Battery cell and battery

Abstract

The invention relates to the technical field of batteries, and discloses a battery cell and a battery. The battery cell comprises N layers of battery cell units, each layer of battery cell unit comprises a positive plate, and the surface of the positive plate is provided with a first region and a second region; the positive plates of the first-layer battery cell unit and the Nth-layer battery cell unit are first positive plates, the positive plates of the second-layer battery cell unit to the (N-1) th-layer battery cell unit are second positive plates, a first groove is formed in the positive active material layer at the first region of the first positive plate, and a second groove is formed in the positive active material layer at the first region of the second positive plate; the porosity (k1) of the positive electrode active material layer in the first region is 1.05-1.5 times the porosity (k2) of the positive electrode active material layer in the second region. The grooves reduce the active material loading capacity of the first region, reduce the unit area capacity of the region, improve the CB value of the corresponding region, reduce the positive electrode lithium removal amount of the corresponding region, balance the potential difference between the second region and the first region, and balance the expansion of the periphery and the edge of the laminated core.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to battery cells and batteries. Background Art

[0002] With the development of the market, consumers have increasingly higher demands for battery energy density, rate performance, and safety performance of battery cells. Laminated batteries have attracted widespread attention from battery manufacturers due to their good rate performance and high energy density. However, due to the unique structure of the laminate, the first and Nth layers of a laminated battery cell are generally single-sided positive electrodes. To prevent the positive electrode from curling on one side during the manufacturing process, the foil of the single-sided positive electrode sheet is generally thicker than that of the double-sided positive electrode sheet. This results in a larger flow area for the single-sided positive electrode sheet, which is prone to lithium deposition on one side. In addition, there is a difference in electric potential between the middle and edge of the laminated battery cell. The electric potential in the middle area of ​​the battery cell is lower, while the electric potential in the edge area of ​​the battery cell is higher. The lithium ions in the middle area will migrate to the edge area, causing the battery cell to expand around, thus deforming and causing lithium deposition on the edge. Summary of the Invention

[0003] In view of this, the present invention provides a battery cell and a battery to solve the problem of battery cell deformation and edge lithium deposition caused by the difference in electric potential between the middle and edge of the battery cell.

[0004] In the first aspect, the present invention provides a battery cell, comprising N layers of battery cell units stacked along the thickness direction thereof, each layer of battery cell units comprising a stacked positive electrode sheet, a separator and a negative electrode sheet, the surface of the positive electrode sheet having a first area and a second area, and the first area being arranged around the second area; along the thickness direction of the battery cell, the N layers of battery cell units are sequentially the first layer of battery cell units, the second layer of battery cell units, ..., the N-1 layer of battery cell units, and the N layer of battery cell units, the positive electrode sheets of the first layer of battery cell units and the N layer of battery cell units are first positive electrode sheets with positive electrode active material layers arranged on one side, and the positive electrode sheets of the second layer of battery cell units to the N-1 layer of battery cell units are second positive electrode sheets with positive electrode active material layers arranged on both sides; a first groove is provided on the positive electrode active material layer at the first area of ​​the first positive electrode sheet, and a second groove is provided on the positive electrode active material layer at the first area of ​​the second positive electrode sheet; the porosity k1 of the positive electrode active material layer in the first area is 1.05 to 1.5 times the porosity k2 of the positive electrode active material layer in the second area.

[0005] In an optional embodiment, the weight loss rate of the first region of the positive electrode sheet is e, the silicon doping amount of the negative electrode sheet is f, and f and e satisfy: f = (4 ~ 20) e, where e = 0.5% ~ 5%, f = 2% ~ 80%.

[0006] In an optional embodiment, in the first positive electrode sheet, the opening area S1 of all the first grooves is 20% to 60% of the area S2 of the positive electrode active material layer in the first region, and the volume V1 of all the first grooves is 10% to 50% of the volume V2 of the positive electrode active material layer in the first region; and / or, in the first positive electrode sheet, a third groove is provided on the positive electrode active material layer in the second region, the sum of the opening area S3 of all the third grooves and the opening area S1 of all the first grooves is 30% to 70% of the area S4 of the first positive electrode sheet, and the sum of the volume V3 of all the third grooves and the volume V1 of all the first grooves is 10% to 40% of the volume V4 of the first positive electrode sheet; and / or, in the second positive electrode sheet, the opening area S6 of all the second grooves is 30% to 50% of the area S7 of the positive electrode active material layer in the first region, and the volume V6 of all the second grooves is 20% to 40% of the volume V7 of the positive electrode active material layer in the first region.

[0007] In an optional embodiment, the first positive electrode sheet includes a first current collector and a first active material layer arranged on one surface of the first current collector, and the second positive electrode sheet includes a second current collector and a second active material layer arranged on both surfaces of the second current collector; the coating surface density ρ1 of the first active material layer is 92% to 98% of the coating surface density ρ2 of the second active material layer.

[0008] In an optional embodiment, the porosity of the positive electrode active material layer at the second region of the first positive electrode sheet is a, and the porosity of the positive electrode active material layer at the second region of the second positive electrode sheet is b, and a and b satisfy: a = (85% to 95%) b; and / or, in the first positive electrode sheet or the second positive electrode sheet, the CB value of the first region is 1.01% to 1.1% of the CB value of the second region; and / or, in the first positive electrode sheet or the second positive electrode sheet, the delithiation amount of the first region is 50% to 90% of the delithiation amount of the second region.

[0009] In an optional embodiment, the depth of the first groove is h1, and the depth of the second groove is h2; h1 and h2 satisfy: h1>h2, and h1-h2=1-20μm; and / or, the total thickness of the first positive electrode sheet is H1, H1 and h1 satisfy: h1=(0.2~1)H1; and / or, the total thickness of the second positive electrode sheet is H2, H2 and h2 satisfy: h2=(0.2~0.3)H2.

[0010] In an optional embodiment, the first positive electrode sheet has a first edge and a third edge arranged opposite to each other along the width direction, and a second edge and a fourth edge arranged opposite to each other along the length direction; along the width direction, the minimum distance W1 between the first edge and the first groove is 0.2mm~2mm, and the minimum distance W3 between the third edge and the first groove is 0.2mm~2mm; along the length direction, the minimum distance W2 between the second edge and the first groove is 0.2mm~2mm, and the minimum distance W4 between the fourth edge and the first groove is 0.2mm~2mm.

[0011] In an optional embodiment, a fourth groove is provided on the negative electrode sheet; the opening area of ​​all the fourth grooves is 5% to 40% of the total area of ​​the negative electrode sheet; and / or the depth of the fourth groove is 0.3 to 1 times the thickness of the negative electrode sheet; and / or the negative electrode sheet has a fifth edge and a seventh edge arranged opposite to each other along the width direction, and a sixth edge and an eighth edge arranged opposite to each other along the length direction; along the width direction, the minimum distance W5 between the fifth edge and the fourth groove is 0.2 mm to 2 mm, and the minimum distance W7 between the seventh edge and the fourth groove is 0.2 mm to 2 mm; along the length direction, the minimum distance W6 between the sixth edge and the fourth groove is 0.2 mm to 2 mm, and the minimum distance W8 between the eighth edge and the fourth groove is 0.2 mm to 2 mm.

