by this invention features a grooved positive electrode plate with electrolyte storage, improving electrolyte shortage and extending battery life while reducing the risk of expansion in pouch cells. This also reduces costs at the pack end, as the reduced expansion risk eliminates the need for buffer filling to further increase the pack's energy density. However, during actual battery cycling, uneven internal forces cause variations in the expansion of the positive electrode plate. The closer to the innermost layer of the positive electrode plate, the greater the constraint, resulting in less expansion space and making electrolyte wetting extremely difficult. This weakens the electrolyte's "breathing effect," accelerating battery degradation. Therefore, the battery cell provided by this invention employs a "deeper inside, shallower outside" groove design for each positive electrode layer to optimize expansion rates, improving cell expansion and addressing the difficulty of electrolyte absorption in thicker cells. Thus, the battery cell provided by this invention, due to its special positive electrode plate design, exhibits low expansion risk and long service life. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a schematic diagram of the battery cell structure provided in an embodiment of the present invention; Figure 2 A schematic diagram of the structure of the positive electrode sheet with the shallowest groove (top image) and schematic diagrams of the structure of the positive electrode sheet with grooves of other depths (bottom image); Figure 3 The groove distribution method is as described in Example 1; Figure 4 The groove distribution method is shown in Example 5; Figure 5 The curve showing the fitting of electrolyte residue E(i) and layer number i during the later stage of the cycle in Example 1; Figure 6 This is a fitting curve of the electrolyte residue E(i) and the number of layers i in the later stage of the cycle in Example 2. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0021] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0022] like Figure 1 and Figure 2 As shown in the figure, an embodiment of the present invention provides a battery cell, which is a laminated or wound battery cell. One side of the positive electrode sheet of the battery cell is provided with uniformly distributed grooves. The depth of the grooves of each positive electrode sheet gradually decreases from the center outward. The bottom surface of each groove is arc-shaped with R being 1~3µm and the groove diameter being 2R. The number of grooves η on each square centimeter of positive electrode sheet is 200~4000.
[0023] The inventors discovered that the root cause of cell expansion lies in the decomposition reaction of the electrolyte and the lithium deposition phenomenon caused by excessive electrolyte consumption. The cell provided by this invention has a pressure groove on its positive electrode, which can store electrolyte, improving the electrolyte deficiency problem, thus extending cell lifespan and reducing the risk of expansion in pouch cells. The pack end also suffers from cost reduction; because the risk of cell expansion is reduced, the pack end does not need to be filled with buffer material to further increase the energy density of the cell pack.
[0024] However, during actual battery cell cycling, uneven stress within the cell causes changes in the expansion of the positive electrode. The closer to the innermost layer of the positive electrode, the greater the constraint force, resulting in less expansion space and greater difficulty in electrolyte wetting. This weakens the electrolyte's "breathing effect" and accelerates cell degradation. Therefore, the present invention employs a "deeper inside, shallower outside" design for the groove depth of each positive electrode layer to optimize the expansion rate of each layer, improving cell expansion and addressing the difficulties in electrolyte absorption in thicker cells.
[0025] Therefore, the battery cell provided by this invention has the characteristics of low expansion risk and long service life due to the special design of the positive electrode.
[0026] Specifically, because the surface of the positive electrode is grooved, a protrusion is formed on the back of the electrode at the corresponding groove. The size of the protrusion is close to that of the groove, but slightly smaller than the groove.
[0027] Furthermore, on the positive electrode sheet, the line connecting the centers of any three adjacent grooves forms an equilateral triangle. To ensure the tension of the positive electrode sheet is "uniformed," a triangular stable structure design is adopted for the arrangement of the grooves, so that the tension of the positive electrode sheet is released uniformly and the disadvantages caused by the groove design are avoided.
[0028] Optionally, the total number of positive electrode layers, n, is 10 to 40 layers. This number of layers is commonly used in battery cells, ensuring optimal cell performance. Figure 1 As shown, Figure 1 The structure given is when the number of positive electrode layers is 4.
