CN116979020A - Negative electrode plate, secondary battery, battery module, battery pack and power utilization device - Google Patents

Abstract

The application provides a negative electrode plate, a secondary battery, a battery module, a battery pack and an electric device. The negative electrode sheet includes: the first negative electrode film layer is arranged on the surface of the negative electrode current collector, and at least one edge of the upper surface of the first negative electrode film layer is inclined to the direction of the negative electrode current collector by an alpha angle of 10-60 degrees; the second negative electrode film layer is arranged along the inclined edge of the first negative electrode film layer; the upper surface of the second negative electrode film layer is flush with the upper surface of the middle part of the first negative electrode film layer, or the upper surface of the second negative electrode film layer inclines to the negative electrode current collector by an angle beta of 5-55 DEG and is not higher than the upper surface of the middle part of the first negative electrode film layer; the first negative electrode film layer comprises a carbon-based negative electrode active material, the second negative electrode film layer comprises a silicon-based negative electrode active material, the mass content of carbon in the first negative electrode film layer is 90% -99.5%, and the mass content of silicon in the second negative electrode film layer is 1% -77%. The application relieves the formation of the wavy edge at the edge of the negative electrode plate, reduces the lithium precipitation degree at the edge of the negative electrode plate, and improves the cycle performance and the safety of the secondary battery.

Description

Negative electrode sheet, secondary battery, battery module, battery pack and power-consuming device

Technical Field

The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device.

Background Art

In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

At present, in the process of manufacturing negative electrode sheets, due to practical needs (such as welding pole ears), the edges of the negative electrode sheets will be thinned, which leads to different pressures and different extensions in the middle and edges of the negative electrode sheets during the cold pressing process, resulting in wavy edges on the edges of the negative electrodes. The wavy edges of the negative electrode edges make the gaps between the middle and edges of adjacent negative electrode sheets (or negative electrode sheets and diaphragms) different in size, which is prone to edge lithium deposition problems. In addition, edge lithium deposition causes the middle of the negative electrode sheet to expand/extend more and the edge to expand/extend less, which further aggravates the generation of wavy edges, thereby further worsening the edge lithium deposition problem. In addition, the possible overhang area further aggravates the edge lithium deposition problem of the negative electrode sheets. Lithium deposition on the edges of the negative electrode sheets shortens the cycle life of the battery and reduces the safety of the battery. Therefore, it is urgent to solve the problem of wavy edges on the edges of the negative electrode sheets and the lithium deposition on the edges of the negative electrode sheets, shortened cycle life of the secondary battery, and reduced safety caused by this.

Summary of the invention

The present application is made in view of the above-mentioned problems, and its purpose is to solve the problem of wavy edges on the edges of the negative electrode plates, so as to solve the problem of edge lithium deposition caused by the wavy edges of the negative electrode plates and possible overhang areas, the problem of shortened cycle life of secondary batteries and the problem of reduced safety of secondary batteries.

In order to achieve the above-mentioned object, the first aspect of the present application provides a negative electrode sheet, including a negative electrode current collector, a first negative electrode film layer and a second negative electrode film layer; wherein,

A first negative electrode film layer is disposed on at least one surface of the negative electrode current collector, and at least one edge of the upper surface of the first negative electrode film layer is inclined at an angle ɑ toward the negative electrode current collector to form an inclined edge, wherein the angle ɑ is 10°-60°;

The second negative electrode film layer is arranged along the inclined edge of the first negative electrode film layer; the upper surface of the second negative electrode film layer is substantially flush with the upper surface of the middle portion of the first negative electrode film layer, or the upper surface of the second negative electrode film layer is inclined at an angle β toward the negative electrode current collector and the upper surface of the second negative electrode film layer is not higher than the upper surface of the middle portion of the first negative electrode film layer, wherein the angle β is 5°-55°;

The first negative electrode film layer contains carbon-based negative electrode active material, the second negative electrode film layer contains silicon-based negative electrode active material, the mass content of carbon in the first negative electrode film layer is 90%-99.5%, and the mass content of silicon in the second negative electrode film layer is 1%-77%.

