Battery

Abstract

The present invention relates to the technical field of batteries, and particularly to a battery. The battery includes a positive electrode sheet and an electrolyte; the positive electrode sheet has a first surface and a second surface that are oppositely arranged in the thickness direction; the first surface has a plurality of concave portions, and the second surface has a plurality of convex portions; the positions of the concave portions on the first surface correspond to the positions of the convex portions on the second surface; the width of the concave portions is 0.2 mm - 8 mm; the electrolyte includes a first carboxylic acid ester, and the first carboxylic acid ester includes propyl acetate; the depth h1 of the concave portions and the mass content c1 of the first carboxylic acid ester in the electrolyte satisfy: 5 ≤ h1 / c1 ≤ 200, where the unit of h1 is μm. The battery of the present invention has a high energy density and a long service life under high-rate charge and discharge conditions, and can effectively improve the problem of lithium plating.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a battery. Background Art

[0002] Lithium-ion batteries have become an indispensable part of production and life, and the requirements for battery performance in the current market are also continuously increasing. Under this background, as a key component in lithium-ion batteries, the performance of the positive electrode sheet directly affects key indicators such as the energy density, power density, cycle life, and safety of the battery. Traditional positive electrode sheets often fail to meet the requirements under high-energy and high-power demands, resulting in low energy density, short service life of the battery, and an increased safety hazard caused by lithium plating.

[0003] Therefore, it is necessary to improve the energy density and service life of the battery under high-energy and high-power demands (i.e., under high-rate conditions), and to improve the problem of lithium plating. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above problems existing in the prior art, and provide a battery. The battery of the present invention can have a high energy density and a long service life under high-rate (for example, greater than 2C) charge and discharge conditions, and can effectively improve the problem of lithium plating by adopting an embossing process on the positive electrode sheet and cooperating with an electrolyte having a specific carboxylic acid ester.

[0005] In the related art, there are problems that the energy density and cycle life of the battery are poor under high-rate charge and discharge conditions, and lithium plating is likely to occur. If an embossing process is adopted for the positive electrode sheet, one side surface of the positive electrode sheet has concave portions, and the other side surface has convex portions. On the one hand, it can increase the specific surface area of the positive electrode sheet, thereby improving its electrochemical reaction activity; on the other hand, it can also enhance the mechanical strength and electrical conductivity of the positive electrode sheet, thereby being beneficial to the insertion and extraction speed of lithium ions in the positive electrode sheet.

[0006] However, the inventors of the present invention have found that if only the positive electrode sheet is embossed, it will instead have an adverse effect on the energy density, cycle life, and lithium deposition problem of the battery under high-rate charge and discharge conditions. The reason is that in the battery, when the embossing process is applied to the positive electrode sheet, the distance between the convex part on one side surface of the positive electrode sheet and the adjacent negative electrode sheet is close, and the path for lithium ions to transfer from the positive electrode sheet to the negative electrode sheet (or from the negative electrode sheet to the positive electrode sheet) is short; while the distance between the concave part on the other side surface and the adjacent negative electrode sheet is far, and the path for lithium ions to transfer from the positive electrode sheet to the negative electrode sheet (or from the negative electrode sheet to the positive electrode sheet) is long. This will cause a time difference in the migration of lithium ions on both sides of the positive electrode sheet, resulting in uneven deintercalation and intercalation of lithium on both sides of the positive electrode sheet. This uneven deintercalation and intercalation of lithium easily causes low energy conversion efficiency and lithium deposition on the surface of the negative electrode sheet, leading to a decrease in the cycle capacity retention rate of the battery and even causing safety risks. Therefore, it is necessary to reduce the time difference in the migration of lithium ions on both sides of the positive electrode sheet to improve the problem of kinetic imbalance on both sides of the positive electrode sheet. Based on the above findings, the inventors of the present invention have conducted a large number of targeted studies and proposed the following solutions:

[0007] The present invention provides a battery, which includes a positive electrode sheet and an electrolyte; the positive electrode sheet has a first surface and a second surface oppositely arranged along the thickness direction; the first surface has a plurality of concave parts, and the second surface has a plurality of convex parts; the positions of the concave parts on the first surface correspond to the positions of the convex parts on the second surface; the width of the concave parts is 0.2 mm - 8 mm; the electrolyte includes a first carboxylic acid ester, and the first carboxylic acid ester includes propyl acetate; the depth h1 of the concave parts and the mass content c1 of the first carboxylic acid ester in the electrolyte satisfy: 5 ≤ h1 / c1 ≤ 200, where the unit of h1 is μm.

[0008] Adding a specific carboxylic acid ester to the electrolyte can effectively reduce the time difference of lithium-ion migration on both sides of the positive electrode plate. The reasons are as follows: First, adding propyl acetate to the electrolyte can increase the migration rate of lithium ions in the electrolyte and reduce the difficulty of lithium ions inserting into or extracting from the active material. This is because: propyl acetate can surround lithium ions through its polar groups and interact with lithium ions to form a solvation shell. This solvation shell can not only make lithium ions exist more stably in the electrolyte; moreover, compared with carbonate solvents, the interaction force between propyl acetate and lithium ions is smaller. Therefore, it can promote the movement and desolvation process of lithium ions. That is, propyl acetate can increase the migration rate of lithium ions, weaken the influence of the migration distance difference of lithium ions from the concave part to the negative electrode plate and from the convex part to the negative electrode plate, reduce the lithium-ion concentration polarization on the surface of the negative electrode plate due to the electric field effect, slow down the risks of lithium deposition and black spots on the surface of the negative electrode plate, and improve the fast charging ability and cycling ability of the battery. Second, adding propyl acetate to the electrolyte can reduce the overall viscosity of the electrolyte. The greater the viscosity of the electrolyte, the greater the difference in the migration speed of lithium ions on both sides of the positive electrode plate. And the low-viscosity electrolyte can not only make lithium ions form good contact with the surface of the positive electrode plate, thus improving the efficiency of the electrochemical reaction; but also can reduce the time difference of lithium-ion migration on both sides of the positive electrode plate and balance the kinetics on both sides of the positive electrode plate.

