Battery cell, lithium ion battery and electric equipment

Abstract

The invention discloses a battery cell, a lithium ion battery and electric equipment, the battery cell comprises a first pole piece, a second pole piece and a diaphragm which are laminated and wound, the first pole piece forms a first bending part in each winding circle, and the second pole piece forms a second bending part corresponding to the first bending part in each winding circle; the first pole piece comprises a first current collector and a first active substance layer arranged on the first current collector, and the compaction density of the first active substance layer located at the first bending part is gradually reduced from the inner ring to the outer ring; the second pole piece comprises a second current collector and a second active substance layer arranged on the second current collector; and the compaction density of the second active substance layer positioned on the second bending part is gradually increased from the inner ring to the outer ring. By optimizing the compaction density distribution of the active material layer, lithium precipitation can be reduced, expansion and breakage of the pole piece can be inhibited, and the electrolyte infiltration effect can be improved, so that the safety, the cycle performance and the energy conversion efficiency of the battery cell are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a battery cell, a lithium ion battery and electrical equipment. Background Art

[0002] Lithium batteries refer to lithium-ion batteries that contain lithium (including metallic lithium, lithium alloys, lithium ions, and lithium polymers) in their electrochemical systems. In recent years, lithium batteries have been widely used in digital products, electric vehicles, energy storage systems, and other fields due to their many advantages such as long cycle life, good safety performance, and rapid charging and discharging.

[0003] Currently, in the lithium-ion battery industry, anode sheets, cathode sheets, and separators are typically wound together to form a wound battery cell. In practical applications of lithium-ion batteries, the corners of the cell become a critical area affecting battery performance and safety due to structural characteristics and uneven current distribution.

[0004] In the prior art, lithium deposition often occurs in the corner areas of the electrode during the cycling process of battery cells. Lithium deposition can cause battery capacity decay, increase internal resistance, and in severe cases even cause a short circuit in the battery, affecting the safety and service life of the battery. At the same time, the electrode of the battery cell will expand after long-term cycling. When the degree of expansion is too large, the electrode is prone to breakage, which in turn causes a short circuit problem, greatly limiting the cycling performance and reliability of the battery cell. In addition, the electrolyte infiltration effect in the corner area of ​​the electrode is poor, and the electrode cannot be fully infiltrated, so that the active material in this area cannot effectively participate in the electrochemical reaction, reducing the overall energy conversion efficiency and long-cycle performance of the battery cell. Summary of the Invention

[0005] The main purpose of the present invention is to propose a battery cell, a lithium-ion battery and an electrical device, aiming to solve the technical problems in the prior art such as lithium deposition at the corners of the battery cell pole pieces leading to performance degradation and short circuit, pole piece expansion and breakage, and insufficient electrolyte infiltration resulting in limited reaction of active substances, thereby reducing the energy conversion and cycle performance of the battery cell.

[0006] To achieve the above objectives, the present invention provides a battery cell comprising a first pole piece, a second pole piece, and a separator disposed between the first pole piece and the second pole piece, wherein the first pole piece and the second pole piece have opposite polarities, the first pole piece, the second pole piece, and the separator are stacked and wound, the first pole piece forming a first bend in each winding turn, and the second pole piece forming a second bend corresponding to the first bend in each winding turn;

[0007] Among them, the first pole piece includes a first current collector and a first active material layer arranged on the first current collector, and the compaction density of the first active material layer located at the first curved portion gradually decreases from the inner circle to the outer circle; the second pole piece includes a second current collector and a second active material layer arranged on the second current collector, and the compaction density of the second active material layer located at the second curved portion gradually increases from the inner circle to the outer circle.

[0008] In some embodiments, the compaction density of the first active material layer of the first curved portion changes in a gradient manner from the inner circle to the outer circle.

[0009] In some embodiments, the compaction density of the second active material layer of the second curved portion changes in a gradient manner from the inner circle to the outer circle.

[0010] In some embodiments, in each winding of the first pole piece, the absolute value of the difference in compaction density between the first curved portions of any two adjacent windings is greater than 0.01 g / cm 3 And less than 0.25g / cm 3 .

[0011] In some embodiments, in each winding of the second pole piece, the absolute value of the difference in compaction density between the second curved portions of any two adjacent windings is greater than 0.01 g / cm 3 And less than 0.1g / cm 3 .

[0012] In some embodiments, the total number of windings of the first pole piece is N, where N is an integer greater than 1, and the length L of the first bent portion of the nth winding is n Satisfies the relationship:

[0013] L n =π×(D1+(N-1)×△T1) / 2;

[0014] Among them, D1=8d1+d2 / 2+d3 / 2, △T1=2d1+d2+d3, d1 is the thickness of the diaphragm located in the nth circle; d2 is the thickness of the second pole piece located in the nth circle; d3 is the thickness of the first pole piece located in the nth circle.

