Wound cells and electrochemical devices

Abstract

The present invention relates to the technical field of lithium-ion batteries, and discloses a wound cell and an electrochemical device. The wound cell comprises a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound in sequence, and the wound cell comprises a straight region and arc regions located at both ends of the straight region; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector; along the winding direction of the positive electrode sheet, the positive electrode sheet has a plurality of first regions and second regions connected in sequence, the first region is located in the straight region, and the second region is located in the arc region; the positive electrode sheet has a thickness T1 in the first region and a thickness T2 in the second region, 1.01≤T2 / T1≤1.3; the porosity of the positive electrode active layer in the first region is φ1, and the porosity of the positive electrode active layer in the second region is φ2, 1.5≤φ2 / φ1≤2. The wound cell can improve the problems of lithium precipitation and interface failure.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a wound battery cell and an electrochemical device. Background Art

[0002] Lithium-ion batteries are the most widely used batteries in portable electronics, electric vehicles, power tools and various power grid applications due to their high power and energy density, low cost and long life cycle. In order to meet the rapidly growing endurance requirements of the electronics and electric vehicle industries, researchers usually choose to add silicon negative electrodes with higher specific capacity and compress the electrode rolling thickness to the extreme in order to produce lithium-ion batteries with high volume energy density.

[0003] The silicon negative electrode material itself has a large volume expansion, especially at the arc part, the pole piece is constrained by the membrane shell space after expansion, and the pole piece at the arc part will be subject to greater stress. In addition, due to the large volume change during the lithium insertion and de-lithiation process of silicon materials, the pole piece has an expansion-contraction "breathing" effect, and is subject to greater stress after lithium insertion and expansion, which makes the bonding force between the negative electrode active material and the diaphragm greater. After de-lithiation and shrinkage, part of the negative electrode material will be bonded to the diaphragm, causing the active material and the current collector to debond, resulting in interface failure. The negative electrode material at the debonding position cannot receive positive electrode lithium ions, causing lithium ions to be embedded or precipitated at other locations on the current collector where they remain bonded, causing lithium precipitation and internal short circuits, which can cause safety problems in severe cases. Summary of the invention

[0004] In view of this, the present invention provides a wound battery cell and an electrochemical device to solve the problem of interface failure of debonding between active material and current collector and lithium deposition caused by stress concentration in the arc area.

[0005] In a first aspect, the present invention provides a wound battery cell, the wound battery cell comprising a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound in sequence; the wound battery cell comprises a straight area and arc areas at both ends of the straight area; the positive electrode sheet comprises a positive electrode collector and a positive electrode active layer arranged on the surface of the positive electrode collector, and along the winding direction of the positive electrode sheet, the positive electrode sheet comprises a plurality of first areas and second areas connected in sequence, the first area is located in the straight area, and the second area is located in the arc area; the positive electrode sheet has a thickness T1 in the first area and a thickness T2 in the second area, 1.01≤T2 / T1≤1.3; the porosity of the positive electrode active layer in the first area is The porosity of the positive electrode active layer in the second region is

[0006] In some optional embodiments, 20um≤T1≤150um, and / or, 20.2um≤T2≤195um; and / or, and / or,

[0007] In some optional embodiments, the compaction density of the positive electrode active layer in the first region is ρ1, and the compaction density of the positive electrode active layer in the second region is ρ2, 0.8≤ρ2 / ρ1≤0.99; and / or the surface density of the positive electrode active layer in the first region is ρ3, and the surface density of the positive electrode active layer in the second region is ρ4, 0.6≤ρ4 / ρ3≤0.99.

[0008] In some optional embodiments, 2g / cc≤ρ1≤5g / cc, and / or, 1.6g / cc≤ρ2≤4.95g / cc; and / or, 0.005g / cm 2 ≤ρ3≤0.1g / cm 2 , 0.003g / cm 2 ≤ρ4≤0.099g / cm 2 .

[0009] In some optional embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. Along the winding direction of the negative electrode sheet, the negative electrode sheet includes a plurality of third regions and fourth regions connected in sequence, the third region is located in the straight region, and the fourth region is located in the arc region; the negative electrode sheet has a thickness T3 in the third region and a thickness T4 in the fourth region, 1.01≤T4 / T3≤1.5; and / or the porosity of the negative electrode active layer in the third region is The porosity of the negative electrode active layer in the fourth region is

[0010] In some optional embodiments, 20um≤T3≤200um, and / or, 20.2um≤T4≤300um; and / or, and / or,

[0011] In some optional embodiments, the compaction density of the negative electrode active layer in the third region is ρ5, and the compaction density of the negative electrode active layer in the fourth region is ρ6, 0.8≤ρ6 / ρ5≤0.99; the surface density of the negative electrode active layer in the third region is ρ7, and the surface density of the negative electrode active layer in the fourth region is ρ8, 1≤ρ8 / ρ7≤1.3.

[0012] In some optional embodiments, 1g / cc≤ρ5≤2.5g / cc, and / or, 0.8g / cc≤ρ6≤2.475g / cc; and / or, 0.003g / cm 2 ≤ρ7≤0.07g / cm 2 , 0.003g / cm2 ≤ρ8≤0.091g / cm 2 .

[0013] In some optional embodiments, the positive electrode sheet has a first surface and a second surface arranged opposite to each other in the first direction, and the first surface or the second surface located in the second area is provided with a plurality of protrusions; and / or, the negative electrode sheet has a third surface and a fourth surface arranged opposite to each other in the first direction, and the third surface or the fourth surface located in the fourth area is provided with a plurality of protrusions.

[0014] In some optional embodiments, the height of the protrusion located in the second area is H1, 0.01≤H1 / T1≤0.2, 1um≤H1≤10um; and / or the height of the protrusion located in the fourth area is H2, 0.01≤H2 / T3≤0.2, 1um≤H2≤10um.

[0015] In some optional embodiments, the center distance between the projections of two adjacent protrusions located in the second area in the first direction is d1, 1≤d1 / T1≤50, 1mm≤d1≤10mm; and / or the center distance between the projections of two adjacent protrusions located in the fourth area in the first direction is d2, 1≤d2 / T3≤50, 1mm≤d2≤10mm.

[0016] In some optional embodiments, the protrusion has a first projection in the first direction, and the shape of the first projection is one of a circle, a regular polygon and an irregular polygon; the radius of the circumscribed circle of the first projection is r, 0.5mm≤r≤100mm.

[0017] In some optional embodiments, the material of the protrusions may be at least one of ceramics, fibers, alumina mixed with PMMA glue, alumina mixed with PVDF glue, or alumina mixed with SBR glue.

[0018] In some optional embodiments, the thickness of the wound battery cell in the arc region is R, and the thickness of the straight region is T. and 2mm≤R≤20mm.

[0019] In some optional embodiments, the negative electrode active layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage content of silicon in the negative electrode active layer is x. 1%≤x≤50%.

[0020] In a second aspect, the present invention further provides an electrochemical device, comprising the wound battery cell described in the first aspect and a shell, wherein the wound battery cell is accommodated in the shell.

[0021] The wound battery cell of the present invention satisfies 1.01≤T2 / T1≤1.3 by setting the thickness T2 of the second region of the positive electrode sheet and the thickness T1 of the first region, and the porosity of the second region The porosity of the first region satisfy The thickness and porosity of the arc area are made larger, thereby ensuring that the positive electrode active layer in the arc area has a larger compressible volume to absorb the expansion of the silicon volume of the negative electrode sheet during the lithium insertion and delithiation process; in addition, the expansion of the negative electrode sheet in the arc area will preferentially utilize the pores to avoid the debonding of the active material on the negative electrode sheet and the current collector due to the excessive expansion size of the negative electrode silicon material. The porosity of the arc area is larger and the ionic conductivity is larger, so the lithium precipitation problem in the arc area can also be alleviated. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is one of the structural schematic diagrams of a wound battery cell according to an embodiment of the present invention;

[0024] Figure 2 This is a second structural schematic diagram of a wound battery cell according to an embodiment of the present invention;

[0025] Figure 3 It is a schematic structural diagram of a positive electrode sheet of a wound battery cell according to an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of the structure of the negative electrode sheet of the wound battery cell according to an embodiment of the present invention

[0027] Figure 5 This is the third structural schematic diagram of the wound battery cell according to an embodiment of the present invention;

[0028] Figure 6 It is a schematic structural diagram of a base film and protrusions of a wound battery cell according to an embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 1. Wound battery cell; 11. Straight area; 12. Arc area;

[0031] 100, positive electrode sheet; 110, first region; 120, second region; 130, positive electrode current collector; 140, positive electrode active layer; 150, first surface; 160, second surface;

[0032] 300, negative electrode sheet; 310, third region; 320, fourth region; 330, negative electrode current collector; 340, negative electrode active layer; 350, third surface; 360, fourth surface;

[0033] 400, positive pole tab; 500, negative pole tab; 700, bulge. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 those skilled in the art without creative work are within the scope of protection of the present invention.