[0009] However, if only the embossing process is simply used for the positive electrode plate and propyl acetate is added to the electrolyte, the improvement of the energy density, service life and lithium deposition problem of the battery at high rates is limited. This is because, the deeper the depth of the concave part, it indicates that the time difference of lithium-ion migration on both sides of the positive electrode plate is greater, and at this time, more propyl acetate is needed to reduce the time difference of lithium-ion migration on both sides of the positive electrode plate; on the contrary, the shallower the depth of the concave part, the smaller the time difference of lithium-ion migration on both sides of the surface positive electrode plate, and at this time, less propyl acetate is needed to reduce the time difference of lithium-ion migration on both sides of the positive electrode plate. Therefore, only when the depth of the concave part and the content of propyl acetate satisfy a specific relationship can the two match to exert the best performance of the battery.

[0010] Through the above technical solutions, the present invention has at least the following advantages compared with the prior art: The battery of the present invention has a higher energy density and a longer service life under high-rate charge and discharge conditions, and can effectively improve the lithium deposition problem.

[0011] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. Description of the Drawings

[0012] Figure 1 The figure shows a schematic cross-sectional view of a positive electrode sheet in the thickness direction in an example of the present invention. Detailed Embodiments

[0013] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0014] The present invention provides a battery, comprising a positive electrode sheet and an electrolyte. The positive electrode sheet has a first surface and a second surface oppositely disposed in the thickness direction. The first surface may have a plurality of concave portions, and the second surface may have a plurality of convex portions; the positions of the concave portions on the first surface correspond to the positions of the convex portions on the second surface. As Figure 1 The figure shows a schematic cross-sectional view of a positive electrode sheet in the thickness direction in an example of the present invention. It can be seen from the figure that the positive electrode sheet has a first surface and a second surface oppositely disposed in the thickness direction, the first surface has a plurality of concave portions, and the second surface has a plurality of convex portions; the positions of the concave portions on the first surface correspond to the positions of the convex portions on the second surface. The width of the concave portions may be 0.2 mm - 8 mm, for example, 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm.

[0015] In the present invention, "a plurality of" means that the number of concave portions on one side surface of the positive electrode sheet is greater than or equal to 2; the number of convex portions on the other side surface of the positive electrode sheet is greater than or equal to 2.

[0016] In the present invention, the electrolyte may include a first carboxylic acid ester, and the first carboxylic acid ester includes propyl acetate.

[0017] In the present invention, the depth h1 of the concave portion and the mass content c1 of the first carboxylic acid ester in the electrolyte satisfy: 5 ≤ h1 / c1 ≤ 200, for example, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200, where the unit of h1 is μm.

[0018] In one example, 10 ≤ h1 / c1 ≤ 150.

[0019] In one example, 12.5 ≤ h1 / c1 ≤ 75.

[0020] In the present invention, the positive electrode sheet can be prepared by embossing to obtain a positive electrode sheet containing a plurality of concave portions and corresponding convex portions. It can be understood that "the position of the concave portion on the first surface corresponds to the position of the convex portion on the second surface" means that: the projection of the concave portion in the thickness direction of the positive electrode sheet and the projection of the convex portion in the thickness direction of the positive electrode sheet at least partially overlap; for example, the former (the projection of the concave portion in the thickness direction of the positive electrode sheet) completely covers the latter (the projection of the convex portion in the thickness direction of the positive electrode sheet); or the latter completely covers the former; or a partial area of the two overlaps.

[0021] In the present invention, the projected area of the concave portion in the thickness direction of the positive electrode sheet is 80%-120% of the projected area of the convex portion in the thickness direction of the positive electrode sheet, for example, 80%, 90%, 100%, 110% or 120%.

[0022] In the present invention, the depth h1 of the concave portion can be 3-40, and the unit of h1 is μm; for example, 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm or 40μm.

[0023] In one example, h1 is 5-30, and the unit of h1 is μm.

[0024] When the depth of the concave portion is relatively shallow (for example, less than 3μm), the improvement of the specific surface area of the positive electrode sheet is small, so the electrochemical activity of the positive electrode sheet and the lithium ion insertion / extraction rate are not obvious; while when the depth of the concave portion is relatively deep (for example, greater than 40μm), there may be a problem of overvoltage in the positive electrode sheet, which will not only affect the transport of lithium ions in the positive electrode sheet, but also may cause the fracture of the positive electrode current collector, triggering a safety risk. And when the depth of the concave portion is too deep, the kinetic difference on both sides of the positive electrode sheet is too large, and the effect of only adding the first carboxylic ester to reduce the difference is limited. On the premise that h1 / c1 satisfies a specific range, when the depth of the concave portion is within a specific range, the closely arranged positive electrode active material particles can form better ion channels and enhance the migration of lithium ions in the electrolyte.

[0025] In the present invention, the depth h1 of the concave portion refers to the vertical distance from the lowest point in the concave portion to the surface of the positive electrode sheet. The depth h1 of the concave portion can be measured by conventional methods in the art, for example, using a scanning electron microscope (SEM) or a 3D profiler to measure the depth of at least 20 concave portions or all concave portions on one surface of the positive electrode sheet and taking the average value.

[0026] In the present invention, the shape of the projection of the recess in the thickness direction of the positive electrode sheet is not limited and can be circular or rectangular. When the shape of the projection of the recess in the thickness direction of the positive electrode sheet is circular, the width of the recess is the diameter of the circle; when the shape of the projection of the recess in the thickness direction of the positive electrode sheet is non-circular, the width of the recess is the equivalent diameter of the circle with the same area as the non-circular shape. The pitch of the recesses can be 0.5 mm - 8 mm, such as 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm. The width of the recess and the pitch of the recesses can be measured by conventional methods in the art. For example, using SEM, at least 10 recesses are selected on the surface of the positive electrode sheet, the width of each recess is measured, and the average value is taken; at least 10 sets of adjacent recesses are selected on the surface of the positive electrode sheet, the shortest distance between the edges of each set of recesses is measured, and the average value is taken.

