Lithium ion battery

Abstract

A lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating on at least one side surface of the positive electrode current collector, and the surface on the side of the positive electrode coating that is away from the positive electrode current collector is provided with a recess; the negative electrode sheet comprises a negative electrode current collector and a negative electrode coating on at least one side surface of the negative electrode current collector, and the surface on the side of the negative electrode coating that is away from the negative electrode current collector is provided with a recess; and the width of the recess in the positive electrode coating is less than or equal to the width of the recess in the negative electrode coating. The cycle life of the lithium ion battery can be prolonged.

Description

A lithium-ion battery Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular to a lithium-ion battery.

[0002] Background of the Invention

[0003] With the rapid development of lithium-ion battery technology, people have placed higher demands on the energy density, fast charging capability, and charge and discharge rates of lithium-ion batteries. High-energy-density, fast-charging lithium batteries are the development trend of consumer lithium-ion batteries. However, as energy density increases, the thickness of the positive and negative electrodes in lithium-ion batteries becomes thicker, resulting in longer transmission distances for lithium ions. In addition, as charging speeds increase, lithium ions are more likely to accumulate on the surface of the negative electrode during the charge and discharge process, causing congestion on the negative electrode surface, seriously shortening the service life of the lithium-ion battery.

[0004] Therefore, it is very important to invent a lithium-ion battery with a high cycle life.

[0005] Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned problems existing in the prior art and provide a lithium-ion battery. The lithium-ion battery disclosed in the present invention can improve the cycle life.

[0007] The present disclosure provides a lithium-ion battery, which includes a positive electrode sheet and a negative electrode sheet; the positive electrode sheet includes a positive electrode current collector and a positive electrode coating on at least one side of the positive electrode current collector, and the surface of the positive electrode coating on the side away from the positive electrode current collector contains a concave portion; the negative electrode sheet includes a negative electrode current collector and a negative electrode coating on at least one side of the negative electrode current collector, and the surface of the negative electrode coating on the side away from the negative electrode current collector contains a concave portion; the width of the concave portion of the positive electrode coating is less than or equal to the width of the concave portion of the negative electrode coating.

[0008] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0009] (1) The lithium-ion battery disclosed in the present invention is provided with a recess on the surface of the positive electrode coating, which can improve the wettability of the electrolyte to the positive electrode active material close to the positive electrode current collector, thereby improving the utilization rate of the positive electrode active material close to the positive electrode current collector, improving the capacity, and improving the energy density and fast charging performance of the lithium-ion battery; and the recess is provided on the surface of the negative electrode coating, which can fully improve the problem that lithium ions accumulate on the surface of the negative electrode sheet due to the large thickness of the negative electrode sheet and the long lithium ion transmission distance, and cannot be quickly embedded in the negative electrode active material close to the negative electrode current collector, so that the negative electrode active material cannot be fully utilized and lithium is deposited on the surface of the negative electrode sheet, thereby effectively improving the cycle life of the lithium-ion battery;

[0010] (2) The width of the concave portion of the positive electrode coating of the lithium ion battery disclosed herein is ≤ that of the concave portion of the negative electrode coating, which can optimize the speed at which lithium ions are released from the positive electrode sheet and the speed at which lithium ions are embedded in the negative electrode sheet during charging. The two work together to improve the charging capacity and charging speed of the lithium ion battery.

[0011] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG1 is a schematic cross-sectional view of a positive electrode sheet in an example of the present disclosure.

[0013] FIG2 is a schematic cross-sectional view of a negative electrode sheet in an example of the present disclosure.

[0014] FIG3 is a schematic diagram showing the groove width of the grooves of the positive electrode coating in an example of the present disclosure.

[0015] FIG4 is a schematic diagram showing the slot pitch of a slot in an example of the present disclosure.

[0016] FIG5 is a schematic diagram showing the morphology of pores in an example of the present disclosure (taking the positive electrode sheet as an example).

[0017] FIG6 is a schematic diagram showing the bottom of a hole in an example of the present disclosure (a cross section along the thickness direction of the positive electrode sheet).

[0018] FIG7 is a schematic diagram of a groove in an example of the present disclosure (a cross section along the thickness direction of the positive electrode sheet).

[0019] FIG8 is a schematic diagram showing the distribution of slots in an example of the present disclosure.

[0020] FIG9 is a schematic diagram showing the network structure of the outer surface of the positive electrode coating in an example of the present disclosure. DETAILED DESCRIPTION

[0021] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

[0022] The present disclosure provides a lithium-ion battery, which may include a positive electrode sheet and a negative electrode sheet.

[0023] The positive electrode sheet may include a positive electrode current collector and a positive electrode coating on at least one side of the positive electrode current collector. FIG1 is a schematic cross-sectional view of a positive electrode sheet in an embodiment of the present disclosure, wherein FIG1(a) shows a case where the positive electrode coating is provided on one side; FIG1(b) and FIG1(c) show cases where the positive electrode coating is provided on both sides. In FIG1(a), the positive electrode sheet includes a positive electrode current collector 1-1 and a positive electrode coating 1-2 on one side of the positive electrode current collector 1-1; in FIG1(b) and FIG1(c), the positive electrode sheet includes a positive electrode current collector 1-1 and a positive electrode coating 1-2 on both sides of the positive electrode current collector 1-1. The surface of the positive electrode coating away from the positive electrode current collector may contain a recessed portion.

[0024] The negative electrode sheet may include a negative electrode current collector and a negative electrode coating on at least one side of the negative electrode current collector. FIG2 is a schematic cross-sectional view of a negative electrode sheet in an embodiment of the present disclosure, wherein FIG2(a) shows a case where the negative electrode coating is provided on one side; FIG2(b) and FIG2(c) show cases where the negative electrode coating is provided on both sides. In FIG2(a), the negative electrode sheet includes a negative electrode current collector 2-1 and a negative electrode coating 2-2 on one side of the negative electrode current collector 2-1; in FIG2(b) and FIG2(c), the negative electrode sheet includes a negative electrode current collector 2-1 and a negative electrode coating 2-2 on both sides of the negative electrode current collector 2-1. The surface of the negative electrode coating away from the negative electrode current collector may contain a recessed portion.

[0025] During the charge and discharge cycle of a lithium-ion battery, if the thickness of the positive electrode sheet / negative electrode sheet is too large (for example, the thickness of the positive electrode coating on one side of the positive electrode sheet is 30μm-110μm, and the thickness of the negative electrode coating on one side of the negative electrode sheet is 35μm-120μm), the electrolyte will deteriorate in the positive electrode active material near the positive electrode current collector / negative electrode active material near the negative electrode current collector, resulting in a long lithium ion transmission distance. For the positive electrode sheet, this will result in low utilization of the positive electrode active material, ultimately leading to incomplete capacity utilization of the lithium-ion battery; for the negative electrode sheet, during the charge and discharge process, lithium ions are more likely to accumulate on the surface of the negative electrode sheet, causing congestion on the surface of the negative electrode sheet, preventing the lithium ions from quickly embedding into the negative electrode active material near the negative electrode current collector, resulting in lithium deposition on the negative electrode surface, seriously shortening the service life of the lithium-ion battery. Research has found that providing recesses on both the outer surface of the positive electrode coating and the outer surface of the negative electrode coating can effectively improve the wettability of the electrolyte to the positive electrode active material near the positive electrode current collector and the negative electrode active material near the negative electrode current collector, shortening the transmission distance of lithium ions, and increasing the effective utilization rate of the positive electrode active material and the embedding rate of lithium ions in the negative electrode active material. The combination of the two can simultaneously improve the energy density, rate performance, and service life of the lithium-ion battery. Further research has found that when recesses are provided on both the outer surface of the positive electrode coating and the outer surface of the negative electrode coating, the two have a synergistic effect, which can effectively extend the service life of the lithium-ion battery. The reasons may be: 1-When the outer surface of the positive electrode coating and the outer surface of the negative electrode coating both contain recesses, the amount of stored electrolyte increases significantly, and the electrolyte is not easy to dry out during the cycle of the lithium-ion battery, which is beneficial to increasing the cycle life of the lithium-ion battery; 2-The recesses located on the outer surface of the positive electrode coating and the outer surface of the negative electrode coating can provide space for the volume expansion of the positive electrode active material and the negative electrode active material, and can convert the vertical expansion of the positive electrode active material and the negative electrode active material into horizontal expansion, thereby reducing the expansion of the lithium-ion battery; 3-When the outer surface of the positive electrode coating and the outer surface of the negative electrode coating both contain recesses, the speed at which the positive electrode sheet releases lithium ions becomes faster, and the speed at which the negative electrode sheet embeds lithium ions also becomes faster (the lithium-ion battery can reach 100% SOC in a shorter time), thereby increasing the charging speed of the lithium-ion battery.

