CN114975862B

CN114975862B - Secondary battery, electronic device and preparation method of secondary battery

Info

Publication number: CN114975862B
Application number: CN202210895107.1A
Authority: CN
Inventors: 刘奥
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-07-28
Filing date: 2022-07-28
Publication date: 2023-05-26
Anticipated expiration: 2042-07-28
Also published as: CN114975862A

Abstract

The application provides a secondary battery, an electronic device and a preparation method of the secondary battery, an electrode assembly of the secondary battery comprises a cathode pole piece, a cathode active material layer in the cathode pole piece comprises a cathode active material and a lithium supplementing material, the cathode active material layer comprises a first surface far away from a cathode current collector, and a concave part penetrating through the first surface is arranged on the cathode active material layer. The lithium element in the lithium supplementing material can form active lithium when the cathode plate is formed, so that the irreversible capacity of the first charge and discharge is supplemented, and the discharge performance of the battery is improved; the concave part can be used as a diffusion channel of substances generated by the decomposition of the lithium supplementing material, so that the accumulation of the decomposed substances in the cathode active material layer is reduced, the defect of the adhesion force of the cathode pole piece caused by the accumulation of the decomposed substances is alleviated, the processing performance of the cathode pole piece is improved, the concave part can also be used as a diffusion channel of lithium ions, the diffusion efficiency of the lithium ions generated by the decomposition of the lithium supplementing material is quickened, the decomposition rate of the lithium supplementing material is improved, and the decomposition of the lithium supplementing material is more sufficient.

Description

Secondary battery, electronic device and preparation method of secondary battery

Technical Field

The present disclosure relates to the field of energy storage technologies, and in particular, to a secondary battery, an electronic device, and a method for manufacturing the secondary battery.

Background

The secondary battery is a battery that can be continuously used by activating an active material by charging after discharging the battery. Secondary batteries are widely used in various electronic devices.

In the development of battery technology, secondary batteries such as lithium ion batteries have been widely used because of their advantages of high output power, long cycle life, and little environmental pollution. How to improve the processing performance of the battery and obtain better performance is always the research direction of workers in the energy storage technical field.

Disclosure of Invention

The present application provides a secondary battery, an electronic device, and a method for manufacturing a secondary battery capable of improving processability while improving discharge performance.

In order to achieve the above purpose, the present application adopts the following technical scheme:

in a first aspect, the present application provides a secondary battery comprising an electrode assembly comprising a cathode electrode tab comprising a cathode current collector and a cathode active material layer disposed on the cathode current collector; the cathode active material layer comprises a cathode active material and a cathode binder, and is subjected to lithium supplementing treatment; the cathode active material layer has a first surface far away from the cathode current collector, and is provided with a concave part penetrating the first surface.

In the scheme, the lithium supplementing material is added into the cathode active material layer when the cathode active material layer is subjected to lithium supplementing treatment, lithium elements in the lithium supplementing material form active lithium when the cathode electrode plate is formed, the irreversible capacity of primary charge and discharge is supplemented, and the primary coulomb efficiency and the battery capacity retention rate of the battery are improved, so that the discharge performance of the battery is improved. The concave part can be used as a diffusion channel of substances generated by decomposing the lithium supplementing material, the decomposed substances can be smoothly discharged along the concave part, the accumulation of the decomposed substances in the cathode active material layer is reduced, the problem of insufficient adhesion of the cathode electrode plate caused by the accumulation of the decomposed substances is solved, and the processing performance of the cathode electrode plate is improved, so that the processing performance of the secondary battery is improved; the concave part can also be used as a diffusion channel of lithium ions, so that the diffusion efficiency of lithium ions generated by the decomposition of the lithium supplementing material is quickened, the decomposition rate of the lithium supplementing material is improved, and the decomposition of the lithium supplementing material is more sufficient.

In some embodiments, the recess comprises a hole and/or a slot. The concave part comprises holes, so that the concave part is positioned accurately in the processing process, and accurate control of the concave part is facilitated; the concave part comprises a groove, so that continuous processing of the concave part can be realized, and the processing efficiency of the concave part is improved.

In some embodiments, the radius of the recess is R.ltoreq.R.ltoreq.50. The concave part with the size range not only can smoothly discharge substances generated by the decomposition of the lithium supplementing material, but also can reduce the influence of the concave part on the cathode active material layer so as to maintain the original shape of the cathode active material layer and reduce the adverse effect on the electrochemical performance of the cathode active material layer.

In some embodiments, the depth of the recess is H μm, 5.ltoreq.H.ltoreq.30. The concave part in the depth range can extend into the cathode active material layer, so that not only is lithium ion diffusion generated by decomposition of the lithium supplementing material in the cathode active material layer facilitated, but also substances generated by decomposition of the lithium supplementing material in the cathode active material layer are discharged, the possibility of accumulation of decomposed substances in the cathode active material layer is reduced, the adhesion force of the cathode active material layer on a cathode current collector is facilitated to be improved, and the processability of a cathode pole piece is improved.

In some embodiments, the cathode active material layer is provided with a plurality of recesses, and the distance between two adjacent recesses is L μm, 50.ltoreq.L.ltoreq.300. The plurality of concave parts have enough capability of discharging decomposed substances, and can smoothly discharge substances generated by decomposing lithium supplementing materials in the cathode active material layer, so that the possibility of gas accumulation in the cathode active material layer is reduced; the diffusion of lithium ions generated by the decomposition of the lithium supplementing material inside the cathode active material layer can be promoted; meanwhile, the distance between the concave parts is not too small, and the processing difficulty of the cathode pole piece is reduced.

In some embodiments, the cathode active material layer is provided with a plurality of recesses having a radius R μm, a depth H μm, and a distance L μm between two adjacent recesses, defining a=l/(r×h), 0.2+.5, and a parameter a of the recesses is 0.2 or more and 5 or less, so that the recesses are not only easy to process but also can have sufficient capability of discharging decomposed substances.

In some embodiments, the height of the edge portion of the recess protruding from the first surface is h μm, 3.ltoreq.h.ltoreq.10. The edge part of the concave part protrudes out of the cathode active material layer, so that the diffusion area of the diffusion channel is increased, the diffusion effect of the concave part on lithium ions is improved, the contact area of the cathode active material layer and the reaction of the electrolyte is increased, the reaction site of the cathode active material layer and the reaction of the electrolyte is increased, and the discharge rate performance of the secondary battery is improved.

In some embodiments, the cross-sectional shape of the recess is V-shaped, which can reduce the processing difficulty of the recess, is beneficial to improving the processing efficiency of the recess, is beneficial to the outward expansion of decomposed substances at the bottom of the recess along the recess, can be smoothly discharged from the recess through the opening of the recess, and is beneficial to reducing the possibility of accumulation of the decomposed substances in the recess.

In some embodiments, the recess is formed by a laser processing process, which may eliminate the material on the cathode active material layer to form the recess, so that the recess has a better effect on diffusion of ions and diffusion of electrolyte.

In some embodiments, the cathode active material layer is disposed on the surface of the cathode current collector, facilitating direct contact of the cathode active material with the cathode current collector, facilitating conduction of electrons, and improving electrical performance.

In some embodiments, the bonding strength between the cathode active material layer and the cathode current collector is F N/m, and F is 15-30, so that the cathode active material layer can be firmly connected to the surface of the cathode current collector, the possibility that the cathode active material layer falls off from the cathode current collector in the cathode pole piece processing process can be reduced, the cathode active material layer can be firmly connected to the cathode current collector, and the processing performance of the cathode pole piece is improved.