Therefore, the present application arranges the second negative electrode film layer along the inclined edge of the first negative electrode film layer (inclined at an angle ɑ toward the negative electrode current collector), so that the upper surface of the second negative electrode film layer and the upper surface of the middle part of the first negative electrode film layer are basically flush or the upper surface of the second negative electrode film layer is inclined at an angle β toward the negative electrode current collector, and limits the carbon content in the first negative electrode film layer and the silicon content in the second negative electrode film layer, thereby alleviating the formation of wavy edges at the edges of the negative electrode sheets, making the middle and edges of the expanded negative electrode sheets tightly fit with the diaphragm or the adjacent negative electrode sheets, reducing the degree of lithium plating at the edges of the negative electrode sheets, extending the cycle life of the secondary battery, and improving the safety of the secondary battery. In addition, the edges of the negative electrode sheets of the present application have no overvoltage problem, and lithium ions are easily embedded.

In any embodiment, the carbon mass contained in the part surrounded by the inclined edge and the lower surface of the first negative electrode film layer is m1, the silicon mass contained in the second negative electrode film layer is m2, and m2/(m1+m2) is 1%-39%. In this way, the formation of the wavy edge of the edge of the negative electrode plate can be further reduced, so that the middle and edge of the expanded plate are closely attached to the diaphragm or the adjacent plate, further reducing the degree of lithium precipitation at the edge of the negative electrode plate, ensuring that lithium ions are easily embedded, further extending the cycle life of the secondary battery, and improving the safety of the secondary battery; and it can ensure that the amount of negative electrode active material lost due to thinning at the edge of the first negative electrode film layer is compensated by the negative electrode active material added by the second negative electrode film layer, ensuring that the battery cell has a high energy density.

In any embodiment, the width of the inclined edge of the first negative electrode film layer is 5-30mm. Thus, the overvoltage phenomenon of the negative electrode plate can be reduced, making it easier for lithium ions to be embedded. The formation of the wavy edge of the edge of the negative electrode plate can be further reduced through the cooperation between the first negative electrode film layer and the second negative electrode film layer, so that the middle and edge of the expanded plate can be more closely fitted with the diaphragm or the adjacent plate, thereby further reducing the degree of lithium precipitation at the edge of the negative electrode plate, further extending the cycle life of the secondary battery and improving the safety of the secondary battery; at the same time, the negative electrode plate is not prone to edge overvoltage problems, lithium ions are easy to embed, and the high energy density of the battery cell is maintained.

In any embodiment, the inclined edge includes an Overhang area, and the width of the Overhang area accounts for 2%-70% of the width of the inclined edge. The existence of the Overhang area may aggravate the degree of lithium deposition at the edge of the pole piece. By limiting the width of the Overhang area, the formation of the wavy edge of the edge of the negative pole piece can be further reduced, so that the middle and edge of the expanded pole piece can be more closely fitted with the diaphragm, further reducing the degree of lithium deposition at the edge of the negative pole piece, further extending the cycle life of the secondary battery, and improving the safety of the secondary battery.

In any embodiment, the thickness of the middle part of the first negative electrode film layer is 20-700 μm. Therefore, the first negative electrode film layer and the second negative electrode film layer of the present application are easy to manufacture, and the formation of the wavy edge of the edge of the negative electrode plate can be further reduced by the cooperation between the first negative electrode film layer and the second negative electrode film layer, so that the middle part and the edge of the expanded plate are more closely attached to the diaphragm or the adjacent plate, further reducing the degree of lithium deposition at the edge of the negative electrode plate, further extending the cycle life of the secondary battery, improving the safety of the secondary battery, and improving the conductivity of the plate.

In any embodiment, the silicon-based negative electrode active material in the second negative electrode film layer is selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

In any embodiment, the carbon-based negative electrode active material in the first negative electrode film layer is selected from at least one of graphite, soft carbon and hard carbon.

The first negative electrode film layer of the present application adopts the above-mentioned carbon-based negative electrode active material, and the second negative electrode film layer adopts the above-mentioned silicon-based negative electrode active material, which is beneficial to ensure that the carbon content in the first negative electrode film layer and the silicon content in the second negative electrode film layer meet the requirements, so as to alleviate the edge lithium plating problem caused by the wavy edge of the negative electrode plate, extend the cycle life of the secondary battery, and improve the safety of the secondary battery.

