Secondary battery, electronic device, and method for preparing secondary battery

Abstract

A secondary battery, an electronic device, and a method for preparing a secondary battery, wherein an electrode assembly (10) of the secondary battery comprises an anode electrode sheet (5), the anode electrode sheet (5) comprises an anode current collector (1) and an anode active material layer (2), the anode active material layer (2) comprises an anode active material, and a first surface (21) of the anode active material layer (2) is subjected to a lithium replenishment process, whereby active lithium is formed during the formation of the anode electrode sheet, replenishing the irreversible capacity of the first charge and discharge, thereby facilitating the improvement of the battery's first coulomb efficiency and battery capacity retention rate, thereby improving the battery's discharge performance. A recess (23) provided on the first surface (21) can serve as a lithium ion transmission channel, thereby increasing the speed of lithium ion diffusion, facilitating the shortening of the time required for static lithium replenishment, and reducing side reactions occurring during static lithium replenishment, and also alleviating the problem of uneven lithium ion concentration in the thickness direction of the anode active material layer, accelerating the reaction within the anode active material layer, and enabling the lithium replenishment material to react more fully.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a secondary battery, an electronic device, and a method for preparing the secondary battery. Background Art

[0002] Secondary batteries are batteries that can be recharged after discharge to reactivate the active materials and continue to be used. They are widely used in electronic devices such as mobile phones and laptops.

[0003] In the development of battery technology, lithium-ion batteries are widely used due to their advantages such as high output power, long cycle life, and low environmental pollution. Improving the processing properties of secondary batteries and achieving better performance has always been a research direction for those in the field of energy storage technology. Summary of the Invention

[0004] The present application provides a secondary battery, an electrical device, and a method for preparing the secondary battery. The secondary battery can improve discharge performance while shortening processing time, thereby improving processing efficiency.

[0005] In the first aspect, the present application proposes a secondary battery, comprising an electrode assembly, the electrode assembly comprising an anode electrode sheet, the anode electrode sheet comprising an anode current collector and an anode active material layer provided on the anode current collector, the anode active material layer comprising an anode active material; the anode active material layer has a first surface away from the anode current collector, the anode active material layer is provided with a recessed portion recessed from the first surface toward the anode current collector, and the first surface has been treated with a lithium replenishment process.

[0006] Because the first surface of the anode active material layer undergoes a lithium replenishment process, active lithium is formed during the formation of the anode electrode, replenishing the irreversible capacity of the initial charge and discharge cycle. This helps improve the battery's initial coulombic efficiency and capacity retention, thereby enhancing the battery's discharge performance. The recessed portions extending through the first surface serve as lithium ion transport channels, increasing the rate of lithium ion diffusion, shortening the static lithium replenishment period and reducing side reactions during static lithium replenishment. Furthermore, the recessed portions alleviate the uneven lithium ion concentration across the thickness of the anode active material layer, accelerating reactions within the anode active material layer and ensuring a more complete reaction of the lithium replenishment material.

[0007] In one embodiment provided herein, the recess comprises a hole and / or a groove. The hole allows for precise positioning of the recess during machining, facilitating precise control of the recess; the groove allows for continuous machining of the recess, facilitating improved machining efficiency.

[0008] In one embodiment provided in the present application, the anode active material layer is provided with a plurality of recesses, the radius of the recess is R μm, the depth of the recess is H μm, the distance between two adjacent recesses is L μm, and A=L / (R×H), 0.20≤A≤5.00 is defined, and the parameter A of the recess is greater than or equal to 0.2 and less than or equal to 5, so that the recess is not only easy to process, but also enables the recess to have sufficient ability to diffuse lithium ions.

[0009] In one embodiment provided in the present application, 0.20≤A≤3.50, which is beneficial to further improve the diffusion capacity of the recess for lithium ions.

[0010] In one embodiment provided in the present application, the radius of the recess is R μm, 10≤R≤50. The recess in this size range serves as a lithium ion transmission channel, which can improve the transmission efficiency of lithium ions, shorten the static lithium replenishment time, and reduce the impact of the recess on the first surface to maintain the original morphology of the first surface and reduce the adverse effects on the electrochemical properties of the anode active material layer.

[0011] In one embodiment provided in the present application, 30≤R≤50 can further improve the lithium ion transmission efficiency on the basis of reducing the influence of the recess 23 on the first surface 21 while maintaining the original morphology of the first surface 21, thereby achieving a more significant effect of shortening the static lithium replenishment time.

[0012] In one embodiment provided in the present application, the depth of the recess is H μm, 8≤H≤30. The recess can not only effectively diffuse ions, but also reduce the effect on the adhesion of the anode active material layer, thereby reducing the possibility of the anode active material layer falling off from the anode current collector.

[0013] In an embodiment provided in the present application, 15≤H≤30, so that the concave portion can effectively diffuse ions while minimizing the effect on the adhesion of the anode active material layer.

[0014] In one embodiment provided in the present application, the anode active material layer is provided with a plurality of recesses, and the distance between two adjacent recesses is L μm, 50≤L≤300, so that the plurality of recesses have sufficient ability to diffuse lithium ions, and can enable the lithium ions generated by the lithium replenishment process on the first surface of the anode active material layer to diffuse quickly and fully into the interior of the anode active material layer.

[0015] In one embodiment provided in the present application, 50≤L≤150, and the distribution intervals of the plurality of recesses on the anode active material layer are within a preset range, further enabling the plurality of recesses to have sufficient capacity to diffuse lithium ions.

[0016] In one embodiment provided in the present application, the anode active material layer has a stripe portion exposed on the first surface and extending along the first direction, and the width of the stripe portion in a direction perpendicular to the extension direction of the stripe portion is 0.1 mm to 2.0 mm. This width range facilitates the processing of the metal lithium foil during the lithium replenishment process, and is conducive to reducing the processing difficulty by forming the stripe portion through metal lithium foil processing; and / or the thickness of the stripe portion is 0.04 μm to 0.50 μm, and this thickness range is controlled by the side reaction of the metal lithium during the lithium replenishment process.

[0017] In one embodiment provided in the present application, the anode active material layer also includes a lithium compound exposed on the first surface, and the lithium compound includes at least one of lithium carbonate and lithium oxide. The presence of the lithium compound on the first surface is beneficial to improving the surface resistance of the anode electrode, reducing the short-circuit current of the secondary battery, and reducing the risk of thermal runaway caused by short circuit of the anode electrode.

[0018] In one embodiment provided in the present application, the anode electrode also includes a conductive layer provided on the first surface, and the conductive layer includes a conductive agent and a binder. The conductive layer is provided on the first surface of the anode active material layer, which is beneficial to improving the conductivity of the anode active material layer and accelerating the speed at which lithium ions enter the anode active material during the lithium replenishment process, thereby improving the lithium replenishment efficiency.

[0019] In one embodiment provided in the present application, the thickness of the conductive layer is B μm, 0.5≤B≤8.0, which not only makes the conductive layer have good conductivity, but also reduces the occupation of the conductive layer by the thickness of the anode electrode.

[0020] In one embodiment provided in the present application, the porosity of the conductive layer is C, 30%≤C≤60%, so that the conductive layer has a porous structure, which is beneficial to improving the conductivity of the conductive layer.

[0021] In one embodiment provided in the present application, the recess is formed by a laser processing process. The laser processing process can eliminate the material on the anode active material layer to form the recess, so that the recess has a better effect on ion diffusion.

[0022] In one embodiment provided in the present application, the cross-sectional shape of the recess is V-shaped, so that the recess is conical, and the area of ​​the opening of the recess on the first surface is larger than the area of ​​the bottom of the recess. A recess of this shape is not only easy to process, but also can reduce the processing difficulty and is conducive to improving the processing efficiency of the recess.

[0023] In one embodiment provided in the present application, the height of the edge portion of the recess protruding from the first surface is h μm, 3≤h≤10, which not only increases the diffusion area of ​​the diffusion channel, which is beneficial to improving the diffusion effect of the recess on lithium ions, but also increases the contact area of ​​the anode active material layer and the electrolyte, which is beneficial to increasing the reaction sites of the anode active material layer and the electrolyte, and is beneficial to improving the discharge rate performance of the secondary battery; in addition, h is not too large to affect the interface contact between the anode and cathode sheets.