[0026] In the present disclosure, the width of the concave portion of the positive electrode coating layer is ≤ the width of the concave portion of the negative electrode coating layer.

[0027] Research has found that when the width of the concave portion of the positive electrode coating is ≤ the width of the concave portion of the negative electrode coating, the speed at which lithium ions escape from the positive electrode sheet and embed into the negative electrode sheet during charging can be optimized, allowing lithium ions to quickly escape from the positive electrode sheet and quickly embed into the side wall of the concave portion of the negative electrode sheet, thereby improving the charging capacity and charging speed of the lithium-ion battery.

[0028] In the present disclosure, the width of the concave portion of the positive electrode coating and the width of the concave portion of the negative electrode coating have conventional meanings in the art. When the concave portion is a hole, the width of the concave portion is considered to be the pore diameter of the hole. For example, when the shape of the projection of the hole on the positive electrode coating is a "regular circle", the pore diameter of the hole is the diameter of the regular circle; when the shape of the projection of the hole on the positive electrode coating is a non-"regular circle" (such as an ellipse or an irregular curved polygon), the pore diameter of the hole is the diameter of an equivalent circle with the same area as the non-"regular circle"; similarly, when the shape of the projection of the hole on the negative electrode coating is a "regular circle", the pore diameter of the hole is the diameter of the regular circle; when the shape of the projection of the hole on the negative electrode coating is a non-"regular circle" (such as an ellipse or an irregular curved polygon), the pore diameter of the hole is the diameter of an equivalent circle with the same area as the non-"regular circle". The "pore diameter" can be obtained by conventional means in the art, such as by scanning electron microscopy (SEM).

[0029] In the present disclosure, when the recessed portion is a groove, the width of the recessed portion is considered to be the groove width of the groove. For example, the projection of the groove on the positive electrode coating includes two long sides, and the groove width refers to the average distance from one long side to the other long side in the length direction or width direction of the positive electrode sheet. Figure 3 is a schematic diagram of the groove width of the groove of the positive electrode coating in an example of the present disclosure, wherein the two long sides of the groove in Figures 3(a) to 3(c) are straight lines, and the two long sides of the groove in Figure 3(d) are curved lines. In FIG3(a) and FIG3(b), the two long sides are arranged in parallel. Therefore, in the width direction of the positive electrode sheet, the distance from any point on one long side to the other long side is equal. In this case, the slot width is the distance from any point on one long side to the other long side in the length direction or width direction of the positive electrode sheet. In FIG3(c), the two long sides of the slot are straight lines, but are not arranged in parallel. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the slot width can be averaged, that is, on one long side, the length of the side is used as the reference, and 50 points (i.e., each long side) are selected at equal distances. The distances between the points are equal, so the selection of points can make the calculation results more accurate), the width corresponding to each point is measured, and the average value is taken to obtain the groove width of the groove; in Figure 3 (d), the two long sides are curved, so the distance from any point on one long side to the other long side is not equal. At this time, the width of the groove can also be averaged, that is, 50 points are randomly selected on one long side (because the two long sides in Figure 3 (d) are curved, there is no relationship between the two long sides in Figure 3 (c), so 50 points can be randomly selected for measurement), the width corresponding to each point is measured, and the average value is taken to obtain the groove width of the groove. Similarly, it is generally believed that the projection of the groove on the negative electrode coating includes two long sides, and the groove width refers to the average distance from one long side to the other long side in the length direction or width direction of the negative electrode sheet. The "groove width" can be obtained by conventional means in this field, such as by SEM.

[0030] In the present disclosure, the volume of the concave portion of the negative electrode coating layer may be equal to or greater than the volume of the concave portion of the positive electrode coating layer.

[0031] In one example, the volume of the concave portion of the negative electrode coating is greater than the volume of the concave portion of the positive electrode coating.

[0032] Research has found that when the volume of the concave portion of the negative electrode coating is larger than that of the positive electrode coating, the mass loss of the positive electrode active material in the positive electrode sheet is smaller than that of the negative electrode sheet (that is, the energy density and capacity of the lithium-ion battery can be guaranteed), and the capacity of the positive electrode active material can be fully utilized; and compared with the positive electrode sheet, the volume of the concave portion of the negative electrode sheet is larger, and the porosity of the negative electrode sheet is higher, which can speed up the speed of lithium ion embedding into the negative electrode active material, thereby effectively avoiding the lithium plating problem caused by the accumulation of lithium ions on the surface of the negative electrode sheet, and improving the service life of the lithium-ion battery.

[0033] In the present disclosure, the "volume of the concave portions of the negative electrode coating" refers to the total volume of all concave portions formed on the surface of the negative electrode sheet; similarly, the "volume of the concave portions of the positive electrode coating" refers to the total volume of all concave portions formed on the surface of the positive electrode sheet.

[0034] In the present disclosure, the ratio of the depth of the concave portion of the positive electrode coating to the depth of the concave portion of the negative electrode coating may be (0.2-1):1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1.

[0035] In one example, the ratio of the depth of the concave portion of the positive electrode coating to the depth of the concave portion of the negative electrode coating is (0.4-0.9):1.

[0036] Research has found that when the ratio of the depth of the concave portion of the positive electrode coating to the depth of the concave portion of the negative electrode coating is within a specific range, the speed at which lithium ions escape from the positive electrode sheet and the speed at which lithium ions embed into the negative electrode sheet during charging can be optimized, allowing lithium ions to quickly escape from the positive electrode sheet and quickly embed into the side walls of the concave portion of the negative electrode sheet, thereby improving the charging capacity and charging speed of the lithium-ion battery; at the same time, the small depth of the concave portion of the positive electrode coating can minimize the loss of positive electrode active material and reduce the capacity loss of the lithium-ion battery, thereby improving the charging speed and cycle life while taking into account the energy density. When the ratio of the depth of the concave portion of the positive electrode coating to the depth of the concave portion of the negative electrode coating is greater than the specific range, it is easy to cause the lithium ions of the positive electrode sheet to escape too quickly, resulting in the negative electrode sheet being unable to accept them quickly, causing lithium plating and worsening the cycle life of the lithium-ion battery. It will also cause excessive loss of positive electrode active material, resulting in a decrease in energy density; when the ratio of the depth of the concave portion of the positive electrode coating to the depth of the concave portion of the negative electrode coating is less than the specific range, it may lead to insufficient utilization of the positive electrode active material, especially the positive electrode active material close to the positive electrode current collector side, resulting in a decrease in energy density.

[0037] In this disclosure, the depth of a concave portion of a positive electrode coating refers to the maximum vertical distance from any point within the concave portion to the surface of the positive electrode coating. Similarly, the depth of a concave portion of a negative electrode coating refers to the maximum vertical distance from any point within the concave portion to the surface of the negative electrode coating. In this disclosure, the "depth of the concave portion" can be measured by conventional means in the art, such as a 3D profilometer or a scanning electron microscope (SEM).

[0038] In the present disclosure, the ratio of the width of the concave portion of the positive electrode coating to the width of the concave portion of the negative electrode coating may be (0.3-1):1, for example, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1.

