Positive electrode sheet and battery

Abstract

A positive electrode sheet and a battery comprising the positive electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer on at least one side surface of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprising first particles and second particles, and the median diameter Dv 50 of the first particles being greater than the median diameter Dv 50 of the second particles; the surface of the positive electrode active layer away from the positive electrode current collector contains holes, each hole contains recessed portions, and the number n of the concave portions in each hole is greater than or equal to 2; and the recessed portions contain the second particles, and in the recessed portions of an optional hole, there are 10-150 second particles. The positive electrode sheet has both a high energy density and fast charge performance.

Description

Positive electrode and battery Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular to a positive electrode sheet and a battery comprising the positive electrode sheet. Technical Background

[0002] With the advent of the 5G era and the rapid development of lithium-ion battery technology, people are placing higher demands on lithium-ion battery energy density, fast charging capabilities, and charge and discharge rates. High-energy-density, fast-charging lithium-ion batteries are the trend in consumer lithium-ion battery development. However, as the energy density increases, the thickness of the lithium-ion battery's positive electrode increases, leading to longer charging times and incomplete utilization of the lithium-ion battery's capacity.

[0003] Therefore, it is very important to find a battery that combines high energy density and fast charging performance.

[0004] Summary of the Invention

[0005] The present invention aims to overcome the problem of the prior art that high energy density and fast charging cannot be achieved at the same time, and provides a positive electrode sheet and a battery including the positive electrode sheet. The battery including the positive electrode sheet of the present invention can achieve both high energy density and fast charging performance.

[0006] In a first aspect, the present disclosure provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer on at least one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises first particles and second particles, wherein the median particle size Dv50 of the first particles is greater than the median particle size Dv50 of the second particles; the positive electrode active layer comprises pores on a surface away from the positive electrode current collector, wherein the pores comprise recesses, and the number n of the recesses in each pore is ≥2; the recesses comprise the second particles, and in any recess of the pore, the number of the second particles is 10-150.

[0007] A second aspect of the present disclosure provides a battery, comprising the positive electrode sheet described in the first aspect of the present disclosure.

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

[0009] (1) The positive electrode sheet disclosed herein is provided with holes on the surface of the positive electrode active layer, which can improve the wettability of the electrolyte to the positive electrode active material near the positive electrode current collector, thereby improving the utilization rate of the positive electrode active material near the positive electrode current collector and improving the energy density and fast charging performance of the battery;

[0010] (2) The positive electrode sheet disclosed in the present invention is provided with holes on the surface of the positive electrode active layer, and the holes contain recesses. The recesses formed do not destroy the complete positive electrode active material particles, thereby ensuring the stability of the positive electrode active material structure and improving the cycle life of the battery; and the number of recesses in each hole is within a specific range. The recesses provide sites for the embedding and extraction of lithium ions, which is beneficial to the embedding of lithium ions and the infiltration of the electrolyte, and can further improve the cycle life of the battery; at the same time, controlling the number of second particles in the recesses can increase the contact area between the electrolyte and the positive electrode active material, improve the structural stability of the positive electrode sheet, and thus improve the energy density of the 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 scanning electron microscope (SEM) image of a positive electrode sheet in an example of the present disclosure.

[0014] FIG3 is a scanning electron microscope (SEM) image of a partial cross section of a positive electrode sheet in an example of the present disclosure.

[0015] FIG4 is a local scanning electron microscope (SEM) image of a positive electrode sheet in an example of the present disclosure.

[0016] FIG5 is a scanning electron microscope (SEM) image of a positive electrode sheet in an example of the present disclosure.

[0017] FIG6 shows a scanning electron microscope (SEM) image of a cross section of a positive electrode sheet in an example of the present disclosure. DETAILED DESCRIPTION

[0018] 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.

[0019] The first aspect of the present disclosure provides a positive electrode sheet, which may include a positive electrode current collector and a positive electrode active layer on at least one side of the positive electrode current collector. As shown in Figure 1, a cross-sectional schematic diagram of a positive electrode sheet in an example of the present disclosure is shown, wherein Figure 1(a) shows the case where the positive electrode active layer is set on one side; Figure 1(b) and Figure 1(c) show the cases where the positive electrode active layer is set on both sides. In Figure 1(a), the positive electrode sheet includes a positive electrode current collector 1 and a positive electrode active layer 2 on one side of the positive electrode current collector 1; in Figure 1(b) and Figure 1(c), the positive electrode sheet includes a positive electrode current collector 1 and a positive electrode active layer 2 on both sides of the positive electrode current collector 1.

[0020] In the present disclosure, the positive active layer may include a positive active material. The positive 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.