[0024] In one embodiment provided herein, the anode active material includes at least one of a carbon material, a silicon material, and a tin material. These materials are chemically stable, corrosion-resistant, acid- and alkali-resistant, and have good electrical conductivity, which is beneficial for improving the electrochemical performance of the anode electrode.

[0025] In one embodiment provided in the present application, the electrode assembly also includes a cathode electrode plate and a separator. The cathode electrode plate, the separator and the anode electrode plate are stacked, and the first surface is connected to the separator. The separator can isolate the anode electrode plate from the cathode electrode plate to prevent the cathode electrode plate and the anode electrode plate from short-circuiting. It is also beneficial for the separator to directly transfer the electrolyte to the inside of the anode electrode plate through the recess, and it is beneficial for the lithium ions released from the cathode to pass through the separator and directly enter the inside of the anode active material layer through the recess.

[0026] In a second aspect, the present application provides an electronic device comprising a secondary battery provided by any of the above technical solutions.

[0027] In a third aspect, the present application provides a method for preparing a secondary battery, the method comprising: preparing an anode active material and an anode binder into an anode slurry according to a preset ratio; placing the anode slurry on an anode current collector to form an anode active material layer and obtain an anode electrode; forming a recess on the anode active material layer, the anode active material layer having a first surface away from the anode current collector, the recess extending through the first surface; placing a lithium-supplementing material on the first surface; assembling the anode electrode sheets into an electrode resistor; assembling the electrode assembly to obtain a secondary battery; and forming the secondary battery. The above-mentioned method for preparing a secondary battery can obtain a secondary battery having an anode electrode sheet containing a lithium-supplementing material and having a recess. The secondary battery can not only reduce the electrode sheet impedance and have better discharge performance, but also shorten the processing time, which is conducive to improving processing efficiency.

[0028] In one embodiment provided herein, the lithium supplement material is lithium foil, which is placed on the first surface and then rolled. This helps improve the manufacturing efficiency of the lithium supplement process and reduces side reactions between the lithium supplement material and environmental factors during lithium supplementation.

[0029] In one embodiment provided herein, a concave portion is formed on the anode active material layer by laser processing. The energy provided by the laser can be used to remove the anode active material and binder from the anode active material layer, with minimal impact on the material stacking state of the anode active material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can also be obtained based on the drawings.

[0031] Figure 1 is a schematic diagram of the electrode assembly structure disclosed in some embodiments provided in this application;

[0032] Figure 2 is a schematic structural diagram of an anode electrode disclosed in some embodiments provided in this application;

[0033] Figure 3 is a schematic structural diagram of the anode active material layer disclosed in some embodiments provided in this application;

[0034] Figure 4 is a schematic top view of the structure of the anode active material layer when the recessed portions disclosed in some embodiments provided in this application are holes;

[0035] Figure 5 is a schematic diagram of the internal structure of the anode active material layer when the recessed portions disclosed in some embodiments provided in this application are pores;

[0036] Figure 6 is a schematic top view of the structure of the anode active material layer when the recessed portion is a groove as disclosed in some embodiments provided in this application;

[0037] Figure 7 is a schematic diagram of the internal structure of the anode active material layer when the recessed portion is a groove as disclosed in some embodiments provided in this application;

[0038] Figure 8 is a schematic structural diagram of the edge portion of the recess disclosed in some embodiments provided in this application;

[0039] Figure 9 It is a schematic structural diagram of the electronic device disclosed in some embodiments provided in this application.

[0040] In the drawings, the drawings are not drawn to scale.

[0041] Marking instructions: 1. Anode current collector; 2. Anode active material layer; 21. First surface; 22. Second surface; 23. Concave portion; 3. Stripe portion; 5. Anode pole piece; 6. Cathode pole piece; 7. Cathode current collector; 8. Cathode active material layer; 9. Separator; 10. Electrode assembly; 101. Anode tab; 102. Cathode tab; 2000. Secondary battery; 3000. Electronic device. DETAILED DESCRIPTION

[0042] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0043] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inside", "outside", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Vertical" is not strictly perpendicular, but is within the allowable error range. "Parallel" is not strictly parallel, but is within the allowable error range.

[0044] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0045] The directional words appearing in the following description are all directions shown in the figures, and do not limit the specific structure of this application. In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0046] Currently, market developments indicate that batteries are increasingly being used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in communications equipment, military equipment, and aerospace. As battery applications continue to expand, market demand is also growing.

[0047] The technical solutions of a secondary battery, an electronic device, and a method for preparing a secondary battery provided in this application are further described below through specific implementation methods.

[0048] Some embodiments of the present application provide a secondary battery, such as Figure 1 As shown, the secondary battery includes an electrode assembly 10, which includes a cathode electrode piece 6, an anode electrode piece 5, and a separator 9 disposed between the cathode electrode piece 6 and the anode electrode piece 5. Figure 2 As shown, the anode electrode 5 includes an anode current collector 1 and an anode active material layer 2 provided on the anode current collector 1, the anode active material layer 2 includes an anode active material; the anode active material layer 2 includes a first surface 21 away from the anode current collector 1, the anode active material layer 2 is provided with a recessed portion 23 recessed from the first surface 21 toward the anode current collector 1, and the first surface 21 has been treated with a lithium replenishment process.

[0049] A secondary battery can be used as a single power source to output electrical energy for use. Alternatively, multiple secondary batteries can be connected in series, in parallel, or in a hybrid configuration to form a battery pack, which uses the battery pack as a power source to output electrical energy. A hybrid configuration refers to multiple secondary batteries connected both in series and in parallel. The secondary battery can be a lithium-ion battery. A lithium-ion battery can refer to a secondary battery that primarily relies on the movement of lithium ions between the cathode electrode 6 and the anode electrode 5 during operation. The secondary battery can be cylindrical, flat, rectangular, or in other shapes. The following uses a lithium-ion battery as an example for further explanation.

[0050] During the first cycle of a lithium-ion battery, the SEI film (solid electrolyte interface) forms on the surface of the graphite negative electrode, resulting in an initial irreversible capacity loss of 5% to 15%. High-capacity silicon-based materials lose 15% to 35%. Pre-lithiation technology can eliminate this capacity loss. Pre-lithiation technology replenishes lithium in the electrode material so that the active lithium released during the charging process compensates for the initial irreversible lithium loss and is used to form the SEI film on the negative electrode surface, thereby improving the reversible cycle capacity and cycle life of the lithium battery.

[0051] The electrode assembly 10 is an important component of the secondary battery, in which the anode electrode 5 includes an anode current collector 1 and an anode active material layer 2 arranged on the anode current collector 1. The anode active material layer 2 can be directly formed on the surface of the anode current collector 1, or other functional layers can be provided between the anode active material layer 2 and the anode current collector 1 to achieve preset functions.

[0052] The anode active material layer 2 can be formed by applying the corresponding material to the anode current collector 1 through a coating process, and the anode current collector 1 not coated with the anode active material layer 2 protrudes from the anode current collector 1 coated with the anode active material layer 2. The anode current collector 1 not coated with the anode active material layer 2 serves as the anode tab 101. In some embodiments, the anode tab 101 can also be formed by connecting a component serving as the anode tab 101 to the anode current collector by welding or other means. In some embodiments of the present application, the material of the anode current collector 1 can be metallic copper, which is processed into copper foil to form the anode current collector 1.

[0053] The anode active material includes at least one of a carbon material, a silicon material, and a tin material. Specifically, the anode active material may include at least one of graphite, amorphous carbon, Si, Sn, SiO, SnO, Si / C, Sn / C, Si halides, Sn halides, Si alloys, and Sn alloys. Those skilled in the art may select the anode active material based on actual conditions, as long as it does not affect the electrochemical performance of the anode plate 5. Preferably, the anode active material may be graphite or amorphous carbon, both of which are chemically stable, corrosion-resistant, acid- and alkali-resistant, and have good electrical conductivity, thereby improving the electrochemical performance of the anode plate 5.