[0035] The inventor of the present invention has found that as the lithium battery cycle progresses, the positive and negative electrodes of the lithium-ion battery continue to expand. On the horizontal plane (unbent area) of the wound lithium battery (a battery including a wound battery cell), the expansion is not constrained and can expand freely. There is no stress accumulation between the positive and negative electrode sheets, and between the separator and the electrode sheets, or the stress accumulation is small and does not affect the cycle performance. However, at the arc (bent area) of the wound lithium battery, due to the constraint of the aluminum-plastic film and the characteristics of the battery cell itself at the arc, it cannot expand freely in the width direction of the battery cell, which ultimately causes stress accumulation at the arc. In addition, in order to meet the rapidly growing endurance requirements of the electronics and electric vehicle industries, researchers usually choose to add silicon negative electrodes with higher specific capacity. As the silicon content increases and the electrode volume continues to compress, the negative electrode sheet continues to expand during the battery cycle, and the arc area is more prone to stress concentration, resulting in severe compression of the volume of the arc area, making the bonding force between the negative electrode active material and the diaphragm greater. After de-lithiation and shrinkage, some of the negative electrode active materials will adhere to the diaphragm, causing the active material to debond from the current collector, and lithium ions will be embedded or precipitated in other places on the negative electrode sheet where they remain bonded, causing lithium precipitation and internal short circuits. In other words, conventional lithium batteries containing silicon negative electrodes will have obvious interface failure and lithium precipitation problems, which seriously affect the cycle life and safety of lithium-ion batteries.

[0036] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0037] like Figure 1-Figure 6As shown, according to an embodiment of the present invention, on the one hand, a wound battery cell 1 is provided, the wound battery cell 1 comprises a positive electrode sheet 100, a separator and a negative electrode sheet 300 which are stacked and wound, and the wound battery cell 1 comprises a straight region 11 and arc regions 12 located at both ends of the straight region 11. The positive electrode sheet 100 is connected to a positive electrode tab 400, and the negative electrode sheet 300 is connected to a negative electrode tab 500.

[0038] The positive electrode sheet 100 includes a positive electrode current collector 130 and a positive electrode active layer 140 disposed on the surface of the positive electrode current collector 130. Along the winding direction of the positive electrode sheet 100, the positive electrode sheet 100 includes a plurality of first regions 110 and second regions 120 connected in sequence. The first region 110 is located in the straight region 11, and the second region 120 is located in the arc region 12. The positive electrode sheet 100 has a thickness T1 in the first region 110 and a thickness T2 in the second region 120. The porosity of the positive electrode active layer 140 in the first region 110 is The porosity of the positive electrode active layer 140 in the second region 120 is

[0039] Where, 1.01≤T2 / T1≤1.3, and T2 / T1 can be 1.01, 1.1, 1.2 or 1.3. It can be 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0040] In the wound battery cell 1, a first region 110 and a second region 120 are arranged on the positive electrode sheet 100, and a smaller rolling pressure is applied to the second region during the rolling process, so that the positive electrode sheet has a larger compacted thickness in the second region, that is, the second region has more pores, and the positive electrode active layer 140 of the positive electrode sheet 100 can be compressed and deformed to absorb the expansion of the silicon volume of the negative electrode sheet 300 during the lithium removal and lithium insertion process, so that the positive electrode active layer 140 of the second region 120 can be guaranteed to have a larger compressible volume, and thus the arc region 1 2 reserves a larger expansion space for the negative electrode sheet 300, thereby reducing the stress on the positive electrode sheet 100, reducing the probability of the positive electrode sheet 100 being broken due to the large stress, and improving the safety of the wound battery cell 1; and also reducing the stress between the negative electrode active material and the diaphragm after expansion, thereby reducing the bonding force between the negative electrode active material and the diaphragm, avoiding the situation where part of the negative electrode active material is bonded to the diaphragm and debonded from the current collector after de-lithiation shrinkage due to the large bonding force, reducing the occurrence of interface failure, thereby reducing the probability of lithium precipitation, and optimizing the cycle performance.

[0041] In addition, by limiting the thickness of the first region 110 and the second region 120 to satisfy the above-mentioned range, it is possible to avoid the thickness T2 of the second region 120 being too large, which would lead to excessive internal resistance of the second region 120. While avoiding debonding of the negative electrode active material and the current collector, the internal resistance of the second region 120 can be controlled within a certain appropriate range, thereby improving the cycle performance of the battery.

[0042] In addition, in the wound cell 1, the porosity of the positive electrode active layer 140 in the second region 120 is increased. The porosity of the positive electrode active layer 140 is greater than that of the first region 110. On the one hand, compared with the first region 110, the positive electrode active layer 140 of the second region 120 has more compressible pores. When the negative electrode sheet 300 expands, the positive electrode active layer 140 of the second region 120 has a larger deformation space. Therefore, the compressive stress between the negative electrode active material and the separator after expansion is smaller, which can effectively alleviate the problem of debonding between the active material and the current collector caused by the stress of the arc region 12. On the other hand, the positive electrode active layer 140 of the second region 120 can absorb more electrolyte to improve the aging wettability of the arc region 12. The more sufficient the electrolyte infiltration is, the greater the effective lithium ion conductivity is. Therefore, by increasing the porosity of the positive electrode active layer 140 of the second region 120, the effective lithium ion conductivity of the arc region 12 is also increased. The reaction uniformity of the wound battery cell 1 is high, and the arc region 12 is not easy to precipitate lithium, which effectively improves the cycle stability.

[0043] At the same time, when the negative electrode sheet 300 expands, the electrolyte flows from the straight area 11 to the arc area 12 and is stored in the arc area 12. During discharge, the electrolyte flows from the arc area 12 to the straight area 11 and is stored in the straight area 11. That is, when the negative electrode sheet 300 expands, the amount of electrolyte in the arc area 12 is still relatively large. In terms of impedance or other aspects, the arc area 12 is closer to the straight area 11, which can ensure that the wound battery cell 1 reacts uniformly, better solve the problem of debonding of the active material and the current collector caused by stress, reduce the problem of lithium plating caused by excessive electrolyte extrusion from the arc area 12 when the negative electrode sheet 300 expands, and improve the safety performance and cycle performance of the battery.

[0044] In some optional embodiments, 20um≤T1≤150um, 20.2um≤T2≤195um, wherein T1 can be 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um, 120um, 110um, 130um, 140um or 150um; T2 can be 20.2um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um, 120um, 110um, 130um, 140um, 150um, 160um, 170um, 180um, 190um or 195um.

[0045] By setting T1 to be not less than 20um and T2 to be not less than 20.2um, the positive electrode active layer 140 of the positive electrode sheet 100 can be prevented from being too thin, thereby preventing the positive electrode sheet 100 from breaking; by setting T1 to be not greater than 150um and T2 to be not greater than 195um, the positive electrode active layer 140 of the positive electrode sheet 100 can be prevented from being too thick, thereby preventing the internal resistance of the positive electrode sheet 100 from being too large, thereby improving the lithium plating problem caused by excessive impedance.

[0046] in addition, in, It can be 1.5%, 2%, 3%, 4%, 5% or 6%; It can be 1%, 1.5%, 2%, 2.5% or 3%.

[0047] By setting Not less than 1% and Not less than 1.5%, which can avoid the porosity of the positive active layer 140 of the positive electrode sheet 100 being too small, ensure the aging wettability and cycle stability of the positive electrode sheet 100, and leave more compressible space, which is conducive to relieving the stress of the arc area 12; by setting Not more than 3% and The value is not greater than 6%, so as to avoid an increase in impedance due to an excessively large particle distance between the positive electrode active layer 140 of the positive electrode sheet 100, thereby improving the lithium plating problem caused by the excessively large impedance.

[0048] In some embodiments, the compaction density of the positive electrode active layer 140 in the first region 110 is ρ1, and the compaction density of the positive electrode active layer 140 in the second region 120 is ρ2, 0.8≤ρ2 / ρ1≤0.99, 1.6g / cc≤ρ2≤4.95g / cc, 2g / cc≤ρ1≤5g / cc. Among them, ρ2 / ρ1 can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99; ρ1 can be 2g / cc, 3g / cc, 4g / cc or 5g / cc; ρ2 can be 1.6g / cc, 1.8g / cc, 2g / cc, 3g / cc, 4g / cc or 4.95g / cc.