[0012] In an optional embodiment, the opening diameter D1 of the first groove is 50μm~300μm, and the opening diameter D2 of the second groove is 50μm~300μm; and / or, along the length direction of the first positive electrode sheet, the spacing L1 between any two adjacent first grooves is 100μm~3mm; along the width direction of the first positive electrode sheet, the spacing L2 between any two adjacent first grooves is 100μm~3mm; and / or, along the length direction of the second positive electrode sheet, the spacing L3 between any two adjacent second grooves is 100μm~3mm; along the width direction of the second positive electrode sheet, the spacing L4 between any two adjacent second grooves is 100μm~3mm; and / or, the shape of the first groove is circular, elliptical or polygonal, and the shape of the second groove is circular, elliptical or polygonal.

[0013] In a second aspect, the present invention further provides a battery, comprising: the above-mentioned battery cell.

[0014] The technical solution of this application has the following advantages:

[0015] The first groove and the second groove are respectively provided in the first area of ​​the first positive electrode sheet and the second positive electrode sheet, which reduces the active material loading in the first area of ​​the first positive electrode sheet and the second positive electrode sheet, thereby reducing the unit area capacity of the area, and can improve the CB value of the corresponding area, reduce the amount of positive electrode delithiation in the corresponding area, balance the potential difference between the second area and the first area, thereby balancing the expansion of the first area and the second area of ​​the stacked core, and avoiding deformation of the battery cell and lithium deposition at the edges and corners during the cycle; in addition, the provision of the first groove and the second groove increases the porosity of the first area, increases the liquid storage capacity, and also promotes the rapid penetration of the electrolyte into the active layer, thereby improving the kinetic performance of the positive electrode sheet.

[0016] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or explained through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 A three-dimensional diagram of a battery cell according to an embodiment of the present invention;

[0019] Figure 2 for Figure 1 A top view of the positive electrode sheet shown;

[0020] Figure 3 for Figure 1 A top view of the second positive electrode sheet shown;

[0021] Figure 4 for Figure 1 A top view of the first positive electrode sheet shown;

[0022] Figure 5 for Figure 4 The structural diagram of the upper right corner of the first positive electrode sheet shown;

[0023] Figure 6 for Figure 1 A cross-sectional view of the second positive electrode sheet shown;

[0024] Figure 7 for Figure 1 A cross-sectional view of the first positive electrode sheet shown;

[0025] Figure 8 for Figure 1 A top view of the negative electrode sheet is shown.

[0026] Description of reference numerals:

[0027] 1. Positive electrode sheet; 101. First positive electrode sheet; 1011. First current collector; 1012. First active material layer; 1013. First groove; 102. Second positive electrode sheet; 1021. Second current collector; 1022. Second active material layer; 1023. Second groove; 103. First region; 104. Second region; 106. First edge; 107. Second edge; 108. Third edge; 109. Fourth edge;

[0028] 2. Diaphragm;

[0029] 3. Negative electrode sheet; 301. Fifth edge; 302. Sixth edge; 303. Seventh edge; 304. Eighth edge. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying 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 making creative efforts shall fall within the scope of protection of the present invention.

[0031] The following combination Figures 1 to 8 , describing embodiments of the present invention.

[0032] According to an embodiment of the present invention, on the one hand, a battery cell is provided, comprising N layers of battery cell units stacked along the thickness direction thereof, each layer of battery cell units comprising a stacked positive electrode sheet 1, a separator 2 and a negative electrode sheet 3, the surface of the positive electrode sheet 1 having a first area 103 and a second area 104, the first area 103 being arranged around the second area 104; in the thickness direction of the battery cell, the N layers of battery cell units are sequentially the first layer of battery cell units, the second layer of battery cell units, ..., the N-1 layer of battery cell units, and the N layer of battery cell units, and the positive electrode sheets 1 of the first layer of battery cell units and the N layer of battery cell units are single-sided. The first positive electrode sheet 101 is provided with a positive electrode active material layer, and the positive electrode sheet 1 of the second layer of battery cell units to the N-1 layer of battery cell units is a second positive electrode sheet 102 with a positive electrode active material layer on both sides; a first groove 1013 is provided on the positive electrode active material layer in the first area 103 of the first positive electrode sheet 101, and a second groove 1023 is provided on the positive electrode active material layer in the first area 103 of the second positive electrode sheet 102; the porosity k1 of the positive electrode active material layer in the first area 103 is 1.05 to 1.5 times the porosity k2 of the positive electrode active material layer in the second area 104.

[0033] In the battery cell of this embodiment, a second groove 1023 is provided in the positive electrode active material layer at the first region 103 of the second positive electrode sheet 102. The second groove 1023 reduces the active material loading in the first region 103 of the second positive electrode sheet 102, which is equivalent to reducing the surface density of the first region 103 of the second positive electrode sheet 102, thereby reducing the unit area capacity of the region, and can increase the CB value of the corresponding region, reduce the amount of positive electrode delithiation in the corresponding region, balance the potential difference between the second region 104 and the first region 103, thereby balancing the expansion of the first region 104 and the second region 104 of the stacked core, and solving the problems of deformation of the battery cell and lithium deposition at the edges and corners during the cycle.

[0034] Furthermore, the first groove 1013 and the second groove 1023 are filled with electrolyte, and some lithium ions in the electrolyte can be transmitted to the current collector of the positive electrode sheet 1 through the inner walls of the first groove 1013 and the second groove 1023, thereby reducing the transmission distance of some lithium ions, improving the dynamic performance of the electrode sheet, and further reducing the risk of lithium plating at the edge of the stacked battery.

[0035] The laminated battery will consume electrolyte after long-term use, and the electrolyte at the edge of the battery is consumed first. Compared with the second area 104 of the positive electrode sheet 1, a groove is set in the first area 103 of the positive electrode sheet 1, and the porosity of the first area 103 is 1.05 to 1.5 times that of the second area 104, thereby increasing the porosity and liquid storage capacity of the first area 103 of the positive electrode sheet 1. The electrolyte stored in the groove has a certain depth and is therefore consumed more slowly. That is, the groove can provide electrolyte to the edge of the battery in the middle and late stages of the battery life, ensuring the amount of electrolyte in the subsequent later stages, thereby effectively reducing the risk of lithium plating at the edge of the battery due to insufficient electrolyte.

[0036] It should be noted that cell expansion primarily refers to the expansion of the negative electrode sheet 3; the expansion of the positive electrode is essentially negligible. The negative electrode sheet 3 will expand if lithium is inserted, and if too much lithium is inserted, lithium deposition will occur without space. The CB value refers to the ratio of the surface capacity of the negative electrode sheet 3 to the surface capacity of the positive electrode sheet 1, or in other words, the ratio of the negative electrode's lithium insertion space to the positive electrode's lithium removal capacity.

[0037] Furthermore, the thickness of the current collector of the first positive electrode sheet 101 is thicker than that of the current collector of the second positive electrode sheet 102, so that the flow area of ​​the first positive electrode sheet 101 is larger. Compared with the second positive electrode sheet 102, the corresponding negative electrode sheet 3 is more prone to lithium deposition, especially around the edges of the stack. In terms of electrolyte, since the expansion around the stack is greater than that of the second area 104, it is easy to cause the electrolyte to be squeezed around the stack, which can easily cause local liquid shortage around the edges, lithium ion transmission bridge breaking, and cause purple spots and lithium deposition.

