Negative electrode sheet and electrochemical device

Abstract

A negative electrode sheet and an electrochemical device. The negative electrode sheet comprises a negative electrode active material layer, which comprises a negative electrode active material, conductive carbon fiber tubes and carbon nanotubes, wherein the negative electrode active material comprises a silicon substrate, the conductive carbon fiber tubes are distributed between particles of the negative electrode active material, and the carbon nanotubes are adsorbed on both the surface of the negative electrode active material and the surfaces of the conductive carbon fiber tubes. The mass percentage content Ms of the silicon substrate in the negative electrode sheet is 5.0% to 50.0%, and the silicon substrate, the conductive carbon fiber tubes and the carbon nanotubes also coordinate with each other. In the case of the expansion of the silicon substrate, a plurality of negative electrode active material particles can still be connected in series by means of the conductive carbon fiber tubes to form a long-range conductive path and a short-range conductive path, and do not easily disconnect, and therefore a stable three-dimensional conductive network is constructed; and the carbon nanotubes can also still be wound and adsorbed on the surface of the negative electrode active material to play a conductive role, and can reduce the direct contact between the negative electrode active material and an electrolyte, thereby reducing the occurrences of side reactions.

Description

Negative electrode sheet and electrochemical device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 31, 2024, with application number 202410383461.5 and invention name “Negative Electrode Plate and Electrochemical Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of electrochemical devices, and in particular to a negative electrode sheet and an electrochemical device. Background Art

[0003] Electrochemical devices, such as lithium-ion batteries, offer outstanding characteristics such as high energy density, long cycle life, low pollution, and no memory effect. As a clean energy source, their application has gradually expanded from electronic products to large-scale devices such as electric vehicles, adapting to sustainable environmental and energy development strategies.

[0004] Among them, regarding the negative electrode of the electrochemical device, the negative electrode active material layer is connected to the surface of the negative electrode current collector. Materials such as silicon in the negative electrode active material layer are prone to expansion, affecting the stability of the negative electrode active material layer, thereby reducing the kinetic performance of the electrochemical device. Summary of the Invention

[0005] The embodiments of the present application provide a negative electrode plate and an electrochemical device, which can improve the charge rate performance of the electrochemical device by improving the stability of the negative electrode plate.

[0006] In a first aspect, an embodiment of the present application provides a negative electrode plate, comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive carbon fiber tube and a carbon nanotube; the negative electrode active material comprises a silicon matrix, and based on the negative electrode active material layer, the mass percentage of the silicon matrix is ​​Ms, 5.0%≤Ms≤50.0%; the conductive carbon fiber tube is distributed between the particles of the negative electrode active material, and the carbon nanotubes are adsorbed on the surface of the negative electrode active material and the surface of the conductive carbon fiber tube.

[0007] In some exemplary embodiments, the negative electrode active material layer satisfies at least one of the following conditions:

[0008] (1) The length of the conductive carbon fiber tube is L1, and L1 satisfies: 3 μm ≤ L1 ≤ 30 μm;

[0009] (2) A line connecting three points along the length of the same conductive carbon fiber tube forms a first angle α, 30°≤α≤180°;

[0010] (3) The gram capacity of the conductive carbon fiber tube is S, and S satisfies: 120 mAh / g≤S≤300 mAh / g;

[0011] (4) The primary efficiency of the conductive carbon fiber tube is P, and P satisfies: 50%≤P≤85%;

[0012] (5) The outer diameter of the conductive carbon fiber tube is R1, and R1 satisfies: 20nm≤R1≤100nm;

[0013] (6) The inner diameter of the conductive carbon fiber tube is R2, and R2 satisfies: 5nm≤R2≤10nm.

[0014] In some exemplary embodiments, the negative electrode active material further includes a carbon shell layer coated on the surface of the silicon substrate, and the thickness of the carbon shell layer is h, where h satisfies: 1 nm ≤ h ≤ 10 nm.

[0015] In some exemplary embodiments, based on the negative electrode active material layer, the mass percentage of the conductive carbon fiber tubes is Mx, the mass percentage of the carbon nanotubes is My, and the negative electrode active material layer satisfies at least one of the following conditions:

[0016] (1)0.1≤Mx / My≤10;

[0017] (2) 0.1% ≤ Mx ≤ 5.0%;

[0018] (3)0.1%≤My≤3.0%.

[0019] In some exemplary embodiments, the negative electrode active material layer satisfies at least one of the following conditions:

[0020] (1) The outer diameter of the carbon nanotube is R3, and R3 satisfies: 0.5 nm ≤ R3 ≤ 15 nm;

[0021] (2) The length of the carbon nanotube is L2, and L2 satisfies: 1 μm ≤ L2 ≤ 30 μm;

[0022] (3) The carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0023] In some exemplary embodiments, the negative electrode active material layer further includes a carbon-containing active material, the carbon-containing active material is distributed between particles of the negative electrode active material, and the carbon nanotubes are adsorbed on the surface of the carbon-containing active material.

[0024] In some exemplary embodiments, based on the negative electrode active material layer, the mass percentage of the carbon-containing active material is Mc, and the mass percentage of the conductive carbon fiber tube is Mx; the negative electrode active material layer satisfies at least one of the following conditions:

[0025] (1) 0.05≤Ms / Mc≤1.25;

[0026] (2)1%Ms+0.05%Mc≤Mx≤10%Ms+0.1%Mc;

[0027] (3)40.0%≤Mc≤94.0%.

[0028] In some exemplary embodiments, the particle size of the carbonaceous active material includes D vc 50 and D vc 90, the particle size of the silicon substrate includes D vs 50. The negative electrode active material layer satisfies at least one of the following conditions:

[0029] (1)1≤(D vc 90-D vc 50) / D vs 50≤5;

[0030] (2)0.2≤(L1-D vs 50) / D vc 50≤3.0;

[0031] (3) 1μm≤D vs 50≤10μm;

[0032] (4) 10μm≤D vc 90≤30μm;

[0033] (5)5μm≤D vc 50≤15μm.

[0034] In some exemplary embodiments, the negative electrode active material layer further includes a chain binder, wherein the chain binder is connected to at least two of the negative electrode active material, the conductive carbon fiber tube, and the carbon nanotube;

[0035] Based on the negative electrode active material layer, the mass percentage of the chain binder is Mz, and Mz satisfies: 0.5%≤Mz≤3.0%.

[0036] In some exemplary embodiments, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode active material layer is connected to the surface of the negative electrode current collector;

[0037] The negative electrode active material layer has a cohesive force F2, and F2 satisfies: 15 N / m≤F2≤90 N / m.

[0038] In a second aspect, the present application provides an electrochemical device comprising the negative electrode sheet as described above.