[0027] In one example, the width of the recess is 0.2 mm - 4 mm.

[0028] In one example, the width of the recess is 0.2 mm - 3 mm.

[0029] In one example, the pitch of the recesses is 1 mm - 4 mm.

[0030] In the present invention, the height h2 of the protrusion can be 2 μm - 40 μm, such as 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm.

[0031] In one example, the height h2 of the protrusion is 4 μm - 30 μm.

[0032] In the present invention, the height h2 of the protrusion refers to the vertical distance from the highest point on the protrusion to the surface of the positive electrode sheet. The height h2 of the protrusion can be measured by conventional methods in the art. For example, using SEM or a 3D profiler, the height of at least 20 protrusions or all protrusions on one surface of the positive electrode sheet is measured, and the average value is taken.

[0033] In the present invention, the width of the protrusion can be 0.2 mm - 8 mm, such as 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm.

[0034] In the present invention, the shape of the projection of the convex portion in the thickness direction of the positive electrode sheet is not limited, and it can be circular or rectangular. When the shape of the projection of the convex portion in the thickness direction of the positive electrode sheet is circular, the width of the convex portion is the diameter of the circle; when the shape of the projection of the convex portion in the thickness direction of the positive electrode sheet is non-circular, the width of the convex portion is the equivalent diameter of a circle with the same area as the non-circular shape. The spacing between the convex portions can be 0.5 mm - 8 mm, such as 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm. The width of the convex portion and the spacing between the convex portions can be obtained by conventional methods in the art, for example, by SEM. Select at least 10 convex portions on the surface of the positive electrode sheet, measure the width of each convex portion, and take the average value; select at least 10 groups of adjacent convex portions on the surface of the positive electrode sheet, measure the shortest distance between the edges of each group of convex portions (i.e., the shortest distance between the orthographic projections formed by each group of convex portions on the surface of the positive electrode sheet), and take the average value.

[0035] In one example, the width of the convex portion is 0.2 mm - 4 mm.

[0036] In one example, the width of the convex portion is 0.2 mm - 3 mm.

[0037] In one example, the spacing between the convex portions is 1 mm - 4 mm.

[0038] <Electrolyte>

[0039] In the present invention, the mass content c1 of the first carboxylic acid ester can be 10% - 80%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%.

[0040] In one example, c1 is 40% - 60%.

[0041] When the mass content of the first carboxylic acid ester in the electrolyte is low (for example, less than 10%), the effect of the electrolyte on reducing the kinetic difference on both sides of the positive electrode sheet is not obvious, and there are significant differences in the migration of lithium ions on both sides of the positive electrode sheet, resulting in uneven deintercalation and intercalation of lithium on the surface of the negative electrode sheet, thus easily causing lithium deposition and reducing the capacity retention rate of the battery or even causing it to drop significantly; while when the mass content of the first carboxylic acid ester is high (for example, greater than 80%), it will affect the high-temperature performance of the battery.

[0042] In the present invention, the mass content c1 of the first carboxylic acid ester in the electrolyte can be obtained by conventional methods in the art, for example, using GC-MS.

[0043] In one example, the first carboxylic acid ester is propyl acetate (PA).

[0044] In the present invention, the electrolyte may further include a first lithium salt. The first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0045] Specific first lithium salts exhibit higher conductivity and lithium ion transference number within the normal temperature range, which can increase the number of lithium ions migrating in the electrolyte, thereby enhancing the overall kinetic performance of the battery. Enabling more lithium ions to participate in the formation and desolvation of the solvation shell is beneficial to enhancing the electrochemical reaction activity on the negative electrode sheet. Therefore, the first lithium salt also has good compatibility with the positive electrode sheet of the present invention, which can further reduce the time difference of lithium ion migration on both sides of the positive electrode sheet, improve the energy density and service life of the battery under high-rate charge and discharge conditions, and improve lithium deposition.

[0046] In one example, the first lithium salt includes LiFSI.

[0047] In the present invention, the mass content c2 of the first lithium salt and the mass content c1 of the first carboxylate in the electrolyte satisfy: 2.5 ≤ c1 / c2 ≤ 100, for example, 2.5, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100.

[0048] In one example, 5 ≤ c1 / c2 ≤ 20.

[0049] The first lithium salt can not only increase the lithium ion transference number but also improve the overall high-temperature performance and electrochemical stability of the electrolyte. However, too much first lithium salt will significantly increase the viscosity of the electrolyte, resulting in an increase in the time difference of lithium ion migration on both sides of the positive electrode sheet, which is not conducive to the energy density, service life, and lithium deposition problem of the battery under high-rate charge and discharge conditions. Therefore, when adding the first lithium salt, it is necessary to regulate the relationship between the first lithium salt and the first carboxylate so that the contents of the first lithium salt and the first carboxylate are compatible, and on the premise that the first lithium salt has a small impact on the viscosity of the electrolyte, further enhance its positive impact on the lithium ion migration rate.

[0050] In the present invention, the mass content c2 of the first lithium salt in the electrolyte can be 0.5% - 10%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0051] In one example, c2 is 2% - 8%.

[0052] In the present invention, the mass content c2 of the first lithium salt in the electrolyte can be measured by conventional methods in the art, such as ion chromatography.

[0053] In the present invention, the electrolyte may further include a first additive. The first additive includes at least one of 1,3 - propane sultone (PS), 1,3 - propylene sultone (PST), 2,4 - butane sultone, 1,4 - butane sultone, propylene sultone, butane sultone, methylene methanedisulfonate, dimethyl sulfate, vinylene sulfate (DTD), 4 - methyl - vinylene sulfate, methyl vinylene sulfate, propylene sulfate, and ethylene sulfite.

[0054] In one example, the first additive includes PS and DTD. Among them, the mass ratio of PS to DTD is 2 - 8, such as 2, 3, 4, 5, 6, 7, or 8.

[0055] In the present invention, the mass content c3 of the first additive in the electrolyte and the mass content c2 of the first lithium salt in the electrolyte satisfy: 0.07 ≤ c2 / c3 ≤ 10, such as 0.07, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0056] In one example, 0.4 ≤ c2 / c3 ≤ 4.