In some embodiments, the cathode active material layer further includes a lithium supplementing material including LiN ₃ 、Li ₂ O ₂ 、Li ₂ O、Li ₂ C ₃ O ₃ 、Li ₂ C ₄ O ₄ 、Li ₂ C ₂ O ₄ 、Li ₂ C ₃ O ₅ 、Li ₂ C ₅ O ₅ 、Li ₂ C ₆ O ₆ 、Li ₂ C ₄ O ₆ 、Li _x S _y Wherein x is more than or equal to 1 and less than or equal to 10, y is more than or equal to 1 and less than or equal to 10, and the lithium supplementing material can release enough lithium ions when the secondary battery is formed and charged, is favorable for supplementing lithium ions consumed by the secondary battery for the first time, and has a good lithium supplementing effect.

In some embodiments, the cathode active material includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and such cathode active material can provide sufficient lithium ions, not only has superior electrochemical performance, but also is advantageous in improving the stability of the performance of the secondary battery.

In some embodiments, the electrode assembly further comprises an anode pole piece and a diaphragm, the cathode pole piece, the diaphragm and the anode pole piece are arranged in a stacked mode, the first surface is connected with the diaphragm, the diaphragm can isolate the anode pole piece from the cathode pole piece, the cathode pole piece and the anode pole piece are prevented from being in contact and short circuit, and electrolyte absorbed in the diaphragm is also beneficial to being transmitted into the cathode pole piece through the concave part and improving the transmission speed and efficiency of ions between the cathode and the anode through the concave part.

In a second aspect, the present application provides an electronic device, which includes the secondary battery provided in any one of the above technical aspects.

In a third aspect, the present application provides a method for manufacturing a secondary battery, the method comprising: preparing cathode slurry from lithium supplementing material, cathode active material and cathode binder according to a preset proportion; disposing a cathode slurry on a cathode current collector to form a cathode active material layer, and obtaining a cathode sheet; forming a recess on a cathode active material layer, the cathode active material layer having a first surface remote from the cathode current collector, the recess penetrating the first surface; assembling the cathode pole piece into an electrode assembly; assembling the electrode assembly to obtain a secondary battery; the secondary battery is formed. The secondary battery with the concave part and the lithium supplementing material in the cathode plate can be obtained by the preparation method of the secondary battery, and the secondary battery has better discharge performance and processability. In some embodiments, the lithium supplementing material in the above preparation method comprises LiN ₃ 、Li ₂ O ₂ 、Li ₂ O、Li ₂ C ₃ O ₃ 、Li ₂ C ₄ O ₄ 、Li ₂ C ₂ O ₄ 、Li ₂ C ₃ O ₅ 、Li ₂ C ₅ O ₅ 、Li ₂ C ₆ O ₆ 、Li ₂ C ₄ O ₆ 、Li _x S _y Wherein x is 1-10 and y is 1-10.

In some embodiments, the recess is formed in the cathode sheet by a laser machining process.

The foregoing description is only an overview of the technical solutions of the present application, and may be implemented according to the content of the specification in order to make the technical means of the present application more clearly understood, and in order to make the above-mentioned and other objects, features and advantages of the present application more clearly understood, the following detailed description of the present application will be given.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:

FIG. 1 is a schematic view of an electrode assembly according to some embodiments of the present application;

FIG. 2 is a schematic view of a cathode sheet according to some embodiments of the present disclosure;

fig. 3 is a schematic structural view of a cathode active material layer according to some embodiments of the present application;

fig. 4 is a schematic top view of a cathode active material layer when the recess provided in some embodiments of the present application is a hole;

Fig. 5 is a schematic view showing the internal structure of a cathode active material layer when the recess provided in some embodiments of the present application is a hole;

fig. 6 is a schematic top view of a cathode active material layer when the recess provided in some embodiments of the present application is a groove;

fig. 7 is a schematic view showing an internal structure of a cathode active material layer in the case where a recess provided in some embodiments of the present application is a groove;

FIG. 8 is a schematic view of a recess edge portion provided in some embodiments of the present application;

fig. 9 is a schematic structural diagram of an electronic device according to some embodiments of the present application.

In the figure: 1. a cathode current collector; 2. a cathode active material layer; 21. a first surface; 22. a second surface; 23. a concave portion; 3. lithium supplementing materials; 4. a cathode active material; 5. an anode pole piece; 6. a cathode pole piece; 7. an anode current collector; 8. an anode active material layer; 9. a diaphragm; 10. an electrode assembly; 101. an anode tab; 102. a cathode tab; 2000. a secondary battery; 3000. an electronic device.

Detailed Description

Embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical solutions of the present application, and thus are only examples, and are not intended to limit the scope of protection of the present application.

It should be noted that unless otherwise indicated, technical or scientific terms used in the embodiments of the present application should be given the ordinary meanings as understood by those skilled in the art to which the embodiments of the present application belong.

In the description of the embodiments of the present application, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the embodiments of the present application.

Furthermore, the technical terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the embodiments of the present application, the meaning of "plurality" is two or more unless explicitly defined otherwise.

In the description of the embodiments of the present application, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured" and the like are to be construed broadly and may, for example, be fixedly connected, detachably connected, or be integrated; or may be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the embodiments of the present application will be understood by those of ordinary skill in the art according to the specific circumstances.

In the description of embodiments of the present application, unless explicitly specified and limited otherwise, a first feature "up" or "down" on a second feature may be that the first and second features are in direct contact, or that the first and second features are in indirect contact via an intermediary. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

Currently, the more widely the battery is used in view of the development of market situation. The battery is not only applied to energy storage power supply systems such as hydraulic power, firepower, wind power and solar power stations, but also widely applied to electric vehicles such as electric bicycles, electric motorcycles, electric automobiles, and the like, and a plurality of fields such as communication equipment, military equipment, aerospace, and the like. With the continuous expansion of the battery application field, the market demand thereof is also continuously expanding.

The following describes a secondary battery and an electronic device according to the present application in detail.

Some embodiments of the present application provide a secondary battery, as shown in fig. 1, including an electrode assembly 10, the electrode assembly 10 including a cathode tab 6, as shown in fig. 1 and 2, the cathode tab 6 including a cathode current collector 1 and a cathode active material layer 2 provided on the cathode current collector 1; the cathode active material layer 2 comprises a cathode active material 4 and a cathode binder, and the cathode active material layer 2 is subjected to lithium supplementing treatment; the cathode active material layer 2 includes a first surface 21 remote from the cathode current collector 1, and the cathode active material layer 2 is provided with a recess 23 penetrating the first surface 21.

The secondary batteries can be independently used as a power supply to output electric energy outwards, and can also be connected in series or in parallel or in series-parallel connection to form a battery pack, and the battery pack is used as the power supply to output electric energy outwards, wherein the series-parallel connection means that the plurality of secondary batteries are connected in series or in parallel. The secondary battery may be a lithium ion battery. The secondary battery may be in the shape of a cylinder, a flat body, a rectangular parallelepiped, or other shapes, etc. The following will describe a secondary battery as an example of a lithium ion battery.

In the first cycle of the lithium ion battery, an SEI film (solid electrolyte interface film) is formed on the surface of a graphite negative electrode, wherein the first irreversible capacity loss is 5% -15%, the high-capacity silicon-based material loss is 15% -35%, and the pre-lithiation technology can eliminate the capacity loss. The lithium is supplemented to the electrode material by the pre-lithiation technology, so that active lithium released in the charging process compensates for the first irreversible lithium loss, and the active lithium is used for forming an SEI film on the surface of the negative electrode so as to improve the reversible cycle capacity and cycle life of the lithium battery.