[0049] In this way, by setting the compaction density of the positive electrode active layer 140 in the first region 110 and the positive electrode active layer 140 in the second region 120 to be different, and the compaction density of the positive electrode active layer 140 in the second region 120 is less than the compaction density of the positive electrode active layer 140 in the first region 110, the thickness of the positive electrode active layer 140 in the second region 120 can be greater than the thickness of the positive electrode active layer 140 in the first region 110, and the porosity of the positive electrode active layer 140 in the second region 120 can be greater than the porosity of the positive electrode active layer 140 in the first region 110. At this time, the surface density of the positive electrode active layer 140 in the second region 120 and the positive electrode active layer 140 in the first region 110 can be the same or different.

[0050] In addition, ρ2 / ρ1 satisfies the above formula, which can avoid too large a difference in compaction density between the positive electrode active layer 140 in the second region 120 and the positive electrode active layer 140 in the first region 110, and ensure uniform reaction of the wound battery cell 1. In addition, ρ1 is not less than 2g / cc, and ρ2 is not less than 1.6g / cc, which can avoid too small a porosity of the positive electrode sheet 100, and ensure the infiltration effect of the electrolyte; ρ1 is not greater than 5g / cc, and ρ2 is not greater than 4.95g / cc, which can avoid too large an internal resistance of the positive electrode sheet 100, and reduce the probability of lithium precipitation.

[0051] In some embodiments, the surface density of the first region 110 is ρ3, the surface density of the second region 120 is ρ4, 0.6≤ρ4 / ρ3≤0.99, 0.005 g / cm 2 ≤ρ3≤0.1g / cm 2 , 0.003g / cm 2 ≤ρ4≤0.099g / cm 2 Wherein, ρ4 / ρ3 can be 0.6, 0.7, 0.8, 0.9 or 0.99; ρ3 can be 0.005 g / cm 2, 0.01g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.07g / cm 2 , 0.08g / cm 2 , 0.09g / cm 2 Or 0.1g / cm 2 ; ρ4 can be 0.003g / cm 2 , 0.01g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.07g / cm 2 , 0.08g / cm 2 , 0.09g / cm 2 Or 0.099g / cm 2 .

[0052] In this way, by setting the surface density of the positive electrode active layer 140 in the first region 110 and the positive electrode active layer 140 in the second region 120 to be different, and the surface density of the positive electrode active layer 140 in the second region 120 is smaller than the surface density of the positive electrode active layer 140 in the first region 110, it is possible to achieve that the thickness of the positive electrode active layer 140 in the second region 120 is greater than the thickness of the positive electrode active layer 140 in the first region 110, and the porosity of the positive electrode active layer 140 in the second region 120 is greater than the porosity of the positive electrode active layer 140 in the first region 110.

[0053] In addition, ρ4 / ρ3 satisfies the above formula, which can avoid a large difference in the surface density between the positive electrode active layer 140 in the first region 110 and the positive electrode active layer 140 in the second region 120, thereby ensuring uniform reaction of the wound battery cell 1. In addition, ρ3 is not less than 0.005 g / cm 2 , ρ4 is not less than 0.003g / cm 2 c, it can prevent the porosity of the positive electrode sheet 100 from being too small, and ensure the infiltration effect of the electrolyte; ρ3 is not greater than 0.1g / cm 2 , ρ4 is not more than 0.099g / cm 2 , which can prevent the internal resistance of the positive electrode sheet 100 from being too large and reduce the probability of lithium plating.

[0054] like Figure 2-Figure 4As shown, in some embodiments, the negative electrode sheet 300 includes a negative electrode current collector 330 and a negative electrode active layer 340 disposed on the surface of the negative electrode current collector 330. Along the winding direction of the negative electrode sheet 300, the negative electrode sheet 300 includes a plurality of third regions 310 and fourth regions 320 connected in sequence, the third region 310 is located in the straight region 11, and the fourth region 320 is located in the arc region 12. The negative electrode sheet 300 has a thickness T3 in the third region 310 and a thickness T4 in the fourth region 320. The porosity of the negative electrode active layer 340 in the third region 310 is The porosity of the negative electrode active layer 340 in the fourth region 320 is

[0055] Where, 1.01≤T4 / T3≤1.5, and T4 / T3 can be 1.01, 1.1, 1.2, 1.3, 1.4 or 1.5. It can be 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0056] It should be noted that, in the present invention, although the thickness of the negative electrode active layer 340 of the fourth region 320 is greater than the thickness of the negative electrode active layer 340 of the third region 310, there is no difference or a small difference in silicon content between the negative electrode active layer 340 of the fourth region 320 and the negative electrode active layer 340 of the third region 310, and the silicon content of the negative electrode active layer 340 of the fourth region 320 is not increased.

[0057] In the wound battery cell 1, a third region 310 and a fourth region 320 are arranged on the negative electrode sheet 300, and a smaller rolling pressure is applied to the fourth region during the rolling process, so that the negative electrode sheet has a larger compacted thickness in the fourth region, that is, the fourth region has more pores, and the negative electrode active layer 340 of the negative electrode sheet 300 can be compressed and deformed to absorb the expansion of the silicon volume of the negative electrode sheet 300 during the lithium removal and lithium insertion process, so that the negative electrode active layer 340 of the fourth region 320 can be guaranteed to have a larger compressible volume, and thus can be the arc region 1 2 reserves a larger expansion space for the negative electrode sheet 300, thereby reducing the stress on the positive electrode sheet 100, reducing the probability of the positive electrode sheet 100 being broken due to the large stress, and improving the safety of the wound battery cell 1; and also reducing the compressive stress between the negative electrode active material and the diaphragm after expansion, thereby reducing the bonding force between the negative electrode active material and the diaphragm, avoiding the situation where part of the negative electrode active material is bonded to the diaphragm and debonded from the current collector after de-lithiation shrinkage due to large bonding force, reducing the occurrence of interface failure, thereby reducing the probability of lithium precipitation, and optimizing the cycle performance.

[0058] By limiting the thickness of the third region 310 and the fourth region 320 to meet the above range, it is possible to avoid the thickness T4 of the fourth region 320 being too large, which would lead to excessive internal resistance of the fourth region 320. While ensuring stress reduction, the internal resistance of the fourth region 320 can be controlled within a certain appropriate range, thereby improving the cycle performance of the battery.

[0059] In addition, in the wound cell 1, the porosity of the negative electrode active layer 340 in the fourth region 320 is increased. The porosity of the negative electrode active layer 340 is greater than that of the third region 310. On the one hand, compared with the third region 310, the negative electrode active layer 340 of the fourth region 320 has more compressible pores. When the negative electrode sheet 300 expands, the deformation space of the negative electrode active layer 340 of the fourth region 320 is larger. Therefore, the compressive stress between the negative electrode active material and the separator after expansion is smaller, which can effectively alleviate the problem of debonding between the active material and the current collector caused by the stress of the arc area 12. On the other hand, the negative electrode active layer 340 of the fourth region 320 can absorb more electrolyte to improve the aging wettability of the arc area 12. The more sufficient the electrolyte infiltration is, the greater the effective lithium ion conductivity is. Therefore, by increasing the porosity of the negative electrode active layer 340 of the fourth region 320, the effective lithium ion conductivity of the arc area 12 is increased, the reaction uniformity of the wound battery cell 1 is high, the arc area 12 is not easy to precipitate lithium, and the cycle stability is effectively improved.

[0060] At the same time, when the negative electrode sheet 300 expands, the electrolyte flows from the straight area 11 to the arc area 12 and is stored in the arc area 12. During discharge, the electrolyte flows from the arc area 12 to the straight area 11 and is stored in the straight area 11. That is, when the negative electrode sheet 300 expands, the amount of electrolyte in the arc area 12 is still relatively large. In terms of impedance or other aspects, the arc area 12 is closer to the straight area 11, which can ensure that the wound battery cell 1 reacts uniformly, better solve the problem of debonding of the active material and the current collector caused by stress, reduce the problem of lithium plating caused by excessive electrolyte extrusion from the arc area 12 when the negative electrode sheet 300 expands, and improve the safety performance and cycle performance of the battery.

[0061] In some optional embodiments, 20um≤T3≤200um, 20.2um≤T4≤300um. Wherein, T3 can be 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um, 110um, 120um, 130um, 140um, 150um, 160um, 170um, 180um, 190um, 200um; T4 can be 20.2um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um, 110um, 120um, 130um, 140um, 150um, 160um, 170um, 180um, 190um, 200um, 220um, 240um, 260um, 280um or 300um.