In any embodiment, the first negative electrode film layer and the second negative electrode film layer each independently contain at least one selected from a binder, a conductive agent, a thickener and a plasticizer; optionally, the mass content of the binder in the second negative electrode film layer is 1%-70%.

The use of a binder within a certain content range in the present application is beneficial to maintaining the silicon content of the second negative electrode film layer, thereby further reducing the formation of wavy edges at the edges of the negative electrode plates, making the middle and edges of the expanded plates fit more closely with the diaphragm, further reducing the degree of lithium plating at the edges of the negative electrode plates, further extending the cycle life of the secondary battery, improving the safety of the secondary battery, and ensuring the normal embedding of lithium ions.

A second aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the first aspect of the present application.

In any embodiment, the secondary battery further comprises a tab, and the location of the tab corresponds to the location of the inclined edge of the first negative electrode film layer.

A third aspect of the present application provides a battery module, comprising the secondary battery of the second aspect of the present application.

A fourth aspect of the present application provides a battery pack, comprising the battery module of the third aspect of the present application.

A fifth aspect of the present application provides an electrical device comprising at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, and the battery pack of the fourth aspect of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of an embodiment of a negative electrode plate of the present application.

FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2 .

FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application.

FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to an embodiment of the present application.

FIG. 7 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

FIG. 8 is a top view of a secondary battery before cyclic expansion in a cyclic expansion experiment of the present application.

FIG. 9 is a side view of a secondary battery before cyclic expansion in a cyclic expansion experiment of the present application.

FIG. 10 is a top view of a secondary battery after cyclic expansion in a cyclic expansion experiment of the present application.

FIG. 11 is a side view of a secondary battery after cyclic expansion in a cyclic expansion experiment of the present application.

Description of reference numerals:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; 6 first negative electrode film layer; 7 second negative electrode film layer; 8 overhang area.

DETAILED DESCRIPTION

Below, the embodiments of the negative electrode plate, secondary battery, battery module, battery pack and electric device of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

"Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b, etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, "include" and "comprising" may represent that other components not listed may also be included or only listed components may be included or only listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

If not otherwise specified, in the present application, the term "upper surface" refers to a surface away from the negative electrode current collector; in contrast, the term "lower surface" refers to a surface facing the negative electrode current collector.

If there is no special explanation, in the present application, the term "middle part of the first negative electrode film layer" refers to the remaining part except the edge of the first negative electrode film layer.

[Secondary battery]

Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can continue to be used by recharging the active materials after the battery is discharged.

Normally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct active ions.

[Negative electrode]

As shown in FIG1 , one embodiment of the present application provides a negative electrode sheet, including a negative electrode current collector, a first negative electrode film layer 6 and a second negative electrode film layer 7; wherein:

A first negative electrode film layer 6 is provided on at least one surface of the negative electrode current collector, and at least one edge of the upper surface of the first negative electrode film layer 6 is inclined at an angle ɑ toward the negative electrode current collector to form an inclined edge, wherein the angle ɑ is 10°-60° (e.g., 20°, 30°, 40°);

The second negative electrode film layer 7 is arranged along the inclined edge of the first negative electrode film layer 6; the upper surface of the second negative electrode film layer 7 is substantially flush with the upper surface of the middle portion of the first negative electrode film layer 6, or the upper surface of the second negative electrode film layer 7 is inclined at an angle β toward the negative electrode current collector and the upper surface of the second negative electrode film layer 7 is not higher than the upper surface of the middle portion of the first negative electrode film layer 6, wherein the angle β is 5°-55° (e.g., 9°);

The first negative electrode film layer contains a carbon-based negative electrode active material, and the second negative electrode film layer contains a silicon-based negative electrode active material. The mass content of carbon in the first negative electrode film layer is 90%-99.5% (for example, 95%, 96.9%, 97%, 98%), and the mass content of silicon in the second negative electrode film layer is 1%-77% (for example, 20%, 30%, 40%, 46%, 50%, 60%).

