WO2024031216A1

WO2024031216A1 - Negative electrode plate and preparation method therefor, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2024031216A1
Application number: PCT/CN2022/110769
Authority: WO
Inventors: 陈兴布; 孙信; 吴李力; 李璇; 董苗苗; 云亮; 宋佩东; 刘润蝶
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-08-08
Filing date: 2022-08-08
Publication date: 2024-02-15

Abstract

Provided in the present application is a negative electrode plate, comprising a first negative active material layer, a first current collector, a lithium supplement layer, a second current collector and a second negative active material layer, which are stacked in sequence, wherein the negative electrode plate further comprises a buffer material; at least one of the first current collector and the second current collector is provided with a through hole; and the buffer material is filled in at least one of the through hole of the first current collector and the through hole of the second current collector.

Description

Negative electrode plate and preparation method thereof, secondary battery, battery module, battery pack and electrical device

Technical field

The present application relates to the field of secondary batteries, specifically to a negative electrode plate and its preparation method, secondary batteries, battery modules, battery packs and electrical devices.

Background technique

With the growth of new energy demand, the market has put forward increasingly higher requirements for the endurance and service life of secondary batteries such as lithium-ion batteries. As the number of cycles of a lithium-ion battery increases, the active lithium in the battery will gradually decrease, thus affecting its energy density and cycle life. Traditional technology usually presses metallic lithium onto the surface of the active material layer for lithium replenishment. However, because the lithium replenishment rate is too fast, a large amount of heat will be generated instantly, posing safety risks. At the same time, after the battery is filled with liquid, metal lithium is quickly replenished with lithium. If the amount of lithium supplement is large, lithium deposition will easily occur during the cycle, which will affect the cycle life of the battery.

Contents of the invention

Based on the above problems, this application provides a negative electrode plate and a preparation method thereof, a secondary battery, a battery module, a battery pack and a power device, which can improve the cycle performance of the secondary battery.

One aspect of the present application provides a negative electrode sheet, including a first negative active material layer, a first current collector, a lithium replenishing layer, a second current collector and a second negative active material layer that are stacked in sequence; the negative electrode The pole pieces also include cushioning material;

At least one of the first current collector and the second current collector has a through hole; the buffer material is filled in the through hole of the first current collector and the through hole of the second current collector. At least one of them.

In some embodiments, the negative electrode sheet further includes a first buffer layer, which is disposed between the first current collector and the lithium replenishing layer and partially embedded in the first current collector. In the through hole of the fluid, so that the buffer material is filled in the through hole of the first current collector;

And/or, the negative electrode piece further includes a second buffer layer, the second buffer layer is disposed between the second current collector and the lithium replenishing layer, and is partially embedded in the passage of the second current collector. hole, so that the buffer material is filled in the through hole of the second current collector.

In some embodiments, the thickness of the first buffer layer is 3 μm ~ 10 μm; optionally, the thickness of the first buffer layer is 3 μm ~ 7 μm;

And/or, the thickness of the second buffer layer is 3 μm˜10 μm; optionally, the thickness of the second buffer layer is 3 μm˜7 μm.

In some embodiments, the first buffer layer and the second buffer layer have lithium ion conductivity.

In some embodiments, the first buffer layer and the second buffer layer each include an ion conductor material;

Optionally, the ion conductor material includes at least one of an ion conductor polymer, an ion conductor oxide, an ion conductor sulfide, and an ion conductor halide.

In some embodiments, the ion conductor material has an ion conductivity of 10 ^-9 S/cm ² to 10 ^-2 S/cm ² .

In some embodiments, the ion conductor polymer is selected from at least one of polyethylene oxide, polyvinylidene fluoride, and polyanionic conductor polymers;

And/or, the ion conductor oxide is selected from at least one selected from the group consisting of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, and lithium titanium aluminum phosphate.

In some embodiments, the mass percentage of the ion conductor material in the first buffer layer is 60% to 80%; and/or the mass percentage of the ion conductor material in the second buffer layer is 60%～80%;

Optionally, in the first buffer layer, the mass percentage of the ion conductor material is 70% to 80%; and/or in the second buffer layer, the mass percentage of the ion conductor material is 70%. ~80%.

In some embodiments, the porosity of the first buffer layer and the second buffer layer is 2% to 50%;

Optionally, the porosity of the first buffer layer and the second buffer layer is 20% to 40%.

In some embodiments, the total area occupied by the through holes of the first current collector accounts for 0.1% to 30% of the area on the first current collector;

Optionally, the total area occupied by the through holes of the first current collector accounts for 2% to 15% of the area on the first current collector.

In some embodiments, the area ratio of the through holes of the second current collector on the second current collector is 0.1% to 30%;

Optionally, the area ratio of the through holes of the second current collector on the second current collector is 2% to 15%.

In some embodiments, the maximum pore diameter of the first current collector and/or the second current collector is 5 μm to 1 mm;

Optionally, the maximum pore diameter of the through holes of the first current collector and/or the second current collector is 30 μm to 200 μm.

The negative electrode sheet of the present application can avoid the problem of avoiding the If the lithium replenishment layer is in direct contact with the negative active material, the lithium replenishment rate is too fast and there is a risk of heat generation; the buffer material can regulate the lithium replenishment rate of the lithium replenishment layer to avoid lithium dendrites caused by excessive lithium replenishment rate. The secondary battery has a long lifespan. cycle life.

In a second aspect, this application also provides a method for preparing a negative electrode sheet, including the following steps:

Coat the negative electrode slurry on one surface of the current collector surface to prepare a negative electrode active material layer;

Punching the current collector from a surface of the current collector away from the negative active material layer to form a through hole;

Coating a buffer material slurry on the surface of the current collector away from the negative active material layer so that the buffer material fills the through holes to obtain a sub-negative electrode piece;

Take two of the sub-negative electrode pieces and prepare a lithium replenishing layer on the surface of the buffer material of at least one of the sub-negative electrode pieces, and place the sub-negative electrode piece provided with the lithium replenishing layer with the The surface of the lithium replenishing layer is bonded to the surface of the buffer material of the other sub-negative electrode piece to prepare the negative electrode piece.