[0057] In one example, 0.6 ≤ c2 / c3 ≤ 2.

[0058] Adding the first lithium salt to the electrolyte will cause the battery to easily generate gas during high - temperature storage. Therefore, it is necessary to add the first additive synergistically and regulate the content relationship between the first lithium salt and the first additive to reduce the adverse effect of the first lithium salt on the high - temperature storage performance of the battery.

[0059] In the present invention, c3 is 0.1% - 7%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 7%.

[0060] In one example, c3 is 0.5% - 5%.

[0061] In one example, c3 is 2% - 5%.

[0062] In the present invention, the mass content c3 of the first additive in the electrolyte can be obtained by testing through conventional methods in the art, such as by GC - MS.

[0063] In the present invention, the electrolyte may further include a second lithium salt. The second lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalato)phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, and lithium tris(trifluoromethylsulfonyl)methyl.

[0064] In the present invention, the sum of the mass contents of the first lithium salt and the second lithium salt in the electrolyte may be 10% - 22%, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21% or 22%.

[0065] In the present invention, the electrolyte may further include a second additive. The second additive includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), ethylene vinylene carbonate (VEC), and triallyl phosphate.

[0066] In the present invention, the electrolyte may further include an organic solvent. The organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), ethyl butyrate (EB), ethyl acetate (EA), difluoroethyl acetate (DFEA), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0067] <Positive electrode sheet>

[0068] In the present invention, the positive electrode sheet may include a positive electrode active material. The positive electrode active material may include first particles and / or second particles. The first particles include a substance with the chemical formula LiNi x1 Co y1 Mn z1 M 1 a1 O2, where 0.5 ≤ x1 ≤ 0.95, 0.01 ≤ y1 ≤ 0.2, 0.01 ≤ z1 ≤ 0.4, 0 ≤ a1 ≤ 0.1, and M 1 includes at least one of Al, Mg, Y, W, B, Zr, Ti, Sr, Si, La, and Nb. The second particles include a substance with the chemical formula LiNi x2 Co y2 Mn z2 M 2 a2 O2, where 0.5 ≤ x2 ≤ 0.95, 0.01 ≤ y2 ≤ 0.2, 0.01 ≤ z2 ≤ 0.4, 0 ≤ a2 ≤ 0.1, and M 2Comprising at least one of Al, Mg, Y, W, B, Zr, Ti, Sr, Si, La, and Nb.

[0069] In one example, the first particles comprise single crystal particles. The second particles comprise polycrystalline particles.

[0070] In one example, the first particles are single crystal particles. The second particles are polycrystalline particles.

[0071] In one example, the positive electrode active material comprises the first particles and the second particles.

[0072] Due to the uniformity of its internal crystal structure, the same grain orientation, and the absence of grain boundaries, single crystal particles have excellent structural stability; however, the relatively large spacing between single crystal particles will increase the + transport distance of Li, reducing the transport efficiency of lithium ions and deteriorating the capacity performance and rate performance of the material. Polycrystalline particles are composed of several primary particles, and the internal grain boundaries have a certain adverse effect on the structural stability of the material itself. Moreover, the risk of side reactions between the primary particles in polycrystalline particles and the electrolyte is relatively high, which will further increase the possibility of structural collapse of polycrystalline particles during cycling; however, due to the relatively small particle size of the primary particles in polycrystalline particles, the + transport distance of Li is greatly shortened. Therefore, it is beneficial to the + transport of Li, thereby obtaining better capacity performance and rate performance. Blending polycrystalline particles and single crystal particles can, to a certain extent, reduce the internal resistance of the positive electrode sheet and increase the intercalation / deintercalation rate of lithium ions in the positive electrode sheet, thereby improving the cycle performance and rate performance of the battery.

[0073] In the present invention, the mass content of the first particles in the positive electrode active material can be 50% - 80%, such as 50%, 55%, 60%, 65%, 70%, 75%, or 80%. The mass content of the second particles in the positive electrode active material can be 20% - 50%, such as 50%, 45%, 40%, 35%, 30%, 25%, or 20%.

[0074] By further controlling the mass content of the first particles in the positive electrode active material, it is beneficial to increase the transport rate of lithium ions in the positive electrode sheet and reduce the risk of side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance and rate performance of the battery.

[0075] In the present invention, the average particle size of the first particles may be 1 μm - 6 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm. The average particle size of the second particles may be 6 μm - 15 μm, such as 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0076] In the present invention, the average particle size of the first particles and the average particle size of the second particles can be obtained by testing with conventional methods in the art, such as SEM. Take a cross-sectional micrograph of the positive electrode sheet, select at least 20 first particles or 20 second particles in the figure, measure the particle size of each particle, and take the average value.

[0077] In the present invention, the median particle size Dv50 of the first particles may be 1 μm - 6 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm. The median particle size Dv50 of the second particles may be 6 μm - 15 μm, such as 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0078] In the present invention, the median particle size Dv50 of the first particles and the median particle size Dv50 of the second particles can be obtained by testing with conventional methods in the art, such as a laser particle size analyzer.

[0079] In the present invention, the specific surface area of the first particles may be 0.5 m 2 / g - 1.4 m 2 / g, such as 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g or 1.4 m 2 / g. The specific surface area of the second particles may be 0.3 m 2 / g - 1 m 2 / g, such as 0.3 m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g or 1 m 2 / g.

[0080] In the present invention, the specific surface area of the first particles and the specific surface area of the second particles can be obtained by testing using conventional methods in the art, such as the multi-molecular layer adsorption theory method (BET method).

[0081] In the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The positive electrode active material layer may include the positive electrode active material. The positive electrode active material layer may further include a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent may include conductive agents commonly used in the art, such as at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, and carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes). The positive electrode binder may include binders commonly used in the art, such as at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0082] In the present invention, based on the total mass of the positive electrode active material layer, the content of the positive electrode active material may be 90% - 99.8% (such as 90%, 92%, 94%, 96%, 98%, 99%, or 99.8%), the content of the positive electrode conductive agent may be 0.1% - 5% (such as 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%), and the content of the positive electrode binder may be 0.1% - 5% (such as 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%).