[0015] In some embodiments, the total number of windings of the second pole piece is M, where M is an integer greater than 1, and the length L of the second bent portion of the mth winding is m Satisfies the relationship:

[0016] L m =π×(D2+(M-1)×△T2) / 2;

[0017] Wherein, D2=6d1+d2 / 2; ΔT2=2d1+d2+d3, d1 is the thickness of the diaphragm located in the mth circle; d2 is the thickness of the second pole piece located in the mth circle; d3 is the thickness of the first pole piece located in the mth circle.

[0018] In some embodiments, the first pole piece is a cathode piece, and the second pole piece is an anode piece.

[0019] The present invention also provides a lithium ion battery, comprising a shell and a battery core, wherein the battery core is arranged in the shell.

[0020] The present invention also provides an electrical device comprising a lithium-ion battery.

[0021] The battery cell provided by the present application is composed of a first electrode sheet, a second electrode sheet, and a diaphragm stacked and wound with opposite polarities. The first and second electrode sheets form corresponding curved portions in each winding turn, wherein the compaction density of the first active material layer of the curved portion of the first electrode sheet decreases from the inner circle to the outer circle, and the compaction density of the second active material layer of the curved portion of the second electrode sheet increases from the inner circle to the outer circle. By optimizing the compaction density distribution of the active material layers of the curved portions of the first and second electrode sheets, the present application can improve the distribution and migration of lithium ions in the corner areas of the electrode sheets, reduce the accumulation of lithium ions in local areas, thereby effectively suppressing the occurrence of lithium precipitation, and improving the safety and service life of the battery. Moreover, the reasonable compaction density distribution provides adaptability to the volume change of the electrode sheets during the cycle, reduces the stress inside the electrode sheets, and helps to suppress the expansion of the electrode sheets. At the same time, it reduces the risk of electrode sheet breakage caused by expansion, and improves the cycle performance and reliability of the battery cell. The larger compaction density of the inner circle of the first electrode sheet and the larger compaction density of the outer circle of the second electrode sheet make the structure of the curved portion of the electrode sheet more reasonable, which is conducive to the penetration and infiltration of the electrolyte. The electrolyte can better contact the active material, allowing the active material to more fully participate in the electrochemical reaction, thereby improving the overall energy conversion efficiency and long cycle performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic cross-sectional view of a battery cell according to an embodiment of the present invention.

[0023] Description of Figure Numbers:

[0024] Label name Label name 100 battery cells 10 First pole piece 20 Second pole piece 30 diaphragm 11 First bend 21 Second bend

[0025] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0026] The following will be combined with the accompanying drawings to clearly and completely describe the solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0028] It should also be noted that when an element is referred to as being "fixed on" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element.

[0029] In addition, the descriptions of "first", "second", etc. in the present invention are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0030] Please refer to Figure 1 The present application provides a battery cell 100, comprising a first electrode sheet 10, a second electrode sheet 20, and a separator 30 disposed between the first electrode sheet 10 and the second electrode sheet 20. The first electrode sheet 10 and the second electrode sheet 20 have opposite polarities, wherein the first electrode sheet 10 can serve as a cathode sheet and the second electrode sheet 20 can serve as an anode sheet. The first electrode sheet 10, the second electrode sheet 20, and the separator 30 are stacked and wound. A first bend 11 is formed in each winding of the first electrode sheet 10, and a second bend 21 corresponding to the first bend 11 is formed in each winding of the second electrode sheet 20.

[0031] Among them, the first pole piece 10 includes a first current collector and a first active material layer provided on the first current collector, and the compaction density of the first active material layer located at the first curved portion 11 gradually decreases from the inner circle to the outer circle; the second pole piece 20 includes a second current collector and a second active material layer provided on the second current collector, and the compaction density of the second active material layer located at the second curved portion 21 gradually increases from the inner circle to the outer circle.

[0032] In this embodiment, the polarities of the first electrode piece 10 and the second electrode piece 20 are opposite, and the first electrode piece 10 may be a cathode piece and the second electrode piece 20 may be an anode piece.

[0033] The first electrode 10 consists of a first current collector and a first active material layer. The first current collector acts as a carrier for electron transport, conducting electrons generated by the electrochemical reaction or providing electrons for the reaction. The first active material layer is the core area for lithium ion storage and reaction. During charging, lithium ions are embedded in it from the second electrode 20; during discharge, lithium ions are released from here, achieving the conversion of electrical energy into chemical energy. The unique compaction density distribution of the curved portion of the first electrode 10 further optimizes its performance in corner areas.

[0034] The second pole piece 20 comprises a second current collector and a second active material layer. The second current collector conducts current. The second active material layer collaborates with the first active material layer to facilitate lithium ion insertion and extraction. The unique compaction density design of the curved portion of the second pole piece 20 enhances electrolyte wetting and ensures sufficient electrochemical reaction.

