CN118679593A

CN118679593A - Negative electrode plate, preparation method thereof, secondary battery, battery module, battery pack and power utilization device

Info

Publication number: CN118679593A
Application number: CN202280088146.9A
Authority: CN
Inventors: 陈兴布; 孙信; 吴李力; 李璇; 董苗苗; 云亮; 宋佩东; 刘润蝶
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-08-08
Filing date: 2022-08-08
Publication date: 2024-09-20
Also published as: WO2024031216A1

Abstract

The application provides a negative electrode plate which comprises a first negative electrode active material layer, a first current collector, a lithium supplementing layer, a second current collector and a second negative electrode active material layer which are sequentially stacked; the negative pole piece also comprises a buffer material; at least one of the first current collector and the second current collector is provided with a through hole; the buffer material is filled in at least one of the through-holes of the first current collector and the through-holes of the second current collector.

Description

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

Technical Field

The application relates to the field of secondary batteries, in particular to a negative electrode plate, a preparation method of the negative electrode plate, a secondary battery, a battery module, a battery pack and an electric device.

Background

With the increase of new energy demand, higher and higher requirements are put on the endurance capacity and service life of secondary batteries such as lithium ion batteries in the market. As the cycle times of lithium ion batteries increase, the active lithium in the battery gradually decreases, thereby affecting the energy density and cycle life thereof. The traditional technology generally presses the metal lithium to the surface of the active material layer for lithium supplementation, however, a large amount of heat can be instantaneously generated due to the excessively high lithium supplementation speed, and the safety risk is brought; meanwhile, after the battery is filled with liquid, lithium is quickly supplemented at one time, lithium deposition is easy to generate in the circulation process due to the large lithium supplementing amount, and the circulation life of the battery is influenced.

Disclosure of Invention

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

The application provides a negative electrode plate, which comprises a first negative electrode active material layer, a first current collector, a lithium supplementing layer, a second current collector and a second negative electrode active material layer which are sequentially stacked; the negative electrode piece further comprises a buffer material;

At least one of the first current collector and the second current collector is provided with a through hole; the buffer material is filled in at least one of the through holes of the first current collector and the through holes of the second current collector.

In some embodiments, the negative electrode tab further includes a first buffer layer disposed between the first current collector and the lithium-compensating 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 plate further comprises a second buffer layer, wherein the second buffer layer is arranged between the second current collector and the lithium supplementing layer and is partially embedded into the through hole of the second current collector, so that the buffer material is filled in the through hole of the second current collector.

In some of these embodiments, the first buffer layer has a thickness of 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 3-10 μm; optionally, the thickness of the second buffer layer is 3 μm to 7 μm.

In some of these embodiments, the first buffer layer and the second buffer layer have lithium ion conducting capabilities.

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

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

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

In some of these embodiments, 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 at least one selected from 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% -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% -80%; and/or, in the second buffer layer, the mass percentage of the ion conductor material is 70% -80%.

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

optionally, the first buffer layer and the second buffer layer have a porosity of 20% -40%.

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

optionally, the area ratio of the total area occupied by the through holes of the first current collector on the first current collector is 2% -15%.

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

optionally, the area ratio of the through hole of the second current collector on the second current collector is 2% -15%.

In some of these embodiments, the maximum aperture of the through hole of the first current collector and/or the second current collector is 5 μm to 1mm;

Optionally, the maximum aperture of the through hole of the first current collector and/or the second current collector is 30-200 μm.

According to the negative electrode plate, the lithium supplementing layer is clamped between the two current collectors with the through holes, the buffer materials are filled in the through holes, and the negative electrode active material layer is arranged on the surface, far away from the lithium supplementing layer, of the current collectors, so that the lithium supplementing layer can be prevented from being in direct contact with the negative electrode active material, and the lithium supplementing speed is too high and the heat generation risk is avoided; the buffer material can regulate and control the lithium supplementing rate of the lithium supplementing layer, lithium dendrites caused by overlarge lithium supplementing rate are avoided, and the secondary battery has longer cycle life.

In a second aspect, the application also provides a preparation method of the negative electrode plate, which comprises the following steps:

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

punching the current collector from a surface of the current collector remote from the anode active material layer to form a through hole;

Coating buffer material slurry on the surface of the current collector, which is far away from the negative electrode active material layer, so that the buffer material fills the through holes to obtain sub-negative electrode pieces;

and preparing a lithium supplementing layer on the surface of the buffer material of at least one of the sub negative pole pieces, and attaching the surface of the sub negative pole piece provided with the lithium supplementing layer to the surface of the buffer material of the other sub negative pole piece by the surface of the lithium supplementing layer to prepare the negative pole piece.

In a third aspect, the application also provides a secondary battery, comprising the negative electrode plate or the negative electrode plate manufactured according to the preparation method of the negative electrode plate.

In some embodiments, the negative electrode tab includes a first buffer layer and a second buffer layer; the secondary battery includes a positive electrode active material and a negative electrode active material; the first coulombic efficiency of the positive electrode active material is more than 90%, and the first coulombic efficiency of the negative electrode active material is more than 90%; the thickness of the first buffer layer is 4-7 mu m; the thickness of the second buffer layer is 4-7 mu m;

or the first coulombic efficiency of the positive electrode active material is less than or equal to 90 percent, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90 percent; the thickness of the first buffer layer is 3-5 mu m; the thickness of the second buffer layer is 3-5 μm.