The electrode assembly 10 is used as an important component in a secondary battery, wherein the cathode sheet 6 comprises a cathode current collector 1 and a cathode active material layer 2 arranged on the cathode current collector 1, and the cathode active material layer 2 can be directly formed on the surface of the cathode current collector 1, or other functional layers are arranged between the cathode active material layer 2 and the cathode current collector 1 to realize preset functions.

The cathode active material layer 2 may be formed by coating a corresponding material on the cathode current collector 1 through a coating process, the cathode current collector 1 of the uncoated cathode active material layer 2 protruding from the cathode current collector 1 of the coated cathode active material layer 2, the cathode current collector 1 of the uncoated cathode active material layer 2 serving as the cathode tab 102. In some embodiments, the cathode tab 102 may also be formed by connecting a member that is the cathode tab 102 to the cathode current collector 1 by welding or the like. In some embodiments of the present application, the material of the cathode current collector 1 may be metallic aluminum, which is processed into an aluminum foil to form the cathode current collector 1.

In some embodiments of the present application, the cathode active material layer 2 further includes a lithium supplementing material 3. The lithium supplementing material 3 comprises a compound containing lithium elements, the compound is decomposed during formation and charging of the secondary battery, decomposed substances can be released, lithium ions in the decomposed substances can supplement irreversible capacity of primary charging and discharging, the primary coulomb efficiency and the battery capacity retention rate of the battery are improved, meanwhile, the porosity of the cathode pole piece 6 is increased after the lithium supplementing material 3 is decomposed, and the discharge rate performance of the secondary battery is improved.

In some embodiments of the present application, the lithium supplementing material 3 includes LiN ₃ 、Li ₂ O ₂ 、Li ₂ O、Li ₂ C ₃ O ₃ 、Li ₂ C ₄ O ₄ 、Li ₂ C ₂ O ₄ 、Li ₂ C ₃ O ₅ 、Li ₂ C ₅ O ₅ 、Li ₂ C ₆ O ₆ 、Li ₂ C ₄ O ₆ 、Li _x S _y Wherein x is 1-10 and y is 1-10.

The lithium supplementing material 3 can release enough lithium ions when the secondary battery is formed and charged, is favorable for supplementing lithium ions consumed by the secondary battery for the first time, and has a good lithium supplementing effect. The lithium-supplementing material 3 may be one of the above materials, or may be a mixture of two or more of the above materials, and the lithium-supplementing material 3 may be selected by those skilled in the art according to actual conditions. LiN ₃ 、Li ₂ O ₂ 、Li ₂ O、Li ₂ C ₃ O ₃ 、Li ₂ C ₄ O ₄ 、Li ₂ C ₂ O ₄ 、Li ₂ C ₃ O ₅ 、Li ₂ C ₅ O ₅ 、Li ₂ C ₆ O ₆ 、Li ₂ C ₄ O ₆ 、Li _x S _y The decomposed substances generated during the formation and charging of the secondary battery comprise gases such as hydrogen, carbon dioxide, alkane gas and the like, and the gas can increase the porosity of the cathode plate 6 during the generation of the gases, thereby being beneficial to improving the discharge rate performance of the secondary battery; meanwhile, as the concave part 23 is arranged on the cathode active material layer 2, the concave part 23 can be used as a diffusion channel for the gas generated by the decomposition of the lithium supplementing material, and the decomposed substances can be smoothly discharged along the concave part 23, so that the accumulation of the gas in the cathode active material layer 2 is reduced, and the gas is relievedThe problem of insufficient adhesion of the cathode plate 6 caused by accumulation is beneficial to improving the processing performance of the cathode plate 6, thereby improving the processing performance of the secondary battery. Preferably, the lithium supplementing material 3 includes Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The lithium ion battery has good oxidation stability and moisture stability, is beneficial to manufacturing of the secondary battery, can decompose and release lithium ions and gas when the secondary battery is subjected to formation and charging, not only supplements consumed lithium ions, but also can release gas to increase the porosity of the cathode plate 6; in addition, the generated gas may be used as an inert gas to inhibit decomposition of an electrolyte to protect a battery, and to optimize a negative electrode SEI film and improve cycle performance.

The cathode active material 4 may include at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate, and the cathode active material 4 may be selected by those skilled in the art according to practical circumstances as long as the electrochemical performance of the cathode sheet 6 is not affected. Preferably, the cathode active material 4 may be lithium cobaltate, which is advantageous not only in electrochemical performance but also in improving stability of the performance of the secondary battery.

The charge cutoff potential of the cathode active material 4 is greater than the decomposition potential of the lithium-supplementing material 3 when it is decomposed into lithium ions and gas, which enables the lithium-supplementing material 3 to be decomposed into lithium ions and gas before the charge is cut off when the secondary battery is charged, to complete the lithium-supplementing process of the cathode sheet 6.

The first surface 21 is the surface on the structure of the cathode active material layer 2, the surface is far away from the cathode current collector 1, the concave part 23 arranged on the cathode active material layer 2 penetrates through the first surface 21, so that the concave part 23 is far away from the cathode current collector 1, the concave part 23 can be used as a discharge channel for gas generated by decomposition of the lithium supplementing material 3, the gas is smoothly discharged from the surface far away from the cathode current collector 1 along the concave part 23, the accumulation of the gas in the cathode active material layer 2 is reduced, the problem of insufficient adhesion of the cathode pole piece 6 caused by the generation of the gas is solved, the processing performance of the cathode pole piece 6 can be improved, and the processing performance of the secondary battery is improved. In addition, the concave portion 23 can also serve as a diffusion channel for lithium ions, so that the diffusion efficiency of lithium ions generated by the decomposition of the lithium-supplementing material 3 is increased, the decomposition rate of the lithium-supplementing material 3 is improved, and the decomposition of the lithium-supplementing material 3 is more complete.

Meanwhile, the concave part 23 on the cathode active material layer 2 can reduce the tortuosity of the cathode plate 6, reduce the path through which ions pass, and is beneficial to improving the discharge rate performance of the secondary battery, thereby improving the discharge performance of the secondary battery.

The concave portion 23 is a concave structure provided on the cathode active material layer 2, which is formed by recessing the cathode active material layer 2 from the side close to the first surface 21 to the side far from the first surface 21, and is required to be distinguished from a place where unevenness may exist on the first surface 21 after the process of coating, rolling, etc. in the related art. The recess may be formed by removing a material by laser drilling, machining, or the like, or may be formed by pressing the first surface 21 by machining, or the like, so that a part of the first surface 21 is recessed into the cathode active material layer 2.

The recess 23 is formed on the first surface 21 of the cathode active material layer 2 by removing a material, and the cathode active material layer 2 is processed outside the first surface 21 by removing a material such that the recess 23 is a recess inside the cathode active material layer 2.

In some embodiments of the present application, the cathode active material layer 2 further includes a cathode binder. The cathode binder is a material that is mixed with a material forming the cathode active material layer 2 to perform a binding function, and it is possible to bond not only the cathode active material layer 2 to the cathode current collector 1, but also the cathode active materials 4 in the cathode active material layer 2 to each other as a unit, so that the cathode active material layer 2 maintains a certain shape and structure.

In some embodiments of the present application, the cathode active material layer 2 further includes a conductive agent. The conductive agent can improve the charge and discharge performance of the cathode electrode plate 6, can collect micro-current between the cathode active materials 4 and the cathode current collector 1, can reduce the contact resistance of the cathode electrode plate 6 to accelerate the movement rate of electrons, and can effectively improve the migration rate of lithium ions in the material of the cathode electrode plate 6, thereby improving the charge and discharge efficiency of the cathode electrode plate 6.