[0035] During the charge and discharge process of the battery cell 100, lithium ions undergo dynamic migration between the first electrode 10 and the second electrode 20. The higher compaction density of the first curved portion 11 within the inner ring of the first electrode 10 physically hinders the release of lithium ions, effectively reducing the rate of lithium ion release and making the lithium ion concentration gradient in the corner area more uniform, thus avoiding lithium precipitation caused by excessive local lithium ion concentration. At the same time, the higher compaction density within the inner ring of the first electrode 10 reserves space for the expansion of the second electrode 20 during the cycle, alleviating the accumulation of stress within the electrode and avoiding the risk of electrode breakage and short circuits caused by excessive expansion.

[0036] The second bend 21 of the second pole piece 20 adopts a design in which the compaction density gradually increases from the inside to the outside, which complements the design in which the compaction density of the first bend 11 of the first pole piece 10 gradually decreases from the inside to the outside. Under this design, the compaction density of the second bend 21 corresponding to the first bend 11 is relatively small, making the structure of this area looser. The loose structure significantly improves the electrolyte infiltration rate and provides more penetration channels for the electrolyte, so that the corner area of ​​the battery cell 100 can accommodate more electrolyte. Adequate electrolyte ensures full contact between the active material and the electrolyte, promotes the efficient conduct of the electrochemical reaction, and ultimately significantly improves the long cycle performance of the battery cell 100.

[0037] This application can improve the distribution and migration of lithium ions in the corner area of ​​the pole pieces by optimizing the compaction density distribution of the active material layer in the curved part of the first pole piece 10 and the second pole piece 20, reduce the accumulation of lithium ions in local areas, thereby effectively suppressing the occurrence of lithium plating and improving the safety and service life of the battery. Moreover, a reasonable compaction density distribution provides adaptability to the volume change of the pole piece during the cycle, reduces the stress inside the pole piece, and helps to suppress the expansion of the pole piece. At the same time, it reduces the risk of pole piece breakage due to expansion, and improves the cycle performance and reliability of the battery cell 100. The smaller compaction density of the inner circle of the first pole piece 10 and the larger compaction density of the outer circle of the second pole piece 20 make the structure of the curved part of the pole piece more reasonable, which is conducive to the penetration and infiltration of the electrolyte. The electrolyte can better contact the active material, allowing the active material to more fully participate in the electrochemical reaction, thereby improving the overall energy conversion efficiency and long cycle performance of the battery cell 100.

[0038] In some embodiments, the compaction density of the first active material layer of the first curved portion 11 changes in a gradient manner from the inner circle to the outer circle.

[0039] During the charge and discharge process, the migration rate and insertion / extraction behavior of lithium ions in the active material layer will change due to differences in compaction density. The compaction density of the first active material layer in the first curved portion 11 of this embodiment changes in a gradient from the inner circle to the outer circle. The higher compaction density in the inner circle allows the active material particles to be tightly packed, making the ion diffusion path tortuous and narrow. This effectively slows the rate of lithium ion extraction and prevents lithium ion accumulation and deposition in the inner circle due to overly rapid reactions. The lower compaction density in the outer circle creates a relatively loose structure, providing a smoother diffusion path for lithium ions, accelerating ion migration, and ensuring that the active materials in the outer circle can quickly respond to charge and discharge demands, achieving efficient electrochemical reactions.

[0040] In this embodiment, the compaction density of the first active material layer in the first curved portion 11 changes in a gradient from the inner circle to the outer circle. This creates a dynamic equilibrium mechanism, ensuring a consistent electrochemical reaction rate across the entire first curved portion 11, preventing localized overheating or uneven reactions, thereby improving the overall performance of the battery cell 100. Furthermore, this gradient in compaction density accommodates volume changes in the active material during charge and discharge. The high density in the inner circle limits excessive expansion, while the low density in the outer circle allows for deformation, reducing internal stress in the electrode and maintaining a stable electrode structure.

[0041] In some embodiments, the compaction density of the second active material layer of the second curved portion 21 changes in a gradient manner from the inner circle to the outer circle.

[0042] During the charging process of the battery cell 100, lithium ions are released from the first electrode sheet 10 and embedded in the second electrode sheet 20. In this embodiment, the compaction density of the second active material layer in the second curved portion 21 gradually increases from the inner circle to the outer circle in a gradient manner. The lower compaction density in the inner circle makes the second active material layer structure relatively loose, allowing lithium ions to embed quickly and smoothly, reducing the resistance to lithium ion embedding and ensuring high efficiency in the initial charging. As lithium ions continue to embed and extend toward the outer circle, the gradually increasing compaction density forms a mechanism to regulate the lithium ion embedding speed, avoiding localized excessive concentration in the outer circle due to excessively rapid lithium ion embedding. This prevents problems such as active material lattice distortion and structural collapse, thereby ensuring the stability of the electrode structure.