[0039] Based on the negative electrode plate and electrochemical device of the embodiments of the present application, by utilizing the characteristics of the conductive carbon fiber tube, such as greater rigidity, larger outer diameter, not easy to bend, and being in a long straight state and not entangled, and utilizing the characteristics of the carbon nanotube, which is relatively soft and can be wrapped around and adsorbed on the surface of the negative electrode active material, by selecting the mass percentage content Ms of the silicon matrix to be in the range of 5.0%≤Ms≤50.0%, the silicon matrix, the conductive carbon fiber tube and the carbon nanotube are combined. When the silicon matrix expands, the conductive carbon fiber tube can still connect multiple negative electrode active material particles in series to form long-range conductive paths and short-range conductive paths that are not easy to break, so as to build a stable three-dimensional conductive network. The carbon nanotubes can also still wrap around and adsorb on the surface of the negative electrode active material to play a conductive role, and reduce the direct contact between the negative electrode active material and the electrolyte, thereby reducing the occurrence of side reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0041] FIG1 is a schematic structural diagram of carbon nanotubes coated on the surface of negative electrode active materials and conductive carbon fiber tubes in one embodiment of the present application.

[0042] Reference numerals: 10, negative electrode active material; 11, silicon substrate; 12, carbon shell layer; 20, conductive carbon fiber tube; 30, carbon nanotube; 40, carbon-containing active material. DETAILED DESCRIPTION

[0043] The following describes embodiments of the electrochemical device and electrical device of the present application in detail with reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary length in the following description and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0044] As used herein, "ranges" are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, i.e., any lower limit may be combined with any upper limit to form a range.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0047] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] Regarding the negative electrode of an electrochemical device, the negative electrode active material layer is connected to the surface of the negative electrode current collector. Silicon-containing materials in the negative electrode active material layer are prone to expansion, affecting the stability of the negative electrode active material layer and, in turn, reducing the kinetic performance of the electrochemical device. Based on this, embodiments of the present application provide a negative electrode sheet and an electrochemical device that can improve the stability of the negative electrode sheet and, in turn, improve the kinetic performance of the electrochemical device.

[0049] The negative electrode plate of one embodiment of the present application includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material and a conductive carbon fiber tube.

[0050] The conductive carbon fiber tubes are distributed between the particles of the negative electrode active material. The conductive carbon fiber tubes are long, straight or rod-shaped with a certain curvature, and each conductive carbon fiber tube is not entangled with itself, and there is no entanglement between adjacent conductive carbon fiber tubes. The conductive carbon fiber tubes have a certain length and can be connected to materials with different spacings, exerting short-range and long-range conductive effects, and are easy to connect with more conductive materials, which is conducive to building a dense three-dimensional conductive network, improving the conductive properties of the negative electrode active material layer, and thus improving the kinetic performance of the electrochemical device. The conductive carbon fiber tubes have a certain length and can also increase the probability of contact with other conductive substances, which helps to further reduce the internal resistance of the negative electrode active material layer.

[0051] The untangled state of the conductive carbon fiber tube is defined as follows: a line connecting three points along the length of the tube forms a first angle α, 30°≤α≤180°. For example, the conductive carbon fiber tube is straight or curved. By selecting the conductive carbon fiber tube in an untangled state, the tube can maximize the conduction between two conductive materials that are far apart, fully utilizing its long-range conductivity. It also facilitates the adsorption or adhesion of other substances, thereby helping to enhance the cohesion of the negative electrode active material layer. When α is less than 30°, the conductive carbon fiber tube 20 has a large degree of bending and is prone to entanglement in the negative electrode active material layer. Even when the length of the conductive carbon fiber tube 20 is extended, its long-range conductive effect cannot be fully exerted. In addition, it is easy to cause the material connected to the conductive carbon fiber tube 20 to fail to disperse evenly. For example, the carbon nanotubes 30 connected to the conductive carbon fiber tube 20 below fail to disperse evenly, which will cause its short-range conductive effect to deteriorate, and thus is not conducive to improving the internal resistance of the negative electrode plate; the adhesive connected to the conductive carbon fiber tube 20 fails to disperse evenly, resulting in the adhesive failing to fully exert its adhesive effect to connect with more materials, which in turn leads to a decrease in the cohesive force in the negative electrode active material layer. When the negative electrode plate is used in an electrochemical device, the thickness expansion rate of the electrochemical device is poorly improved.

[0052] The length of the conductive carbon fiber tube is L1, and L1 satisfies: 3μm≤L1≤30μm. For example, L1 can be 3μm, 8μm, 10μm, 15μm, 20μm, 30μm or any range of the above two. When L1 satisfies 3μm≤L1≤30μm, the conductive network in the negative electrode active material layer can form a three-dimensional conductive network with a stable and uniform spatial distribution. When L1 is lower than the lower limit of 3μm, the conductive carbon fiber tube is too short, and the probability of each conductive carbon fiber tube contacting other conductive materials is reduced, which is not conducive to improving the conductive performance of the negative electrode sheet. When L2 is higher than the upper limit of 30μm, the conductive carbon fiber tube is too long and difficult to disperse, resulting in the conductive carbon fiber tube being easily cross-linked and entangled, making the conductive performance of the negative electrode active material layer unevenly distributed, which is not conducive to ion transport.

[0053] As shown in Figure 1, the negative electrode active material 10 includes a silicon substrate 11 and a carbon shell 12 coated on the surface of the silicon substrate 11. The carbon shell 12 can partially coat the surface of the silicon substrate 11 or completely coat the surface of the silicon substrate 11. The silicon substrate 11 has the ability to occlude and release metal ions. The carbon shell 12 can constrain the silicon substrate 11, reducing its expansion. In addition, the carbon shell 12 coating the silicon substrate 11 can also reduce contact between the silicon substrate 11 and the electrolyte, reducing the occurrence of side reactions. The material of the silicon substrate 11 is elemental silicon.

[0054] The thickness of the carbon shell 12 is h, and h satisfies: 1nm≤h≤10nm. For example, h can be 1nm, 2nm, 4nm, 6nm, 8nm, 10nm, or any range thereof. By selecting the thickness h of the carbon shell 12 to be within the range of 1nm≤h≤10nm, the carbon shell 12 can effectively play the role of limiting the expansion of the silicon substrate 11, and can still play a good role in isolating the silicon substrate 11 when the silicon substrate 11 has an expansion tendency or slight expansion. When h is lower than the lower limit of 1nm, the carbon shell has a poor ability to limit the expansion of the silicon substrate 11 and is also prone to damage when the silicon substrate 11 expands. When h is higher than the upper limit of 10nm, the carbon shell 12 is too thick, which is not conducive to the passage of metal ions when the silicon substrate 11 absorbs and releases metal ions. In addition, a too thick carbon shell 12 tends to occupy more space, which is not conducive to improving the energy density of the electrochemical device.