In a third aspect, the present application also provides a secondary battery, including the above-mentioned negative electrode sheet or the negative electrode sheet prepared according to the above-mentioned preparation method of the negative electrode sheet.

In some embodiments, the negative electrode sheet includes a first buffer layer and a second buffer layer; the secondary battery includes a positive active material and a negative active material; the first Coulombic efficiency of the positive active material is >90%, The first Coulombic efficiency of the negative active material is >90%; the thickness of the first buffer layer is 4 μm to 7 μm; the thickness of the second buffer layer is 4 μm to 7 μm;

Alternatively, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the thickness of the first buffer layer is 3 μm to 5 μm; and the second buffer layer The thickness is 3μm~5μm.

In some embodiments, the negative electrode sheet includes a first buffer layer and a second buffer layer; the secondary battery includes a positive active material and a negative active material; the first Coulombic efficiency of the positive active material is >90%, The first Coulombic efficiency of the negative active material is >90%; the ion conductivity of the ion conductor material is 10 ^-9 S/cm ² ~ 10 ^-5 S/cm ² ;

Alternatively, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the ion conductivity of the ion conductor material is 10 ^-6 S/cm ² ~10 ^-2 S/cm ² .

In some embodiments, the negative electrode sheet includes a first buffer layer and a second buffer layer; the secondary battery includes a positive active material and a negative active material; the first Coulombic efficiency of the positive active material is >90%, The first Coulombic efficiency of the negative active material is >90%; the porosity of the first buffer layer and the second buffer layer is 30% to 40%;

Alternatively, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the porosity of the first buffer layer and the second buffer layer is 20%. ~30%.

In a fourth aspect, the present application also provides a battery module, including the above-mentioned secondary battery.

In a fifth aspect, the present application further provides a battery pack, including at least one of the above-mentioned secondary battery and the above-mentioned battery module.

In a sixth aspect, the present application further provides an electrical device, including at least one selected from the above-mentioned secondary battery, the above-mentioned battery module, or the above-mentioned battery pack.

The details of one or more embodiments of the present application are set forth in the following drawings and description, and other features, objects, and advantages of the present application will be apparent from the description, drawings, and claims.

Description of drawings

Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

Figure 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in Figure 1;

Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

Figure 5 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 4;

Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover; 6 electrical device.

To better describe and illustrate embodiments and/or examples of those inventions disclosed herein, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the drawings should not be construed as limiting the scope of any of the disclosed inventions, the embodiments and/or examples presently described, and the best modes currently understood of these inventions.

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the accompanying drawings. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough understanding of the disclosure of the present application will be provided.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing specific embodiments only and is not intended to limit the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Conventional surface lithium replenishment technology for secondary batteries will instantly generate a large amount of heat when metallic lithium is pressed onto the surface of the active material layer, thus posing a risk of fire during the production process. At the same time, the metallic lithium layer on the surface is quickly embedded into the active material layer after the secondary battery is injected, forming a one-time lithium replenishment. In order to prevent lithium precipitation in the negative active material layer during subsequent use, the amount of negative active material needs to be increased to absorb the lithium supplemented by the surface metal lithium, thus causing a loss in the energy density of the battery.

After extensive research, the inventor of the present application has provided a negative electrode sheet with a special lithium replenishing structure, which can reasonably control the lithium replenishing rate of the lithium replenishing structure, so that the lithium replenishing rate ≤ the active lithium loss rate of the secondary battery, so the secondary battery It has higher energy density and longer cycle life.

The present application provides a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device using the negative electrode plate. This kind of secondary battery is suitable for various electrical devices that use batteries, such as mobile phones, portable devices, laptops, battery cars, electric toys, power tools, electric cars, ships and spacecraft. For example, spacecraft include aircraft, rockets , space shuttles and spacecrafts, etc.

The secondary battery, battery module, battery pack and electrical device of the present application will be described below with appropriate reference to the drawings.

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

Negative pole piece

In one embodiment of the present application, a negative electrode piece is provided. In the embodiment of the present application, the negative electrode sheet includes a first negative electrode active material layer, a first negative electrode current collector, a lithium replenishing layer, a second negative electrode current collector, and a second negative electrode active material layer that are stacked in sequence. The negative electrode plate also includes buffer material. At least one of the first negative electrode current collector and the second negative electrode current collector has a through hole; the buffer material is filled in at least one of the through hole of the first negative electrode current collector and the through hole of the second negative electrode current collector.

In the negative electrode sheet of the present application, a lithium replenishing layer is sandwiched between two negative electrode current collectors with through holes, the through holes are filled with buffer materials, and a negative electrode active material layer is provided on the surface of the negative electrode current collector away from the lithium replenishing layer. It can prevent the lithium replenishment layer from being in direct contact with the negative active material and the lithium replenishment rate is too fast; the buffer material can regulate the lithium replenishment rate of the lithium replenishment layer to avoid lithium dendrites caused by excessive lithium replenishment rate. The secondary battery has a longer cycle life. .

It can be understood that when one of the first negative electrode current collector and the second negative electrode current collector has a through hole, the lithium supplement layer supplements lithium to the negative electrode active material layer on the side close to the through hole.

In some of these embodiments, the buffer material has lithium ion conductivity. Further, the buffer material may be an ion conductor material. The ion conductor material has the ability to conduct lithium ions. It fills the through holes of the negative electrode current collector and can conduct lithium ions, thus realizing the lithium replenishment of the negative electrode sheet.

In some embodiments, the first negative electrode current collector has multiple through holes, and the buffer material fills part or all of the through holes. The second negative electrode current collector has a plurality of through holes, and the buffer material fills part or all of the through holes. Further, the buffer material fills all the through holes.

In some embodiments, the negative electrode sheet further includes a first buffer layer, which is disposed between the first negative electrode current collector and the lithium replenishing layer, and is partially embedded in the through hole of the first negative electrode current collector, so that The buffer material is filled in the through hole of the first negative electrode current collector. The negative electrode sheet also includes a second buffer layer. The second buffer layer is disposed between the second negative electrode current collector and the lithium replenishing layer, and is partially embedded in the through hole of the second negative electrode current collector, so that the buffer material is filled in the second negative electrode. in the through hole of the current collector.