[0043] During discharge, the outer ring's higher compaction density tightly arranges the active materials, constraining the release of lithium ions and preventing rapid, large-scale release of lithium ions that could cause excessive local current flow, ensuring a smooth discharge process. The inner ring's lower compaction density, on the other hand, rapidly releases lithium ions, collaborating with the outer ring to achieve balanced lithium ion release across the entire curved region. Furthermore, the gradient of compaction density better accommodates the volume changes of the second electrode sheet 20 during the charge and discharge cycles. The inner ring's loose structure buffers expansion stress, while the outer ring's high-density structure limits excessive expansion, reducing stress concentration within the electrode sheet, maintaining its structural integrity, and ensuring the long-term, stable operation of the battery cell 100.

[0044] In some embodiments, in each winding of the first electrode 10, the absolute value of the difference in compaction density between the first curved portions 11 of any two adjacent windings is greater than 0.01 g / cm 3 And less than 0.25g / cm 3 .

[0045] Among them, a moderate difference in compaction density can optimize the diffusion and migration process of lithium ions between different layers in the first bend 11. If the difference is too small (less than 0.01g / cm3), the compaction density of each layer is almost the same, making it difficult to form an effective concentration gradient and diffusion driving force, and unable to fully improve the problem of uneven current distribution in the corner area, resulting in the accumulation of lithium ions in local areas and easily triggering lithium precipitation. If the difference is too large (greater than 0.25g / cm3), the physical structure and electrochemical performance between adjacent layers will differ too much, causing a sudden change in the migration resistance of lithium ions at the transition point of the layers, which not only increases the polarization degree of the electrochemical reaction, but also may cause stress concentration and accelerate damage to the electrode structure.

[0046] Within the difference range of 0.01-0.25g / cm3, adjacent first curved portions 11 form a continuous and moderate compaction density gradient. The higher compaction density of the inner ring slows down the release of lithium ions, while the lower compaction density of the outer ring accelerates the release of lithium ions. The reasonable difference between the two ensures that lithium ions can smoothly transition between the ring layers, achieving a dynamic balance of electrochemical reaction rates. From a structural mechanics perspective, this difference range avoids excessive internal stress in the electrode due to sudden changes in compaction density. This allows the various ring layers to synergistically adapt to volume changes during the charge and discharge cycle, reducing the risk of fracture and deformation of the electrode and maintaining the stability of the electrode structure.

[0047] This embodiment optimizes the distribution and migration of lithium ions in the first bend 11 by precisely controlling the compaction density difference, effectively avoiding the lithium plating phenomenon caused by excessive local current density and imbalance of lithium ion concentration. Reducing lithium plating can not only reduce the risk of increased internal resistance and capacity decay of the battery, but also prevent lithium dendrites from piercing the diaphragm 30 and causing short circuits, significantly improving the safety and reliability of the battery cell 100. Moreover, a reasonable range of compaction density difference ensures that the stress distribution of each layer of the electrode is uniform during the cycle, so that stress concentration will not occur between adjacent first bends 11 due to excessive differences in compaction density, thereby effectively suppressing problems such as electrode expansion and breakage, extending the service life of the electrode, and ensuring that the battery cell 100 maintains stable performance during long-term use.

[0048] In some embodiments, in each winding of the second pole piece 20, the absolute value of the difference in compaction density between the second curved portions 21 of any two adjacent windings is greater than 0.01 g / cm 3 And less than 0.1g / cm 3 .

[0049] Among them, in 0.01-0.1g / cm 3Within the difference range, adjacent second bends 21 form a moderate compaction density gradient. The lower compaction density of the inner circle is conducive to the rapid insertion of lithium ions, while the higher compaction density of the outer circle plays a buffering role in the subsequent insertion process, ensuring that the lithium ion insertion process in the entire second bend 21 area is uniform and controllable, maintaining the stability of the active material structure. If the difference is less than 0.01g / cm 3 The compaction density of adjacent second curved portions 21 is too close to form an effective concentration gradient, resulting in similar lithium ion embedding speeds between the layers. During the charging process, it is easy to cause excessive lithium ion embedding in local areas, causing active material lattice distortion, phase change stress accumulation, and reduced material stability. The difference is greater than 0.1g / cm 3 When the compaction density difference between adjacent layers is too large, the lithium ion embedding resistance at the transition point of the layers will suddenly change, causing the embedding process to be disordered, increasing the polarization phenomenon and aggravating the material attenuation.

[0050] In this embodiment, the absolute value of the difference in compaction density between any two adjacent circles of the second curved portion 21 is greater than 0.01 g / cm 3 And less than 0.1g / cm 3 This difference effectively coordinates the volume changes of the electrode during cycling. The second electrode 20 expands and contracts during charge and discharge. A suitable compaction density difference ensures uniform stress distribution across the layers, preventing deformation and cracking of the electrode due to stress concentration and ensuring the integrity of the electrode structure. Furthermore, in actual production, this range meets process precision requirements while achieving stable performance improvements, balancing production feasibility with the performance optimization needs of the battery cell 100.