In some embodiments, the cathode active material 4 includes lithium cobaltate, and the mass fraction of the lithium cobaltate in the cathode active material layer 2 is 95.5%. The cathode binder included polyvinylidene fluoride, and the mass fraction of polyvinylidene fluoride in the cathode active material layer 2 was 1.7%. The conductive agent includes conductive carbon black, and the mass fraction of the conductive carbon black in the cathode active material layer 2 is 1.6%. Preferably, the conductive carbon black can be super p conductive carbon black, has good conductivity, moderate specific surface area, excellent processability and no influence on electrochemical mechanism. The mass fraction of the lithium supplementing material 3 in the cathode active material layer 2 was 1.2%.

In some embodiments of the present application, the cathode active material layer 2 is provided on the surface of the cathode current collector 1. The cathode active material layer 2 is directly arranged on the surface of the cathode current collector 1, no other functional layers are arranged between the cathode active material layer 2 and the cathode current collector 1, the bonding force between the cathode active material layer 2 and the surface of the cathode current collector 1 can be improved, the connection firmness between the cathode active material layer 2 and the cathode current collector 1 is improved, and the processing performance of the cathode pole piece 6 is improved.

In some embodiments of the present application, the bonding strength of the cathode active material layer 2 to the surface of the cathode current collector 1 is F N/m, 15.ltoreq.F.ltoreq.30. The bonding strength between the cathode active material layer 2 and the surface of the cathode current collector 1 is in the range of 15N/m to 30N/m, so that the cathode active material layer 2 can be firmly connected to the surface of the cathode current collector 1, the possibility that the cathode active material layer 2 falls off from the cathode current collector 1 in the process of processing the cathode pole piece 6 can be reduced, the cathode active material layer 2 can be firmly connected to the cathode current collector 1, and the processing performance of the cathode pole piece 6 is improved. The adhesive strength of the cathode active material layer 2 to the surface of the cathode current collector 1 may be 20N/m, 25N/m, or 25N/m.

In some embodiments of the present application, as shown in fig. 3, the cathode active material layer 2 is provided with a second surface 22, the second surface 22 is a surface of the cathode active material layer 2 on its own structure, and is disposed parallel to the first surface 21 at intervals, the second surface 22 is disposed close to the cathode current collector 1 relative to the first surface 21, the cathode current collector 1 is disposed on the second surface 22 of the cathode active material layer 2, the cathode active material layer 2 including the cathode active material 4 is formed between the first surface 21 and the second surface 22, and the recess 23 on the first surface 21 enables the gas in the cathode active material layer 2 to be smoothly discharged from the side far from the cathode current collector 1.

In some embodiments of the present application, the recess 23 is formed by a laser machining process. Since the laser has energy, the laser beam interacts with the material, and can eliminate the material to form the concave portion 23 on the first surface 21 of the cathode active material layer 2, and the laser processing technology can eliminate the material on the cathode active material layer 2 to form the concave portion 23, so that the concave portion 23 has better effect on ion diffusion and electrolyte diffusion, and the bonding strength and compaction density of the material around the concave portion 23 are not affected while removing the bonding agent of the processing part.

In some embodiments of the present application, the recess 23 includes a hole and/or a slot. As shown in fig. 4 and 5, the holes are hole-like structures provided on the cathode active material layer 2, the cross-sectional shape thereof may be circular, triangular, square or polygonal, the cross-sectional shape of the holes may also be other irregularly closed curves, and those skilled in the art may set the cross-sectional shape of the holes according to actual circumstances. Because the holes are convenient to position during the machining process, the concave part 23 comprises the holes, so that the concave part 23 is positioned accurately during the machining process, and accurate control of the concave part is facilitated. It will be appreciated that the diameters of the plurality of holes may be set to be the same or may be set to be different; the arrangement positions of the holes can be arranged in a matrix, a circumferential array and other preset rules, and also can be arranged in a disordered way, and the arrangement modes of the holes can be set by a person skilled in the art according to actual conditions.

As shown in fig. 6 and 7, the grooves are groove-like structures provided on the cathode active material layer 2, which have lengths along the arrangement direction of the cathode active material layer 2, and the cross-sectional shape of the grooves may be V-shaped, U-shaped, and those skilled in the art may set the cross-sectional shape of the grooves according to actual circumstances. Since the grooves can be continuously machined, the machining efficiency is high, and the concave portions 23 comprise the grooves, the continuous machining of the concave portions 23 can be realized, and the machining efficiency of the concave portions 23 can be improved. It is understood that the continuous extending direction of the grooves may be arranged along the length direction of the cathode active material layer 2, or may be arranged along the width direction of the cathode active material layer 2, the length direction of the cathode active material layer 2 being the X direction shown in fig. 6, and the width direction of the cathode active material layer 2 being the Y direction shown in fig. 6. It will be appreciated that the direction of continuous extension of the grooves can be set by those skilled in the art according to the actual circumstances.

In some embodiments of the present application, the cross-sectional shape of the concave portion 23 in the thickness direction of the cathode active material layer 2 is V-shaped. The thickness direction of the cathode active material layer 2 refers to the Z direction shown in fig. 3. As shown in fig. 3, the cross-sectional shape of the recess 23 is a V shape, that is, the recess 23 is tapered, the area of the opening of the recess 23 on the first surface 21 is larger than the area of the bottom of the recess 23, and the recess 23 with such a shape is not only convenient for processing, but also beneficial for improving the processing difficulty of the recess 23, and beneficial for expanding the gas at the bottom of the recess 23 outwards along the recess 23, and capable of smoothly discharging from the recess 23 through the opening of the recess 23, and beneficial for reducing the possibility of gas accumulation in the recess 23. In addition, the V-shaped concave portion 23 can increase the contact area between the electrolyte and the diffusion channel, and thus the diffusion efficiency of lithium ions can be increased.

In some embodiments of the present application, the radius of the recess 23 is R μm, 10.ltoreq.R.ltoreq.50. The radius of the concave portion 23 refers to a radius of a circle equivalent to the area of the concave portion 23, that is, the radius of an equivalent circle calculated by taking the area of the pattern formed by the concave portion 23 at the first surface 21 as the area of the equivalent circle, that is, the radius of the concave portion 23. When the recess 23 is a hole, the area of the pattern formed by the hole at the first surface 21 is measured first, and the radius of the equivalent circle calculated from the measured area is the radius of the recess 23. When the concave portion 23 is a groove, the area of the pattern formed by the groove at the first surface 21 is measured first, and the radius of the equivalent circle calculated from the measured area is the radius of the concave portion 23.

The area of the pattern of the recess 23 formed at the first surface 21 can be obtained by a charge coupled device (CCD, charge coupled Device) camera taking an image of the first surface 21 of the cathode pole piece 6 by measuring the area of the image of the recess 23 in the image.

The radius of the concave portion 23 is 10 μm or more and 50 μm or less, and the concave portion 23 in this size range not only enables smooth discharge of the gas generated by decomposition of the lithium-compensating material 3, but also reduces the influence of the concave portion 23 on the first surface 21 to maintain the original morphology of the first surface 21 and reduce adverse effects on the electrochemical performance of the cathode active material layer 2.

In some embodiments of the present application, the depth of the recess 23 is H μm, 5.ltoreq.H.ltoreq.30. As shown in fig. 3, the depth of the recess 23 refers to the distance from the cathode active material layer 2 to the bottom of the recess 23.

The depth of the recess 23 may be obtained by irradiating the first surface 21 of the cathode active material layer 2 in the cathode sheet 6 with a CCD camera, or may be obtained by photographing a slice sample in the thickness direction of the cathode sheet 6 with a scanning electron microscope and measuring it in an image obtained by the scanning electron microscope. The person skilled in the art can choose the method of measuring the depth of the recess 23 according to the actual situation.

