Negative electrode sheet, secondary battery, and electric device

Abstract

The application discloses a negative pole piece, a secondary battery and an electric device, and relates to the field of batteries. The negative pole piece comprises a current collector and an active material layer arranged on at least one surface of the current collector, and is provided with a first through hole. The active material layer comprises a silicon-based material. In the application, the silicon-based material is used as the active material of the negative pole piece. The silicon-based material has a low working potential, is rich in content, has a high theoretical specific capacity of 3579 mAh g ‑1 at room temperature, which is 10 times that of graphite, and can provide channels for lithium ion insertion and extraction from all directions, and has excellent fast charging performance. Meanwhile, the first through hole arranged on the negative pole piece can reserve space for the expansion of the silicon-based material, and can form an electrolyte infiltration channel along the thickness direction of the battery, greatly shortens the electrolyte infiltration path, improves the problem of insufficient electrolyte backflow, and thus improves the expansion performance of the silicon-based negative pole piece and the cycle performance of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] The current collectors of the positive and negative electrodes of a battery serve as carriers of the active materials for both electrodes and conduct electricity during charging and discharging, making them an important component of the battery. Currently, in large-size silicon-based negative electrode batteries, the silicon-based material expands significantly, squeezing out the electrolyte from the pores during charging. During discharging, the silicon negative electrode material shrinks, increasing the pore size and causing the electrolyte to not flow back in time. This results in poor electrolyte wetting of the negative electrode sheet in the middle region, leading to lithium plating and deterioration of cycle performance. Summary of the Invention

[0003] The main objective of this application is to provide a negative electrode sheet, a secondary battery, and an electrical device, which aims to improve the expansion performance of the silicon-based negative electrode sheet and the cycle performance of the battery.

[0004] In a first aspect, this application provides a negative electrode sheet, including a current collector and an active material layer disposed on at least one surface of the current collector, the negative electrode sheet having a first through hole, and the active material layer comprising a silicon-based material.

[0005] In the technical solution of this application embodiment, silicon-based material is used as the active material of the negative electrode sheet. Silicon-based material has a low working potential and is abundant, and has a capacity of 3579 mAh g at room temperature. -1 Silicon boasts a theoretical specific capacity 10 times that of graphite, and it provides channels for lithium-ion insertion and extraction from all directions, resulting in excellent fast-charging performance. Furthermore, the presence of a first through-hole on the negative electrode not only allows for expansion of the silicon-based material but also creates an electrolyte wetting channel along the battery thickness, significantly shortening the electrolyte wetting path and mitigating insufficient electrolyte reflux. This, in turn, improves the expansion performance of the silicon-based negative electrode and the cycle performance of the battery.

[0006] In some embodiments, an opening region is provided in the middle of the negative electrode sheet, and the first through hole is provided in the opening region. Since insufficient electrolyte reflux wetting generally only occurs in the middle region of the negative electrode sheet, while the two end regions are fully wetted due to the short reflux path, the first through hole is only provided in the middle region of the negative electrode sheet, reducing the area of ​​the negative electrode sheet body with the first through hole, thereby reducing the impact of the opening on the mechanical strength of the negative electrode sheet.

[0007] In some embodiments, the distance between the opening area and the edge of the negative electrode plate is 10 mm to 50 mm, and can be optionally 20 mm to 40 mm. Experiments show that when the distance between the opening area and the edge of the negative electrode plate is within the above range, the problem of insufficient electrolyte infiltration caused by the large expansion of the silicon-based material can be significantly alleviated, and the mechanical strength of the negative electrode plate is ensured, improving the cycle performance of the battery.

[0008] In some embodiments, the negative electrode plate is provided with a plurality of first through-holes, and the distance between any two of the first through-holes is 1 mm to 10 mm, that is, the first through-holes are evenly distributed on the negative electrode plate, and the distance between the holes is 1 mm to 10 mm, ensuring more uniform electrolyte infiltration.

[0009] In some embodiments, the inner diameter of the first through-hole is 0.01 mm to 0.1 mm. Research shows that at the above inner diameter, the silicon-based material will not block the through-hole after expansion, and the mechanical strength of the negative electrode plate can be ensured.

[0010] In some embodiments, in the active material layer, the mass ratio of the silicon-based material is 10% to 50%. At the above content, the battery has good cycle performance.

[0011] In some embodiments, the silicon-based material includes at least one of silicon oxide material and silicon carbide material. Compared with elemental silicon material, although the specific capacity of silicon oxide material is slightly lower, its cycle performance has more advantages; the energy density of silicon carbide material is high. Therefore, using at least one of the above silicon-based materials makes the battery performance more excellent.