[0055] The negative electrode active material layer also includes carbon nanotubes 30. Conductive carbon fiber tubes 20 are distributed between the particles of the negative electrode active material 10, and carbon nanotubes 30 are adsorbed on the surfaces of both the negative electrode active material 10 and the conductive carbon fiber tubes 20. Compared to carbon nanotubes 30, conductive carbon fiber tubes 20 have a higher degree of graphitization, resulting in greater rigidity and a larger outer diameter. They are less prone to bending and remain straight, untangled. These tubes can connect multiple particles of the negative electrode active material 10 in series, forming a long-range conductive path that is less susceptible to disconnection after the negative electrode electrode expands. Carbon nanotubes 30 are relatively flexible and can wrap around and adsorb on the surface of the negative electrode active material 10, providing short-range conductivity while also reducing direct contact between the negative electrode active material 10 and the electrolyte, thereby minimizing side reactions.

[0056] Among them, the carbon shell layer 12 coated on the surface of the silicon substrate 11, in addition to limiting the expansion of the silicon substrate 11, can also be connected to the conductive carbon fiber tube 20 and the carbon nanotube 30 respectively to construct a three-dimensional conductive network, further reducing the internal resistance of the negative electrode plate, and can effectively improve the volume expansion effect of the electrochemical device during the cycle.

[0057] The gram capacity of the conductive carbon fiber tube 20 refers to the ratio of the capacitance that the conductive carbon fiber tube 20 can release to the mass of the conductive carbon fiber tube 20. In some exemplary embodiments, the gram capacity of the conductive carbon fiber tube 20 is S, and S satisfies: 120mAh / g≤S≤300mAh / g. For example, S can be 120mAh / g, 140mAh / g, 160mAh / g, 180mAh / g, 200mAh / g, or any range thereof. By selecting the gram capacity S of the conductive carbon fiber tube 20 to be in the range of 120mAh / g≤S≤300mAh / g, the conductive carbon fiber tube 20 has good electrical conductivity. When the negative electrode sheet is used in an electrochemical device, the electrochemical device can have a higher energy density. When the gram capacity S of the conductive carbon fiber tube 20 is lower than the lower limit of 120mAh / g, the conductivity of the conductive fiber of the conductive carbon fiber tube 20 is too low, which is not conducive to lithium insertion, resulting in a decrease in energy density. When the gram capacity S of the conductive carbon fiber tube 20 is higher than the upper limit of 200 mAh / g, the conductive carbon fiber tube 20 needs to have a higher degree of graphitization, which causes the conductive carbon fiber tube 20 to become brittle and easily break during the production process, making it difficult to achieve the required length.

[0058] The first efficiency of the conductive carbon fiber tube 20 can reflect the ability of the conductive carbon fiber tube 20 to store and release lithium. In some exemplary embodiments, the first efficiency of the conductive carbon fiber tube 20 is P, and P satisfies: 50%≤P≤85%. For example, P can be 50%, 55%, 60%, 70%, 80%, 85% or any range thereof. By selecting the first efficiency P of the conductive carbon fiber tube 20 to satisfy 50%≤P≤85%, the conductive carbon fiber tube 20 has a low first efficiency performance, which can improve the degree of lithiation. The process of lithium ions inserting into the gaps between the conductive carbon fiber tubes 20 to form lithium compounds is the lithiation process. This process will increase the movement of ions and electrons in other materials in the negative electrode active material layer, thereby improving the electronic conductivity of other materials. For example, when graphite is present in the negative electrode active material layer, the conductive carbon fiber tube 20 has a low first efficiency. During the lithiation process, the movement of ions and electrons in the graphite will increase, which can improve the electronic conductivity of the graphite, reduce the internal resistance of the electrochemical device, and further improve the discharge performance of the electrochemical device. When the initial S of the conductive carbon fiber tube 20 is lower than the lower limit of 50%, excessive lithium ion loss will occur, adversely affecting the graphite. When the initial S of the conductive carbon fiber tube 20 is higher than the upper limit of 85%, the degree of lithiation of the conductive agent will be too low, reducing the electronic conductivity.

[0059] In some exemplary embodiments, the outer diameter of the conductive carbon fiber tube 20 is R1, and R1 satisfies: 20nm≤R1≤100nm. For example, R1 can be 20nm, 30nm, 40nm, 60nm, 80nm, 100nm, or any range thereof. By selecting the outer diameter R1 of the conductive carbon fiber tube 20 to satisfy 20nm≤R1≤100nm, the outer diameter of the conductive carbon fiber tube 20 is suitable, which can exert good conductive properties and reduce the resistance of the negative electrode. When the outer diameter R1 of the conductive carbon fiber tube 20 is lower than the lower limit of 20nm, the stiffness of the conductive fiber is reduced, it is easy to entangle, and the effect of long-range conductivity is reduced. When the outer diameter R1 of the conductive carbon fiber tube 20 is higher than the upper limit of 100nm, the number of conductive fibers is reduced under the same weight, the density of the conductive network is reduced, and the performance of the electrode is deteriorated.

[0060] The inner diameter of the conductive carbon fiber tube 20 is R2, where R2 satisfies the following: 5 nm ≤ R2 ≤ 10 nm. For example, R2 can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any range thereof. The hollow structure of the conductive carbon fiber tube 20 results in a relatively large specific surface area, which helps improve ion transport performance within the negative electrode active material layer, thereby enhancing the discharge performance of the electrochemical device.

[0061] Based on the negative electrode active material layer, the mass percentage of the conductive carbon fiber tubes 20 is Mx, and the mass percentage of the carbon nanotubes 30 is My, where 0.1≤Mx / My≤10. For example, Mx / My can be 0.1, 0.4, 0.6, 0.8, 10, or any range thereof. In the conductive network within the negative electrode active material layer, the conductive carbon fiber tubes 20 can be used for long-range conductivity, while the carbon nanotubes 30 can be used for short-range conductivity. By selecting a ratio between the conductive carbon fiber tubes 20 and the carbon nanotubes 30 within a range of 0.1 to 10, long-range and short-range conductivity can be combined, strengthening the three-dimensional conductive network and further reducing the resistance of the negative electrode sheet. When Mx / My is lower than the lower limit of 0.1, the content of the conductive carbon fiber tube 20 is too low, which is not conducive to the formation of a three-dimensional conductive network, or the degree of connection between the conductive materials is low, which is not conducive to reducing the resistance. When Mx / My is higher than the upper limit of 10, the content of the conductive carbon fiber tube 20 is too high, entanglement is likely to occur, and the short-range conductivity is insufficient, which is also not conducive to the formation of a three-dimensional conductive network.

[0062] In some exemplary embodiments, the mass percentage Mx of the conductive carbon fiber tube 20 satisfies: 0.1%≤Mx≤5.0%. For example, Mx can be 0.1%, 2.0%, 3.0%, 4.0%, 5.0% or any range thereof.

[0063] In some exemplary embodiments, the mass percentage My of the carbon nanotubes 30 satisfies: 0.1%≤My≤3.0%. For example, My may be 0.1%, 1.5%, 2.0%, 2.5%, 3.0% or any range thereof.