[0083] <Separator>

[0084] In the present invention, the battery may further include a separator. The separator may include a substrate layer and an adhesive layer. The adhesive layer is located on at least one outer surface of the separator and faces the positive electrode sheet.

[0085] Performing an embossing process on the positive electrode sheet will cause an increase in the gap between the positive electrode sheet and the separator, making it difficult for the positive electrode sheet and the separator to fit tightly. Therefore, an adhesive layer is provided on at least one outer surface of the separator and the adhesive layer faces the positive electrode sheet, which can enhance the adhesion between the separator and the positive electrode sheet, enabling them to fit tightly and not easily fall off during the charge and discharge cycle of the battery, and also making the transmission of lithium ions between the positive electrode sheet and the separator smoother, improving the overall kinetic performance of the battery.

[0086] In the present invention, the adhesive layer may include at least one of polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, vinylidene fluoride - trichloroethylene copolymer, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, and polyvinylpyrrolidone.

[0087] In the present invention, the thickness H1 of the adhesive layer and the depth h1 of the recess satisfy: 0.007 ≤ H1 / h1 ≤ 0.6, where the unit of H1 is μm and the unit of h1 is μm; for example, H1 / h1 is 0.007, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 or 0.6.

[0088] In one example, 0.01 ≤ H1 / h1 ≤ 0.35.

[0089] In one example, 0.02 ≤ H1 / h1 ≤ 0.1.

[0090] By controlling the relationship between the thickness of the adhesive layer and the depth of the recess, the adhesion between the separator and the positive electrode sheet can be improved, which is beneficial to further improving the energy density and cycle life of the battery under high-rate charge and discharge conditions.

[0091] In the present invention, H1 can be 0.2 μm - 3 μm, for example, 0.2 μm, 0.5 μm, 1 μm, 2 μm or 3 μm.

[0092] In the present invention, the separator may further include a ceramic layer. The ceramic layer may be located on at least one surface of the substrate layer. The ceramic layer may include at least one of aluminum oxide, aluminum hydroxide, boehmite, silicon oxide, titanium oxide, barium sulfate, silicon nitride, aluminate, aluminum nitride and zirconium oxide.

[0093] In the present invention, the thickness of the ceramic layer may be 1 μm - 5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm. By controlling the thickness of the ceramic layer, the thermal stability of the separator can be enhanced, thereby improving the stability of the battery in a high-temperature environment, and the kinetic performance of lithium-ion transport can be further improved.

[0094] In one example, the separator includes the substrate layer, the ceramic layer located on at least one surface of the substrate layer, and the adhesive layer located on the outer surface of the separator.

[0095] In the present invention, the substrate layer may include polyolefin. For example, it includes polypropylene and / or polyethylene.

[0096] In the present invention, the battery may further include a negative electrode sheet. The negative electrode sheet may be a negative electrode sheet conventionally used in the art.

[0097] It should be noted that the numerical representation methods such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent the difference in order.

[0098] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0099] In the following examples, unless otherwise specified, the materials used are commercially available analytical pure.

[0100] The following examples are used to illustrate the battery of the present invention.

[0101] Example 1

[0102] Prepare the battery according to the following method:

[0103] (1) Prepare the electrolyte

[0104] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), EC, PC and PP are mixed evenly according to a mass ratio of 4:7:29 to form an organic solvent; the first carboxylic acid ester PA is added to the above organic solvent, c1 is 20%, to form a mixed solvent; the first lithium salt LiFSI is added to the above mixed solvent, c2 is 4%, the first additive (PS and DTD are mixed according to a mass ratio of 2) is added, c3 is 2%, the second lithium salt LiPF6 based on 11% of the total mass of the electrolyte is added, and the second additive FEC based on 5% of the total mass of the electrolyte is added, and stirred evenly. After passing the moisture and free acid tests, the electrolyte is obtained, where the mass contents of the organic solvent, the first carboxylic acid ester, the first lithium salt, the first additive, the second lithium salt and the second additive add up to 100%;

[0105] c1 / c2 is 5, and c2 / c3 is 2.

[0106] (2) Prepare the positive electrode sheet

[0107] The positive electrode active material (the first particles and the second particles are mixed according to a mass ratio of 65:35, where the first particles are single crystal particles with the chemical formula LiNi 0.92 Co 0.04 Mn 0.04 O2, with an average particle size of 3 μm; the second particles are polycrystalline particles with the chemical formula LiNi 0.9 Co 0.05 Mn 0.05O2 with an average particle size of 10 μm), conductive carbon black, and polyvinylidene fluoride were mixed evenly in a mass ratio of 97.6:1.35:1.05 and placed in N-methylpyrrolidone (NMP), stirred evenly to prepare a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of the aluminum foil; successively dried and roll-pressed to obtain a positive electrode sheet with a thickness of 90 μm; then subjected to slitting treatment, and then processed using a special roller with protrusions to obtain a positive electrode sheet with concave portions on one side surface and convex portions on the other side surface;

[0108] Among them, the width of the concave portion is 2 mm, the spacing is 2 mm, and the depth h1 is 15 μm; the width of the convex portion is 2 mm, the spacing is 2 mm, and the height h2 is 14 μm; h1 / c1 is 75.

[0109] (3) Preparation of negative electrode sheet

[0110] Artificial graphite, silicon-carbon material (silicon content is 47%), conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed evenly in a mass ratio of 78.5:20.5:0.5:0.25:0.25, added with deionized water, and fully stirred to form a uniform negative electrode slurry; the negative electrode slurry was coated on the copper foil, dried, roll-pressed, cut, and washed to obtain a negative electrode sheet.