[0051] In some embodiments, the total number of windings of the first pole piece 10 is N, where N is an integer greater than 1, and the length L of the first bent portion 11 of the nth winding is n Satisfies the relationship:

[0052] L n =π×(D1+(N-1)×△T1) / 2;

[0053] Among them, D1=8d1+d2 / 2+d3 / 2, △T1=2d1+d2+d3, d1 is the thickness of the diaphragm 30 located in the nth circle; d2 is the thickness of the second pole piece 20 located in the nth circle; d3 is the thickness of the first pole piece 10 located in the nth circle.

[0054] During the winding process of the battery cell 100, the diaphragm 30, the first pole piece 10 and the second pole piece 20 are stacked layer by layer. With each additional turn, the winding diameter increases accordingly. The first curved portion 11 is a semicircular arc structure, and its length is directly related to the winding diameter.

[0055] In the formula, D1=8d1+d2 / 2+d3 / 2 represents the initial diameter parameter of the winding structure. 8d1 reflects the multi-layer wrapping characteristics of the diaphragm 30 in the winding structure. The diaphragm 30 needs to completely wrap the pole piece, and its thickness contributes more to the initial diameter; d2 / 2 and d3 / 2 are half of the thickness of the second pole piece 20 and the first pole piece 10 respectively, because the pole piece is in the middle of the winding layer, and its thickness affects the diameter as a single-sided thickness. △T1=2d1+d2+d3 represents the increase in diameter for each additional turn of winding. 2d1 reflects the increase in thickness of the diaphragm 30 on both the inner and outer sides when a new turn is added; d2 and d3 are the thickness contributions of the second pole piece 20 and the first pole piece 10 for each additional turn. Add D1 to (N-1)×△T1 to get the diameter of the nth winding, multiply it by π to calculate the circumference under this diameter, and then divide it by 2 (because the first curved portion 11 is a semicircular arc) to get the length L of the first curved portion 11 of the nth winding. n This formula accurately quantifies the relationship between the thickness of each material in the winding structure of the battery cell 100 and the length of the first bend 11, providing an accurate calculation basis for the pole piece design and winding process.

[0056] In this embodiment, through this relationship, those skilled in the art can accurately calculate the length of the first bend 11 under different numbers of winding turns according to the design requirements of the battery cell 100, and then reasonably plan the sizes of the first pole piece 10, the second pole piece 20 and the diaphragm 30. Ensure that after the battery cell 100 is wound and formed, the various components are closely matched, the internal space layout is optimized, and the energy density and structural stability of the battery cell 100 are improved. In actual production, this formula provides a clear standard for setting the winding process parameters. Those skilled in the art can calculate the corresponding length of the first bend 11 through the formula based on the designed number of winding turns, and adjust the tension, speed and other parameters of the winding equipment to keep the winding size of each battery cell 100 consistent, effectively reduce the defective rate caused by dimensional deviation, and improve production efficiency and product quality.

[0057] In some embodiments, the total number of windings of the second pole piece 20 is M, where M is an integer greater than 1, and the length L of the second bent portion 21 of the mth winding is m Satisfies the relationship:

[0058] L m =π×(D2+(M-1)×△T2) / 2;

[0059] Wherein, D2=6d1+d2 / 2; ΔT2=2d1+d2+d3, d1 is the thickness of the diaphragm 30 located in the mth circle; d2 is the thickness of the second pole piece 20 located in the mth circle; d3 is the thickness of the first pole piece 10 located in the mth circle.

[0060] During the winding process of the battery cell 100, the diaphragm 30, the first pole piece 10 and the second pole piece 20 are stacked layer by layer. With each additional turn, the winding diameter increases accordingly. The second curved portion 21 is a semicircular arc structure, and its length is directly related to the winding diameter.

[0061] Among them, D2=6d1+d2 / 2 in the formula represents the initial diameter parameter of the winding structure. Among them, 6d1 reflects the multi-layer wrapping characteristics of the diaphragm 30 in the winding structure of the second pole piece 20. The diaphragm 30 needs to wrap the second pole piece 20, and its thickness contributes more to the initial diameter; d2 / 2 is half of the thickness of the second pole piece 20 because the second pole piece 20 is in the middle of the winding layer, and its thickness affects the diameter as a single-sided thickness. △T2=2d1+d2+d3 represents the increase in diameter for each additional turn of winding. 2d1 reflects the increased thickness of the diaphragm 30 on the inner and outer sides when a new turn is added; d2 and d3 are the thickness contributions of the second pole piece 20 and the first pole piece 10 for each additional turn, respectively. Add D2 to (M-1)×△T2) to obtain the diameter of the mth turn of winding, multiply by π to calculate the circumference under this diameter, and then divide by 2 (because the second bend 21 is a semicircular arc), so as to obtain the length L of the second bend 21 of the mth turn. m This formula accurately quantifies the relationship between the thickness of each material in the winding structure of the battery cell 100 and the length of the second bend 21, providing an accurate calculation basis for the pole piece design and winding process.