[0038] Therefore, a first groove 1013 is provided at the edge of the first positive electrode sheet 101, which reduces the active material loading in the first region 103 of the first positive electrode sheet 101, thereby reducing the unit area capacity of the region, and can increase the CB value of the corresponding region, reduce the amount of positive electrode delithiation in the corresponding region, balance the potential difference between the second region 104 and the first region 103, thereby balancing the expansion of the first region 103 and the second region 104 of the stacked core, and avoiding deformation of the battery cell and lithium deposition at the edges and corners during the cycle.

[0039] Furthermore, in each positive electrode sheet 1, the porosity k1 of the positive electrode active material layer in the first region 103 is 1.05 to 1.5 times the porosity k2 of the positive electrode active material layer in the second region 104. That is, the porosities of the positive electrode active material layers of the first positive electrode sheet 101 and the second positive electrode sheet 102 both satisfy the above relationship.

[0040] 47, 1.48, 1.49, 1.5 or is within a range consisting of any two of the above values.

[0041] Furthermore, k1 is 20%-35%, and k2 is 15%-25%.

[0042] Illustratively, k1 is 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35% or in the range consisting of any two of the above values, and k2 is 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or in the range consisting of any two of the above values.

[0043] It should be noted that the porosity of the positive electrode active material layer is tested by the electrolyte infiltration method. The electrolyte infiltration method calculates the porosity by the weight change before and after infiltration of the electrolyte. Specifically, the battery is weighed before infiltration of the electrolyte and the battery is weighed after infiltration of the electrolyte. The pore volume is calculated based on the liquid density. The ratio of the pore volume to the volume of the positive electrode active material layer is the porosity of the positive electrode active material layer. Among them, the volume of the positive electrode active material layer can be calculated based on the density and mass of the positive electrode active material layer.

[0044] In one embodiment, the weight loss rate of the first region 103 of the positive electrode sheet 1 is e, and the silicon doping content of the negative electrode sheet 3 is f, where f and e satisfy the following: f = (4-20)e, where e = 0.5%-5% and f = 2%-80%. The higher the silicon doping content of the negative electrode sheet 3, the more prone to lithium deposition, the greater the probability of deformation, and the more severe the expansion of the battery cell. The deeper or larger the groove area of ​​the positive electrode sheet 1, the greater the weight loss rate, and the greater the capacity loss. The lower the weight loss rate, the less significant improvement in lithium deposition.

[0045] Therefore, by limiting the relationship between the weight loss rate e of the positive electrode sheet 1 and the silicon doping amount f of the negative electrode sheet 3, the migration of lithium ions is facilitated, the CB value is improved, the potential difference between the second region 104 and the first region 103 is balanced, the problem of lithium plating is solved, and the SOC (state of charge) distribution is improved.

[0046] Exemplarily, f / e is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or within the range of any two of the above values; the weight loss rate e of the first region 103 of the positive electrode sheet 1 is 0.5%, 1%, 2%, 3%, 4%, 5% or within the range of any two of the above values, and the silicon doping amount f of the negative electrode sheet 3 is 2%, 4%, 8%, 10%, 12%, 16%, 20%, 30%, 40%, 50%, 60%, 80% or within the range of any two of the above values.

[0047] It should be noted that the test method for the weight loss rate of the first area 103 of the positive electrode sheet 1 is: take a positive electrode sheet 1 of the battery, first wash off the electrolyte on the positive electrode sheet 1 and then dry it, then cut the positive electrode sheet with a groove and the positive electrode sheet without a groove, the length and width of the cut positive electrode sheet are both 1mm×1mm, weigh the positive electrode sheet with a groove and the weight is W1, weigh the positive electrode sheet without a groove and the weight is W2, e1=(W2-W1) / W2; then cut the positive electrode sheets at different positions multiple times to obtain e2, e3,..., eN, take the average of e1, e2, e3,..., eN, and obtain e=(e1+e2+e3+...+eN) / N.

[0048] In one embodiment, in the first positive electrode sheet 101, the opening area S1 of all the first grooves 1013 is 20% to 60% of the area S2 of the positive electrode active material layer in the first region 103, and the volume V1 of all the first grooves 1013 is 10% to 50% of the volume V2 of the positive electrode active material layer in the first region 103. Providing the first grooves 1013 in the first region 103 of the first positive electrode sheet 101 can increase the depth and density of the first grooves 1013, thereby increasing the ratio of the opening area to the volume of the first grooves 1013, further improving lithium deposition at edges and corners.

[0049] Exemplarily, S1 / S2 is 20%, 30%, 40%, 50%, 60% or within the range of any two of the above values; V1 / V2 is 10%, 20%, 30%, 40%, 50% or within the range of any two of the above values.

[0050] It should be noted that the opening area of ​​all the first grooves 1013 is the product of the number of the first grooves 1013 and the opening area of ​​a single first groove 1013, the opening area of ​​a single first groove 1013 is the area enclosed by the projected outer contour of the first groove 1013 on the current collector of the first positive electrode sheet 101, and the volume of all the first grooves 1013 is the product of the number of the first grooves 1013 and the volume of a single first groove 1013. For example, when the shape of the first groove 1013 is cylindrical, the volume of a single first groove 1013 is the product of the opening area of ​​the first groove 1013 and the depth of the first groove 1013; when the shape of the first groove 1013 is conical, the volume of a single first groove 1013 is 1 / 3 of the product of the opening area of ​​the first groove 1013 and the depth of the first groove 1013.

[0051] It is worth noting that the area of ​​the positive electrode active material layer in the first region 103 refers to the area enclosed by the outer contour and the inner contour of the positive electrode active material layer in the first region 103, and the volume of the positive electrode active material layer in the first region 103 refers to the product of the area of ​​the positive electrode active material layer in the first region 103 and the thickness of the positive electrode active material layer in the first region.

[0052] In one embodiment, in the first positive electrode sheet 101, third grooves are provided on the positive electrode active material layer of the second region 104, and the sum of the opening areas S3 of all the third grooves and the opening areas S1 of all the first grooves 1013 is 30% to 70% of the area S4 of the first positive electrode sheet 101, and the sum of the volumes V3 of all the third grooves and the volumes V1 of all the first grooves 1013 is 10% to 40% of the volume V4 of the first positive electrode sheet 101.

[0053] Furthermore, when grooves are provided in both the first region 103 and the second region 104 of the first positive electrode sheet 101, the depth and density of the grooves need to be reduced to avoid excessive capacity loss and severe shortage of positive electrode lithium ions, thereby causing purple spots due to insufficient lithium insertion.

[0054] Therefore, by keeping (S3+S1) / S4 and (V3+V1) / V4 within the above ranges, the battery capacity is guaranteed, thereby avoiding the phenomenon of insufficient lithium insertion purple spots caused by severe shortage of lithium ions in the positive electrode.