In some embodiments, the first buffer layer may be a continuous film layer structure between the first negative electrode current collector and the lithium supplement layer, so as to completely isolate the first negative electrode current collector and the lithium supplement layer; or, A buffer layer may also be distributed discontinuously between the first negative electrode current collector and the lithium replenishing layer.

In some embodiments, the second buffer layer may be a continuous film layer structure between the first negative electrode current collector and the lithium supplement layer, so as to completely isolate the second negative electrode current collector and the lithium supplement layer; or, The two buffer layers may also be distributed discontinuously between the first negative electrode current collector and the lithium replenishing layer.

In some embodiments, the thickness of the first buffer layer ranges from 3 μm to 10 μm. Optionally, the thickness of the first buffer layer is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm. Further, the thickness of the first buffer layer is 3 μm˜7 μm. The thickness of the second buffer layer is 3 μm to 10 μm. Optionally, the thickness of the second buffer layer is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm. Further, the thickness of the second buffer layer is 3 μm˜7 μm.

Specifically, the thickness of the first buffer layer or the second buffer layer refers to the thickness of the buffer material filled in the first negative electrode current collector or the second negative electrode current collector through hole and the first buffer layer or the second buffer layer covering the first negative electrode current collector. The sum of the thicknesses of the negative electrode current collector or the second negative electrode current collector surface. In other words, the thickness of the first buffer layer or the second buffer layer is the minimum distance between the lithium supplement layer and the first negative electrode active material layer or the second negative electrode active material layer.

As an example, the thickness of the first buffer layer or the second buffer layer can be obtained by observing the cross-section of the negative electrode piece using a scanning electron microscope (SEM).

When the thickness of the buffer layer is too small, the lithium replenishment rate is too fast and lithium dendrites are formed, which affects the cycle life of the secondary battery; when the buffer layer thickness is too large, the lithium replenishment rate is slow and the energy density of the secondary battery is reduced. Controlling the thickness of the buffer layer within the above range can control the appropriate lithium replenishment rate of the negative electrode sheet. Preferably, the lithium replenishment rate of the negative electrode plate is less than or equal to the active lithium loss rate of the secondary battery, so that the secondary battery can have both high energy density and long cycle life.

The active lithium loss rate of a secondary battery refers to the rate of active lithium loss during the cycle of the secondary battery. It can be estimated by the slope of the curve of the capacity of the secondary battery changing with the number of cycles during the cycle of the secondary battery, that is, the capacity fading rate. Specifically, the active lithium loss rate of the secondary battery can be estimated by the following equation.

In a secondary battery that does not contain a lithium replenishment structure, the lithium replenishment rate is 0, and the secondary battery capacity decreases as the number of cycles increases; when the lithium replenishment rate < the active lithium loss rate, the slope of the curve of the capacity changing with the number of cycles is relative to The slope of the lithium replenishment rate is partially increased; when the lithium replenishment rate ≈ the active lithium loss rate, the slope of the curve of capacity changing with the number of cycles mainly depends on the loss of the positive electrode active material's own lithium intercalation capacity; when the lithium replenishment rate > When the active lithium loss rate is high, compared to the situation where the lithium replenishment rate ≈ the active lithium loss rate, the slope of the curve of capacity changing with the number of cycles cannot be further improved. Instead, lithium will be deposited on the surface of the negative electrode, which can easily lead to internal micro short circuits and self-discharge. Increased problems bring security risks.

In some embodiments, the first Coulombic efficiency of the positive active material is >90%, and the first Coulombic efficiency of the negative active material is >90%; the thickness of the first buffer layer is 4 μm ~ 7 μm; the thickness of the second buffer layer is 4 μm ~ 7 μm . The first Coulombic efficiency of the positive electrode refers to the first lithium insertion capacity/first lithium removal capacity of the positive electrode active material. The first Coulombic efficiency of the negative electrode refers to the first lithium removal capacity/first lithium insertion capacity of the negative electrode active material. It can be determined by the positive electrode active material or the negative electrode active material alone. Prepare button cells for measurement. Generally, when the positive electrode active material and the negative electrode active material have high first Coulombic efficiency, the secondary battery has a slower active lithium loss rate, and the thickness of the buffer layer is controlled within the above range, the secondary battery has a more suitable lithium replenishment rate. speed, both high energy density and long cycle life.

Specifically, the first Coulombic efficiency of cathode active materials such as lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), lithium nickel cobalt manganese oxide (NCM), lithium manganate (LMO), lithium cobalt oxide (LCO), etc. >90%. The first Coulombic efficiency of negative active materials such as natural graphite, artificial graphite, lithium titanate (LTO), soft carbon, etc. is >90%.

In some embodiments, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the thickness of the first buffer layer is 3 μm to 5 μm; and the thickness of the second buffer layer is 3μm～5μm. Generally, when the first Coulombic efficiency of the positive active material and the negative active material is low, the irreversible capacity of the positive active material and the negative active material is large and the loss rate of active lithium is large, the thickness of the buffer layer is controlled within the above range, and the secondary The battery has a more appropriate lithium replenishment rate, higher energy density and longer cycle life.

Specifically, the first Coulombic efficiency of positive active materials such as lithium-rich lithium manganate, lithium-rich lithium nickelate, etc. is ≤90%. The first Coulombic efficiency of negative active materials such as silicon-based materials, tin-based materials, lithium metal negative electrodes, and some porous carbons is ≤90%.

In some embodiments, both the first buffer layer and the second buffer layer include ion conductor materials. Optionally, the ion conductor material includes at least one of an ion conductor polymer, an ion conductor oxide, an ion conductor sulfide, and an ion conductor halide. The ion conductor material has lithium ion conductivity and can conduct lithium ions on both sides of the negative electrode current collector to achieve lithium replenishment in the secondary battery.

In some embodiments, the ion conductor polymer may be selected from at least one of, but not limited to, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), and polyanionic conductor polymers.

In some embodiments, the ion conductor oxide may be selected from at least one of, but not limited to, lithium lanthanum titanium oxide (LLTO), lithium lanthanum zirconium oxide (LLZO), and lithium aluminum titanium phosphate (LATP).