[0062] In this embodiment, through this relationship, those skilled in the art can accurately calculate the length of the second bend 21 under different numbers of winding turns according to the design requirements of the battery cell 100, and then reasonably plan the sizes of the second pole piece 20, the first pole piece 10 and the diaphragm 30. Ensure that after the battery cell 100 is wound and formed, the various components are closely matched, the internal space layout is optimized, and the energy density and structural stability of the battery cell 100 are improved. In actual production, this formula provides a clear standard for setting the winding process parameters. Those skilled in the art can calculate the corresponding length of the second bend 21 through the formula based on the designed number of winding turns, and adjust the tension, speed and other parameters of the winding equipment to keep the winding size of each battery cell 100 consistent, effectively reduce the defective rate caused by dimensional deviation, and improve production efficiency and product quality.

[0063] The present invention will be further described below with reference to specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0064] Example 1:

[0065] (1) Preparation of the first pole piece 10

[0066] The active material LiCoO2, the conductive agent superconducting carbon (Super P), the conductive agent carbon nanotubes, and the binder polyvinylidene fluoride (PVDF) are fully dispersed in N-methylpyrrolidone solvent at a mass ratio of 97.6:0.6:0.5:1.3, coated on the aluminum foil current collector, and then cold-pressed by a relief roller to obtain the first pole piece 10 with a compaction density gradient distribution of the first curved portion 11. The compaction density gradient of the first curved portion 11 is set to: P n+1 -P n =0.05g / cm 3 Where n is the number of windings of the first pole piece 10, the n+1 first bend 11 is farther away from the inner circle than the nth first bend 11, and the compaction density of the n+1 first bend 11 is P n+1 , the compaction density at the nth first bend 11 is P n , and satisfies P n+1 <P n .

[0067] (2) Preparation of the second pole piece 20

[0068] The silicon-carbon material, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are mixed thoroughly in a deionized water solvent at a mass ratio of 97.8:0.6:0.6:1, and then coated on a Cu foil. After drying and gravure rolling, the second electrode 20 with a compaction density gradient distribution of the second curved portion 21 is obtained. The compaction density gradient of the second curved portion 21 is set to: P m -P m+1 =0.02g / cm 3 Where m is the number of windings of the second pole piece 20, the m+1 second bend 21 is farther away from the inner circle than the m-th second bend 21, and the compaction density at the m+1 second bend 21 is P m+1 The compaction density of the mth second bend 21 is P m , and satisfies P m+1 >P m .

[0069] (3) Preparation of isolation membrane

[0070] The surface of the PE film is coated with ceramic as the separator 30 .

[0071] (4) Preparation of electrolyte

[0072] Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4, and then the fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0073] (5) Preparation of lithium-ion batteries

[0074] The first pole piece 10, the isolation film, and the second pole piece 20 are used to make a bare cell 100, which is then packaged and injected with electrolyte to make a finished lithium-ion battery.

[0075] Example 2:

[0076] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.01g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.02g / cm 3 , and the rest remain the same.

[0077] Example 3:

[0078] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.01g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.01g / cm 3 , and the rest remain the same.

[0079] Example 4:

[0080] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.25g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.02g / cm 3 , and the rest remain the same.

[0081] Example 5:

[0082] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.05g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m=0.1g / cm 3 , and the rest remain the same.

[0083] Example 6:

[0084] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.005g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.01g / cm 3 , and the rest remain the same.

[0085] Example 7:

[0086] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.03g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.01g / cm 3 , and the rest remain the same.

[0087] Example 8:

[0088] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.05g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.005g / cm 3 , and the rest remain the same.

[0089] Example 9:

[0090] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.05g / cm 3 , the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.15g / cm 3 , and the rest remain the same.

[0091] Comparative Example 1:

[0092] Different from the embodiment 1, the first pole piece 10 is not provided with a compaction density gradient, and the compaction density of the first bent portion 11 of the first pole piece 10 is 4.38 g / cm 3 The second pole piece 20 does not have a compaction density gradient, and the compaction density of the second curved portion 21 of the second pole piece 20 is 1.6 g / cm 3 , and the rest remain the same.

[0093] Comparative Example 2:

[0094] Different from the embodiment 1, the compaction density gradient of the first bent portion 11 of the first pole piece 10 is set to: P n -P n+1 =0.05g / cm 3 The second pole piece 20 does not have a compaction density gradient, and the compaction density of the second curved portion 21 of the second pole piece 20 is 1.6 g / cm 3 , and the rest remain the same.

[0095] Comparative Example 3:

[0096] Different from the embodiment 1, the compaction density gradient of the second curved portion 21 of the second pole piece 20 is set to: P m+1 -P m =0.02g / cm 3 The first pole piece 10 does not have a compaction density gradient, and the compaction density of the first curved portion 11 of the first pole piece 10 is 4.38 g / cm 3 , and the rest remain the same.

[0097] The design parameters of the specific embodiment are as follows Table 1:

[0098]

[0099]

[0100] Table 1

[0101] The lithium-ion batteries of all the above embodiments and comparative examples were subjected to performance tests, including energy density, cycle retention rate, cycle expansion rate, cycle expansion rate, liquid retention capacity, and electrode integrity, and the test results shown in Table 2 below were obtained.