[0054] The lithium replenishment process refers to a process for replenishing active lithium in response to the consumption of a portion of the active lithium during the first cycle of charge and discharge of the anode electrode 5. Active lithium will be formed when the anode electrode 5 is formed to replenish the irreversible capacity of the first charge and discharge, which is beneficial to improving the battery's first coulombic efficiency and battery capacity retention rate, thereby improving the battery's discharge performance.

[0055] The lithium replenishment process can be to set a lithium strip, lithium block or lithium powder on the first surface 21. When the secondary battery is formed, the lithium metal can react with the anode active material, embed into the anode active material, and diffuse into the interior of the anode active material, which is beneficial to improve the initial efficiency of the anode electrode 5.

[0056] In some embodiments, the lithium replenishment process can be to roll and thin the metal lithium foil to a thickness of microns. Utilizing the ductility of the metal lithium, by controlling the conveying speed of the anode pole piece 5 and the rolling speed of the metal lithium foil, a striped rolled lithium strip is obtained on the first surface 21. The rolled lithium strip is then composited with the first surface 21 of the anode active material layer 2 to obtain the anode pole piece 5. The lithium replenishment process can also be to roll lithium powder onto the first surface 21 to obtain a lithium powder layer on the first surface 21. The rolled lithium powder layer is then composited with the first surface 21 of the anode active material layer 2 to obtain the anode pole piece 5. After the obtained anode pole piece 5 is made into a secondary battery, the lithium metal, which serves as the lithium replenishment material, will decompose and disappear after undergoing the primary battery reaction.

[0057] Among them, the metal lithium foil is rolled to form a lithium replenishing layer on the anode active material layer 2. This not only has low processing cost and high processing efficiency, but also can reduce the contact between the metal lithium and the environment, which is beneficial to reducing the side reactions of the metal lithium during the lithium replenishing process.

[0058] The lithium replenishment layer on the first surface 21 can be arranged in a striped pattern or as a continuous sheet. Those skilled in the art can adjust the arrangement based on actual conditions. Preferably, the lithium replenishment layer is arranged in a striped pattern, with the gaps between the striped lithium replenishment layers set according to actual conditions. This ensures that the amount of metallic lithium replenished by the lithium replenishment layer meets the requirements of the lithium replenishment process while not being excessive enough to waste metallic lithium.

[0059] The first surface 21 is a surface on the structure of the anode active material layer 2 itself, which is arranged away from the anode current collector 1. The recess 23 arranged on the anode active material layer 2 is recessed from the first surface 21 toward the anode current collector 1, so that the recess 23 is away from the anode current collector 1. The recess 23 can serve as a transmission channel for lithium ions, which not only increases the diffusion speed of lithium ions, but also helps to shorten the time for static lithium replenishment and reduce the side reactions occurring during static lithium replenishment, but also alleviates the problem of uneven lithium ion concentration in the thickness direction of the anode active material layer 2, accelerates the reaction inside the anode active material layer 2, and makes the lithium replenishment material react more fully; at the same time, the recess 23 on the anode active material layer 2 serves as a transmission channel for lithium ions, which helps to improve the discharge rate performance of the secondary battery, thereby improving the discharge performance of the secondary battery.

[0060] In some embodiments of the present application, Figure 3As shown, the anode active material layer 2 is provided with a second surface 22, which is a surface on the structure of the anode active material layer 2 itself, and is arranged parallel to and spaced apart from the first surface 21. The second surface 22 is arranged close to the anode current collector 1 relative to the first surface 21, and the anode current collector 1 is arranged on the second surface 22 of the anode active material layer 2. The anode active material layer 2 including the anode active material is formed between the first surface 21 and the second surface 22. The recess 23 on the first surface 21 enables the active lithium generated by the lithium supplement material arranged on the first surface 21 to quickly diffuse into the anode active material layer 2.

[0061] The recess 23 refers to a recessed structure provided on the anode active material layer 2. It is formed by the inward depression of the first surface 21 of the anode active material layer 2 and must be distinguished from any uneven areas that may exist on the first surface 21 in the prior art. The recess here can be formed by removing material through methods such as laser drilling and machining, or by compressing the first surface 21 through machining, causing a portion of the first surface 21 to be recessed into the anode active material layer 2. The recess 23 is formed on the first surface 21 of the anode active material layer 2 by removing material. The anode active material layer 2 is processed outside the first surface 21 by removing material, resulting in the recess 23 being a depression within the anode active material layer 2.

[0062] In some embodiments of the present application, the anode active material layer 2 further includes an anode binder. The anode binder refers to a material mixed in the materials forming the anode active material layer 2 to play a binding role. The anode binder not only enables the anode active material layer 2 to adhere to the anode current collector 1, but also enables the anode active materials in the anode active material layer 2 to adhere to each other into one body.

[0063] The anode binder includes at least one of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated rubber, polyurethane, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, and sodium alginate. Preferably, the anode binder includes styrene-butadiene rubber, which has wear resistance, heat resistance, and aging resistance, which helps extend the service life of the anode plate 5.

[0064] In some embodiments of the present application, the anode active material layer 2 also includes a thickener, which refers to a material mixed in the material forming the anode active material layer 2, and is used to improve the system density, so that the system maintains a uniform and stable suspension state or emulsion state, which is conducive to the uniform distribution of various materials in the anode active material layer 2.

[0065] In some embodiments of the present application, the anode active material layer 2 further includes an anode conductive agent. The anode conductive agent includes at least one of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and Ketjen black. Preferably, the anode conductive agent includes conductive carbon black, and the conductive carbon black includes at least one of Super P, Super S, and 350G. These conductive carbon blacks have good conductivity, a moderate specific surface area, excellent processing properties, and no effect on the electrochemical mechanism.

[0066] In some embodiments of the present application, the anode binder includes silicone resin, the mass fraction of the silicone resin in the anode active material layer 2 is 1%, and the thickener includes sodium carboxymethyl cellulose, the mass fraction of sodium carboxymethyl cellulose in the anode active material layer 2 is 1%.

[0067] In some embodiments of the present application, the recess 23 is formed by a laser processing process. Because laser energy interacts with materials, the laser beam can eliminate materials such as the anode active material and the binder to form the recess 23 on the first surface 21 of the anode active material layer 2. The laser processing process can eliminate material on the anode active material layer 2 to form the recess 23, making the recess 23 more effective for ion diffusion. While removing the binder from the processed area, it does not affect the bonding strength and compaction density of the material surrounding the recess 23.

[0068] In some embodiments of the present application, the recess 23 comprises a hole and / or a groove. Figure 4 and Figure 5 As shown, the hole is a pore-like structure provided on the anode active material layer 2, and the shape of its cross section can be circular, triangular, square or polygonal. The shape of the cross section of the hole can also be other irregular closed curves. Those skilled in the art can set the shape of the cross section of the hole according to actual conditions. Since the hole is convenient for positioning during the processing, the recess 23 includes a hole, so that the recess 23 is accurately positioned during the processing, which is conducive to achieving precise control of the recess 23. It is understandable that the diameters of the multiple holes can be set to be the same or different; the arrangement positions of the multiple holes can be arranged in a matrix, a circular array or other preset regular arrangement, or in a random arrangement. The arrangement of the multiple holes can be set by those skilled in the art according to actual conditions.

[0069] like Figure 6 and Figure 7As shown, the groove is a groove-like structure provided on the anode active material layer 2, which has a length along the arrangement direction of the anode active material layer 2. The cross-sectional shape of the groove can be V-shaped or U-shaped. Those skilled in the art can set the cross-sectional shape of the groove according to actual conditions. Since the groove can achieve continuous processing and has high processing efficiency, the recess 23 includes a groove, which can achieve continuous processing of the recess 23, which is beneficial to improving the processing efficiency of the recess 23. It can be understood that the continuous extension direction of the groove can be arranged along the length direction of the anode active material layer 2, or can be arranged along the width direction of the anode active material layer 2. The length direction of the anode active material layer 2 is as shown in FIG. Figure 6 The X direction is shown, and the width direction of the anode active material layer 2 is as shown in FIG. Figure 6 It is understood that the continuous extension direction of the groove can be set by those skilled in the art according to actual conditions.