[0029] Optionally, the groove depth of the shallowest positive electrode is... H i =R, such as Figure 2 As shown in the diagram above; the groove depth of other positive electrode plates is... H i >R, the actual volume of the groove is equal to the sum of a semicircle and a frustum with the same radius as the semicircle, such as Figure 2 As shown in the image below.
[0030] Furthermore, the method for determining the groove depth of each positive electrode layer is as follows: The relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer after cycling of a conventional battery cell was obtained by data fitting (1): E(i)=E mid +k*∣i i mid | 2 ; In the formula, E(i) is the amount of residual electrolyte in the i-th layer after cell cycling, in mg. mid The constant is k (which can be understood as the minimum amount of residual electrolyte in the intermediate layer), k is the electrolyte consumption attenuation coefficient, and i is the layer number. mid = (n+1) / 2, where n is the total number of layers in the positive electrode; On the coordinate system, we obtain the curve symmetric to equation (1) about the y-axis, and equation (2): E( H i )=K m -E(i), E( H i ) represents the amount of electrolyte stored in the i-th layer of positive electrode cell; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R))η; The positive electrode sheet of the pressure groove is assembled into a battery cell. The positive electrode sheet of the battery cell is multi-layered, and each layer has a pressure groove. The bottom of the pressure groove is an arc surface, and the groove depth is obtained according to formula (3). H i .
[0031] Arranging the depth of the voltage groove in the positive electrode sheet of the battery cell according to the above method can further prevent battery cell expansion and extend battery cell life.
[0032] Optionally, in the above determination method, the number of cycles is x, where x ranges from 0 to 3000. This range of cycle count corresponds to the range of cycle counts typically observed when a battery cell exhibits significant expansion.
[0033] Furthermore, to improve the accuracy of the fitting formula, the data fitting method is to take multiple cells from the same batch and cycle them for the same number of times, measure the amount of residual electrolyte in each layer of the positive electrode of each cell, and take the average value of the data from multiple cells for data fitting.
[0034] This invention provides a method for manufacturing a battery cell, wherein the battery cell is a laminated or wound battery cell, comprising: A positive electrode is provided, wherein one side of the positive electrode is provided with uniformly distributed grooves, and the other side has protrusions corresponding to the grooves; The positive electrode is assembled into a battery cell. Along the direction from the center outward, the depth of the grooves in each layer of positive electrode gradually decreases. The bottom surface of each groove is arc-shaped with R = 1~3µm and the groove diameter is 2R. The number of grooves η on each square centimeter of positive electrode is 200~4000.
[0035] Optionally, the groove depth of each positive electrode layer is obtained in the following way: The relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer after cycling of a conventional battery cell was obtained by data fitting (1): E(i)=E mid +k*∣i i mid | 2 ; In the formula, E(i) is the amount of residual electrolyte in the i-th layer after cell cycling, E mid Let k be a constant, k be the electrolyte consumption attenuation coefficient, and i be the stratification number. mid = (n+1) / 2, where n is the total number of layers in the positive electrode; On the coordinate system, we obtain the curve symmetric to equation (1) about the y-axis, and equation (2): E( H i )=K m -E(i), E( H i) represents the amount of electrolyte stored in the i-th layer of positive electrode cell; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R))η (Equation 3 is the formula for calculation based on the shallowest groove depth being R, and other groove structures being a semi-circle + frustum structure). The positive electrode sheet of the pressure groove is assembled into a battery cell. The positive electrode sheet of the battery cell is multi-layered, and each layer has a pressure groove. The bottom of the pressure groove is an arc surface, and the groove depth is obtained according to formula (3). H i .
[0036] The preparation method provided by the present invention can produce battery cells with low expansion risk and long service life as provided in the embodiments of the present invention.
[0037] The following describes this case in detail with reference to several specific embodiments.