In some embodiments, the ion conductor material has an ionic conductivity of 10 ^-9 S/cm ² to 10 ^-2 S/cm ² . As an example, according to the law of resistance, the buffer layer is assembled into a localized symmetrical battery. The resistance R of the buffer layer is measured using the EIS method, and the ion conductivity σ=L/(R*S) is obtained. L is the thickness of the buffer layer. S is the effective contact area between the buffer layer and the electrode during testing.

In some embodiments, the first Coulombic efficiency of the positive active material is >90%, and the first Coulombic efficiency of the negative active material is >90%; the ionic conductivity of the ion conductor material is 10 ^-9 S/cm ² ~ 10 ^-5 S/ cm ² . By selecting an ion conductor material with a small ionic conductivity, the ionic conductivity of the buffer layer is small, and the lithium replenishment rate of the secondary battery can be controlled to be relatively small. In a secondary battery system with a small lithium consumption rate, the replenishment rate can be reduced. The lithium rate matches the lithium consumption rate, and the secondary battery has longer energy density and longer cycle life.

As examples, ion conductor materials such as polyethylene oxide (PEO), 42.5Li ₂ O·57.5B ₂ O ₃ , Li _2.9 PO _3.3 N _0.46 , Li _3.6 Si _0. 6P _0.4 O _0.4 , Li _3.25 Ge _0.25 P _0.75 S ₄ The ionic conductivity is 10 ^-9 S/cm ² to 10 ^-5 S/cm ² .

In some embodiments, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the ionic conductivity of the ion conductor material is 10 ^-6 S/cm ² ~10 ^{- 2} S/cm ² . By selecting an ion conductor material with a large ionic conductivity, the ionic conductivity of the buffer layer is large, and the lithium replenishment rate of the secondary battery can be controlled to be relatively large. In a secondary battery system with a large lithium consumption rate, the replenishment rate can be achieved. The lithium rate matches the lithium consumption rate, and the secondary battery has longer energy density and longer cycle life.

As an example, the ion conductivity of ion conductor materials such as lithium lanthanum titanium oxide (LLTO), lithium lanthanum zirconium oxide (LLZO), Li ₆ PS ₅ Cl, etc. is 10 ^-6 S/cm ² to 10 ^-2 S/cm ² .

In some embodiments, the mass percentage of the ion conductor material in the first buffer layer is 60% to 90%. Optionally, in the first buffer layer, the mass percentage of the ion conductor material is 60%, 62%, 64%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 84%, 85%, 88% or 90%. Further, the mass percentage of the ion conductor material in the first buffer layer is 70% to 80%.

In some embodiments, the mass percentage of the ion conductor material in the second buffer layer is 60% to 90%. Optionally, the mass percentage of the ion conductor material in the second buffer layer is 60%, 62%, 64%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 84%, 85%, 88% or 90%. Further, in the second buffer layer, the mass percentage of the ion conductor material is 70% to 80%. By controlling the mass percentage of the ion conductor material in the buffer layer to be within the above range, the buffer layer has appropriate lithium ion conductivity.

In some embodiments, the first buffer layer and/or the second buffer layer further includes an adhesive and a conductive agent.

In some embodiments, the porosity of the first buffer layer and the second buffer layer is 2% to 50%. Optionally, the porosity of the first buffer layer and the second buffer layer is 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%. Further, the porosity of the first buffer layer and the second buffer layer is 20% to 40%.

As an example, the true density method is used to test the porosity, and the inert gas (helium) replacement method with a small molecular diameter is used, combined with Archimedes' principle and Bohr's law, to accurately measure the true volume of the material being tested, thereby obtaining the sample to be tested porosity. Porosity P = (V ₂ -V ₁ )/V ₂ *100%, apparent volume V ₂ =S*H*A, where: S-area, cm ² ; H-thickness, cm; A-number of samples , EA; V ₁ - true volume of sample, cm ³ ; V ₂ - apparent volume of sample, cm ³ .

The inventor's research found that the porosity of the buffer layer will affect its lithium ion conductivity. If the porosity of the buffer layer is smaller, the ion conductivity of the buffer layer will be lower, and the lithium replenishment rate of the secondary battery will be slower; the pores of the buffer layer If the ratio is larger, the ionic conductivity of the buffer layer is higher, and the lithium replenishment rate of the secondary battery is faster; by adjusting the porosity of the buffer layer, it can adapt to secondary battery systems with different active lithium loss rates.

In some embodiments, the first Coulombic efficiency of the positive active material is >90%, and the first Coulombic efficiency of the negative active material is >90%; the porosity of the first buffer layer and the second buffer layer is 30% to 40%.

In some embodiments, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the porosity of the first buffer layer and the second buffer layer is 20% to 30%. .

In some embodiments, the total area of the through holes of the first negative electrode current collector accounts for 0.1% to 30% of the area of the first negative electrode current collector. The function of the through hole is to allow lithium ions in the lithium replenishment layer to pass through the current collector to replenish lithium for the negative active material layer. If the area ratio of the through hole is within the above range, lithium ions can pass through. If the area ratio of the through holes is too low, the lithium replenishment rate will be too low; if the area ratio of the through holes is too high, the lithium replenishment rate will be too fast and the strength of the current collector will be reduced. Optionally, the total area occupied by the through holes of the first negative electrode current collector accounts for 0.1%, 0.5%, 1%, 2%, 5%, 10%, 15%, 20%, 25% or 30%. Further, the total area occupied by the through holes of the first negative electrode current collector accounts for 2% to 15% of the area of the first negative electrode current collector.

In some embodiments, the area ratio of the through hole of the second negative electrode current collector on the second negative electrode current collector ranges from 0.1% to 30%. The function of the through hole is to allow lithium ions in the lithium replenishment layer to pass through the current collector to replenish lithium for the negative active material layer. If the area ratio of the through hole is within the above range, lithium ions can pass through. If the area ratio of the through holes is too low, the lithium replenishment rate will be too low; if the area ratio of the through holes is too high, the lithium replenishment rate will be too fast. Optionally, the total area occupied by the through holes of the second negative electrode current collector accounts for 0.1%, 0.5%, 1%, 2%, 5%, 10%, 15%, 20%, 25% or 30%. Further, the area ratio of the through hole of the second negative electrode current collector on the second negative electrode current collector is 2% to 15%.