[0055] Exemplarily, (S3+S1) / S4 is 30%, 40%, 50%, 60%, 70% or within the range of any two of the above values, and (V3+V1) / V4 is 10%, 20%, 30%, 40% or within the range of any two of the above values.

[0056] It should be noted that the calculation method of the opening area and volume of the third groove is the same as that of the first opening area and volume, and will not be repeated in detail here. The area of ​​the first positive electrode sheet 101 refers to the area enclosed by the outer contour of the first positive electrode sheet 101, and the volume of the first positive electrode sheet 101 refers to the product of the area and thickness of the first positive electrode sheet 101. For example, when the first positive electrode sheet 101 is rectangular, the product of the length and width of the first positive electrode sheet 101. The volume of the first positive electrode sheet 101 refers to the product of the length, width and thickness of the first positive electrode sheet 101. In one embodiment, in the second positive electrode sheet 102, the opening area S6 of all the second grooves 1023 is 30% to 50% of the area S7 of the positive electrode active material layer in the first region 103, and the volume V6 of all the second grooves 1023 is 20% to 40% of the volume V7 of the positive electrode active material layer in the first region 103. If the number of the second grooves 1023 is too small, the lithium deposition improvement effect is not obvious; if the number of the second grooves 1023 is too large, the pore formation capacity loss is too large.

[0057] Therefore, by controlling S6 / S7 and V6 / V7 within the above ranges, not only the lithium plating effect is significantly improved, but also excessive capacity damage is avoided.

[0058] Exemplarily, S6 / S7 is 30%, 35%, 40%, 45%, 50% or within the range formed by any two of the above values, and V6 / V7 is 20%, 25%, 30%, 35%, 40% or within the range formed by any two of the above values.

[0059] It should be noted that the calculation method of the opening area and volume of the second groove 1023 is the same as that of the first opening area and volume, and the calculation directions of S7 and S2 are also opposite, which will not be described in detail here.

[0060] In one embodiment, the first positive electrode sheet 101 includes a first current collector 1011 and a first active material layer 1012 arranged on one surface of the first current collector 1011, and the second positive electrode sheet 102 includes a second current collector 1021 and a second active material layer 1022 arranged on both surfaces of the second current collector 1021; the coating surface density ρ1 of the first active material layer 1012 is 92% to 98% of the coating surface density ρ2 of the second active material layer 1022.

[0061] Since the flow area of ​​the first positive electrode sheet 101 is larger than that of the second positive electrode sheet 102, lithium deposition is more likely to occur. By reducing the coating surface density of the first positive electrode sheet 101, the lithium deposition phenomenon can be improved, thereby improving the safety, cycle life and performance of the battery.

[0062] Exemplarily, ρ1 / ρ2 is 92%, 93%, 94%, 95%, 96%, 97%, 98% or within the range formed by any two of the above values.

[0063] Furthermore, ρ1 is 13 mg / cm 2 -29mg / cm 2 , ρ2 is 14-30 mg / cm 2 .

[0064] For example, ρ1 is 13 mg / cm 2 , 14mg / cm 2 、15mg / cm 2 、16mg / cm 2 , 17mg / cm 2 、18mg / cm 2 、19mg / cm 2 , 20mg / cm 2 , 21mg / cm 2 , 22mg / cm 2 , 23mg / cm 2 , 24mg / cm 2 , 25mg / cm 2 , 26mg / cm 2 , 27mg / cm 2 , 28mg / cm 2 , 29mg / cm 2 In the range of any two values ​​above, ρ2 is 14 mg / cm 2 、15mg / cm 2 、16mg / cm 2 , 17mg / cm 2 、18mg / cm 2 、19mg / cm 2 , 20mg / cm2 , 21mg / cm 2 , 22mg / cm 2 , 23mg / cm 2 , 24mg / cm 2 , 25mg / cm 2 , 26mg / cm 2 , 27mg / cm 2 , 28mg / cm 2 , 29mg / cm 2 、30mg / cm 2 is within the range formed by any two of the above values.

[0065] It should be noted that the coating area density of the first active material layer 1012 refers to the ratio of the mass to the area of ​​the first active material layer 1012 .

[0066] In one embodiment, the porosity of the positive electrode active material layer in the second region 104 of the first positive electrode sheet 101 is a, and the porosity of the positive electrode active material layer in the second region 104 of the second positive electrode sheet 102 is b, where a and b satisfy the following: a = (85% to 95%) b. Because the first positive electrode sheet 101 is more compacted than the second positive electrode sheet 102, the increased compaction reduces the porosity, thereby suppressing the capacity of the first positive electrode sheet 101, reducing the amount of positive electrode lithium desorption, and alleviating single-sided lithium plating.

[0067] Exemplarily, a / b is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or within the range formed by any two of the above values.

[0068] In one embodiment, in the first positive electrode sheet 101 or the second positive electrode sheet 102 , the CB value of the first region 103 is 1.01% to 1.1% of the CB value of the second region 104 ; in the first positive electrode sheet 101 or the second positive electrode sheet 102 , the delithiation amount of the first region 103 is 50% to 90% of the delithiation amount of the second region 104 .

[0069] Furthermore, the setting of the groove causes the loss of a portion of the active material layer, the CB value of the first region 103 is higher than the CB value of the second region 104, and the amount of lithium depletion of the positive electrode in the first region 103 is lower than the amount of lithium depletion of the positive electrode in the second region 104, which can improve local lithium deposition and thereby improve the safety, cycle life and performance of the battery.

[0070] Exemplarily, the CB value of the first region 103 is 1.02% to 1.06% of the CB value of the second region 104, the CB value of the first region 103 is 1.02%, 1.03%, 1.04%, 1.05%, 1.06% of the CB value of the second region 104, or is within the range formed by any two of the above values, and the delithiation amount of the first region 103 is 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 75%, 78%, 80%, 85%, 90% of the delithiation amount of the second region 104, or is within the range formed by any two of the above values.

[0071] In one embodiment, Figures 6 and 7 As shown, the depth of the first groove 1013 is h1, and the depth of the second groove 1023 is h2; h1 and h2 satisfy: h1>h2, and h1-h2=1-20μm. The current collector of the first positive electrode sheet 101 is thicker, and its flow area is larger than that of the second positive electrode sheet 102, and its overall potential is higher than that of the second positive electrode sheet 102. The positive electrode sheet 1 delithiation rate is faster, and the negative electrode sheet 3 is more prone to lithium deposition. Therefore, the depth of the groove of the first positive electrode sheet 101 is greater than the depth of the groove of the second positive electrode sheet 102 to better improve the lithium deposition effect.

[0072] Furthermore, the total thickness of the first positive electrode sheet 101 is H1, and H1 and h1 satisfy the following relationship: h1 = (0.2-1)H1. When h1 is less than H1, it indicates that the groove of the first positive electrode sheet 101 has not penetrated the current collector. When h1 = H1, it indicates that the groove of the first positive electrode sheet 101 has penetrated the current collector. When the current collector is penetrated, the flow area of ​​the current collector is smaller, thereby improving the lithium deposition effect.

[0073] Illustratively, h1 / H1 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within a range consisting of any two of the above values.