[0012] In some embodiments, the chemical formula of the silicon oxide material is SiO x , 0 < x < 2; and / or,

[0013] The silicon carbide material includes porous carbon, and silicon is embedded inside the porous carbon. Using at least one of the above silicon oxide material and silicon carbide material with the above structure and applying it to the battery negative electrode can greatly improve the battery energy density and maintain high stable cycle performance.

[0014] In some embodiments, the chemical formula of the prelithiated region is M y SiO x , where M is at least one of Li and Mg, 0 < y ≤ 1, 0 < x < 2; along the direction from the surface layer to the center of the silicon oxide material, the size of the prelithiated region ≤ 100 nm; the number of molecules of the silicon oxide material in the prelithiated region accounts for 20% to 40% of the total number of molecules of the silicon oxide material. The prelithiated region is arranged near the outer surface layer of the silicon oxide material, and the silicon oxide material includes lithium element or magnesium element, which significantly improves the fast charging performance of the battery. In addition, the cycle life of the battery is also improved, and the initial efficiency is increased.

[0015] In some embodiments, the silicon-based material further includes a coating layer. Optionally, the coating layer is made of at least one of carbon-based materials, organic polymers, metals, and metal oxides. Providing a coating layer can further improve the energy density and cycle performance of the battery.

[0016] In some embodiments, the coating layer is made of a carbon-based material. This can further improve the energy density and cycle performance of the battery.

[0017] In some embodiments, the silicon-based material includes a silicon-oxygen material, wherein the carbon content in the silicon-oxygen material is 1 wt.% to 15 wt.%; more specifically, 4 wt.% to 10 wt.%, and the carbon content is controlled within the above concentration based on the total weight of the silicon-oxygen material to further improve the cycle performance of the battery.

[0018] In some embodiments, the silicon-based material includes a silicon-oxygen material with a particle size of 2 μm to 15 μm; further, the particle size of the silicon-oxygen material is 3 μm to 8 μm; within the above particle size range, the silicon-based material expands without clogging the first through-hole, and the battery has excellent cycle performance.

[0019] In some embodiments, the carbon content in the silicon-carbon material is 40 wt.% to 60 wt.%; further, the carbon content in the silicon-carbon material is 45 wt.% to 55 wt.% based on the total weight of the silicon-carbon material; controlling the carbon content within the above concentration further improves the cycle performance of the battery.

[0020] In some embodiments, the silicon-based material comprises a silicon-carbon material with a particle size of 3 μm to 15 μm. Further, the silicon-carbon material has a particle size of 4 μm to 12 μm. Within this particle size range, the silicon-based material expands without clogging the pores, resulting in excellent battery cycle performance.

[0021] Secondly, this application provides a secondary battery, including a positive electrode and a negative electrode as described in the above embodiments.

[0022] In some embodiments, the positive electrode sheet is provided with a second through hole, so that both the positive and negative electrode sheets are provided with through holes, making the electrolyte wetting more uniform.

[0023] In some embodiments, the first through hole corresponds one-to-one with the second through hole. This prevents areas in the electrode without through holes from obstructing the electrolyte and affecting the wetting effect of the electrolyte.

[0024] Thirdly, this application provides an electrical device, including the secondary battery in the above embodiments. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram comparing the wetting effect of a battery electrode sheet according to an embodiment of this application with that of a conventional battery electrode sheet;

[0027] Figure 2 This is a schematic diagram illustrating the wetting effect of the battery electrode sheet according to another embodiment of the application;

[0028] Figure 3 This is a schematic diagram of the structure of the silicon-oxygen material according to an embodiment of this application;

[0029] Figure 4 This is a schematic diagram of the structure of the silicon-carbon material in an embodiment of this application.

[0030] Explanation of the symbols in the attached diagram: Negative electrode 1, Positive electrode 2.

[0031] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0033] It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0034] As is well known, the current collectors of the positive and negative electrodes in a battery serve as both carriers of the active materials and conductors of electricity during charging and discharging, making them a crucial component of the battery. Silicon materials have a higher specific capacity than graphite materials, and silicon can provide channels for lithium-ion insertion and extraction from various directions, offering excellent fast-charging performance, making it one of the future development directions for negative electrodes. Currently, in large-size silicon-based negative electrode batteries, the large expansion of the silicon material causes the electrolyte to be squeezed out of the pores during charging, and during discharging, the silicon negative electrode material shrinks, increasing the pore size and hindering timely electrolyte return. This results in poor electrolyte wetting of the negative electrode sheet in the middle region, leading to lithium plating and deterioration of cycle performance.