[0039] In one example, the ratio of the width of the concave portion of the positive electrode coating to the width of the concave portion of the negative electrode coating is (0.35-0.9):1.

[0040] Research has found that when the ratio of the width of the concave portion of the positive electrode coating to the width of the concave portion of the negative electrode coating is within a specific range, the speed at which lithium ions escape from the positive electrode sheet and the speed at which lithium ions embed into the negative electrode sheet during charging can be optimized, allowing lithium ions to quickly escape from the positive electrode sheet and quickly embed into the side wall of the concave portion of the negative electrode sheet, thereby improving the charging capacity and charging speed of the lithium-ion battery; at the same time, the small width of the concave portion of the positive electrode coating can minimize the loss of positive electrode active material and reduce the capacity loss of the lithium-ion battery, thereby improving the charging speed and cycle life while taking into account the energy density. When the ratio of the width of the concave portion of the positive electrode coating to the width of the concave portion of the negative electrode coating is greater than the specific range, it is easy to cause the lithium ions of the positive electrode sheet to escape too quickly, resulting in the negative electrode sheet being unable to accept them quickly, causing lithium plating and worsening the cycle life of the lithium-ion battery. It will also cause excessive loss of positive electrode active material, resulting in a decrease in energy density; when the ratio of the width of the concave portion of the positive electrode coating to the width of the concave portion of the negative electrode coating is less than the specific range, it may lead to insufficient utilization of the positive electrode active material, especially the positive electrode active material close to the positive electrode current collector side, resulting in a decrease in energy density.

[0041] In the present disclosure, the recess may include a hole and / or a groove.

[0042] In the present disclosure, the ratio of the pore pitch of the positive electrode coating to the pore pitch of the negative electrode coating may be 1:(0.5-1), for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1.

[0043] In one example, the ratio of the pore pitch of the positive electrode coating to the pore pitch of the negative electrode coating is 1:(0.61-0.92).

[0044] Research has found that when the ratio of the pore pitch of the positive electrode coating to the pore pitch of the negative electrode coating is within a specific range, the speed at which lithium ions escape from the positive electrode sheet and the speed at which lithium ions embed into the negative electrode sheet during charging can be optimized, allowing lithium ions to quickly escape from the positive electrode sheet and quickly embed into the side walls of the recessed portion of the negative electrode sheet, thereby improving the charging capacity and charging speed of the lithium-ion battery. At the same time, the large pore pitch of the positive electrode coating can minimize the loss of positive electrode active material and reduce the capacity loss of the lithium-ion battery, thereby improving the charging speed and cycle life while taking into account the energy density. When the ratio of the pore spacing of the positive electrode coating to the pore spacing of the negative electrode coating is less than the specific range, it is easy to cause the positive electrode sheet to release lithium ions too quickly, resulting in the negative electrode sheet being unable to accept them quickly, causing lithium plating and worsening the cycle life of the lithium-ion battery. It will also cause excessive loss of positive electrode active material, resulting in a decrease in energy density; when the ratio of the pore spacing of the positive electrode coating to the pore spacing of the negative electrode coating is greater than the specific range, it may lead to insufficient utilization of the positive electrode active material, especially the positive electrode active material close to the positive electrode current collector side, resulting in a decrease in energy density.

[0045] In this disclosure, the pore pitch of the positive electrode coating refers to the shortest distance between the edges of two adjacent pores in the positive electrode coating; similarly, the pore pitch of the negative electrode coating refers to the shortest distance between the edges of two adjacent pores in the negative electrode coating. The "pore pitch" can be measured by conventional means in the art, such as SEM.

[0046] In the present disclosure, the ratio of the pitch of the grooves of the positive electrode coating to the pitch of the grooves of the negative electrode coating may be 1:(0.5-1), for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1.

[0047] In one example, the ratio of the groove pitch of the positive electrode coating to the groove pitch of the negative electrode coating is 1:(0.55-0.9).

[0048] Research has found that when the ratio of the groove pitch of the positive electrode coating to the groove pitch of the negative electrode coating is within a specific range, the speed at which lithium ions are released from the positive electrode sheet and the speed at which lithium ions are embedded in the negative electrode sheet during charging can be optimized, allowing lithium ions to quickly escape from the positive electrode sheet and quickly embed into the side walls of the recessed portion of the negative electrode sheet, thereby improving the charging capacity and charging speed of the lithium-ion battery; at the same time, the large groove pitch of the grooves of the positive electrode coating can minimize the loss of positive electrode active material and reduce the capacity loss of the lithium-ion battery, thereby improving the charging speed and cycle life while taking into account the energy density. When the ratio of the slot pitch of the positive electrode coating to the slot pitch of the negative electrode coating is less than the specific range, it is easy to cause the positive electrode sheet to release lithium ions too quickly, resulting in the negative electrode sheet being unable to accept them quickly, causing lithium plating and worsening the cycle life of the lithium-ion battery. It will also cause excessive loss of positive electrode active materials, resulting in a decrease in energy density; when the ratio of the slot pitch of the positive electrode coating to the slot pitch of the negative electrode coating is greater than the specific range, it may lead to insufficient utilization of positive electrode active materials, especially the positive electrode active materials close to the positive electrode current collector side, resulting in a decrease in energy density.

[0049] In the present disclosure, the pitch of the grooves of the positive electrode coating refers to the average distance between the two adjacent long sides of two adjacent grooves on the positive electrode coating in the length direction or width direction of the positive electrode sheet; similarly, the pitch of the grooves of the negative electrode coating refers to the average distance between the two adjacent long sides of two adjacent grooves on the negative electrode coating in the length direction or width direction of the negative electrode sheet. Figure 4 is a schematic diagram of the pitch of the grooves in an example of the present disclosure, where Figure 4(a) shows the case where the two adjacent long sides are straight and parallel, Figure 4(b) shows the case where the two adjacent long sides are straight and non-parallel, and Figure 4(c) shows the case where the two adjacent long sides are curved. In Figure 4(a), the two adjacent long sides are straight and parallel. Therefore, in the width direction, the distance from any point on one long side to the other long side is equal. In this case, the slot pitch is the distance D from any point on one long side to the other long side in the width direction. In Figure 4(b), the two adjacent long sides are straight but not parallel. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the slot pitch can be averaged, that is, on one long side, with the length of the side as the reference, 50 points are selected at equal distances (that is, the distance between each point is equal to 1 / 4). The distance between the two long sides is equal, so selecting the points in this way can make the calculation result more accurate), measure the width corresponding to each point, and take the average value to obtain the slot pitch; in Figure 4(c), the two adjacent long sides are curved. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the slot pitch can also be averaged, that is, 50 points are randomly selected on one long side (because the two long sides in Figure 4(c) are curved, there is no relationship between the two long sides in Figure 4(b), so 50 points can be randomly selected for measurement), measure the width corresponding to each point, and take the average value to obtain the slot pitch. The "slot pitch" can be tested by conventional means in this field, such as by SEM.

[0050] In the present disclosure, the ratio of pore diameter to pore depth of the pores of the cathode coating may be (1.6-8):1, for example, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or 8:1.

[0051] In one example, the ratio of the pore diameter to the pore depth of the positive electrode coating is (3-5):1.

[0052] Research has found that when the ratio of the pore diameter to the pore depth of the positive electrode coating is within a specific range, it is beneficial for the sidewalls of the pores to release more lithium ions into the electrolyte, which is beneficial for the positive electrode active material near the positive electrode current collector to release lithium ions into the electrolyte; at the same time, it can reduce the loss of positive electrode active material and reduce energy density loss. When the ratio of the pore diameter to the pore depth of the positive electrode coating is greater than this specific range, the positive electrode active material near the positive electrode current collector cannot be infiltrated by the electrolyte, resulting in its inability to be fully utilized, which will result in a loss of capacity and energy density. When the ratio of the pore diameter to the pore depth of the positive electrode coating is less than this specific range, lithium ions cannot be quickly released from the positive electrode active material along the thickness of the positive electrode sheet, especially near the positive electrode current collector, in a short period of time, and the charging speed of the lithium-ion battery cannot be guaranteed to be improved.