[0074] Furthermore, the total thickness of the second positive electrode sheet 102 is H2, and H2 and h2 satisfy: h2 = (0.2-0.3)H2. The second positive electrode sheet 102 only has a potential difference between the first region 103 and the second region 104. This only requires increasing the CB value; there is no need to penetrate the current collector. Therefore, h2 = (0.2-0.3)H2.

[0075] Illustratively, h2 / H2 is 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, or within a range consisting of any two of the above values.

[0076] It should be noted that, on the second positive electrode sheet 102 , the grooves may penetrate the current collector, which may have a better effect, but will cause excessive capacity loss, resulting in a reduction in energy density.

[0077] In one embodiment, the first positive electrode sheet 101 has a first edge 106 and a third edge 108 disposed opposite each other along the width direction, and a second edge 107 and a fourth edge 109 disposed opposite each other along the length direction. Along the width direction, the minimum distance W1 between the first edge 106 and the first groove 1013 is 0.2 mm to 2 mm, and the minimum distance W3 between the third edge 108 and the first groove 1013 is 0.2 mm to 2 mm. Along the length direction, the minimum distance W2 between the second edge 107 and the first groove 1013 is 0.2 mm to 2 mm, and the minimum distance W4 between the fourth edge 109 and the first groove 1013 is 0.2 mm to 2 mm.

[0078] Furthermore, W1, W2, W3, and W4 should be neither too large nor too small. If W1, W2, W3, and W4 are too large, they will not improve the deformation of the battery cell and lithium deposition at the edges and corners. If W1, W2, W3, and W4 are too small, when the positive electrode sheet 1 is die-cut after the groove is set, the cutting area in the area where the groove is located will cause burrs and powder falling of the electrode sheet, thereby causing safety problems.

[0079] Therefore, when W1, W2, W3, and W4 are within the above range, not only can the deformation of the battery cell and lithium deposition at the edges and corners be improved, but also burrs and powder loss of the electrode sheets can be avoided in the area where the grooves are located when die-cutting the stacked sheets after hole formation, thereby improving the safety of the battery.

[0080] Preferably, W1 is 0.5 mm to 1 mm, W2 is 0.5 mm to 1 mm, W3 is 0.5 mm to 1 mm, and W4 is 0.5 mm to 1 mm.

[0081] Illustratively, W1 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or is within the range formed by any two of the above values; W2 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or is within the range formed by any two of the above values; W3 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or is within the range formed by any two of the above values; W4 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or is within the range formed by any two of the above values.

[0082] In one embodiment, a fourth groove is provided on the negative electrode sheet 3. The provision of the fourth groove can reduce the tortuosity of lithium insertion, reduce the lithium insertion impedance, improve the negative electrode lithium insertion dynamics, and also increase the liquid storage capacity. Providing grooves on both the positive electrode sheet 1 and the negative electrode sheet 3 can achieve even greater improvement.

[0083] Specifically, grooves are provided in both the first region 103 and the second region 104 of the negative electrode sheet 3 .

[0084] It is understandable that, in another embodiment, only the first region 103 of the negative electrode sheet 3 is provided with the groove.

[0085] Furthermore, the opening area S8 of all fourth grooves is 5% to 40% of the total area S9 of the negative electrode sheet 3; and the depth of the fourth groove is 0.3 to 1 times the thickness of the negative electrode sheet 3. The opening area and depth of the fourth grooves should be neither too large nor too small. If the opening area and depth of the fourth grooves are too large, the active material on the negative electrode sheet 3 is reduced, reducing the battery capacity. If the opening area and depth of the fourth grooves are too small, the edge lithium deposition phenomenon cannot be improved.

[0086] Therefore, controlling the depth of S8 / S9 and the fourth groove within the above range can not only ensure the capacity of the battery but also improve the lithium plating phenomenon.

[0087] Exemplarily, S8 / S9 is 5%, 10%, 20%, 30%, 40% or within the range of any two of the above values, and the depth of the groove on the negative electrode sheet 3 is 0.3 times, 0.4 times, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times the thickness of the negative electrode sheet 3 or within the range of any two of the above values.

[0088] It should be noted that the calculation method of the opening area and volume of the fourth groove is the same as that of the first opening area and volume, and will not be described in detail here.

[0089] In one embodiment, the negative electrode sheet 3 has a fifth edge 301 and a seventh edge 303 disposed opposite each other along the width direction, and a sixth edge 302 and an eighth edge 304 disposed opposite each other along the length direction. Along the width direction, the minimum distance W5 between the fifth edge 301 and the fourth groove is 0.2 mm to 2 mm, and the minimum distance W7 between the seventh edge 303 and the fourth groove is 0.2 mm to 2 mm. Along the length direction, the minimum distance W6 between the sixth edge 302 and the fourth groove is 0.2 mm to 2 mm, and the minimum distance W8 between the eighth edge 304 and the fourth groove is 0.2 mm to 2 mm.

[0090] Furthermore, W5, W6, W7, and W8 should be neither too large nor too small. If W5, W6, W7, and W8 are too large, they will not improve the deformation of the battery cell and lithium deposition at the edges and corners; if W5, W6, W7, and W8 are too small, when the negative electrode sheet 3 is die-cut after the groove is set, the cutting area will cause burrs and powder falling in the groove area, which will cause safety problems.

[0091] Therefore, controlling W5, W6, W7, and W8 within the above range can not only improve the deformation of the battery cell and lithium plating at the edges and corners, but also avoid burrs and powder loss in the groove area of ​​the electrode when die-cutting the stacked sheets after hole formation, thereby improving the safety of the battery.

[0092] Preferably, W5 is 0.5 mm to 1 mm, W6 is 0.5 mm to 1 mm, W7 is 0.5 mm to 1 mm, and W8 is 0.5 mm to 1 mm.

[0093] Illustratively, W5 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm or is within the range formed by any two of the above values, W6 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm or is within the range formed by any two of the above values, W7 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm or is within the range formed by any two of the above values, and W8 is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm or is within the range formed by any two of the above values.

[0094] In one embodiment, the opening diameter D1 of the first groove 1013 is 50 μm to 300 μm, and the opening diameter D2 of the second groove 1023 is 50 μm to 300 μm; along the length direction of the first positive electrode sheet 101, the spacing L1 between any two adjacent first grooves 1013 is 100 μm to 3 mm; along the width direction of the first positive electrode sheet 101, the spacing L2 between any two adjacent first grooves 1013 is 100 μm to 3 mm; along the length direction of the second positive electrode sheet 102, the spacing L3 between any two adjacent second grooves 1023 is 100 μm to 3 mm; along the width direction of the second positive electrode sheet 102, the spacing L4 between any two adjacent second grooves 1023 is 100 μm to 3 mm;

[0095] Furthermore, D1, D2, L1, L2, L3, and L4 should be neither too large nor too small. If D1, D2, L1, L2, L3, and L4 are too large, active materials will be lost; if D1, D2, L1, L2, L3, and L4 are too small, processing will be inconvenient and difficult.

[0096] Therefore, by limiting the opening diameter of the grooves and the spacing between the grooves, the loss of active material caused by an excessively large opening diameter and an excessively small groove spacing can be avoided, and processing is also facilitated and the processing difficulty is reduced.