[0064] In some exemplary embodiments, the outer diameter of the carbon nanotube 30 is R3, and R3 satisfies the following: 0.5 nm ≤ R3 ≤ 15 nm. For example, R3 can be 0.5 nm, 5 nm, 10 nm, 12 nm, 15 nm, or any range thereof. By selecting the outer diameter R3 of the carbon nanotube 30 to satisfy the following: 0.5 nm ≤ R3 ≤ 15 nm, the carbon nanotube 30 can obtain good flexibility, thereby better coating the surface of the negative electrode active material 10 and the conductive carbon fiber tube 20, and improving the conductivity of the negative electrode sheet. Preferably, R3 satisfies the following: 1 nm ≤ R3 ≤ 3 nm.

[0065] In some exemplary embodiments, the length of the carbon nanotubes 30 is L2, and L2 satisfies the following conditions: 1 μm ≤ L2 ≤ 30 μm. For example, L2 can be 1 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any range thereof. By selecting the length L2 of the carbon nanotubes 30 to satisfy the following conditions: 1 μm ≤ L2 ≤ 30 μm, the carbon nanotubes 30 can be stably attached to the surfaces of the negative electrode active material 10 and the conductive carbon fiber tubes 20. Preferably, L2 satisfies the following conditions: 5 μm ≤ L2 ≤ 20 μm.

[0066] In some exemplary embodiments, the carbon nanotubes 30 include single-walled carbon nanotubes and multi-walled carbon nanotubes. Preferably, the carbon nanotubes 30 include single-walled carbon nanotubes. Single-walled carbon nanotubes have a high specific surface area and good electrical conductivity, and their surface can also provide a good diffusion path for lithium ions.

[0067] The negative electrode active material layer also includes a carbon-containing active material 40, which is distributed between the particles of the negative electrode active material 10. Carbon nanotubes 30 are adsorbed on the surface of the particles of the carbon-containing active material 40, further facilitating the formation of a dense three-dimensional conductive network to reduce internal resistance. The carbon-containing active material 40 includes at least one of graphite and hard carbon. Preferably, the carbon-containing active material 40 is graphite. Since the silicon matrix 11 of the negative electrode active material 10 expands during the charge and discharge process of the electrochemical device, the carbon-containing active material 40 is distributed between the particles of the negative electrode active material 10. The carbon-containing active material 40 and the carbon shell 12 work together to limit the expansion of the silicon matrix 11, preventing the expansion of the silicon matrix 11 from affecting the stability of the negative electrode active material layer. The carbon-containing active material 40 also exhibits conductive properties, further reducing the internal resistance of the negative electrode active material layer.

[0068] In some exemplary embodiments, based on the negative electrode active material layer, the mass percentage of the silicon substrate 11 is Ms, and the mass percentage of the carbon-containing active material 40 is Mc, and 0.05 ≤ Ms / Mc ≤ 1.25. For example, Ms / Mc can be 0.05, 0.25, 0.50, 0.80, 1.05, 1.25, or any range thereof. The silicon substrate 11 has high specific capacity, and the carbon-containing active material 40 has low expansion. By selecting the content of both the silicon substrate 11 and the carbon-containing active material 40 to satisfy 0.05 ≤ Ms / Mc ≤ 1.25, it is possible to achieve both improved energy density and prevent performance degradation of the electrochemical device due to excessive expansion. When Ms / Mc is below the lower limit of 0.05, the energy density of the electrochemical device will be reduced. When Ms / Mc is above the upper limit of 1.25, the electrochemical device will expand excessively.

[0069] In some exemplary embodiments, the mass percentage content Ms of the silicon substrate 11 satisfies the following: 5.0% ≤ Ms ≤ 50.0%. For example, Ms can be 5.0%, 15.0%, 20.0%, 30.0%, 40.0%, 50.0%, or any range thereof. By selecting the mass percentage content Ms of the silicon substrate 11 to be within the range of 5.0% ≤ Ms ≤ 50.0%, the silicon substrate 11, the conductive carbon fiber tubes, and the carbon nanotubes cooperate. When the silicon substrate 11 expands, the conductive carbon fiber tubes can still connect multiple negative electrode active material particles in series, forming long-range and short-range conductive pathways that are not easily disconnected, thereby building a stable three-dimensional conductive network. The carbon nanotubes can still wrap around and be adsorbed on the surface of the negative electrode active material to perform a conductive role, thereby reducing direct contact between the negative electrode active material and the electrolyte, thereby reducing the occurrence of side reactions.

[0070] In some exemplary embodiments, the mass percentage Mc of the carbon-containing active material 40 satisfies: 40.0%≤Mc≤94.0%. For example, Mc can be 40.0%, 45.0%, 50.0%, 60.0%, 80.0%, 94.0% or any range thereof.

[0071] In some exemplary embodiments, 1% Ms + 0.05% Mc ≤ Mx ≤ 10% Ms + 0.1% Mc. By selecting the mass percentage Ms of the silicon substrate 11, the mass percentage Mc of the carbon-containing active material 40, and the mass percentage Mx of the conductive carbon fiber tube 20 to satisfy the above conditional formula, the electrochemical device can have good charge and discharge cycle performance.

[0072] In some exemplary embodiments, the particle size of the carbonaceous active material 40 includes D vc 50 and D vc 90, the particle size of the silicon substrate 11 includes Dvs 50, where 1≤(D vc 90-D vc 50) / D vs 50≤5, for example, (D vc 90-D vc 50) / D vs 50 can be 1, 2, 3, 4, 5 or any range of the above two. By selecting the particle size of the carbonaceous active material 40 to satisfy 1≤(D vc 90-D vc 50) / D vs 50≤5, so that the particles of the silicon substrate 11 are distributed between the particles of the carbon-containing active material 40, which helps to improve the compaction density of the negative electrode active material layer and can also limit the expansion of the silicon substrate 11, thereby achieving the effect of improving the expansion of the electrochemical device.

[0073] In some exemplary embodiments, 0.2≤(L1-D vs 50) / D vc 50≤3.0, for example, (L1-D vs 50) / D vc 50 can be 0.2, 1.2, 1.6, 2.0, 2.5, 2.8, 3.0 or any range thereof. By selecting the length L1 of the conductive carbon fiber tube 20 and the particle size of the carbon-containing active material 40 to satisfy 0.2≤(L1-D vs 50) / D vc 50≤3.0, which helps the conductive carbon fiber tubes 20 to be connected in series between the particles of the negative electrode active material 10 to form a stable long-range conductive network.

[0074] In some exemplary embodiments, the particle size D of the silicon substrate 11 is vs 50 satisfies: 1μm≤D vs 50≤10μm, for example, D vs 50 can be 1 μm, 2 μm, 5 μm, 8 μm, 10 μm or any range thereof.

[0075] In some exemplary embodiments, the particle size D of the carbonaceous active material 40 is vc 90 satisfies: 10μm≤D vc 90≤30μm, for example, D vc 90 can be 10 μm, 12 μm, 15 μm, 25 μm, 30 μm or any range thereof.

[0076] In some exemplary embodiments, the particle size D of the carbonaceous active material 40 is vc 50 satisfies: 5μm≤D vc 50≤15μm, for example, Dvc 90 can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm or any range thereof.