In some embodiments, the negative electrode tab includes a first buffer layer and a second buffer layer; the secondary battery includes a positive electrode active material and a negative electrode active material; the first coulombic efficiency of the positive electrode active material is more than 90%, and the first coulombic efficiency of the negative electrode active material is more than 90%; the ionic conductivity of the ionic conductor material is 10 ^-9S/cm ²～10 ^-5S/cm ²;

Or the first coulombic efficiency of the positive electrode active material is less than or equal to 90 percent, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90 percent; the ionic conductivity of the ion conductor material is 10 ^-6S/cm ²～10 ^-2S/cm ².

In some embodiments, the negative electrode tab includes a first buffer layer and a second buffer layer; the secondary battery includes a positive electrode active material and a negative electrode active material; the first coulombic efficiency of the positive electrode active material is more than 90%, and the first coulombic efficiency of the negative electrode active material is more than 90%; the porosity of the first buffer layer and the second buffer layer is 30% -40%;

Or the first coulombic efficiency of the positive electrode active material is less than or equal to 90 percent, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90 percent; 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 secondary battery.

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

In a sixth aspect, the present application also provides an electric device, including at least one selected from the secondary battery, the battery module, or the battery pack.

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

Drawings

Fig. 1 is a schematic view of a secondary battery according to an embodiment of the present application;

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

fig. 3 is a schematic view of a battery module according to an embodiment of the present application;

fig. 4 is a schematic view of a battery pack according to an embodiment of the present application;

fig. 5 is an exploded view of the battery pack of the embodiment of the present application shown in fig. 4;

fig. 6 is a schematic view of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source;

Reference numerals illustrate:

1, a battery pack; 2, upper box body; 3, lower box body; 4, a battery module; 5 a secondary battery; 51 a housing; 52 electrode assembly; 53 cover plates; and 6, an electric device.

For a better description and illustration of embodiments and/or examples of those inventions disclosed herein, reference may be made to one or more of the accompanying drawings. Additional details or examples used to describe the drawings should not be construed as limiting the scope of the disclosed invention, the presently described embodiments and/or examples, and any of the presently understood modes of carrying out the invention.

Detailed Description

In order that the application may be readily understood, a more complete description of the application will be rendered by reference to the appended drawings. Preferred embodiments of the present application are shown in the drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

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

The conventional surface lithium supplementing technology of the secondary battery can instantaneously generate a large amount of heat when the metal lithium is pressed to the surface of the active material layer, thereby bringing about the risk of fire in the production process. Meanwhile, the metal lithium layer on the surface layer is quickly embedded into the active material layer after the secondary battery is injected with liquid, so that disposable lithium supplementing is formed. In order to prevent the lithium precipitation phenomenon of the negative electrode active material layer in the subsequent use process, the dosage of the negative electrode active material is required to be increased to receive the lithium supplemented by the surface layer metal lithium, so that the energy density of the battery is lost.

Through a great deal of research, the inventor provides a negative plate with a special lithium supplementing structure, and the lithium supplementing rate of the lithium supplementing structure can be reasonably controlled, so that the lithium supplementing rate is less than or equal to the active lithium loss rate of the secondary battery, and the secondary battery has higher energy density and longer cycle life.

The application provides a negative electrode plate, and a secondary battery, a battery module, a battery pack and an electric device using the negative electrode plate. Such secondary batteries are suitable for various electric devices using batteries, such as cellular phones, portable devices, notebook computers, battery cars, electric toys, electric tools, electric automobiles, ships, and spacecraft, etc., including, for example, airplanes, rockets, space shuttles, and spacecraft, etc.

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

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

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During the charge and discharge of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The isolating film is arranged between the positive pole piece and the negative pole piece, and mainly plays a role in preventing the positive pole piece and the negative pole piece from being short-circuited, and meanwhile ions can pass through the isolating film.

Negative pole piece

In one embodiment of the present application, a negative electrode tab is provided. In an embodiment of the application, the negative electrode tab comprises a first negative electrode active material layer, a first negative electrode current collector, a lithium supplementing layer, a second negative electrode current collector and a second negative electrode active material layer which are sequentially stacked. The negative pole piece also comprises a buffer material. At least one of the first negative electrode current collector and the second negative electrode current collector is provided with a through hole; the buffer material is filled in at least one of the through holes of the first negative electrode current collector and the through holes of the second negative electrode current collector.

According to the negative electrode plate, the lithium supplementing layer is clamped between the two negative electrode current collectors with the through holes, the buffer material is filled in the through holes, and the negative electrode active material layer is arranged on the surface, far away from the lithium supplementing layer, of the negative electrode current collector, so that the direct contact between the lithium supplementing layer and the negative electrode active material can be avoided, and the lithium supplementing speed is too high; the buffer material can regulate and control the lithium supplementing rate of the lithium supplementing layer, lithium dendrites caused by overlarge lithium supplementing rate are avoided, and the secondary battery has longer cycle life.

It is understood that when one of the first and second anode current collectors has a through-hole, the lithium supplementing layer supplements lithium to the anode active material layer near one side of the through-hole.

In some of these embodiments, the buffer material has lithium ion conducting capacity. Further, the buffer material may be selected to be an ion conductor material. The ion conductor material has lithium ion conduction capability, is filled in the through hole of the negative electrode current collector, and can conduct lithium ions, so that the lithium supplementing of the negative electrode plate is realized.

In some of these embodiments, the number of through holes of the first negative electrode current collector is plural, and the buffer material fills part or all of the through holes. The number of through holes of the second negative electrode current collector is multiple, and the buffer material fills part or all of the through holes. Further, the buffer material fills all of the through holes.

