Negative electrode sheet, secondary battery, and electrical device

Abstract

This application discloses a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is provided on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and an additive having compression and repulsion characteristics. After a pressure X is applied in the thickness direction of the negative electrode sheet, the repulsion rate of the negative electrode sheet is 2% to 40%, and the compression rate of the negative electrode sheet is 2% to 40%. The pressure X satisfies 0.3 Mpa ≤ X ≤ 5 Mpa.

Description

Technical Field

[0001] Cross - reference to Related Applications This disclosure claims the priority and benefit of Chinese Patent Application No. 202210708415.9, entitled "NEGATIVE ELECTRODE SHEET AND APPLICATION THEREFOR", filed on June 21, 2022. The entire content of the above application is incorporated herein by reference.

[0002] This disclosure belongs to the field of batteries, and more particularly, relates to a negative electrode sheet, a secondary battery, and an electrical device.

Background Art

[0003] As the demand for electric vehicles with a long cruising range in the market is gradually increasing, the need to further improve the energy density of power batteries has become increasingly urgent. A battery with a high energy density cannot be achieved without the development of a negative electrode sheet with a high energy density. Currently, the main methods for improving the storage capacity of the negative electrode sheet are to add a certain proportion of silicon negative electrode material to the graphite negative electrode, and further to adopt a lithium metal negative electrode. Both the silicon negative electrode and the lithium metal negative electrode have a serious problem that their volume expands during cycling. In most battery usage scenarios, since the battery needs to operate within a fixed space, excessive volume expansion, on the one hand, brings bottleneck problems to the battery pack process, and on the other hand, uncontrolled volume expansion leads to a rapid deterioration of the battery's cycle performance. When a battery made of a high - capacity negative electrode is charged, lithium ions enter the negative electrode and the volume of the battery expands. During the discharge of the battery, as lithium ions move from the negative electrode and are embedded in the positive electrode, the volume of the battery gradually decreases. Therefore, during each charge - discharge cycle process of the battery, the thickness of the battery undergoes a process in which the volume gradually increases and then gradually decreases. This process is particularly prominent in lithium - metal batteries and silicon - negative - electrode batteries. We call this periodic change in volume "battery breathing".

[0004] When the volume of the battery pack body is fixed due to the significant "breathing effect" during the cycling of a battery fabricated by using a high-capacity negative electrode, the pressure exerted by the battery on the pack body periodically increases and decreases due to the volume expansion of the battery core during the charge-discharge process. The non-uniform change in the pressure generated by the battery core does not contribute to the good cycle performance of the battery and leads to the rapid deterioration of the cycle of the high-capacity negative electrode. In addition, the significant volume change of the high-capacity negative electrode during cycling, i.e., the significant volume expansion of the negative electrode sheet during charging to the significant volume contraction during discharging, on the one hand, worsens the physical contact between the active particles of the negative electrode sheet, resulting in the inactivation of the material, and on the other hand, the significant volume change of the electrode sheet poses a major challenge to the extensibility and fatigue resistance of the diaphragm. All these lead to the degradation of battery performance.

[0005] Therefore, the conventional negative electrode sheet needs to be improved.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present disclosure aims to solve at least to some extent one of the technical problems in the related art. Therefore, an object of the present disclosure is to provide a negative electrode sheet and its use. The negative electrode sheet has a low volume change rate during the cycling of the battery, and on the other hand, has good physical contact between the negative active material particles of the negative electrode sheet, thereby ensuring the volume stability of the battery core in a single battery cycle process and simultaneously improving the cycle performance of the battery.

Means for Solving the Problems

[0007] According to one aspect of the present disclosure, the present disclosure provides a negative electrode sheet. According to an embodiment of the present disclosure, the negative electrode sheet a negative electrode current collector, a negative electrode active material layer disposed on the surface of the negative electrode current collector and containing a negative electrode active material and an additive having compression and repulsion characteristics, and includes.

[0008] After pressure X is applied in the thickness direction of the negative electrode sheet, the rebound rate of the negative electrode sheet is 2% to 40%, and the compression rate of the negative electrode sheet is 2% to 40%. Pressure X satisfies 0.3 Mpa ≤ X ≤ 5 Mpa.

[0009] According to the negative electrode sheet of an embodiment of the present disclosure, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material and an additive having compression and repulsion characteristics. Since the additive having compression and repulsion characteristics in the negative electrode active material layer has compression and repulsion characteristics, the negative electrode active material layer exhibits compression and repulsion characteristics. During charging, as lithium is embedded in the negative electrode, the volume of the negative electrode active material gradually increases, and the thickness of the negative electrode active material layer increases. Under the condition that the volume of the battery pack or the battery housing is fixed, the pressure from the outside (for example, the pack body and the housing) supported by the battery core increases. At this time, under the action of the pressure, the volume of the additive having compression and repulsion characteristics in the negative electrode active material layer contracts under the action of the pressure, releasing some space to the active material, thereby buffering the significant volume expansion of the active material during lithium embedding and suppressing the significant volume expansion of the negative electrode active material layer during lithium embedding. During discharging, as lithium ions are released, the volume of the active material of the negative electrode sheet decreases. The pressure generated by the battery core is reduced or even eliminated. The volume of the additive having compression and repulsion characteristics rebounds and gradually recovers to the initial volume, occupying the space released by the volume contraction of the active material, thereby buffering the volume contraction caused by the lithium release of the active material in the negative electrode active material layer. Therefore, the negative electrode active material layer having compression and repulsion characteristics can buffer the large volume change of the negative electrode sheet during charge and discharge. On the other hand, the additive having compression and repulsion characteristics in the negative electrode active material layer can ensure good physical contact between the negative electrode active material particles in the negative electrode active material layer and avoid the inactivation of the material. Therefore, since the negative electrode sheet has the function of elastically changing its volume and self-recovering, the negative electrode sheet has a relatively low volume change rate during the cycle of the battery. On the other hand, the physical contact between the negative electrode active material particles in the negative electrode sheet is good, thereby ensuring the volume stability of the battery core during a single battery cycle and simultaneously improving the cycle performance of the battery.

