Negative electrode sheet and electrochemical device

Abstract

The application discloses a negative electrode sheet and an electrochemical device. The negative electrode sheet comprises a negative electrode active material layer, 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, the conductive carbon fiber tube is distributed between particles of the negative electrode active material, and the surface of the negative electrode active material and the surface of the conductive carbon fiber tube are both adsorbed with the carbon nanotube. When the mass percentage of the silicon matrix Ms is 5.0% to 50.0%, the silicon matrix, the conductive carbon fiber tube and the carbon nanotube are matched together. In the case that the silicon matrix expands, the conductive carbon fiber tube can still connect a plurality of negative electrode active material particles together to form a long-range conductive path and a short-range conductive path, and the conductive carbon fiber tube is not easy to break, so that a stable three-dimensional conductive network is built. The carbon nanotube can still be wound and adsorbed on the surface of the negative electrode active material to play a conductive role, and the direct contact between the negative electrode active material and the electrolyte is reduced, and then the occurrence of a side reaction is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical devices, and particularly relates to a negative electrode sheet and an electrochemical device. BACKGROUND

[0002] Electrochemical devices represented by lithium ion batteries have the outstanding characteristics of high energy density, long cycle life, and small pollution, no memory effect, etc. As clean energy, the application of electrochemical devices has gradually popularized from electronic products to large device fields such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.

[0003] Among them, for the negative electrode of the electrochemical device, the negative electrode active material layer is connected to the surface of the negative electrode current collector, and the materials containing silicon in the negative electrode active material layer are prone to swelling, which affects the stability of the negative electrode active material layer, and further leads to the reduction of the kinetic performance of the electrochemical device. SUMMARY

[0004] The embodiments of the present application provide a negative electrode sheet and an electrochemical device, which can improve the charging rate performance of the electrochemical device by improving the stability of the negative electrode sheet.

[0005] In a first aspect, the embodiments of the present application provide a negative electrode sheet, 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 mass percentage content of the material of the silicon matrix is Ms, 5.0%≤Ms≤50.0% based on the negative electrode active material layer; the negative electrode active material comprises a silicon matrix, the conductive carbon fiber tube is distributed between the particles of the negative electrode active material, and the surfaces of the negative electrode active material and the conductive carbon fiber tube are both adsorbed with the carbon nanotube.

[0006] In some exemplary embodiments, the negative electrode active material layer satisfies at least one of the following conditions:

[0007] (1) the length of the conductive carbon fiber tube is L1, and L1 satisfies: 3μm≤L1≤30μm;

[0008] (2) the same conductive carbon fiber tube forms a first included angle a along the length direction of the conductive carbon fiber tube, and 30°≤a≤180°;

[0009] (3) the specific capacity of the conductive carbon fiber tube is S, and S satisfies: 120mAh / g≤S≤300mAh / g;

[0010] (4) the initial efficiency of the conductive carbon fiber tube is P, and P satisfies: 50%≤P≤85%;

[0011] (5) the outer diameter of the conductive carbon fiber tube is R1, and R1 satisfies: 20nm≤R1≤100nm;

[0012] (6) the inner diameter of the conductive carbon fiber tube is R2, and R2 satisfies 5 nm≤R2≤10 nm.

[0013] In some exemplary embodiments, the negative electrode active material further comprises a carbon shell layer coated on the surface of the silicon substrate, and the thickness of the carbon shell layer is h, h satisfying 1 nm≤h≤10 nm.

[0014] In some exemplary embodiments, the mass percentage content of the conductive carbon fiber tube is Mx, and the mass percentage content of the carbon nanotube is My, with reference to the negative electrode active material layer, and the negative electrode active material layer satisfies at least one of the following conditions:

[0015] (1) 0.1≤Mx / My≤10;

[0016] (2) 0.1%≤Mx≤5.0%;

[0017] (3) 0.1%≤My≤3.0%.

[0018] In some exemplary embodiments, the negative electrode active material layer satisfies at least one of the following conditions:

[0019] (1) the outer diameter of the carbon nanotube is R3, and R3 satisfies 0.5 nm≤R3≤15 nm;

[0020] (2) the length of the carbon nanotube is L2, and L2 satisfies 1 μm≤L2≤30 μm;

[0021] (3) the carbon nanotube comprises at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.

[0022] In some exemplary embodiments, the negative electrode active material layer further comprises a carbon-containing active material, the carbon-containing active material is distributed among the particles of the negative electrode active material, and the surface of the carbon-containing active material is adsorbed with the carbon nanotube.

[0023] In some exemplary embodiments, the mass percentage content of the carbon-containing active material is Mc, and the mass percentage content of the conductive carbon fiber tube is Mx, with reference to the negative electrode active material layer, and the negative electrode active material layer satisfies at least one of the following conditions:

[0024] (1) 0.05≤Ms / Mc≤1.25;

[0025] (2) 1%Ms+0.05%Mc≤Mx≤10%Ms+0.1%Mc;

[0026] (3) 40.0%≤Mc≤94.0%.

[0027] In some exemplary embodiments, the particle size of the carbon-containing 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:

[0028] (1) 1 ≤ (D vc 90-D vc 50) / D vs 50≤5;

[0029] (2) 0.2 ≤ (L1 - D vs 50) / D vc 50≤3.0;

[0030] (3) 1μm≤D vs 50≤10μm;

[0031] (4) 10μm≤D vc 90≤30μm;

[0032] (5) 5μm≤D vc 50≤15μm.

[0033] In some exemplary embodiments, the negative electrode active material layer further includes a chain adhesive that connects at least two of the negative electrode active material, the conductive carbon fiber tube, and the carbon nanotube.

[0034] Based on the negative electrode active material layer, the mass percentage of the chain adhesive is Mz, and Mz satisfies: 0.5% ≤ Mz ≤ 3.0%.

[0035] 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;

[0036] The negative electrode active material layer has a cohesive force F2, which satisfies: 15N / m≤F2≤90N / m.