[0102]

[0103] Table 2

[0104] Among them, the energy density of lithium-ion battery = fractional discharge capacity / (width of battery cell 100 * thickness of battery cell 100 * length of battery cell 100), unit Wh / L; cycle retention rate is the percentage of the remaining capacity of battery cell 100 after charging to 4.15V at 4C step, charging to 4.25V at 3.0C, charging to 4.35V at 1.5C, charging to 4.53V at 1.0C, and cycling 500 times; cycle expansion rate is the percentage of the difference between the thickness of battery cell 100 and the initial half-charge thickness after charging to 4.15V at 4C step, charging to 4.25V at 3.0C, charging to 4.35V at 1.5C, charging to 4.53V at 1.0C, and cycling 500 times. The percentage of the initial half-electric thickness; the lithium deposition interface is obtained by disassembling the battery cell 100 in a fully charged state after 500 cycles. No lithium deposition at the corner means that the corner is smooth and clean, and the interface is golden or yellow; slight lithium deposition at the corner means that lithium deposition occurs at the corner, and the color of the deposited lithium is gray or gray-black, and appears in dots or sporadically; moderate lithium deposition at the corner means that lithium deposition occurs at the corner, and the color of the deposited lithium is gray or silver, and appears in spots; severe lithium deposition at the corner means that the color of the deposited lithium is silver-white, strip-shaped and continuous, indicating that the amount of lithium deposition is large and the deposited lithium is relatively dense; the liquid retention amount is obtained by the difference between the weight of the battery cell 100 after packaging and the weight of the battery cell 100 before liquid injection, and the unit is g; the integrity of the electrode is obtained by observing the degree of damage and cracking of the electrode after disassembly.

[0105] It can be seen from Examples 1, 5 and Comparative Example 1 in the table that when the compaction density gradient of a single second electrode 20 increases too much, although the energy density increases, the liquid absorption capacity of the second electrode 20 becomes weaker, resulting in a decrease in liquid retention capacity, electrolyte bridge breakage phenomenon occurs in the later stage of the cycle, lithium precipitation at the corners is aggravated, and the large expansion causes aggravated damage to the electrode.

[0106] As shown in Examples 1 and 3 and Comparative Example 1 in the table, when the compaction density gradient of a single second pole piece 20 is increased too little, the energy density decreases, the liquid absorption capacity becomes stronger, and the liquid retention capacity increases. However, since the compaction density does not change much, it is equivalent to insufficient reserved corner space, resulting in slight lithium deposition in the late cycle and slight damage to the second pole piece 20. When not set, the energy density decreases, the liquid absorption capacity becomes stronger, and the liquid retention capacity increases. However, no compaction density gradient is set, which is equivalent to insufficient reserved corner space, slight lithium deposition occurs in the late cycle, severe expansion, and moderate damage to the pole piece.

[0107] It can be seen from Examples 1 and 2 and Comparative Examples 1 and 3 in the table that when the compaction density gradient of a single first electrode 10 is reduced too little, the energy density increases slightly, but the electrode's liquid absorption capacity becomes weaker, resulting in a decrease in liquid retention. In the later stage of the cycle, the electrolyte bridge breaks, lithium precipitation at the corners is aggravated, and the larger expansion causes increased damage to the electrode.

[0108] As shown in the table, Examples 1 and 4 and Comparative Examples 1 and 3 show that when the compaction density gradient of a single first electrode 10 is reduced too much, the energy density is greatly lost, the liquid absorption capacity is enhanced, and the liquid retention capacity is increased. When the first electrode 10 is not provided with a compaction density gradient, the energy density is improved, but the liquid absorption capacity is weakened, the liquid retention capacity is significantly reduced, the electrolyte bridge phenomenon occurs in the late cycle, lithium deposition at the corners is aggravated, expansion is severe, and the electrode is moderately damaged.

[0109] It can be seen from Examples 6 and 7 in the table that if the difference in compaction density between the first curved portions 11 of adjacent first pole pieces 10 is too small (less than 0.01 g / cm 3 ), the compaction density of each ring layer is almost the same, it is difficult to form an effective concentration gradient and diffusion driving force, and it is impossible to fully improve the problem of uneven current distribution in the corner area, resulting in the accumulation of lithium ions in the local area, which is easy to cause lithium precipitation; and the compaction density difference of the first curved portion 11 of the adjacent first pole piece 10 is too large (greater than 0.25g / cm 3 ), the physical structure and electrochemical performance between adjacent layers will be too different, causing a sudden change in the migration resistance of lithium ions at the transition point of the layers, which not only increases the polarization degree of the electrochemical reaction, but also may cause stress concentration and accelerate the damage of the electrode structure.