[0097] For example, D1 is 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm, 300 μm, or a range between any two of the above values. and D2 is 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300μm or in the range formed by any two of the above values.

[0098] Illustratively, L1 is 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1 mm, 2 mm, 3 mm, or within a range formed by any two of the above values. L2 is 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1mm, 2mm, 3mm or within the range formed by any two of the above values; L3 is 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1mm, 2mm, 3mm or within the range formed by any two of the above values; L4 is 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1mm, 2mm, 3mm or within the range formed by any two of the above values.

[0099] It should be noted that the spacing between the grooves can reflect the density of the grooves.

[0100] In one embodiment, the first groove 1013 is circular, elliptical, or polygonal in shape, and the second groove 1023 is circular, elliptical, or polygonal in shape.

[0101] Furthermore, the second area 104 is in the shape of a rectangle, and the second area 104 has a first side and a third side arranged opposite to each other along the width direction, and the second area 104 has a second side and a fourth side arranged opposite to each other along the length direction. Along the width direction, the distance between the first side and the first edge 106 is the first distance, and the distance between the third side and the third edge 108 is the third distance. Along the length direction, the distance between the second side and the second edge 107 is the second distance, and the distance between the fourth side and the fourth edge 109 is the fourth distance. The first distance, the second distance, the third distance and the fourth distance are 10 mm, etc.

[0102] In one embodiment, the first positive electrode sheet 101 includes a first current collector 1011 and a first active material layer 1012 disposed on one surface of the first current collector 1011, and the second positive electrode sheet 102 includes a second current collector 1021 and a second active material layer 1022 disposed on both surfaces of the second current collector 1021. The thickness T4 of the first current collector 1011 is 12 μm to 25 μm, and the thickness T3 of the second current collector 1021 is 8 μm to 10 μm.

[0103] Furthermore, the first positive electrode sheet 101 is a single-sided sheet, that is, the first active material layer 1012 is provided on one surface of the first positive electrode sheet 101 and the first active material layer 1012 is not provided on the other surface. If the thickness of the first current collector 1011 is too thin, it cannot meet the process. During the process, the thinner first positive electrode sheet 101 will curl up. Therefore, the thickness of the first current collector 1011 is 12μm~25μm. At this time, the thickness of the first current collector 1011 meets the process.

[0104] Preferably, the thickness of the first positive electrode sheet 101 is 15 μm to 20 μm, and the thickness of the first positive electrode sheet 101 is 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or within a range formed by any two of the above values.

[0105] Furthermore, the second positive electrode sheet 102 is a double-sided sheet, which can meet the manufacturing process. The thickness of the second current collector 1021 does not need to be too thick, and is generally 8 μm to 10 μm.

[0106] Preferably, the thickness of the second current collector 1021 is 8 μm, 9 μm, 10 μm, or within a range formed by any two of the above values.

[0107] In one embodiment, the thickness T1 of the first active material layer 1012 , the total thickness T2 of the second positive electrode sheet 102 , and the thickness T3 of the second current collector 1021 satisfy: T1≤(T2−T3) / 2.

[0108] Furthermore, since the flow area of ​​the first positive electrode sheet 101 is larger than that of the second positive electrode sheet 102, lithium deposition is more likely to occur. By increasing the compaction of the first positive electrode sheet 101, the lithium deposition phenomenon can be improved, thereby improving the safety, cycle life and performance of the battery.

[0109] In one embodiment, the difference between the potential of the first region 103 of the first positive electrode sheet 101 and the overall potential of the second positive electrode sheet 102 is 0 to 0.1 V; the difference between the potential of the first region 103 of the first positive electrode sheet 101 and the potential of the second region 104 of the first positive electrode sheet 101 is 0 to 0.05 V; the difference between the potential of the first region 103 of the second positive electrode sheet 102 and the potential of the second region 104 of the second positive electrode sheet 102 is 0 to 0.05 V.

[0110] Furthermore, the current collector of the first positive electrode sheet 101 is relatively thick, and the flow area of ​​the first positive electrode sheet 101 is relatively large, so the potential of the first positive electrode sheet 101 is higher than that of the second positive electrode sheet 102. The grooves in the first positive electrode sheet 101 can increase the CB value of the first positive electrode sheet 101, thereby reducing the potential difference between the two. The high current density in the first region 103 of the positive electrode sheet 1 leads to a relatively high edge potential, causing localized uneven lithium insertion, which in turn leads to core deformation and localized lithium deposition. Therefore, providing grooves at the edge of the positive electrode sheet 1 to reduce the potential difference between the second region 104 and the first region 103 can improve core deformation and localized lithium deposition.

[0111] Preferably, the difference between the potential of the first region 103 of the first positive electrode sheet 101 and the overall potential of the second positive electrode sheet 102 is 0, 0.01V, 0.02V, 0.03V, 0.04V, 0.05V, 0.06V, 0.07V, 0.08V, 0.09V, 0.1V, or within a range of any two of the above values. The potential difference between the first region 103 of the second positive electrode sheet 102 and the second region 104 of the second positive electrode sheet 102 is 0, 0.01V, 0.02V, 0.03V, 0.04V, 0.05V, or within the range formed by any two of the above values. The potential difference between the first region 103 of the second positive electrode sheet 102 and the second region 104 of the second positive electrode sheet 102 is 0, 0.01V, 0.02V, 0.03V, 0.04V, 0.05V, or within the range formed by any two of the above values.

[0112] It should be noted that the overall potential of the second positive electrode sheet 102 refers to the sum of the potential of the first region 103 of the second positive electrode sheet 102 and the potential of the second region 104 of the second positive electrode sheet 102 .

[0113] Furthermore, the total thickness of the first positive electrode sheet 101 is H1, and H1 and h1 satisfy the following relationship: h1 = (0.2-1)H1. When h1 is less than H1, it indicates that the groove of the first positive electrode sheet 101 has not penetrated the current collector. When h1 = H1, it indicates that the groove of the first positive electrode sheet 101 has penetrated the current collector. When the current collector is penetrated, the flow area of ​​the current collector is smaller, thereby improving the lithium deposition effect.

[0114] In one embodiment, the negative electrode sheet 3 includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a silicon-based material. The silicon-based material includes at least one of elemental silicon, silicon-carbon material, silicon-oxygen material and silicon alloy. Based on the mass of the negative electrode active material, the mass content of the silicon-based material is 2%-80%.

[0115] In one embodiment, the silicon-carbon material includes a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon layer located on the surface of the porous carbon matrix. The specific surface area of ​​the silicon-carbon material is 0.5 m 2 / g~10m 2 / g; the particle size Dv50 of the silicon-carbon material is 6 μm to 20 μm; the silicon content in the silicon-carbon material is 30% to 75%; and the sphericity of the silicon-carbon material is 0.6 to 1.

[0116] Preferably, the specific surface area of ​​the silicon-carbon material is 0.5 m 2 / g、1m 2 / g, 2m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g or within the range formed by any two of the above values, the particle size Dv50 of the silicon-carbon material is 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or within the range formed by any two of the above values, and the silicon content in the silicon-carbon material is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or within the range formed by any two of the above values.

[0117] It should be noted that Dv50 refers to the particle size value when the cumulative distribution percentage of silicon-carbon material particles reaches 50%.