[0037] Secondly, this application provides an electrochemical device, including the negative electrode as described above.

[0038] Based on the negative pole piece and the electrochemical device of the embodiment of the present application, by utilizing the characteristics of the conductive carbon fiber tube, such as large rigidity, large outer diameter, not easy to bend, long straight state, no winding, and by utilizing the characteristics of the carbon nanotube, such as relatively soft, can be wound and adsorbed on the surface of the negative pole active material, by selecting the mass percentage content Ms of the silicon substrate in the range of 5.0%≤Ms≤50.0%, the silicon substrate, the conductive carbon fiber tube and the carbon nanotube cooperate, in the case of expansion of the silicon substrate, the conductive carbon fiber tube can still connect a plurality of negative pole active material particles together to form a long-range conductive path and a short-range conductive path, not easy to break, to build a stable three-dimensional conductive network, the carbon nanotube can also be wound and adsorbed on the surface of the negative pole active material to play a conductive role, and reduce the direct contact between the negative pole active material and the electrolyte, thereby reducing the occurrence of side reactions. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 The structure schematic diagram of the carbon nanotube coated on the surface of the negative pole active material and the conductive carbon fiber tube of an embodiment of the present application.

[0041] Reference signs:

[0042] 10, negative pole 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] Hereinafter, the embodiments of the electrochemical device and the electric device of the present application will be specifically described with reference to the drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well and repeated description of substantially the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided in order for those skilled in the art to fully understand the present application, and is not intended to limit the subject matter recited in the claims.

[0044] The "range" disclosed in the present application is defined in the form of lower limit and upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can include or not include the end value, and can be arbitrarily combined, i.e. any lower limit can 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 new technical solutions.

[0046] Unless otherwise specified, the "includes" and "contains" mentioned in the present application represent open type, and can also be closed type. For example, the "includes" and "contains" can represent that other components not listed can also be included or contained, or only the listed components can be included or contained.

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

[0048] 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, and the material containing silicon and the like in the negative electrode active material layer is prone to swelling, affecting the stability of the negative electrode active material layer, and further leading to the reduction of the kinetic performance of the electrochemical device. Based on this, the embodiments of the present application provide a negative electrode sheet and an electrochemical device, which can improve the stability of the negative electrode sheet, and further improve the kinetic performance of the electrochemical device.

[0049] The negative electrode sheet 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 tube is distributed between the particles of the negative electrode active material, the conductive carbon fiber tube is in the form of a long straight or a rod with a certain curvature, and each conductive carbon fiber tube is not wound by itself, and the adjacent conductive carbon fiber tubes are not wound. The conductive carbon fiber tube has a certain length, can be connected to materials with different spacings, plays a role of short-range and long-range conduction, and is convenient for connecting with more conductive materials, is beneficial to building a three-dimensional conductive network with a dense structure, improves the conductivity of the negative electrode active material layer, and further improves the kinetic performance of the electrochemical device. The conductive carbon fiber tube has a certain length, can also increase the probability of contact with other conductive substances, and is helpful to further reduce the internal resistance of the negative electrode active material layer.

[0051] The unwound state of the conductive carbon fiber tube is defined as follows: Three points are randomly selected along the length of the same conductive carbon fiber tube, forming a first included angle α, where 30° ≤ α ≤ 180°. For example, the conductive carbon fiber tube can be long and straight or curved with a certain degree of curvature. By selecting a stretched-out state for the conductive carbon fiber tube, it can maximize the conductivity between two conductive materials that are far apart, fully utilizing its long-range conductivity. Furthermore, it facilitates the adsorption or adhesion of other substances, thereby enhancing 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 within the negative electrode active material layer. Even with an increased length of the conductive carbon fiber tube 20, its long-range conductivity cannot be fully utilized. Furthermore, the materials connected to the conductive carbon fiber tube 20 are also prone to uneven dispersion. For example, the carbon nanotubes 30 connected to the conductive carbon fiber tube 20 are not evenly dispersed, which will lead to a poorer short-range conductivity and thus hinder the improvement of the internal resistance of the negative electrode sheet. The adhesive connected to the conductive carbon fiber tube 20 is not evenly dispersed, which prevents the adhesive from fully exerting its bonding effect and connecting with more materials. This leads to a decrease in the cohesion within the negative electrode active material layer, resulting in a poor effect on improving the thickness expansion rate of the electrochemical device when the negative electrode sheet is used in an electrochemical device.

[0052] The length of the conductive carbon fiber tube is L1, which satisfies the condition: 3μm ≤ L1 ≤ 30μm. For example, L1 can be 3μm, 8μm, 10μm, 15μm, 20μm, 30μm, or any range thereof. When L1 satisfies 3μm ≤ L1 ≤ 30μm, the conductive network within the negative electrode active material layer can form a spatially stable and uniform three-dimensional conductive network. When L1 is below the lower limit of 3μm, the conductive carbon fiber tube is too short, reducing the probability of contact between each conductive carbon fiber tube and other conductive materials, which is detrimental to improving the conductivity of the negative electrode sheet. When L1 is above the upper limit of 30μm, the conductive carbon fiber tube is too long and difficult to disperse, leading to easy cross-linking and entanglement of the conductive carbon fiber tube, resulting in uneven conductivity distribution in the negative electrode active material layer, which is detrimental to ion transport.

[0053] like Figure 1 As shown, 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 or completely coat the surface of the silicon substrate 11. The silicon substrate 11 has the ability to adsorb and release metal ions. The carbon shell 12 can bind the silicon substrate 11, reducing its expansion. Furthermore, the coating of the silicon substrate 11 by the carbon shell 12 can reduce the contact between the silicon substrate 11 and the electrolyte, thus reducing the occurrence of side reactions. The silicon substrate 11 is made of elemental silicon.