[0077] In some exemplary embodiments, the negative electrode active material layer further includes a chain binder. The chain binder is connected to at least two of the negative electrode active material 10, the conductive carbon fiber tubes 20, the carbon nanotubes 30, and the carbon-containing active material 40. The chain binder binds the various materials in the negative electrode active material layer together, thereby improving the cohesive force of the negative electrode active material layer. The chain binder can also adhere to the negative electrode current collector of the negative electrode sheet, thereby ensuring stable adhesion of the negative electrode active material layer to the negative electrode current collector.

[0078] The present embodiments do not limit the type of chain binder; any chain binder capable of connecting materials within the negative electrode active material layer is suitable for use in this application. For example, the chain binder includes at least one of a lithium salt organic compound and a non-lithium salt organic compound. Specifically, the lithium salt organic compound includes at least one of lithium polyacrylate, lithium carboxymethyl cellulose, lithium acrylate, and a polymer of polyaniline. The non-lithium salt organic compound includes at least one of sodium carboxymethyl cellulose and acrylic acid.

[0079] Preferably, the chain binder includes a lithium salt organic compound. Selecting a lithium salt organic compound as the chain binder can increase the concentration of lithium ions in the negative electrode active material layer, accelerate the transmission of lithium ions in the negative electrode active material layer, and thus help improve the kinetic performance of the electrochemical device.

[0080] Based on the negative electrode active material layer, the mass percentage of the chain binder is denoted as Mz, where Mz satisfies the following conditions: 0.5% ≤ Mz ≤ 3.0%. For example, Mz can be 0.5%, 0.8%, 1.0%, 2.0%, 3.0%, or any range thereof. Selecting the mass percentage of the chain binder Mz to satisfy the following conditions: 0.5% ≤ Mz ≤ 3.0% helps achieve a good bonding effect.

[0081] The negative electrode plate of the embodiment of the present application also includes a negative electrode current collector, and the negative electrode active material layer is connected to the surface of the negative electrode current collector. Specifically, the negative electrode current collector includes two surfaces arranged opposite to each other in the thickness direction thereof, and the negative electrode active material layer is connected to at least one of the two surfaces of the negative electrode current collector.

[0082] Cohesion reflects the interaction between materials within the negative electrode active material layer. A greater cohesion reflects the interaction between materials within the negative electrode active material layer, and the less likely the negative electrode active material layer is to detach from the negative electrode current collector. In some exemplary embodiments, the negative electrode active material layer has a cohesion F2, where F2 satisfies the following: 15 N / m ≤ F2 ≤ 90 N / m. For example, F2 can be 15 N / m, 30 N / m, 50 N / m, 60 N / m, 85 N / m, or any range within these two ranges.

[0083] The negative electrode sheet of the embodiments of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The present application does not particularly limit the negative electrode current collector, as long as it can achieve the objectives of this application. In some embodiments, the negative electrode current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative electrode current collector is copper foil.

[0084] In some embodiments, the structure of the negative electrode sheet is a negative electrode structure known in the art that can be used in electrochemical devices.

[0085] The present application also provides an electrochemical device in an embodiment, which may be a lithium-ion battery or any other suitable electrochemical device. Without departing from the disclosure of the present application, the electrochemical device in the embodiment of the present application includes any device in which an electrochemical reaction occurs, and its specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In particular, the electrochemical device is a lithium secondary battery, which includes but is not limited to a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0086] The electrochemical device of the present application is an electrochemical device having a positive electrode sheet with a positive electrode active material capable of occluding and releasing metal ions, and a negative electrode sheet with a negative electrode active material capable of occluding and releasing metal ions. Its main feature is that it includes any of the above-mentioned negative electrode sheets of the present application.

[0087] The electrochemical device of the present application also includes a negative electrode tab, a positive electrode tab, a separator, an electrolyte and an outer packaging. The positive electrode tab is arranged on the positive electrode sheet, the negative electrode tab is arranged on the negative electrode sheet, and the separator is arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the separator and the negative electrode sheet are stacked to form a laminated electrode assembly, or the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form a wound electrode assembly. The electrode assembly is placed in the internal space of the outer packaging, the positive electrode tab and the negative electrode tab are led out from the internal space of the outer packaging and electrically connected to the external circuit, and the electrolyte is filled in the internal space of the outer packaging.

[0088] The embodiments of the present application have no special restrictions on the positive electrode sheet, negative electrode tab, positive electrode tab, separator, electrolyte and outer packaging. All materials applicable to this field are applicable to the present application.

[0089] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector. The present application has no special restrictions on the positive electrode plate. The positive electrode active material layer includes a positive electrode active material. The embodiments of the present application have no special restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material includes a compound that can reversibly embed and deintercalate lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide containing lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material is selected from at least one of the following: lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4).

[0090] In some embodiments, the positive electrode active material layer further includes a binder, which can improve the bonding between the positive electrode active material particles and the bonding between the positive electrode active material and the positive electrode current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0091] In some embodiments, the positive electrode active material layer may optionally further include a conductive material to impart conductivity to the positive electrode active material layer. The conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0092] In some embodiments, the positive electrode current collector is a metal, such as but not limited to aluminum foil.

[0093] In some embodiments, the structure of the positive electrode sheet is a positive electrode structure known in the art that can be used in electrochemical devices.

[0094] The isolation membrane that can be used in the embodiments of the present application can be an isolation membrane known in the prior art. The isolation membrane has insulating properties, and the material of the isolation membrane is selected from a polymer film, a multilayer polymer film, or a non-woven fabric formed by any one of the following polymers or a mixture of two or more thereof: polyethylene, polypropylene, polyethylene terephthalate, polyphenylene phthalamide, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, and polyethylene naphthalene. The polyethylene is selected from at least one component of high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

[0095] The electrolytes that can be used in the embodiments of the present application can be any electrolyte known in the prior art. Electrolytes can be divided into aqueous electrolytes and non-aqueous electrolytes. Compared to aqueous electrolytes, electrochemical devices using non-aqueous electrolytes can operate over a wider voltage window, thereby achieving higher energy density. In some embodiments, the non-aqueous electrolyte includes an organic solvent, an electrolyte, and an additive.

[0096] The electrolytes that can be used in the electrolyte of the embodiment of the present application include, but are not limited to: inorganic lithium salts, such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, etc.; fluorine-containing organic lithium salts, such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonyl imide lithium, cyclic 1,2-tetrafluoroethane disulfonyl imide lithium, LiPF4(CF3)2, LiN(C F3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; lithium salts containing dicarboxylic acid complexes, such as lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, etc. In addition, the above electrolytes can be used alone or in combination of two or more. For example, in some embodiments, the electrolyte includes a combination of LiPF6 and LiBF4. In some embodiments, the electrolyte includes LiPF6.

[0097] In some embodiments, the concentration of the electrolyte is in the range of 0.8 mol / L to 3 mol / L, for example, in the range of 0.8 mol / L to 2.5 mol / L, in the range of 0.8 mol / L to 2 mol / L, in the range of 1 mol / L to 2 mol / L, for example, 1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L or 2.5 mol / L.