The depth of the concave part 23 is more than or equal to 5 mu m and less than or equal to 30 mu m, and the concave part 23 with the depth range can extend into the cathode active material layer 2, so that not only is lithium ion diffusion generated by decomposition of the lithium supplementing material 3 in the cathode active material layer 2 facilitated, but also gas generated by decomposition of the lithium supplementing material 3 in the cathode active material layer 2 is discharged, the possibility of gas accumulation in the cathode active material layer 2 is reduced, the adhesion of the cathode active material layer 2 on the cathode current collector 1 is facilitated, and the processing performance of the cathode pole piece 6 is improved.

Alternatively, the depth of the concave portion 23 may be set to 15 μm or 25 μm, and the concave portion 23 may discharge the gas generated by decomposition of the lithium-compensating material 3 in the cathode active material layer 2 in a certain depth, preventing the gas from accumulating inside the cathode active material layer 2.

In some embodiments of the present application, the cathode active material layer 2 is provided with a plurality of recesses 23, and the distance between adjacent two recesses 23 is L μm, 50.ltoreq.L.ltoreq.300.

The plurality of concave portions 23 means that the number of concave portions 23 provided on the cathode active material layer 2 is three or more, and the plurality of concave portions 23 makes the cathode active material layer 2 in a porous structure, which is advantageous for improving the porosity of the cathode electrode sheet 6 and for improving the discharge rate performance of the secondary battery.

The distance between the adjacent two recesses 23 may refer to the shortest distance between the edges of the adjacent two recesses 23, and by setting the distance between the adjacent two recesses 23, the plurality of recesses 23 can be distributed on the first surface 21 of the cathode active material layer 2 with a certain uniformity, so that the decomposed gas of the lithium-compensating material 3 in the cathode active material layer 2 can be uniformly discharged outwards along the recesses 23, and the possibility of gas accumulation at local positions is reduced.

The distance between two adjacent concave parts 23 is greater than or equal to 50 μm and less than or equal to 300 μm, and the distance range enables the plurality of concave parts 23 to have enough gas discharge capacity, so that the gas generated by decomposing the lithium supplementing material 3 in the cathode active material layer 2 can be smoothly discharged, and the possibility of gas accumulation in the cathode active material layer 2 is reduced; the diffusion of lithium ions generated by the decomposition of the lithium supplementing material 3 inside the cathode active material layer 2 can also be promoted; at the same time, the distance between the concave parts 23 is not too small, which is helpful to reduce the processing difficulty of the cathode pole piece 6. Alternatively, the distance between two adjacent recesses 23 is set to 150 μm or 250 μm, which not only makes the recesses 23 have sufficient capability of exhausting gas, but also makes the recesses 23 on the cathode active material layer 2 easy to process, contributing to reducing the difficulty of processing the cathode electrode sheet 6.

In some embodiments of the present application, the cathode active material layer 2 is provided with a plurality of concave portions 23, the radius of the concave portions 23 is R μm, the depth of the concave portions 23 is H μm, the distance between two adjacent concave portions 23 is L μm, and a=l/(r×h) is defined, and 0.2+.a+.5.

A is defined as a parameter of the concave portion 23, and a=l/(r×h), and a is used as a parameter of the concave portion 23 in order to facilitate setting of the relationship among the radius, depth, and pitch of the concave portion 23, and the parameter a of the concave portion 23 is 0.2 or more and 5 or less, which is advantageous in improving the exhaust capacity of the concave portion 23. Preferably, the parameter a of the recess 23 is 2, where l=200, r= 5,H =20, which not only facilitates processing, but also enables the recess 23 to have sufficient capability to exhaust gas.

In some embodiments of the present application, the height of the edge portion of the concave portion 23 protruding from the first surface 21 is h μm, 3.ltoreq.h.ltoreq.10.

The edge portion of the recess 23 refers to the opening of the recess 23 on the cathode active material layer 2, as shown in fig. 8, when the recess 23 is processed on the cathode active material layer 2, a certain influence is caused on the first surface 21, so that the material at the opening of the recess 23 is accumulated and protrudes out of the first surface 21, the edge portion of the recess 23 protrudes out of the first surface 21, which not only increases the diffusion area of the diffusion channel, and is beneficial to improving the diffusion effect of the recess 23 on lithium ions, but also increases the contact area of the cathode active material layer 2 and the electrolyte, and is beneficial to increasing the reaction site of the cathode active material layer 2 and the electrolyte, and is beneficial to improving the discharge rate performance of the secondary battery. The edge portion of the recess 23 may be formed when the recess 23 is processed by a laser processing process, and since the laser has a certain energy, the material at the opening of the recess 23 is deposited when the cathode active material layer 2 is melted, so that the edge portion of the recess 23 protrudes from the first surface 21, and a person skilled in the art can adjust the height of the protruding edge portion of the recess 23 from the first surface 21 by adjusting the power and irradiation time of the laser.

The edge portion of the concave portion 23 protrudes from the first surface 21 by a height of 3 μm or more and 10 μm or less, so that the edge portion can function as an increase in contact area, and the influence of the concave portion 23 on the roughness of the first surface 21 of the cathode active material layer 2 can be reduced, thereby reducing the influence on the cathode-anode interface.

In some embodiments of the present application, the electrode assembly 10 in the secondary battery further includes an anode tab 5 and a separator 9, the cathode tab 6, the separator 9, and the anode tab 5 are stacked, and the first surface 21 is connected to the separator 9.

The anode sheet 5 includes an anode current collector 7 and an anode active material layer 8, the anode active material layer 8 is coated on the surface of the anode current collector 7, the anode active material layer 8 can be formed by coating corresponding materials on the surface of the anode current collector 7 through a coating process, the anode current collector 7 of the uncoated anode active material layer 8 protrudes from the anode current collector 7 of the coated anode active material layer 8, and the anode current collector 7 of the uncoated anode active material layer 8 serves as an anode tab 101. In some embodiments of the present application, the material of anode current collector 7 may be metallic copper, which is processed into copper foil to form anode current collector 7.

The anode active material layer 8 includes an anode active material including graphite, the mass fraction of graphite in the anode active material layer 8 being 98%, an anode binder including a silicone resin, the mass fraction of the silicone resin in the anode active material layer 8 being 1%, and a thickener including sodium carboxymethyl cellulose, the mass fraction of sodium carboxymethyl cellulose in the anode active material layer 8 being 1%.

The diaphragm 9 can isolate the anode pole piece 5 from the cathode pole piece 6, and prevent the cathode pole piece 6 from being in contact with the anode pole piece 5 for short circuit. In some embodiments of the present application, the separator 9 is a highly adhesive composite film, which can isolate the anode electrode sheet 5 from the cathode electrode sheet 6 and has good adhesion, so that the first surface 21 of the cathode active material layer 2 is firmly connected with the separator 9.

The following further describes the advantageous effects of the secondary battery provided in the embodiments of the present application through comparative experiments.

A secondary battery composed of a cathode electrode sheet formed of a cathode active material layer provided with no recess in the related art was taken as an experimental object in comparative examples of comparative experiments; a secondary battery composed of a cathode electrode sheet formed of a cathode active material layer provided with a concave portion was taken as an experimental object in examples of comparative experiments.