In some embodiments, the negative electrode tab further includes a first buffer layer disposed between the first negative electrode current collector and the lithium supplementing layer and 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 plate further comprises a second buffer layer, wherein the second buffer layer is arranged between the second negative electrode current collector and the lithium supplementing layer and is partially embedded into the through hole of the second negative electrode current collector, so that the buffer material is filled in the through hole of the second negative electrode current collector.

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

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

In some of these embodiments, the first buffer layer has a thickness of 3 μm to 10 μm. Alternatively, 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 to 7 μm. The thickness of the second buffer layer is 3 μm to 10 μm. Alternatively, 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 to 7 μm.

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

As an example, the thickness of the first buffer layer or the second buffer layer may be obtained by a cross-sectional analysis of the negative electrode tab observed by a Scanning Electron Microscope (SEM).

When the thickness of the buffer layer is too small, the lithium supplementing speed is too high, and lithium dendrites are formed to influence the cycle life of the secondary battery; if the thickness of the buffer layer is too large, the lithium supplementing rate is slow and the energy density of the secondary battery is lowered. The thickness of the buffer layer is controlled within the range, so that the cathode pole piece can be controlled to have proper lithium supplementing rate. Preferably, the lithium supplementing rate of the negative electrode plate is smaller than or equal to the active lithium loss rate of the secondary battery, so that the secondary battery can have higher energy density and longer cycle life.

The active lithium loss rate of the secondary battery refers to the rate at which active lithium is lost during the cycle of the secondary battery, and can be estimated by the slope of a curve of capacity with the number of cycles of the secondary battery, i.e., the capacity fade rate. Specifically, the active lithium loss rate of the secondary battery can be estimated by the following formula.

In the secondary battery not including the lithium supplementing structure, the lithium supplementing rate is 0, and the capacity of the secondary battery decreases with the increase of the cycle number; when the lithium supplementing rate is less than the active lithium loss rate, the slope of the curve of the capacity change along with the cycle number is partially improved relative to the slope of the lithium supplementing rate being 0; when the lithium supplementing rate is approximately equal to the active lithium loss rate, the slope of the curve of the capacity change along with the cycle number is mainly determined by the loss of the self-lithium intercalation capacity of the positive electrode active material; when the lithium supplementing rate is larger than the active lithium loss rate, compared with the case that the lithium supplementing rate is approximately equal to the active lithium loss rate, the curve slope of the capacity changing along with the cycle times cannot be further improved, and on the contrary, the problem that the internal micro short circuit and the self discharge are increased are easily caused due to the fact that negative electrode surface lithium chromatography is caused, so that the safety risk is brought.

In some of these embodiments, the first coulombic efficiency of the positive electrode active material is > 90%, and the first coulombic efficiency of the negative electrode active material is > 90%; the thickness of the first buffer layer is 4-7 mu m; the thickness of the second buffer layer is 4-7 μm. The positive electrode first coulombic efficiency refers to the first lithium intercalation capacity/first lithium deintercalation capacity of the positive electrode active material, and the negative electrode first coulombic efficiency refers to the first lithium deintercalation capacity/first lithium intercalation capacity of the negative electrode active material, which can be measured by separately preparing the positive electrode active material or the negative electrode active material into a coin cell. Generally, when the positive electrode active material and the negative electrode active material have high first coulombic efficiency, the secondary battery has a slow active lithium loss rate, the thickness of the buffer layer is controlled within the above range, and the secondary battery has a suitable lithium supplementing rate, a high energy density and a long cycle life.

Specifically, the first coulombic efficiency of positive electrode active materials such as lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel cobalt manganese oxide (NCM), lithium Manganate (LMO), lithium Cobaltate (LCO), etc., is > 90%. The first coulombic efficiency of the negative electrode active material such as natural graphite, artificial graphite, lithium Titanate (LTO), soft carbon, etc. is > 90%.

In some of these embodiments, the first coulombic efficiency of the positive electrode active material is less than or equal to 90%, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90%; the thickness of the first buffer layer is 3-5 μm; the thickness of the second buffer layer is 3 μm to 5 μm. Generally, when the first coulombic efficiency of the positive electrode active material and the negative electrode active material is low, the irreversible capacity of the positive electrode active material and the negative electrode active material is large, the active lithium loss rate is large, the thickness of the control buffer layer is within the above range, and the secondary battery has a suitable lithium supplementing rate, a high energy density and a long cycle life.

Specifically, the first coulombic efficiency of the positive electrode active material such as lithium-rich lithium manganate, lithium-rich lithium nickelate and the like is less than or equal to 90 percent. The first coulombic efficiency of the anode active material such as silicon-based material, tin-based material, lithium metal anode, partially porous carbon and the like is less than or equal to 90 percent.

In some of these embodiments, the first buffer layer and the second buffer layer each comprise an ion conductor material. Optionally, the ion conductor material comprises 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 conduction capability, and can conduct lithium ions at two sides of the negative electrode current collector, so that lithium supplementation of the secondary battery is realized.

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

In some of these embodiments, the ion conductor oxide may be selected from, but is not limited to, at least one of Lithium Lanthanum Titanium Oxide (LLTO), lithium Lanthanum Zirconium Oxide (LLZO), and Lithium Aluminum Titanium Phosphate (LATP).

In some of these embodiments, the ion conductivity of the ion conductor material is 10 ^-9S/cm ²～10 ^-2S/cm ². As an example, according to the law of resistance, the buffer layers are assembled into a finite field symmetric battery, the resistance R of the buffer layers is measured by using the EIS method, so as to obtain the ionic conductivity σ=l/(r×s), L is the thickness of the buffer layers, and S is the effective contact area between the buffer layers and the electrodes during the test.