[0062] By setting T3 to be not less than 20um and T4 to be not less than 20.2um, the negative electrode sheet 300 can be prevented from being too thin, thereby preventing the negative electrode sheet 300 from breaking; by setting T4 to be not greater than 300um and T3 to be not greater than 200um, the negative electrode sheet 300 can be prevented from being too thick, thereby preventing the internal resistance of the negative electrode sheet 300 from being too large, thereby improving the lithium plating problem caused by excessive impedance.

[0063] in addition, in, It can be 1%, 1.5%, 2%, 2.5% or 3%; It can be 1.5%, 2%, 3%, 4%, 5% or 6%.

[0064] By setting Not less than 1% and Not less than 1.5%, which can avoid the negative electrode sheet 300 having too small a porosity, ensure the aging wettability and cycle stability of the negative electrode sheet 300, and leave more compressible space, which is conducive to relieving the stress of the arc area 12; by setting Not more than 3% and The value is not greater than 6%, so as to avoid an increase in impedance caused by an excessively large particle distance between the negative electrode active layer 340 of the negative electrode sheet 300, thereby improving the lithium deposition problem caused by the excessively large impedance.

[0065] In some embodiments, the compaction density of the third region 310 is ρ5, the compaction density of the fourth region 320 is ρ6, 0.8≤ρ6 / ρ5≤0.99, 1 g / cc≤ρ5≤2.5 g / cc, 0.8 g / cc≤ρ6≤2.475 g / cc. Among them, ρ6 / ρ5 can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99; ρ5 can be 1g / cc, 1.5g / cc, 2g / cc or 2.5g / cc; ρ6 can be 0.8g / cc, 0.9g / cc, 1g / cc, 1.5g / cc, 2g / cc or 2.475g / cc.

[0066] In this way, by setting the compaction density of the negative electrode active layer 340 in the third region 310 and the negative electrode active layer 340 in the fourth region 320 to be different, and the compaction density of the negative electrode active layer 340 in the fourth region 320 is less than the compaction density of the negative electrode active layer 340 in the third region 310, the thickness of the negative electrode active layer 340 in the fourth region 320 can be greater than the thickness of the negative electrode active layer 340 in the third region 310, and the porosity of the negative electrode active layer 340 in the fourth region 320 can be greater than the porosity of the negative electrode active layer 340 in the third region 310. At this time, the surface density of the negative electrode active layer 340 in the third region 310 and the negative electrode active layer 340 in the fourth region 320 can be the same or different.

[0067] In addition, ρ6 / ρ5 satisfies the above formula, which can avoid too large a difference in compaction density between the negative electrode active layer 340 in the third region 310 and the negative electrode active layer 340 in the fourth region 320, and ensure uniform reaction of the wound battery cell 1. In addition, ρ5 is not less than 1g / cc, and ρ6 is not less than 0.8g / cc, which can avoid too small porosity of the negative electrode sheet 300 and ensure the infiltration effect of the electrolyte; ρ5 is not greater than 2.5g / cc, and ρ6 is not greater than 2.475g / cc, which can avoid too large internal resistance of the negative electrode sheet 300 and reduce the probability of lithium precipitation.

[0068] In some embodiments, the surface density of the third region 310 is ρ7, and the surface density of the fourth region 320 is ρ8, 1≤ρ8 / ρ7≤1.3, 0.003 g / cm 2 ≤ρ7≤0.07g / cm 2 , 0.003g / cm 2 ≤ρ8≤0.091g / cm 2 ρ8 / ρ7 can be 1, 1.1, 1.2 or 1.3; ρ7 can be 0.003 g / cm 2 , 0.005g / cm2 , 0.008g / cm 2 , 0.01g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 or 0.07g / cm 2 ; ρ8 can be 0.003g / cm 2 , 0.005g / cm 2 , 0.008g / cm 2 , 0.01g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.07g / cm 2 , 0.08g / cm 2 、0.091g / cm 2 .

[0069] In this way, by setting the surface density of the negative electrode active layer 340 in the fourth region 320 and the negative electrode active layer 340 in the third region 310 to be different, and the surface density of the negative electrode active layer 340 in the fourth region 320 is greater than the surface density of the negative electrode active layer 340 in the third region 310, the CB (cell Balance) value of the arc region 12 can be increased without affecting the porosity relationship and thickness relationship between the third region 310 and the fourth region 320, which can reduce the probability of lithium plating in the arc region 12 and the expansion amount of the negative electrode sheet 300, thereby further reducing the stress, thereby reducing the bonding force between the negative electrode active material and the diaphragm, and reducing the occurrence of interface failure.

[0070] In addition, ρ8 / ρ7 satisfies the above formula, which can avoid a large difference in the surface density between the negative electrode active layer 340 in the third region 310 and the negative electrode active layer 340 in the fourth region 320, thereby ensuring uniform reaction of the wound battery cell 1. In addition, ρ7 is not less than 0.003 g / cm 2 , ρ8 is not less than 0.003g / cm 2 , which can prevent the porosity of the negative electrode sheet 300 from being too small and ensure the infiltration effect of the electrolyte; ρ7 is not greater than 0.07g / cm 2 , ρ8 is not greater than 0.091g / cm 2 , which can prevent the negative electrode sheet 300 from having an excessive internal resistance and reduce the probability of lithium plating.

[0071] like Figure 5-Figure 6 As shown, in some embodiments, the second region 120 has a first surface 150 and a second surface 160 arranged opposite to each other in the first direction, and a plurality of protrusions 700 are provided on the first surface 150 or the second surface 160 of the second region 120. The plurality of protrusions 700 are arranged at intervals, wherein the plurality of protrusions 700 can be arranged in a matrix structure of multiple rows and columns along the second direction and the third direction.

[0072] In some embodiments, the negative electrode sheet 300 has a third surface 350 and a fourth surface 360 ​​disposed opposite to each other in the first direction, and the third surface 350 or the fourth surface 360 ​​located in the fourth region 320 is provided with a plurality of protrusions 700. The plurality of protrusions 700 are disposed at intervals, wherein the plurality of protrusions 700 may be arranged in a matrix structure of multiple rows and columns along the second direction and the third direction.

[0073] It should be noted that the first direction, the second direction and the third direction can be arranged perpendicularly in pairs. The first direction can be the stacking direction of the positive electrode sheet 100, the separator and the negative electrode sheet 300, that is, the thickness direction of the positive electrode sheet 100 and the thickness direction of the negative electrode sheet 300; the second direction can be the winding direction of the positive electrode sheet 100, the separator and the negative electrode sheet 300, that is, the length direction of the positive electrode sheet 100 and the length direction of the negative electrode sheet 300; the third direction can be the circumferential direction of the wound battery cell 1, that is, the width direction of the positive electrode sheet 100 and the width direction of the negative electrode sheet 300.

[0074] For example, the protrusion 700 includes a substance that does not participate in electrochemistry, for example, the protrusion 700 includes but is not limited to ceramics, glue or fiber and other materials that do not participate in the battery charge and discharge reaction, such as alumina mixed with PMMA (PolyMethylMethacrylate) glue, alumina mixed with PVDF (polyvinylidene difluoride) glue, alumina mixed with SBR (emulsion styrene butadiene rubber) glue or a single rubber particle. In this way, the protrusion 700 does not participate in the electrode reaction, does not provide or accept a lithium source, can avoid the loss of the protrusion 700, and improve the service life of the protrusion 700.

[0075] By setting the protrusion 700 on the second area 120, the thickness of the second area 120 can be increased. By setting the protrusion 700 on the fourth area 320, the thickness of the fourth area 320 can be increased, thereby providing a buffer space for the arc area 12. During the expansion of the negative electrode sheet 300, the protrusion 700 can be deformed to absorb the expansion of the negative electrode sheet 300, relieve the expansion stress of the arc area 12, thereby reducing the probability of the positive electrode sheet 100 being broken by force, and at the same time reducing the bonding force between the negative electrode active material and the diaphragm. In addition, the arc area 12 has a good wetting effect, which can reduce the probability of lithium plating and avoid the risk of poor interface during the cycle.

[0076] Specifically, the plurality of protrusions 700 may be distributed in an island shape, a line-shaped staggered distribution, a grid-shaped staggered distribution, a sheet-shaped overall distribution, or any other geometric shape distribution. The projection of the protrusion 700 along the first direction may be a circle, a regular polygon, or other polygons. In this way, the structural diversity of the protrusion 700 can be increased.

[0077] In some embodiments, the arrangement area of ​​the plurality of protrusions 700 in the second area 120 may be the entire second area 120, and the arrangement area of ​​the plurality of protrusions 700 in the fourth area 320 may be the entire fourth area 320. In this way, the area of ​​the arrangement area of ​​the protrusions 700 is large, which can ensure that most of the space in the second area 120 is arranged with the protrusions 700, and most of the space in the fourth area 320 is arranged with the protrusions 700, which is conducive to absorbing the expansion of the arc area 12.