[0054] The thickness of the carbon shell layer 12 is h, and h satisfies 1 nm≤h≤10 nm. For example, h can be 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, or any range between any two of the above. By selecting the thickness h of the carbon shell layer 12 in the range of 1 nm≤h≤10 nm, the carbon shell layer 12 can well play a role in limiting the expansion of the silicon matrix 11, and can still play a good role in isolating the silicon matrix 11 in the case that the silicon matrix 11 has a tendency to expand or slightly expands. When h is lower than the lower limit 1 nm, the carbon shell layer has poor ability to limit the expansion of the silicon matrix 11, and is also prone to breakage when the silicon matrix 11 expands. When h is higher than the upper limit 10 nm, the carbon shell layer 12 is too thick, which is not conducive to the passage of metal ions when the silicon matrix 11 absorbs and releases metal ions. In addition, the carbon shell layer 12 is too thick and is prone to occupy more space, which is not conducive to improving the energy density of the electrochemical device.

[0055] The negative active material layer further comprises carbon nanotubes 30, the conductive carbon fiber tubes 20 are distributed between the particles of the negative active material 10, and the surfaces of the negative active material 10 and the conductive carbon fiber tubes 20 are both adsorbed with carbon nanotubes 30. Compared with the carbon nanotubes 30, the conductive carbon fiber tubes 20 have a higher graphitization degree, a larger rigidity, and a larger outer diameter, and are not easy to bend and are in a long straight state without winding. The conductive carbon fiber tubes 20 can connect multiple negative active material 10 particles in series to form a long-range conductive path, and are not easy to break after the negative electrode plate expands. The carbon nanotubes 30 are relatively soft and can be wound and adsorbed on the surface of the negative active material 10. On the one hand, the carbon nanotubes 30 play a short-range conductive role, and on the other hand, the carbon nanotubes 30 can reduce the direct contact between the negative active material 10 and the electrolyte, thereby reducing the occurrence of side reactions.

[0056] The carbon shell layer 12 coated on the surface of the silicon matrix 11 can be connected with the conductive carbon fiber tubes 20 and the carbon nanotubes 30 respectively, and a three-dimensional conductive network can be constructed to further reduce the internal resistance of the negative electrode plate, which can effectively improve the effect of volume expansion of the electrochemical device during the cycle process.

[0057] The gram capacity of the conductive carbon fiber tube 20 is the ratio of the discharge capacity of the conductive carbon fiber tube 20 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: 120 mAh / g≤S≤300 mAh / g, for example, S can be 120 mAh / g, 140 mAh / g, 160 mAh / g, 180 mAh / g, 200 mAh / g, or any range between any of the foregoing. By selecting the gram capacity S of the conductive carbon fiber tube 20 in the range of 120 mAh / g≤S≤300 mAh / g, the conductive carbon fiber tube 20 has good electrical conductivity while enabling the electrochemical device to have a higher energy density when the negative electrode sheet is applied to the electrochemical device. When the gram capacity S of the conductive carbon fiber tube 20 is lower than the lower limit 120 mAh / g, the electrical conductivity of the conductive carbon fiber tube 20 is too low to facilitate lithium intercalation, resulting in a reduced energy density. When the gram capacity S of the conductive carbon fiber tube 20 is higher than the upper limit 200 mAh / g, the conductive carbon fiber tube 20 needs to have a higher degree of graphitization, resulting in a brittle conductive carbon fiber tube 20 that is prone to breakage during production and difficult to achieve the desired length.

[0058] The initial 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 initial 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 between any of the foregoing. By selecting the initial efficiency P of the conductive carbon fiber tube 20 to satisfy 50%≤P≤85%, the conductive carbon fiber tube 20 has a low initial efficiency that can improve the degree of lithiation, where the process of lithium ions intercalating into the interstitial spaces of the conductive carbon fiber tube 20 to form lithium compounds is the lithiation process, which increases the movement of ions and electrons in other materials in the negative electrode active material layer, thereby improving the electronic conductivity of the other materials. For example, when the negative electrode active material layer has graphite, the conductive carbon fiber tube 20 has a low initial efficiency, and the movement of ions and electrons in the graphite increases during the lithiation process, which improves the electronic conductivity of the graphite, reduces the internal resistance of the electrochemical device, and further improves the discharge performance of the electrochemical device. When the initial efficiency S of the conductive carbon fiber tube 20 is lower than the lower limit 50%, too many lithium ions are lost, which adversely affects the graphite. When the initial efficiency S of the conductive carbon fiber tube 20 is higher than the upper limit 85%, the degree of lithiation of the conductive agent is too low, which reduces the electronic conductivity.

[0059] In some example embodiments, the outer diameter of the conductive carbon fiber tube 20 is R1, and R1 satisfies 20 nm≤R1≤100 nm. For example, R1 can be 20 nm, 30 nm, 40 nm, 60 nm, 80 nm, 100 nm, or any range between any two of the aforementioned values. By selecting the outer diameter R1 of the conductive carbon fiber tube 20 to satisfy 20 nm≤R1≤100 nm, the outer diameter of the conductive carbon fiber tube 20 is appropriate, which can exhibit good conductivity and reduce the resistance of the negative electrode sheet. When the outer diameter R1 of the conductive carbon fiber tube 20 is less than the lower limit 20 nm, the stiffness of the conductive fiber is reduced, which is prone to winding and reduces the long-range conductivity. When the outer diameter R1 of the conductive carbon fiber tube 20 is greater than the upper limit 100 nm, the number of conductive fibers is reduced under the same weight, which reduces the density of the conductive network and deteriorates the performance of the electrode sheet.

[0060] In some example embodiments, the outer diameter of the conductive carbon fiber tube 20 is R1, and R1 satisfies 20 nm≤R1≤100 nm. For example, R1 can be 20 nm, 30 nm, 40 nm, 60 nm, 80 nm, 100 nm, or any range between any two of the aforementioned values. By selecting the outer diameter R1 of the conductive carbon fiber tube 20 to satisfy 20 nm≤R1≤100 nm, the outer diameter of the conductive carbon fiber tube 20 is appropriate, which can exhibit good conductivity and reduce the resistance of the negative electrode sheet. When the outer diameter R1 of the conductive carbon fiber tube 20 is less than the lower limit 20 nm, the stiffness of the conductive fiber is reduced, which is prone to winding and reduces the long-range conductivity. When the outer diameter R1 of the conductive carbon fiber tube 20 is greater than the upper limit 100 nm, the number of conductive fibers is reduced under the same weight, which reduces the density of the conductive network and deteriorates the performance of the electrode sheet.