[0021] The inventors of the present disclosure have discovered 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 battery.

[0022] In the present disclosure, the positive electrode active layer may contain pores on a surface away from the positive electrode current collector.

[0023] In the present disclosure, the hole may contain recesses, and the number n of the recesses in each hole is ≥ 2 (for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 or 35).

[0024] In the present disclosure, the recess may contain the second particles, and in the recess of any of the holes, the number of the second particles may be 10-150 (e.g., 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145 or 150).

[0025] When the surface density of the positive electrode is greater than or equal to 10 mg / cm 2When the positive electrode sheet is too thick during the charge and discharge cycle, the electrolyte's wettability to the positive electrode active material close to the positive electrode current collector becomes poor, and the transmission distance of lithium ions is long, which results in a low utilization rate of the positive electrode active material, and ultimately leads to incomplete battery capacity. The inventors of the present disclosure have discovered that providing holes on the outer surface of the positive electrode active layer can effectively improve the electrolyte's wettability to the positive electrode active material close to the positive electrode current collector, shorten the transmission distance of lithium ions, and increase the effective utilization rate of the positive electrode active material, thereby simultaneously improving the energy density and rate performance of the battery. The inventors of the present disclosure have further discovered that when the holes provided on the outer surface of the positive electrode active layer contain recesses, and the number of recesses in each hole is within a specific range, the cycle life of the battery can be improved. The reason may be that the above-mentioned concave portion is generally caused by the absence of the first particle in the positive electrode active layer, and the first particle includes the positive electrode active material. The absence of this first particle is the absence of a complete positive electrode active material particle, and no new positive electrode active material interface will be formed, which can avoid the occurrence of side reactions, thereby effectively improving the cycle life of the battery. On the contrary, the absence of the above-mentioned concave portion indicates that the complete positive electrode active material particle is broken, resulting in the new surface inside the particle being exposed to the outside and in contact with the electrolyte, causing the occurrence of side reactions, consuming the electrolyte, and worsening the cycle life. The following is an example of lithium cobalt oxide particles with modified positive electrode active materials (the modification process includes coating the surface of the positive electrode active material and bulk doping the positive electrode active material):

[0026] This specific concave portion will not destroy the coating layer on the surface of the lithium cobalt oxide particles. The function of the coating layer is to reduce the contact between the active sites on the surface of the lithium cobalt oxide particles and the electrolyte, thereby reducing side reactions. On the contrary, the absence of the above-mentioned specific concave portion will destroy the coating layer on the surface of the lithium cobalt oxide particles, increase the contact between the surface of the lithium cobalt oxide particles and the electrolyte, and increase the risk of side reactions. This specific concave portion will also not destroy the bulk doping. The function of doping is to stabilize the surface structure and prevent the entire particle from collapsing during the charge and discharge process. On the contrary, the absence of the above-mentioned specific concave portion will destroy the bulk doping, weaken the structural stability of the lithium cobalt oxide particles, and thus affect the cycle life of the battery. Therefore, this specific concave portion can reduce the side reactions between the positive electrode sheet and the electrolyte, effectively improving the high-temperature cycle life of the battery.

[0027] At the same time, by controlling the number of second particles in the recess, the contact area between the electrolyte and the second particles can be increased, the contact sites can be increased, and the wetting effect of the electrolyte can be improved; in addition, the recess itself also increases the wettability of the electrolyte. The two work together to significantly improve the wetting effect of the electrolyte.

[0028] In one embodiment, n is 2-20.

[0029] In one embodiment, n is 5-10.

[0030] In one example, the diameter of the recess may be 5 μm-55 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or 55 μm.

[0031] In one example, the depth of the recess may be 5 μm-55 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or 55 μm.

[0032] In one example, the diameter of the recess is 10 μm-45 μm.

[0033] In one example, the depth of the recess is 10 μm-45 μm.

[0034] In the present disclosure, n can be obtained by conventional testing methods in the art, such as observation using a scanning electron microscope (SEM). The diameter of the recess can be obtained by conventional testing methods in the art, such as measurement using an SEM. The depth of the recess can be obtained by conventional testing methods in the art, such as measurement using a 3D profilometer.

[0035] In the present disclosure, the diameter of the recess has the conventional meaning in this field. When the recess is a regular sphere, the diameter of the recess is the diameter of the sphere; when the recess is an irregular sphere, the diameter of the recess is the diameter of the circumscribed sphere of the irregular sphere.

[0036] In the present disclosure, the depth of the recess refers to the maximum value of the vertical distance from the bottom of the recess to the outer surface of the positive electrode active layer.

[0037] In the present disclosure, the pores may be obtained by laser pore creation.