The manufacturing method of the cathode plate in the secondary battery comprises the following steps: mixing a cathode active material, conductive carbon black serving as a conductive agent and polyvinylidene fluoride serving as a binder according to a certain mass ratio, adding N-methyl pyrrolidone (NMP), and uniformly stirring under the action of a vacuum stirrer to obtain cathode slurry, wherein the solid content of the cathode slurry is 70wt%. The cathode slurry is uniformly coated on one surface of a cathode current collector aluminum foil with the thickness of 12 mu m, and the aluminum foil is dried at 120 ℃ for 1h, so that a cathode pole piece with a cathode active material layer coated on one side is obtained. Repeating the steps on the other surface of the aluminum foil to obtain the cathode pole piece with the cathode active material layer coated on both sides. Then cold pressing, cutting and slitting, and drying for 1h under the vacuum condition of 120 ℃ to obtain the cathode pole piece with the specification of 74 mm multiplied by 867 mm. And welding and connecting a cathode tab on the cathode plate, wherein the cathode tab is made of aluminum foil.

The manufacturing method of the anode plate in the secondary battery comprises the following steps: mixing anode active material graphite, binder styrene-butadiene rubber and thickener sodium carboxymethyl cellulose according to the mass ratio of 97.4:1.4:1.2, adding deionized water, and uniformly stirring under the action of a vacuum stirrer to obtain anode slurry, wherein the solid content of the anode slurry is 75wt%. The anode slurry was uniformly coated on one surface of an anode current collector copper foil having a thickness of 12 μm, and the copper foil was dried at 120 ℃ to obtain an anode having a coating thickness of 130 μm, one side of which was coated with an anode active material layer. Repeating the steps on the other surface of the aluminum foil to obtain the anode plate with the anode active material layer coated on both sides. Then cold pressing, cutting and slitting, and drying for 1h under the vacuum condition of 120 ℃ to obtain the anode pole piece with the specification of 78 mm multiplied by 875 mm. And welding and connecting an anode tab on the anode sheet, wherein the anode tab is made of copper foil nickel plating.

The separator in the secondary battery is a porous polyethylene film with a thickness of 7 μm.

And sequentially stacking the prepared cathode pole piece, the diaphragm and the anode pole piece, so that the diaphragm is positioned between the cathode pole piece and the anode pole piece to play a role in isolation, and winding to obtain the electrode assembly. And assembling the electrode assembly with the case to obtain the packaged secondary battery. Removing water at 80deg.C, injecting into the prepared electrolyte, packaging, standing, and forming to obtain secondary battery. The electrolyte can be prepared from ethylene carbonate, propylene carbonate and diethyl carbonate according to the mass ratio of 1:1:1, wherein the concentration of lithium hexafluorophosphate is 1.15 mol/L.

The difference of the cathode sheets in each comparative example and example is as follows:

comparative example 1

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The mass fraction of the electrolyte was 1.2%, the cathode sheet 6 was not provided with the concave portion 23, and a secondary battery using the cathode sheet 6 was used as an experimental subject.

Example 1

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 2

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =1 of the concave portion 23, where l=200, r=10, and h=20.

Example 3

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =0.33 of the concave portion 23, where l=200, r=30, and h=20.

Example 4

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =0.2 of the concave portion 23, where l=200, r=50, and h=20.

Example 5

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =0.18 of the concave portion 23, where l=200, r=55, and h=20.

Example 6

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =13.33 of the concave portion 23, where l=200, r= 5,H =3.

Example 7

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ Li2C4O4 is 1.2 percent by mass, and the cathode plate 6 is processed by laser drillingThe recess 23 is provided, and the parameter a=l/(r×h) =4 of the recess 23, where l=200, r= 5,H =10.

Example 8

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =1.33 of the concave portion 23, where l=200, r= 5,H =30.

Example 9

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =1.14 of the concave portion 23, where l=200, and r= 5,H =35.

Example 10

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =0.5 of the concave portion 23, where l=50, r= 5,H =20.

Example 11

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =1 of the concave portion 23, where l=100, r= 5,H =20.

Example 12

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =1.5 of the concave portion 23, where l=150, r= 5,H =20.

Example 13

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =3 of the concave portion 23, where l=300, and r= 5,H =20.

Example 14

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =5 of the concave portion 23, where l=500, r= 5,H =20.

Example 15

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The mass fraction of Li2C4O4 is 1.2%, the cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =6 of the concave portion 23, where l=600, r= 5,H =20.

Example 16

The mass fraction of the cathode active material 4 in the cathode active material slurry was95.5 percent of cathode active material 4 is lithium nickelate, the mass fraction of polyvinylidene fluoride is 1.7 percent, the mass fraction of super p conductive carbon black is 1.6 percent, and lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 17

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium manganate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 18

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobalt phosphate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 19

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the mass fraction of the cathode active material 4 is 1:1 mixed lithium cobaltate and lithium nickelate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 20

Cathode active material slurryThe mass fraction of the cathode active material 4 in the material is 95.5%, the mass fraction of the cathode active material 4 is 1:1 mixed lithium cobaltate and lithium manganate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 21

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the mass fraction of the cathode active material 4 is 1:1 mixed lithium cobalt oxide and lithium cobalt phosphate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ ，Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 22

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₃ O ₃ ，Li ₂ C ₃ O ₃ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the concave portion 3 has a parameter a=l/(r×h) =2, where l=200, and r= 5,H =20.

Example 23

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₅ O ₅ ，Li ₂ C ₅ O ₅ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 24

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is Li ₂ C ₆ O ₆ ，Li ₂ C ₆ O ₆ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 25

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, and the lithium supplementing material 3 is LiN ₃ ，LiN ₃ The cathode sheet 6 is provided with a concave portion 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the concave portion 23, where l=200, r= 5,H =20.

Example 26

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is 1:1 mixed Li ₂ C ₃ O ₃ And Li (lithium) ₂ C ₄ O ₄ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the recess 23, where l=200, r= 5,H =20.

Example 27

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is 1:1 mixed Li ₂ C ₃ O ₃ And Li (lithium) ₂ C ₅ O ₅ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the recess 23, where l=200, r= 5,H =20.

Example 28

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is 1:1 mixed Li ₂ C ₃ O ₃ And Li (lithium) ₂ C ₆ O ₆ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the recess 23, where l=200, r= 5,H =20.

Example 29

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is 1:1 mixed Li ₂ C ₃ O ₃ And LiN ₃ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the recess 23, where l=200, r= 5,H =20.

Example 30

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the mass fraction of the cathode active material 4 is 1:1 mixed lithium cobaltate and lithium nickelate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the mass fraction of the lithium supplementing material 3 is 1:1 mixed Li ₂ C ₃ O ₃ And Li (lithium) ₂ C ₅ O ₅ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the recess 23, where l=200, r= 5,H =20.

Example 31

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the mass fraction of the cathode active material 4 is 1:1 mixed lithium cobalt oxide and lithium cobalt phosphate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the mass fraction of the lithium supplementing material 3 is 1:1 mixed Li ₂ C ₃ O ₃ And Li (lithium) ₂ C ₆ O ₆ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =2 of the recess 23, where l=200, r= 5,H =20.

Example 32

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =1 of the recess 23, where l=50, r=10, and h=5.

Example 33

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =0.2 of the recess 23, where l=300, r=50, and h=30.

Example 34

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =0.03 of the recess 23, where l=50, r=50, and h=30.

Example 35

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a concave part 23 by a laser drilling process, and the concave part 23The parameter a=l/(r×h) =6, where l=300, r=10, h=5.

Example 36

The mass fraction of the cathode active material 4 in the cathode active material slurry is 95.5%, the cathode active material 4 is lithium cobaltate, the mass fraction of polyvinylidene fluoride is 1.7%, the mass fraction of super p conductive carbon black is 1.6%, the mass fraction of the lithium supplementing material 3 is 1.2%, and the lithium supplementing material 3 is Li ₂ C ₄ O ₄ The cathode sheet 6 is provided with a recess 23 by a laser drilling process, and the parameter a=l/(r×h) =5 of the recess 23, where l=300, r=10, and h=6.