[0010] Furthermore, the negative electrode sheet according to the foregoing embodiment of the present disclosure can further have the following additional technical features.

[0011] In some embodiments of the present disclosure, the thickness of one side of the negative electrode active material layer is 10 μm to 150 μm. Therefore, the cycle stability performance of the battery can be improved.

[0012] In some embodiments of the present disclosure, the mass ratio of the negative electrode active material to the additive having compression and repulsion characteristics is 100:3 to 50. Therefore, the volume change rate of the negative electrode sheet during a single charge-discharge cycle can be reduced.

[0013] In some embodiments of the present disclosure, the mass ratio of the negative electrode active material to the additive having compression and repulsion characteristics is 100:3 to 30. Therefore, the volume change rate of the negative electrode sheet during a single charge-discharge cycle can be reduced.

[0014] In some embodiments of the present disclosure, the negative electrode active material includes at least one of graphite, hard carbon, Si, SiO x , silicon-carbon material Si / C, Sn, Sb, silicon-based alloy, lithium silicon oxide, or silicon magnesium oxide. The silicon-based alloy further includes at least one of Li, Al, Mg, B, Ni, Fe, Cu, or Co in addition to Si, and the value of x is 0 < x < 2. According to an embodiment of the present disclosure, the negative electrode active material layer further includes a binder. The binder includes at least one of polyacrylic acid, sodium alginate, or polyimide. The mass ratio of the negative electrode active material to the binder is 100:0.05 to 15.

[0015] In some embodiments of the present disclosure, the additive having compression and repulsion characteristics is three-dimensional graphene. Therefore, the negative electrode sheet has a function of elastically changing its volume and self-recovering, and reduces the volume change rate of the negative electrode sheet during a single charge-discharge cycle.

[0016] In some embodiments of the present disclosure, the three-dimensional graphene satisfies at least one of the following conditions (1) to (5): (1) the particle size of the three-dimensional graphene is 500 nm to 20 μm; (2) the pore volume of the three-dimensional graphene is 1 cm 3 / g to 10 cm 3 / g; (3) the three-dimensional graphene includes overlapping graphene sheets, and the breaking strength between the graphene sheets is 20 N / m to 50 N / m; (4) the three-dimensional graphene includes overlapping graphene sheets, and the lateral dimension of the graphene sheet is 10 nm to 100 nm; or (5) the average pore diameter of the three-dimensional graphene is 250 nm or less.

[0017] In some embodiments of the present disclosure, the lateral dimension of the graphene sheet is 10 nm to 20 nm.

[0018] In some embodiments of the present disclosure, the negative electrode active material layer further includes a conductive agent.

[0019] In some embodiments of the present disclosure, the mass ratio of the negative electrode active material to the conductive agent is 100:0 to 2.5.

[0020] In some embodiments of the present disclosure, the conductive agent includes at least one of single-walled carbon nanotubes or carbon black.

[0021] According to a second aspect of the present disclosure, the present disclosure provides a secondary battery. The secondary battery includes the aforementioned negative electrode sheet. Therefore, the secondary battery has excellent cycle stability performance.

[0022] According to a third aspect of the present disclosure, the present disclosure provides an electrical device. The electrical device has the aforementioned lithium battery.

[0023] The advantages of the embodiments of the present disclosure are partially described in the following specification. Some of them are obvious from the present specification, or may be acquired through the implementation manners of the embodiments of the present disclosure.

[0024] The accompanying drawings are intended to provide a further understanding of the present disclosure, constitute a part of this specification, and are used to explain the present disclosure together with the following specific embodiments, but do not constitute a limitation to the present disclosure.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0026] The embodiments of the present disclosure are described in detail below, are intended to explain the present disclosure, and should not be understood as a limitation to the present disclosure.

[0027] According to one aspect of the present disclosure, the present disclosure provides a negative electrode sheet. According to an embodiment of the present disclosure, referring to FIG. 1, the negative electrode sheet includes a negative electrode current collector 100 and a negative electrode active material layer 200.

[0028] It should be noted that those skilled in the art can select the material of the negative electrode current collector 100 according to actual needs, for example, using a copper foil.