[0070] In some embodiments of the present application, the cross-sectional shape of the recess 23 is V-shaped. The thickness direction of the anode active material layer 2 refers to Figure 3 As shown in the Z direction. Figure 3 As shown, the cross section of the recess 23 refers to the cross section in the thickness direction of the anode active material layer 2, and the V-shaped cross section of the recess 23 means that the recess 23 is conical, and 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. The recess 23 of this shape is not only easy to process, but also can reduce the difficulty of processing and is conducive to improving the processing efficiency of the recess 23.

[0071] In some embodiments of the present application, the radius of the recess 23 is R μm, where 10 ≤ R ≤ 50. The radius of the recess 23 refers to the radius of a circle equivalent to the area of ​​the recess 23. That is, the area of ​​the pattern formed by the recess 23 on the first surface 21 is taken as the area of ​​the equivalent circle, and the radius of the equivalent circle calculated from the area of ​​the equivalent circle is the radius of the recess 23. When the recess 23 is a hole, the area of ​​the pattern formed by the hole on the first surface 21 is first measured, and the radius of the equivalent circle calculated using the measured area is the radius of the recess 23. When the recess 23 is a groove, the area of ​​the pattern formed by the groove on the first surface 21 is first measured, and the radius of the equivalent circle calculated using the measured area is the radius of the recess 23.

[0072] The area of ​​the pattern formed by the recess 23 on the first surface 21 can be obtained by measuring the area of ​​the image of the recess 23 in the image obtained by a charge coupled device (CCD) camera to obtain an image of the first surface 21 of the anode plate 5 .

[0073] The radius of the recess 23 is greater than or equal to 10 μm and less than or equal to 50 μm. The recess 23 in this size range serves as a lithium ion transmission channel, which can improve the transmission efficiency of lithium ions, shorten the static lithium replenishment time, and reduce the impact of the recess 23 on the first surface 21 to maintain the original morphology of the first surface 21 and reduce the adverse effects on the electrochemical properties of the anode active material layer 2.

[0074] In some embodiments of the present application, 30≤R≤50. The radius of the recess 23 is greater than or equal to 30 μm and less than or equal to 50 μm. The recess 23 within this size range serves as a lithium ion transmission channel. While reducing the impact of the recess 23 on the first surface 21, it can maintain the original morphology of the first surface 21, further improve the lithium ion transmission efficiency, and achieve a more significant effect of shortening the static lithium replenishment time.

[0075] In some embodiments of the present application, the depth of the recess 23 is H μm, 8≤H≤30. Figure 3 As shown, the depth of the recess 23 is greater than or equal to 5 μm and less than or equal to 30 μm, so that the recess 23 can not only effectively diffuse ions, but also reduce the impact on the adhesion of the anode active material layer 2 and reduce the possibility of the anode active material layer 2 falling off from the anode current collector 1.

[0076] In some embodiments of the present application, 15≤H≤30. The depth of the recess 23 is greater than or equal to 15 μm and less than or equal to 30 μm, so that the recess 23 can effectively diffuse ions while minimizing the effect on the adhesion of the anode active material layer 2.

[0077] In some embodiments of the present application, the anode active material layer 2 is provided with a plurality of recesses 23 , and the distance between two adjacent recesses 23 is L μm, where 50≤L≤300.

[0078] Multiple recesses 23 means that the number of recesses 23 provided on the anode active material layer 2 is three or more. Multiple recesses 23 make the anode active material layer 2 porous, which is beneficial to improving the porosity of the anode electrode 5 and improving the discharge rate performance of the secondary battery.

[0079] The distance between two adjacent recesses 23 may refer to the shortest distance between the edges of two adjacent recesses 23. By setting the distance between two adjacent recesses 23, a plurality of recesses 23 can be distributed on the first surface 21 of the anode active material layer 2 with a certain uniformity, so that the lithium ions generated by the reaction of the lithium-replenishing material in the anode active material layer 2 can diffuse evenly along the recesses 23 into the interior of the anode active material layer 2, thereby reducing the possibility of uneven distribution of lithium ion concentration in local positions.

[0080] The distance between two adjacent recesses 23 is greater than or equal to 50 μm and less than or equal to 300 μm. This spacing range ensures that the multiple recesses 23 have sufficient lithium ion diffusion capacity, allowing lithium ions generated during the lithium replenishment process on the first surface 21 of the anode active material layer 2 to quickly and fully diffuse into the interior of the anode active material layer 2. At the same time, this spacing range also prevents the distance between the recesses 23 from being too small, helping to reduce the difficulty of processing the anode electrode 5. Optionally, the distance between two adjacent recesses 23 is set to 150 μm or 250 μm, which not only ensures that the recesses 23 have sufficient lithium ion diffusion capacity, but also makes the recesses 23 on the anode active material layer 2 easier to process, helping to reduce the difficulty of processing the anode electrode 5.

[0081] In some embodiments of the present application, 50≤L≤150. The distance between two adjacent recesses 23 is greater than or equal to 50 μm and less than or equal to 150 μm. This spacing range allows the multiple recesses 23 to have sufficient lithium ion diffusion capacity while reducing processing difficulty.

[0082] In some embodiments of the present application, the anode active material layer 2 is provided with a plurality of recesses 23, each having a radius of R μm, a depth of H μm, and a distance between two adjacent recesses 23 of L μm. A is defined as L / (R×H), with 0.20≤A≤5.00. A is defined as a parameter of the recesses 23, A=L / (R×H). Using A as a parameter of the recesses 23 facilitates setting the relationship between the radius, depth, and spacing of the recesses 23. The parameter A of the recesses 23 is greater than or equal to 0.20 and less than or equal to 5.00, which is beneficial for improving the lithium ion diffusion capacity of the recesses 23. Preferably, the parameter A of the recesses 23 is 2.00, where L=200, R=5, and H=20. The recesses 23 with these parameters are not only easy to process, but also have sufficient lithium ion diffusion capacity.

[0083] In some embodiments of the present application, 0.20≤A≤3.50, and the parameter A of the recess 23 is greater than or equal to 0.20 and less than or equal to 3.50, which is beneficial to further improve the diffusion capacity of the recess 23 for lithium ions.

[0084] In some embodiments of the present application, the edge portion of the recess 23 protrudes from the first surface 21 by a height of h μm, where 3≤h≤10.

[0085] The edge portion of the recess 23 refers to the opening of the recess 23 on the first surface 21 of the anode active material layer 2. Figure 8As shown, when recesses 23 are machined on the anode active material layer 2, the first surface 21 is affected to a certain extent, causing material to accumulate at the opening of the recess 23, causing it to protrude from the first surface 21. The edge of the recess 23 protrudes from the first surface 21. This not only increases the diffusion area of ​​the diffusion channel, which is beneficial for improving the diffusion effect of the recess 23 on lithium ions, but also increases the contact area between the anode active material layer 2 and the electrolyte, which is beneficial for increasing the reaction sites of the anode active material layer 2 and the electrolyte, and is beneficial for improving the discharge rate performance of the secondary battery. The edge of the recess 23 can be formed when the recess 23 is machined using a laser process. Because the laser has a certain amount of energy, when melting the anode active material layer 2, material at the opening of the recess 23 is accumulated, causing the edge of the recess 23 to protrude from the first surface 21. Those skilled in the art can adjust the height of the edge of the recess 23 protruding from the first surface 21 by adjusting the laser power and irradiation time.

[0086] The height of the edge portion of the recess 23 protruding from the first surface 21 is greater than or equal to 3 μm and less than or equal to 10 μm, which can not only increase the contact area of ​​the edge portion, but also reduce the impact of the recess 23 on the roughness of the first surface 21 of the anode active material layer 2, thereby reducing the impact on the interface between the cathode electrode 6 and the anode electrode 5.

[0087] In some embodiments of the present application, Figures 1 to 3 As shown, the anode electrode 5 has a stripe portion 3 exposed on the first surface 21 and extending along the first direction, and in a direction perpendicular to the first direction, the width of the stripe portion 3 ranges from 0.1 mm to 2.0 mm; and / or the thickness of the stripe portion 3 ranges from 0.04 μm to 0.50 μm.