[0098] The additives that can be used in the electrolytes of the embodiments of the present application can be additives known in the art that can be used to improve the electrochemical performance of the battery. In some embodiments, the additives include, but are not limited to, at least one of a polynitrile compound, a sulfur-containing additive, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and 1,4-butane sultone.

[0099] The organic solvent that can be used in the electrolyte of the embodiment of the present application can be any organic solvent known in the prior art. In some embodiments, the organic solvent includes, but is not limited to: a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. Examples of carbonate compounds include, but are not limited to, a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0100] In some embodiments, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, or ethyl propionate.

[0101] The present application provides an electronic device comprising the aforementioned electrochemical device.

[0102] The negative electrode sheet according to the embodiment of the present application can improve the power dynamics performance of the electrochemical device, so that the electrochemical device manufactured thereby is suitable for electronic equipment in various fields, especially for electronic equipment that requires working under high-rate charging conditions.

[0103] The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. For example, the electronic device includes, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc. In addition, in addition to being applicable to the electronic devices listed above, the electrochemical device of the present application is also applicable to energy storage power stations, marine vehicles, and air vehicles. Air vehicles include air vehicles within the atmosphere and air vehicles outside the atmosphere.

[0104] The present application is further described below using lithium-ion batteries as an example and in conjunction with specific embodiments and comparative examples. However, the present application is not limited to these embodiments without departing from the main purpose. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments and comparative examples can be obtained commercially or synthesized.

[0105] The following method was used to test the performance of lithium-ion batteries in the examples and comparative examples of the present application.

[0106] 1. Testing Method for the Length, Inner Diameter, and Outer Diameter of the Conductive Carbon Fiber Tube 20 and the Carbon Nanotube 30

[0107] (1) Disassembling the finished battery to obtain the negative electrode sheet;

[0108] (2) The negative electrode was soaked in DMC (dimethyl carbonate) at 25°C for 60 min to remove the electrolyte, taken out, and dried at 25°C.

[0109] (3) The negative electrode sheet in (2) is fractured by liquid nitrogen to obtain a cross section of the negative electrode active material layer on the negative electrode sheet.

[0110] (4) Observe the cross section of the negative electrode active material layer obtained in (3) under SEM, test the length, inner diameter, and outer diameter of the target material at at least 5 different positions, and a total of no less than 15 lines, and take the average value as the target value.

[0111] 2. Test method for folding and winding of conductive carbon fiber tube 20

[0112] (1) Disassembling the finished battery to obtain the negative electrode sheet;

[0113] (2) The negative electrode was soaked in DMC (dimethyl carbonate) at 25°C for 60 min, taken out, and dried at 25°C.

[0114] (3) The negative electrode sheet in (2) is fractured by liquid nitrogen to obtain a cross section of the negative electrode active material layer on the negative electrode sheet.

[0115] (4) Observe the cross section of the negative electrode active material layer obtained in (3) under an SEM, testing at least 5 different positions, and a total of no less than 15 target materials. If the conductive carbon fiber tube 20 is in a stretched state, and a line connecting three points along the length of the same conductive carbon fiber tube 20 forms a first angle α, 30°≤α≤180°, then it is an unwound conductive carbon fiber tube 20 of the present application.

[0116] 3. Cohesion test method

[0117] (1) Disassembling the finished battery to obtain the negative electrode sheet;

[0118] (2) The negative electrode was soaked in DMC (dimethyl carbonate) at 25°C for 60 min, taken out, and dried at 25°C.

[0119] (3) Use a high-speed rail tensile test machine and a 90° angle method to test the cohesion of the negative electrode in (2). The specific steps are as follows:

[0120] a. Make the negative electrode into a strip, with the side with the negative electrode active material layer facing up, and stick the other side along the length direction to the steel plate with double-sided tape.

[0121] b. Use the center area of ​​the negative electrode active material layer facing upward as the stable area, and apply tape to the surface of the stable area, leaving a 5 cm blank end of the tape.

[0122] c. Secure the steel plate in the corresponding position of the high-speed rail tensile testing machine. Place the blank end into the chuck and clamp it. When the chuck tension is greater than 0 kgf and less than 0.02 kgf, begin the high-speed rail tensile testing machine. Use a tensile speed of 5 mm / min and stretch until it breaks. The average tensile force measured in the stable area is recorded as the cohesion of the target interface. Specifically, the ratio of the standard deviation of the cohesion data in this stable area to the average value must not exceed 10%.

[0123] 4. Test method for battery thickness expansion rate and capacity retention rate after 500 cycles

[0124] Complete the following process at 45°C:

[0125] (1) Take the finished battery cell and let it stand for 2 hours, then discharge it at 0.5C until the voltage reaches 3.0V, and let it stand for 5 minutes.

[0126] (2) Charge at 2.0C to 4.30V, then charge at 4.30V to 1.0C.

[0127] (3) Charge again at 1.0C to 4.40V, and then charge again at 4.40V to a current of 0.7C.

[0128] (4) Charge the battery at 0.7C to 4.50V, then charge it at 4.50V to a current of 0.025C and let it rest for 5 minutes.

[0129] (5) 0.5C discharge until the voltage reaches 3.0V.

[0130] (6) The steps in (2)-(5) are used as a charge and discharge cycle, and the process in (2)-(5) is repeated 50 times. In the 50th cycle, the battery is charged to 4.5V at 0.5C, charged to 0.025C at 4.5V, and left to stand for 5 minutes. The thickness of the battery cell is then tested, and then the battery cell is discharged to 3.0V at 0.5C.

[0131] (7) Repeat (2)-(6) 10 times

[0132] Thickness expansion rate: Take the battery after the first full charge and place it in an environment of 25±2℃, and measure the thickness of the battery where the positive electrode tab is embedded as T1; take the battery in (7) that is fully charged to 4.30V after 500 cycles and place it in an environment of 25±2℃, and measure the thickness of the battery where the positive electrode tab is embedded as T500.

[0133] The thickness expansion rate of the battery after 500 cycles is: (T500-T1) / T1*100%.

[0134] Capacity retention rate: Take the capacity at the 6th week as C0, the capacity at the 500th week as C500, and the capacity retention rate of the battery cell after 500 cycles is C500 / C6*100%

[0135] 5. Testing method for the thickness h of the carbon shell

[0136] (1) Disassembling the finished battery to obtain the negative electrode sheet;

[0137] (2) The negative electrode was soaked in DMC (dimethyl carbonate) at 25°C for 60 min to remove the electrolyte, taken out, and dried at 25°C.

[0138] (3) The negative electrode sheet in (2) is cut by plasma to obtain a cross section of the negative electrode active material layer on the negative electrode sheet.

[0139] (4) Observe the cross section of the negative electrode active material layer obtained in (3) under SEM, measure the carbon shell coating thickness of 20 different silicon particles, and take the average value as h.