[0029] According to an embodiment of the present disclosure, the negative electrode active material layer 200 is disposed on the surface of the negative electrode current collector 100, and the negative electrode active material layer 200 includes a negative electrode active material and an additive having compression and repulsion characteristics. After the pressure X is applied in the thickness direction of the negative electrode sheet, the repulsion rate of the negative electrode sheet is 2% to 40%, and the compression rate of the negative electrode sheet is 2% to 40%. The pressure X satisfies 0.3 Mpa ≤ X ≤ 5 Mpa. For example, the repulsion rate of the negative electrode sheet is 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc. The compression rate of the negative electrode sheet is 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc. The pressure X satisfies 0.3 Mpa, 0.5 Mpa, 0.8 Mpa, 1 Mpa, 1.5 Mpa, 2 Mpa, 2.5 Mpa, 3 Mpa, 3.5 Mpa, 4 Mpa, 4.5 Mpa, 5 Mpa, etc.

[0030] The inventor has found that an additive having compression and repulsion characteristics in the negative electrode active material layer 200 has compression and repulsion characteristics, and as a result, the negative electrode active material layer 200 exhibits compression and repulsion characteristics. During charging, as lithium is embedded in the negative electrode, the volume of the negative electrode active material gradually increases, and the thickness of the negative electrode sheet increases. In a situation where the volume of the battery pack or the battery housing is fixed, the pressure from the outside (e.g., the pack body and the housing) generated by the battery core increases. At this time, under the action of the pressure, the volume of the additive having compression and repulsion characteristics in the negative electrode active material layer 200 shrinks, releasing some space to the active material, thereby buffering the significant volume expansion of the active material during lithium embedding. During discharging, as lithium ions are released, the volume of the negative electrode active material is reduced. At this time, the external pressure generated by the battery core is reduced and even eliminated. The volume of the additive having compression and repulsion characteristics rebounds and occupies the space released by the volume contraction of the active material, thereby buffering the volume contraction caused by the lithium release of the active material in the negative electrode active material layer 200. On the other hand, the volume of the additive having compression and repulsion characteristics in the negative electrode active material layer 200 rebounds during discharging, which can ensure good physical contact between the negative electrode active material particles in the negative electrode active material layer and avoid the inactivation of the material.

[0031] In some embodiments of the present disclosure, the thickness of one side of the aforementioned negative electrode active material layer 200 is 10 μm to 150 μm, for example, 10 μm, 15 μm, 20 μm, 25 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm.

[0032] The coating layer of the negative electrode sheet may be coated on one side of the current collector or on both sides of the current collector. Therefore, when the coating layer is coated on one side of the current collector, the "thickness of one side" in the present disclosure refers to the thickness of the negative electrode active material layer 200 on the coated side. When the coating layer is coated on both sides of the current collector, the "thickness of one side" in the present disclosure refers to the thickness of the negative electrode active material layer 200 of the coating layer on either one of the two sides.

[0033] In some embodiments of the present disclosure, the mass ratio of the negative electrode active material to the additive having compression and repulsion characteristics is 100:3 to 50, for example, 100:5 to 45, 100:10 to 40, 100:15 to 35, 100:20 to 30, 100:25 to 30. The inventor has found that when the addition amount of the binder is too large, not only the cost increases, the energy density of the battery core decreases, but also the polarization of the battery increases and the internal resistance of the battery increases. When the addition amount of the binder is too small, during the cycling of the battery, in the process where expansion and contraction are repeated due to the high-capacity negative electrode active material, electrode pulverization is caused, and the cycle performance rapidly decreases. When the addition amount of the additive having compression and repulsion characteristics is too large, not only the cost increases, but also the energy density of the battery decreases. When the addition amount of the additive having compression and repulsion characteristics is too small, good compression and repulsion characteristics of the electrode sheet cannot be achieved. Therefore, by adding the additive having compression and repulsion characteristics in the aforementioned ratio to the negative electrode active material layer 200, the cycle stability of the battery can be improved while reducing the cost. In some embodiments of the present disclosure, the mass ratio of the negative electrode active material to the additive having compression and repulsion characteristics is 100:3 to 30.

[0034] In some embodiments of the present disclosure, the negative electrode active material is graphite, hard carbon, Si, SiO xIt contains at least one of silicon-carbon materials Si / C, Sn, Sb, silicon-based alloys, lithium silicon oxides, or silicon magnesium oxides. The silicon-based alloy further contains at least one of Li, Al, Mg, B, Ni, Fe, Cu, or Co in addition to Si, and the value of x satisfies 0 < x < 2.

[0035] In some embodiments of the present disclosure, the additive having compression and rebound properties is three-dimensional graphene. Three-dimensional graphene has good compression and rebound properties as well as electrical conductivity and can play a part of the role of a conductive agent. On the other hand, three-dimensional graphene has lithium affinity. In a highly lithium-rich negative electrode sheet, lithium is induced to deposit in the pores of the electrode sheet, which prevents lithium from depositing on the surface of the electrode sheet and reduces the volume expansion of the negative electrode sheet during lithium deposition.