[0038] In the present disclosure, a conductive agent and / or a binder is included between the second particles and the recessed portion, and a conductive agent and / or a binder is included between the second particles.

[0039] In the present disclosure, the hole may further include a convex portion, the convex portion being formed at the junction of two adjacent concave portions, and the convex portion may include the second particles.

[0040] By adjusting the working parameters of laser hole making (such as power, etc.), the number of holes, the number of protrusions, etc. can be controlled.

[0041] In the present disclosure, the average particle size of the second particles may be 1 μm-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0042] In one example, the average particle size of the second particles is 2 μm-8 μm.

[0043] In one example, the average particle size of the second particles is 3 μm-7 μm.

[0044] In the present disclosure, the number of the second particles contained in the protrusion is 10-150, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145 or 150.

[0045] In the present disclosure, the average particle size of the second particles can be measured using conventional testing methods in the art, such as SEM. The number of the second particles in the concave portion of each hole and the number of the second particles contained in the convex portion can be measured using conventional testing methods in the art, such as SEM. By controlling the solid content of the slurry used, the number of the second particles in the concave portion and the number of the second particles contained in the convex portion can be controlled.

[0046] In the present disclosure, the particle sizes Dv50 and Dv90 of the positive electrode active material and the depth H of the pores may satisfy the following relationship: 15×Dv50 / Dv90 <H<(10×Dv90 / Dv50)+28。

[0047] The inventors of the present disclosure have discovered that when the particle size Dv50 and Dv90 of the positive electrode active material and the depth H of the pores satisfy a specific relationship, the rate performance and cycle life of the battery can be further improved. When H is too small, the electrolyte does not wet the positive electrode active material close to the current collector well, affecting the rate performance of the battery; and when H is too large, it is necessary to increase the energy to form pores. At this time, excessive energy may damage the intact positive electrode active material particles, thereby affecting the service life of the battery. When the particle size of the positive electrode active material and the depth H of the pores satisfy the above relationship, the laser acts on the positive electrode active material particles, and the energy absorbed by the particle surface can just break the binder between the particles, causing them to fail and fall off, thereby improving the service life of the battery while ensuring the rate performance of the battery.

[0048] In the present disclosure, the particle sizes Dv50 and Dv90 of the positive electrode active material can be measured by conventional testing methods in the art, such as by a laser particle size analyzer.

[0049] In the present disclosure, 11 μm≦Dv50≦20 μm, for example, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm.

[0050] In the present disclosure, 25 μm ≤ Dv90 ≤ 33 μm, for example, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, or 33 μm.

[0051] The inventors of the present disclosure discovered that when the particle sizes Dv50 and Dv90 of the positive electrode active material are within a specific range, the combination of its particles can increase the gaps between the particles, thereby improving the wetting effect of the electrolyte, increasing the active sites, and at the same time helping the electrolyte to form a CEI film on the surface of the recess, thereby protecting the positive electrode sheet; when the particle sizes Dv50 and Dv90 of the positive electrode active material are within a specific range, it can form the recess without destroying the complete positive electrode active material particles, so no new active material interface will be formed, thereby ensuring the stability of the positive electrode active material structure and improving the cycle life of the battery.

[0052] In the present disclosure, the depth H of the hole may be the maximum value of the depth of the recess.

[0053] In the present disclosure, 5 μm ≤ H ≤ 55 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or 55 μm.

[0054] In one example, 10 μm ≤ H ≤ 47 μm.

[0055] Figure 2 shows a scanning electron microscope (SEM) image of a positive electrode sheet in an example of the present disclosure, and Figure 3 shows a scanning electron microscope (SEM) image of a partial cross-section of a positive electrode sheet in an example of the present disclosure. As can be seen from Figures 2 and 3, the outer surface of the positive electrode active layer has pores. Figure 4 shows a scanning electron microscope (SEM) image of a partial section of a positive electrode sheet in an example of the present disclosure, where the portion outlined by the black dashed line in the figure is a concave portion. As can be seen from Figure 4, the number n of concave portions in the pores is 7, and the diameter of the concave portion is 10μm-30μm.

[0056] In the present disclosure, during the pore-forming process, the projection of the pores onto the positive electrode active layer may have an irregular curved polygonal shape. FIG5 shows a scanning electron microscope (SEM) image of a positive electrode sheet in one embodiment of the present disclosure. FIG5 shows that the projection of the pores onto the positive electrode active layer has an irregular curved polygonal shape.

[0057] In the present disclosure, the straight-line distance between any two points on the projection of the hole on the surface of the positive electrode active layer is L, where 0 < L ≤ 160 μm, such as 0.1 μm, 0.5 μm, 1 μm, 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, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm or 160 μm.