[0088] The first direction may refer to the running direction of the anode electrode piece 5 when the anode electrode piece 5 rolls the metal lithium foil onto the first surface 21 during the lithium replenishment process.

[0089] The striped portion 3 may refer to a structure formed on the first surface 21 of the anode active material layer 2 during the lithium replenishment process. During the lithium replenishment process, due to the high activity of metallic lithium and the presence of oxygen and moisture in the environment, the metallic lithium foil rolled onto the first surface 21 to form the lithium replenishment layer reacts with the oxygen and moisture in the environment to produce a layer of byproducts. After the subsequent galvanic cell reaction and formation of the anode electrode 5, the metallic lithium foil, acting as the lithium replenishment material, reacts and disappears, while the byproducts remain on the first surface 21 to form the striped portion 3.

[0090] The width of the stripe portion 3 is perpendicular to the first direction on the first surface 21. The width of the stripe portion 3 is consistent with the width of the lithium replenishment layer formed during the lithium replenishment process. The width of the stripe portion 3 ranges from 0.1 mm to 2.0 mm (that is, the width of the lithium replenishment layer formed during the lithium replenishment process ranges from 0.1 mm to 2.0 mm). This width range facilitates the handling of the metal lithium foil during the lithium replenishment process and helps reduce processing difficulty. Preferably, the width of the stripe portion 3 is set to 1.0 mm or 1.5 mm, which helps to increase the processing difficulty of the lithium replenishment layer during the lithium replenishment process and improve processing efficiency.

[0091] The thickness of the stripe portion 3 is oriented in the direction of the anode active material layer 2. The thickness of the stripe portion 3 refers to the thickness of byproducts generated during the lithium replenishment process. The thickness of the stripe portion 3 ranges from 0.04 μm to 0.50 μm. This thickness range is controlled by the side reactions of the metallic lithium during the lithium replenishment process. Those skilled in the art can control the side reactions of the metallic lithium during the lithium replenishment process by controlling the oxygen and moisture content in the environment to control the thickness of the stripe portion 3. Preferably, the thickness of the stripe portion 3 is set to 0.11 μm or 0.30 μm, which helps maintain a reasonable surface resistance on the first surface 21 of the anode plate 5.

[0092] The width of the stripe portion 3 can be obtained by taking an image and then measuring it. A CCD camera is used to take a picture of the first surface 21 of the anode active material layer 2, and an image of the first surface 21 of the anode active material layer 2 is obtained. The width of the stripe portion 3 can then be obtained by measuring the width of the stripe portion 3 in the image.

[0093] The thickness of the stripe portion 3 can be obtained by taking an image of a slice sample of the anode pole piece 5 and then measuring it. First, the anode pole piece 5 is cut along the thickness direction of the anode pole piece 5 to obtain a slice sample, and the cross-section of the anode pole piece 5 is photographed to obtain an image of the cross-section of the anode pole piece 5. Then, the thickness of the stripe portion 3 in the image can be obtained.

[0094] In some embodiments of the present application, the anode active material layer 2 further includes a lithium compound exposed on the first surface 21 , and the lithium compound includes at least one of lithium carbonate and lithium oxide.

[0095] The lithium compound refers to the component of the stripe portion 3 formed on the first surface 21 of the anode active material layer 2 after the lithium replenishment process. The lithium compound is generated by the side reaction of metallic lithium during the lithium replenishment process. The presence of the lithium compound on the first surface 21 is beneficial to improving the surface resistance of the anode electrode 5, reducing the short-circuit current of the secondary battery, and reducing the risk of thermal runaway caused by a short circuit of the anode electrode 5. Lithium compounds such as lithium carbonate and lithium oxide are substances produced by side reactions of lithium foil or lithium powder during the lithium replenishment process. They remain on the first surface 21 of the anode active material layer 2. If the amount of the lithium compound is within a certain range, it can be used as an insulating layer. If the amount of the lithium compound exceeds a certain range, it will affect the embedding of lithium ions and there is a risk of lithium precipitation.

[0096] In some embodiments of the present application, the stripe portion 3 includes the above-mentioned lithium compound, that is, the stripe portion 3 includes at least one of lithium carbonate and lithium oxide.

[0097] In some embodiments of the present application, the anode plate 5 further includes a conductive layer provided on the first surface 21 , and the conductive layer includes a conductive agent and a binder.

[0098] The conductive layer can be formed by coating the corresponding material on the anode active material layer 2 through a coating process, and then arranging the lithium replenishing material on the conductive layer, which is beneficial to improving the conductivity of the anode active material layer and improving the efficiency of the lithium replenishing process.

[0099] The conductive agent includes at least one of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and Ketjen black. Preferably, the anode conductive agent includes conductive carbon black, and the conductive carbon black includes at least one of Super P, Super S, and 350G. The conductive carbon black has good conductivity, a moderate specific surface area, excellent processing properties, and no effect on the electrochemical mechanism.

[0100] The binder is a material mixed in the material forming the conductive layer to play a bonding role. It not only enables the conductive layer to adhere to the anode active material layer 2, but also enables the conductive agent and other materials in the conductive layer to adhere to each other and form a whole.

[0101] The binder includes at least one of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated rubber, polyurethane, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, and sodium alginate. Preferably, the binder includes styrene-butadiene rubber, which has wear resistance, heat resistance, and aging resistance, and is conducive to extending the service life of the anode plate 5.

[0102] In some embodiments of the present application, the thickness of the conductive layer is B μm, 0.5 ≤ B ≤ 8.0. The thickness direction of the conductive layer refers to the thickness direction of the anode active material layer 2 in the anode plate 5. A conductive layer with a thickness range of 0.5 μm to 8.0 μm not only provides good electrical conductivity but also reduces the thickness of the anode plate 5. Preferably, the thickness of the conductive layer is set to 3.5 μm or 6.5 μm, which not only provides good electrical conductivity but also reduces the thickness of the anode plate 5.

[0103] In some embodiments of the present application, the porosity of the conductive layer is C, 30% ≤ C ≤ 60%. The conductive layer may be provided with pores, so that the conductive layer has a porous structure, which is beneficial to improving the conductivity of the conductive layer. The porosity of the conductive layer can be obtained by measuring the porosity of a conductive layer sample peeled off from the anode electrode 5. The method for measuring the porosity of the conductive layer is:

[0104] peeling off the conductive layer on the anode active material layer 2 and removing the test sample therefrom;

[0105] Select an appropriate dilatometer based on the predicted density and porosity of the test specimen;

[0106] Place the test sample in an oven and bake for 2 hours to remove moisture from the test sample;

[0107] Weigh the test sample after removing the moisture;

[0108] Place the test sample into the dilatometer, seal it, and weigh it. This is the weight of the test sample and the dilatometer.

[0109] Install the dilatometer into the low-pressure station and perform low-pressure analysis according to the preset low-pressure analysis program, so that the pressure is in the range of 0.5psi to 50psi;

[0110] After the low-pressure analysis is completed, the dilatometer is taken out and weighed. This is the weight of the test sample, dilatometer, and mercury.

[0111] Install the dilatometer into the high-pressure station, fix the dilatometer and then screw in the high-pressure chamber head. Screw the high-pressure chamber head into the bottom and remove the bubbles in the dilatometer.

[0112] Perform high pressure analysis according to a preset high pressure analysis program, with the pressure ranging from 100 psi to 60,000 psi;

[0113] After the high pressure analysis is completed, the dilatometer is cleaned and the test is completed.

[0114] Through the above testing process, the pore volume of the test sample is obtained by dividing the measured mercury weight by the mercury density. The porosity of the test sample can then be calculated. This process is a common technical means and method used by those skilled in the art and will not be described in detail here.

[0115] In some embodiments of the present application, the electrode assembly 10 also includes a cathode electrode 6 and a diaphragm 9. The cathode electrode 6, the diaphragm 9 and the anode electrode 5 are stacked, and the first surface 21 is connected to the diaphragm 9, which is conducive to the electrolyte being directly conducted to the interior of the anode electrode 5 through the recess 23, and is also conducive to the lithium ions released from the cathode electrode 6 passing through the diaphragm 9 and then directly entering the interior of the anode electrode 5 through the recess 23, thereby improving the cycle performance and rate performance.