[0035] Therefore, researchers in related fields have improved the current collector, for example, by using a sandwich-like structure for the silicon-carbon anode sheet, consisting of a mesh-like microporous copper foil current collector, a conductive carbon coating, and a layer of anode active material from the inside out. The preparation method includes: 1) preparing the conductive carbon coating; 2) selecting a mesh-like microporous copper foil current collector and coating the conductive carbon coating onto its surface; 3) preparing the anode slurry; 4) coating the anode slurry onto the mesh-like microporous copper foil current collector with the conductive carbon coating, and then baking, rolling, slitting, and die-cutting to obtain the anode sheet. The material through the gaps in the copper foil and the material on both sides of the microporous copper foil can form an "I"-shaped interlocking state, which improves the adhesion of the foil surface and can effectively solve the problem of electrode shedding and pulverization caused by the volume expansion of the silicon-based carbon anode material after battery cycling. It can also effectively slow down the thickening of the silicon-carbon anode sheet during battery cycling.

[0036] However, after being assembled into a battery, the expansion of the silicon-carbon anode material squeezes out the electrolyte in the pores. During the repeated charging and discharging process, the electrolyte return path is long and the return is not timely, resulting in poor electrolyte wetting in the middle area, leading to lithium plating and deterioration of cycle performance.

[0037] The inventors noted that the key technical point of this application is to mitigate the impact of the expansion of silicon anode material on electrolyte reflux by starting with the anode sheet. When the anode material expands, through holes can be set to leave expansion space for the silicon-based material, and also to allow the electrolyte to reflux from the through holes.

[0038] Based on the above analysis, after a large number of repeated experiments, the inventors discovered that by opening through holes in the silicon-based negative electrode sheet, leaving expansion space for the silicon-based material, the electrolyte can be returned in a timely manner, and the electrolyte can be fully wetted in the middle area of ​​the negative electrode sheet, thus avoiding lithium plating and deterioration of cycle performance.

[0039] Specifically, the negative electrode sheet proposed in this application includes a current collector and an active material layer disposed on at least one surface of the current collector. The negative electrode sheet has a first through-hole, and the active material layer comprises a silicon-based material. Compared with the prior art, the beneficial effects of this application are:

[0040] In the technical solution of this application embodiment, silicon-based material is used as the active material of the negative electrode sheet. Silicon-based material has a low working potential and is abundant, and has a capacity of 3579 mAh g at room temperature. -1 Silicon boasts a theoretical specific capacity 10 times that of graphite, and it provides channels for lithium-ion insertion and extraction from all directions, resulting in excellent fast-charging performance. Furthermore, the presence of a first through-hole on the negative electrode not only allows for expansion of the silicon-based material but also creates an electrolyte wetting channel along the battery thickness, significantly shortening the electrolyte wetting path and mitigating insufficient electrolyte reflux. This, in turn, improves the expansion performance of the silicon-based negative electrode and the cycle performance of the battery.

[0041] Please see Figure 1 The existing electrolyte wetting path is shown in the lower left figure. The electrolyte can only be wetted from two directions, which is prone to poor wetting. However, this application provides a first through hole on the negative electrode 1, so that the electrolyte can be wetted from four directions, and the wetting effect is significantly improved.

[0042] In some embodiments, an opening region is provided in the middle of the negative electrode sheet, and the first through hole is provided in the opening region. Since insufficient electrolyte reflux wetting generally only occurs in the middle region of the negative electrode sheet, while the two end regions are fully wetted due to the short reflux path, the first through hole is only provided in the middle region of the negative electrode sheet, reducing the area occupied by the first through hole on the negative electrode sheet, thereby reducing the impact of the opening on the mechanical strength of the negative electrode sheet.

[0043] Understandably, the central region of the negative electrode in this application refers to the area near the center, and is not limited to the center. As long as it is not located at the edge of the electrode, it is within the protection scope of this application.

[0044] The width of the perforation area is limited by two factors: improving electrolyte wetting and the mechanical strength of the negative electrode sheet. If the perforation area is too wide, the mechanical strength of the negative electrode sheet will deteriorate to some extent, increasing the risk of breakage during coating, cold pressing, die cutting, winding, and subsequent use. If the perforation area is too narrow, it will not be able to adequately improve electrolyte wetting in the central area.