[0058] In one example, 0 < L ≤ 135 μm.

[0059] In one example, 0 < L ≤ 115 μm.

[0060] In the present disclosure, the aperture diameter of the hole on the side away from the positive electrode current collector is D1, and the aperture diameter of the hole on the side close to the positive electrode current collector is D2, where D1 > D2.

[0061] In the present disclosure, the aperture diameter of the hole has the conventional meaning in the art. Generally, when the shape of the projection of the hole on the positive electrode coating is a "regular circle", the aperture 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 not a "regular circle" (such as an ellipse or an irregular curved polygon), the aperture diameter of the hole is the diameter of an equivalent circle with the same area as the non-"regular circle".

[0062] In the present disclosure, the pitch of the holes can be 10 μm - 970 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 970 μm.

[0063] In one example, the pitch of the holes is 50 μm - 600 μm.

[0064] In one example, the pitch of the holes is 100 μm - 550 μm.

[0065] In the present disclosure, the pitch of the holes refers to the shortest distance between the edges of two adjacent holes.

[0066] In the present disclosure, the areal density of the positive electrode sheet can be 10 mg / cm 2 -35 mg / 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 .

[0067] The inventors of the present disclosure have discovered that when the surface density of the positive electrode sheet is within a specific range, the energy density of the battery can be improved; at the same time, providing holes on the outer surface of the positive electrode active layer 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 battery.

[0068] In the present disclosure, the thickness of the positive electrode active layer may be 30 μm-110 μm, for example, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or 110 μm.

[0069] In the present disclosure, the depth of the pores is smaller than the thickness of the positive electrode active layer.

[0070] In one example, the difference between the thickness of the positive electrode active layer and the depth of the pores is ≤5 μm.

[0071] In the present disclosure, the thickness of the positive electrode active layer refers to the thickness of the positive electrode active layer on one side.

[0072] In the present disclosure, the periphery of the hole may include a protrusion, and the height of the protrusion may be 0-5 μm (e.g., 0 μm, 0.01 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm). When 0 μm is less than the height of the protrusion and ≤ 5 μm, it is beneficial to increase the contact area between the positive electrode sheet and the electrolyte.

[0073] In one example, the height of the protrusion is 0 μm-0.2 μm.

[0074] The inventors of the present disclosure have discovered that when the height of the protrusion is within a specific range, the contact area between the positive electrode sheet and the electrolyte can be increased, thereby improving the reaction rate and charge transfer efficiency of the battery; at the same time, the activity of the positive electrode active material can be ensured, thereby improving the cycle stability and energy density of the battery.

[0075] In the present disclosure, the height of the protrusions can be measured by conventional means in the art, such as by a 3D profilometer.

[0076] In the present disclosure, the positive active layer may include N coating layers, where N≧1 (eg, N=1, 2, 3, 4, 5, 6, 7, or 8).

[0077] In one embodiment, the positive electrode active layer is a single layer.

[0078] In one example, the positive electrode active layer includes a first coating layer and a second coating layer sequentially stacked along the thickness direction of the positive electrode sheet.

[0079] In one example, the positive electrode active layer includes a first coating layer, a second coating layer, and a third coating layer stacked in sequence along the thickness direction of the positive electrode sheet.

[0080] In the present disclosure, the N-layer coating layer can be obtained by drying the same positive electrode active layer slurry, or by drying different positive electrode active layer slurries.

[0081] In the present disclosure, the positive electrode sheet may further include a ceramic layer, which may be located on the outer surface of the positive electrode active layer. FIG6 shows a scanning electron microscope (SEM) image of a cross-section of a positive electrode sheet in one embodiment of the present disclosure. As can be seen from the figure, the portion enclosed by the dotted square is the ceramic layer, and the portion enclosed by the dotted circle is the pore. The ceramic layer is located on the outer surface of the positive electrode active layer, and the ceramic layer covers the surface of the pore.

[0082] The inventors of the present disclosure discovered that when the outer surface of the positive electrode active layer includes a ceramic layer, the ceramic layer can form a closed structure with the pores on the outer surface of the positive electrode active layer. The closed structure is similar to a liquid storage tank, which is conducive to storing electrolyte and infiltrating the positive electrode active material. In addition, the ceramic layer has liquid storage capacity and can be tightly attached to the pore wall to increase the liquid storage capacity at this position. The ceramic layer can also improve the safety of the battery.

[0083] In the present disclosure, the thickness of the ceramic layer may be 0.3 μm-3 μm, for example, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm.

[0084] In the present disclosure, the ceramic layer may include ceramic particles. The ceramic particles may have a median particle size Dv50 of 1 nm to 3 μm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm or 3 μm.