The wavy edges of the thinned edges of existing negative electrode sheets make the gap sizes between the middle and edges of adjacent sheets (or sheets and diaphragms) inconsistent, and edge lithium deposition is more likely to occur at locations with larger edge gaps. In addition, during the use of the negative electrode sheets, the middle of the sheet expands normally, but the edge of the sheet expands less due to the lithium deposition problem, which aggravates the formation of the wavy edges of the negative electrode sheets, thereby making the lithium deposition at the edge of the sheet more serious. Although the mechanism is not yet clear, the applicant unexpectedly discovered that: the present application provides a second negative electrode film layer 7 at the inclined edge of the first negative electrode film layer 6 (inclined at an angle ɑ toward the negative electrode current collector), so that the upper surface of the second negative electrode film layer 7 is inclined at an angle β toward the negative electrode current collector, thereby alleviating the problem of large gaps at the edges of adjacent negative electrode plates (or plates and separators), and reducing the degree of lithium plating at the edges of the plates; and, the present application limits the carbon content in the first negative electrode film layer 6 and the silicon content in the second negative electrode film layer 7. During use, the participation of silicon materials increases the expansion degree of the second negative electrode film layer, so that the upper surface of the second negative electrode film layer after expansion is basically flush with the upper surface of the middle part of the first negative electrode film layer, thereby solving the problem of aggravated formation of wavy edges at the edges of the negative electrode plates, further reducing the degree of lithium plating at the edges of the plates, thereby extending the cycle life of the secondary battery and improving the safety of the secondary battery. In addition, the edges of the negative electrode plates of the present application have no overvoltage problem, and lithium ions are easily embedded.

In some embodiments, the carbon mass contained in the portion enclosed by the inclined edge and the lower surface of the first negative electrode film layer 6 is m1, the silicon mass contained in the second negative electrode film layer 7 is m2, and m2/(m1+m2) is 1%-39% (e.g., 2%, 11%, 16%, 18%, 22%, 24%, 30%, 37%). Thus, the formation of the wavy edge of the edge of the negative electrode pole piece can be further reduced, so that the middle and edge of the expanded pole piece can be more closely fitted with the diaphragm, and the degree of lithium precipitation at the edge of the negative electrode pole piece can be further reduced, so as to ensure that lithium ions are easily embedded, further extend the cycle life of the secondary battery, and improve the safety of the secondary battery; and it can ensure that the amount of negative electrode active material lost due to thinning at the edge of the first negative electrode film layer is compensated by the amount of negative electrode active material added by the second negative electrode film layer 7, so as to ensure that the battery cell has a high energy density.

In some embodiments, the width of the inclined edge of the first negative electrode film layer 6 is 5-30 mm. Thus, the overvoltage phenomenon of the negative electrode plate can be reduced, making it easier for lithium ions to be embedded. The formation of the wavy edge of the edge of the negative electrode plate can be further reduced through the cooperation between the first negative electrode film layer 6 and the second negative electrode film layer 7, so that the middle and edge of the expanded plate are more closely fitted with the diaphragm or the adjacent plate, thereby further reducing the degree of lithium precipitation at the edge of the negative electrode plate, further extending the cycle life of the secondary battery and improving the safety of the secondary battery; at the same time, the negative electrode plate is not prone to edge overvoltage problems, lithium ions are easy to embed, and the battery cell has a high energy density.

In some embodiments, the inclined edge includes an overhang region 8 , and the width of the overhang region 8 accounts for 2%-70% of the width of the inclined edge, such as 10%, 20%, or 60%.

There may be an overhang area 8 at the edge of the negative electrode. When the secondary battery is charged, some lithium ions may diffuse and embed into the overhang area 8, but these lithium ions cannot return to the positive electrode normally during discharge. During subsequent charging, these lithium ions may first embed into the normal area of the edge of the adjacent electrode, resulting in the inability of normally charged lithium ions to embed, causing the problem of lithium precipitation at the edge of the electrode to intensify. The present application can further reduce the formation of wavy edges at the edge of the negative electrode by limiting the width of the overhang area 8, so that the middle and edge of the expanded electrode are more closely fitted with the diaphragm or adjacent electrode, further reducing the degree of lithium precipitation at the edge of the negative electrode, further extending the cycle life of the secondary battery, and improving the safety of the secondary battery.