[0116] The cathode electrode 6 includes a cathode current collector 7 and a cathode active material layer 8. The cathode active material layer 8 is coated on the surface of the cathode current collector 7. The cathode active material layer 8 can be formed by coating the corresponding material on the surface of the cathode current collector 7 through a coating process. The cathode current collector 7 not coated with the cathode active material layer 8 protrudes from the cathode current collector 7 coated with the cathode active material layer 8. The cathode current collector 7 not coated with the cathode active material layer 8 serves as the cathode tab 102. In some embodiments of the present application, the material of the cathode current collector 7 can be metallic aluminum, and the aluminum is processed into aluminum foil to form the cathode current collector 7.

[0117] The cathode active material layer 8 includes a cathode active material, a cathode binder, and a cathode conductive agent. In some embodiments, the cathode active material includes lithium cobalt oxide, and the mass fraction of lithium cobalt oxide in the cathode active material layer 8 is 95.2%. The cathode binder includes polyvinylidene fluoride, and the mass fraction of polyvinylidene fluoride in the cathode active material layer 8 is 1.7%. The conductive agent includes conductive carbon black, and the mass fraction of conductive carbon black in the cathode active material layer 8 is 1.6%. Preferably, the conductive carbon black can be super p conductive carbon black, which has good conductivity, moderate specific surface area, excellent processing performance, and no effect on the electrochemical mechanism.

[0118] In some embodiments of the present application, the diaphragm 9 is a high-adhesion composite film that can not only isolate the anode electrode 5 from the cathode electrode 6 , but also has good adhesion, so that the first surface 21 of the anode active material layer 2 is firmly connected to the diaphragm 9 .

[0119] The beneficial effects of the secondary battery provided by the specific embodiments of the present application are further illustrated below through comparative experiments.

[0120] The secondary battery composed of the anode pole piece 5 formed by the anode active material layer 2 without the recess 23 in the related art was used as the experimental object in the comparative example of the comparative experiment; the secondary battery composed of the anode pole piece 5 formed by the anode active material layer 2 with the recess 23 was used as the experimental object in the embodiment of the comparative experiment.

[0121] The cathode electrode 6 in a secondary battery can be manufactured by mixing the cathode active material lithium cobalt oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride in a certain mass ratio, adding N-methylpyrrolidone (NMP), and stirring uniformly in a vacuum mixer to obtain a cathode slurry having a solid content of 70 wt%. The cathode slurry is evenly coated on one surface of a 12 μm thick aluminum foil cathode current collector 7, and the aluminum foil is dried at 120°C for 1 hour to obtain a cathode electrode 6 coated on one side with a cathode active material layer 8. The above steps are repeated on the other surface of the aluminum foil to obtain a cathode electrode 6 coated on both sides with a cathode active material layer 8. The cathode electrode 6 is then cold pressed, cut, and slit, and then dried under vacuum at 120°C for 1 hour to obtain a cathode electrode 6 with a size of 74 mm x 867 mm. A cathode tab 102 made of aluminum foil is welded to the cathode electrode 6.

[0122] The anode plate 5 in a secondary battery can be manufactured by mixing the anode active material, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 97.4:1.4:1.2, adding deionized water, and stirring uniformly in a vacuum mixer to obtain an anode slurry having a solids content of 75 wt%. The anode slurry is evenly coated on one surface of a 12 μm thick copper foil anode current collector 1. The copper foil is then dried at 120°C to obtain an anode with a coating thickness of 130 μm and coated on one side with the anode active material layer 2. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode plate coated on both sides with the anode active material layer 2. The plate is then cold pressed, cut, and slit, and then dried under vacuum at 120°C for 1 hour to obtain an anode plate 5 measuring 78 mm x 875 mm. An anode tab 101 made of nickel-plated copper foil is welded to the anode plate 5.

[0123] The separator 9 in the secondary battery is a porous polyethylene film with a thickness of 7 μm.

[0124] The cathode electrode sheet 6, separator 9, and anode electrode sheet 5 prepared above are stacked in sequence, with the separator 9 positioned between the cathode electrode sheet 6 and the anode electrode sheet 5 to act as an insulator, and then wound to form an electrode assembly 10. The electrode assembly 10 is assembled with the housing to obtain a packaged secondary battery, which is then dehydrated at 80°C and injected into a prepared electrolyte. The secondary battery is then packaged, allowed to stand, and subjected to other steps such as formation. The electrolyte can be composed of ethylene carbonate, propylene carbonate, and diethyl carbonate in a mass ratio of 1:1:1, wherein the concentration of lithium hexafluorophosphate is 1.15 mol / L.

[0125] The differences between the anode plates 5 in the comparative examples and the examples are as follows:

[0126] Comparative Example 1

[0127] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode pole piece 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 24 hours. No recess 23 is set on the anode active material layer 2, and the secondary battery made using the anode pole piece 5 is used as the experimental object.

[0128] Example 1

[0129] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 24 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0130] Example 2

[0131] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0132] Example 3

[0133] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=1.00, where L=200, R=10, and H=20.

[0134] Example 4

[0135] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.50, where L=200, R=20, and H=20.

[0136] Example 5

[0137] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.33, where L=200, R=30, and H=20.

[0138] Example 6

[0139] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.25, where L=200, R=40, and H=20.

[0140] Example 7

[0141] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.20, where L=200, R=50, and H=20.

[0142] Example 8

[0143] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.18, where L=200, R=55, and H=20.

[0144] Example 9

[0145] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=13.33, where L=200, R=5, and H=3.

[0146] Example 10

[0147] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=8.00, where L=200, R=5, and H=5.

[0148] Example 11

[0149] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=5.00, where L=200, R=5, and H=8.

[0150] Example 12

[0151] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=4.00, where L=200, R=5, and H=10.

[0152] Example 13

[0153] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.67, where L=200, R=5, and H=15.

[0154] Example 14

[0155] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0156] Example 15

[0157] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=1.33, where L=200, R=5, and H=30.

[0158] Example 16

[0159] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=1.14, where L=200, R=5, and H=35.

[0160] Example 17

[0161] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.40, where L=40, R=5, and H=20.

[0162] Example 18

[0163] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=0.50, where L=50, R=5, and H=20.

[0164] Example 19

[0165] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=1.00, where L=100, R=5, and H=20.

[0166] Example 20

[0167] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=1.50, where L=150, R=5, and H=20.

[0168] Example 21

[0169] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0170] Example 22

[0171] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=3.00, where L=300, R=5, and H=20.

[0172] Example 23

[0173] The anode active material is Si, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=3.50, where L=350, R=5, and H=20.

[0174] Example 24

[0175] The anode active material is Sn, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0176] Example 25

[0177] The anode active material is Sn alloy, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0178] Example 26

[0179] The anode active material is SnO, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0180] Example 27

[0181] The anode active material is Si / C, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0182] Example 28

[0183] The anode active material is Sn / C, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0184] Example 29

[0185] The anode active material is a Si halide, and metallic lithium foil is used as a lithium supplement material. Before the anode electrode 5 is cold-pressed, the metallic lithium foil is rolled onto the surface of the anode active material layer 2 and left to supplement lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0186] Example 30

[0187] The anode active material is a Sn halide, and metallic lithium foil is used as a lithium supplement material. Before the anode electrode 5 is cold-pressed, the metallic lithium foil is rolled onto the surface of the anode active material layer 2 and left to supplement lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0188] Example 31

[0189] The anode active material is Si alloy, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0190] Example 32

[0191] The anode active material is Sn alloy, and metal lithium foil is used as the lithium replenishing material. Before the anode electrode 5 is cold-pressed, the metal lithium foil is rolled onto the surface of the anode active material layer 2 and left to replenish lithium for 7 hours. A recess 23 is set on the anode active material layer 2 by laser drilling. The parameters of the recess 23 are A=L / (R×H)=2.00, where L=200, R=5, and H=20.

[0192] The static lithium replenishment time in the above embodiment refers to the static time when the electrode assembly 10 of the secondary battery is not injected with electrolyte under specific conditions.