[0140] Example 1-1

[0141] 1. Preparation of lithium-ion batteries

[0142] 1. Preparation of negative electrode sheet

[0143] (1) Preparation of negative electrode active materials:

[0144] a. Preparation of silicon substrate: Chemical vapor deposition is used to react a silicon source (such as silane gas or silicon chloride) with a reducing agent (hydrogen) at high temperature to generate silicon element, which is then attached to a substrate (quartz or silicon wafer) and gradually grows. The size of the silicon core is controlled by controlling the temperature and time parameters.

[0145] b. The silicon core is placed in a reaction chamber, and then a gas containing a carbon source is supplied into the reaction chamber through chemical vapor deposition (CVD). Commonly used carbon source gases include methane (CH4) or ethylene (C2H4), which react chemically on the surface of the silicon core to form a carbon shell. By adjusting the CVD reaction conditions, the thickness of the carbon shell can be controlled. Longer deposition times and higher carbon source concentrations generally result in thicker carbon shells.

[0146] (2) The chain binder is dissolved in deionized water at a solid content of 5%, and stirred and dispersed evenly to form a glue solution. 30% of the total amount of the glue solution is taken and mixed with the carbon-containing active material 40 (graphite), the negative electrode active material 10, the conductive carbon fiber tube 20, and the single-walled carbon nanotube 30. Then, the remaining glue solution and an appropriate amount of deionized water are added to prepare a negative electrode active material layer slurry with a solid content of 10%. After stirring evenly, it is coated on a 5μm copper foil and dried to form a negative electrode plate.

[0147] 2. Preparation of positive electrode

[0148] The positive electrode active material, lithium cobalt oxide, the conductive agent, acetylene black, carbon nanotubes, and the binder, polyvinylidene fluoride (PVDF), were mixed in a solvent, N-methylpyrrolidone (NMP), at a mass ratio of 97.5:0.7:0.5:1.3. The mixture was thoroughly stirred in a vacuum mixer to obtain a positive electrode slurry (70% solid content). This positive electrode material was coated onto a 9μm-thick positive electrode current collector aluminum foil, dried, and cold-pressed to form a positive electrode active material layer approximately 75μm thick. The positive electrode sheet was then cut into pieces and the tabs welded together.

[0149] 3. Preparation of electrolyte

[0150] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly at a mass ratio of EC:PC:EMC:DEC = 10:25:35:30. Then, 2% by mass of fluoroethylene carbonate was added, dissolved, and thoroughly stirred. LiPF6 was then added and mixed uniformly to obtain an electrolyte. The concentration of LiPF6 was 1 mol / L.

[0151] 4. Preparation of isolation membrane

[0152] A polypropylene film with a thickness of 5 μm was selected as the isolation membrane.

[0153] 5. Preparation of lithium-ion batteries

[0154] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the positive tabs attached to the positive sheet and the negative tabs to the negative sheet, respectively. The separator is positioned between the positive and negative electrodes to provide insulation, and then wound to form an electrode assembly. The electrode assembly is then placed in an outer foil and aluminum-plastic film packaging, and electrolyte is injected. The lithium-ion battery is then produced through a series of vacuum packaging, resting, and formation processes.

[0155] In the following examples and comparative examples, the difference in the preparation of the negative electrode sheets lies mainly in the difference in the parameters of the negative electrode sheet materials used. Table 1 shows the relevant performance parameters of the negative electrode sheets of Examples 1-1 to 1-32 and the corresponding lithium-ion battery performance.

[0156] In the negative electrode active material layer of Example 1-1, based on the negative electrode active material layer, the mass percentage Mx of the conductive carbon fiber tube 20 is 0.3%, the mass percentage My of the single-walled carbon nanotube 30 is 0.4%, the mass percentage Mz of the chain adhesive is 1.5%, the mass percentage Ms of the silicon matrix 11 is 10%, and the mass percentage Mc of the carbon-containing active material 40 is 87.8%.

[0157] The difference between Examples 1-2 to 1-32 and Example 1-1 lies in the different parameters of the negative electrode active material layer. The relevant parameters are specifically shown in Table 1.

[0158] According to Examples 1-1 to 1-4 and 1-32 in Table 1, it can be seen that by selecting the length L1 of the conductive carbon fiber tube 20 to satisfy 3μm≤L1≤30μm, the thickness expansion rate and capacity retention rate of the lithium-ion battery can be effectively improved. When the length L1 of the conductive carbon fiber tube 20 is lower than the lower limit of 3μm, the length of the conductive carbon fiber tube 20 is too short, and it is difficult to achieve the purpose of long-distance electrical conduction between the two conductive materials, which reduces the conductivity of the negative electrode active material layer and also leads to the negative impact of increased battery expansion during the cycle. When the length L1 of the conductive carbon fiber tube 20 is higher than the upper limit of 30μm, it will lead to the negative impact of uneven winding distribution.

[0159] It can be seen from Examples 1-1 to 1-4, 1-21 to 1-22, and 1-32 in Table 1 that, compared to Example 1-32 in which the negative electrode active material is not provided with a carbon shell layer, in Examples 1-1 to 1-4, by selecting the thickness h of the carbon shell layer to satisfy 1 nm ≤ h ≤ 10 nm, the thickness expansion rate and capacity retention rate of the lithium-ion battery can be effectively improved.

[0160] According to Examples 1-5 to 1-7 in Table 1, it can be seen that the diameter R1 of the conductive carbon fiber tube 20 satisfies 20nm≤R1≤100nm, and the thickness expansion rate and capacity retention rate of the lithium-ion battery can be effectively improved. Specifically, as the diameter R1 of the conductive carbon fiber tube 20 gradually increases, the thickness expansion rate of the lithium-ion battery gradually increases and the battery's capacity retention rate gradually decreases. This is because as the diameter R1 of the conductive carbon fiber tube 20 increases, the number of conductive carbon fiber tubes 20 at the same weight decreases, the conductive network within the negative electrode sheet becomes loose, the conductivity deteriorates, and the battery's charge and discharge performance gradually deteriorates.

[0161] According to Examples 1-8 to 1-10, and 1-11 to 1-12 in Table 1, the gram capacity S of the conductive carbon fiber tube 20 satisfies 120 mAh / g ≤ S ≤ 300 mAh / g, and the first efficiency P satisfies 50% ≤ P ≤ 85%, effectively improving the capacity retention rate of the lithium-ion battery. This is because a gram capacity S in the range of 120 mAh / g to 200 mAh / g has the advantages of improving the energy density of the electrochemical device and making the conductive carbon fiber tube 20 less likely to break, and a first efficiency P in the range of 50% to 85% has the advantage of good conductivity.

[0162] As can be seen from Examples 1-13 to 1-16 in Table 1, the diameter R3 of the carbon nanotubes 30 satisfies 0.5 nm ≤ R3 ≤ 15 nm, allowing the carbon nanotubes 30 to be evenly dispersed while ensuring good electrical conductivity. When the diameter R3 of the carbon nanotubes 30 is below the lower limit of 0.5 nm, they are difficult to disperse and may become entangled with the conductive carbon fiber tubes 20. When the diameter R3 of the carbon nanotubes 30 is above the upper limit of 15 nm, the number of carbon nanotubes 30 per weight is reduced, leading to a loose conductive network.