In some embodiments, the maximum pore diameter of the first negative electrode current collector and/or the second negative electrode current collector is 5 μm to 1 mm. Optionally, the maximum pore diameter of the through hole of the first negative electrode current collector and/or the second negative electrode current collector is 5 μm, 10 μm, 30 μm, 50 μm, 100 μm, 150 μm, 200 μm, 400 μm, 500 μm, 800 μm or 1000 μm. Furthermore, the maximum pore diameter of the through hole of the first negative electrode current collector and/or the second negative electrode current collector is 30 μm to 200 μm. The maximum pore diameter of the through holes is within the above range. The first negative electrode current collector and/or the second negative electrode current collector have through holes with smaller pore diameters and a larger number, which can make the lithium replenishment diffuse more uniformly.

As an example, the total area ratio and pore diameter of the through holes of the first negative electrode current collector and/or the second negative electrode current collector can be analyzed by observing the surface of the negative electrode sheet where the current collector is located with a scanning electron microscope (SEM).

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can 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 base material. The composite current collector can be formed by forming metal materials such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate. Polymer material substrates include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) ) and other base materials.

In some embodiments, the negative active material may be a negative active material known in the art for batteries. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.

In some embodiments, the negative active material layer optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl At least one of acrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative active material layer optionally further includes a conductive agent. 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.

In some embodiments, the negative active material layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

Another embodiment of the present application also provides a method for preparing a negative electrode piece, including steps S110 to S140.

Step S110: Coat the negative electrode slurry on one surface of the negative electrode current collector to prepare a negative electrode active material layer.

Step S120: Drill holes into the negative electrode current collector from the surface of the negative electrode current collector away from the negative electrode active material layer to form a through hole.

In some embodiments, the drilling step in step S120 may use laser drilling, roller pinning, or other methods to form through holes.

Step S130: Coat the buffer material slurry on the surface of the negative electrode current collector away from the negative electrode active material layer, so that the buffer material fills the through holes to obtain a sub-negative electrode piece.

Step S140: Take two sub-negative electrode sheets and prepare a lithium replenishing layer on the surface of the buffer material of at least one of the sub-negative electrode sheets, and connect the sub-negative electrode sheet with the lithium replenishing layer to the surface of the lithium replenishing layer of the other sub-negative electrode sheet. The surfaces of the buffer material of the negative electrode piece are bonded together to prepare the negative electrode piece. Specifically, the two sub-negative electrode plates may be the same or different.

In some of the embodiments, in step S140, lithium replenishing layers can be separately prepared on the surfaces of the buffer materials of the two sub-negative electrode plates to prepare two sub-negative electrode plates with lithium replenishing layers; The surfaces of the sub-negative electrode pieces with the lithium-supplementing layer are bonded together to prepare the negative electrode piece.

In some embodiments, in step S120, a through hole may be formed in one of the negative current collectors of the two sub-negative electrode pieces.

Positive electrode piece

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

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

In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can 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 base layer. The composite current collector can be formed by forming metal materials such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate. Polymer material substrates include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) ) and other base materials.

In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode 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 of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (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 (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 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 its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some of these embodiments, the positive active material layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer. At least one of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer and a fluorine-containing acrylate resin.

In some of these embodiments, the positive active material layer optionally further includes a conductive agent. As an 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 above-mentioned components used to prepare the positive electrode sheet, such as positive active materials, conductive agents, binders 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 current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

electrolyte

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium trifluoromethane At least one of lithium methanesulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate. , butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, butyric acid At least one of ethyl ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some of these embodiments, the electrolyte optionally further includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

Isolation film

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one selected from the group consisting of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece, and the separator film can be formed into an electrode assembly through a winding process or a lamination process.

In some of these embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and 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 bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 5 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 6 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into 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, the secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

FIG. 7 shows the battery module 4 as an example. Referring to FIG. 7 , 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, it can also be arranged in any other way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

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

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

8 and 9 show the battery pack 1 as an example. Referring to FIGS. 8 and 9 , 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 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple 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 by the present application. The secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device, or as an energy storage unit of the power-consuming device. Electrical devices may include mobile equipment, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc. , but not limited to this.

As a power-consuming device, secondary batteries, battery modules or battery packs can be selected according to its usage requirements.

FIG. 10 shows an electrical device 6 as an example. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Preparation of negative electrode plate:

(1) Mix and disperse the negative electrode active materials graphite, silicon oxide, conductive agent carbon nanotubes and binder styrene-butadiene rubber in deionized water in a mass ratio of 67:30:1:2, and the resulting negative electrode slurry is coated on one side Apply it on copper foil, dry it, and then cold-press and cut it to obtain a single-sided negative electrode piece.

(2) According to the preset through hole area ratio and through hole aperture, holes are evenly drilled on the surface of the copper foil of the single-sided negative electrode piece that is not coated with negative electrode slurry. The depth of the hole channel is equal to the thickness of the copper foil.

(3) Mix and disperse the ion conductor material LLZO, the conductive agent superconducting carbon and the binder polyvinylidene fluoride in NMP in a mass ratio of 80:10:10 to prepare a buffer layer slurry, and then gravure print it on the copper foil uncoated negative electrode The buffer layer slurry is coated on the surface of the slurry, and after drying, the buffer layer is obtained by cold pressing. The porosity of the buffer layer is 25%, and a sub-negative electrode piece is obtained.

(4) Prepare a metallic lithium layer with a thickness of 12 μm (volume density of 0.534g/cm ³ ) on the surface of the buffer layer away from the copper foil by rolling a lithium strip.

(5) Take two sub-negative electrode pieces with metal lithium layers processed in step (4) and laminated their metal lithium layers to obtain a negative electrode piece.