[0085] The inventors of the present disclosure discovered that when the median particle size Dv50 of the ceramic particles is within a specific range, it can provide more channels and paths for the transmission of lithium ions, which is conducive to the rapid transmission of lithium ions, absorbs more electrolyte, increases the battery electrolyte retention, and extends the battery cycle life.

[0086] In the present disclosure, the ceramic particles may include at least one of boehmite, silica, magnesia, alumina, and aluminum hydroxide.

[0087] In the present disclosure, the positive electrode active layer may include a positive electrode active material, a binder, and a conductive agent. The positive electrode active material may include at least one of lithium cobalt oxide, 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 binder may include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide. The 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.

[0088] In one example, the positive electrode active material includes a doping-modified and / or coating-modified positive electrode active material.

[0089] 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.

[0090] 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.

[0091] 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), The doping amount of the doped metal element Mg can be 100ppm-4500ppm (for example, 100ppm, 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).

[0092] The inventors of the present disclosure have discovered 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 holes are 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 improving the cycle life of the battery.

[0093] In one example, the doping metal element M includes at least one of Ti, Y, and La.

[0094] 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 wt%-5 wt%, for example, 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.18 wt%, 0.25 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%.

[0095] The inventors of the present disclosure discovered 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 suppressed, and when holes are 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 improving the cycle life of the battery.

[0096] 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).

[0097] In the present disclosure, based on the total weight of the positive electrode active layer, the content of the positive electrode active material may be 80 wt%-99.8 wt% (e.g., 80 wt%, 85 wt%, 90 wt%, 95 wt% or 99.8 wt%), the content of the conductive agent may be 0.1 wt%-10 wt% (e.g., 10 wt%, 7.5 wt%, 5 wt%, 2.5 wt% or 0.1 wt%), and the content of the binder may be 0.1 wt%-10 wt% (e.g., 10 wt%, 7.5 wt%, 5 wt%, 2.5 wt% or 0.1 wt%).

[0098] In one example, based on the total weight of the positive electrode active layer, the content of the positive electrode active material is 90 wt %-99.6 wt %, the content of the conductive agent is 0.2 wt %-5 wt %, and the content of the binder is 0.2 wt %-5 wt %.

[0099] The positive electrode sheet disclosed in the present invention can fully improve the problem that during the charge and discharge process of the battery with large surface density, the thickness of the positive electrode sheet is too large, resulting in poor electrolyte penetration into the positive electrode active material near the positive electrode current collector, causing the lithium ion transmission distance to be too long, the positive electrode active material cannot be effectively utilized, and ultimately leading to incomplete battery capacity. Furthermore, the surface of the positive electrode sheet disclosed in the present invention is covered with a ceramic layer, which can form a liquid storage tank with the holes on the positive electrode active layer, which is more conducive to storing the electrolyte, penetrating the positive electrode active material near the positive electrode sheet near the current collector, and improving the utilization rate of the positive electrode active material.

[0100] A second aspect of the present disclosure provides a battery, comprising the positive electrode sheet described in the first aspect of the present disclosure.

[0101] In the present disclosure, the components of the battery other than the positive electrode sheet (such as the negative electrode sheet, the separator, and the electrolyte, etc.) can be conventionally selected in the art.

[0102] In one example, the battery further includes a negative electrode sheet, a separator, and an electrolyte.

[0103] In the present disclosure, the negative electrode sheet may include a negative electrode current collector and a negative electrode active layer on at least one side of the negative electrode current collector. The negative electrode active layer may include a negative electrode active material.

[0104] In the present disclosure, the negative electrode active material may include at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-oxygen, silicon-carbon, and silicon alloy.

[0105] In the present disclosure, the negative electrode active layer may further include a negative electrode conductive agent, a negative electrode binder, and a thickener. The negative electrode conductive agent may include a conductive agent commonly 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 a binder commonly 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 a thickener commonly used in the art, such as sodium carboxymethyl cellulose.

[0106] In the present disclosure, based on the total weight of the negative electrode active layer, the content of the negative electrode active material may be 70 wt % to 99.7 wt % (e.g., 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt % or 99.7 wt %), and the content of the negative electrode conductive agent may be 0.1 wt % to 10 wt % (e.g., 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt %, 0.5 wt % or 0.1 wt %). %), the content of the negative electrode binder may be 0.1 wt %-10 wt % (e.g., 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt %, 0.5 wt % or 0.1 wt %), and the content of the thickener may be 0.1 wt %-10 wt % (e.g., 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt %, 0.5 wt % or 0.1 wt %).