[0036] In some embodiments of the present disclosure, the three-dimensional graphene satisfies at least one of the following conditions (1) to (5). (1) The particle size of the three-dimensional graphene is 500 nm to 20 μm, for example, 1 μm to 20 μm, 3 μm to 18 μm, 5 μm to 15 μm, 7 μm to 13 μm, 10 μm to 12 μm, etc. (2) The pore volume of the three-dimensional graphene is 1 cm 3 / g to 10 cm 3 / g, for example, 3 cm 3 / g to 8 cm 3 / g, 5 cm 3 / g to 7 cm 3 / g, etc. (3) The three-dimensional graphene contains overlapping graphene sheets, and the breaking strength between the graphene sheets is 20 N / m to 50 N / m, for example, 25 N / m to 45 N / m, 30 N / m to 45 N / m, 35 N / m to 45 N / m, 40 N / m to 45 N / m, etc. (4) The three-dimensional graphene includes overlapping graphene sheets, and the lateral dimension of the graphene sheet is from 10 nm to 100 nm, for example, 10 nm to 20 nm, 20 nm to 100 nm, 30 nm to 90 nm, 40 nm to 80 nm, 50 nm to 70 nm, or (5) The average pore diameter of the three-dimensional graphene is 250 nm or less, for example, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 170 nm, 200 nm, 220 nm, 250 nm, etc.

[0037] In some embodiments of the present disclosure, the maximum pore diameter of the three-dimensional graphene is 300 nm.

[0038] The pore volume of the above-mentioned three-dimensional graphene may be measured by performing a nitrogen adsorption method on the three-dimensional graphene. The fracture strength between the above-mentioned graphene sheets may be obtained by performing a nanoindentation test on the overlapping position of the three-dimensional graphene by using an atomic force microscope (AFM). The three-dimensional graphene is fixed to a silicon wafer having small holes formed on its surface. Pressure is applied to the silicon wafer in the small holes by using a probe. The position where the pressure is applied is close to the overlapping position of adjacent graphene sheets. The critical pressure at which the overlapping position of two graphene sheets can be broken is recorded, and the fracture strength at the overlapping position between the graphene sheets is obtained. The above-mentioned lateral dimension of the graphene sheet refers to the length, width, etc. of the graphene sheet, and may be obtained through an electron micrograph of the three-dimensional graphene.

[0039] Specifically, a sufficient pore volume can ensure that the three-dimensional graphene has excellent compression properties. An appropriate pore diameter and the breaking strength between graphene sheets ensure that the three-dimensional graphene has good rebound properties after being compressed and cannot cause structural collapse and loss of rebound properties due to pressure. On the other hand, the compression-rebound characteristics of the battery are stably maintained during the cycling of the battery. The three-dimensional graphene having the above characteristics has excellent compression-rebound performance, so that the fabricated negative electrode active material layer 200 exhibits high compression and rebound characteristics, thereby buffering the significant volume expansion of the negative electrode sheet during charge and discharge.

[0040] In some embodiments of the present disclosure, the aforementioned three-dimensional graphene may be grown by plasma enhanced chemical vapor deposition (PECVD). An exemplary manufacturing method includes the following steps. A mixed gas of a carbon source (e.g., C2H2) and H2 is introduced into a deposition chamber heated to the temperature of a plasma deposition apparatus. A plasma generator is activated to grow a three-dimensional graphene material on a substrate (e.g., Cu) disposed in the deposition chamber by the PECVD method. After the growth of the three-dimensional graphene, auxiliary gases (e.g., Ar and He) are introduced to cool the deposition chamber to room temperature in an inert atmosphere. Thereafter, the obtained sample is taken out of the deposition chamber, the three-dimensional graphene material is peeled off from the substrate, and pulverized to a required particle size. The growth conditions may be adjusted so as to obtain graphene satisfying at least one of the following conditions (1) to (5). (1) The particle size of the three-dimensional graphene is 500 nm to 20 μm. (2) The pore volume of the three-dimensional graphene is 1 cm 3 / g to 10 cm 3 / g. (3) The three-dimensional graphene includes overlapping graphene sheets, and the breaking strength between the graphene sheets is 20 N / m to 50 N / m. (4) The three-dimensional graphene includes overlapping graphene sheets, and the lateral dimension of the graphene sheet is 10 nm to 100 nm, or (5) The average pore diameter of the three-dimensional graphene is 250 nm or less.

[0041] The exemplary fabrication method includes the following steps. A mixed gas of a carbon source (e.g., C2H2) and H2 is introduced into a deposition chamber heated to the temperature of a plasma deposition apparatus. A plasma generator is activated to grow a three-dimensional graphene material on a substrate (e.g., Cu) disposed in the deposition chamber by the PECVD method. After the growth of the three-dimensional graphene, an auxiliary gas (e.g., Ar and He) is introduced, and the deposition chamber is cooled to room temperature in an inert atmosphere. Thereafter, the obtained sample is taken out of the deposition chamber, the three-dimensional graphene material is peeled off from the substrate, and pulverized to the required particle size. In the PECVD process, a large-capacity plasma with a high energy density can be generated, and the carbon source C2H2 is decomposed into many carbon-containing reactive free radicals, whereby the growth of the three-dimensional graphene can be achieved. The inflow rate of C2H2 is 20 mL / min, the inflow rate of H2 is 250 mL / min, the temperature for deposition and growth may be 950 °C, the inflow rate of the auxiliary gas Ar is 200 mL / min, and the operating power of the plasma generator is 300 W.