[0061] In some example embodiments, the outer diameter of the conductive carbon fiber tube 20 is R1, and R1 satisfies 20 nm≤R1≤100 nm. For example, R1 can be 20 nm, 30 nm, 40 nm, 60 nm, 80 nm, 100 nm, or any range between any two of the aforementioned values. By selecting the outer diameter R1 of the conductive carbon fiber tube 20 to satisfy 20 nm≤R1≤100 nm, the outer diameter of the conductive carbon fiber tube 20 is appropriate, which can exhibit good conductivity and reduce the resistance of the negative electrode sheet. When the outer diameter R1 of the conductive carbon fiber tube 20 is less than the lower limit 20 nm, the stiffness of the conductive fiber is reduced, which is prone to winding and reduces the long-range conductivity. When the outer diameter R1 of the conductive carbon fiber tube 20 is greater than the upper limit 100 nm, the number of conductive fibers is reduced under the same weight, which reduces the density of the conductive network and deteriorates the performance of the electrode sheet.

[0062] In some example embodiments, the outer diameter of the conductive carbon fiber tube 20 is R1, and R1 satisfies 20 nm≤R1≤100 nm. For example, R1 can be 20 nm, 30 nm, 40 nm, 60 nm, 80 nm, 100 nm, or any range between any two of the aforementioned values. By selecting the outer diameter R1 of the conductive carbon fiber tube 20 to satisfy 20 nm≤R1≤100 nm, the outer diameter of the conductive carbon fiber tube 20 is appropriate, which can exhibit good conductivity and reduce the resistance of the negative electrode sheet. When the outer diameter R1 of the conductive carbon fiber tube 20 is less than the lower limit 20 nm, the stiffness of the conductive fiber is reduced, which is prone to winding and reduces the long-range conductivity. When the outer diameter R1 of the conductive carbon fiber tube 20 is greater than the upper limit 100 nm, the number of conductive fibers is reduced under the same weight, which reduces the density of the conductive network and deteriorates the performance of the electrode sheet.

[0063] In some example embodiments, the mass percentage My of the carbon nanotubes 30 satisfies: 0.1%≤My≤3.0%, for example, My can be 0.1%, 1.5%, 2.0%, 2.5%, 3.0% or any range between any of the aforementioned two.

[0064] In some example embodiments, the outer diameter of the carbon nanotubes 30 is R3, and R3 satisfies: 0.5nm≤R3≤15nm, for example, R3 can be 0.5nm, 5nm, 10nm, 12nm, 15nm or any range between any of the aforementioned two. By selecting the outer diameter R3 of the carbon nanotubes 30 to satisfy: 0.5nm≤R3≤15nm, the carbon nanotubes 30 can obtain good flexibility to better coat the surface of the negative active material 10 and the conductive carbon fiber tube 20, and improve the conductivity of the negative electrode sheet. Preferably, R3 satisfies: 1nm≤R3≤3nm.

[0065] In some example embodiments, the length of the carbon nanotubes 30 is L2, and L2 satisfies: 1μm≤L2≤30μm, for example, L2 can be 1μm, 10μm, 15μm, 20μm, 25μm, 30μm or any range between any of the aforementioned two. By selecting the length L2 of the carbon nanotubes 30 to satisfy: 1μm≤L2≤30μm, the carbon nanotubes 30 can stably adhere to the surface of the negative active material 10 and the conductive carbon fiber tube 20. Preferably, L2 satisfies: 5μm≤L2≤20μm.

[0066] In some example embodiments, the carbon nanotubes 30 include single-walled carbon nanotubes and multi-walled carbon nanotubes, and preferably, the carbon nanotubes 30 include single-walled carbon nanotubes. The single-walled carbon nanotubes have high specific surface area and good conductivity, and their surfaces can also provide good diffusion paths for lithium ions.

[0067] The negative active material layer further includes carbon-containing active material 40 distributed between the particles of the negative active material 10, wherein the surface of the carbon-containing active material 40 particles adsorbs the carbon nanotubes 30, which further helps to form a three-dimensional conductive network with a dense structure to reduce the internal resistance. The carbon-containing active material 40 includes at least one of graphite and hard carbon, and preferably, the carbon-containing active material 40 is graphite. In the process of charging and discharging of the electrochemical device, the silicon matrix 11 of the negative active material 10 will expand. By arranging the carbon-containing active material 40 to be distributed between the particles of the negative active material 10, the carbon-containing active material 40 and the carbon shell layer 12 jointly limit the expansion of the silicon matrix 11, prevent the expansion of the silicon matrix 11 from affecting the stability inside the negative active material layer, and the carbon-containing active material 40 can also play a conductive role to further reduce the internal resistance of the negative active material layer.

[0068] In some example embodiments, the mass percentage of the material of the silicon matrix 11 is Ms, 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 between any two of the above. The silicon matrix 11 has high capacity performance, and the carbon-containing active material 40 has low expansion performance. By selecting the content of both the silicon matrix 11 and the carbon-containing active material 40 to satisfy 0.05≤Ms / Mc≤1.25, both the energy density and the performance of the electrochemical device can be improved. When Ms / Mc is lower than the lower limit 0.05, the energy density of the electrochemical device will be lost. When Ms / Mc is higher than the upper limit 1.25, the electrochemical device will expand too much.