The adhesion test was performed on the cathode tab 6 in the secondary batteries of the above comparative examples and examples. The adhesive force test method of the cathode sheet 6 is as follows:

and discharging the formed full-charge secondary battery to 3V at a discharge rate of 1C, disassembling the secondary battery, cutting out a rectangular sample with the length of 100 mm and the width of 10 mm from the cathode pole piece 6, adhering the side surface of the pole piece sample, which is far away from the cathode current collector 1, on a stainless steel plate by utilizing double-sided adhesive at one end of the pole piece sample, fixing the stainless steel plate, connecting the cathode current collector 1 at the other end of the pole piece sample with tension measuring equipment, testing the stripping force between the cathode active material layer 2 and the cathode current collector 1 in the cathode pole piece 6 by adopting a 180-DEG stripping strength test method, wherein the stripping speed in the test process is 300 mm/min, the stripping length in the test process is 40 mm, and obtaining the adhesion force of the cathode pole piece 6 through the test.

In some embodiments of the present application, the decomposition rate of the lithium-compensating material 3 in the cathode tab 6 in the secondary battery in the above comparative example and embodiment may be tested, using the actual capacity of the secondary battery divided by the design capacity as the decomposition rate of the lithium-compensating material 3, the higher the decomposition rate of the lithium-compensating material 3, the more sufficient the decomposition of the lithium-compensating material 3.

The design capacity of the secondary battery can be calculated from the charge gram capacity after the cathode material is completely delithiated, and the theoretical capacity of the lithium supplementing material 3 can be added.

The method for testing the actual capacity of the secondary battery is as follows: constant-current charging is carried out on the secondary battery at a charging rate of 0.2 ℃ under the environment of 25 ℃ until the voltage of the secondary battery reaches 4.45V; constant voltage charging is carried out on the secondary battery at the charging voltage of 4.45V until the charging multiplying power reaches 0.025C; constant-current discharging is carried out on the secondary battery at the discharge multiplying power of 0.2C until the voltage of the secondary battery reaches 3.0V; the above procedure was repeated 3 times with the average capacity of the secondary battery as the actual capacity of the secondary battery.

In some embodiments of the present application, qualitative tests may also be performed on whether there is a residue of the lithium-compensating material 3 in the cathode tab 6 in the secondary batteries of the above comparative examples and embodiments.

The testing method comprises the following steps: taking the secondary battery after the formation, and performing constant-current discharge on the secondary battery at a discharge rate of 0.2C until the voltage of the secondary battery reaches 3.0V; disassembling the secondary battery and scraping off all the materials on the cathode active material layer 2; drying the scraped material for 24 hours at the temperature of 80 ℃; the scraped material is subjected to analysis of whether there is a residue in the cathode active material layer 2 by X-ray diffraction analysis or raman spectroscopy.

The secondary batteries fabricated with the cathode sheet 6 in the above comparative examples and examples were subjected to discharge capacity retention rate test, and the discharge capacity retention rate test method at a discharge rate of 1C at 25 ℃ was as follows:

constant-current charging is carried out on the secondary battery at a charging rate of 0.2C until the voltage of the secondary battery reaches 4.45V; constant voltage charging is carried out on the secondary battery at the charging voltage of 4.45V until the charging multiplying power reaches 0.025C; constant-current discharging is carried out on the secondary battery at the discharge multiplying power of 0.2C until the voltage of the secondary battery reaches 3.0V; repeating the above procedure 3 times, taking the average discharge capacity of the secondary battery as the actual discharge capacity (discharge capacity at 0.2C discharge rate) of the secondary battery;

constant-current charging is carried out on the secondary battery at a charging rate of 0.2C until the voltage of the secondary battery reaches 4.45V; constant voltage charging is carried out on the secondary battery at the charging voltage of 4.45V until the charging multiplying power reaches 0.025C; constant-current discharging is carried out on the secondary battery at the discharge multiplying power of 1C until the voltage of the secondary battery reaches 3.0V; repeating the above procedure for 3 times, taking the average discharge capacity as the actual discharge capacity of the secondary battery at the discharge rate of 1C;

the discharge capacity retention rate of the secondary battery at the 1C discharge rate can be obtained by dividing the actual discharge capacity of the secondary battery at the 1C discharge rate by the actual discharge capacity of the secondary battery.

The discharge capacity retention test method at a discharge rate of 2C in an environment of 25 ℃ is as follows:

constant-current charging is carried out on the secondary battery at a charging rate of 0.2C until the voltage of the secondary battery reaches 4.45V; constant voltage charging is carried out on the secondary battery at the charging voltage of 4.45V until the charging multiplying power reaches 0.025C; constant-current discharging is carried out on the secondary battery at the discharge multiplying power of 2C until the voltage of the secondary battery reaches 3.0V; repeating the above procedure for 3 times, taking the average discharge capacity as the actual discharge capacity of the secondary battery at the discharge rate of 2C;

the discharge capacity retention rate of the secondary battery at the 2C discharge rate can be obtained by dividing the actual discharge capacity of the secondary battery at the 2C discharge rate by the actual discharge capacity of the secondary battery.

The porosity test of the cathode sheet 6 in the above comparative examples and examples was carried out by using a mercury porosimeter during the porosity test, and the porosity test method of the cathode sheet 6 was as follows:

taking a cathode plate 6 provided with a cathode active material layer 2 as a test sample;

selecting an appropriate dilatometer based on predictions of density and porosity of the test sample;

placing the test sample in an oven for baking for 2 hours to remove moisture in the test sample;

weighing the test sample from which the moisture has been removed;

loading the test sample into a dilatometer, and weighing after sealing, wherein the weight is the weight of the test sample and the dilatometer;

loading the dilatometer into a low pressure station, performing a low pressure analysis according to a predetermined low pressure analysis program to bring the pressure to a range of 0.5psi to 50 psi;

after the low-pressure analysis is finished, taking out the dilatometer and weighing, wherein the dilatometer is the weight of the test sample, the dilatometer and mercury;

loading the expansion meter into a high-pressure station, fixing the expansion meter, screwing the high-pressure bin head into the high-pressure station, screwing the high-pressure bin head into the bottom, and driving away bubbles of the expansion meter;

performing high-pressure analysis according to a preset high-pressure analysis program to ensure that the pressure is in the range of 100psi to 60000 psi;

after the high pressure analysis is completed, the dilatometer is cleaned and the structure is tested.

The method for testing the bonding strength of the cathode pole piece 6 comprises the following steps:

the test is carried out by using a high-speed rail tension machine, a cathode (width is 30mm, length is 100mm to 160 mm), double-sided adhesive paper (model: 3M9448A, width is 20mm, length is 90mm to 150 mm)) is fixed on a steel plate, paper tape with the same width as the cathode is fixed with the adhesive paper on one side of the cathode, a limit block of the tension machine is adjusted to a proper position, the paper tape is folded upwards and slides by 40 mm, the sliding speed is 50 mm/min, and the bonding strength between the cathode active material layer 2 and the cathode current collector 1 under 180 DEG (namely reverse direction stretching) is tested.

The pore volume of the test sample can be obtained by dividing the measured mercury weight by the mercury density through the test process, and the porosity of the test sample can be obtained through calculation. This process is a common technical means and method for a person skilled in the art and will not be described in detail here.

Table 1 is an example of respective parameters of the secondary batteries and the cathode tab 6 in the comparative examples and examples obtained by the test in the comparative experiments of the present application.