In some embodiments, the thickness of the middle part of the first negative electrode film layer 6 is 20-700 μm, for example, 190 μm. Therefore, the first negative electrode film layer 6 and the second negative electrode film layer 7 of the present application are easy to manufacture, and the formation of the wavy edge of the edge of the negative electrode plate can be further reduced by the cooperation between the first negative electrode film layer 6 and the second negative electrode film layer 7, so that the middle and edge of the expanded plate are more closely attached to the diaphragm or the adjacent plate, further reducing the degree of lithium deposition at the edge of the negative electrode plate, further extending the cycle life of the secondary battery, improving the safety of the secondary battery, and improving the conductivity of the plate.

In some embodiments, the silicon-based negative electrode active material in the second negative electrode film layer 7 is selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites and silicon alloys; optionally, the silicon mass content in the silicon-based negative electrode active material is 1%-100%, for example, 40%, 46%, 83%, 90%; optionally, the silicon-carbon composite is selected from at least one of a silicon-carbon mixture (for example, a mixture of silicon and graphite) and a silicon-carbon compound.

In some embodiments, the carbon-based negative electrode active material in the first negative electrode film layer 6 is selected from at least one of graphite, soft carbon and hard carbon.

The first negative electrode film layer of the present application adopts the above-mentioned carbon-based negative electrode active material, and the second negative electrode film layer adopts the above-mentioned silicon-based negative electrode active material, which is beneficial to ensure that the carbon content in the first negative electrode film layer and the silicon content in the second negative electrode film layer meet the requirements, so as to alleviate the edge lithium plating problem caused by the wavy edge of the negative electrode plate, extend the cycle life of the secondary battery, and improve the safety of the secondary battery.

In some embodiments, the first negative electrode film layer 6 and the second negative electrode film layer 7 each independently contain at least one selected from a binder, a conductive agent, a thickener and a plasticizer; optionally, the mass content of the binder in the second negative electrode film layer 7 is 1%-70%, for example 1.8%, 13.2%, 20.8%.

The use of a binder within a certain content range in the present application is beneficial to maintaining the silicon content of the second negative electrode film layer, thereby further reducing the formation of wavy edges at the edges of the negative electrode plates, making the middle and edges of the expanded plates fit more closely with the diaphragm, further reducing the degree of lithium plating at the edges of the negative electrode plates, further extending the cycle life of the secondary battery, improving the safety of the secondary battery, and ensuring the normal embedding of lithium ions.

In some embodiments, the angle α is greater than the angle β.

As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

As an example, the binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[Positive electrode]

The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O 2 (also referred to as NCM _{622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 )} , and LiNi _0.8 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Electrolytes]

The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte may further include additives. As examples, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[Isolation film]

In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG2 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

FIG4 is a battery module 4 as an example. Referring to FIG4 , in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

FIG5 and FIG6 are battery packs 1 as an example. Referring to FIG4 and FIG6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

FIG7 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[Example]

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

Example 1

(I) Preparation of negative electrode sheet

(1) Dissolving the negative electrode active material (artificial graphite), the conductive agent (conductive carbon black), the binder (styrene-butadiene rubber), and the thickener (sodium carboxymethyl cellulose) in deionized water in a mass ratio of 96.9%:0.4%:1.5%:1.2%, and stirring and mixing them thoroughly to prepare a first negative electrode slurry;

(2) The negative electrode active material, a mixture of silicon and graphite (mass ratio 46:38.6), the conductive agent, conductive carbon black and carbon nanotubes (mass ratio 5:1), the binder, styrene-butadiene rubber and polyacrylic acid (mass ratio 0.9:1.1), and the thickener, sodium carboxymethyl cellulose, were dissolved in deionized water at a mass ratio of 84.6%:1.6%:13.2%:0.6%, and the mixture was stirred and mixed to prepare a second negative electrode slurry;