[0042] According to an embodiment of the present disclosure, the aforementioned negative electrode active material layer 200 further includes a conductive agent, and the mass ratio of the negative electrode active material to the conductive agent is 100:0 to 2.5, for example, 100:0.05 to 2.2, 100:0.1 to 2, 100:0.3 to 1.8, 100:0.5 to 1.5, 100:0.7 to 1.2, 100:1 to 1.2, etc. Therefore, the conductivity of the negative electrode sheet can be improved. Those skilled in the art can select the specific type of conductive agent according to actual needs. For example, it should be noted that the conductive agent includes at least one of single-walled carbon nanotubes and carbon black, and preferably includes single-walled carbon nanotubes, but is not limited thereto.

[0043] In some embodiments of the present disclosure, the aforementioned negative electrode active material layer 200 further includes a binder, and the mass ratio of the negative electrode active material to the binder is 100:0.05 to 15, for example, 100:0.1 to 15, 100:0.2 to 15, 100:0.5 to 15, 100:1 to 15, 100:3 to 15, 100:5 to 15, 100:7 to 15, 100:10 to 15, 100:12 to 15, and the like. Therefore, while the energy density of the battery core is improved, the polarization of the electrode sheet can be reduced.

[0044] Those skilled in the art can select a specific type of binder according to actual needs. It should be noted that, for example, the binder includes, but is not limited to, at least one of polyacrylic acid, sodium alginate, or polyimide. In some embodiments of the present disclosure, the binder includes polyacrylic acid.

[0045] In the present disclosure, a method for testing the repulsive characteristics and compression characteristics of a negative electrode sheet is as follows. A pressure of X1 Mpa is applied to the negative electrode sheet along the thickness direction of the negative electrode sheet, the thickness of the negative electrode sheet under the pressure of X1 Mpa is measured as H1, then the pressure is removed, and after the thickness of the negative electrode sheet is stabilized, the thickness of the negative electrode sheet is measured and denoted as H2. The thickness repulsion rate of the negative electrode sheet is r1 = (H2 - H1) / H1. A pressure of X2 Mpa is applied to the negative electrode sheet with an initial thickness of H3 along the thickness direction of the negative electrode sheet, the thickness of the negative electrode sheet under the pressure of X2 Mpa is measured as H4, and the thickness compression rate of the negative electrode sheet is p = (H3 - H4) / H3. Therefore, the aforementioned "after a pressure X is applied in the thickness direction of the negative electrode sheet, the repulsion rate of the negative electrode sheet is 2% to 40%, the compression rate of the negative electrode sheet is 2% to 40%, and the pressure X satisfies 0.3 Mpa ≤ X ≤ 5 Mpa" means that a pressure X1 Mpa where 0.3 Mpa ≤ X1 ≤ 5 Mpa is applied to the negative electrode sheet along the thickness direction of the negative electrode sheet, the thickness of the negative electrode sheet under the pressure of X1 Mpa is measured as H1, then the pressure is removed, and after the thickness of the negative electrode sheet is stabilized, the thickness of the negative electrode sheet is measured and denoted as H2. The thickness repulsion rate of the negative electrode sheet is r1 = (H2 - H1) / H1, and r1 is in the range of 2% to 40%. To the negative electrode sheet with an initial thickness of H3, a pressure X2 Mpa where 0.3 ≤ X2 ≤ 5 Mpa is applied along the thickness direction of the negative electrode sheet, the thickness of the negative electrode sheet under the pressure of X2 Mpa is measured and denoted as H4. The thickness compression rate of the negative electrode sheet is p = (H3 - H4) / H3, and p is in the range of 2% to 40%. r1 and p may be the same or different, and X1 and X2 may be the same or different, which may be understood accordingly.

[0046] Therefore, since the negative electrode sheet of the present disclosure has the function of elastically changing its volume and self-recovering, the negative electrode sheet has a relatively low volume change rate during the cycling of the battery. On the other hand, the physical contact between the negative electrode active material particles in the negative electrode sheet is good, thereby ensuring the stability of the volume of the battery core during a single battery cycle and simultaneously improving the cycle performance of the battery.

[0047] To facilitate understanding, the method for manufacturing the aforementioned negative electrode sheet will be described below. According to an embodiment of the present disclosure, the method includes the following steps. A negative electrode slurry containing a negative electrode active material and an additive having compression and repulsion characteristics is applied to a negative electrode current collector to form a negative electrode active material layer on the negative electrode current collector, thereby obtaining a negative electrode sheet.

[0048] According to an embodiment of the present disclosure, the aforementioned negative electrode slurry further contains a conductive agent. Therefore, the conductivity of the negative electrode sheet can be improved.

[0049] Therefore, a negative electrode sheet having a function of elastically changing in volume and self-recovering may be manufactured by this method. As a result, the volume expansion rate generated by a single cycle of the battery during charge and discharge can be reduced, and the cycle stability of the battery can be improved. It should be noted that the aforementioned features and advantages described for the negative electrode sheet are applicable to the method for manufacturing the negative electrode sheet, and the description will not be repeated here.