[0069] In some example embodiments, the mass percentage of the silicon matrix 11 is Ms, and 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 between any two of the above. By selecting the mass percentage of the silicon matrix 11 to be in the range of 5.0%≤Ms≤50.0%, the silicon matrix 11, the conductive carbon fiber tube, and the carbon nanotube cooperate to, in the case of expansion of the silicon matrix 11, still enable the conductive carbon fiber tube to connect multiple negative electrode active material particles together to form long-range and short-range conductive paths, which are not prone to breaking, to build a stable three-dimensional conductive network, and the carbon nanotube can still wrap and adsorb on the surface of the negative electrode active material to play a conductive role and reduce direct contact between the negative electrode active material and the electrolyte, thereby reducing the occurrence of side reactions.

[0070] In some example embodiments, the mass percentage of the carbon-containing active material 40 is Mc, and 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 between any two of the above.

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

[0072] In some example embodiments, the particle size of the carbon-containing active material 40 includes D vc 50 and D vc 90, and the particle size of the silicon matrix 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 two. By selecting the particle size of the carbon-containing active material 40 to satisfy 1 ≤ (D vc 90 - D vc 50) / D vs 50 ≤ 5, the particles of the silicon matrix 11 are distributed among the particles of the carbon-containing active material 40, which helps to increase the packing density of the negative active material layer and also limits the expansion of the silicon matrix 11, which can improve the expansion of the electrochemical device.

[0073] In some example 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 of the two. 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, the conductive carbon fiber tube 20 is helped to be connected in series among the particles of the negative active material 10, forming a stable long-range conductive network.

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

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

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

[0077] In some example embodiments, the negative active material layer further comprises a chain-like adhesive, the chain-like adhesive is connected to at least two of the negative active material 10, the conductive carbon fiber tube 20, the carbon nanotube 30, and the carbon-containing active material 40, and the chain-like adhesive bonds each substance in the negative active material layer into one body, which helps to improve the cohesion of the negative active material layer. The chain-like adhesive can also be bonded to the negative current collector of the negative electrode sheet, so that the negative active material layer is stably bonded to the negative current collector.

[0078] The type of the chain-like adhesive is not limited in the embodiments of the present application, and any chain-like adhesive that can connect the materials in the negative active material layer is suitable for the present application. For example, the chain-like adhesive comprises at least one of a lithium salt organic matter and a non-lithium salt organic matter. Specifically, the lithium salt organic matter comprises at least one of lithium polyacrylate, lithium carboxymethyl cellulose, lithium acrylate, and a polymer of polyaniline. The non-lithium salt organic matter comprises at least one of sodium carboxymethyl cellulose and acrylic acid.

[0079] Preferably, the chain-like adhesive comprises a lithium salt organic matter. Selecting the lithium salt organic matter as the chain-like adhesive can increase the concentration of lithium ions in the negative active material layer, accelerate the transmission of lithium ions in the negative active material layer, and thus help to improve the kinetic performance of the electrochemical device.

[0080] The mass percentage content of the chain-like adhesive is Mz based on the negative active material layer, and Mz satisfies: 0.5%≤Mz≤3.0%. For example, Mz can be 0.5%, 0.8%, 1.0%, 2.0%, 3.0%, or any range between any of the two. Selecting the mass percentage content Mz of the chain-like adhesive to satisfy: 0.5%≤Mz≤3.0% helps to achieve good bonding effect.

[0081] The negative electrode sheet of the embodiments of the present application further comprises a negative current collector, and the negative active material layer is connected to the surface of the negative current collector. Specifically, the negative current collector comprises two surfaces oppositely arranged in the thickness direction, and the negative active material layer is connected to at least one of the two surfaces of the negative current collector.

[0082] The cohesion force can reflect the interaction force between the materials inside the negative active material layer. The greater the cohesion force, the more difficult the negative active material layer is to fall off the negative current collector. In some exemplary embodiments, the negative active material layer has a cohesion force F2, which satisfies: 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 between any of the aforementioned values.

[0083] The negative electrode tab of the embodiments of the present application comprises a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative current collector of the present application is not particularly limited as long as the purpose of the present application can be achieved. In some embodiments, the negative current collector comprises, but is not limited to, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative current collector is a copper foil.

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

[0085] The embodiments of the present application also provide an electrochemical device, which can be a lithium ion battery or any other suitable electrochemical device. Without departing from the disclosure of the present application, the electrochemical device of the embodiments of the present application comprises any device that undergoes an electrochemical reaction, and specific examples thereof 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 tab provided with a positive active material capable of occluding and releasing metal ions, and a negative electrode tab provided with a negative active material capable of occluding and releasing metal ions, and the main feature is that it comprises any of the above-mentioned negative electrode tabs of the present application.

[0087] The electrochemical device of the present application further comprises a negative electrode tab, a positive electrode tab, a separator, an electrolyte, and an outer package. The positive electrode tab is disposed on the positive electrode tab, the negative electrode tab is disposed on the negative electrode tab, the separator is disposed between the positive electrode tab and the negative electrode tab, the positive electrode tab, the separator, and the negative electrode tab are overlapped and stacked to form a laminated electrode assembly, or the positive electrode tab, the separator, and the negative electrode tab are overlapped and stacked and wound to form a wound electrode assembly. The electrode assembly is placed in the inner space of the outer package, the positive electrode tab and the negative electrode tab are led out from the inner space of the outer package and electrically connected to the external circuit, and the electrolyte is filled in the inner space of the outer package.

[0088] The positive electrode tab, the negative electrode tab, the positive electrode tab, the separator, the electrolyte, and the outer packaging are not particularly limited in the embodiments of the present application, and any material suitable for use in the art is suitable for use in the present application.

[0089] The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. The positive electrode tab is not particularly limited in the present application, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material is not particularly limited in the embodiments of the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithium intercalation compound). In some embodiments, the positive electrode active material can 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 lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel manganate (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. The binder can improve the binding between the positive electrode active material particles and each other, and can improve the binding 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, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, nylon, and the like.

[0091] In some embodiments, the positive electrode active material layer optionally further includes a conductive material, thereby imparting electrical conductivity to the positive electrode active material layer. The conductive material can include any conductive material, as long as it does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powder, metal fibers, 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, for example, including but not limited to aluminum foil.