In some of these embodiments, the first coulombic efficiency of the positive electrode active material is > 90%, and the first coulombic efficiency of the negative electrode active material is > 90%; the ionic conductivity of the ion conductor material was 10 ^-9S/cm ²～10 ^-5S/cm ². By selecting the ion conductor material with smaller ion conductivity, the buffer layer has smaller ion conductivity, so that the lithium supplementing rate of the secondary battery can be controlled to be relatively smaller, and in a secondary battery system with smaller lithium consuming rate, the lithium supplementing rate can be matched with the lithium consuming rate, and the secondary battery has longer energy density and longer cycle life.

As an example, the ion conductivity of an ion conductor material such as polyethylene oxide (PEO)、42.5Li ₂O·57.5B ₂O ₃、Li _2.9PO _3.3N _0.46、Li _3.6Si _0.6P _0.4O _0.4、Li _3.25Ge _0.25P _0.75S ₄ or the like is 10 ^-9S/cm ²～10 ^-5S/cm ².

In some of these embodiments, the first coulombic efficiency of the positive electrode active material is less than or equal to 90%, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90%; the ionic conductivity of the ion conductor material was 10 ^-6S/cm ²～10 ^-2S/cm ². The ion conductor material with larger ion conductivity is selected, so that the ion conductivity of the buffer layer is larger, the lithium supplementing rate of the secondary battery can be controlled to be relatively larger, and in a secondary battery system with larger lithium consuming rate, the lithium supplementing rate can be matched with the lithium consuming rate, and the secondary battery has longer energy density and longer cycle life.

As an example, ion conductivity of ion conductor materials such as Lithium Lanthanum Titanium Oxide (LLTO), lithium Lanthanum Zirconium Oxide (LLZO), li ₆PS ₅ Cl, and the like is 10 ^-6S/cm ²～10 ^-2S/cm ².

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

In some embodiments, the mass percentage of the ion conductor material in the second buffer layer is 60% -90%. Optionally, the mass percent 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% -80%. By controlling the mass percentage of the ion conductor material in the buffer layer within the above range, the buffer layer has a suitable lithium ion conductivity.

In some embodiments, the first buffer layer and/or the second buffer layer further comprise a binder and a conductive agent.

In some embodiments, the first buffer layer and the second buffer layer have a porosity of 2% to 50%. Optionally, the first buffer layer and the second buffer layer have a porosity of 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% -40%.

As an example, the porosity is measured by a true density method, and the true volume of the measured material is precisely measured by using an inert gas (helium) substitution method with a small molecular diameter in combination with archimedes 'principle and bohr's law, so as to obtain the porosity of the sample to be measured. Porosity p= (V ₂-V ₁)/V ₂ x 100%, apparent volume V ₂ = S x H x 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 researches find that the porosity of the buffer layer can influence the lithium ion conduction capacity of the buffer layer, and if the porosity of the buffer layer is smaller, the ion conductivity of the buffer layer is lower, and the lithium supplementing rate of the secondary battery is slower; the buffer layer has higher porosity, so that the ion conductivity of the buffer layer is higher, and the lithium supplementing rate of the secondary battery is faster; by adjusting the porosity of the buffer layer, secondary battery systems of different active lithium loss rates can be accommodated.

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

In some of these embodiments, the first coulombic efficiency of the positive electrode active material is less than or equal to 90%, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90%; the first buffer layer and the second buffer layer have a porosity of 20% -30%.

In some of these embodiments, the total area occupied by the through holes of the first negative electrode current collector is 0.1% to 30% of the area on the first negative electrode current collector. The through holes have the function of enabling lithium ions of the lithium supplementing layer to penetrate through the current collector to supplement lithium for the negative electrode active material layer, and the area ratio of the through holes is in the range, so that the lithium ions can penetrate through. The area occupation ratio of the through holes is too low, so that the lithium supplementing rate is too low; if the area ratio of the through holes is too high, the lithium supplementing speed is too high, and the strength of the current collector is reduced. Optionally, the total area occupied by the through holes of the first negative electrode current collector is 0.1%, 0.5%, 1%, 2%, 5%, 10%, 15%, 20%, 25% or 30% of the area on the first negative electrode current collector. Further, the area ratio of the total area occupied by the through holes of the first negative electrode current collector on the first negative electrode current collector is 2% -15%.

In some of these embodiments, the area of the through hole of the second negative current collector on the second negative current collector is 0.1% to 30%. The through holes have the function of enabling lithium ions of the lithium supplementing layer to penetrate through the current collector to supplement lithium for the negative electrode active material layer, and the area ratio of the through holes is in the range, so that the lithium ions can penetrate through. The area occupation ratio of the through holes is too low, so that the lithium supplementing rate is too low; and if the area ratio of the through holes is too high, the lithium supplementing speed is too high. Optionally, the total area occupied by the through holes of the second negative electrode current collector is 0.1%, 0.5%, 1%, 2%, 5%, 10%, 15%, 20%, 25% or 30% of the area on the second negative electrode current collector. Further, the area ratio of the through hole of the second negative electrode current collector on the second negative electrode current collector is 2% -15%.

In some of these embodiments, the maximum pore diameter of the through-holes of the first negative electrode current collector and/or the second negative electrode current collector is 5 μm to 1mm. Alternatively, the maximum pore diameter of the through-holes 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. Further, the maximum aperture of the through hole of the first negative electrode current collector and/or the second negative electrode current collector is 30-200 μm. The maximum aperture of the through holes is in the range, and the first negative electrode current collector and/or the second negative electrode current collector are/is provided with the through holes with smaller aperture and more number, so that the diffusion of the lithium supplement is more uniform.