[0111] (4) Preparation of battery

[0112] The positive electrode sheet prepared in step (2), the negative electrode sheet prepared in step (3), and the separator (the base material layer is a polypropylene film with a thickness of 5 μm, a ceramic layer with a thickness of 1 μm is provided on one side surface of the base material, and a polyvinylidene fluoride adhesive layer with a thickness H1 of 1 μm is provided on the outer surface of the ceramic layer) were wound into a core according to a predetermined process, the electrolyte prepared in step (1) was injected, and after processes such as vacuum sealing, standing, formation, sorting, and secondary sealing, a battery was prepared;

[0113] Among them, the adhesive layer faces the positive electrode sheet; H1 / h1 is 0.067.

[0114] Example 2

[0115] Refer to Example 1, the difference is the composition of the electrolyte, the preparation of the positive electrode sheet, and the thickness of the separator adhesive layer, specifically as follows:

[0116] (1) Preparation of electrolyte

[0117] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), EC, PC, and PP were mixed evenly in a mass ratio of 4:7:29 to form an organic solvent; the first carboxylate PA was added to the above organic solvent, with c1 being 40%, to form a mixed solvent; the first lithium salt LiFSI was added to the above mixed solvent, with c2 being 2%, the first additive (PS and DTD were mixed in a mass ratio of 4) was added, with c3 being 3%, the second lithium salt LiPF6 based on 13% of the total mass of the electrolyte was added, and the second additive FEC based on 5% of the total mass of the electrolyte was added. After stirring evenly and passing the moisture and free acid tests, the electrolyte was obtained;

[0118] The ratio of c1 / c2 was 20, and the ratio of c2 / c3 was 0.67.

[0119] (2) Preparation of the positive electrode sheet

[0120] The positive electrode active material (the first particles and the second particles were mixed in a mass ratio of 50:50, where the first particles were single crystal particles with the chemical formula LiNi 0.9 Co 0.05 Mn 0.05 O2, with an average particle size of 1 μm; the second particles were polycrystalline particles with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2, with an average particle size of 6 μm), conductive carbon black, and polyvinylidene fluoride were mixed evenly in a mass ratio of 97.6:1.35:1.05 and placed in N-methylpyrrolidone (NMP). After stirring evenly, a positive electrode slurry was prepared; the positive electrode slurry was evenly coated on both the front and back sides of the aluminum foil; after drying and rolling processes in sequence, a positive electrode sheet with a thickness of 90 μm was obtained; then, it was slit, and finally processed using a special roller with protrusions to obtain a positive electrode sheet with a concave part on one side surface and a convex part on the other side surface;

[0121] Among them, the width of the concave part was 2.8 mm, the spacing was 4 mm, and the depth h1 was 5 μm; the width of the convex part was 2.7 mm, the spacing was 4 mm, and the height h2 was 4 μm; the ratio of h1 / c1 was 12.5.

[0122] (4)Preparation of the battery

[0123] The thickness H1 of the glue layer was 0.5 μm, and the ratio of H1 / h1 was 0.1.

[0124] Example 3

[0125] Refer to Example 1, the difference is the composition of the electrolyte, the preparation of the positive electrode sheet, and the thickness of the diaphragm glue layer, which are specifically as follows:

[0126] (1)Preparation of the electrolyte

[0127] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), EC, PC, and PP were mixed evenly in a mass ratio of 4:7:29 to form an organic solvent; the first carboxylic acid ester PA was added to the above organic solvent, with c1 being 60%, to form a mixed solvent; the first lithium salt LiFSI was added to the above mixed solvent, with c2 being 8%, the first additive (PS and DTD were mixed in a mass ratio of 8) was added, with c3 being 5%, the second lithium salt LiPF6 based on 7% of the total mass of the electrolyte was added, and the second additive FEC based on 5% of the total mass of the electrolyte was added, and then stirred evenly. After passing the moisture and free acid tests, the electrolyte was obtained;

[0128] The ratio of c1 / c2 was 7.5, and the ratio of c2 / c3 was 1.6.

[0129] (2) Preparation of the positive electrode sheet

[0130] The positive electrode active material (the first particles and the second particles were mixed in a mass ratio of 80:20, where the first particles were single crystal particles with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2, with an average particle size of 6 μm; the second particles were polycrystalline particles with the chemical formula LiNi 0.7 Co 0.1 Mn 0.2 O2, with an average particle size of 15 μm), conductive carbon black, and polyvinylidene fluoride were mixed evenly in a mass ratio of 97.6:1.35:1.05 and placed in N-methylpyrrolidone (NMP), and then stirred evenly to prepare a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of the aluminum foil; after drying and rolling processes in sequence, a positive electrode sheet with a thickness of 90 μm was obtained; then it was slit, and finally processed using a special roller with protrusions to obtain a positive electrode sheet with concave portions on one side surface and convex portions on the other side surface;

[0131] Among them, the width of the concave portion was 0.2 mm, the spacing was 1 mm, and the depth h1 was 30 μm; the width of the convex portion was 0.2 mm, the spacing was 1 mm, and the height h2 was 28 μm; the ratio of h1 / c1 was 50.

[0132] (4) Preparation of the battery

[0133] The thickness H1 of the glue layer was 0.75 μm, and the ratio of H1 / h1 was 0.025.

[0134] Example 4

[0135] Used to verify the influence brought by the change of "h1 / c1".

[0136] Performed with reference to Example 2, the difference being that the composition of the electrolyte was changed as follows:

[0137] c1 is 60%, c2 is 8%, c3 is 5%, the mass content of the second lithium salt LiPF6 is 7%, and the mass content of the second additive FEC is 5%;

[0138] Among them, h1 / c1 is 8.3.

[0139] Example Group 5

[0140] This group of examples is used to verify the influence brought by the change of "the depth h1 of the concave part".

[0141] This group of examples is carried out with reference to Example 1. The difference is that the depth h1 of the concave part is changed (while keeping the width and spacing of the concave part unchanged), specifically as follows:

[0142] Example 5a, h1 is 3μm, h2 is 2μm;

[0143] Example 5b, h1 is 40μm, h2 is 38μm.

[0144] Example Group 6

[0145] This group of examples is used to verify the influence brought by the change of "the mass content c1 of the first carboxylic acid ester in the electrolyte".