[0045] Therefore, this application makes special limitations on the opening area, fully considering the trade-off between improving electrolyte wetting and the mechanical strength of the negative electrode sheet, ensuring that all areas of the negative electrode sheet are fully wetted by electrolyte, while minimizing the range of the opening area and reducing the impact on the mechanical strength of the negative electrode sheet.

[0046] In some embodiments, the distance between the opening area and the edge of the negative electrode sheet is 10mm to 50mm, for example, it can be 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, etc. Experiments show that when the distance between the opening area and the edge is within the above range, it can significantly alleviate the problem of insufficient electrolyte wetting caused by the large expansion of silicon-based materials, while ensuring the mechanical strength of the negative electrode sheet and improving the cycle performance of the battery.

[0047] In some embodiments, the distance between the opening area and the edge of the negative electrode sheet is 20mm to 40mm. This further alleviates the problem of insufficient electrolyte wetting caused by the large expansion of silicon-based materials, and ensures the mechanical strength of the negative electrode sheet, thereby further improving the cycle performance of the battery.

[0048] Understandably, the edge of the negative electrode sheet mentioned in this application refers to the end of the negative electrode sheet. In wound batteries, the edge of the negative electrode sheet refers to both ends of the negative electrode sheet along the winding axis; in stacked batteries, the edge of the negative electrode sheet refers to the circumferential end of the negative electrode sheet.

[0049] In some embodiments, the negative electrode sheet is provided with a plurality of first through holes, and the distance between any two first through holes is 1mm to 10mm, for example, it can be 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, etc., that is, the first through holes are evenly distributed on the negative electrode sheet, and the spacing between the holes is 1mm to 10mm, so as to ensure that the electrolyte wetting is more uniform.

[0050] This application does not limit the diameter of the first through hole. In some embodiments, the inner diameter of the first through hole is 0.01mm to 0.1mm, for example, it can be 0.01mm, 0.02mm, 0.03mm, 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, 0.09mm, 0.1mm, etc. Studies have shown that with the above inner diameter, the silicon-based material will not block the first through hole after expansion, and the mechanical strength of the negative electrode sheet can be guaranteed.

[0051] In some embodiments, the silicon-based material in the active material layer accounts for 10% to 50% by mass, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. Under the above contents, the battery has better cycle performance.

[0052] In some embodiments, the silicon-based material includes at least one of silicon-oxygen material and silicon-carbon material. Compared with elemental silicon material, although the specific capacity of silicon-oxygen material is slightly lower, its cycling performance has more advantages; the energy density of silicon-carbon material is high. Therefore, adopting at least one of the above silicon-based materials makes the obtained battery performance more excellent.

[0053] This application does not limit the specific structure and composition of the silicon-based material. In some embodiments, the chemical formula of the silicon-oxygen material is SiO x , 0 < x < 2; the silicon-carbon material includes porous carbon, and silicon is embedded inside the porous carbon. Adopting at least one of the silicon-oxygen material and silicon-carbon material with the above structure and applying it to the battery negative electrode can greatly improve the battery energy density and maintain high stable cycling performance.

[0054] In some embodiments, in some embodiments, the chemical formula of the prelithiated region is M y SiO x , where M is at least one of Li and Mg, 0 < y ≤ 1, 0 < x < 2; along the direction from the surface layer to the center of the silicon-oxygen material, the size of the prelithiated region ≤ 100 nm; the number of molecules of the prelithiated silicon-oxygen material in the silicon-oxygen material accounts for 20% to 40% of the total number of molecules of the silicon-oxygen material. For example, in the silicon-oxygen material, the number of molecules of the prelithiated silicon-oxygen material is a, and the number of molecules of the non-prelithiated silicon-oxygen material is b, then a / (a + b) = 20% - 40%. The prelithiated region is arranged near the outer surface layer of the silicon-oxygen material, and the silicon-oxygen material includes lithium element or magnesium element, which can significantly improve the fast charging performance of the battery. In addition, the cycle life of the battery is also improved, and the initial efficiency is increased.

[0055] It can be understood that the boundary of the above prelithiated region in the silicon-oxygen material is not obvious. In the region of the silicon-oxygen material where there is no prelithiation, there may also be the existence of lithium element, which is different from the coating layer with an obvious boundary.

[0056] In some embodiments, the silicon-based material further includes a coating layer. Optionally, the material of the coating layer includes at least one of carbon-based material, organic polymer, metal and metal oxide. Setting the coating layer can further improve the energy density and cycling performance of the battery.

[0057] In some embodiments, the material of the coating layer is carbon-based material. In this way, the energy density and cycling performance of the battery can be further improved.