[0050] According to a second aspect of the present disclosure, the present disclosure provides a secondary battery. According to an embodiment of the present disclosure, the secondary battery includes the aforementioned negative electrode sheet. Therefore, since the secondary battery uses the aforementioned negative electrode sheet with high cycle stability, the secondary battery exhibits excellent cycle stability. It should be noted that the aforementioned features and advantages described for the negative electrode sheet and its manufacturing method are applicable to the secondary battery, and the description will not be repeated here.

[0051] According to a third aspect of the present disclosure, the present disclosure provides an electrical device. The electrical device may be a means of transportation such as a vehicle or a ship, or may be a notebook computer, a mobile terminal, etc. According to an embodiment of the present disclosure, the electrical device has the aforementioned secondary battery. Therefore, since the electrical device is equipped with the aforementioned secondary battery with excellent cycle stability, the electrical device has excellent cruising range and safety performance. It should be noted that the aforementioned features and advantages described for the secondary battery are applicable to the electrical device, and the description will not be repeated here.

[0052] The present disclosure will be described below with reference to specific examples. It should be noted that these examples are merely illustrative and are not intended to limit the present disclosure in any way.

[0053] (Example 1) The method for manufacturing the negative electrode sheet included the following.

[0054] A silicon-carbon Si / C negative electrode with a specific capacity of 1250 mAh / g, polyacrylic acid, and three-dimensional graphene were mixed according to a mass ratio of 100:5:8 to prepare a negative electrode slurry. Then, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface density on both sides was the same, and the surface density on one side was 45 g / m 2 (it was), rolled after curing, and a negative electrode active material layer with a single-sided thickness of 32 μm was formed on each of the two sides of the copper foil to obtain a negative electrode sheet.

[0055] The three-dimensional graphene used in Example 1 included overlapping graphene sheets, and the three-dimensional graphene had a porous structure. The average particle size of the three-dimensional graphene was 0.6 μm, the pore volume was 3 cm 3 / g, and the average pore diameter of the porous structure in the three-dimensional graphene was 150 nm. A nanoindentation test was performed via AFM, and a fracture strength of 35 N / m was obtained at the overlapping position of the overlapping graphene sheets in the three-dimensional graphene, and the lateral dimension of the overlapping graphene sheets was 10 nm to 100 nm.

[0056] (Example 2) The difference from Example 1 is that the method for manufacturing the negative electrode sheet includes the following.

[0057] SiO x (x = 1.02), polyacrylic acid, single-walled carbon nanotubes, and three-dimensional graphene were mixed according to a mass ratio of 100:14:0.5:15 to prepare a negative electrode slurry. Then, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface density on both sides was the same, and the surface density on one side was 40 g / m 2It was rolled after curing, and a negative electrode active material layer with a single-sided thickness of 28 μm was formed on each of both sides of the copper foil to obtain a negative electrode sheet. A lithium film with a thickness of 10 microns and the obtained negative electrode sheet were heat-pressed in an inert atmosphere to obtain a lithium-rich negative electrode sheet.

[0058] (Example 3) The difference from Example 1 was as follows. SiO x (x = 1.02), polyacrylic acid, single-walled carbon nanotubes, and three-dimensional graphene were mixed according to a mass ratio of 100:14:0.5:15 to prepare a negative electrode slurry. Then, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface density on both sides was the same, and the surface density on one side was 47.5 g / m 2 It was rolled after curing, and a negative electrode active material layer with a single-sided thickness of 33 μm was formed on each of both sides of the copper foil to obtain a negative electrode sheet.

[0059] (Example 4) The difference from Example 1 was as follows. SiO x (x = 1.02), polyacrylic acid, single-walled carbon nanotubes, and three-dimensional graphene were mixed according to a mass ratio of 70:30:7:0.2:5 to prepare a negative electrode slurry. Then, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface density on both sides was the same, and the surface density on one side was 87 g / m 2 It was rolled after curing, and a negative electrode active material layer with a single-sided thickness of 54 μm was formed on each of both sides of the copper foil to obtain a negative electrode sheet.

[0060] (Example 5) The difference from Example 1 was that the three-dimensional graphene used in Example 5 included overlapping graphene sheets, and the three-dimensional graphene had a porous structure. The average particle size of the three-dimensional graphene was 1.5 μm, and the pore volume was 5 cm 3 / g. The average pore diameter of the porous structure in the three-dimensional graphene was 200 nm. A nanoindentation test was performed via AFM, and a fracture strength of 30 N / m was obtained at the overlapping position of the overlapping graphene sheets in the three-dimensional graphene. The lateral dimension of the overlapping graphene sheets was 10 nm to 100 nm.

[0061] (Example 6) The difference from Example 1 was that a silicon-carbon Si / C negative electrode with a specific capacity of 1250 mAh / g, polyacrylic acid, and three-dimensional graphene were mixed according to a mass ratio of 100:10:47 to prepare a negative electrode slurry, and the surface density on one side of the negative electrode slurry was 62.5 g / m 2 That is, the same surface capacity as in Example 1 was maintained.

[0062] (Example 7) The difference from Example 1 was that the average particle size of the three-dimensional graphene was 12 μm, the pore volume was 11 cm 3 / g, and the average pore diameter of the porous structure in the three-dimensional graphene was 150 nm. A nanoindentation test was performed via AFM, and a fracture strength of 20 N / m was obtained at the overlapping position of the overlapping graphene sheets in the three-dimensional graphene.