[0078] Further, the height of the protrusion 700 located in the second region 120 is H1, 0.01≤H1 / T1≤0.2, wherein the height of the protrusion 700 located in the second region 120 refers to the distance from the vertex of the protrusion 700 to the second region 120 along the first direction, 1um≤H1≤10um.

[0079] The height of the protrusion 700 in the fourth region 320 is H2, 0.01≤H2 / T3≤0.2, wherein the height of the protrusion 700 in the fourth region 320 refers to the distance from the vertex of the protrusion 700 to the fourth region 320 along the first direction, 1um≤H2≤10um.

[0080] Among them, H1 / T1 can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or 0.2; H1 can be 1um, 2um, 3um, 4um, 5um, 6um, 7um, 8um, 9um or 10um.

[0081] H2 / T2 can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or 0.2; H2 can be 1um, 2um, 3um, 4um, 5um, 6um, 7um, 8um, 9um or 10um.

[0082] By setting H1 to be not less than 1um and H1 / T1 to be not less than 0.01, or H2 to be not less than 1um and H2 / T3 to be not less than 0.01, it is possible to ensure that the height of the protrusion 700 is high enough to achieve the purpose of expanding the volume of the ground buffer arc area 12; by setting H1 to be not greater than 10um and H1 / T1 to be not greater than 0.2, and H2 to be not greater than 10um and H2 / T3 to be not greater than 0.2, it is possible to avoid the protrusion 700 being too high, thereby ensuring the space utilization of the wound battery cell 1 to ensure the energy density, and the manufacturing difficulty of the protrusion 700 is reduced, which is beneficial to the processing of the positive electrode sheet 100 and the negative electrode sheet 300.

[0083] Furthermore, the center distance of the projections of two adjacent protrusions 700 in the second area 120 in the first direction is d1, 1≤d1 / T1≤50, 1mm≤d1≤10mm. Wherein, d1 / T1 can be 1, 10, 20, 30, 40 or 50; d1 can be 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0084] The center distance between the projections of two adjacent protrusions 700 in the fourth area 320 in the first direction is d2, 1≤d2 / T3≤50, 1mm≤d2≤10mm. Wherein, d2 / T3 can be 1, 10, 20, 30, 40 or 50; d2 can be 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0085] In this way, not only can the distance between two adjacent protrusions 700 be avoided from being too close, which facilitates the processing and manufacturing of the protrusions 700, but also the distance between two adjacent protrusions 700 can be avoided from being too far, thereby increasing the density of the protrusions 700 in the arc area 12 so that stress distribution in each area of ​​the arc area 12 can be uniform.

[0086] Specifically, the protrusion 700 has a first projection in the first direction, and the radius of the circumscribed circle of the first projection is r, 0.5mm≤r≤100mm, and r can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 9mm or 100mm.

[0087] In this way, the diameter of each protrusion 700 will not be too small, which is beneficial to improve the structural strength of the protrusion 700 and reduce the damage probability of the protrusion 700. The protrusion 700 is easy to manufacture, and the diameter of each protrusion 700 will not be too large, which is beneficial to the deformation of the protrusion 700.

[0088] like Figure 1 As shown, the thickness of the arc area 12 is R, and the thickness of the straight area 11 is T. and 2mm≤R≤20mm. The ratio of R to T / 2 can be 0.9, 0.92, 0.94, 0.96, 0.98, 1, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, 1.22, 1.24, 1.26; R can be 2mm, 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm or 20mm.

[0089] In the related art, the thickness of the positive active layer of the positive electrode sheet is uniformly set, the thickness of the negative active layer of the negative electrode sheet is uniformly set, the separator in the arc area wound into the battery cell cannot play a supporting role, the stress accumulation in the arc area caused by the winding tension during the winding process of the battery cell cannot be effectively released, and the radius of the arc area Significantly lower than 0.9, usually between 0.75 and 0.9, and cannot be met by process control As a result, the battery cell has a slight interface problem during the cycle: the graphite system has a slight interface problem, and as the amount of silicon added increases, the interface problem is further aggravated, causing the battery performance to decay rapidly, and even causing problems such as thermal runaway.

[0090] By increasing the thickness of the positive electrode active layer 140 of the second region 120 and the negative electrode active layer 340 of the fourth region 320, the diameter of the arc region 12 can be increased. When the ratio of R to T / 2 is within the above range, it can effectively avoid the stress of the arc region 12 being greater than the stress of the straight region 11 during the battery cycle, prevent the problem of battery cycle failure, and significantly improve the battery cycle interface stability.

[0091] Furthermore, the negative electrode active layer 340 includes a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage of silicon in the negative electrode active layer 340 is x. 1%≤x≤50%, where x can be 1%, 10%, 20%, 30%, 40% or 50%. Specifically, for every 1% increase in x, the ratio of R to T increases by at least 0.5%. For example, if x is 0, x is 5%, ; x is 10%,

[0092] As the silicon doping amount increases, the expansion of the electrode increases. Therefore, to increase the silicon doping amount, it is necessary to increase the radius of the arc area 12, so that the arc area 12 has a larger space to accommodate the second area 120 and the fourth area 320, and the thickness and porosity of the second area 120 and the fourth area 320 can be increased, so that the second area 120 and the fourth area 320 can match the expansion of the negative electrode sheet 300.

[0093] In some embodiments, the arc region 12 of the two arc regions 12 close to the positive electrode tab 400 has a thickness R1, and the arc region 12 of the two arc regions 12 close to the negative electrode tab 500 has a thickness R2, and 0.98≤R1 / R1≤1.2. It should be noted that the thickness change of the arc region 12 is achieved by increasing the interlayer gap of the active material and the particle gap of the active material in the arc region 12, rather than by increasing the thickness of the pole piece at the arc in isolation.

[0094] According to an embodiment of the present invention, on the other hand, an electrochemical device is provided, comprising the above-mentioned wound battery cell 1 and a shell, wherein the wound battery cell 1 is accommodated in the shell. There is no limitation on the type of the shell, for example, it can be an aluminum-plastic film or other similar or dissimilar materials.

[0095] The lithium ion battery of the present invention is prepared according to the following method.

[0096] (1) Preparation of positive electrode sheet 100:

[0097] The positive electrode current collector 130 is usually made of aluminum foil or aluminum composite film, hereinafter referred to as aluminum foil.

[0098] First, lithium cobalt oxide: carbon nanotubes: polyvinylidene fluoride are added into a stirring tank in a mass ratio of 97.5:1.1:1.4, and NMP solvent is added, and the mixture is fully stirred according to a known batching process to prepare a positive electrode slurry;

[0099] Then, the surface density or compaction density of the first region 110 and the second region 120 is adjusted so that the thickness of the first region 110 and the second region 120 are different and the porosity of the first region 110 and the second region 120 are different.

[0100] For example, in preparation method 1, the compaction density of the first region 110 and the second region 120 are different, but the surface density is the same:

[0101] The positive electrode slurry is transferred to the opposite sides of the aluminum foil by coating equipment, with a coating thickness of 45um and a surface density of 0.005g / cm 2 ~0.1g / cm 2The positive electrode sheet 100 is unrolled and compacted on a variable roll gap roller press, and the first region 110 is compacted with normal pressure. The compaction density of the first region 110 is 2 g / cm 3 ~7g / cm 3 Then, the roller pressing device changes rollers every 2s to 10s, reduces pressure to compact the second area 120, and restores normal roller pressure after pressing for 10ms to 1s, so that the compaction density of the second area 120 is reduced by 1% to 50%. By continuously running the above actions, the compaction density of the first area 110 and the second area 120 can be different;

[0102] Preparation method 2: the surface density and compaction density of the first region 110 and the second region 120 are different:

[0103] The coating equipment intermittently loads the material at the designed frequency, and coats the first area 110 at a normal surface density for 2s to 10s. The surface density of the first area 110 is 0.005g / cm 2 ~0.1g / cm 2 , and then the second region 120 is coated with a lower surface density for 10ms to 1s to reduce the surface density of the second region 120 by 1% to 50%. The extrusion coating equipment transfers the positive electrode slurry to the opposite sides of the aluminum foil in different ways, and the coating thickness is 45um. The pole piece is unrolled and compacted on the roller press. The gap of the roller press is constant. Since the surface density of the second region 120 is lower, the compaction density of the second region 120 after rolling is reduced by 1% to 50% compared with the compaction density of the first region 110. The compaction density of the first region 110 is 2g / cm 3 ~7g / cm 3 By continuously operating the above-mentioned feeding method, it is possible to achieve that the surface density and the compaction density of the first area 110 and the second area 120 are different.