[0107] In one example, based on the total weight of the negative electrode active layer, the content of the negative electrode active material is 85 wt %-99.4 wt %, the content of the negative electrode conductor is 0.2 wt %-5 wt %, the content of the negative electrode binder is 0.2 wt %-5 wt %, and the content of the thickener is 0.2 wt %-5 wt %.

[0108] 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, wherein the diaphragm ceramic layer is arranged on one side of the positive electrode sheet (that is, the diaphragm ceramic layer is adjacent to the positive electrode sheet, and the polymer layer is adjacent to the negative electrode sheet).

[0109] 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.

[0110] In the present disclosure, the ceramic layer on the outer surface of the positive electrode sheet can be obtained by directly coating the ceramic layer slurry on the outer surface of the positive electrode active layer and then drying it; or the diaphragm ceramic layer on the outer surface of the diaphragm can be formed on the outer surface of the positive electrode sheet by hot pressing, wherein there is no restriction on the parameters of the hot pressing, as long as the transfer of the diaphragm ceramic layer can be completed, for example, the temperature of the hot pressing is 80°C and the pressure is 1.1MPa.

[0111] 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).

[0112] 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.

[0113] In one example, the battery is a lithium-ion battery.

[0114] In one embodiment, the battery is a lithium-ion secondary battery.

[0115] The battery can be assembled in accordance with conventional methods in the art.

[0116] 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.

[0117] 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.

[0118] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0119] The following examples are provided to illustrate the batteries of the present disclosure.

[0120] Example 1

[0121] Prepare the battery as follows:

[0122] (1) Preparation of negative electrode sheet

[0123] 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, dried at 100°C, and rolled and cut to obtain a negative electrode sheet.

[0124] (2) Preparation of positive electrode sheet

[0125] Lithium cobalt oxide (doped with Al, Mg and Y in amounts of 8000ppm, 3000ppm and 8000ppm respectively; the shell includes Zr with a Zr content of 1.7%), conductive carbon black and polyvinylidene fluoride are mixed uniformly 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, dried at 120°C, and heated to 37°C. The outer surface of the positive electrode active layer is perforated, wherein the parameters of the pores are shown in Table 1; aluminum oxide particles (median particle size Dv50 is 0.5 μm), methacrylic acid and sodium carboxymethyl cellulose are mixed in a mass ratio of 90:4:6, and NMP is added to prepare a ceramic layer slurry with a solid content of 20%. The ceramic layer slurry is coated on the outer surface of the positive electrode active layer after the perforation using a gravure coater according to the required thickness; the positive electrode sheet is dried, rolled and cut to obtain a positive electrode sheet with a surface density of 23 mg / cm 2 The thickness of the positive electrode active layer is 60 μm. The first particles and the second particles used in this embodiment are both the above-mentioned lithium cobalt oxide, wherein the median particle size Dv50 of the first particles is larger than the median particle size Dv50 of the second particles.

[0126] (3) Preparation of batteries

[0127] 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 battery is obtained by a hot pressing process.

[0128] Examples 2-10 are carried out with reference to Example 1, except that by adjusting the materials and operating parameters, n (the number of recesses in each hole), the recess diameter, the recess depth, the number of second particles in the recess, H, the number of second particles in the protrusion, the average particle size of the second particles, Dv50 and Dv90 of the positive electrode active material, L, spacing, protrusion height, the presence or absence of a ceramic layer, and the thickness of the ceramic layer are changed, as shown in Table 1.

[0129] Table 1

[0130] Example 11

[0131] The process is carried out in accordance with Example 1, except that, in step (2), the 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%) is replaced with the same mass of lithium cobalt oxide that has not been doped or coated.

[0132] Comparative Example 1

[0133] The process is carried out in accordance with Example 1, except that the energy parameters of the punching are adjusted in step (2) to obtain n of 5-10, a diameter of the recess of 32 μm, a depth of the recess of 29 μm, and 170 second particles in the recess.

[0134] Comparative Example 2

[0135] The process is carried out in accordance with Example 1, except that the positive electrode sheet is not punched.

[0136] Test Case I

[0137] (1) Concave number test

[0138] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were tested for the number of recesses. The specific testing method is as follows:

[0139] Using SEM, 50 holes were randomly selected on the entire positive electrode sheet, and the number of recesses in each hole was observed. The results were recorded in Table 1. For example, in Example 1, n was 5-10, that is, in the 50 holes randomly selected on the positive electrode sheet of Example 1, the number of recesses in each hole was different, but all were within the range of 5-10 (including the two end point values).