[0038] Example 1 This embodiment provides a stacked battery cell with a capacity of 30Ah. The positive electrode has a total of 23 layers, the negative electrode current collector is a 6μm copper foil, and the active layer composition is 94.7wt% artificial graphite, 2wt% acetylene black, 1.5wt% sodium carboxymethyl cellulose and 1.8wt% styrene-butadiene rubber. The positive electrode current collector is a 13μm aluminum foil, and the active layer composition is 96.3wt% lithium iron phosphate, 2.0wt% acetylene black and 1.7wt% polyvinylidene fluoride. The separator is a 16μm PP base film. The electrolyte formulation is: 13wt% LiPF6, 2wt% VC (ethylene carbonate), 1.5wt% DTD (ethylene sulfate), 3wt% FEC (fluoroethylene carbonate) and the balance solvent (EC (ethylene carbonate) + EMC (ethyl methyl carbonate) + DMC (dimethyl carbonate) in a mass ratio of 3:2:5). The positive electrode sheet of the battery cell has a total of 23 layers. Each positive electrode sheet has a groove with an arc-shaped bottom surface. The groove opening diameter is 2µm, and the groove density is 3 grooves / cm. 2 The quantity η is 700, and the center line connecting three adjacent pressing grooves forms an equilateral triangle. The pressing groove depth is determined as follows: Five conventional laminated cells (without pressure grooves compared to the laminated cells in this embodiment) were taken, and the total number of electrode layers n was 23. These cells were circulated for 1500 cycles. After the cycles, they were disassembled and the amount of residual electrolyte in each positive electrode layer was measured. The average value of the five cells was taken, and the relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer was fitted by formula (1): E(i) = 25 + 8.998 |i - 12| 2 , that is, E(i)=8.998i 2 215.95i + 1320.68, as Figure 5 As shown; On the coordinate system, we obtain the curve symmetric to equation (1) about the y-axis, and equation (2): E( Hi)=-8.998i 2 +215.95i +679.32; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R)) eta, R is taken as 1µm, eta is taken as 700.
[0039] Therefore, the groove depth of the positive electrode sheet, from one side to the other side, is respectively... Hi = 1.60, 1.87, 2.11, 2.33, 2.52, 2.69, 2.83, 2.95, 3.04, 3.10, 3.14, 3.15, 3.14, 3.10, 3.04, 2.95, 2.83, 2.69, 2.52, 2.33, 2.11, 1.87, 1.60, in µm.
[0040] Example 2 This embodiment provides a laminated battery cell with a capacity of 50Ah. The positive electrode has a total of 33 layers, and the negative electrode and electrolyte are the same as in Example 1. The separator is a 14μm PP base film. The positive electrode has 33 layers, and each positive electrode has a groove with an arc-shaped bottom surface. The groove opening diameter is 3µm, and the groove density is 2 grooves / cm². 2 The quantity η is 600, and the center line connecting three adjacent pressure grooves forms an equilateral triangle.
[0041] Five conventional laminated cells (without pressure grooves compared to the laminated cells in this embodiment) were taken, with a total of 33 electrode layers. These cells were cycled 800 times. After the cycle, they were disassembled, and the amount of residual electrolyte in each positive electrode layer was measured. The average value of the five cells was taken, and the relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer was fitted by the formula (1): E(i)=30+3.556|i-17| 2 That is, E(i) = 3.556i 2 120.91i+1079.68, as Figure 6 As shown; On the coordinate system, we obtain the curve symmetric to equation (1) about the y-axis, and equation (2): E( Hi)=-3.556i 2 +120.91i+542.32; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R)) eta, R is 1.5µm, eta is 600.
[0042] Therefore, the groove depth of the positive electrode sheet, from one side to the other side, is respectively... H i =1.60, 1.78, 1.96, 2.12, 2.26, 2.40, 2.52, 2.64, 2.74, 2.83, 2.90, 2.97, 3.02, 3.06, 3.09, 3.11, 3.12, 3.11, 3.09, 3.06, 3.02, 2.97, 2.90, 2.83, 2.74, 2.64, 2.52, 2.40, 2.26, 2.12, 1.96, 1.78, 1.60, in µm.
[0043] Example 3 The battery cell in this embodiment is basically the same as that in Embodiment 1, except that: the number of slots pressed on the positive electrode is 1000, the slot size is 2µm, the bottom of the slot is an arc surface, and the radius value corresponding to the arc surface is the same as that in Embodiment 1.