[0058] Please refer to Figure 3In some embodiments, the silicon-oxygen material is characterized by silicon crystal particles embedded in a SiO2 matrix, with an outer layer of soft carbon coating and pre-lithiation. Thus, during charging, the volume expansion of silicon and silicon dioxide during lithium intercalation is constrained by the outer carbon layer, reducing the overall expansion rate of the silicon-oxygen material. This reduced volume change rate during charging and discharging is more conducive to protecting the integrity of the material structure, preventing damage, and minimizing the damage to the conductive network caused by volume expansion and contraction. It also facilitates electrolyte reflow and wetting.

[0059] The silicon-oxygen material can be prepared by the following method: heating silicon and silicon dioxide in a reactor to form silicon suboxide vapor, cooling the mixture to crystallize and form silicon-oxygen crystal particles, then grinding the silicon-oxygen crystals to adjust the particle size, then using alkanes and alkynes as carbon sources to perform vapor deposition on the silicon-oxygen crystals to achieve soft carbon-encapsulated carbon, then using lithium foil to pre-lithiate the material, and finally heating and shaping to form a crystalline pre-lithiated silicon-oxygen material.

[0060] Specific pre-lithiation methods can include physical pre-lithiation, chemical pre-lithiation, and electrochemical pre-lithiation, which are common in the field. Physical pre-lithiation can be achieved by directly mixing lithium powder with silicon-oxygen materials; chemical pre-lithiation, for example, involves mixing a lithium source with silicon-oxygen materials and then heating the mixture at high temperature under vacuum conditions to obtain Li-SiO. x Electrochemical pre-lithiation, for example, involves electrolyzing a lithium salt solution in an electrolytic cell, where the lithium salt simultaneously serves as both the electrolyte and the lithium source for pre-lithiation.

[0061] This application does not limit the carbon content in the silicon-oxygen material. In some embodiments, the silicon-oxygen material further includes carbon, and the carbon content in the silicon-oxygen material is from 1 wt.% to 15 wt.%, for example, it can be 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, etc.; further, the carbon content in the silicon-oxygen material is from 4 wt.% to 10 wt.%, and controlling the carbon content within the above concentration further improves the cycle performance of the battery.

[0062] This application does not limit the particle size of the silicon oxide material. In some embodiments, the particle size of the silicon oxide material is 2μm to 15μm, such as 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc.; further, the particle size of the silicon oxide material is 3μm to 8μm. Within the above particle size range, the silicon-based material does not block the first through-hole when it expands, and the battery cycle performance is excellent.

[0063] In some embodiments, the silicon-based material includes a silicon-carbon material, wherein the silicon-carbon material comprises carbon coated on porous carbon, and silicon is embedded within the porous carbon. See also... Figure 4 The structural characteristics of silicon-carbon materials are that they are based on porous carbon, with silicon particles deposited in the gas phase on the substrate, and finally coated with a soft carbon material. Similarly, the presence of porous carbon provides a certain buffering effect, making the expansion of silicon-carbon materials in terms of external structure less obvious, which is more conducive to the reflow and wetting of electrolyte.

[0064] The silicon-carbon material is prepared by the following method: using porous carbon as a substrate and dimethyldichlorosilane as a silicon source, the substrate is subjected to vapor phase deposition to synthesize intermediate silicon-carbon materials. Finally, using alkanes and alkynes as carbon sources, the intermediate silicon-carbon materials are subjected to vapor phase deposition to complete soft carbon coating and form the final silicon-carbon material.

[0065] In some embodiments, the silicon-based material comprises a silicon-carbon material, wherein the carbon content in the silicon-carbon material is 40 wt.% to 60 wt.%, for example, 40 wt.%, 41 wt.%, 45 wt.%, 47 wt.%, 50 wt.%, 51 wt.%, 54 wt.%, 58 wt.%, 59 wt.%, etc.; further, the carbon content in the silicon-carbon material is 45 wt.% to 55 wt.%; controlling the carbon content within the above concentration further improves the cycle performance of the battery.

[0066] This application does not limit the particle size of the silicon-carbon material. In some embodiments, the silicon-based material includes silicon-carbon material with a particle size of 3 μm to 15 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc. Further, the particle size of the silicon-carbon material is 4 μm to 12 μm. Within this particle size range, the silicon-based material does not clog the first through-hole when it expands, and the battery cycle performance is excellent.

[0067] When at least one of the silicon-oxygen and silicon-carbon materials with the above-mentioned structure is applied to the negative electrode of a battery, the energy density of the battery is greatly improved, and high stable cycle performance can be maintained.