As an example, the total area ratio and the aperture occupied by the through holes of the first negative electrode current collector and/or the second negative electrode current collector can be obtained by analyzing the surface of the current collector on the negative electrode plate by observing the Scanning Electron Microscope (SEM).

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

In some of these embodiments, the negative active material may employ a negative active material for a battery, which is well known in the art. As an example, the anode 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 at least one selected from elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery anode active material may be used. These negative electrode active materials may be used alone or in combination of two or more.

In some of these embodiments, the negative electrode active material layer may further optionally include a binder. The binder may be at least one selected from 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).

In some of these embodiments, the anode active material layer may further optionally include a conductive agent. The conductive agent is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some of these embodiments, the anode active material layer may optionally further include other adjuvants, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In another embodiment of the present application, a method for preparing a negative electrode sheet is provided, including steps S110 to S140.

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

Step S120: and punching the negative electrode current collector from the surface of the negative electrode current collector far away from the negative electrode active material layer to form a through hole.

In some embodiments, the punching step in step S120 may form the through holes by laser drilling, roll pinning, or the like.

Step S130: and coating buffer material slurry on the surface of the negative current collector, which is far away from the negative active material layer, so that the buffer material fills the through holes to obtain the sub-negative electrode plate.

Step S140: and preparing a lithium supplementing layer on the surface of the buffer material of at least one of the two sub-negative pole pieces, and attaching the surface of the sub-negative pole piece provided with the lithium supplementing layer to the surface of the buffer material of the other sub-negative pole piece to prepare the negative pole piece. Specifically, the two sub-negative electrode pieces may be the same or different.

In some embodiments, in step S140, lithium supplementing layers may be further prepared on the surfaces of the buffer materials of the two sub-negative electrode pieces, so as to prepare two sub-negative electrode pieces provided with the lithium supplementing layers; and bonding the surfaces of the lithium supplementing layers of the two sub negative electrode plates provided with the lithium supplementing layers to prepare the negative electrode plate.

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

Positive electrode plate

The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material.

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

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

In some of these embodiments, the positive electrode active material may be a positive electrode active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Wherein, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., liCoO ₂), lithium nickel oxide (e.g., liNiO ₂), lithium manganese oxide (e.g., liMnO ₂、LiMn ₂O ₄), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi _1/3Co _1/3Mn _1/3O ₂ (which may also be abbreviated as NCM ₃₃₃)、LiNi _0.5Co _0.2Mn _0.3O ₂ (which may also be abbreviated as NCM ₅₂₃)、LiNi _0.5Co _0.25Mn _0.25O ₂ (which may also be abbreviated as NCM ₂₁₁)、LiNi _0.6Co _0.2Mn _0.2O ₂ (which may also be abbreviated as NCM ₆₂₂)、LiNi _0.8Co _0.1Mn _0.1O ₂ (which may also be abbreviated as NCM ₈₁₁)), lithium nickel manganese oxide (which may also be abbreviated as NCM ₃₃₃)、LiNi _0.5Co _0.2Mn _0.3O ₂ (which may also be abbreviated as NCM 42 examples of the olivine structured lithium-containing phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (which may also be abbreviated as LFP)), a composite of lithium iron phosphate and carbon, a composite of lithium manganese phosphate (such as LiMnPO ₄), a composite of lithium manganese phosphate and carbon, a composite of lithium manganese phosphate, lithium iron phosphate, and a composite of lithium manganese phosphate and carbon.

In some of these embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluoroacrylate resin.

In some of these embodiments, the positive electrode active material layer may further optionally include 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 of these embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and (3) coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode plate after the procedures of drying, cold pressing and the like.

Electrolyte composition

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The application is not particularly limited in the kind of electrolyte, and may be selected according to the need. For example, the electrolyte may be liquid, gel, or all solid.

In some of these embodiments, the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

In some of these embodiments, the electrolyte salt may 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 difluorooxalato borate, lithium difluorodioxaato phosphate, and lithium tetrafluorooxalato phosphate.

In some of these embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, sulfolane, dimethylsulfone, methylsulfone, and diethylsulfone.

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

Isolation film

In some of these embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known porous separator having good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolating film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some of these embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some of these embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

In some of these embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The exterior package of the secondary battery may also be a pouch type pouch, for example. The material of the flexible bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The shape of the secondary battery is not particularly limited in the present application, and may be cylindrical, square, or any other shape. For example, fig. 5 is a secondary battery 5 of a square structure as one example.

In some of these embodiments, referring to fig. 6, the overpack may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the receiving chamber. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select according to specific practical requirements.

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

Fig. 7 is a battery module 4 as an example. Referring to fig. 7, in the battery module 4, a plurality of secondary batteries 5 may be sequentially arranged in the longitudinal direction of the battery module 4. Of course, the arrangement may be performed in any other way. The plurality of secondary batteries 5 may be further fixed by fasteners.

Alternatively, the battery module 4 may further include a case having an accommodating space in which the plurality of secondary batteries 5 are accommodated.

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

Fig. 8 and 9 are battery packs 1 as an example. Referring to fig. 8 and 9, a battery case and a plurality of battery modules 4 disposed in the battery case may be included in the battery pack 1. 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 and forms a closed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

In addition, the application also provides an electric device which comprises at least one of the secondary battery, the battery module or the battery pack. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, boats and ships, and satellites, energy storage systems, and the like. The mobile device may be, for example, a mobile phone, a notebook computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf car, an electric truck, or the like, but is not limited thereto.

As the electricity consumption device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirements thereof.