[0044] Example 4 The battery cell in this embodiment is basically the same as that in Embodiment 1, except that: the number of slots pressed on the positive electrode is 200, the slot size is 4µm, the bottom of the slot is an arc surface, and the radius value corresponding to the arc surface is the same as that in Embodiment 1.
[0045] Example 5 The cell in this embodiment is basically the same as that in Embodiment 1, except that the grooves on the positive electrode are arranged in a row and column pattern, with the two closest grooves in two adjacent rows in the same column. The row spacing a is 384µm and the column spacing b is 400µm.
[0046] Comparative Example 1 The conventional laminated cell in Example 1 is from the same batch as the conventional laminated cell in Example 1.
[0047] Comparative Example 2 The battery cell in this comparative example is basically the same as the battery cell in Example 1, except that the groove depth on each positive electrode is the same, and the groove depth is the same as the groove depth of the middle positive electrode.
[0048] Comparative Example 3 The battery cell in this comparative example is basically the same as the battery cell in Example 1, except that the groove depth on each positive electrode is the same, and the groove depth is the same as the groove depth of the outermost positive electrode.
[0049] Comparative Example 4 The conventional laminated cells in Example 2 are from the same batch as the conventional laminated cells in Example 2.
[0050] Comparative Example 5 like Figure 6 As shown, the battery cell in this comparative example is basically the same as the battery cell in Example 2, except that the groove depth on each positive electrode is the same, and the groove depth is the same as the groove depth of the middle positive electrode.
[0051] Comparative Example 6 The battery cell in this comparative example is basically the same as the battery cell in Example 2, except that the groove depth on each positive electrode is the same, and the groove depth is the same as the groove depth of the outermost positive electrode.
[0052] Experimental Example The electrochemical performance of the battery cells in each embodiment and comparative example was tested. The specific test methods are as follows: 1. At 25℃, let stand for 30 minutes; 2. At 25℃, the voltage drops from 0.5C to 3.65V, and the cutoff current is 0.05C. 3. At 25℃, let stand for 30 minutes; 4. 25℃, 0.5C DC to 2.5V; 5. At 25℃, let stand for 30 minutes; 6. Repeat the above steps 2-5 4000 times; observe the change in cell thickness before and after the cycle.
[0053] Record the test results in Table 1.
[0054] Table 1 Electrochemical performance of each example and comparative example
[0055] As can be seen from Table 1, the battery cells provided in the embodiments of the present invention show almost no expansion after 4000 cycles. The initial thickness and the thickness after cycling of Examples 1 and 2 are almost unchanged, while the thickness of Comparative Examples 1 and 4 is significantly larger after cycling. Examples 1 and 2 have a longer cycle life and better interface conditions compared to Comparative Examples 1 and 4. Comparing Comparative Examples 2 and 3 with Examples 1 and 1, although the expansion rates of Comparative Examples 2 and 3 after cycling were less than those of Comparative Example 1, they were significantly worse than those of Example 1. This indicates that when the groove depth of the positive electrode is distributed in a way that is deeper inside and shallower outside, the performance can be better improved. Comparing Comparative Examples 5 and 6 with Examples 2 and 4, although the expansion rates of Comparative Examples 5 and 6 after cycling were less than those of Comparative Example 4, they were significantly worse than those of Example 2. This further illustrates that when the groove depth of the positive electrode is distributed in a way that is deeper inside and shallower outside, the performance can be better improved. Comparing Example 5 with Example 1, the cycle performance of Example 5 is slightly worse. Compared with Example 1, Example 5 does not arrange the slot distribution according to the triangular stable structure, which shows that arranging the slot distribution according to the triangular stable structure can improve the cycle performance of the cell.
[0056] In summary, the battery cell provided in this embodiment of the invention has excellent electrochemical performance due to the special design of its positive electrode, and exhibits almost no expansion after 4000 cycles.