[0068] Secondly, this application provides a secondary battery, including a positive electrode and a negative electrode as described in the above embodiments.

[0069] A single battery cell includes a negative electrode as described in the above embodiments, as well as a positive electrode, an electrolyte, and a separator. Taking a lithium-ion battery as an example, a lithium-ion battery cell mainly relies on the movement of lithium ions between the positive and negative electrode plates to function. In a cylindrical battery cell, the three-layer thin-film structure is wound into a cylindrical electrode assembly, while in a cuboid battery cell, the thin-film structure is wound or stacked into an electrode assembly with a generally cuboid shape.

[0070] In a typical battery cell structure, a battery cell includes a casing, electrode assemblies, and electrolyte. The electrode assemblies are housed within the casing and include a positive electrode, a negative electrode, and a separator. The casing includes a housing and end caps. The casing includes a receiving cavity formed by multiple walls and an opening. The end caps are positioned at the openings to close the receiving cavities. In addition to the electrode assemblies, the receiving cavities also contain the electrolyte. The positive and negative electrode assemblies in the electrode assemblies include tabs. To ensure that large currents can pass through without melting, multiple positive tabs and multiple negative tabs are stacked together. The tabs are electrically connected to electrode terminals located outside the battery cell via connecting members. The electrode terminals generally include positive and negative electrode terminals. For cuboid battery cells, the electrode terminals are generally located in the end cap portion. Multiple battery cells are connected in series and / or parallel via electrode terminals for various applications.

[0071] A battery composed of cells assembled in a wound manner is called a wound battery. Wound batteries are also known as cells, or in the battery industry, "wound cores." Compared to flat-plate batteries, wound batteries are made by high-voltage winding of plates only about 1mm thick. Through special processes, these batteries possess many characteristics: superior high-rate discharge capability (maximum discharge rate 18C–30C); excellent high and low temperature performance (operating from -55℃ to 150℃); stable high output voltage and higher energy density; robust structure with excellent shock resistance; no free electrolyte (e.g., using colloidal acid), allowing for placement in any orientation; fast charging capability (reaching over 95% charge in 40 minutes (1C charging); ultra-long lifespan (designed float charge life of over 8 years); and extremely high tolerance for deep discharge at low currents.

[0072] In some embodiments, the positive electrode sheet is provided with a second through hole, so that both the positive and negative electrode sheets are provided with through holes, making the electrolyte wetting more uniform.

[0073] In some embodiments, the first through hole corresponds one-to-one with the second through hole. This prevents areas in the electrode without through holes from obstructing the electrolyte and affecting the wetting effect. In addition, the channel also serves as a flow guide, improving the wetting effect.

[0074] Please see Figure 1 and Figure 2 , Figure 1 In the case where both the negative electrode 1 and the positive electrode 2 of this application are perforated, the negative electrode 1 is provided with a first through hole and the positive electrode 2 is provided with a second through hole. The first through hole and the second through hole correspond one-to-one to form a channel for the electrolyte to pass through, which greatly improves the wetting effect.

[0075] Figure 2 In the case where the negative electrode 1 is perforated and the positive electrode 2 is not perforated, that is, only the negative electrode 1 has the first through hole, the wetting effect is improved compared with the existing technology.

[0076] The secondary battery proposed in this application possesses all the beneficial effects of the aforementioned negative electrode sheet, which will not be elaborated upon here.

[0077] A battery module is formed by electrically connecting a certain number of secondary batteries together and placing them in a frame to protect individual battery cells from external impacts, heat, and vibration. A typical battery module generally consists of two end plates, with multiple battery cells (lithium-ion batteries) arranged between the two end plates. The end plate with the battery module's output terminals is also called the output terminal plate, and the end plate without output terminals is called the non-output terminal plate.

[0078] In some battery manufacturing technologies, multiple individual battery cells are first integrated into battery modules, and then the battery modules are packaged in a battery casing to form a battery pack. A battery pack can contain multiple battery modules in one row, or multiple rows of multiple battery modules. The arrangement of multiple rows of multiple battery modules can be double-row multi-column, multi-row double-column, multi-row multi-column, etc. Taking a battery pack with double-row multi-column battery modules as an example, the first end plate of each column is generally the head output terminal plate, the two adjacent end plates between two rows of battery modules are the middle non-output terminal plates, and the last end plate of each column is the tail non-output terminal plate. The head output terminal plate and one of the middle non-output terminal plates belong to the first row of battery modules, and one of the middle non-output terminal plates and the tail output terminal plate belong to the second row of battery modules.