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

[0094] The separator film that can be used in embodiments of the present application can be a separator film known in the art. The separator film has insulating properties, and the material of the separator film is selected from any one of a polymer film, a multilayer polymer film, or a nonwoven fabric formed of a mixture of two or more of the following polymers: polyethylene, polypropylene, polyethylene terephthalate, polyphenylene terephthalamide, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymer, polyphenylene sulfide, and polyvinyl 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 electrolyte that can be used in embodiments of the present application can be an electrolyte known in the art. The electrolyte can be classified into an aqueous electrolyte and a nonaqueous electrolyte, and an electrochemical device using the nonaqueous electrolyte can operate in a wider voltage window than an electrochemical device using the aqueous electrolyte, thereby achieving a higher energy density. In some embodiments, the nonaqueous electrolyte includes an organic solvent, an electrolyte, and an additive.

[0096] The electrolyte in the electrolyte that can be used in embodiments of the present application includes, but is not limited to, inorganic lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, and the like; fluorine-containing organic lithium salts such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, LiPF4(CF3)2, LiN(CF3SO2)(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; dicarboxylic acid complex-containing lithium salts such as lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and the like. In addition, the above electrolytes can be used alone or simultaneously with two or more. For example, in some embodiments, the electrolyte includes a combination of LiPF6and LiBF4. In some embodiments, the electrolyte includes LiPF6.

[0097] In some embodiments, the electrolyte has a concentration in a range from 0.8 mol / L to 3 mol / L, for example, in a range from 0.8 mol / L to 2.5 mol / L, in a range from 0.8 mol / L to 2 mol / L, in a range from 1 mol / L to 2 mol / L, and 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 additive used in the electrolyte of the embodiments of the present application can be an additive known in the art that can be used to improve the electrochemical performance of the battery. In some embodiments, the additive includes, but is not limited to, at least one of a polycarbonitrile compound, a sulfur-containing additive, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and 1,4 butane sultone.

[0099] The organic solvent used in the electrolyte of the embodiments of the present application can be any organic solvent known in the 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. Among them, examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluoro-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 including the aforementioned electrochemical device.

[0102] The negative electrode tab according to the embodiments of the present application can improve the dynamic kinetic performance of the electrochemical device, so that the electrochemical device manufactured therefrom is suitable for electronic devices in various fields, and in particular, is suitable for electronic devices that work under large 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 art. For example, the electronic device includes, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio players, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors, etc. In addition, the electrochemical device of the present application is applicable not only to the above-mentioned electronic devices, but also to energy storage power stations, sea-borne vehicles, and air-borne vehicles. The air-borne vehicles include air-borne vehicles within the atmosphere and air-borne vehicles outside the atmosphere.

[0104] The present application will be further specifically explained below by taking lithium-ion batteries as examples and in combination with specific examples and comparative examples, but the present application is not limited to these examples as long as the gist thereof is not deviated from. In the following examples and comparative examples, the reagents, materials and instruments used are commercially available or synthetically obtained unless otherwise specified.

[0105] The performance of the lithium-ion batteries in the examples and comparative examples of the present application is tested by using the following methods.

[0106] 1. Test method for the length, inner diameter and outer diameter of both the conductive carbon fiber tube 20 and the carbon nanotube 30

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

[0108] (2) Soak the negative electrode sheet in DMC (dimethyl carbonate) at 25°C for 60 min to remove the electrolyte, and then take it out and dry at 25°C.

[0109] (3) Obtain the cross section of the negative electrode active material layer on the negative electrode sheet by brittle fracture of the negative electrode sheet in (2) with liquid nitrogen.

[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 at least 5 different positions, and take the average value of the target material as the target value.

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

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

[0113] (2) The negative electrode sheet is 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) The cross section of the negative electrode active material layer obtained in (3) is observed under SEM, and at least 5 different positions are tested, with a total of not less than 15 target materials. If the relaxed state of the conductive carbon fiber tube 20 exists, and a first included angle a is formed by connecting any three points on the same conductive carbon fiber tube 20 along the length direction thereof, 30°≤a≤180°, then it is the non-winding conductive carbon fiber tube 20 of the present application.

[0116] 3. Cohesive force test method

[0117] (1) Disassemble the finished battery to obtain a negative electrode sheet.

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

[0119] (3) The cohesive force of the negative electrode sheet in (2) is tested by using a high-iron tension machine and a 90° angle method, and the specific steps are as follows:

[0120] a. The negative electrode sheet is made into a strip, with the negative electrode active material layer facing up, and the other side is taped to a steel plate along the length direction.

[0121] b. The center area of the upward-facing negative electrode active material layer surface is taken as a stable area, and adhesive tape is applied to the surface of the stable area, leaving a 5 cm blank end.

[0122] c. The steel plate is fixed in the corresponding position of the high-iron tension machine, and the blank end is clamped in the chuck. When the tension of the chuck is greater than 0 kgf and less than 0.02 kgf, the high-iron tension machine can be started to test, with a stretching speed of 5 mm / min, and stretched to the breaking state. The average value of the tension of the stable area is recorded as the cohesive force of the target interface. In particular, the ratio of the standard deviation of the cohesive force data of this stable area to the average value is not more than 10%.

[0123] 4. Battery thickness expansion rate and capacity retention rate test method after 500 cycles

[0124] The following procedures are completed at 45°C:

[0125] (1) Take the finished battery cell and stand for 2 h, and discharge at 0.5C to a voltage of 3.0V, and stand for 5 min.

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

[0127] (3) charge to 4.40V at 1.0C, then charge to 0.7C at 4.40V.

[0128] (4) charge to 4.50V at 0.7C, then charge to 0.025C at 4.50V, stand for 5min.

[0129] (5) 0.5C discharge to 3.0V.