[0110] It can be seen from Examples 8 and 9 in the table that if the difference in the second curved portions 21 of adjacent second pole pieces 20 is less than 0.01 g / cm 3 The compaction density of adjacent second curved portions 21 is too close to form an effective concentration gradient, resulting in similar lithium ion embedding speeds between the layers. During the charging process, it is easy to cause excessive lithium ion embedding in local areas, causing active material lattice distortion, phase change stress accumulation, and reduced material stability. The difference in the second curved portions 21 of adjacent second pole pieces 20 is greater than 0.1g / cm 3 When the compaction density difference between adjacent layers is too large, the lithium ion embedding resistance at the transition point of the layers will suddenly change, causing the embedding process to be disordered, increasing the polarization phenomenon and aggravating the material attenuation.

[0111] To sum up, the first electrode piece 10 and the second electrode piece 20 are both provided with a compaction density gradient, which can significantly improve the liquid retention capacity of the battery cell 100, and can effectively improve the problem of lithium deposition in the corners during the cycle. This is mainly because after the first electrode piece 10 is provided with a compaction density gradient, the compaction density of the inner circle is large, which can effectively suppress the release rate of lithium ions and improve the problem of lithium deposition in the corners of the battery cell 100; at the same time, the corner area corresponding to the first electrode piece 10 and the second electrode piece 20 provides a cycle expansion space, which avoids the problem of broken pieces due to excessive expansion of the electrode piece in the later stage of the cycle. Therefore, the integrity of the electrode piece after disassembling the interface is also greatly improved.

[0112] The present application also provides a lithium-ion battery, comprising a housing and the battery cell 100 as described above, wherein the battery cell 100 is disposed within the housing. The lithium-ion battery may have all the technical features and corresponding beneficial effects of the battery cell 100 described above, which will not be described in detail here.

[0113] This application also provides an electrical device comprising the lithium-ion battery described above. Specifically, the electrical device may be a new energy vehicle, a power storage device, a computer, a mobile phone, or other electrical device. The electrical device may possess all the technical features and corresponding beneficial effects of the lithium-ion battery described above, and further description thereof is omitted here.

[0114] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not possible to enumerate all embodiments here. Any obvious variations or modifications arising from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A battery cell, characterized in that: The invention comprises a first pole piece, a second pole piece, and a diaphragm disposed between the first pole piece and the second pole piece, wherein the first pole piece and the second pole piece have opposite polarities, the first pole piece, the second pole piece, and the diaphragm are stacked and wound, the first pole piece forms a first bend in each winding turn, and the second pole piece forms a second bend corresponding to the first bend in each winding turn; Among them, the first pole piece includes a first current collector and a first active material layer arranged on the first current collector, and the compaction density of the first active material layer located at the first curved portion gradually decreases from the inner circle to the outer circle; the second pole piece includes a second current collector and a second active material layer arranged on the second current collector, and the compaction density of the second active material layer located at the second curved portion gradually increases from the inner circle to the outer circle.

2. The battery cell according to claim 1, characterized in that The compaction density of the first active material layer in the first curved portion changes in a gradient from the inner circle to the outer circle.

3. The battery cell according to claim 1, characterized in that The compaction density of the second active material layer in the second curved portion changes in a gradient from the inner circle to the outer circle.

4. The battery cell according to claim 1, characterized in that In each winding of the first pole piece, the absolute value of the difference in compaction density between the first curved portions of any two adjacent windings is greater than 0.01 g / cm 3 And less than 0.25g / cm 3 .

5. The battery cell according to claim 1, characterized in that In each winding of the second pole piece, the absolute value of the difference in compaction density between the second curved portions of any two adjacent windings is greater than 0.01 g / cm 3 And less than 0.1g / cm 3 .

6. The battery cell according to claim 1, characterized in that The total number of windings of the first pole piece is N, where N is an integer greater than 1, and the length L of the first bent portion of the nth winding is n Satisfies the relationship: IT n =π×(D1+(N-1)×△T1) / 2; Among them, D1=8d1+d2 / 2+d3 / 2, △T1=2d1+d2+d3, d1 is the thickness of the diaphragm located in the nth circle; d2 is the thickness of the second pole piece located in the nth circle; d3 is the thickness of the first pole piece located in the nth circle.

7. The battery cell according to claim 1, characterized in that The total number of windings of the second pole piece is M, where M is an integer greater than 1, and the length L of the second curved portion of the mth winding is m Satisfies the relationship: L m =π×(D2+(M-1)×△T2) / 2; Wherein, D2=6d1+d2 / 2; ΔT2=2d1+d2+d3, d1 is the thickness of the diaphragm located in the mth circle; d2 is the thickness of the second pole piece located in the mth circle; d3 is the thickness of the first pole piece located in the mth circle.

8. The battery cell according to any one of claims 1 to 7, characterized in that: The first pole piece is a cathode piece, and the second pole piece is an anode piece.

9. A lithium-ion battery, characterized in that: The invention comprises a housing and the battery core according to any one of claims 1 to 8, wherein the battery core is arranged in the housing.

10. An electrical device, characterized in that: Comprising the lithium-ion battery as claimed in claim 9.

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