[0079] Thirdly, this application provides an electrical device, including the secondary battery in the above embodiments.

[0080] The electrical devices proposed in this application include, but are not limited to: mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0081] The electrical device proposed in this application possesses all the beneficial effects of the aforementioned negative electrode plate, which will not be elaborated upon here.

[0082] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0083] The parameters of the negative electrode sheets in Examples 1 to 20 and Comparative Examples 1 to 8 are shown in Table 1 below:

[0084] Table 1. Parameters of negative electrode sheets in Examples 1 to 20 and Comparative Examples 1 to 8

[0085]

[0086]

[0087]

[0088] In Examples 18 to 20, the size of the pre-lithiation region is 80 nm. In Example 18, the number of silicon-oxygen material molecules in the pre-lithiation region accounts for 20% of the total number of silicon-oxygen material molecules. In Example 19, the number of silicon-oxygen material molecules in the pre-lithiation region accounts for 40% of the total number of silicon-oxygen material molecules. In Example 20, the number of silicon-oxygen material molecules in the pre-lithiation region accounts for 20% of the total number of silicon-oxygen material molecules.

[0089] The negative electrode sheets of Examples 1 to 20 and Comparative Examples 1 to 8 were prepared according to the following method, and the corresponding wound batteries were made:

[0090] Preparation of negative electrode sheet:

[0091] A negative electrode slurry was prepared by dissolving silicon-based materials (silicon-carbon and / or silicon-oxygen materials), conductive agents (acetylene black), binders (styrene-butadiene rubber (SBR), and thickeners (sodium carboxymethyl cellulose (CMC-Na)) in deionized water at a weight ratio of 96:1:2:1 and stirring until homogeneous. The negative electrode slurry was then prepared at a concentration of 9.7 mg / cm³. 2The coating density is uniformly coated on the negative electrode current collector copper foil, and after drying, cold pressing and slitting, the negative electrode sheet is obtained.

[0092] electrolyte

[0093] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / ethyl methyl carbonate (EMC) organic solvents were mixed evenly at a volume ratio of 3 / 7. 12.5% ​​by weight (based on the weight of ethylene carbonate / ethyl methyl carbonate solvent) of LiPF6 was added and dissolved in the above organic solvents and stirred evenly to obtain the electrolyte.

[0094] Separating membrane

[0095] The material used was a commercially available PP-PE copolymer microporous film with a thickness of 20 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd., model 20).

[0096] Secondary batteries

[0097] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. These are then wound to obtain a bare battery cell. The bare battery cell is placed in an outer package, infused with the aforementioned electrolyte, and sealed to obtain a secondary battery.

[0098] The adhesion strength and tensile strength of the negative electrode sheets obtained in Examples 1 to 20 and Comparative Examples 1 to 8 were measured, and the number of cycles of the corresponding secondary batteries were measured, as shown in Table 2.

[0099] The adhesion test involves attaching a standard adhesion test sticker to the surface of the electrode film area and connecting it to a tensile testing machine. The tensile testing machine will record the magnitude of the pulling force required to pull the coating off the electrode.

[0100] Electrode tensile strength test: The electrode is loaded onto a tensile strength measuring device, and the machine will record the maximum tensile force during the process of the machine pulling the electrode as the tensile strength of the electrode.

[0101] Cycle life test: The battery cell is connected to a charger and subjected to a 0.5C charge and 1C discharge cycle test at 25℃. The number of cycles is the number of cycles required for the battery capacity to decay to 80% of its initial capacity.

[0102] Table 2 Performance measurements of Examples 1 to 20 and Comparative Examples 1 to 8

[0103]

[0104]

[0105] As can be seen from Table 2, the negative electrode sheet of this application embodiment, after opening the hole, has a smaller decrease in adhesion and tensile strength, which is close to that of the negative electrode sheet without opening the hole (Comparative Example 1). Moreover, after opening the hole, the cycle life is higher, exceeding 1000 cycles, indicating that the problems of expansion and insufficient electrolyte reflux are improved, thereby improving the cycle performance of the battery.

[0106] Compared to Example 1, the negative electrode of Comparative Example 1 has no openings, resulting in a significant decrease in cycle performance. In Comparative Examples 2 and 3, the distance between the opening area and the electrode edge is either too small or too large. If it is too small, the adhesion and tensile strength will be significantly reduced. If it is too large or too small, the cycle performance will also be reduced. It can be seen that the distance between the opening area and the electrode edge is important. The aperture and aperture spacing of Comparative Examples 5 to 7 are not within the range, which will also lead to a decrease in battery cycle performance. The aperture of the first through hole in Comparative Example 5 is too large, which will lead to a significant decrease in the tensile strength of the battery electrode and easy failure. It can be seen that the aperture and aperture spacing are also important. The silicon-based material content of Comparative Example 8 is too high, resulting in a significant decrease in battery cycle performance.