[0063] (Comparative Example 1) The method for manufacturing the negative electrode sheet included the following.

[0064] A silicon-carbon Si / C negative electrode with a specific capacity of 1250 mAh / g and polyacrylic acid were mixed according to a mass ratio of 100:5 to prepare a negative electrode slurry. Then, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface densities on both sides were the same, and the surface density on one side was 41.5 g / m 2 That is, the same surface capacity as in Example 1 was maintained), rolled after curing, and a negative electrode active material layer with a thickness of 30 μm on one side was formed on each of the two sides of the copper foil to obtain a negative electrode sheet.

[0065] (Comparative Example 2) The method for manufacturing the negative electrode sheet included the following.

[0066] SiO x (x = 1.02), polyacrylic acid, and single-walled carbon nanotubes were mixed according to a mass ratio of 100:14:0.5 to prepare a negative electrode slurry. Next, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface density on both sides was the same, and the surface density on one side was 35.4 g / m 2 (and the same surface capacity as in Example 2 was maintained), and after curing, it was rolled to form a negative electrode active material layer with a thickness of 25 μm on each side of the copper foil to obtain a negative electrode sheet. A lithium film with a thickness of 10 μm and the obtained negative electrode sheet were hot-pressed in an inert atmosphere to obtain a lithium-rich negative electrode sheet.

[0067] (Comparative Example 3) The method for manufacturing the negative electrode sheet included the following.

[0068] A silicon-carbon Si / C negative electrode sheet with a specific capacity of 1250 mAh / g, polyacrylic acid, and three-dimensional graphene were mixed according to a mass ratio of 100:5:2.5 to prepare a negative electrode slurry. Next, the negative electrode slurry was coated on both sides of a copper foil with a thickness of 8 μm (the surface density on both sides was the same, and the surface density on one side was 42 g / m 2 (and the same surface capacity as in Example 1 was maintained), and after curing, it was rolled to form a negative electrode active material layer with a thickness of 30 μm on each side of the copper foil to obtain a negative electrode sheet. The three-dimensional graphene in Comparative Example 3 was the same as that in Example 1.

[0069] (Comparative Example 4) The difference between Comparative Example 4 and Example 2 was that SiO x (x = 1.02), polyacrylic acid, single-walled carbon nanotubes, and three-dimensional graphene were mixed according to a mass ratio of 100:14:0.5:55 to prepare a negative electrode slurry.

[0070] (Fabrication of a battery for specific capacity test) The battery was assembled by using the negative electrode sheet, polyethylene (PE) diaphragm, and 100-μm-thick lithium foil fabricated in various examples and comparative examples, and 1 mol / L LiPF6 functioning as an electrolyte, where ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were in a volume ratio of 1:1, and the battery was charged and discharged between 0.005 V and 1.5 V.

[0071] (Fabrication of Batteries for Cycle Tests) NCM811, polyvinylidene fluoride (PVDF) functioning as a binder, and conductive agent Sup-P were mixed according to a mass ratio of 100:3:1 to prepare a mixed slurry, and the mixed slurry was coated on the surface of an aluminum foil according to a surface density of 225 g / m 2 to fabricate a negative electrode sheet. Subsequently, the fabricated positive electrode sheet, the negative electrode sheets or lithium-rich negative electrode sheets obtained in various examples and comparative examples, the PE diaphragm, and 1 mol / L LiPF6 functioning as an electrolyte were used to assemble the battery, where EC and EMC were in a volume ratio of 1:1. The cycle performance of the corresponding batteries was tested.

[0072] (Initial Charge-Discharge Specific Capacity Test of Negative Electrode) The battery was discharged to 0.005 V at a constant current of 0.1 C, then discharged to 0.005 V at a constant current of 0.05 C, and then charged to 1.5 V at 0.1 C. The initial discharge specific capacity of the negative electrode = discharge capacity / total mass of the negative electrode active material layer, and the initial charge specific capacity of the negative electrode = charge capacity / total mass of the negative electrode active material layer.

[0073] (Capacity Retention Rate Test) The battery was first charged to 4.25 V at 0.5 C, then charged at a constant voltage of 4.25 V until the cut-off current reached 0.1 C, and then discharged to 2.5 V at 1 C for 300 cycles. The initial discharge capacity and the discharge capacity after 300 cycles were recorded. The capacity retention rate = discharge capacity after 300 cycles / initial discharge capacity. The test results are shown in Tables 1 and 2.

Table 1

[0074] It can be seen from Table 1 and Figure 2 that the cycle performance of the battery of Example 1 is significantly superior to that of the batteries of Comparative Example 1 and Comparative Example 3. The cycle stability of the battery of Example 2 is significantly superior to that of the battery of Comparative Example 2. Comparing Embodiment 2 with Comparative Example 4, it can be seen that an excessive additive having compression and repulsion characteristics is added, which cannot improve the cycle performance of the battery and at the same time reduces the specific capacity of the electrode sheet. The data in Table 1 show that the negative electrode sheet with a small volume expansion rate according to the present disclosure can relieve the pressure supported inside the battery core and can significantly improve the cycle stability performance of the battery.