[0130] (6) take the steps in (2)-(5) as one charge-discharge cycle, cycle the processes in (2)-(5) for 50 times, and then test the thickness of the battery after the 50th cycle, then 0.5C discharge to 3.0V,

[0131] (7) cycle (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℃, measure the thickness of the battery embedded with the positive electrode tab as T1; take the battery after 500 cycles in (7) and full charge to 4.30V, place it in an environment of 25±2℃, measure the thickness of the battery embedded with the positive electrode tab 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 of the 6th week as C0, and the capacity of the 500th week as C500, the capacity retention rate of the battery after 500 cycles is C500 / C6*100%

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

[0136] (1) disassemble the finished battery to obtain the negative electrode tab;

[0137] (2) soak the negative electrode tab in DMC (dimethyl carbonate) at 25℃ for 60min to remove the electrolyte, take out and dry at 25℃.

[0138] (3) obtain the cross section of the negative electrode active material layer on the negative electrode tab in (2) by plasma cutting.

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

[0140] Example 1-1

[0141] I. Preparation of lithium ion battery

[0142] 1. Preparation of negative electrode sheet

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

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

[0145] b. Place the silicon core in the reaction chamber, then supply the carbon source gas into the reaction chamber by chemical vapor deposition method (CVD method). Common carbon source gases include methane (CH4) or ethylene (C2H4), which will chemically react 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 time and higher carbon source concentration usually result in thicker carbon shell.

[0146] (2) Dissolve the chain binder in deionized water at a solid content of 5%, stir and disperse uniformly to form a glue solution, take 30% of the total amount of glue solution and mix with carbon-containing active material 40 (graphite), negative electrode active material 10, conductive carbon fiber tube 20, single-walled carbon nanotube 30, then add the remaining glue solution, appropriate amount of deionized water, and adjust the solid content of the negative electrode active material layer slurry to 10%, stir uniformly, then coat it on a 5 μm copper foil, and dry to form a negative electrode sheet.

[0147] 2. Preparation of positive electrode sheet

[0148] Mix the positive electrode active material lithium cobaltate, conductive agent acetylene black, carbon nanotube, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97.5:0.7:0.5:1.3 in the solvent N-methyl pyrrolidone (NMP), and stir uniformly in a vacuum stirrer to obtain a positive electrode slurry (solid content 70%). Coat the positive electrode material on a 9 μm thick positive electrode current collector aluminum foil, dry, cold press to form a positive electrode active material layer about 75 μm thick, then cut and weld the tabs to obtain a positive electrode sheet.

[0149] 3. Preparation of electrolyte

[0150] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:PC:EMC:DEC=10:25:35:30, then 2% fluorinated ethylene carbonate was added, after dissolution and sufficient stirring, lithium salt LiPF6 was added, and the electrolyte was obtained after mixing uniformly. The concentration of LiPF6 was 1 mol / L.

[0151] 4. Preparation of the separator film

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

[0153] 5. Preparation of the lithium ion battery

[0154] The obtained positive electrode sheet, the separator film, and the negative electrode sheet were stacked in order, and the positive electrode tab was installed on the positive electrode sheet and the negative electrode tab was installed on the negative electrode sheet, so that the separator film was between the positive electrode sheet and the negative electrode sheet to play a separating role, and then the electrode assembly was obtained by winding. The electrode assembly was placed in an outer packaging foil aluminum plastic film, electrolyte was injected, and the lithium ion battery was obtained after vacuum packaging, standing, and formation processes.

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

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

[0157] Examples 1-2 to 1-32 differ from Example 1-1 in that the parameters of the negative electrode active material layer are different, and the related parameters are shown in Table 1.

[0158]

[0159] According to Table 1, it can be seen from Examples 1-1 to 1-4, 1-32 that when the length L1 of the conductive carbon fiber tube 20 satisfies 3 pm ≤ L1 ≤ 30 pm, the thickness expansion rate and the capacity retention rate of the lithium ion battery can be effectively improved. When the length L1 of the conductive carbon fiber tube 20 is less than the lower limit of 3 pm, the length of the conductive carbon fiber tube 20 is too short, and it is difficult to achieve the purpose of electrically connecting two conductive materials at a long distance, which reduces the conductivity of the negative active material layer, and also causes the negative effect of increased battery expansion during the cycle. When the length L1 of the conductive carbon fiber tube 20 is greater than the upper limit of 30 pm, it will cause the negative effect of uneven distribution of winding.

[0160] According to Table 1, it can be seen from Examples 1-1 to 1-4, 1-21 to 1-22, 1-32 that compared with the negative active material without a carbon shell layer in Example 1-32, by selecting the thickness h of the carbon shell layer to satisfy 1 nm ≤ h ≤ 10 nm in Examples 1-1 to 1-4, the thickness expansion rate and the capacity retention rate of the lithium ion battery can be effectively improved.

[0161] According to Table 1, it can be seen from Examples 1-5 to 1-7 that when the diameter R1 of the conductive carbon fiber tube 20 satisfies 20 nm ≤ R1 ≤ 100 nm, the thickness expansion rate and the capacity retention rate of the lithium ion battery can be effectively improved. Among them, 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 capacity retention rate of the battery gradually decreases, because when the diameter R1 of the conductive carbon fiber tube 20 increases, the number of conductive carbon fiber tubes 20 decreases under the same weight, the conductive network in the negative electrode sheet is dispersed, the conductivity is poor, and the battery charge and discharge performance gradually deteriorates.

[0162] According to Table 1, it can be seen from Examples 1-8 to 1-10, 1-11 to 1-12 that when the specific capacity S of the conductive carbon fiber tube 20 satisfies 120 mAh / g ≤ S ≤ 300 mAh / g and the initial efficiency P satisfies 50% ≤ P ≤ 85%, the capacity retention rate of the lithium ion battery can be effectively improved. Because the specific 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 the conductive carbon fiber tube 20 is not easy to break, and the initial efficiency P in the range of 50% to 85% has the advantage of good conductivity.