[0118] According to another aspect of an embodiment of the present invention, a battery is provided, including the above-mentioned battery cell.

[0119] Furthermore, the battery also includes an electrolyte and an aluminum-plastic film. The battery cell is encapsulated by the aluminum-plastic film. During the charging and discharging process of the battery, lithium ions are embedded and released back and forth between the positive electrode sheet 1 and the negative electrode sheet 3. The electrolyte plays a role in conducting ions between the positive electrode sheet 1 and the negative electrode sheet 3. The diaphragm 2 is arranged between the positive electrode sheet 1 and the negative electrode sheet 3, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing lithium ions to pass through.

[0120] The present application is further described in detail below with reference to specific examples, which should not be construed as limiting the scope of protection claimed in the present application. In all examples and comparative examples of the present application, the unit wt% represents the percentage by mass.

[0121] Example 1

[0122] The preparation method of the battery of this embodiment includes the following steps:

[0123] 1. Preparation of double-sided positive electrode sheet 1

[0124] Lithium cobalt oxide, a conductive agent (a mixture of conductive carbon black and carbon nanotubes), and PVDF were placed in NMP at a mass ratio of 97.60:1.35:1.05 and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry was evenly coated on the front and back sides of the aluminum foil in a zebra coating manner, with a coating surface density of 0.01744 g / cm 2 ; The thickness of the aluminum foil is 9μm, and it is dried and rolled (rolling compaction is 4.13) in sequence to produce a positive electrode sheet 1 with a double-sided thickness of 96μm; the cut positive electrode sheet 1 is used to set grooves around the electrode sheet using a laser processor. The shape of the groove is circular, the depth of the groove is 15μm, and the groove spacing is 300μm.

[0125] 2. Preparation of single-sided positive electrode sheet 1

[0126] Lithium cobalt oxide, a conductive agent (a mixture of conductive carbon black and carbon nanotubes), and PVDF were placed in NMP at a mass ratio of 97.60:1.35:1.05 and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry was evenly coated on one side of an aluminum foil in a zebra coating manner, with a coating surface density of 0.01714 g / cm 2 The thickness of the aluminum foil is 15 μm, and it is dried, rolled (roller compaction is 4.23 g / cm 3 ) was processed to produce a positive electrode sheet 1 with a single-sided thickness of 63μm; the cut positive electrode sheet 1 was used to set grooves on the entire surface of the single-sided sheet using a laser processor. The shape of the grooves was circular, the depth of the grooves was 30μm, and the groove spacing was 500μm.

[0127] 3. Preparation of negative electrode sheet 3

[0128] Silicon-containing artificial graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are placed in deionized water in a mass ratio of 97.2:0.5:1.3:1, wherein the silicon content in the silicon-containing artificial graphite is 10%; the above slurry is stirred evenly to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector, and the negative electrode slurry is sequentially dried and rolled, cleaned, and cut; the cut negative electrode sheet 3 is laser grooved, and grooves are provided on the entire surface of the negative electrode sheet 3. Here, the grooves are in the shape of long strips, the spacing between adjacent grooves is set to 1.5 mm, and the groove depth is 18 μm; the laser-treated negative electrode sheet 3 is cleaned and sheeted to obtain a negative electrode sheet 3;

[0129] 4. Preparation of batteries

[0130] The separator 2 is composed of a 9μm-thick substrate, ceramic, and a coated separator 2. The electrolyte comprises lithium salt LiPF6 and a solvent, wherein the solvent comprises ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), with a molar ratio of DEC:EC:EMC = 1:1:1. The aforementioned cut positive electrode sheet 1, separator 2, and negative electrode sheet 3 are stacked in sequence to form a laminated cell. The cell is then packaged, injected, formed, and sealed to produce a lithium-ion battery.

[0131] Test Case

[0132] 1. Liquid retention test

[0133] Each battery is filled with liquid according to a certain amount of liquid, for example, the amount of liquid filled in each battery n1 is 8.5g±0.1g. After filling, it is aged, and after aging, it is formed - sorted and sealed twice. The second sealing is to extract the excess electrolyte, and the remaining amount of electrolyte is the liquid retention amount n2; then n2 = weight after second sealing m2 - weight before filling m1.

[0134] 2. Potential test

[0135] The test was conducted using a copper wire three-electrode. Copper wires were inserted at the edge and middle of the stacked core for lithium plating. The standard for lithium plating is generally 20μA current charge / discharge for 2 hours; then 1.5C charge to 4.53V, cut off 0.7C, and 0.05C discharge to 3V for testing, observing the potential at different positions;

[0136] 3. Test the appearance of the battery cell after setting the groove

[0137] Use a 3D profilometer to observe whether the battery cell is deformed.

[0138] 4. Battery capacity test

[0139] The lithium-ion battery was subjected to a cycle test in a test cabinet. The test conditions were 25℃±2℃, and the battery was left to stand for 5 minutes. The battery was charged at 0.5C to 4.35V, then at 1C to 4.58V, and the cycle was cut off at 0.05C. The battery capacity was measured and this process was repeated 800 times.

[0140] It is necessary to observe the disassembly pictures of the battery after 800 cycles to observe whether lithium is deposited on the first positive electrode sheet of the stack and the first area 103 of the stack. The degree of lithium deposition is divided into no lithium deposition, slight lithium deposition, moderate lithium deposition, and severe lithium deposition.

[0141] Table 1 Porosity, weight loss rate, silicon content and performance parameters of the battery

[0142]

[0143] Table 2 Coating area density and performance parameters of the battery

[0144]

[0145]

[0146] It is worth noting that “ / ” in Table 1 indicates non-existence, and the difference in structural parameters between the batteries in Examples 2-1 to 2-5 and Example 1-1 is only that ρ1 is different, and the difference in structural parameters between the batteries in Examples 2-6 and 2-7 and Example 1-1 is that ρ1 and ρ2 are different, and the structural parameters of the batteries in Comparative Example 1 and Comparative Example 2 and Example 1 are different in k1, k2, k1 / k2, e, and f / e. No groove is set in the first area in Comparative Example 1, and grooves are set in the first area in Examples 1-1 to 1-12, Examples 2-1 to 2-7, and Comparative Example 2.

[0147] From Table 1 and Table 2, we can see that:

[0148] It can be seen from Comparative Examples 1 and 2 that setting grooves in the first area can alleviate the deformation of the battery cell and the degree of lithium deposition at the edge, but it will cause a loss in the capacity of the battery; compared with Comparative Example 1-2, Examples 1-1 to 1-12 show that controlling k1 / k2 at 1.05-1.5 can further alleviate the degree of lithium deposition at the edge of the electrode. However, as the number of grooves increases, the weight loss rate will increase, and the battery capacity loss will become greater. Compared with other examples, Example 1-11 can show that when the silicon doping content of the negative electrode is large, although the battery capacity is good, the battery cell will be severely deformed. Therefore, in order to take into account the battery capacity and ensure that the electrode does not suffer from severe deformation and lithium deposition, it is necessary to control f / e within the protection range.