[0193] The design capacity of a secondary battery can be calculated based on the charging capacity of the anode material after complete delithiation, plus the theoretical capacity of the lithium-supplementing material.

[0194] The testing method for the actual capacity of a secondary battery is: in an environment of 25°C, the secondary battery is charged with a constant current at a charging rate of 0.2C until the voltage of the secondary battery reaches 4.45V; the secondary battery is charged with a constant voltage at a charging voltage of 4.45V until the charging rate reaches 0.025C; the secondary battery is discharged with a constant current at a discharge rate of 0.2C until the voltage of the secondary battery reaches 3.0V; the above process is repeated 3 times, and the average capacity of the secondary battery is taken as the actual capacity of the secondary battery.

[0195] Table 1

[0196]

[0197] In some embodiments of the present application, a qualitative test may be performed to determine whether any lithium-supplementing material remains in the anode electrode 5 of the secondary battery in the comparative example and the embodiment.

[0198] The test method is as follows: take the formed secondary battery, discharge the secondary battery at a constant current at a discharge rate of 0.2C until the voltage of the secondary battery reaches 3.0V; disassemble the secondary battery and scrape off all the materials on the anode active material layer 2 (including the striped portion 3); dry the scraped material at 80°C for 24 hours; and perform X-ray diffraction analysis or Raman spectroscopy on the scraped material to determine whether there is any residue in the anode active material layer 2.

[0199] The discharge capacity retention rate test was conducted on the secondary battery made of the cathode electrode 6 in the above comparative example and embodiment. The discharge capacity retention rate test method at a discharge rate of 2C at 25°C was as follows:

[0200] The secondary battery is charged at a constant current at a charge rate of 0.2C until the voltage of the secondary battery reaches 4.45V; the secondary battery is charged at a constant voltage at a charging voltage of 4.45V until the charge rate reaches 0.025C; the secondary battery is discharged at a constant current at a discharge rate of 0.2C until the voltage of the secondary battery reaches 3.0V; the above process is repeated three times, and the average discharge capacity of the secondary battery is taken as the actual discharge capacity of the secondary battery (the discharge capacity at the 0.2C discharge rate);

[0201] The secondary battery is charged at a constant current at a charge rate of 0.2C until the voltage of the secondary battery reaches 4.45V; the secondary battery is charged at a constant voltage at a charging voltage of 4.45V until the charge rate reaches 0.025C; the secondary battery is discharged at a constant current at a discharge rate of 2C until the voltage of the secondary battery reaches 3.0V; the above process is repeated three times, and the average discharge capacity is taken as the actual discharge capacity of the secondary battery at a discharge rate of 2C;

[0202] 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.

[0203] In an environment of 25°C, the discharge capacity retention rate test method at a 3C discharge rate is as follows:

[0204] The secondary battery is charged at a constant current at a charge rate of 0.2C until the voltage of the secondary battery reaches 4.45V; the secondary battery is charged at a constant voltage at a charging voltage of 4.45V until the charge rate reaches 0.025C; the secondary battery is discharged at a constant current at a discharge rate of 0.2C until the voltage of the secondary battery reaches 3.0V; the above process is repeated three times, and the average discharge capacity of the secondary battery is taken as the actual discharge capacity of the secondary battery (the discharge capacity at the 0.2C discharge rate);

[0205] The secondary battery is charged at a constant current at a charge rate of 0.2C until the voltage of the secondary battery reaches 4.45V; the secondary battery is charged at a constant voltage at a charging voltage of 4.45V until the charge rate reaches 0.025C; the secondary battery is discharged at a constant current at a discharge rate of 3C until the voltage of the secondary battery reaches 3.0V; the above process is repeated three times, and the average discharge capacity is taken as the actual discharge capacity of the secondary battery at a discharge rate of 2C;

[0206] The discharge capacity retention rate of the secondary battery at the 3C discharge rate can be obtained by dividing the actual discharge capacity of the secondary battery at the 3C discharge rate by the actual discharge capacity of the secondary battery.

[0207] The secondary batteries made of the cathode electrode pieces 6 in the comparative example and the embodiment are tested for impedance improvement ratio. The test method for the impedance improvement ratio using the relaxation method is as follows.

[0208] The DC impedance of the secondary battery manufactured using the anode electrode sheet 5 (without the recess 23) in the comparative example and the embodiment was measured. The specific method is as follows:

[0209] The secondary battery was placed in a constant temperature box at 25°C and allowed to stand for 30 minutes to allow the secondary battery to reach a constant temperature; the secondary battery was discharged at a constant current at a discharge rate of 0.5C until the voltage of the secondary battery reached the cut-off voltage; the secondary battery was then discharged at a constant current at a discharge rate of 0.1C until the voltage of the secondary battery reached the cut-off voltage to completely discharge the secondary battery; the secondary battery was charged at a constant current at a charging rate of 2C for 15 minutes; after standing for 120 minutes, the DC impedance of the secondary battery was measured at a battery state of charge of 25% in an environment of 25°C, and the DC impedance of the secondary battery made using the anode electrode 5 in the comparative example and the embodiment was obtained.

[0210] The improvement ratio of the DC impedance of the secondary battery in the embodiment is calculated using the DC impedances of the secondary batteries in the comparative example and the embodiment. The improvement ratio is calculated by dividing the difference between the DC impedance of the secondary battery in the embodiment and the DC impedance of the secondary battery in the comparative example by the DC impedance of the secondary battery in the embodiment.

[0211] Table 1 is an example of various parameters of the secondary battery and cathode electrode 6 in the comparative example and the embodiment obtained in the comparative experiment of this application:

[0212] Table 1 shows that, when compared with the comparative example and the example, the recess 23 provided in the material layer of the anode electrode 5 can accelerate the decomposition of the lithium-supplementing material and shorten the resting time, even under the same resting time. This is because the recess 23 provided on the first surface 21 serves as a lithium ion transmission channel, increasing the diffusion rate of lithium ions, thereby accelerating the decomposition of the lithium-supplementing material and shortening the resting time.

[0213] A comparison of Examples 2 to 23 shows that: when 0.20≤A≤5.00, the impedance improvement ratio of the battery can reach 10% or more, indicating that when the parameter A of the recess 23 is in the range of 0.20≤A≤5.00, the recess 23 can effectively improve the DC impedance of the battery; the discharge capacity retention rate of the secondary battery at a 2C discharge rate can reach 90% or more, and the discharge capacity retention rate of the secondary battery at a 3C discharge rate can reach 80% or more, indicating that when the parameter A of the recess 23 is in the range of 0.20≤A≤5.00, the recess 23 can effectively improve the discharge rate performance of the secondary battery. When A is less than 0.20, the radius R and / or the depth H of the recess 23 are large, or the distance L between two adjacent recesses 23 is small, and the effect of the recess 23 on further improving the DC impedance and discharge rate performance of the battery is not significant. In this case, the recess 23 removes a large amount of anode active material, reducing the amount of anode active material, which will affect the capacity of the secondary battery and also pose a risk of lithium plating. When A is greater than 5.00, the radius R and / or the depth H of the recess 23 are small, or the distance L between two adjacent recesses 23 is large, and the recess 23 is less effective as an ion diffusion channel, and the effect of the recess 23 on improving the DC impedance and discharge rate performance of the battery is less.

[0214] A comparison of Examples 2 to 8 shows that when 10≤R≤50, the battery impedance improvement ratio can reach 15% or more, indicating that when the radius R of the recess 23 is 10≤R≤50, the recess 23 can effectively improve the DC impedance of the battery. The discharge capacity retention rate of the secondary battery at a 2C discharge rate can reach 93% or more, and the discharge capacity retention rate of the secondary battery at a 3C discharge rate can reach 84% or more, indicating that when the radius R of the recess 23 is 10≤R≤50, the recess 23 can effectively improve the discharge rate performance of the secondary battery. When R<10, the radius R of the recess 23 is small, the recess 23 is less effective as an ion diffusion channel, and the improvement effect of the recess 23 on the DC impedance and discharge rate performance of the battery is not significant. When R>50, although the radius R of the recess 23 is larger, the further improvement effect is not significant. Moreover, the recess 23 removes more anode active material, reducing the amount of anode active material, which will affect the capacity of the secondary battery and also pose the risk of lithium plating.