[0053] In the present disclosure, the ratio of pore diameter to pore depth of the pores of the negative electrode coating may be (1.6-8):1, for example, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or 8:1.

[0054] In one example, the ratio of the pore diameter to the pore depth of the negative electrode coating is (3.5-5):1.

[0055] Research has found that when the ratio of the pore diameter to pore depth of the negative electrode coating is within a specific range, the pore opening can absorb more free lithium ions into the pore interior, and the pore depth can quickly accept lithium ions from the pore opening per unit time. This can further improve the electrolyte's wettability of the negative electrode active material, reduce lithium ion accumulation on the negative electrode surface, and increase the service life of the lithium-ion battery. When the pore diameter to pore depth ratio of the negative electrode coating is greater than this specific range, the pore inner wall area is small, making it difficult to quickly absorb a large number of lithium ions from the pore opening. At the same time, it is not conducive to the rapid embedding of lithium ions into the negative electrode active material near the negative electrode current collector, resulting in insufficient utilization of the negative electrode active material. When the pore diameter to pore depth ratio of the negative electrode coating is less than this specific range, it cannot absorb more lithium ions in a short period of time, and the pore interior is not fully utilized, which is not conducive to improving the kinetic performance of the negative electrode sheet.

[0056] In the present disclosure, the ratio of groove width to groove depth of the grooves of the positive electrode coating may be (1.6-8):, for example, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1.

[0057] In one example, the ratio of the groove width to the groove depth of the positive electrode coating is (3-5):1.

[0058] Studies have shown that when the ratio of the groove width to the groove depth of the positive electrode coating is within a specific range, the wettability of the electrolyte to the positive electrode active material can be further improved, thereby improving the utilization rate of the positive electrode active material.

[0059] In the present disclosure, the ratio of groove width to groove depth of the grooves of the negative electrode coating may be (1.6-8):1, for example, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1.

[0060] In one example, the ratio of the groove width to the groove depth of the grooves of the negative electrode coating is (3.5-5):1.

[0061] Research has found that when the ratio of the groove width to the groove depth of the negative electrode coating is within a specific range, the electrolyte can further improve the wettability of the negative electrode active material, reduce the accumulation of lithium ions on the surface of the negative electrode sheet, and increase the service life of the lithium-ion battery. When the groove width to the groove depth ratio of the negative electrode coating is greater than this specific range, it is not conducive to the occurrence of capillary phenomena and electrolyte infiltration. When the groove width to the groove depth ratio of the negative electrode coating is less than this specific range, air cavities are easily formed at the bottom of the groove, which is not conducive to the electrolyte infiltration of the negative electrode sheet.

[0062] In the present disclosure, the pores of the positive electrode coating may have a pore size of 5 μm to 125 μm (e.g., 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, or 125 μm). The pores of the positive electrode coating may have a pore depth of 3 μm to 44 μm (e.g., 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 44 μm). The pores of the positive electrode coating may have a pore pitch of 50 nm to 500 nm (eg, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm).

[0063] In one example, the pores of the positive electrode coating have a pore size of 40 μm to 90 μm.

[0064] In one example, the pores of the positive electrode coating have a depth of 10 μm to 20 μm.

[0065] In one example, the pore pitch of the positive electrode coating is 200 nm to 480 nm.

[0066] In the present disclosure, the pores of the negative electrode coating may have a pore diameter of 8 μm to 125 μm (e.g., 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, or 125 μm). The pores of the negative electrode coating may have a pore depth of 1 μm to 44 μm (e.g., 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 44 μm). The pores of the negative electrode coating may have a pore pitch of 50 nm to 500 nm (eg, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm).

[0067] In one example, the pores of the negative electrode coating have a pore size of 10 μm to 115 μm.

[0068] In one example, the pores of the negative electrode coating have a depth of 2 μm to 30 μm.

[0069] In one example, the pore pitch of the negative electrode coating is 150 nm to 300 nm.

[0070] In the present disclosure, the groove width of the groove of the positive electrode coating can be 10μm-148μm (for example, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm or 148μm). The grooves of the positive electrode coating may have a depth of 6 μm to 52 μm (e.g., 6 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or 52 μm). The grooves of the positive electrode coating may have a pitch of 100 μm to 2000 μm (e.g., 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 1000 μm, 1500 μm, or 2000 μm).

[0071] In one example, the grooves of the positive electrode coating have a width of 30 μm to 90 μm.

[0072] In one example, the grooves of the positive electrode coating have a depth of 10 μm to 20 μm.

[0073] In one example, the groove pitch of the positive electrode coating is 500 μm-1500 μm.

[0074] In the present disclosure, the groove width of the negative electrode coating may be 30 μm-148 μm (e.g., 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, or 148 μm). The groove depth of the negative electrode coating may be 20 μm-52 μm (e.g., 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or 52 μm). The grooves of the negative electrode coating may have a groove pitch of 100 μm to 2000 μm (eg, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 1000 μm, 1500 μm, or 2000 μm).

[0075] In one example, the grooves of the negative electrode coating have a width of 80 μm to 110 μm.

[0076] In one example, the grooves of the negative electrode coating have a depth of 20 μm to 30 μm.

[0077] In one example, the groove pitch of the negative electrode coating is 300 μm-1350 μm.

[0078] In the present disclosure, the volume of the pores and / or grooves of the negative electrode coating and the volume of the pores and / or grooves of the positive electrode coating can be measured and obtained by conventional technical means in the art. For example, the volume of the pores and / or grooves can be calculated by measuring the pore diameter, pore depth and pore spacing of the pores and / or the groove width, groove depth and groove spacing of the grooves.

[0079] In the present disclosure, there is no special limitation on the morphology of the holes on the positive electrode coating or the holes on the negative electrode coating. The holes can be straight-through holes, that is, the projection of the holes on the positive electrode sheet / the negative electrode sheet is the same at all locations in the thickness direction of the positive electrode sheet and / or the negative electrode sheet; the holes can also be quasi-conical holes, that is, the pore diameter of the holes away from the positive electrode collector / the negative electrode collector is larger than the pore diameter of the holes close to the positive electrode collector / the negative electrode collector. As shown in Figure 5, a schematic diagram of the morphology of the holes in an example of the present disclosure (taking the positive electrode sheet as an example), where Figure 5 (a) shows the case where the hole is a straight-through hole, and Figure 5 (b) shows the case where the hole is a quasi-conical hole. There is no special limitation on the shape of the bottom of the hole. The shape of the cross section of the bottom of the hole along the thickness direction of the positive electrode sheet / the negative electrode sheet can be an inverted triangle, a semicircle or a semi-ellipse. As shown in FIG6 , this is a schematic diagram of the bottom of the hole in an example of the present disclosure (a cross section along the thickness direction of the positive electrode sheet). As can be seen from FIG6 , the cross-section shapes of the bottom of the hole along the thickness direction of the positive electrode sheet are an inverted triangle, a semicircle, and a semi-ellipse, respectively.

[0080] In the present disclosure, there is no special limitation on the morphology of the grooves on the positive electrode coating or the grooves on the negative electrode coating, and the shape of the cross section of the grooves along the thickness direction of the positive electrode sheet / the negative electrode sheet can be rectangular or conical. As shown in FIG7 , a schematic diagram of the grooves in an example of the present disclosure (a cross section along the thickness direction of the positive electrode sheet) can be shown. It can be seen from FIG7 that the cross section of the grooves 1-4 in the thickness direction of the positive electrode sheet can be rectangular or conical. In the present disclosure, the grooves can be distributed along the length direction of the positive electrode sheet / the negative electrode sheet, or along the width direction of the positive electrode sheet / the negative electrode sheet. As shown in FIG8 , a schematic diagram of the distribution of the grooves in an example of the present disclosure is shown, wherein FIG8 (a) shows the distribution along the length direction of the positive electrode sheet, and FIG8 (b) shows the distribution along the width direction of the positive electrode sheet.