Fig. 10 is 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 by the power consumption device, a battery pack or a battery module may be employed.

As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Examples

Hereinafter, embodiments of the present application are described. The following examples are illustrative only and are not to be construed as limiting the application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Preparing a negative electrode plate:

(1) And mixing and dispersing the negative electrode active material graphite, silicon oxide, a conductive agent carbon nano tube and a binder styrene-butadiene rubber in deionized water according to a mass ratio of 67:30:1:2, coating the obtained negative electrode slurry on a copper foil on one side, drying, and carrying out cold pressing and parting to obtain a single-sided negative electrode plate.

(2) And uniformly punching holes on the surface of the copper foil of the single-sided negative electrode plate, which is not coated with the negative electrode slurry, according to the preset area occupation ratio of the through holes and the aperture of the through holes, wherein the depth of the holes is equal to the thickness of the copper foil.

(3) Mixing and dispersing an ion conductor material LLZO, a conductive agent superconducting carbon and a binder polyvinylidene fluoride in a mass ratio of 80:10:10 in NMP to prepare buffer layer slurry, coating the buffer layer slurry on the surface of the copper foil, which is not coated with the cathode slurry, through gravure printing, drying, and cold pressing to prepare a buffer layer, wherein the porosity of the buffer layer is 25%, so as to obtain the sub-cathode pole piece.

(4) A metallic lithium layer having a thickness of 12 μm (bulk density of 0.534g/cm ³) was prepared on the surface of the buffer layer remote from the copper foil by means of lithium tape casting.

(5) And (3) taking two sub negative electrode pieces with metal lithium layers treated in the step (4), and attaching the metal lithium layers to each other to obtain the negative electrode piece.

Preparing a positive electrode plate:

And (3) coating a slurry single-sided obtained by mixing and dispersing an anode active material LiNi _0.8Co _0.1Mn _0.1O ₂ (also can be simply called NCM ₈₁₁), a conductive agent superconducting carbon and a binder polyvinylidene fluoride on NMP according to a mass ratio of 96:2:2 on an aluminum foil, drying, and carrying out cold pressing and slitting to obtain the anode plate.

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

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

Preparation of a secondary battery:

And preparing a bare cell according to the sequential lamination of the positive electrode plate/the isolating film/the double-sided negative electrode plate/the isolating film/the positive electrode plate, assembling the bare cell with the top cover and the shell after hot pressing, injecting electrolyte, and performing the processes of formation, exhaust, sealing, testing and the like to obtain the secondary battery.

Examples 2 to 6:

Examples 2 to 6 differ from example 1 in the buffer layer thicknesses of examples 2 to 6.

Examples 7 to 12:

Examples 7 to 12 differ from example 2 in that the buffer layer porosities of examples 7 to 12 are different.

Examples 13 to 17:

examples 13 to 17 differ from example 2 in the content of the ion conductor material in the buffer layers of examples 13 to 17.

In example 13, the mass ratio of the ion conductor material LLZO, the conductive agent superconducting carbon, and the binder polyvinylidene fluoride was 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 was 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 was 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 was 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 was 95:2.5:2.5.

Examples 18 to 23:

Examples 18 to 23 are different from example 2 in that the through holes of examples 18 to 23 have different area ratios on the current collector.

Examples 24 to 28:

Examples 24 to 28 are different from example 2 in that the through hole diameters of examples 24 to 28 are different.

Example 29:

Example 29 differs from example 1 in that the ion conductor material of the buffer layer of example 29 is different.

Example 30:

Example 30 differs from example 29 in that the buffer layer porosity of example 30 is different.

Example 31:

example 31 differs from example 30 in that the buffer layer thickness of example 31 is different.

Example 32:

Embodiment 32 differs from embodiment 31 in that the area ratio of the through holes of embodiment 32 on the current collector is different.

Example 33:

Example 33 differs from example 32 in that the thickness of the metallic lithium layer of example 33 is different.

Example 34:

embodiment 34 differs from embodiment 1 in that the first buffer layer and the second buffer layer have different compositions, wherein 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.

Example 35:

Example 35 is substantially identical to the negative electrode tab structure of example 1, except that the second current collector in example 35 is a copper foil without a through hole without a punching process; the first current collector is the same as the current collector of example 1.

Examples 36 to 38:

Examples 36 to 38 are different from example 1 in that the negative electrode active material is artificial graphite, and accordingly, the structural composition of the negative electrode tab is also different.

Examples 39 to 41:

Examples 39 to 41 differ from examples 36 to 38 in that the positive electrode active material was lithium iron phosphate (LFP), and correspondingly, the structural composition of the negative electrode sheet was also different.

Comparative example 1:

comparative example 1 differs from example 1 in that the negative electrode tab was obtained by bonding the copper foil of example 1, step (1), from which the negative electrode tab was prepared.

Comparative example 2:

Comparative example 2 differs from example 1 in that the buffer layer was omitted in the negative electrode tab.

Comparative example 3:

comparative example 3 differs from example 36 in that the negative electrode tab was obtained by lamination of the copper foil of example 7, step (1), from which the negative electrode tab was prepared.

Comparative example 4:

Comparative example 4 differs from example 36 in that the buffer layer was omitted in the negative electrode tab.

Comparative example 5:

comparative example 5 differs from example 39 in that the negative electrode tab was obtained by bonding the copper foil of the negative electrode tab prepared in step (1) of example 9.

Comparative example 6:

Comparative example 6 differs from example 39 in that the buffer layer was omitted in the negative electrode tab.

In the secondary batteries of examples 1 to 41 and comparative examples 1 to 6, the structural composition of the negative electrode tab is shown in table 1.