Preparation of positive electrode plate:

The cathode active material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (can also be referred to as NCM ₈₁₁ ), the conductive agent superconducting carbon and the binder polyvinylidene fluoride are mixed and dispersed in the NMP slurry in a mass ratio of 96:2:2 The material is coated on one side of the aluminum foil, and after drying, it is cold pressed and cut to obtain the positive electrode piece.

Isolation film: 12μm thick polyethylene separator, coated with 3μm thick ceramic layer on both sides.

The electrolyte is 1M LiPF ₆ /EC:EMC:DEC (volume ratio 1:1:1)

Secondary battery preparation:

The bare cells are prepared by stacking them in the order of positive electrode piece/isolation film/double-sided negative electrode piece/isolation film/positive electrode piece. After hot pressing, the bare battery core is assembled with the top cover and shell, and then the electrolyte is injected and formed. , exhaust, sealing, testing and other processes to obtain secondary batteries.

Examples 2 to 6:

The difference between Examples 2 to 6 and Example 1 is that the thickness of the buffer layer in Examples 2 to 6 is different.

Examples 7 to 12:

The difference between Examples 7 to 12 and Example 2 is that the porosity of the buffer layer in Examples 7 to 12 is different.

Examples 13 to 17:

The difference between Examples 13 to 17 and Example 2 is that the content of the ion conductor material in the buffer layer of Examples 13 to 17 is different.

In Example 13, the mass ratio of the ion conductor material LLZO, the conductive agent superconducting carbon, and the binder polyvinylidene fluoride is 58:32:10.

In Example 14, the mass ratio of the ion conductor material LLZO, the conductive agent superconducting carbon, and the binder polyvinylidene fluoride is 60:30:10.

In Example 15, the mass ratio of the ion conductor material LLZO, the conductive agent superconducting carbon, and the binder polyvinylidene fluoride is 70:20:10.

In Example 16, the mass ratio of the ion conductor material LLZO, the conductive agent superconducting carbon, and the binder polyvinylidene fluoride is 90:5:5.

In Example 17, the mass ratio of the ion conductor material LLZO, the conductive agent superconducting carbon, and the binder polyvinylidene fluoride is 95:2.5:2.5.

Examples 18 to 23:

The difference between Embodiments 18 to 23 and Embodiment 2 is that the area ratio of the through holes on the current collector in Embodiments 18 to 23 is different.

Examples 24 to 28:

The difference between Examples 24 to 28 and Example 2 is that the diameters of the through holes in Examples 24 to 28 are different.

Example 29:

The difference between Example 29 and Example 1 is that the ion conductor material of the buffer layer in Example 29 is different.

Example 30:

The difference between Example 30 and Example 29 is that the porosity of the buffer layer in Example 30 is different.

Example 31:

The difference between Embodiment 31 and Embodiment 30 is that the thickness of the buffer layer in Embodiment 31 is different.

Example 32:

The difference between Embodiment 32 and Embodiment 31 is that the area ratio of the through holes on the current collector in Embodiment 32 is different.

Example 33:

The difference between Example 33 and Example 32 is that the thickness of the metallic lithium layer in Example 33 is different.

Example 34:

The difference between Embodiment 34 and Embodiment 1 is that the first buffer layer and the second buffer layer have different compositions. The first buffer layer is the same as the buffer layer of Embodiment 1, and the second buffer layer is the same as the buffer layer of Embodiment 29. The layers are the same.

Example 35:

The structure of the negative electrode plate in Embodiment 35 is basically the same as that in Embodiment 1. The difference is that in Embodiment 35, the second current collector is not punched and is a copper foil without through holes; the first current collector is the same as that in Embodiment 1. Current collector.

Embodiments 36 to 38:

The difference between Examples 36 to 38 and Example 1 is that the negative active material is artificial graphite, and accordingly, the structural composition of the negative electrode sheet is also different.

Embodiments 39 to 41:

The difference between Examples 39-41 and Examples 36-38 is that the positive active material is lithium iron phosphate (LFP), and accordingly, the structural composition of the negative electrode sheet is also different.

Comparative example 1:

The difference between Comparative Example 1 and Example 1 is that the negative electrode piece is bonded to the copper foil used to prepare the negative electrode piece in step (1) of Example 1.

Comparative example 2:

The difference between Comparative Example 2 and Example 1 is that the buffer layer is omitted from the negative electrode piece.

Comparative example 3:

The difference between Comparative Example 3 and Example 36 is that the negative electrode sheet is bonded to the copper foil used to prepare the negative electrode sheet in step (1) of Example 7.

Comparative example 4:

The difference between Comparative Example 4 and Example 36 is that the buffer layer is omitted from the negative electrode piece.

Comparative example 5:

The difference between Comparative Example 5 and Example 39 is that the negative electrode piece is bonded to the copper foil prepared in step (1) of Example 9.

Comparative example 6:

The difference between Comparative Example 6 and Example 39 is that the buffer layer is omitted from the negative electrode piece.

In the secondary batteries of Examples 1 to 41 and Comparative Examples 1 to 6, refer to Table 1 for the structural composition of the negative electrode plate.

Table 1 Structural composition of the negative electrode plates of Examples 1 to 41 and Comparative Examples 1 to 6

Note: Unless otherwise specified, the first buffer layer and the second buffer layer of the negative electrode plate of the embodiment in Table 1 are the same, and the first current collector and the second current collector are the same.

Test part:

Lithium replenishment amount test: In an environment with RH <2%, disassemble a fresh battery core, scrape a sample per unit area of the lithium replenishment layer between the two negative electrode current collectors and weigh it. Calculate the replenishment amount per unit area of the negative electrode piece. Amount of lithium.

Cycle performance test: At 25°C, charge the lithium-ion battery to 4.25V (NCM811) or 3.65V (LFP) at a rate of 0.5C, then charge it at a constant voltage until the current is less than 0.05C, and then discharge it to 2.5V using a rate of 1C. The cycle test is carried out in this form of full and full discharge until the discharge capacity of the lithium-ion battery decays to 80% of the initial capacity, and the number of cycles at this time is recorded.