[0081] In one example, the outer surface of the positive electrode coating has pores; the outer surface of the negative electrode coating has pores.

[0082] In one example, the outer surface of the positive electrode coating has grooves; the outer surface of the negative electrode coating has grooves.

[0083] In one example, the outer surface of the positive electrode coating has pores and grooves; the outer surface of the negative electrode coating has pores and grooves.

[0084] In the present disclosure, when the outer surface of the positive electrode coating has pores and grooves, the size from the edge of the pore to the edge of the groove may be 100 μm to 500 μm, for example, 100 μm, 200 μm, 300 μm, 400 μm or 500 μm.

[0085] In one example, when the outer surface of the positive electrode coating has pores and grooves, the size from the edge of the pore to the edge of the groove is 100 μm to 250 μm.

[0086] Research has found that the combination of pores and grooves can provide additional channels for the transmission of lithium ions in the coating, thereby optimizing the transmission of lithium ions on the coating, allowing lithium ions to be quickly embedded in the coating close to the current collector, and the active material can be more effectively utilized. It can also improve lithium plating on the surface of the negative electrode and increase the service life of the lithium-ion battery. At the same time, the pores and grooves can store electrolyte, reducing lithium plating caused by insufficient electrolyte.

[0087] In the present disclosure, when the outer surface of the negative electrode coating has pores and grooves, the size from the edge of the pore to the edge of the groove may be 80 μm-480 μm, for example 80 μm, 100 μm, 200 μm, 300 μm, 400 μm or 480 μm.

[0088] In one example, when the outer surface of the negative electrode coating has pores and grooves, the size from the edge of the pore to the edge of the groove is 90 μm to 200 μm.

[0089] In the present disclosure, the outer surface of the positive electrode coating may have a network structure divided by a plurality of the grooves. The shape of the network structure may include a square, a rectangle or a rhombus. As shown in Figure 9, a schematic diagram of the network structure of the outer surface of the positive electrode coating in an example of the present disclosure is shown, wherein the shape of the network structure in Figure 9 (a) includes a square, the shape of the network structure in Figure 9 (b) includes a rectangle, and the shape of the network structure in Figure 9 (c) includes a rhombus.

[0090] The inventors of the present disclosure have discovered that when the outer surface of the positive electrode coating has a network structure divided by several of the grooves, the dynamic performance of the positive electrode sheet can be further improved, the porosity can be increased, and the release rate of lithium ions can be increased, thereby improving the rate performance of the lithium-ion battery.

[0091] In the present disclosure, the outer surface of the negative electrode coating may have a network structure divided by a plurality of the grooves. The shape of the network structure may include square, rectangle or diamond.

[0092] The inventors of the present disclosure have discovered that when the outer surface of the negative electrode coating has a network structure divided by a number of the grooves, the kinetic performance of the negative electrode sheet can be further improved, the porosity can be increased, and the insertion speed of lithium ions can be increased, thereby alleviating the lithium plating caused by the accumulation of lithium ions on the surface of the negative electrode sheet and increasing the service life of the lithium-ion battery.

[0093] In the present disclosure, when the shape of the network structure on the outer surface of the positive electrode coating layer includes a square, the side length of the square may be 500 μm-2000 μm, for example, 500 μm, 1000 μm, 1500 μm or 2000 μm.

[0094] In the present disclosure, when the shape of the network structure on the outer surface of the positive electrode coating layer includes a rectangle, the long side of the rectangle may be 1000 μm-3000 μm (e.g., 1000 μm, 1500 μm, 2000 μm, 2500 μm, or 3000 μm). The short side of the rectangle may be 500 μm-2000 μm (e.g., 500 μm, 1000 μm, 1500 μm, or 2000 μm).

[0095] In one example, when the network structure on the outer surface of the positive electrode coating comprises a rectangle, the length of the long side of the rectangle is 1500 μm to 2500 μm, and the length of the short side of the rectangle is 500 μm to 1500 μm.

[0096] In the present disclosure, when the shape of the network structure on the outer surface of the positive electrode coating layer includes a rhombus, the long diagonal of the rhombus may be 800 μm-5000 μm (e.g., 800 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, 3000 μm, 3500 μm, 4000 μm, 4500 μm, or 5000 μm). The short diagonal of the rhombus may be 600 μm-4000 μm (e.g., 600 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, 3000 μm, 3500 μm, or 4000 μm).

[0097] In the present disclosure, when the shape of the network structure on the outer surface of the negative electrode coating layer includes a square, the side length of the square may be 450 μm-1900 μm, for example, 450 μm, 500 μm, 1000 μm, 1500 μm or 1900 μm.

[0098] In the present disclosure, when the shape of the network structure on the outer surface of the negative electrode coating layer includes a rectangle, the long side of the rectangle may be 950 μm-2900 μm (e.g., 950 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, or 2900 μm). The short side of the rectangle may be 450 μm-1900 μm (e.g., 450 μm, 500 μm, 1000 μm, 1500 μm, or 1900 μm).

[0099] In one example, when the network structure on the outer surface of the negative electrode coating layer is in the shape of a rectangle, the length of the long side of the rectangle is 1000 μm-2300 μm, and the length of the short side of the rectangle is 500 μm-1500 μm.

[0100] In the present disclosure, when the shape of the network structure on the outer surface of the negative electrode coating layer includes a rhombus, the long diagonal of the rhombus may be 750 μm-4900 μm (e.g., 750 μm, 800 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, 3000 μm, 3500 μm, 4000 μm, 4500 μm, or 4900 μm). The short diagonal of the rhombus may be 550 μm-3900 μm (e.g., 550 μm, 600 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, 3000 μm, 3500 μm, or 3900 μm).

[0101] In the present disclosure, the surface density of the positive electrode sheet can be 10 mg / cm 2 -35mg / cm 2 , for example 10 mg / cm 2 、15mg / cm 2 , 20mg / cm 2 , 25mg / cm 2 、30mg / cm 2 or 35 mg / cm 2 .

[0102] In one embodiment, the surface density of the positive electrode sheet can be 13 mg / cm 2 -29mg / cm 2 .

[0103] Research has found that when the surface density of the positive electrode sheet is within a specific range, the energy density of the lithium-ion battery can be improved; at the same time, providing a recess on the outer surface of the positive electrode coating can improve the wettability of the electrolyte to the positive electrode active material close to the positive electrode current collector, shorten the transmission distance of lithium ions, and improve the effective utilization rate of the positive electrode active material, thereby further improving the energy density of the lithium-ion battery.

[0104] In the present disclosure, the thickness of the cathode coating layer may be 30 μm to 110 μm, for example, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or 110 μm.

[0105] In the present disclosure, the positive electrode coating may include N layers of coating, where N≧1 (eg, N=1, 2, 3, 4, 5, 6, 7, or 8).

[0106] In one example, the cathode coating is a single layer.

[0107] In one example, the positive electrode coating includes a first positive electrode coating and a second positive electrode coating sequentially stacked along a thickness direction of the positive electrode sheet.

[0108] In one example, the positive electrode coating includes a first positive electrode coating, a second positive electrode coating, and a third positive electrode coating sequentially stacked along a thickness direction of the positive electrode sheet.

[0109] In the present disclosure, the N-layer coating can be obtained by drying the same positive electrode coating slurry, or by drying different positive electrode coating slurries.

[0110] In the present disclosure, the surface density of the negative electrode sheet can be 7 mg / cm 2 -22mg / cm 2 , for example 7mg / cm 2 、10mg / cm 2 、15mg / cm 2 , 20mg / cm 2 or 22 mg / cm 2 .

[0111] In one embodiment, the surface density of the negative electrode sheet is 7.3 mg / cm 2 -19.5mg / cm 2 .