Table 1 structural compositions of negative electrode sheets of examples 1 to 41 and comparative examples 1 to 6

Note that: without special description, the first buffer layer and the second buffer layer of the negative electrode sheet of the embodiment in table 1 are the same, and the first current collector and the second current collector are the same.

Test part:

And (3) lithium supplementing amount test: in the environment with RH less than 2%, taking fresh battery cells for disassembly, scraping samples in unit area in a lithium supplementing layer between two negative electrode current collectors, weighing, and calculating the lithium supplementing quantity in unit area of the negative electrode pole piece.

And (3) testing the cycle performance: at 25 ℃, the lithium ion battery is charged to 4.25V (NCM 811) or 3.65V (LFP) at 0.5C rate and then charged at constant voltage until the current is lower than 0.05C, then discharged to 2.5V using 1C rate, and the cycle test is performed in such a full charge discharge form until the discharge capacity of the lithium ion battery is attenuated to 80% of the initial capacity, and the number of cycles at this time is recorded.

Self-discharge drop test: and fully charging the battery core, standing for 1 day, connecting the anode and the cathode of the secondary battery through an electrochemical workstation (or a universal meter), recording an open-circuit voltage V1, and recording an open-circuit voltage V2 after standing for 2 days, wherein the self-discharge voltage drop is obtained through the following calculation, and the unit mV/h.

The cycle performance and self-discharge pressure drop of the secondary batteries of examples 1 to 12 and comparative examples 1 to 6 are recorded in table 2.

Sequence number	Cycle number	Self-discharge voltage drop (mV/h)
Example 1	1164	0.165
Example 2	1485	0.078
Example 3	1327	0.075
Example 4	1186	0.074
Example 5	982	0.072
Example 6	903	0.07
Example 7	1295	0.093
Example 8	1369	0.086
Example 9	1457	0.079
Example 10	1438	0.071
Example 11	1382	0.064

Example 12	1301	0.061
Example 13	1286	0.062
Example 14	1317	0.063
Example 15	1425	0.074
Example 16	1352	0.093
Example 17	1267	0.118
Example 18	1173	0.058
Example 19	1296	0.062
Example 20	1425	0.066
Example 21	1483	0.072
Example 22	1251	0.149
Example 23	1086	0.201
Example 24	1579	0.057
Example 25	1431	0.082
Example 26	1309	0.095
Example 27	1176	0.131
Example 28	1042	0.173
Example 29	1276	0.068
Example 30	1193	0.065
Example 31	1089	0.062
Example 32	956	0.057
Example 33	904	0.056
Example 34	1210	0.082
Example 35	1134	0.146
Example 36	3381	0.051
Example 37	3176	0.049
Example 38	2459	0.045
Example 39	5493	0.038
Example 40	5186	0.037
Example 41	4075	0.032
Comparative example 1	716	0.073
Comparative example 2	869	0.379
Comparative example 3	2097	0.046
Comparative example 4	2286	0.154

Comparative example 5	3582	0.035
Comparative example 6	3743	0.097

As can be seen from the data relating to Table 2, the secondary batteries of comparative examples 1 to 2 had 716 and 869 cycles and had self-discharge voltage drops of 0.073mV/h and 0.379mV/h. The secondary batteries of examples 1 to 35 had a cycle number of 903 to 1579 and a self-discharge voltage drop of 0.056mV/h to 0.201mV/h. As can be seen from the comparison of examples 1 to 35 with comparative example 1, the cycle performance of the secondary batteries of examples 1 to 35 is significantly improved relative to the secondary battery without the lithium supplementing layer; as can be seen from comparison with the secondary battery of comparative example 2 without the buffer layer, the buffer layers of examples 1 to 35 can reduce the self-discharge voltage drop of the secondary battery, and prevent the lithium from being separated from the surface of the negative electrode sheet by the lithium supplementing layer, thereby avoiding deterioration of the secondary battery and having better cycle performance.

As can be seen from examples 1 to 6, the secondary battery was more excellent in cycle performance when the thickness of the buffer layer was 3 μm to 7. Mu.m.

In examples 7 to 12, the porosity of the buffer layer is different from that of example 2, the difference in the porosity of the buffer layer causes the self-discharge voltage drop and the cycle number of the secondary battery, and in examples 2 and examples 9 to 10, the cycle number is larger and is more than 1400, so that the effect of controlling the porosity of the buffer layer to be 20 to 40 percent and improving the cycle life of the secondary battery is better. The buffer layer ion conductor material contents of examples 13 to 17 were different from example 2. As can be seen from the data in Table 2, the mass content of the buffer material is 70% -80%, and the cycle performance of the secondary battery is better. The area ratio of the through holes of examples 18 to 23 on the current collector is different from that of example 2. The through hole area ratio of examples 22-23 is 20% -30%, the lithium supplementing speed is high, and the self-discharge voltage drop is higher than that of examples 2 and 18-21. The through hole area ratio of example 18 was 0.1%, the lithium supplementing rate was slow, the self-discharge voltage drop was small, but the number of cycles was smaller than examples 2, 19 to 22. Thus, the through hole area ratio is 2% -15%, and the secondary battery cycle performance is better. The via hole diameters of examples 24 to 28 are different from example 2. As can be seen from the data in Table 2, the pore diameters of the through holes were 30 μm to 200. Mu.m, and the secondary battery cycle performance was better. The battery systems of examples 36 to 38 and 38 to 41 are different from examples 1 to 35, and compared with comparative examples 3 to 6, which do not contain a lithium supplementing layer or a buffer layer, the secondary batteries of examples 36 to 41 have a low self-discharge voltage drop, and can avoid micro-short circuit caused by lithium precipitation of the lithium supplementing layer on the surface of the negative electrode tab, thereby avoiding deterioration of the secondary battery and having a better cycle life.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.