Self-discharge voltage drop test: Fully charge the battery, let it stand for 1 day, connect the positive and negative electrodes of the secondary battery through an electrochemical workstation (or multimeter), and record the open circuit voltage V1, record the open circuit voltage V2 after letting it stand for 2 days, as follows Calculate the self-discharge voltage drop in mV/h.

The cycle performance and self-discharge voltage drop of the secondary batteries of Examples 1 to 12 and Comparative Examples 1 to 6 are recorded in Table 2.

序号serial number	循环圈数number of cycles	自放电压降(mV/h)Self-discharge voltage drop (mV/h)
实施例1Example 1	11641164	0.1650.165
实施例2Example 2	14851485	0.0780.078
实施例3Example 3	13271327	0.0750.075
实施例4Example 4	11861186	0.0740.074
实施例5Example 5	982982	0.0720.072
实施例6Example 6	903903	0.070.07
实施例7Example 7	12951295	0.0930.093
实施例8Example 8	13691369	0.0860.086
实施例9Example 9	14571457	0.0790.079
实施例10Example 10	14381438	0.0710.071
实施例11Example 11	13821382	0.0640.064

实施例12Example 12	13011301	0.0610.061
实施例13Example 13	12861286	0.0620.062
实施例14Example 14	13171317	0.0630.063
实施例15Example 15	14251425	0.0740.074
实施例16Example 16	13521352	0.0930.093
实施例17Example 17	12671267	0.1180.118
实施例18Example 18	11731173	0.0580.058
实施例19Example 19	12961296	0.0620.062
实施例20Example 20	14251425	0.0660.066
实施例21Example 21	14831483	0.0720.072
实施例22Example 22	12511251	0.1490.149
实施例23Example 23	10861086	0.2010.201
实施例24Example 24	15791579	0.0570.057
实施例25Example 25	14311431	0.0820.082
实施例26Example 26	13091309	0.0950.095
实施例27Example 27	11761176	0.1310.131
实施例28Example 28	10421042	0.1730.173
实施例29Example 29	12761276	0.0680.068
实施例30Example 30	11931193	0.0650.065
实施例31Example 31	10891089	0.0620.062
实施例32Example 32	956956	0.0570.057
实施例33Example 33	904904	0.0560.056
实施例34Example 34	12101210	0.0820.082
实施例35Example 35	11341134	0.1460.146
实施例36Example 36	33813381	0.0510.051
实施例37Example 37	31763176	0.0490.049
实施例38Example 38	24592459	0.0450.045
实施例39Example 39	54935493	0.0380.038
实施例40Example 40	51865186	0.0370.037
实施例41Example 41	40754075	0.0320.032
对比例1Comparative example 1	716716	0.0730.073
对比例2Comparative example 2	869869	0.3790.379
对比例3Comparative example 3	20972097	0.0460.046
对比例4Comparative example 4	22862286	0.1540.154

对比例5Comparative example 5	35823582	0.0350.035
对比例6Comparative example 6	37433743	0.0970.097

From the relevant data in Table 2, it can be seen that the cycle numbers of the secondary batteries of Comparative Examples 1 to 2 are 716 and 869, and the self-discharge voltage drops are 0.073mV/h and 0.379mV/h. The number of cycles of the secondary batteries of Examples 1 to 35 was 903 to 1579, and the self-discharge voltage drop was 0.056 mV/h to 0.201 mV/h. Comparing Examples 1 to 35 with Comparative Example 1, it can be seen that compared with the secondary battery without a lithium replenishing layer, the cycle performance of the secondary battery of Examples 1 to 35 is significantly improved; and compared with Comparative Example 2, which does not have a buffer It can be seen from the comparison of secondary batteries with different layers that the buffer layer provided in Examples 1 to 35 can reduce the self-discharge voltage drop of the secondary battery and prevent the lithium supplement layer from depositing lithium on the surface of the negative electrode plate, causing a micro short circuit, thus preventing secondary Battery deterioration, cycle performance is better.

It can be seen from Examples 1 to 6 that when the thickness of the buffer layer is 3 μm to 7 μm, the cycle performance of the secondary battery is better.

The porosity of the buffer layer in Examples 7 to 12 is different from that in Example 2. Different porosity of the buffer layer will affect the self-discharge voltage drop and the number of cycles of the secondary battery. The number of cycles in Example 2 and Examples 9 and 10 is relatively different. Most of them are above 1400. It can be seen that controlling the porosity of the buffer layer between 20% and 40% will have a better effect on improving the cycle life of the secondary battery. The buffer layer ion conductor material content in Examples 13 to 17 is different from that in Example 2. It can be seen from the data in Table 2 that the secondary battery has better cycle performance when the buffer material mass content is 70% to 80%. The area ratio of the through holes on the current collector in Examples 18 to 23 is different from that in Example 2. The through hole area ratio of Examples 22 to 23 is 20% to 30%, the lithium replenishment rate is faster, and the self-discharge voltage drop is higher than that of Examples 2 and 18 to 21. The through hole area ratio of Example 18 is 0.1%, the lithium replenishment rate is slow, the self-discharge voltage drop is small, but the number of cycles is smaller than that of Examples 2 and 19-22. Therefore, the through-hole area ratio is 2% to 15%, and the secondary battery cycle performance is better. Examples 24 to 28 are different from Example 2 in the diameter of the through holes. It can be seen from the data in Table 2 that the secondary battery cycle performance is better when the through hole diameter is 30 μm ~ 200 μm. The battery systems of Examples 36 to 38 and 38 to 41 are different from those of Examples 1 to 35. Compared with the same battery system, Comparative Examples 3 to 6 that do not contain a lithium replenishing layer or a buffer layer, the secondary batteries of Examples 36 to 41 It has a low self-discharge voltage drop, which can prevent the lithium replenishment layer from depositing lithium on the surface of the negative electrode sheet, causing micro short circuit, thereby avoiding the deterioration of the secondary battery and having a better cycle life.

The technical features of the above-described embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, All should be considered to be within the scope of this manual.