As can be seen from table 1, the provision of the concave portion 23 significantly increases the adhesion of the electrode sheet, since the concave portion 23 can serve as a diffusion passage for the gas generated by the decomposition of the lithium-compensating material 3, and can smoothly discharge the gas in the decomposed substance along the concave portion 23, thereby reducing the accumulation of the gas in the decomposed substance in the cathode active material layer 2, alleviating the problem of insufficient adhesion of the cathode electrode sheet 6 due to the accumulation of the decomposed substance gas, and improving the processability of the cathode electrode sheet 6, thereby improving the processability of the secondary battery; in addition, as the concave parts 23 can reduce the concentration difference of lithium ions on the surface layer and the inner layer of the pole piece active material layer, the internal and external reaction rates of the pole piece active material layer can be balanced, so that the decomposition of the lithium supplementing material 3 in the cathode pole piece 6 is more sufficient, the overall porosity of the cathode pole piece 6 is also improved after the lithium supplementing material 3 is fully decomposed, and the discharge rate performance of the secondary battery is improved.

Compared with other examples, when A is more than or equal to 0.2 and less than or equal to 5, the bonding strength of the cathode pole piece 6 is more than 20N/m, the decomposition rate of the lithium supplementing material 3 is more than 90%, the discharge capacity retention rate under 1C discharge rate is more than 90%, and the discharge capacity retention rate under 2C discharge rate is more than 85%; when A exceeds the range of 0.2 to 5, the bonding strength of the cathode pole piece 6 is less than 20N/m, the decomposition rate of the lithium supplementing material 3 is less than or equal to 90%, the discharge capacity retention rate at 1C discharge rate is less than or equal to 90%, and the discharge capacity retention rate at 2C discharge rate is less than 85%. It can be obtained that A is more than or equal to 0.2 and less than or equal to 5, the adhesive force of the cathode plate 6 in the secondary battery can be improved, the decomposition of the lithium supplementing material 3 in the cathode plate 6 is accelerated, and the discharge rate performance of the secondary battery is effectively improved.

The embodiment of the application also provides a preparation method of the secondary battery, which comprises the following steps:

preparing cathode slurry from a lithium supplementing material 3, a cathode active material 4 and a cathode binder according to a preset proportion; disposing a cathode slurry on a cathode current collector 1 to form a cathode active material layer 2, and obtaining a cathode electrode sheet 6; forming a recess 23 on the cathode active material layer 2, the cathode active material layer 2 having a first surface 21 remote from the cathode current collector 1, the recess 23 penetrating the first surface 21; assembling the cathode pole piece 6, the diaphragm 9 and the anode pole piece 5 into an electrode assembly 10; assembling the electrode assembly 10 to obtain a secondary battery; the secondary battery is formed.

TABLE 1

By the preparation method of the secondary battery, the cathode pole piece in the secondary battery provided by the technical scheme can be obtained, and the cathode pole piece not only contains the lithium supplementing material 3 but also has the concave part, so that the secondary battery has good discharge performance and processability, and is beneficial to improving user experience.

As shown in fig. 9, the embodiment of the present application also provides an electronic apparatus 3000 using a secondary battery 2000 as a power source, and the electronic apparatus 3000 may be a mobile phone, a portable device, a notebook computer, an electric toy, an electric tool, or the like. Power tools include metal cutting power tools, cleaning tools, and the like, such as electric drills, electric wrenches, dust collectors, sweeping robots, and the like. The embodiment of the present application does not particularly limit the electronic device 3000.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the embodiments, and are intended to be included within the scope of the claims and description. In particular, the technical features mentioned in the respective embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery comprising an electrode assembly including a cathode electrode sheet including a cathode current collector and a cathode active material layer provided on the cathode current collector, the cathode active material layer being provided on a surface of the cathode current collector;

the cathode active material layer comprises a cathode active material and a cathode binder, and is subjected to lithium supplementing treatment, wherein the lithium supplementing treatment is to add a lithium supplementing material into cathode slurry for forming the cathode active material layer;

the cathode active material layer is provided with a first surface far away from the cathode current collector, and is provided with a concave part penetrating through the first surface and having a cavity structure;

the cathode active material layer is provided with a plurality of concave parts, the radius of each concave part is R mu m, the depth of each concave part is H mu m, the distance between two adjacent concave parts is L mu m, A=L/(R multiplied by H) is defined, A is more than or equal to 0.2 and less than or equal to 5, and R is more than or equal to 10 and less than or equal to 50.

2. The secondary battery according to claim 1, wherein the recess comprises a hole and/or a groove.

3. The secondary battery according to claim 1, wherein 5.ltoreq.H.ltoreq.30.

4. The secondary battery according to claim 1, wherein 50.ltoreq.l.ltoreq.300.

5. The battery according to claim 1, wherein a height of the edge portion of the concave portion protruding from the first surface is h μm, 3.ltoreq.h.ltoreq.10.

6. The secondary battery according to claim 1, wherein the cross-sectional shape of the concave portion is V-shaped.

7. The secondary battery according to claim 1, wherein the concave portion is formed by a laser processing process.

8. The secondary battery according to claim 1, wherein the adhesive strength of the cathode active material layer and the cathode current collector is F N/m, 15.ltoreq.f.ltoreq.30.

9. The secondary battery according to claim 1, wherein the cathode active material layer further comprises the lithium supplementing material, the lithium supplementing material comprising LiN ₃ 、Li ₂ O ₂ 、Li ₂ O、Li ₂ C ₃ O ₃ 、Li ₂ C ₄ O ₄ 、Li ₂ C ₂ O ₄ 、Li ₂ C ₃ O ₅ 、Li ₂ C ₅ O ₅ 、Li ₂ C ₆ O ₆ 、Li ₂ C ₄ O ₆ 、Li _x S _y Wherein x is 1-10 and y is 1-10.

10. The secondary battery according to claim 1, wherein the cathode active material comprises at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate.

11. The battery of claim 1, wherein the electrode assembly further comprises an anode electrode sheet and a separator, the cathode electrode sheet, the separator, and the anode electrode sheet being stacked, the first surface being contiguous with the separator.

12. An electronic device comprising the secondary battery according to any one of claims 1 to 11.

13. A method of manufacturing a secondary battery, comprising:

preparing cathode slurry from lithium supplementing material, cathode active material and cathode binder according to a preset proportion;

disposing a cathode slurry on a cathode current collector to form a cathode active material layer, and obtaining a cathode sheet;

a concave part which is formed on the cathode active material layer and has a cavity structure, the cathode active material layer is provided with a first surface far away from the cathode current collector, the concave part penetrates through the first surface, the cathode active material layer is provided with a plurality of concave parts, the radius of each concave part is R mu m, the depth of each concave part is H mu m, the distance between two adjacent concave parts is L mu m, A=L/(R multiplied by H) is defined, A is more than or equal to 0.2 and less than or equal to 5, and the cathode active material layer is arranged on the surface of the cathode current collector, and R is more than or equal to 10 and less than or equal to 50;

Assembling the cathode plate into an electrode assembly;

assembling the electrode assembly to obtain a secondary battery;

and performing formation on the secondary battery.

14. The method for manufacturing a secondary battery according to claim 13, wherein the lithium supplementing material comprises LiN ₃ 、Li ₂ O ₂ 、Li ₂ O、Li ₂ C ₃ O ₃ 、Li ₂ C ₄ O ₄ 、Li ₂ C ₂ O ₄ 、Li ₂ C ₃ O ₅ 、Li ₂ C ₅ O ₅ 、Li ₂ C ₆ O ₆ 、Li ₂ C ₄ O ₆ 、Li _x S _y Wherein x is 1-10 and y is 1-10.

15. The method of manufacturing a secondary battery according to claim 13, wherein the recess is formed on the cathode active material layer by a laser processing process.