[0104] (2) Preparation of negative electrode sheet 300:

[0105] The negative electrode current collector 330 is usually made of materials such as copper foil or copper composite film, hereinafter referred to as copper foil.

[0106] First, the negative electrode active material graphite mixed with silicon carbon: conductive nano carbon tubes: binder styrene butadiene rubber are added into a stirring tank in a mass ratio of 97%: 1.4%: 1.6%, and deionized water solvent is added, and the mixture is fully stirred according to a known batching process to prepare a negative electrode slurry;

[0107] The negative electrode slurry is transferred to the surfaces of both sides of the copper foil by coating equipment, with a coating thickness of 49um and a double-layer coating surface density of 0.003g / cm 2 ~0.07g / cm 2The negative electrode sheet 300 is unrolled and compacted on a variable roll gap roller press, and the third region 310 is compacted using a normal roller pressure. The compaction density of the third region 310 is 1 g / cm 3 ~2.5g / cm 3 Then, the roller pressing device changes rollers every 2s to 10s, reduces the pressure to compact the fourth region 320, and restores the normal roller pressure after pressing for 10ms to 1s, so that the compaction density of the fourth region 320 is reduced by 1% to 50%. By continuously running the above actions, the compaction density of the third region 310 and the fourth region 320 of the negative electrode sheet 300 can be different, and the surface density is the same.

[0108] (3) Preparation of battery: The positive electrode sheet 100, the negative electrode sheet 300 and a conventional separator are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After being baked to remove moisture, a conventional electrolyte is injected and the battery is formed by a hot pressing process.

[0109] The thickness testing method of the pole piece in the present invention: Method 1, direct measurement by micrometer test; Method 2, preparing the cross section (CP) by using an argon ion mill, magnifying the sample by using a scanning electron microscope, and marking it by using scanning electron microscope test software.

[0110] The porosity test method of the pole piece is as follows: First, place the sample to be tested in the sample test chamber of the true density tester; then, use an inert gas (such as helium) to gradually pressurize it to a specified value, and the gas expands into the expansion chamber; by measuring the equilibrium pressure of the two processes, according to the law of conservation of mass, the volume of the measuring chamber and the expansion chamber is calibrated by a standard ball; finally, by calculating the mass and true volume of the sample, the true density unit g / cm 3 .

[0111] The principle of the porosity test of the pole piece: The test principle of the true density meter is based on the Archimedean principle, and the true density of the sample is measured by the gas expansion displacement method. The true density refers to the density obtained by dividing the mass of the material by the volume (true volume) excluding the voids inside and outside the particles. During the test, the Bohr law (PV=nRT) of inert gas with a small molecular diameter under certain conditions is used to accurately measure the true volume of the sample by measuring the change in gas volume caused by the sample being placed in the test chamber, thereby calculating the true density.

[0112] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical 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 creative work are within the scope of protection of the present invention.

[0113] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0114] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0115] The lithium ion battery of Example 1 was prepared according to the following method.

[0116] (1) Preparation of positive electrode sheet 100:

[0117] Take lithium cobalt oxide: carbon nanotubes: polyvinylidene fluoride in a mass ratio of 97.5:1.1:1.4 and add them to a stirring tank, add NMP solvent, and stir them thoroughly according to the known batching process to prepare positive electrode slurry; transfer the positive electrode slurry to the opposite sides of the aluminum foil through a coating device, and the coating thickness is 45um. The coated aluminum foil is dried, and then rolled, protrusions are set in the second area 120, and cut. In the rolling step of this embodiment, the rolling parameters are adjusted to make the compaction density ρ1 of the first area 110 4.18g / cc, the compaction density ρ2 of the second area 120 3.34g / cc, and the surface density ρ3 of the first area 110 0.01368g / cm 2 , the surface density ρ4 of the second region 120 is 0.01094 g / cm 2 The thickness T1 of the first region 110 is 65 μm, the thickness T2 of the second region 120 is 78 μm, and the porosity of the first region 110 is The porosity of the second region 120 reaches 1.8%. The radius r of the circumscribed circle of the first projection of the protrusions in the second region 120 is 2 mm, the size H1 of the protrusions in the first direction is 8.7 μm, and the center distance d1 of the projections of two adjacent protrusions 700 in the first direction is 10 mm.

[0118] (2) Preparation of negative electrode sheet 300:

[0119] Take the negative electrode active material graphite mixed with silicon carbon: conductive nano carbon tubes: binder styrene butadiene rubber in a mass ratio of 97%: 1.4%: 1.6% and add them to a stirring tank, add deionized water solvent, and stir them thoroughly according to the known batching process to prepare a negative electrode slurry; transfer the negative electrode slurry to the surface of both sides of the copper foil through a coating device, and coat it with a thickness of 49um. Dry the coated copper foil, and then roll it, set a protrusion in the fourth area 320, and cut it. In the rolling step of this embodiment, the rolling parameters are adjusted to make the compaction density ρ6 of the fourth area 320 1.56g / cc, the compaction density ρ5 of the third area 310 1.66g / cc, and the surface density ρ7 of the third area 310 0.00717g / cm2 The surface density ρ8 of the fourth region 320 is 0.0080 g / cm 2 The thickness T3 of the third region 310 is 73 μm, the thickness T4 of the fourth region 320 is 93 μm, and the porosity of the third region 310 is The porosity of the fourth region 320 reaches 2.11%. The radius r of the circumscribed circle of the first projection of the protrusions in the fourth region 320 is 2 mm, the size H2 of the protrusions in the first direction is 8.7 μm, and the center distance d2 of the projections of two adjacent protrusions 700 in the first direction is 10 mm.

[0120] (3) Preparation of electrolyte:

[0121] Add LiPF6-10 wt% lithium salt, add 45 wt% EMC, 20 wt% DMC, 7 wt% EA, 11 wt% PC solvent, mix well, add 5 wt% FEC additive and 2 wt% diluent, mix well to obtain electrolyte.

[0122] (4) Preparation of diaphragm:

[0123] A commercially available separator having a thickness of 9 μm was used.

[0124] (5) Preparation of the battery: The positive electrode sheet 100, the negative electrode sheet 300 and the separator are wound into a core, which is then wrapped with an aluminum-plastic film. After being baked to remove moisture, an electrolyte is injected and a battery is obtained by a hot pressing process. In the battery of the present embodiment, the thickness of the straight area 11 of the battery cell 1 is T=5.01 mm, the radius of the arc area 12 is R=2.58 mm, and the thickness of the negative electrode sheet 300 can be the same.

[0125] Example 2-Example 14 and Comparative Example 1-Comparative Example 6

[0126] The lithium ion batteries of Examples 2 to 14 and Comparative Examples 1 to 6 are prepared by referring to the method of the lithium ion battery of Example 1, except that:

[0127] By adjusting the compaction density ρ1 of the first region 110, the compaction density ρ2 of the second region 120, the surface density ρ3 of the first region 110, and the surface density ρ4 of the second region 120 of each embodiment and comparative example, the thickness T1 of the first region 110, the thickness T2 of the second region 120, the porosity of the first region 110 Porosity of the second region 120 The values ​​shown in Table 1 below are achieved.

[0128] Table 1

[0129] T2 / T1 T2(um) T1(um) φ2 / φ1 φ2 φ1 Example 1 1.2 78 65 1.70 3.00％ 1.80％ Example 2 1.01 65.7 65 1.70 3.00％ 1.80％ Example 3 1.05 68.3 65 1.70 3.00％ 1.80％ Example 4 1.1 71.5 65 1.70 3.00％ 1.80％ Example 5 1.15 74.8 65 1.70 3.00％ 1.80％ Example 6 1.18 76.7 65 1.70 3.00％ 1.80％ Example 7 1.3 84.5 65 1.70 3.00％ 1.80％ Example 8 1.01 20.2 20 1.70 3.00％ 1.80％ Example 9 1.3 195 150 1.70 3.00％ 1.80％ Example 10 1.2 78 65 1.50 2.70％ 1.80％ Embodiment 11 1.2 78 65 1.75 3.15％ 1.80％ Example 12 1.2 78 65 2.00 3.60％ 1.80％ Example 13 1.2 78 65 1.50 1.50％ 1.00％ Embodiment 14 1.2 78 65 2.00 6.00％ 3.00％ Comparative Example 1 1 65 65 1.70 3.00％ 1.80％ Comparative Example 2 1.4 91 65 1.70 3.00％ 1.80％ Comparative Example 3 1.2 78 65 1.00 1.80％ 1.80％ Comparative Example 4 1.2 78 65 2.50 4.50％ 1.80％ Comparative Example 5 1 65 65 1.00 1.80％ 1.80％ Comparative Example 6 1.4 91 65 2.50 4.50％ 1.80％

[0130] The other parameter conditions in Examples 1-14 and Comparative Examples 1-6 are the same as those in Example 1.