The above-described embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

A negative electrode sheet, including a first negative electrode active material layer, a first current collector, a lithium replenishing layer, a second current collector and a second negative electrode active material layer that are stacked in sequence; the negative electrode sheet also includes a buffer material;

At least one of the first current collector and the second current collector has a through hole; the buffer material is filled in the through hole of the first current collector and the through hole of the second current collector. At least one of them.
The negative electrode piece according to claim 1, characterized in that the negative electrode piece further includes a first buffer layer, and the first buffer layer is disposed between the first current collector and the lithium replenishing layer, And partially embedded in the through hole of the first current collector, so that the buffer material is filled in the through hole of the first current collector;

And/or, the negative electrode piece further includes a second buffer layer, the second buffer layer is disposed between the second current collector and the lithium replenishing layer, and is partially embedded in the passage of the second current collector. hole, so that the buffer material is filled in the through hole of the second current collector.
The negative electrode plate according to claim 2, wherein the thickness of the first buffer layer is 3 μm to 10 μm; optionally, the thickness of the first buffer layer is 3 μm to 7 μm;

And/or, the thickness of the second buffer layer is 3 μm ~ 10 μm; optionally, the thickness of the second buffer layer is 3 μm ~ 7 μm.
The negative electrode sheet according to claim 2 or 3, wherein the first buffer layer and the second buffer layer have lithium ion conductivity.
The negative electrode plate according to any one of claims 2 to 4, characterized in that both the first buffer layer and the second buffer layer include ion conductor materials;

Optionally, the ion conductor material includes at least one of an ion conductor polymer, an ion conductor oxide, an ion conductor sulfide, and an ion conductor halide.
The negative electrode plate according to claim 5, wherein the ion conductor material has an ion conductivity of 10 -9 S/cm 2 to 10 -2 S/cm 2 .
The negative electrode plate according to claim 5 or 6, wherein the ion conductor polymer is selected from at least one of polyethylene oxide, polyvinylidene fluoride and polyanionic conductor polymer;

And/or, the ion conductor oxide is selected from at least one selected from the group consisting of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, and lithium titanium aluminum phosphate.
The negative electrode plate according to any one of claims 5 to 7, wherein the mass percentage of the ion conductor material in the first buffer layer is 60% to 90%; and/or the third The mass percentage of the ion conductor material in the second buffer layer is 60% to 90%;

Optionally, in the first buffer layer, the mass percentage of the ion conductor material is 70% to 80%; and/or in the second buffer layer, the mass percentage of the ion conductor material is 70%. ~80%.
The negative electrode piece according to any one of claims 2 to 8, wherein the porosity of the first buffer layer and the second buffer layer is 2% to 50%;

Optionally, the porosity of the first buffer layer and the second buffer layer is 20% to 40%.
The negative electrode piece according to any one of claims 1 to 9, wherein the total area occupied by the through holes of the first current collector accounts for 0.1% to 0.1% of the area on the first current collector. 30%;

Optionally, the total area occupied by the through holes of the first current collector accounts for 2% to 15% of the area on the first current collector.
The negative electrode piece according to any one of claims 1 to 10, wherein the through hole of the second current collector accounts for 0.1% to 30% of the area of the second current collector;

Optionally, the area ratio of the through holes of the second current collector on the second current collector is 2% to 15%.
The negative electrode piece according to any one of claims 1 to 11, wherein the maximum pore diameter of the first current collector and/or the second current collector is 5 μm to 1 mm;

Optionally, the maximum pore diameter of the through holes of the first current collector and/or the second current collector is 30 μm to 200 μm.
A method for preparing a negative electrode piece, including the following steps:

Coat the negative electrode slurry on one surface of the current collector surface to prepare a negative electrode active material layer;

Punching the current collector from a surface of the current collector away from the negative active material layer to form a through hole;

Coating a buffer material slurry on the surface of the current collector away from the negative active material layer so that the buffer material fills the through holes to obtain a sub-negative electrode piece;

Take two of the sub-negative electrode pieces and prepare a lithium replenishing layer on the surface of the buffer material of at least one of the sub-negative electrode pieces, and place the sub-negative electrode piece provided with the lithium replenishing layer with the The surface of the lithium replenishing layer is bonded to the surface of the buffer material of the other sub-negative electrode piece to prepare the negative electrode piece.
A secondary battery including the negative electrode sheet according to any one of claims 1 to 12 or the negative electrode sheet prepared according to the method for preparing the negative electrode sheet according to claim 13.
The secondary battery according to claim 14, wherein the negative electrode plate includes a first buffer layer and a second buffer layer; the secondary battery includes a positive active material and a negative active material; the positive active material The first Coulombic efficiency is >90%, and the first Coulombic efficiency of the negative active material is >90%; the thickness of the first buffer layer is 4 μm to 7 μm; the thickness of the second buffer layer is 4 μm to 7 μm;

Alternatively, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the thickness of the first buffer layer is 3 μm to 5 μm; and the second buffer layer The thickness is 3μm~5μm.
The secondary battery according to claim 14, wherein the negative electrode plate includes a first buffer layer and a second buffer layer; the secondary battery includes a positive active material and a negative active material; the positive active material The first Coulombic efficiency is >90%, the first Coulombic efficiency of the negative active material is >90%; the ion conductivity of the ion conductor material is 10 -9 S/cm 2 ~ 10 -5 S/cm 2 ;

Alternatively, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the ion conductivity of the ion conductor material is 10 -6 S/cm 2 ~10 -2 S/cm 2 .
The secondary battery according to claim 14, wherein the negative electrode plate includes a first buffer layer and a second buffer layer; the secondary battery includes a positive active material and a negative active material; the positive active material The first Coulombic efficiency is >90%, the first Coulombic efficiency of the negative active material is >90%; the porosity of the first buffer layer and the second buffer layer is 30% to 40%;

Alternatively, the first Coulombic efficiency of the positive active material is ≤90%, and/or the first Coulombic efficiency of the negative active material is ≤90%; the porosity of the first buffer layer and the second buffer layer is 20%. ~30%.
A battery module including the secondary battery according to any one of claims 14 to 17.
A battery pack including at least one of the secondary battery according to any one of claims 14 to 17 and the battery module according to claim 18.
An electric device including at least one selected from the group consisting of the secondary battery according to any one of claims 14 to 17, the battery module according to claim 18, or the battery pack according to claim 19.