[0163] According to Examples 1-23 to 1-27 in Table 1, it can be seen that by selecting the particle size of the silicon substrate 11 and the particle size of the carbon-containing active material 40 within an appropriate range, the thickness expansion rate and capacity retention rate of the lithium-ion battery can be effectively improved. This is because by selecting the particle size of the silicon substrate 11 and the particle size of the carbon-containing active material 40 to satisfy 1≤(D vc 90-D vc 50) / D vs 50≤5, which can make silicon distributed between the gaps between the particles of the carbon-containing active material 40, improve the compaction density of the electrode and limit the expansion of silicon. By selecting the particle size of the silicon substrate 11, the particle size of the carbon-containing active material 40 and the length of the conductive carbon fiber tube 20 to meet 0.2≤(L1-D vs 50) / D vc 50≤3.0, which enables the conductive carbon fiber tube 20 to construct a good conductive network between the carbon-containing active material 40 and the silicon particles.

[0164] The difference between Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-3 and Example 1-1 is that the contents of the conductive carbon fiber tubes 20, carbon nanotubes 30, lithium polyacrylate, silicon matrix 11 and carbon-containing active material 40 are different.

[0165] Table 2

[0166] It can be seen from Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-3 in Table 1 that by selecting the mass percentages of the conductive carbon fiber tubes 20, the carbon nanotubes 30, the chain adhesive, and the carbon-containing active material 40 within an appropriate range, the thickness expansion rate and the capacity retention rate of the lithium-ion battery can be effectively improved at the same time.

[0167] According to Examples 2-1 to 2-7 and Comparative Example 2-1, it can be seen that when the negative electrode active material layer does not include the conductive carbon fiber tubes 20, the thickness expansion rate of the lithium-ion battery increases. This is because the silicon substrate 11 particles lack long-range bonding and the mutual restriction is reduced. According to Examples 2-1 to 2-7 and Comparative Example 2-2, it can be seen that when the negative electrode active material layer does not include the carbon nanotubes 30, the capacity retention rate of the lithium-ion battery is not improved. This is because the conductive network structure is loose, which, on the one hand, leads to poor conductivity of the conductive network and failure to properly electrically conduct multiple conductive materials. On the other hand, the expansion of the silicon substrate 11 is not restrained, resulting in poor cohesion within the negative electrode active material layer.

[0168] According to Examples 2-1 to 2-7 and Comparative Example 2-3, it can be seen that when the mass percentage of the silicon material is too high and the mass percentage of the carbon-containing active material 40 is too low, the thickness expansion rate of the lithium-ion battery increases significantly, and the capacity retention rate of the lithium-ion battery decreases significantly. This is because the silicon material causes the anode electrode to expand too much, and many breakpoints appear in the conductive network.

[0169] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive carbon fiber tube and a carbon nanotube; the negative electrode active material comprises a silicon matrix, and the mass percentage of the silicon matrix is ​​Ms, based on the negative electrode active material layer, 5.0%≤Ms≤50.0%; The conductive carbon fiber tubes are distributed between particles of the negative electrode active material, and the carbon nanotubes are adsorbed on the surface of the negative electrode active material and the surface of the conductive carbon fiber tubes.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material layer satisfies at least one of the following conditions: (1) The length of the conductive carbon fiber tube is L1, and L1 satisfies: 3 μm ≤ L1 ≤ 30 μm; (2) A line connecting three points along the length of the same conductive carbon fiber tube forms a first angle α, 30°≤α≤180°; (3) The gram capacity of the conductive carbon fiber tube is S, and S satisfies: 120 mAh / g≤S≤300 mAh / g; (4) The primary efficiency of the conductive carbon fiber tube is P, and P satisfies: 50%≤P≤85%; (5) The outer diameter of the conductive carbon fiber tube is R1, and R1 satisfies: 20nm≤R1≤100nm; (6) The inner diameter of the conductive carbon fiber tube is R2, and R2 satisfies: 5nm≤R2≤10nm.

3. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material further includes a carbon shell layer coated on the surface of the silicon substrate. The thickness of the carbon shell layer is h, and h satisfies the following: 1 nm ≤ h ≤ 10 nm.

4. The negative electrode sheet according to claim 1, characterized in that: Based on the negative electrode active material layer, the mass percentage of the conductive carbon fiber tubes is Mx, the mass percentage of the carbon nanotubes is My, and the negative electrode active material layer satisfies at least one of the following conditions: (1)0.1≤Mx / My≤10; (2) 0.1% ≤ Mx ≤ 5.0%; (3)0.1%≤My≤3.0%.

5. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material layer satisfies at least one of the following conditions: (1) The outer diameter of the carbon nanotube is R3, and R3 satisfies: 0.5 nm ≤ R3 ≤ 15 nm; (2) The length of the carbon nanotube is L2, and L2 satisfies: 1 μm ≤ L2 ≤ 30 μm; (3) The carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

6. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material layer further includes a carbon-containing active material, the carbon-containing active material is distributed between particles of the negative electrode active material, and the carbon nanotubes are adsorbed on the surface of the carbon-containing active material.

7. The negative electrode sheet according to claim 6, characterized in that: Based on the negative electrode active material layer, the mass percentage of the carbon-containing active material is Mc, and the mass percentage of the conductive carbon fiber tube is Mx; the negative electrode active material layer satisfies at least one of the following conditions: (1) 0.05≤Ms / Mc≤1.25; (2)1%Ms+0.05%Mc≤Mx≤10%Ms+0.1%Mc; (3)40.0%≤Mc≤94.0%.

8. The negative electrode sheet according to claim 6, characterized in that: The particle size of the carbonaceous active material includes D vc 50 and D vc 90, the particle size of the silicon substrate includes D vs 50. The negative electrode active material layer satisfies at least one of the following conditions: (1)1≤(D vc 90-D vc 50) / D vs 50≤5; (2)0.2≤(L1-D vs 50) / D vc 50≤3.0; (3)1μm≤D vs 50≤10μm; (4)10μm≤D vc 90≤30μm; (5)5μm≤D vc 50≤15μm。 9. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material layer further includes a chain binder, wherein the chain binder is connected to at least two of the negative electrode active material, the conductive carbon fiber tube, and the carbon nanotube; Based on the negative electrode active material layer, the mass percentage of the chain binder is Mz, and Mz satisfies: 0.5%≤Mz≤3.0%.

10. The negative electrode sheet according to claim 1, characterized in that: The negative electrode plate further includes a negative electrode current collector, and the negative electrode active material layer is connected to the surface of the negative electrode current collector; The negative electrode active material layer has a cohesive force F2, and F2 satisfies: 15 N / m≤F2≤90 N / m.

11. An electrochemical device, characterized in that: The invention comprises the negative electrode sheet according to any one of claims 1 to 9.

Images