[0112] Research has found that when the surface density of the negative electrode sheet is within a specific range, the ability of the negative electrode sheet to receive lithium ions can be improved; at the same time, setting a recess on the outer surface of the negative electrode coating can shorten the transmission distance of lithium ions and increase the speed at which lithium ions are embedded in the negative electrode sheet, thereby further improving the charging speed of the lithium-ion battery and reducing the risk of lithium plating.

[0113] In the present disclosure, the thickness of the cathode coating may be 35 μm-120 μm, for example, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm or 120 μm.

[0114] In the present disclosure, the negative electrode coating may include N layers of coating, where N≧1 (eg, N=1, 2, 3, 4, 5, 6, 7, or 8).

[0115] In one example, the negative electrode coating is a single layer.

[0116] In one example, the negative electrode coating includes a first negative electrode coating and a second negative electrode coating sequentially stacked along a thickness direction of the negative electrode sheet.

[0117] In one example, the negative electrode coating includes a first negative electrode coating, a second negative electrode coating, and a third negative electrode coating sequentially stacked along a thickness direction of the negative electrode sheet.

[0118] In the present disclosure, the N-layer coating can be obtained by drying the same negative electrode coating slurry, or by drying different negative electrode coating slurries.

[0119] In the present disclosure, the positive electrode coating may include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material may include at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganate, lithium nickel manganate, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and lithium-rich manganese oxide. The positive electrode binder may include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene butadiene latex, polytetrafluoroethylene, and polyethylene oxide. The positive electrode conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and carbon fiber.

[0120] In the present disclosure, the positive electrode active material may include first particles and second particles. The median particle size Dv50 of the first particles is greater than the median particle size Dv50 of the second particles.

[0121] Research has found that by using first particles and second particles with different median particle sizes Dv50 in combination, the compaction density of the positive electrode sheet can be increased, thereby increasing the energy density of the lithium-ion battery.

[0122] In one example, the positive electrode active material includes a doping-modified and / or coating-modified positive electrode active material.

[0123] In the present disclosure, the positive electrode active material may include lithium cobalt oxide having a core-shell structure, the core of the core-shell structure includes lithium cobalt oxide doped with a metal element, wherein the doped metal element may include at least one of Al, Mg and M, M may include at least one of Ti, Zr, Y, La, Ni, Mn, Ce and W, and the shell of the core-shell structure includes a compound containing the element R, which may include at least one of Al, Mg, Ti, Zr, Y, La, Ni and Mn.

[0124] In the present disclosure, the compound containing the element R may include at least one of an oxide, a fluoride, and a phosphate of R.

[0125] In the present disclosure, the doping amount of the doped metal element Al can be 100ppm-18000ppm (e.g., 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm or 18000ppm), and the doping amount of the doped metal element Mg can be 100ppm-4500ppm (e.g., 100ppm, 200ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm or 18000ppm). ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 2000ppm, 3000ppm, 4000ppm or 4500ppm), and the total doping amount of the doped metal elements Al, Mg and M can be 3000ppm-35000ppm (for example, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 20000ppm, 30000ppm or 35000ppm).

[0126] Research has found that when the doping amount of the doped metal element is within a specific range, the stability of the positive electrode active material can be improved, and when a recess is provided on the outer surface of the positive electrode active layer, a synergistic effect can be produced to further improve the stability of the positive electrode sheet, thereby increasing the cycle life of the lithium-ion battery.

[0127] In one example, the doping metal element M includes at least one of Ti, Y, and La.

[0128] In the present disclosure, based on the total weight of the lithium cobalt oxide having a core-shell structure, the content of the element R may be 0.01-5 wt%, for example, 0.01, 0.03, 0.05, 0.1, 0.15, 0.18, 0.25, 0.5, 0.7, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 wt%.

[0129] Research has found that when the content of element R in lithium cobalt oxide with a core-shell structure is within a specific range, the side reactions of the electrolyte can be effectively inhibited, and when a recess is provided on the outer surface of the positive electrode active layer, a synergistic effect can be produced, further improving the stability of the positive electrode sheet and the electrolyte infiltration ability, thereby increasing the cycle life of the lithium-ion battery.

[0130] In the present disclosure, the types and contents of the doped metal elements and the element R can be obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0131] In the present disclosure, based on the total weight of the positive electrode coating, the content of the positive electrode active material may be 80-99.8 wt % (e.g., 80, 85, 90, 95 or 99.8 wt %), the content of the positive electrode conductor may be 0.1-10 wt % (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 wt %), and the content of the positive electrode binder may be 0.1-10 wt % (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 wt %).

[0132] In one example, based on the total weight of the positive electrode coating, the content of the positive electrode active material is 90-99.6 wt %, the content of the positive electrode conductor is 0.2-5 wt %, and the content of the positive electrode binder is 0.2-5 wt %.

[0133] In the present disclosure, the negative electrode coating layer may include a negative electrode active material, a negative electrode conductor, a negative electrode binder, and a thickener.

[0134] In the present disclosure, the negative electrode active material may include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, hard carbon, soft carbon, and silicon-based materials. The negative electrode coating may also include the negative electrode conductive agent, which may include a conductive agent conventionally used in the art, such as at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and carbon fiber. The negative electrode binder may be selected from binders conventionally used in the art, such as at least one of polyvinylidene fluoride, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide. The thickener may be selected from thickeners conventionally used in the art, such as sodium carboxymethyl cellulose.

[0135] In the present disclosure, the silicon-based material may include at least one of silicon, silicon oxygen, silicon carbon, and silicon alloy.

[0136] In the present disclosure, the content of the silicon-based material may be 1-25 wt %, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25 wt %, based on the total weight of the negative electrode active material.

[0137] In one example, based on the total weight of the negative electrode active material, the content of the silicon-based material is 3-18 wt %.

[0138] Research has found that when the content of silicon-based materials in the negative electrode active material is within a specific range, the surface capacity of the negative electrode sheet can be increased, and the amount of negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, and further reducing the transmission path of lithium ions, thereby improving the kinetic performance and energy density of lithium-ion batteries.

[0139] In one example, the negative electrode active material includes a mixture of artificial graphite and the silicon-based material.

[0140] In the present disclosure, based on the total weight of the negative electrode coating, the content of the negative electrode active material may be 70-99.7 wt % (e.g., 70, 75, 80, 85, 90, 95 or 99.7 wt %), the content of the negative electrode conductor may be 0.1-10 wt % (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 wt %), the content of the negative electrode binder may be 0.1-10 wt % (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 wt %), and the content of the thickener may be 0.1-10 wt % (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 wt %).

[0141] In one example, based on the total weight of the negative electrode coating, the content of the negative electrode active material is 85-99.4 wt %, the content of the negative electrode conductor is 0.2-5 wt %, the content of the negative electrode binder is 0.2-5 wt %, and the content of the thickener is 0.2-5 wt %.

[0142] In the present disclosure, the components of the lithium-ion battery other than the positive electrode sheet and the negative electrode sheet (such as a separator and an electrolyte) can be conventionally selected in the art.

[0143] In one example, the lithium-ion battery further includes a separator and an electrolyte.

[0144] In the present disclosure, the isolation membrane may include an isolation membrane conventionally used in the art, for example, including at least one of a polyethylene film and a polypropylene film; for example, including a base membrane and the ceramic layer arranged on both sides of the base membrane; for example, including a base membrane and a diaphragm ceramic layer and a polymer layer respectively arranged on both sides of the base membrane.

[0145] The diaphragm ceramic layer may include ceramic particles. The ceramic particles may include at least one of boehmite, silicon dioxide, magnesium oxide, aluminum oxide, and aluminum hydroxide. The base film may be a polyethylene film.

[0146] In the present disclosure, the electrolyte may include a lithium salt and an organic solvent. The lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bistrifluorosulfonylimide, and lithium bisfluorosulfonylimide. The organic solvent may include at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0147] The electrolyte may further include an additive, and the additive may include at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene methanedisulfonate, propylene sultone, and succinic anhydride.

[0148] The lithium-ion battery can be assembled in accordance with conventional methods in the art.