[0075] The above-described full battery after the initial charge-discharge specific capacity test was disassembled. The repulsion characteristics and compression characteristics of the electrode sheet were respectively tested for the negative electrode sheets obtained by disassembling the full batteries corresponding to various examples and comparative examples. The summary of the results is shown in Table 2 and Table 3.

[0076] (Method for testing the repulsion characteristics of the electrode sheet) Apply a pressure of X1 Mpa to the electrode sheet, measure the thickness H1 of the electrode sheet under a pressure of X1 Mpa, remove the pressure, and measure the thickness H2 of the electrode sheet after the thickness of the electrode sheet has stabilized. The repulsion rate of the electrode sheet is The repulsion rate r of the electrode sheet = (H2 - H1) / H1 is.

[0077] (Method for testing the compression characteristics of the electrode sheet) Apply a pressure of X2 Mpa to the electrode sheet with an initial thickness of H3, measure the thickness H4 of the electrode sheet under a pressure of X2 Mpa, and the compression rate of the electrode sheet is The compression rate p of the electrode sheet = (H3 - H4) / H3 is.

Table 2

Table 3

[0078] From Tables 1 to 3, it can be seen that the negative electrode sheets of Examples 1 to 6 have high resilience characteristics and compression characteristics. From the data of Example 2 and Comparative Example 2, after adding an equal amount of three-dimensional graphene and a conventional conductive agent, it can be seen that the compression and resilience characteristics of the electrode sheet of Comparative Example 2 after adding the conventional conductive agent are poor and the same as those of the conventional electrode sheet. The capacity retention rate of the battery assembled with this electrode sheet after 300 cycles is significantly lower than that of the batteries assembled with the electrode sheets of Examples 1 to 6. From Comparative Example 4, it can be seen that although a certain amount of three-dimensional graphene is added and the resilience rate and compression rate of the electrode sheet are not within the range of 2% to 40%, the cycle performance of the battery is reduced to a certain extent compared with that of the examples.

[0079] The foregoing embodiments only show some embodiments of the present disclosure. Although these embodiments have been specifically described in detail, they should not be construed as limitations on the patent scope of the present disclosure. It should be pointed out that those skilled in the art may make some modifications and improvements without departing from the idea of the present disclosure, and all of them belong to the protection scope of the present disclosure. Therefore, the patent protection scope of the present disclosure shall be subject to the appended claims.

Claims

1. A negative electrode current collector, A negative electrode active material layer disposed on the surface of the negative electrode current collector and containing a negative electrode active material and an additive having compression and repulsion characteristics, Comprising, After a pressure X is applied in the thickness direction of the negative electrode sheet, the repulsion rate of the negative electrode sheet is 2% to 40%, the compression rate of the negative electrode sheet is 2% to 40%, and the pressure X satisfies 0.3 MPa ≤ X ≤ 5 MPa, a negative electrode sheet.

2. The negative electrode sheet according to claim 1, wherein the thickness of one side of the negative electrode active material layer is 10 μm to 150 μm.

3. The negative electrode sheet according to claim 1 or 2, wherein the mass ratio of the negative electrode active material to the additive having compression and repulsion characteristics is 100:3 to 50.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein the mass ratio of the negative electrode active material to the additive having compression and repulsion characteristics is 100:3 to 30.

5. The negative electrode active material includes at least one of graphite, hard carbon, Si, SiO ｘ , a silicon-carbon material, Sn, Sb, a silicon-based alloy, a lithium silicon oxide, or a silicon magnesium oxide, the silicon-based alloy further includes at least one of Li, Al, Mg, B, Ni, Fe, Cu, or Co in addition to Si, and the value of x satisfies 0 < x < 2. The negative electrode sheet according to any one of claims 1 to 4.

6. The negative electrode active material layer further contains a binder, the binder contains at least one of polyacrylic acid, sodium alginate, and polyimide, and the mass ratio of the negative electrode active material to the binder is 100:0.05 to 15, the negative electrode sheet according to any one of claims 1 to 5.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein the additive having compression and repulsion characteristics is three-dimensional graphene.

8. The three-dimensional graphene satisfies the following conditions (1) to (5), (1) The particle size of the three-dimensional graphene is 500 nm to 20 μm. (2) The pore volume of the three-dimensional graphene is 1 cm ３ / g to 10 cm ３ / g, (3) The three-dimensional graphene includes overlapping graphene sheets, and the breaking strength between the graphene sheets is 20 N / m to 50 N / m. (4) The three-dimensional graphene includes overlapping graphene sheets, and the lateral dimension of the graphene sheets is 10 nm to 100 nm, preferably 10 nm to 20 nm, or (5) The average pore diameter of the three-dimensional graphene is 250 nm or less. The negative electrode sheet according to any one of claims 1 to 7, satisfying at least one of them.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein the three-dimensional graphene includes overlapping graphene sheets, and the lateral dimension of the graphene sheets is 10 nm to 20 nm.

10. The negative electrode active material layer further contains a conductive agent, the conductive agent contains at least one of single-walled carbon nanotubes and carbon black, and the mass ratio of the negative electrode active material to the conductive agent is 100:0 to 2.

5. The negative electrode sheet according to any one of claims 1 to 9.

11. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 10.

12. An electric device comprising the secondary battery according to claim 11.

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