[0131] Example 15-Example 30

[0132] The lithium-ion batteries of Examples 15 to 30 are all prepared by referring to the method of the lithium-ion battery of Example 1, with the differences being that the compaction density ρ1 of the first region 110, the compaction density ρ2 of the second region 120, the surface density ρ3 of the first region 110, and the surface density ρ4 of the second region 120 are different, as shown in Table 2 below.

[0133] Table 2

[0134]

[0135] The other parameter conditions in Examples 15-30 are the same as those in Example 1.

[0136] Example 31-Example 44 and Comparative Examples 7-12

[0137] The lithium ion batteries of the present embodiments 31-44 and comparative examples 7-12 are all prepared by referring to the method of the lithium ion battery of embodiment 1, except that: by adjusting the compaction density ρ6 of the fourth region 320, the compaction density ρ5 of the third region 310, the surface density ρ7 of the third region 310, and the surface density ρ8 of the fourth region 320 of each embodiment, the thickness T3 of the third region 310, the thickness T4 of the fourth region 320, the porosity φ3 of the third region 310, and the porosity φ4 of the fourth region 320 reach the values ​​shown in Table 3 below.

[0138] Table 3

[0139] T4 / T3 T4(um) T3(um) Φ4 / φ3 Φ4 Φ3 Embodiment 31 1.3 94.9 73 1.70 3.60％ 2.11％ Embodiment 32 1.01 73.7 73 1.70 3.60％ 2.11％ Embodiment 33 1.05 76.7 73 1.70 3.60％ 2.11％ Embodiment 34 1.1 80.3 73 1.70 3.60％ 2.11％ Embodiment 35 1.15 84.0 73 1.70 3.60％ 2.11％ Embodiment 36 1.3 94.9 73 1.70 3.60％ 2.11％ Embodiment 37 1.5 109.5 73 1.70 3.60％ 2.11％ Embodiment 38 1.01 20.2 20 1.70 3.60％ 2.11％ Embodiment 39 1.5 300.0 200 1.70 3.60％ 2.11％ Embodiment 40 1.3 94.9 73 1.50 3.17％ 2.11％ Embodiment 41 1.3 94.9 73 1.75 3.69％ 2.11％ Embodiment 42 1.3 94.9 73 2.00 4.22％ 2.11％ Embodiment 43 1.3 94.9 73 1.50 1.50％ 1.00％ Embodiment 44 1.3 94.9 73 2.00 6.00％ 3.00％ Comparative Example 7 1 73 73 1.70 3.60％ 2.11％ Comparative Example 8 1.6 116.8 73 1.70 3.60％ 2.11％ Comparative Example 9 1.3 94.9 73 1.30 2.74％ 2.11％ Comparative Example 10 1.3 94.9 73 2.30 4.85％ 2.11％ Comparative Example 11 1 73 73 1.30 2.74％ 2.11％ Comparative Example 12 1.6 116.8 73 2.30 4.85％ 2.11％

[0140] The other parameter conditions in Examples 31-44 and Comparative Examples 7-12 are the same as those in Example 1.

[0141] Example 45-Example 60

[0142] The lithium-ion batteries of Examples 45 to 60 are all prepared by referring to the method of the lithium-ion battery of Example 1, with the differences being that the compaction density ρ6 of the fourth region 320, the compaction density ρ5 of the third region 310, the surface density ρ7 of the third region 310, and the surface density ρ8 of the fourth region 320 are different, as shown in Table 4 below.

[0143] Table 4

[0144]

[0145] The other parameter conditions of Examples 45-60 are the same as those of Example 1.

[0146] The related performance tests of the positive electrode sheet 100 and the negative electrode sheet 300 and the battery in the above embodiments and comparative examples are recorded in Tables 5 to 8. The test methods are described as follows:

[0147] (1) Cycle life test

[0148] At an ambient temperature of 25°C, the charge and discharge regime is 2C constant current constant voltage charging to 4.48V and then 0.05C / 1C discharging to 3.0V for 1000 cycles. The capacity retention rate is calculated as follows: Nth discharge capacity / first discharge capacity*100%.

[0149] (2) Battery expansion rate test

[0150] At an ambient temperature of 25°C, the charge and discharge regime is 2C constant current constant voltage charging to 4.48V and then 0.05C / 1C discharging to 3.0V. The battery's full charge expansion thickness is tested every 100 cycles. Expansion rate calculation = (Nth full charge thickness / first full charge thickness-1)*100%.

[0151] (3) Battery lithium deposition detection

[0152] At 25℃, the charge and discharge system is 2C constant current constant voltage charging 4.48V and 0.05C / 1C discharging to 3.0V, and the cycle is 1000 times. After every 100 times, the battery is fully charged, and the battery cell is disassembled in a dry environment to observe the lithium deposition on the negative electrode surface. The degree of lithium deposition is divided into severe lithium deposition > general lithium deposition > slight lithium deposition > no lithium deposition (the degree of lithium deposition decreases in turn).

[0153] (4) Interface condition detection of battery negative electrode

[0154] At 25℃ ambient temperature, the charge and discharge regime is 1.8C constant current constant voltage charging to 4.48V and 0.05C / 4C discharging to 3.0V, for 1000 cycles. After the cycle, fully charge the battery and disassemble the battery in a dry environment.

[0155] Observe whether the active layer has fallen off and evaluate the interface failure; interface failure detection is divided into severe falling off > general falling off > slight falling off > no falling off (the degree of falling off decreases in turn).

[0156] Table 5

[0157]

[0158]

[0159] From the results in Table 5, it can be seen that T1, T2, and The relationship between them all satisfies: 1.01≤T2 / T1≤1.3 and Compared with Comparative Examples 1 to 6, it can be seen that the control of T1, T2, and Within the above range, the problem of lithium deposition of the electrode and the detachment of the negative electrode active material from the current collector can be significantly improved; by comparing Examples 1-7 with Comparative Examples 1-2, and by comparing Examples 10-12 with Comparative Examples 3-4, it can be seen that when the straight area 11 has the same electrode thickness and the same porosity, by adjusting the thickness and porosity of the arc area, 1.01≤T2 / T1≤1.3 and It can effectively improve the capacity retention rate of the battery cell and reduce the expansion rate.

[0160] Table 6

[0161]

[0162] By comparing Example 21, Examples 15-18, and Example 22, it can be seen that when the compaction density ρ1 in the flat area remains unchanged, as the ratio of ρ2 / ρ1 increases, its performance in capacity retention rate, lithium precipitation, expansion rate, and interface condition gradually improves and then decreases, especially when the ratio of ρ2 / ρ1 exceeds 0.99, the performance of the battery cell decreases significantly; therefore, this embodiment can achieve relatively good capacity retention rate, lithium precipitation, expansion rate, and interface condition by controlling the value of ρ2 / ρ1 to be below 0.99, and ρ2 / ρ1 preferably satisfies 0.8≤ρ2 / ρ1≤0.99;

[0163] By comparing Example 27, Examples 23-26 with Example 28, it can be seen that when the surface density ρ3 in the flat area remains unchanged, as the ratio of ρ4 / ρ3 increases, its performance in capacity retention rate, lithium precipitation, expansion rate, and interface condition gradually improves and then decreases, especially when the ratio of ρ4 / ρ3 exceeds 0.99, the performance of the battery cell decreases significantly; therefore, this embodiment can achieve relatively good capacity retention rate, lithium precipitation, expansion rate, and interface condition by controlling the value of ρ4 / ρ3 to be below 0.99, and ρ4 / ρ3 preferably satisfies 0.6≤ρ4 / ρ3≤0.99;

[0164] By comparing Example 30 with Example 22 and Example 28, and comparing Example 29 with Example 21 and Example 27, it can be seen that the embodiments in which the ratios of ρ2 / ρ1 and ρ4 / ρ3 are both outside the range values ​​have an effect that is significantly worse than the embodiments in which only one ratio is outside the range value.

[0165] The above data can effectively prove that controlling the ratio of ρ2 / ρ1 or ρ4 / ρ3 within the range can achieve the purpose of comprehensively and effectively improving the lithium plating problem and interface failure problem, improving the cycle performance and reducing the expansion performance.