[0140] (2) Diameter test of the concave part

[0141] The positive electrode sheets (not coated with a ceramic layer) after punching prepared in the examples and comparative examples were tested for the diameter of the recessed portion. The specific testing method is as follows:

[0142] Using SEM, 50 holes were randomly selected on the entire positive electrode sheet, and the diameter of the concave part in each hole was measured. The average value was taken and the results were recorded in Table 1.

[0143] (3) Depth test of concave part

[0144] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were tested for the depth of the recesses. The specific testing method is as follows:

[0145] Using a 3D profilometer, 50 holes were randomly selected on the entire positive electrode sheet. The depth of the concave portion in each hole was measured and the average value was taken. The results are recorded in Table 1.

[0146] (4) Test of the number of second particles in the concave portion

[0147] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were tested for the number of second particles in the concave portion. The specific testing method is as follows:

[0148] Using SEM, 10 holes were randomly selected on the entire positive electrode sheet, and the number of second particles in the concave portion of each hole was observed. The average value was taken and the results were recorded in Table 1.

[0149] (5)H test

[0150] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were subjected to an H test. The specific test method is as follows:

[0151] Using a 3D profilometer, 50 holes were randomly selected on the entire positive electrode sheet. The depth of each hole was measured and the average value was taken. The results are recorded in Table 1.

[0152] (6) Test of the number of second particles in the convex part

[0153] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were tested for the number of second particles in the convex portion. The specific testing method is as follows:

[0154] Using SEM, 10 holes were randomly selected on the entire positive electrode sheet, and the number of second particles in the convex portion of each hole was observed. The average value was taken and the results were recorded in Table 1.

[0155] (7) Average particle size test of the second particle

[0156] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were subjected to a second average particle size test. The specific test method is as follows:

[0157] Using SEM, 10 holes were randomly selected on the entire positive electrode sheet, and the particle size of the second particles in each hole was observed. The average value was taken and the results were recorded in Table 1.

[0158] (8) L test

[0159] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were subjected to an L test. The specific test method is as follows:

[0160] Using SEM, 50 holes were randomly selected on the entire positive electrode sheet, and the maximum straight-line distance between any two points on the projection of each hole on the positive electrode active layer was measured. The average value was taken and the results were recorded in Table 1.

[0161] (9) Hole spacing test

[0162] The hole spacing of the punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples was tested. The specific testing method is as follows:

[0163] Using SEM, 50 holes were randomly selected on the entire positive electrode sheet, and the distance between two adjacent holes was measured. The minimum value was taken and the results were recorded in Table 1.

[0164] (10) Bump height test

[0165] The punched positive electrode sheets (not coated with a ceramic layer) prepared in the examples and comparative examples were tested for protrusion height. The specific test method is as follows:

[0166] Using a 3D profilometer, 50 holes were randomly selected on the entire positive electrode sheet, and the height of the protrusion around each hole was measured. The maximum value was taken and the results were recorded in Table 1.

[0167] Test Case II

[0168] (1) Capacity retention rate

[0169] The batteries prepared in the examples and comparative examples were tested for capacity retention, and the specific test method is as follows:

[0170] At 25°C, 3.0C step charge / 0.7C discharge (where the charge process starts at 3.0V and the cut-off voltage is 4.5V; the discharge process starts at 4.5V and the cut-off voltage is 3.0V) were performed for 800T cycles. The capacity retention rate was calculated as follows: Capacity retention rate (%) = Ct / C0 × 100%,

[0171] The last discharge capacity is Ct, and the first discharge capacity is C0. The results are recorded in Table 2.

[0172] (2) Expansion rate

[0173] At 25°C, 3.0C step charge / 0.7C discharge (where the starting voltage of the charging process is 3.0V and the cut-off voltage is 4.5V; the starting voltage of the discharging process is 4.5V and the cut-off voltage is 3.0V) was performed for 800T cycle charge and discharge. The expansion ratio is calculated as follows: Expansion ratio (%) = [(Ht / H0)-1] × 100%,

[0174] The thickness of the battery in the last fully charged state is Ht, and the thickness of the battery in the first fully charged state is H0. The results are recorded in Table 2.

[0175] (3) Charging speed

[0176] Perform 3.0C step charging at 25°C until the 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.

[0177] (4) Energy density

[0178] At 25°C, a 3.0C step charge was performed until the battery reached 100% SOC (where the starting voltage of the charging process was 3.0V and the cut-off voltage was 4.5V), followed by a 0.2C discharge to 3.0V (where the starting voltage of the discharge process was 4.5V and the cut-off voltage was 3.0V). The discharge capacity was recorded and the energy density was calculated as follows: Energy density = 0.2C discharge capacity × voltage platform / battery volume.

[0179] 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.