[0146] This group of examples is carried out with reference to Example 1. The difference is that c1 is changed, specifically as follows:

[0147] Example 6a, c1 is 10%;

[0148] Example 6b, c1 is 78%.

[0149] Example Group 7

[0150] This group of examples is used to verify the influence brought by the change of "the first lithium salt".

[0151] This group of examples is carried out with reference to Example 1. The difference is that the first lithium salt is changed, specifically as follows:

[0152] Example 7a, LiFSI is replaced with the same mass of LiTFSI;

[0153] Example 7b, no first lithium salt is added to the electrolyte.

[0154] Example Group 8

[0155] This group of examples is used to verify the influence brought by the change of "the mass content c2 of the first lithium salt in the electrolyte".

[0156] This group of examples is carried out with reference to Example 1. The difference is that c2 is changed, specifically as follows:

[0157] Example 8a, c2 is 0.5%;

[0158] Example 8b, c2 is 10%.

[0159] Example 9

[0160] Used to verify the influence brought by the change of "c1 / c2".

[0161] Carried out with reference to Example 3, the difference is that the mass content c2 of the first lithium salt in the electrolyte is changed. Specifically, c2 is 2% and c1 / c2 is 30.

[0162] In addition, in order to avoid the influence of the change of c2 / c3 on the observation of the effect of c1 / c2, in Example 10, c3 is changed simultaneously. c3 is 3% and c2 / c3 is 0.67.

[0163] Example 10 group

[0164] This group of examples is used to verify the influence brought by the change of "the first additive".

[0165] This group of examples is carried out with reference to Example 1, the difference is that the first additive is changed as follows:

[0166] Example 10a, the first additive is replaced with PS of the same mass;

[0167] Example 10b, the first additive is replaced with a combination of PST and DTD of the same mass, where the mass ratio of PST to DTD is 2;

[0168] In Example 10c, no first additive is added to the electrolyte.

[0169] Example 11 group

[0170] This group of examples is used to verify the influence brought by the change of "the mass content c3 of the first additive in the electrolyte".

[0171] This group of examples is carried out with reference to Example 1, the difference is that c3 is changed as follows:

[0172] Example 11a, c3 is 0.5%;

[0173] Example 11b, c3 is 7%.

[0174] Example 12 group

[0175] This group of examples is used to verify the influence brought by the change of "c2 / c3".

[0176] This group of embodiments is carried out with reference to Embodiment 2 or Embodiment 3 respectively. The difference is that c2 / c3 is regulated by changing c3, specifically as follows:

[0177] Example 12a is carried out with reference to Embodiment 2. The difference is that c3 is 5% and c2 / c3 is 0.4;

[0178] Example 12b is carried out with reference to Embodiment 3. The difference is that c3 is 2% and c2 / c3 is 4.

[0179] Example 13

[0180] It is used to verify the influence brought about by the change of "whether the adhesive layer of the separator faces the positive electrode sheet".

[0181] It is carried out with reference to Example 1. The difference is that the adhesive layer in the separator is removed (that is, the separator includes a base material layer and a ceramic layer located on one surface of the base material layer).

[0182] Example 14 group

[0183] This group of embodiments is used to verify the influence brought about by the change of "H1 / h1".

[0184] This group of embodiments is carried out with reference to Embodiment 2 or Embodiment 3 respectively. The difference is that H1 / h1 is regulated by changing the thickness H1 of the adhesive layer, specifically as follows:

[0185] Example 14a is carried out with reference to Embodiment 2. The difference is that H1 is 1 μm and H1 / h1 is 0.2;

[0186] Example 14b is carried out with reference to Embodiment 3. The difference is that H1 is 0.5 μm and H1 / h1 is 0.017.

[0187] In all the above embodiments, the following are satisfied: The median particle size Dv50 of the first particles can be 6 μm - 15 μm, and that of the second particles is 1 μm - 6 μm. The specific surface area of the first particles is 0.5 m 2 / g - 1.4 m 2 / g; The median particle size Dv50 of the second particles is 6 μm - 15 μm, and the specific surface area of the second particles is 0.3 m 2 / g - 1 m 2 / g.

[0188] Comparative Example 1

[0189] It is carried out with reference to Example 1. The difference is that the first carboxylic acid ester is not added to the electrolyte.

[0190] Comparative Example 2

[0191] It was carried out with reference to Example 1, except that the positive electrode sheet was not embossed (i.e., the first surface of the positive electrode sheet did not have recesses and the second surface did not have protrusions).

[0192] Comparative Example 3

[0193] It was carried out with reference to Example 1, except that by simultaneously changing the depth h1 of the recess and the mass content c1 of the first carboxylic acid ester in the electrolyte, h1 / c1 was regulated. Specifically: h1 was 1 μm, c1 was 78%, and h1 / c1 was 1.28.

[0194] Comparative Example 4

[0195] It was carried out with reference to Example 1, except that by simultaneously changing the depth h1 of the recess and the mass content c1 of the first carboxylic acid ester in the electrolyte, h1 / c1 was regulated. Specifically: h1 was 42 μm, c1 was 10%, and h1 / c1 was 420.

[0196] Comparative Example 5

[0197] It was carried out with reference to Example 1, except that PA was replaced with EB of the same mass.

[0198] Test Example

[0199] (1)25°C Cycling Test

[0200] The batteries prepared in the examples and comparative examples were placed at 25°C for 60 minutes, charged at a constant current of 2C to 4.3V, then charged at a constant voltage of 4.3V to 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 3C to 2.5V and allowed to stand for 5 minutes. This was one charge-discharge cycle; such charge / discharge was carried out for 1000 cycles, and the cycle capacity retention rate was recorded and the results were listed in Table 1; after 1000 cycles, the battery was fully charged and then disassembled, and the lithium deposition situation on the negative electrode sheet was observed. If no lithium deposition occurred on the negative electrode sheet, it was recorded as no lithium deposition; if lithium deposition occurred only in the arc area of the core on the negative electrode sheet, it was recorded as slight lithium deposition; if lithium deposition occurred in the arc area of the core, the top and bottom of the core on the negative electrode sheet, it was recorded as lithium deposition; if lithium deposition occurred in the arc area of the core, the top and bottom of the core, and the flat area of the core on the negative electrode sheet, it was recorded as severe lithium deposition, and the results were listed in Table 1.