[0215] A comparison of Examples 9 to 16 shows that when 8 ≤ H ≤ 30, the battery impedance improvement ratio can reach 10% or more, indicating that when the depth H of the recess 23 is 8 ≤ H ≤ 30, the recess 23 can effectively improve the DC impedance of the battery. The discharge capacity retention rate of the secondary battery at a 2C discharge rate can reach 90% or more, and the discharge capacity retention rate of the secondary battery at a 3C discharge rate can reach 80% or more, indicating that when the depth H of the recess 23 is 8 ≤ H ≤ 30, the recess 23 can effectively improve the discharge rate performance of the secondary battery. When H < 8, the depth H of the recess 23 is small, the recess 23 is less effective as an ion diffusion channel, and the effect of the recess 23 on improving the DC impedance and discharge rate performance of the battery is not significant. When H > 30, although the depth H of the recess 23 is larger, the further improvement effect is not significant. Moreover, the recess 23 removes more anode active material, reducing the amount of anode active material, which will affect the capacity of the secondary battery and also pose the risk of lithium plating.

[0216] A comparison of Examples 17 to 23 shows that when 50≤L≤300, the battery impedance improvement ratio can reach 10% or more, indicating that when the distance L between two adjacent recesses 23 is 50≤L≤300, the recesses 23 can effectively improve the DC impedance of the battery; the discharge capacity retention rate of the secondary battery at a 2C discharge rate can reach 90% or more, and the discharge capacity retention rate of the secondary battery at a 3C discharge rate can reach 81% or more, indicating that when the distance L between two adjacent recesses 23 is 50≤L≤300, the recesses 23 can effectively improve the discharge rate performance of the secondary battery. When L<50, the distance L between two adjacent recesses 23 is small, the arrangement of the recesses 23 is relatively dense, and the effect of the recesses 23 as ion diffusion channels is not significantly improved. However, due to the large number of recesses 23, the processing is more difficult, and the excessive number of recesses 23 removes a large amount of anode active material, reducing the amount of anode active material, which will affect the capacity of the secondary battery and also pose the risk of lithium plating. When L>300, the distance L between two adjacent recesses 23 is larger, the recesses 23 are arranged more sparsely, and the improvement effect of the recesses 23 on the DC impedance and discharge rate performance of the battery has a significant downward trend.

[0217] The present invention also provides a method for preparing a secondary battery, which comprises the following steps:

[0218] preparing an anode slurry by combining an anode active material and an anode binder in a predetermined ratio;

[0219] The anode slurry is placed on the anode current collector 1 to form an anode active material layer 2, and an anode electrode sheet 5 is obtained;

[0220] A recess 23 is formed on the anode active material layer 2 , wherein the anode active material layer 2 has a first surface 21 away from the anode current collector 1 , and the recess 23 is recessed from the first surface 21 toward the anode current collector 1 ;

[0221] Disposing a lithium supplement material on the first surface 21;

[0222] Assemble the anode electrode piece 5, the separator 9 and the cathode electrode piece 6 into an electrode assembly 10;

[0223] Assembling the electrode assembly 10 to obtain a secondary battery;

[0224] The secondary battery is formed.

[0225] The above-mentioned secondary battery preparation method can obtain a secondary battery in which the anode electrode 5 is pre-lithiated and has a recess 23 . This secondary battery can not only reduce the electrode impedance and have better discharge performance, but also shorten the processing time, which is conducive to improving processing efficiency.

[0226] In some embodiments, the lithium supplement material is lithium foil, which is placed on the first surface and rolled, thereby improving the manufacturing efficiency of the lithium supplement process and reducing side reactions between the lithium supplement material and environmental factors during lithium supplementation.

[0227] In some embodiments, the recessed portion is formed on the anode active material layer by laser processing, and the energy provided by the laser can be used to remove the anode active material and binder from the anode active material layer, with minimal impact on the material stacking state of the anode active material layer.

[0228] like Figure 9 As shown, the embodiment of the present application also provides an electronic device 3000 that uses a secondary battery 2000 as a power source. The electronic device 3000 can be a mobile phone, a portable device, a laptop computer, an electric toy, an electric tool, etc. The electric tool includes a metal cutting power tool, a cleaning tool, etc., such as an electric drill, an electric wrench, a vacuum cleaner, a robot vacuum, etc. The embodiment of the present application does not impose any special restrictions on the above-mentioned electronic device 3000.

[0229] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A secondary battery comprising an electrode assembly, the electrode assembly comprising an anode electrode sheet, the anode electrode sheet comprising an anode current collector and an anode active material layer disposed on the anode current collector, the anode active material layer comprising an anode active material; The anode active material layer has a first surface away from the anode current collector, the anode active material layer is provided with a concave portion that is recessed from the first surface toward the anode current collector, the concave portion penetrates the first surface, and the first surface is treated with a lithium supplementation process; The anode active material layer is provided with a plurality of recesses, the radius of the recess is R μm, the depth of the recess is H μm, the distance between two adjacent recesses is L μm, and A=L / (R×H) is defined, 0.20≤A≤2.00, 10≤R≤50, 8≤H≤30, 50≤L≤300.

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 30≤R≤50。 4. The secondary battery according to claim 1, wherein 15≤H≤30。 5. The secondary battery according to claim 1, wherein 50≤L≤150。 6. The secondary battery according to claim 1, wherein The anode active material layer has a stripe portion exposed on the first surface, and a width of the stripe portion in a direction perpendicular to an extending direction of the stripe portion is 0.1 mm to 2.0 mm; and / or The stripe portion has a thickness of 0.04 μm to 0.50 μm.

7. The secondary battery according to claim 1, wherein The anode active material layer further includes a lithium compound exposed on the first surface, and the lithium compound includes at least one of lithium carbonate and lithium oxide.

8. The secondary battery according to claim 1, wherein The anode plate further includes a conductive layer disposed on the first surface, and the conductive layer includes a conductive agent and a binder.

9. The secondary battery according to claim 8, wherein The thickness of the conductive layer is B μm, 0.5≤B≤8.

0.

10. The secondary battery according to claim 9, wherein The porosity of the conductive layer is C, 30%≤C≤60%.

11. The secondary battery according to claim 1, wherein The recessed portion is formed by a laser processing process.

12. The secondary battery according to claim 1, wherein The cross-section of the recess is V-shaped.

13. The secondary battery according to claim 1, wherein The edge of the recess protrudes from the first surface by a height of h μm, where 3≤h≤10.

14. The secondary battery according to claim 1, wherein The anode active material includes at least one of a carbon material, a silicon material, or a tin material.

15. The battery according to claim 1, wherein The electrode assembly further includes a cathode plate and a separator. The cathode plate, the separator and the anode plate are stacked, and the first surface is in contact with the separator. 16 . An electronic device comprising the secondary battery according to claim 1 .

17. A method for preparing a secondary battery, comprising: preparing an anode slurry by combining an anode active material and an anode binder in a predetermined ratio; Disposing the anode slurry on an anode current collector to form an anode active material layer, and obtaining an anode electrode sheet; forming a recess on the anode active material layer, wherein the anode active material layer has a first surface away from the anode current collector, and the recess penetrates the first surface; The anode active material layer is provided with a plurality of recesses, the radius of the recess is R μm, the depth of the recess is H μm, the distance between two adjacent recesses is L μm, and A=L / (R×H), 0.20≤A≤2.00, 10≤R≤50, 8≤H≤30, 50≤L≤300; disposing a lithium supplement material on the first surface; Assembling the anode plates into an electrode assembly; Assembling the electrode assembly to obtain a secondary battery; The secondary battery is formed.

18. The method for preparing a secondary battery according to claim 17, wherein: The lithium supplement material is lithium foil and lithium powder.

19. The method for preparing a secondary battery according to claim 18, wherein: The lithium supplement material is lithium foil, which is placed on the first surface and rolled.

20. The method for preparing a secondary battery according to claim 17, wherein: The recessed portion is formed on the anode active material layer by a laser machining process.

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