[0163] As can be seen from Examples 1-13 to 1-16 in Table 1, when the diameter R3 of the carbon nanotube 30 satisfies 0.5 nm ≤ R3 ≤ 15 nm, the carbon nanotube 30 can be uniformly dispersed and good conductivity efficiency can be ensured. When the diameter R3 of the carbon nanotube 30 is lower than the lower limit 0.5 nm, the carbon nanotube 30 is not easy to disperse and is prone to winding with the conductive carbon fiber tube 20. When the diameter R3 of the carbon nanotube 30 is higher than the upper limit 15 nm, the number of the carbon nanotube 30 is reduced under the same weight, and the conductive network is dispersed.

[0164] As can be seen from Examples 1-23 to 1-27 in Table 1, when the particle size of the silicon matrix 11 and the particle size of the carbon-containing active material 40 are selected in a suitable range, the thickness expansion rate and the capacity retention rate of the lithium ion battery can be effectively improved. This is because, by selecting the particle size of the silicon matrix 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, the silicon can be distributed between the gaps of the carbon-containing active material 40 particles, the electrode sheet compaction density can be improved, and the silicon expansion can be limited. By selecting the particle size of the silicon matrix 11, the particle size of the carbon-containing active material 40, and the length of the conductive carbon fiber tube 20 to satisfy 0.2 ≤ (L1-D vs 50) / D vc 50 ≤ 3.0, the conductive carbon fiber tube 20 can construct a good conductive network between the carbon-containing active material 40 and the silicon particles.

[0165] Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-3 are different from Example 1-1 in that the contents of the conductive carbon fiber tube 20, the carbon nanotube 30, the lithium polyacrylate, the silicon matrix 11, and the carbon-containing active material 40 are different.

[0166] Table 2

[0167]

[0168] As can be seen from Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-3 in Table 1, by selecting the mass percentage contents of the conductive carbon fiber tube 20, the carbon nanotube 30, the chain-like adhesive, and the carbon-containing active material 40 in a suitable range, the thickness expansion rate and the capacity retention rate of the lithium ion battery can be effectively improved at the same time.

[0169] According to the embodiments of Example 2-1 to Example 2-7, Comparative Example 2-1, it can be seen that when the conductive carbon fiber tube 20 is not contained in the negative electrode active material layer, the thickness expansion rate of the lithium ion battery increases because the long-range bonding between the silicon matrix 11 particles is absent, and the mutual restriction is reduced. According to the embodiments of Example 2-1 to Example 2-7, Comparative Example 2-2, it can be seen that when the carbon nanotube 30 is not contained in the negative electrode active material layer, the capacity retention rate of the lithium ion battery fails to be improved because the conductive network architecture is loose, which on the one hand leads to poor conductivity of the conductive network, and on the other hand, the expansion of the silicon matrix 11 cannot be bound, resulting in poor cohesion inside the negative electrode active material layer.

[0170] According to the embodiments of Example 2-1 to Example 2-7, Comparative Example 2-3, it can be seen that when the mass percentage content of the silicon material is too high, and the mass percentage content of the carbon-containing active material 40 is too low, the thickness expansion rate of the lithium ion battery significantly increases, and the capacity retention rate of the lithium ion battery significantly decreases, because the silicon material causes the anode sheet to expand too much, and the conductive network has many breakpoints.

[0171] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and substantially the same configuration as the embodiments and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the configuration elements of the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode sheet, characterized by, The negative electrode active material layer comprises a negative electrode active material, a conductive carbon fiber tube, and a carbon nanotube; the mass percentage of the material of the silicon matrix is Ms, 5.0%≤Ms≤50.0%, based on the negative electrode active material layer; The negative electrode active material comprises a silicon matrix, the conductive carbon fiber tube is distributed between the particles of the negative electrode active material, and the surface of the negative electrode active material and the surface of the conductive carbon fiber tube both adsorb the carbon nanotube.

2. The negative electrode sheet according to claim 1, characterized by 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) the same conductive carbon fiber tube forms a first included angle α along the length direction of the conductive carbon fiber tube, and 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 initial 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 20 nm≤R1≤100 nm; (6) the inner diameter of the conductive carbon fiber tube is R2, and R2 satisfies 5 nm≤R2≤10 nm.

3. The negative electrode sheet according to claim 1, wherein The negative electrode active material further comprises a carbon shell layer coated on the surface of the silicon matrix, the thickness of the carbon shell layer is h, and h satisfies 1 nm≤h≤10 nm.

4. The negative electrode sheet according to claim 1, wherein The mass percentage of the conductive carbon fiber tube is Mx, and the mass percentage of the carbon nanotube is My, based on the negative electrode active material layer; 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, wherein 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 nanotube comprises at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.

6. The negative electrode sheet according to claim 1, wherein The negative electrode active material layer further comprises a carbon-containing active material, the carbon-containing active material is distributed between the particles of the negative electrode active material, and the surface of the carbon-containing active material adsorbs the carbon nanotube.

7. The negative electrode sheet according to claim 6, characterized by The mass percentage of the carbon-containing active material is Mc, and the mass percentage of the conductive carbon fiber tube is Mx, based on the negative electrode active material layer; 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 by The particle size of the carbon-containing active material includes D vc 50 and D vc 90, the particle size of the silicon matrix 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) 1 μm < D vs 50 < 10 μm; (4) 10 μm < D vc 90 < 30 μm; (5) 5 μm < D vc 50 < 15 μm.

9. The negative electrode plate of claim 1, wherein, The negative electrode active material layer further comprises a chain-shaped adhesive connected to at least two of the negative electrode active material, the conductive carbon fiber tube, and the carbon nanotube; The mass percentage content of the chain-like binder is Mz, based on the negative electrode active material layer, Mz satisfies: 0.5%≤Mz≤3.0%.

10. The negative electrode plate of claim 1, wherein, The negative electrode pole piece further comprises 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 cohesion F2, F2 satisfies: 15N / m≤F2≤90N / m.

11. An electrochemical device, characterized by, The negative electrode pole piece comprises the negative electrode active material layer and the chain-like binder.

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