[0149] According to the data of Example 1-1 and Example 2-1 to Example 2-7, it can be seen that by controlling ρ1 / ρ2 within the range of 92% to 98%, the lithium plating phenomenon of the first positive electrode sheet can be improved, thereby improving the safety, cycle life and performance of the battery.

[0150] Although the embodiments of the present invention have been described with reference to 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. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A battery cell, characterized in that: The invention comprises N layers of battery core units stacked in a thickness direction thereof, wherein each layer of the battery core units comprises a stacked positive electrode sheet (1), a separator (2) and a negative electrode sheet (3), wherein the surface of the positive electrode sheet (1) comprises a first region (103) and a second region (104), wherein the first region (103) is arranged around the second region (104); Along the thickness direction of the battery core, the N layers of battery core units are sequentially a first layer of battery core units, a second layer of battery core units, ..., an N-1 layer of battery core units, and an N-1 layer of battery core units; the positive electrode sheets (1) of the first layer of battery core units and the N-1 layer of battery core units are first positive electrode sheets (101) with a positive electrode active material layer provided on one side; and the positive electrode sheets (1) of the second layer of battery core units to the N-1 layer of battery core units are second positive electrode sheets (102) with a positive electrode active material layer provided on both sides; A first groove (1013) is provided on the positive electrode active material layer at the first region (103) of the first positive electrode sheet (101), and a second groove (1023) is provided on the positive electrode active material layer at the first region (103) of the second positive electrode sheet (102); The porosity k1 of the positive electrode active material layer in the first region (103) is 1.05 to 1.5 times the porosity k2 of the positive electrode active material layer in the second region (104).

2. The battery cell according to claim 1, characterized in that The weight loss rate of the first region (103) of the positive electrode sheet (1) is e, the silicon doping amount of the negative electrode sheet (3) is f, and f and e satisfy: f=(4-20)e, wherein e=0.5%-5%, and f=2%-80%.

3. The battery cell according to any one of claims 1 to 2, characterized in that: In the first positive electrode sheet (101), the opening area S1 of all the first grooves (1013) is 20% to 60% of the area S2 of the positive electrode active material layer in the first region (103), and the volume V1 of all the first grooves (1013) is 10% to 50% of the volume V2 of the positive electrode active material layer in the first region (103); And / or, in the first positive electrode sheet (101), a third groove is provided on the positive electrode active material layer of the second region (104), the sum of the opening area S3 of all the third grooves and the opening area S1 of all the first grooves (1013) is 30% to 70% of the area S4 of the first positive electrode sheet (101), and the sum of the volume V3 of all the third grooves and the volume V1 of all the first grooves (1013) is 10% to 40% of the volume V4 of the first positive electrode sheet (101); And / or, in the second positive electrode sheet (102), the opening area S6 of all the second grooves (1023) is 30% to 50% of the area S7 of the positive electrode active material layer in the first region (103), and the volume V6 of all the second grooves (1023) is 20% to 40% of the volume V7 of the positive electrode active material layer in the first region (103).

4. The battery cell according to any one of claims 1 to 2, characterized in that: The first positive electrode sheet (101) comprises a first current collector (1011) and a first active material layer (1012) arranged on one surface of the first current collector (1011); the second positive electrode sheet (102) comprises a second current collector (1021) and second active material layers (1022) arranged on both surfaces of the second current collector (1021); The coating area density ρ1 of the first active material layer (1012) is 92% to 98% of the coating area density ρ2 of the second active material layer (1022).

5. The battery cell according to any one of claims 1 to 2, characterized in that: The porosity of the positive electrode active material layer at the second region (104) of the first positive electrode sheet (101) is a, and the porosity of the positive electrode active material layer at the second region (104) of the second positive electrode sheet (102) is b, and a and b satisfy the following: a=(85% to 95%)b; and / or, in the first positive electrode sheet (101) or the second positive electrode sheet (102), the CB value of the first region (103) is 1.01% to 1.1% of the CB value of the second region (104); And / or, in the first positive electrode sheet (101) or the second positive electrode sheet (102), the amount of lithium desorption in the first region (103) is 50% to 90% of the amount of lithium desorption in the second region (104).

6. The battery cell according to any one of claims 1 to 2, characterized in that: The depth of the first groove (1013) is h1, and the depth of the second groove (1023) is h2; h1 and h2 satisfy: h1>h2, and h1-h2=1-20 μm; And / or, the total thickness of the first positive electrode sheet (101) is H1, and H1 and h1 satisfy: h1=(0.2-1)H1; And / or, the total thickness of the second positive electrode sheet (102) is H2, and H2 and h2 satisfy: h2=(0.2-0.3)H2.

7. The battery cell according to any one of claims 1 to 2, characterized in that: The first positive electrode sheet (101) has a first edge (106) and a third edge (108) arranged opposite to each other along the width direction, and a second edge (107) and a fourth edge (109) arranged opposite to each other along the length direction; Along the width direction, the minimum distance W1 between the first edge (106) and the first groove (1013) is 0.2 mm to 2 mm, and the minimum distance W3 between the third edge (108) and the first groove (1013) is 0.2 mm to 2 mm; Along the length direction, the minimum distance W2 between the second edge (107) and the first groove (1013) is 0.2 mm to 2 mm, and the minimum distance W4 between the fourth edge (109) and the first groove (1013) is 0.2 mm to 2 mm.

8. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode sheet (3) is provided with a fourth groove; The opening area of ​​all the fourth grooves is 5% to 40% of the total area of ​​the negative electrode sheet (3); And / or, the depth of the fourth groove is 0.3 to 1 times the thickness of the negative electrode sheet (3); And / or, the negative electrode sheet (3) has a fifth edge (301) and a seventh edge (303) arranged opposite to each other along the width direction, and a sixth edge (302) and an eighth edge (304) arranged opposite to each other along the length direction; Along the width direction, the minimum distance W5 between the fifth edge (301) and the fourth groove is 0.2 mm to 2 mm, and the minimum distance W7 between the seventh edge (303) and the fourth groove is 0.2 mm to 2 mm; Along the length direction, the minimum distance W6 between the sixth edge (302) and the fourth groove is 0.2 mm to 2 mm, and the minimum distance W8 between the eighth edge (304) and the fourth groove is 0.2 mm to 2 mm.

9. The battery cell according to any one of claims 1 to 2, characterized in that: The opening diameter D1 of the first groove (1013) is 50 μm to 300 μm, and the opening diameter D2 of the second groove (1023) is 50 μm to 300 μm; and / or, along the length direction of the first positive electrode sheet (101), the spacing L1 between any two adjacent first grooves (1013) is 100 μm to 3 mm; along the width direction of the first positive electrode sheet (101), the spacing L2 between any two adjacent first grooves (1013) is 100 μm to 3 mm; and / or, along the length direction of the second positive electrode sheet (102), the spacing L3 between any two adjacent second grooves (1023) is 100 μm to 3 mm; along the width direction of the second positive electrode sheet (102), the spacing L4 between any two adjacent second grooves (1023) is 100 μm to 3 mm; And / or, the shape of the first groove (1013) is circular, elliptical or polygonal, and the shape of the second groove (1023) is circular, elliptical or polygonal.

10. A battery, characterized in that: include: The battery cell according to any one of claims 1 to 9.

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