[0107] In summary, this application uses silicon-based materials as the active material of the negative electrode. Silicon-based materials have low operating potential, are abundant, and provide channels for lithium-ion insertion and extraction from various directions, resulting in excellent fast-charging performance. Simultaneously, the first through-hole on the negative electrode not only provides space for the expansion of the silicon-based material but also forms an electrolyte wetting channel along the battery thickness direction, significantly shortening the electrolyte wetting path and improving the problem of insufficient electrolyte reflux. This, in turn, improves the expansion performance of the silicon-based negative electrode and the cycle performance of the battery.

[0108] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a current collector and an active material layer disposed on at least one surface of the current collector, the negative electrode sheet is provided with a first through hole, and the active material layer includes a silicon-based material; The negative electrode sheet has an opening area in the middle, and the first through hole is located in the opening area. The distance between the opening area and the edge of the negative electrode sheet is 10mm to 50mm; The negative electrode sheet is provided with a plurality of first through holes, and the distance between any two adjacent first through holes is 1mm to 10mm. The inner diameter of the first through hole is 0.01mm~0.1mm.

2. The negative electrode sheet as described in claim 1, characterized in that, The distance between the opening area and the edge of the negative electrode sheet is 20mm to 40mm.

3. The negative electrode sheet as described in claim 1, characterized in that, In the active material layer, the silicon-based material accounts for 10% to 50% of the mass.

4. The negative electrode sheet as described in claim 1, characterized in that, The silicon-based material includes at least one of silicon-oxygen materials and silicon-carbon materials.

5. The negative electrode sheet as described in claim 4, characterized in that, The chemical formula of the silicon-oxygen material is SiO x , 0 < x < 2; and / or, The silicon-carbon material comprises porous carbon, and silicon is embedded within the porous carbon.

6. The negative electrode sheet as described in claim 4, characterized in that, The surface layer of the silicon-oxygen material has a pre-lithiation region in a portion near the center. The chemical formula of the prelithiation region is M y SiO x , where M is at least one of Li and Mg, 0 < y ≤ 1, 0 < x < 2; and / or, Along the direction from the surface to the center of the silicon-oxygen material, the size of the pre-lithiation region is ≤100 nm; and / or, The number of silicon-oxygen material molecules in the pre-lithiation region accounts for 20% to 40% of the total number of silicon-oxygen material molecules.

7. The negative electrode sheet as described in claim 4, characterized in that, The silicon-based material also includes a coating layer.

8. The negative electrode sheet as described in claim 7, characterized in that, The coating material includes at least one of carbon-based materials, organic polymers, metals, and metal oxides.

9. The negative electrode sheet as described in claim 7, characterized in that, The coating layer is made of carbon-based material.

10. The negative electrode sheet as described in claim 4, characterized in that, The carbon content of the silicon-oxygen material is 1 wt% to 15 wt%, based on the total weight of the silicon-oxygen material; and / or, The carbon content in the silicon-carbon material is 40 wt% to 60 wt%, based on the total weight of the silicon-carbon material.

11. The negative electrode sheet as described in claim 4, characterized in that, The carbon content of the silicon-oxygen material is 4 wt% to 10 wt%, based on the total weight of the silicon-oxygen material; and / or, The carbon content in the silicon-carbon material is 45 wt% to 55 wt%, based on the total weight of the silicon-carbon material.

12. The negative electrode sheet as described in claim 4, characterized in that, The particle size of the silicon-oxygen material is 2 μm to 15 μm; and / or, The particle size of the silicon-carbon material is 3 μm to 15 μm.

13. The negative electrode sheet as described in claim 4, characterized in that, The particle size of the silicon-oxygen material is 3 μm to 8 μm; and / or, The particle size of the silicon-carbon material is 4 μm to 12 μm.

14. A secondary battery, characterized in that, It includes a positive electrode and a negative electrode as described in any one of claims 1 to 13.

15. The secondary battery as described in claim 14, characterized in that, The positive electrode sheet has a second through hole.

16. The secondary battery as described in claim 15, characterized in that, The first through hole corresponds one-to-one with the second through hole.

17. An electrical device, characterized in that, Includes the secondary battery as described in any one of claims 14-16.

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