(3) coating the first negative electrode slurry on the negative electrode current collector copper foil and drying it to form a first negative electrode film layer with a thickness of 190 μm on the negative electrode current collector, wherein the carbon mass content in the first negative electrode film layer is 96.90%, and thinning two opposite edges (corresponding to the positions where the pole ears are set) with a width of 15 mm on the first negative electrode film layer at an angle of 10° (ɑ) toward the negative electrode current collector to form inclined edges;

(4) Coating a second negative electrode slurry along the inclined edge and drying to form a second negative electrode film layer, wherein the upper surface of the second negative electrode film layer is not higher than the upper surface of the middle portion of the first negative electrode film layer and the upper surface of the second negative electrode film layer is inclined by 9° (angle β) toward the negative electrode current collector, the silicon mass content in the second negative electrode film layer is 46%, the carbon mass m1 in the portion enclosed by the inclined edge and the lower surface of the first negative electrode film layer, the silicon mass m2 in the second negative electrode film layer, and m2/(m1+m2) is 1%; and cold pressing is performed as a whole to obtain a negative electrode sheet.

(II) Preparation of positive electrode sheet

The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are dissolved in a solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.96%:1%:1.5%, and the mixture is fully stirred and evenly mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

(III) Isolation film: Polypropylene film is used.

(IV) Preparation of electrolyte

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of LiPF6 is 1 mol/L.

(V) Preparation of secondary batteries

The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is added. After packaging, standing, forming, aging and other processes, a secondary battery is obtained.

The inclined edge of the first negative electrode film layer on the negative electrode sheet includes an overhang area, and the width of the overhang area accounts for 20% of the width of the inclined edge.

Examples 2-19 and Comparative Examples 1-17

The secondary battery preparation methods of Examples 2-19 and Comparative Examples 1-17 are similar to those of Example 1, and the different parameter values are detailed in Table 1.

Among them, the mass ratio between the conductive agent, the binder and the thickener in the first negative electrode film layer of Examples 6, 7, 16, 17 and Comparative Examples 5, 14 and 15 is the same as that in Example 1; the mass ratio between the conductive agent and the thickener in the second negative electrode film layer of Examples 8, 9, 18, 19 and Comparative Examples 6, 7, 14-17 is the same as that in Example 1.

Battery Test

(1) Cyclic expansion test

Experimental method: At an ambient temperature of 45°C, charge the secondary battery to 4.17V at 1C, let it stand for 10 minutes, then discharge it to 3.35V at 1C, let it stand for 10 minutes before continuing the next charge and discharge. A total of 10 cycles of charge and discharge were performed to observe the condition of the negative electrode after the cyclic expansion experiment.

The top view and side view of the secondary battery of Examples 1-19 of the present application before cyclic expansion are shown in Figures 8-9, and the top view and side view after cyclic expansion are shown in Figures 10-11.

(2) Edge lithium deposition experiment

Experimental method: At an ambient temperature of 25°C, the secondary battery was charged to 4.17V at 1C, left to stand for 10 minutes, and then discharged to 3.35V at 1C. After standing for 10 minutes, the next charge and discharge was continued. A total of 2107 cycles of charge and discharge were performed to observe the lithium deposition at the edge of the negative electrode.

(3) Cycle life test

Experimental method: At an ambient temperature of 25°C, the secondary battery is charged to 4.17V at 1C, left to stand for 10 minutes, and then discharged to 3.35V at 1C. After standing for 10 minutes, the next charge and discharge is continued. The charge and discharge interval is 3SOC%-97SOC%, until the capacity of the secondary battery decays to 20%SOH, and the number of cycles of the secondary battery is recorded.

Table 2: Test results of Examples 1-19 and Comparative Examples 1-17

From Table 2, we can see that:

After the secondary batteries of Examples 1-19 of the present application are expanded by cycles, the upper surface of the second negative electrode film layer is flush with the middle of the first negative electrode film layer, no wavy edges appear on the edge of the negative electrode pole piece, and the middle and edge of the pole piece are tightly fitted with the diaphragm; while the secondary batteries of Comparative Examples 1-4 and 6-17 cannot achieve the result that the upper surface of the second negative electrode film layer is flush with the middle of the first negative electrode film layer, no wavy edges appear on the edge, and the middle and edge of the pole piece are tightly fitted with the diaphragm after the expansion by cycles, and even have problems such as pole piece overvoltage, difficulty in lithium ion embedding, obvious increase in DCR during the cycle process, poor pole piece conductivity, and increased safety risks;

After the edge lithium deposition test, the secondary batteries of Examples 1-19 of the present application did not have lithium deposition problems at the edges of their negative electrode plates; while the negative electrode plates of Comparative Examples 1-4 and 6-17 had edge lithium deposition problems. Although the negative electrode plate of Comparative Example 5 did not deposit lithium, the cell capacity of its secondary battery was significantly reduced, and it did not have commercial application advantages.