[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A battery cell, wherein the battery cell is a laminated or wound battery cell, characterized in that, The positive electrode sheet of the battery cell has uniformly distributed grooves on one side. The depth of the grooves in each layer of the positive electrode sheet gradually decreases from the center outwards. The bottom surface of each groove is arc-shaped with a radius of 1~3µm and the groove opening is circular with a diameter of 2R. The number of grooves η on each square centimeter of the positive electrode sheet is 200~4000.
2. The battery cell according to claim 1, characterized in that, On each positive electrode, the line connecting the centers of any three adjacent grooves forms an equilateral triangle.
3. The battery cell according to claim 1, characterized in that, The total number of positive electrode layers, n, is 10 to 40 layers.
4. The battery cell according to claim 1, characterized in that, The method for determining the groove depth of each positive electrode layer is as follows: The relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer after cycling of a conventional battery cell was obtained by data fitting (1): E(i)=E mid +k*∣i and mid ∣ 2 ; In the formula, E(i) is the amount of residual electrolyte in the i-th layer after cell cycling, in mg. mid Let k be a constant, k be the electrolyte consumption attenuation coefficient, and i be the stratification number. mid = (n+1) / 2, where n is the total number of layers in the positive electrode; On the coordinate system, we obtain the curve symmetric to equation (1) about the y-axis, and equation (2): E( H i )=K m -E(i), E( H i ) represents the amount of electrolyte stored in the i-th layer of positive electrode cell; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R))η; The positive electrode sheet of the pressure groove is assembled into a battery cell. The positive electrode sheet of the battery cell is multi-layered, and each layer has a pressure groove. The bottom of the pressure groove is an arc surface, and the groove depth is obtained according to formula (3). H i .
5. The battery cell according to claim 4, characterized in that, The number of cycles is x, where x ranges from 0 to 3000.
6. The battery cell according to claim 1, characterized in that, The data fitting method involves taking multiple cells from the same batch and cycling them the same number of times, measuring the amount of residual electrolyte in each layer of the positive electrode of each cell, and taking the average value of the data from multiple cells for data fitting.
7. A method for manufacturing a battery cell, wherein the battery cell is a laminated or wound battery cell, characterized in that, include: A positive electrode is provided, wherein one side of the positive electrode has uniformly distributed grooves; The positive electrode is assembled into a battery cell. Along the direction from the center outward, the depth of the grooves in each layer of positive electrode gradually decreases. The bottom surface of each groove is arc-shaped with R = 1~3µm and the groove diameter is 2R. The number of grooves η on each square centimeter of positive electrode is 200~4000.
8. The manufacturing method according to claim 7, characterized in that, The groove depth of each positive electrode layer is obtained as follows: The relationship between the i-th positive electrode layer and the amount of residual electrolyte in that layer after cycling of a conventional battery cell was obtained by data fitting (1): E(i)=E mid +k*∣i and mid ∣ 2 ; In the formula, E(i) is the amount of residual electrolyte in the i-th layer after cell cycling, in mg. mid Let k be a constant, k be the electrolyte consumption attenuation coefficient, and i be the stratification number. mid = (n+1) / 2, where n is the total number of layers in the positive electrode; On the coordinate system, we obtain the curve symmetric to equation (1) about the y-axis, and equation (2): E( H i )=K m -E(i), E( H i ) represents the amount of electrolyte stored in the i-th layer of positive electrode cell; The depth of the i-th layer of the pressure groove is obtained according to equation (3). H i Equation (3): E( H i ) = (2 / 3πR) 3 +πR 2 ( H i -R))η; The positive electrode sheet of the pressure groove is assembled into a battery cell. The positive electrode sheet of the battery cell is multi-layered, and each layer has a pressure groove. The bottom of the pressure groove is an arc surface, and the groove depth is obtained according to formula (3). H i .
9. The manufacturing method according to claim 7, characterized in that, The number of cycles is x, where x ranges from 0 to 3000.
10. The manufacturing method according to claim 7, characterized in that, On each positive electrode, the line connecting the centers of any three adjacent grooves forms an equilateral triangle; Optionally, the total number of positive electrode layers n is 10 to 40 layers.