[0180] Table 2

[0181] As shown in Table 2, compared to the comparative example, the battery prepared with the cathode sheet of the present disclosure improves the 800T capacity retention rate, reduces the 800T expansion rate, and shortens the charging time while maintaining a high energy density. Batteries including the cathode sheet of the present disclosure can achieve both high energy density and fast charging performance.

[0182] 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 positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer on at least one surface of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, and 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. The surface of the positive electrode active layer away from the positive electrode current collector has pores, and the pores contain recesses. The number n of the recesses in each pore is n≥2. The recesses contain the second particles, and the number of the second particles in the recesses of the optional pores is 10-150.

2. The positive electrode sheet according to claim 1, wherein: n is 2-20; preferably 5-10; and / or, the diameter of the recess is 5μm-55μm; preferably 10μm-45μm; and / or, the depth of the recess is 5μm-55μm; preferably 10μm-45μm.

3. The positive electrode sheet according to claim 1 or 2, wherein: The average particle size of the second particles is 1μm-10μm; preferably 2μm-8μm.

4. The positive electrode sheet according to any one of claims 1 to 3, wherein: The pores also contain protrusions; the protrusions contain the second particles; Preferably, the number of the second particles contained in the protrusions is 10-150.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein: The particle sizes Dv50 and Dv90 of the positive electrode active material and the depth H of the pores satisfy: 15×Dv50 / Dv90<H<(10×Dv90 / Dv50)+28; and / or, 11μm≤Dv50≤20μm; and / or, 25μm≤Dv90≤33μm; and / or, the depth H of the pores is the maximum value of the depth of the recesses, 5μm≤H≤55μm, preferably 10μm≤H≤47μm.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein: The straight-line distance between any two points on the projection of the pores on the surface of the positive electrode active layer is L, 0<L≤160μm, preferably 0<L≤115μm; and / or, the aperture of the pores on the side away from the positive electrode current collector is D1, and the aperture of the pores on the side close to the positive electrode current collector is D2, D1>D2.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein: The spacing of the pores is 10μm-970μm; preferably 100μm-550μm; Preferably, the pores are formed by laser drilling.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein: The depth of the pores is less than the thickness of the positive electrode active layer; and / or, the thickness of the positive electrode active layer is 30μm-110μm; And / or, the surface density of the positive electrode sheet is 10 mg / cm 2 -35mg / cm 2 .

9. The positive electrode sheet according to any one of claims 1 to 8, wherein: The periphery of the pores includes protrusions, and the height of the protrusions is ≤5μm; preferably ≤0.2μm.

10. The positive electrode sheet according to any one of claims 1 to 9, wherein: The positive electrode active layer includes N coatings, where N≥1; Preferably, the positive electrode active layer includes a first coating, a second coating, and a third coating that are sequentially stacked along the thickness direction of the positive electrode sheet.

11. The positive electrode sheet according to any one of claims 1 to 10, wherein: The positive electrode sheet further includes a ceramic layer, and the ceramic layer is located on the outer surface of the positive electrode active layer; Preferably, the ceramic layer covers the surface of the pores.

12. The positive electrode sheet according to claim 11, wherein: The ceramic layer includes ceramic particles; the ceramic particles include at least one of boehmite, silica, magnesium oxide, alumina, and aluminum hydroxide; and / or, the thickness of the ceramic layer is 0.3μm-3μm; and / or, the median particle size Dv50 of the ceramic particles is 1nm-3μm.

13. The positive electrode sheet according to any one of claims 1 to 12, wherein: The positive electrode active material includes lithium cobaltate with a core-shell structure; Preferably, the core of the core-shell structure comprises lithium cobalt oxide doped with metal elements, wherein the doped metal element comprises at least one of Al, Mg and M, and M comprises at least one of Ti, Zr, Y, La, Ni, Mn, Ce and W; preferably, the doping amount of the doped metal element Al is 100ppm-18000ppm; the doping amount of the doped metal element Mg is 100ppm-4500ppm; the total doping amount of the doped metal elements Al, Mg and M is 3000ppm-35000ppm; Preferably, the shell of the core-shell structure comprises a compound containing element R, and R comprises at least one of Al, Mg, Ti, Zr, Y, La, Ni and Mn; preferably, based on the total weight of the lithium cobalt oxide having the core-shell structure, the content of the element R is 0.01-5 weight %.

14. The positive electrode sheet according to any one of claims 1 to 13, wherein: A conductive agent and / or a binder is included between the second particles and the recessed portion, and a conductive agent and / or a binder is included between the second particles.

15. A battery, characterized in that: The battery comprises the positive electrode sheet according to any one of claims 1 to 14; Preferably, the battery is a lithium-ion battery.

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