[0166] Table 7

[0167]

[0168]

[0169] From the results in Table 7, it can be seen that T4, T3, and The relationship is: 1.01≤T4 / T3≤1.5, Compared with Comparative Examples 7 to 12, it can be seen that controlling T4, T3, and Within the above range, the problem of lithium deposition of the electrode and the detachment of the negative electrode active material from the current collector can be significantly improved; by comparing Examples 31-37 with Comparative Examples 7-8, and by comparing Examples 40-42 with Comparative Examples 9-10, it can be seen that when the straight area 11 has the same electrode thickness and the same porosity, by adjusting the thickness and porosity of the arc area, 1.01≤T4 / T3≤1.5 and It can effectively improve the capacity retention rate of the battery cell and reduce the expansion rate.

[0170] Table 8

[0171]

[0172]

[0173] By comparing Example 51, Examples 45-48, and Example 52, it can be seen that when the compaction density ρ5 in the flat area remains unchanged, as the ratio of ρ6 / ρ5 increases, the performance in capacity retention rate, lithium deposition, expansion rate, and interface condition gradually improves and then decreases, especially when the ratio of ρ6 / ρ5 exceeds 0.99, the performance of the battery cell decreases significantly; therefore, this embodiment can achieve relatively good capacity retention rate, lithium deposition, expansion rate, and interface condition by controlling the value of ρ6 / ρ5 to be below 0.99, and ρ6 / ρ5 preferably satisfies 0.8≤ρ6 / ρ5≤0.99;

[0174] By comparing Example 57 with Examples 53-56 and Example 58, it can be seen that when the surface density ρ7 of the flat area remains unchanged, when the ratio of ρ8 / ρ7 is increased to above 1, compared with Example 57 in which the ratio of ρ8 / ρ7 is below 1, its performance in capacity retention rate, lithium precipitation, expansion rate, and interface condition is significantly improved; however, as the ratio of ρ8 / ρ7 increases, the performance improvement gradually slows down, and when the ratio of ρ8 / ρ7 increases to above 1.4, the improvement is very limited; therefore, this embodiment can achieve relatively good capacity retention rate, lithium precipitation, expansion rate, and interface condition by controlling the value of ρ8 / ρ7 to be above 1, preferably satisfying 1≤ρ8 / ρ7≤1.3;

[0175] By comparing Example 60 with Example 52 and Example 58, and comparing Example 59 with Example 51 and Example 57, it can be seen that the embodiments in which the ratios of ρ6 / ρ5 and ρ8 / ρ7 are both outside the range values, have effects that are significantly worse than the embodiments in which only one ratio is outside the range value.

[0176] The above data can effectively prove that controlling the ratio of ρ6 / ρ5 or ρ8 / ρ7 within the range can achieve the purpose of comprehensively and effectively improving the lithium plating problem and interface failure problem, improving the cycle performance and reducing the expansion performance.

[0177] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A wound battery cell, characterized in that: The wound battery cell (1) comprises a positive electrode sheet (100), a separator and a negative electrode sheet (300) which are stacked and wound in sequence; The wound battery core (1) comprises a straight area (11) and arc areas (12) located at two ends of the straight area (11); The positive electrode sheet (100) comprises a positive electrode current collector (130) and a positive electrode active layer (140) disposed on the surface of the positive electrode current collector (130); along the winding direction of the positive electrode sheet (100), the positive electrode sheet (100) comprises a plurality of first regions (110) and second regions (120) connected in sequence, the first regions (110) being located in the straight region (11), and the second regions (120) being located in the arc region (12); The positive electrode sheet (100) has a thickness T1 in the first region (110), and a thickness T2 in the second region (120), 1.01≤T2 / T1≤1.3; The porosity of the positive electrode active layer (140) in the first region (110) is The porosity of the positive electrode active layer (140) in the second region (120) is 2. The wound battery cell according to claim 1, characterized in that: 20um≤T1≤150um, and / or, 20.2um≤T2≤195um; and / or, and / or, 3. The wound battery cell according to claim 1, characterized in that: The compaction density of the positive electrode active layer (140) of the first region (110) is ρ1, the compaction density of the positive electrode active layer (140) of the second region (120) is ρ2, 0.8≤ρ2 / ρ1≤0.99; and / or, The surface density of the positive electrode active layer (140) in the first region (110) is ρ3, and the surface density of the positive electrode active layer (140) in the second region (120) is ρ4, and 0.6≤ρ4 / ρ3≤0.

99.

4. The wound battery cell according to claim 3, characterized in that: 2g / cc≤ρ1≤5g / cc, and / or, 1.6g / cc≤ρ2≤4.95g / cc; and / or, 0.005g / cm 2 ≤ρ3≤0.1g / cm 2 , and / or, 0.003 g / cm 2 ≤ρ4≤0.099g / cm 2 .

5. The wound battery cell according to any one of claims 1 to 4, characterized in that: The negative electrode sheet (300) comprises a negative electrode current collector (330) and a negative electrode active layer (340) arranged on the surface of the negative electrode current collector (330); along the winding direction of the negative electrode sheet (300), the negative electrode sheet (300) comprises a plurality of third regions (310) and fourth regions (320) connected in sequence; the third region (310) is located in the straight region (11), and the fourth region (320) is located in the arc region (12); The negative electrode sheet (300) has a thickness T3 in the third region (310) and a thickness T4 in the fourth region (320), and 1.01≤T4 / T3≤1.5; The porosity of the negative electrode active layer (340) of the third region (310) is The porosity of the negative electrode active layer (340) of the fourth region (320) is 6. The wound battery cell according to claim 5, characterized in that: 20um≤T3≤200um, and / or, 20.2um≤T4≤300um; and / or, and / or, 7. The wound battery cell according to claim 5, characterized in that: The compaction density of the negative electrode active layer (340) of the third region (310) is ρ5, the compaction density of the negative electrode active layer (340) of the fourth region (320) is ρ6, and 0.8≤ρ6 / ρ5≤0.99; And / or, the surface density of the negative electrode active layer (340) in the third region (310) is ρ7, the surface density of the negative electrode active layer (340) in the fourth region (320) is ρ8, and 1≤ρ8 / ρ7≤1.

3.

8. The wound battery cell according to claim 7, characterized in that: 1g / cc≤ρ5≤2.5g / cc, and / or, 0.8g / cc≤ρ6≤2.475g / cc; and / or, 0.003g / cm 2 ≤ρ7≤0.07g / cm 2 , and / or, 0.003 g / cm 2 ≤ρ8≤0.091g / cm 2 .

9. The wound battery cell according to claim 5, characterized in that: The positive electrode sheet (100) has a first surface (150) and a second surface (160) arranged opposite to each other in a first direction, and the first surface (150) or the second surface (160) located in the second area (120) is provided with a plurality of protrusions (700); And / or, the negative electrode sheet (300) has a third surface (350) and a fourth surface (360) arranged opposite to each other in the first direction, and the third surface (350) or the fourth surface (360) located in the fourth area (320) is provided with a plurality of protrusions (700).

10. The wound battery cell according to claim 9, characterized in that: The height of the protrusion (700) located in the second region (120) is H1, 0.01≤H1 / T1≤0.2, 1um≤H1≤10um; And / or, the height of the protrusion (700) located in the fourth region (320) is H2, 0.01≤H2 / T3≤0.2, 1um≤H2≤10um.

11. The wound battery cell according to claim 9, characterized in that: The center distance between the projections of two adjacent protrusions (700) located in the second area (120) in the first direction is d1, 1≤d1 / T1≤50, 1mm≤d1≤10mm; And / or, the center distance between the projections of two adjacent protrusions (700) located in the fourth area (320) in the first direction is d2, 1≤d2 / T3≤50, 1mm≤d2≤10mm.

12. The wound battery cell according to claim 9, characterized in that: The protrusion (700) has a first projection in the first direction, and the shape of the first projection is one of a circle, a regular polygon and an irregular polygon; the radius of the circumscribed circle of the first projection is r, and 0.5mm≤r≤100mm.

13. The wound battery cell according to claim 9, characterized in that: The material of the protrusion (700) can be selected from at least one of ceramic, fiber, alumina mixed with PMMA glue, alumina mixed with PVDF glue, or alumina mixed with SBR glue.

14. The wound battery cell according to claim 5, characterized in that: The thickness of the wound battery core in the arc region (12) is R, and the thickness of the straight region (11) is T. and 2mm≤R≤20mm.

15. The wound battery cell according to claim 14, characterized in that: The negative electrode active layer (340) comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage content of silicon in the negative electrode active layer (340) is x. 1%≤x≤50%.

16. An electrochemical device, characterized in that: It comprises a wound battery cell (1) as claimed in any one of claims 1 to 15 and a shell, wherein the wound battery cell (1) is accommodated in the shell.

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