[0149] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0150] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0151] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0152] The following examples are used to illustrate the lithium-ion batteries of the present disclosure.

[0153] Example 1

[0154] Follow these steps to prepare a lithium-ion battery:

[0155] (1) Preparation of negative electrode sheet

[0156] Artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed uniformly in a mass ratio of 96.9:0.5:1.3:1.3, and deionized water was added to obtain a negative electrode slurry with a solid content of 45%. The negative electrode slurry was coated on a copper foil using a coating machine and dried at 100°C. A concave portion was formed on the outer surface of the negative electrode coating, wherein the parameters of the concave portion are shown in Tables 1-1, 1-2 and 1-3, to obtain a negative electrode sheet, wherein the surface density of the negative electrode sheet is 8.53 mg / cm 2 , the thickness of the negative electrode coating is 45μm.

[0157] (2) Preparation of positive electrode sheet

[0158] Lithium cobalt oxide (doped with Al, Mg and Y in amounts of 8000 ppm, 3000 ppm and 8000 ppm, respectively; the outer shell includes Zr with a Zr content of 1.7%), conductive carbon black and polyvinylidene fluoride are uniformly mixed in a mass ratio of 97.2:1.5:1.3, and N-methylpyrrolidone (NMP) is added to obtain a positive electrode slurry with a solid content of 72%. The positive electrode slurry is coated on an aluminum foil using a coating machine and dried at 120°C. A concave portion is formed on the outer surface of the positive electrode coating, wherein the parameters of the concave portion are shown in Tables 1-1, 1-2 and 1-3. A positive electrode sheet is obtained, wherein the surface density of the positive electrode sheet is 16.03 mg / cm 2 The thickness of the positive electrode active layer is 39 μm.

[0159] (3) Preparation of lithium-ion batteries

[0160] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a weight ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a lithium-ion battery is obtained by a hot pressing process.

[0161] Example 2 and Example 3 are carried out with reference to Example 1, except that the parameters of the positive electrode active material and the recess (pore) are changed, wherein the parameters of the recess (pore) are shown in Tables 1-1, 1-2 and 1-3; in Example 2, the lithium cobalt oxide in Example 1 is replaced by lithium cobalt oxide (the doped metal elements are Al, Mg and Ti, and the doping amounts are 6000ppm, 1000ppm and 1000ppm respectively; the outer shell includes Y, and the content of Y is 1.2%); in Example 3, the lithium cobalt oxide in Example 1 is replaced by lithium cobalt oxide (the doped metal elements are Al, Mg and La, and the doping amounts are 8000ppm, 2500ppm and 1000ppm respectively; the outer shell includes Al, and the content of Al is 0.5%).

[0162] Example 4 Group

[0163] The process is carried out with reference to Example 1, except that the type of the recess is changed, i.e., the recess in Examples 4a-4c is a groove; the recess in Examples 4d-4f is a hole + groove; and the recess in Examples 4g-4i is a network structure divided by grooves. The specific parameters are shown in Tables 1-1, 1-2 and 1-3.

[0164] Example 5 was carried out in accordance with Example 1, except that the ratio of the pore spacing of the positive electrode coating to the pore spacing of the negative electrode coating was changed. The specific parameters are shown in Tables 1-1, 1-2 and 1-3.

[0165] The sixth embodiment was carried out in accordance with the first embodiment, except that the depth and width of the concave portion of the positive electrode coating and the depth and width of the concave portion of the negative electrode coating were changed. The specific parameters are shown in Tables 1-1, 1-2 and 1-3.

[0166] The Example 7 group was carried out in accordance with the Example 1, except that the depth, width and hole pitch of the concave portion of the negative electrode coating were changed, as shown in Tables 1-1, 1-2 and 1-3.

[0167] Example 8 is carried out with reference to Example 1, except that the negative electrode active material is changed. Specifically, the artificial graphite is replaced by a mixture of equal masses of silicon-carbon material and artificial graphite, wherein the mass ratio of the silicon-carbon material to the artificial graphite is 15:85, and the silicon-carbon material is a material formed by silicon filling the pores of porous amorphous carbon.

[0168] Comparative Example 1

[0169] The process is carried out in accordance with Example 1, except that no recess is provided on the outer surfaces of the positive and negative electrode sheets.

[0170] Comparative Example 2

[0171] The process is carried out in accordance with Example 8, except that no recess is provided on the outer surfaces of the positive and negative electrode sheets.

[0172] Comparative Example 3

[0173] The process was carried out in accordance with Example 1, except that the recess was only provided on the outer surface of the negative electrode sheet, as shown in Tables 1-1, 1-2 and 1-3.

[0174] Table 1-1

[0175] Table 1-2

[0176] Table 1-3

[0177] Note: “-” in Tables 1-1, 1-2 and 1-3 indicates no value.

[0178] Among them, in Tables 1-1, 1-2 and 1-3, in Example 4d, the spacing between the holes and grooves on the positive electrode sheet is 225 μm, and the spacing between the holes and grooves on the negative electrode sheet is 146.3 μm; in Example 4e, the spacing between the holes and grooves on the positive electrode sheet is 190 μm, and the spacing between the holes and grooves on the negative electrode sheet is 150.1 μm; in Example 4f, the spacing between the holes and grooves on the positive electrode sheet is 100 μm, and the spacing between the holes and grooves on the negative electrode sheet is 90 μm.

[0179] Test Case I

[0180] (1) Depth test of concave part

[0181] The positive and negative electrode sheets prepared in the examples and comparative examples were tested for the depth of the recesses. The specific testing method is as follows:

[0182] Using a 3D profilometer, randomly select 50 holes on the entire positive / negative electrode sheet or select all the grooves on the entire positive / negative electrode sheet, measure the depth of the recesses, take the average value, and record the results in Tables 1-1, 1-2, and 1-3.

[0183] (2) Aperture test

[0184] The positive and negative electrode sheets prepared in the examples and comparative examples were tested for pore size. The specific testing method is as follows:

[0185] Using SEM, 50 holes were randomly selected on the entire positive electrode sheet / negative electrode sheet, and the pore size of each hole was measured. The average value was taken and the results were recorded in Tables 1-1, 1-2 and 1-3.

[0186] (3) Slot width test

[0187] The positive and negative electrode sheets prepared in the examples and comparative examples were tested for groove width. The specific testing method is as follows:

[0188] Using SEM, all the slots on the entire positive / negative electrode sheet were selected, and the slot width of each slot was measured. The average value was taken and the results were recorded in Tables 1-1, 1-2 and 1-3.

[0189] (4) Hole spacing test

[0190] The positive and negative electrode sheets prepared in the examples and comparative examples were tested for hole spacing. The specific testing method is as follows:

[0191] Using SEM, 50 holes were randomly selected on the entire positive / negative electrode sheet, and the distance between two adjacent holes was measured. The minimum value was taken and the results were recorded in Tables 1-1, 1-2 and 1-3.

[0192] (5) Slot pitch test

[0193] The positive and negative electrode sheets prepared in the examples and comparative examples were tested for slot spacing. The specific testing method is as follows:

[0194] Using SEM, select all the slots on the entire positive / negative electrode sheet, test and obtain the slot distance between two adjacent slots, take the minimum value, and record the results in Tables 1-1, 1-2, and 1-3.

[0195] (6) Testing the side length of rectangular network

[0196] The positive and negative electrode sheets prepared in the examples and comparative examples were tested for the side length of a rectangular network. The specific testing method is as follows:

[0197] Using SEM, all rectangular networks were selected on the entire positive / negative electrode sheet, and the long and short side lengths of each rectangular network were measured. The average value was taken and the results were recorded in Tables 1-1, 1-2 and 1-3.