Claims

The negative electrode plate comprises a first negative electrode active material layer, a first current collector, a lithium supplementing layer, a second current collector and a second negative electrode active material layer which are sequentially stacked; the negative electrode piece further comprises a buffer material;

At least one of the first current collector and the second current collector is provided with a through hole; the buffer material is filled in at least one of the through holes of the first current collector and the through holes of the second current collector.
The negative electrode tab of claim 1, further comprising a first buffer layer disposed between the first current collector and the lithium-compensating layer and partially embedded in the through-hole of the first current collector such that the buffer material fills in the through-hole of the first current collector;

and/or, the negative electrode plate further comprises a second buffer layer, wherein the second buffer layer is arranged between the second current collector and the lithium supplementing layer and is partially embedded into the through hole of the second current collector, so that the buffer material is filled in the through hole of the second current collector.
The negative electrode tab of claim 2, wherein the first buffer layer has a thickness of 3-10 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 3-10 μm; optionally, the thickness of the second buffer layer is 3 μm to 7 μm.
The negative electrode tab of claim 2 or 3, wherein the first buffer layer and the second buffer layer have lithium ion conductivity.
The negative electrode tab of any one of claims 2-4, wherein the first buffer layer and the second buffer layer each comprise an ion conductor material;

Optionally, the ion conductor material comprises at least one of an ion conductor polymer, an ion conductor oxide, an ion conductor sulfide, and an ion conductor halide.
The negative electrode tab of claim 5, wherein the ion conductor material has an ionic conductivity of 10 ^-9S/cm ²～10 ^-2S/cm ².
The negative electrode tab of claim 5 or 6, wherein the ion conductor polymer is selected from at least one of polyethylene oxide, polyvinylidene fluoride, and polyanion conductor polymer;

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

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

optionally, the first buffer layer and the second buffer layer have a porosity of 20% -40%.
The negative electrode tab according to any one of claims 1 to 9, wherein the total area occupied by the through holes of the first current collector is 0.1% to 30% over the area on the first current collector;

optionally, the area ratio of the total area occupied by the through holes of the first current collector on the first current collector is 2% -15%.
The negative electrode tab according to any one of claims 1 to 10, wherein the area ratio of the through hole of the second current collector on the second current collector is 0.1% to 30%;

optionally, the area ratio of the through hole of the second current collector on the second current collector is 2% -15%.
The negative electrode tab according to any one of claims 1 to 11, wherein the maximum aperture of the through-hole of the first current collector and/or the second current collector is 5 μm to 1mm;

Optionally, the maximum aperture of the through hole of the first current collector and/or the second current collector is 30-200 μm.
The preparation method of the negative electrode plate comprises the following steps:

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

punching the current collector from a surface of the current collector remote from the anode active material layer to form a through hole;

Coating buffer material slurry on the surface of the current collector, which is far away from the negative electrode active material layer, so that the buffer material fills the through holes to obtain sub-negative electrode pieces;

and preparing a lithium supplementing layer on the surface of the buffer material of at least one of the sub negative pole pieces, and attaching the surface of the sub negative pole piece provided with the lithium supplementing layer to the surface of the buffer material of the other sub negative pole piece by the surface of the lithium supplementing layer to prepare the negative pole piece.
A secondary battery comprising the negative electrode tab according to any one of claims 1 to 12 or a negative electrode tab produced by the method for producing a negative electrode tab according to claim 13.
The secondary battery according to claim 14, wherein the negative electrode tab includes a first buffer layer and a second buffer layer; the secondary battery includes a positive electrode active material and a negative electrode active material; the first coulombic efficiency of the positive electrode active material is more than 90%, and the first coulombic efficiency of the negative electrode active material is more than 90%; the thickness of the first buffer layer is 4-7 mu m; the thickness of the second buffer layer is 4-7 mu m;

or the first coulombic efficiency of the positive electrode active material is less than or equal to 90 percent, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90 percent; the thickness of the first buffer layer is 3-5 mu m; the thickness of the second buffer layer is 3-5 μm.
The secondary battery according to claim 14, wherein the negative electrode tab includes a first buffer layer and a second buffer layer; the secondary battery includes a positive electrode active material and a negative electrode active material; the first coulombic efficiency of the positive electrode active material is more than 90%, and the first coulombic efficiency of the negative electrode active material is more than 90%; the ionic conductivity of the ionic conductor material is 10 ^-9S/cm ²～10 ^-5S/cm ²;

Or the first coulombic efficiency of the positive electrode active material is less than or equal to 90 percent, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90 percent; the ionic conductivity of the ion conductor material is 10 ^-6S/cm ²～10 ^-2S/cm ².
The secondary battery according to claim 14, wherein the negative electrode tab includes a first buffer layer and a second buffer layer; the secondary battery includes a positive electrode active material and a negative electrode active material; the first coulombic efficiency of the positive electrode active material is more than 90%, and the first coulombic efficiency of the negative electrode active material is more than 90%; the porosity of the first buffer layer and the second buffer layer is 30% -40%;

Or the first coulombic efficiency of the positive electrode active material is less than or equal to 90 percent, and/or the first coulombic efficiency of the negative electrode active material is less than or equal to 90 percent; the porosity of the first buffer layer and the second buffer layer is 20% -30%.
A battery module comprising the secondary battery according to any one of claims 14 to 17.
A battery pack comprising 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 comprising at least one selected from 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.