[0201] (2)45°C Cycling Test

[0202] The batteries prepared in the examples and comparative examples were placed at 45°C for 60 minutes, charged at a constant current of 2C to 4.3V, then charged at a constant voltage of 4.3V to 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 3C to 2.5V and allowed to stand for 5 minutes. This was one charge-discharge cycle; such charge / discharge was carried out for 600 cycles, and the cycle capacity retention rate was recorded and the results were listed in Table 1.

[0203] (3)Energy density test

[0204] Charge the batteries prepared in the examples and comparative examples at 0.7C to the upper limit voltage (4.3V) with a cut-off current of 0.025C, and discharge them at 0.5C to the lower limit voltage (2.5V). Output the discharge capacity and the working platform voltage, measure the weight of the batteries, and calculate the energy density through the formula: Energy density = Discharge capacity × Working platform voltage / Battery weight. Record the results in Table 1.

[0205] Table 1

[0206]

[0207]

[0208] As can be seen from Table 1, compared with the comparative examples, the batteries of the present invention have a higher energy density and a longer service life under high-rate charge and discharge conditions, and can effectively improve the problem of lithium plating.

[0209] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A battery, characterized in that, It includes a positive electrode sheet and an electrolyte solution; The positive electrode sheet has a first surface and a second surface oppositely arranged in the thickness direction; the first surface has a plurality of concave portions, and the second surface has a plurality of convex portions; the positions of the concave portions on the first surface correspond to the positions of the convex portions on the second surface; the width of the concave portions is 0.2 mm - 8 mm; The electrolyte solution includes a first carboxylic acid ester, and the first carboxylic acid ester includes propyl acetate; the mass content c1 of the first carboxylic acid ester in the electrolyte solution is 10% - 60%; the electrolyte solution further includes a first lithium salt, and the first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide; the mass content c2 of the first lithium salt in the electrolyte solution is 0.5% - 10%; 2.5 ≤ c1 / c2 ≤ 100; The electrolyte solution further includes a first additive; the first additive includes at least one of 1,3 - propane sultone and vinylene sulfate; the mass content c3 of the first additive in the electrolyte solution is 0.1% - 6%; 0.5 ≤ c2 / c3 ≤ 10; The depth h1 of the concave portions and c1 satisfy: 5 ≤ h1 / c1 ≤ 200, where h1 is 3 - 40, and the unit is μm; The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes first particles and second particles; the first particles include single crystal particles; the second particles include polycrystalline particles; The battery further includes a separator, and the separator includes a base material layer and an adhesive layer; the adhesive layer is located on at least one outer surface of the separator, and the adhesive layer faces the positive electrode sheet.

2. The battery according to claim 1, wherein, 10 ≤ h1 / c1 ≤ 150; And / or, the spacing of the concave portions is 0.5 mm - 8 mm; And / or, the width of the concave portions is 0.2 mm - 4 mm; And / or, the height h2 of the convex portions is 2 μm - 40 μm; And / or, the width of the convex portions is 0.2 mm - 8 mm; And / or, the spacing of the convex portions is 0.5 mm - 8 mm.

3. The battery according to claim 2, wherein, 12.5 ≤ h1 / c1 ≤ 75; And / or, h1 is 5 - 30, and the unit of h1 is μm; And / or, c1 is 40% - 60%; And / or, the spacing of the concave portions is 1 mm - 4 mm; And / or, h2 is 4 μm - 30 μm; And / or, the width of the convex portions is 0.2 mm - 4 mm; And / or, the spacing of the convex portions is 1 mm - 4 mm.

4. The battery according to claim 1 or 2, wherein, The first lithium salt includes lithium bis(fluorosulfonyl)imide.

5. The battery according to claim 4, wherein, 5 ≤ c1 / c2 ≤ 20; And / or, c2 is 2% - 8%.

6. The battery according to claim 1, wherein, 0.6 ≤ c2 / c3 ≤ 2; And / or, c3 is 0.5% - 5%.

7. The battery according to claim 1 or 2, wherein The first particle includes a substance with the chemical formula LiNi x1 Co y1 Mn z1 M 1 a1 O2, where 0.5 ≤ x1 ≤ 0.95, 0.01 ≤ y1 ≤ 0.2, 0.01 ≤ z1 ≤ 0.4, 0 ≤ a1 ≤ 0.1, and M 1 includes at least one of Al, Mg, Y, W, B, Zr, Ti, Sr, Si, La, and Nb; The second particle includes a substance with the chemical formula LiNi x2 Co y2 Mn z2 M 2 a2 O2, where 0.5 ≤ x2 ≤ 0.95, 0.01 ≤ y2 ≤ 0.2, 0.01 ≤ z2 ≤ 0.4, 0 ≤ a2 ≤ 0.1, and M 2 includes at least one of Al, Mg, Y, W, B, Zr, Ti, Sr, Si, La, and Nb.

8. The battery according to claim 7, wherein, The mass content of the first particles in the positive electrode active material is 50% - 80%; And / or, the average particle size of the first particles is 1 μm - 6 μm; And / or, the average particle size of the second particles is 6 μm - 15 μm; and / or, the specific surface area of the first particles is 0.5 m 2 / g - 1.4 m 2 / g; and / or, the specific surface area of the second particle is 0.3 m 2 / g - 1 m 2 / g.

9. The battery according to claim 1 or 2, wherein The thickness H1 of the adhesive layer and the depth h1 of the concave portions satisfy: 0.007 ≤ H1 / h1 ≤ 0.6, where the unit of H1 is μm and the unit of h1 is μm.

10. The battery according to claim 9, wherein, 0.02 ≤ H1 / h1 ≤ 0.1, where the unit of H1 is μm and the unit of h1 is μm.

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