[0198] Test Case II

[0199] (1) Capacity retention test

[0200] The lithium-ion batteries prepared in the examples and comparative examples were tested for capacity retention, and the specific testing method is as follows:

[0201] At 25°C, 3.0C step charge / 0.7C discharge (where the charge process starts at 3.0V and ends at 4.5V; the discharge process starts at 4.5V and ends at 3.0V) were performed for 800T cycles. The capacity retention rate was calculated as follows:

[0202] Capacity retention rate (%) = Ct / C0×100%,

[0203] The last discharge capacity is Ct, and the first discharge capacity is C0. The results are recorded in Table 2.

[0204] (2) Expansion rate test

[0205] At 25°C, 3.0C step charge / 0.7C discharge (where the charge process starts at 3.0V and ends at 4.5V; the discharge process starts at 4.5V and ends at 3.0V) was performed for 800T cycles. The expansion ratio was calculated as follows:

[0206] Expansion rate (%) = [(Ht / H0)-1] × 100%,

[0207] The thickness of the lithium-ion battery in the last fully charged state is Ht, and the thickness of the lithium-ion battery in the first fully charged state is H0. The results are recorded in Table 2.

[0208] (3) Charging speed test

[0209] Perform 3.0C step charging at 25°C until the lithium-ion battery reaches 100% SOC (where the starting voltage of the charging process is 3.0V and the cut-off voltage is 4.5V). Record the time required from 0% SOC to 100% SOC. The results are recorded in Table 2.

[0210] (4) Energy density test

[0211] At 25°C, a 3.0C step charge was performed until the lithium-ion battery reached 100% SOC, followed by a 0.2C discharge to 3.0V. The starting voltage of the charging process was 3.0V and the cut-off voltage was 4.5V; the starting voltage of the discharging process was 4.5V and the cut-off voltage was 3.0V. The discharge capacity was recorded. The energy density was calculated as follows:

[0212] Energy density = 0.2C discharge capacity × voltage platform / lithium-ion battery volume,

[0213] The voltage platforms of different systems are different. The voltage platform of the embodiment and comparative example of the present disclosure is 3.95V. The results are recorded in Table 2.

[0214] Table 2

[0215] As can be seen from Table 2, the lithium ion battery of the present disclosure improves the 800T capacity retention rate compared with the comparative example.

[0216] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating on at least one side of the surface of the positive electrode current collector, and the surface of the positive electrode coating away from the positive electrode current collector contains a concave portion; the negative electrode sheet comprises a negative electrode current collector and a negative electrode coating on at least one side of the surface of the negative electrode current collector, and the surface of the negative electrode coating away from the negative electrode current collector contains a concave portion; the width of the concave portion of the positive electrode coating is ≤ the width of the concave portion of the negative electrode coating.

2. The lithium ion battery according to claim 1, wherein The volume of the concave portion of the negative electrode coating is greater than or equal to the volume of the concave portion of the positive electrode coating; Preferably, the volume of the concave portion of the negative electrode coating is greater than the volume of the concave portion of the positive electrode coating.

3. The lithium ion battery according to claim 1 or 2, wherein: The ratio of the depth of the concave portion of the positive electrode coating to the depth of the concave portion of the negative electrode coating is (0.2-1):1; preferably (0.4-0.9):1; And / or, the ratio of the width of the concave portion of the positive electrode coating to the width of the concave portion of the negative electrode coating is (0.3-1):1; preferably (0.35-0.9):

1.

4. The lithium ion battery according to any one of claims 1 to 3, wherein: The recess comprises a hole and / or a groove.

5. The lithium ion battery according to any one of claims 1 to 4, wherein: The ratio of the pore distance of the positive electrode coating to the pore distance of the negative electrode coating is 1:(0.5-1); preferably 1:(0.61-0.92); And / or, the pores of the positive electrode coating have a pore pitch of 50nm-500nm; And / or, the pores of the negative electrode coating have a pore pitch of 50 nm to 500 nm; And / or, the ratio of the groove pitch of the positive electrode coating to the groove pitch of the negative electrode coating is 1:(0.5-1); preferably 1:(0.55-0.9); And / or, the groove pitch of the grooves of the positive electrode coating is 100 μm-2000 μm; And / or, the groove pitch of the grooves of the negative electrode coating is 100 μm-2000 μm.

6. The lithium ion battery according to any one of claims 1 to 5, wherein: The ratio of the pore diameter to the pore depth of the positive electrode coating is (1.6-8):1; preferably (3-5):1; And / or, the ratio of the pore diameter to the pore depth of the pores of the negative electrode coating is (1.6-8):1; preferably (3.5-5):1; And / or, the ratio of the groove width to the groove depth of the groove of the positive electrode coating is (1.6-8):1; preferably (3-5):1; And / or, the ratio of the groove width to the groove depth of the groove of the negative electrode coating is (1.6-8):1; preferably (3.5-5):

1.

7. The lithium ion battery according to any one of claims 1 to 6, wherein: The pores of the positive electrode coating have a pore size of 5 μm-125 μm; And / or, the pores of the positive electrode coating have a pore depth of 3 μm-44 μm; And / or, the pores of the negative electrode coating have a pore size of 8 μm-125 μm; And / or, the pores of the negative electrode coating have a pore depth of 1 μm-44 μm; And / or, the groove width of the groove of the positive electrode coating is 10 μm-148 μm; And / or, the groove depth of the groove of the positive electrode coating is 6 μm-52 μm; And / or, the groove width of the groove of the negative electrode coating is 30 μm-148 μm; And / or, the grooves of the negative electrode coating have a depth of 20 μm-52 μm.

8. The lithium ion battery according to any one of claims 1 to 7, wherein: The outer surface of the positive electrode coating has holes and grooves; and / or, the size from the edge of the hole of the positive electrode coating to the edge of the groove of the positive electrode coating is 100 μm-500 μm; And / or, the outer surface of the negative electrode coating has pores and grooves; And / or, a size from an edge of the pores of the negative electrode coating to an edge of the grooves of the negative electrode coating is 80 μm to 480 μm.

9. The lithium ion battery according to any one of claims 1 to 8, wherein: The outer surface of the positive electrode coating has a network structure divided by a plurality of grooves; And / or, the outer surface of the negative electrode coating has a network structure divided by a plurality of grooves.

10. The lithium ion battery according to any one of claims 1 to 9, wherein: The surface density of the positive electrode sheet is 10 mg / cm 2 -35mg / cm 2 ; And / or, the thickness of the positive electrode coating is 30 μm-110 μm; And / or, the surface density of the negative electrode sheet is 7 mg / cm 2 -22mg / cm 2 ; And / or, the thickness of the negative electrode coating is 35 μm-120 μm.

11. The lithium ion battery according to any one of claims 1 to 10, wherein: The positive electrode coating layer includes a positive electrode active material. The positive electrode active material includes first particles and second particles. The median particle size Dv50 of the first particles is greater than the median particle size Dv50 of the second particles.

12. The lithium ion battery according to claim 11, wherein: The positive electrode active material includes lithium cobalt oxide having a core-shell structure.

13. The lithium ion battery according to claim 12, wherein: The core of the core-shell structure includes lithium cobalt oxide doped with metal elements, wherein the doped metal elements include at least one of Al, Mg and M, and M is selected from at least one of Ti, Zr, Y, La, Ni, Mn, Ce and W; Preferably, the doping amount of the doped metal element Al is 100 ppm-18000 ppm; the doping amount of the doped metal element Mg is 100 ppm-4500 ppm; the total doping amount of the doped metal elements Al, Mg and M is 3000 ppm-35000 ppm. And / or, the shell of the core-shell structure includes a compound containing an element R, and R is selected from at least one of Al, Mg, Ti, Zr, Y, La, Ni and Mn.

14. The lithium ion battery according to any one of claims 1 to 13, wherein: The negative electrode coating includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, hard carbon, soft carbon and silicon-based materials.

15. The lithium ion battery according to claim 14, wherein: The silicon-based material includes at least one of silicon, silicon-oxygen, silicon-carbon and silicon alloy; Preferably, the negative electrode active material comprises artificial graphite and the silicon-based material; Preferably, based on the total weight of the negative electrode active material, the content of the silicon-based material is 1-25 wt %.

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