Compared with comparative examples 1-17, the secondary batteries of examples 1-19 of the present application have longer cycle life and higher cycle performance.

In summary, after the secondary battery of the present application is cycled, the upper surface of the second negative electrode film layer is flush with the middle of the first negative electrode film layer, there is no wavy edge on the edge of the negative electrode plate, the middle and edge of the plate are tightly fitted to the diaphragm, there is no lithium plating problem on the edge of the negative electrode plate, and the secondary battery has higher cycle performance and better safety.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (11)

1. A negative electrode sheet, including a negative electrode current collector, a first negative electrode film layer and a second negative electrode film layer; wherein, The first negative electrode film layer is disposed on at least one surface of the negative electrode current collector, and at least one edge of the upper surface of the first negative electrode film layer is inclined at an angle α toward the direction of the negative electrode current collector, forming an inclined edge. , where the ɑ angle is 10°-60°; The second negative electrode film layer is arranged along the inclined edge of the first negative electrode film layer; the upper surface of the second negative electrode film layer is substantially flush with the upper surface of the middle part of the first negative electrode film layer, or the The upper surface of the second negative electrode film layer is inclined at an angle β toward the direction of the negative electrode current collector and the upper surface of the second negative electrode film layer is not higher than the upper surface of the middle part of the first negative electrode film layer, where the β angle is 5°-55°; The first negative electrode film layer includes a carbon-based negative electrode active material, the second negative electrode film layer includes a silicon-based negative electrode active material, the mass content of carbon in the first negative electrode film layer is 90%-99.5%, and the third negative electrode film layer includes a silicon-based negative electrode active material. The mass content of silicon in the two negative electrode film layers is 1%-77%. 2. The negative electrode sheet according to claim 1, wherein the carbon mass contained in the portion enclosed by the inclined edge and the lower surface of the first negative electrode film layer is m1, and the carbon mass contained in the second negative electrode film layer is m1. The mass of silicon is m2, and m2/(m1+m2) is 1%-39%. 3. The negative electrode plate according to claim 1 or 2, wherein the width of the inclined edge of the first negative electrode film layer is 5-30 mm; Optionally, the inclined edge includes an overhang area, and the width of the overhang area accounts for 2% to 70% of the width of the inclined edge. 4. The negative electrode sheet according to any one of claims 1 to 3, wherein the thickness of the middle part of the first negative electrode film layer is 20-700 μm. 5. The negative electrode sheet according to any one of claims 1 to 4, wherein the silicon-based negative active material in the second negative electrode film layer is selected from the group consisting of elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon At least one of a nitrogen compound and a silicon alloy. 6. The negative electrode sheet according to any one of claims 1 to 5, wherein the carbon-based negative active material in the first negative electrode film layer is selected from at least one of graphite, soft carbon and hard carbon. 7. The negative electrode sheet according to any one of claims 1 to 6, wherein the first negative electrode film layer and the second negative electrode film layer each independently contain a binder, a conductive agent, and a thickener. and at least one of plasticizers; Optionally, the mass content of the binder in the second negative electrode film layer is 1%-70%. 8. A secondary battery, comprising the negative electrode plate according to any one of claims 1 to 7; Optionally, the secondary battery further includes a pole tab, and the arrangement position of the pole tab corresponds to the arrangement position of the inclined edge of the first negative electrode film layer. 9. A battery module including the secondary battery according to claim 8. 10. A battery pack, comprising the battery module according to claim 9. 11. An electric device, comprising at least one selected from the group consisting of the secondary battery of claim 8, the battery module of claim 9, and the battery pack of claim 10.