Electrochemical devices and electronic devices

Abstract

An electrochemical device and electronic device, comprising a negative electrode plate, the negative electrode plate comprising a carbon nanotube array, a first negative electrode active material disposed within the carbon nanotube array; a current collector, the carbon nanotube array disposed on the current collector, the first negative electrode active material disposed between the carbon nanotubes, the first negative electrode active material being a silicon-containing material. By bringing the silicon-containing material into contact with the surface of the carbon nanotubes, the contact area between the current collector and the silicon-containing material is increased, reducing electronic resistance and ensuring an effective electron path. Furthermore, the uniformly distributed carbon nanotube structure accelerates ion conduction during the electrochemical reaction, avoiding lithium plating caused by localized lithium ion concentration imbalances, and improving the battery's initial discharge efficiency, rate capability, and cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to an electrochemical device and an electronic device. Background Art

[0002] With the rapid development of electric vehicles and mobile electronic devices in recent years, people have an increasingly higher demand for battery energy density. Silicon-based negative electrode materials have a gram capacity of up to 1500 to 4200 mAh / g and are regarded as the most promising next-generation lithium-ion negative electrode materials for achieving high-energy-density lithium batteries. However, silicon's low electrical conductivity (>108Ω.cm) and its excessive volume expansion during charging and discharging (with a volume expansion of about 300%) have hindered its further application to a certain extent. In addition, during the initial charging process, the formation of SEI requires the consumption of lithium, which results in low initial efficiency of silicon-based negative electrode materials.

[0003] Currently, lithium replenishment technology is mainly used to improve the initial efficiency of silicon-based materials. Lithium strip replenishment is the most common and low-cost lithium replenishment technology, but lithium strip replenishment has the problems of low lithium replenishment efficiency and high lithium replenishment heat, which poses a safety hazard. The following methods are mainly used to improve the expansion of silicon-based materials and enhance the cycle performance and rate performance of silicon-based materials: designing porous silicon-based materials, reducing the size of silicon materials, using oxide / polymer coating, and using plastic adhesives. Among them, designing porous silicon-based materials and reducing the size of silicon materials can improve the rate performance to a certain extent, but as the cycle proceeds, the occurrence of side reactions and the growth of uncontrollable SEI films further limit the cycle stability of silicon materials. The use of oxide and polymer coating can avoid the coating of electrolyte and electrode materials, but due to their poor conductivity (>105Ω.cm), the electrochemical impedance is increased, and the coating layer is easily destroyed during the lithium insertion and deintercalation process, thereby reducing its cycle life. Although the use of plastic adhesives can limit the volume expansion of silicon to a certain extent, there is also the problem of partial adhesive breakage during the expansion process, resulting in poor contact between active material particles, which affects the subsequent cycle performance. Summary of the Invention

[0004] The present application provides an electrochemical device and an electronic device, which can improve the problems of low initial efficiency and low lithium replenishment efficiency of silicon-based materials, and can improve the problem of deterioration of cycle performance caused by volume expansion of silicon-based materials during circulation. It can also improve the problem of poor conductivity of silicon-based materials, improve electron transfer impedance, reduce polarization, and increase capacity. At the same time, it is beneficial to improve ion transport inside the silicon-based electrode, further improving rate performance.

[0005] In a first aspect, the present application provides an electrochemical device, comprising a negative electrode plate; the negative electrode plate comprises a carbon nanotube array, and a first negative electrode active material is provided in the carbon nanotube array.

[0006] In some embodiments, the negative electrode plate also includes a current collector; the carbon nanotube array is located on the current collector; the carbon nanotube array includes carbon nanotubes; the first negative electrode active material is located between the carbon nanotubes; further, the outer tube wall of the carbon nanotube is in contact with the first negative electrode active material.

[0007] By arranging a carbon nanotube array on the current collector, the carbon nanotubes in the carbon nanotube array have high conductivity, and there are uniform gaps between the carbon nanotubes arranged in the array, which can ensure rapid and uniform infiltration of the electrolyte. After the lithium ions on the positive electrode side pass through the diaphragm, the high-concentration lithium ions can be quickly transferred to the inside of the negative electrode sheet along the uniform gap, accelerating the uniform and rapid conduction of ions during the electrochemical reaction, avoiding the phenomenon of local uneven lithium ion concentration, and causing lithium precipitation problems; the first negative electrode active material is loaded on the surface of the outer tube wall of the carbon nanotube with an array structure, which is beneficial to increase the contact area between the current collector and the negative electrode active material, reduce electronic resistance, and increase conductivity.

[0008] In some embodiments, the first negative electrode active material is a silicon-containing material; the silicon-containing material includes at least one of a silicon-carbon material, a silicon-oxygen material, or a pure silicon material. In this patent, a material having a silicon content greater than 80% is considered pure silicon. Attaching the silicon-containing material to the surface of the outer tube wall of the carbon nanotube helps the silicon particles (including silicon-carbon particles, silicon-oxygen particles, or pure silicon particles) fully contact the carbon nanotubes, ensuring an effective electron pathway.

[0009] In some embodiments, the silicon-containing material also includes lithium elements. The lithium elements are formed by depositing the lithium-supplementing material after it contacts with uniformly distributed carbon nanotubes; specifically, after the lithium-supplementing material contacts with the uniformly distributed carbon nanotubes, it can be uniformly and quickly absorbed and deposited into the interior of the silicon-containing material. In the lithium-supplementing process, uniformly distributed carbon nanotubes are arranged on one side of the current collector, and the surface of the carbon nanotubes is loaded with silicon-containing materials; when replenishing lithium, first, the lithium-supplementing material contacts the uniformly distributed carbon nanotubes, and at this time, the safety hazards caused by local overheating caused by uneven deposition can be avoided. Secondly, the lithium-supplementing material is uniformly absorbed and deposited into the interior of the silicon-containing material. At this time, the lithium-precipitation problem caused by uneven lithium replenishment can be avoided. At the same time, the carbon nanotubes with an array structure can play a role in uniform heat conduction, which can well reduce the temperature rise of lithium replenishment. It can be seen that after combining lithium replenishment with the carbon nanotube array structure containing the first negative electrode active material, the problems of low lithium replenishment efficiency, high heat generation, and safety hazards can be improved, thereby improving the first effect.

[0010] In some embodiments, the lithium-to-silicon mass ratio is 5% to 30%. On the one hand, controlling the lithium-to-silicon mass ratio within an appropriate range can compensate for lithium loss caused by SEI film formation at the negative electrode, thereby improving initial efficiency and cycle performance. On the other hand, selecting an appropriate lithium replenishment amount can achieve a balance between lithium replenishment cost, lithium replenishment efficiency / temperature rise, and electrical performance, facilitating large-scale production.

[0011] In some embodiments, a conductive material is provided on at least a portion of the surface of the silicon-containing material; the conductive material includes at least one of a carbon material, a metal material, or other conductive material. A suitable conductive material is introduced to coat the surface of the silicon-containing material to further enhance the conductivity of the silicon-containing material.

[0012] In some embodiments, the carbon nanotube array is patterned on the current collector; or the carbon nanotube array is fully covered on the current collector. In this patent, the term "fully covered" means that the carbon nanotube array is entirely disposed on at least one side of the current collector; the term "patterned" means that the carbon nanotube array is at least partially disposed on at least one side of the current collector.

[0013] In some embodiments, when the carbon nanotube array is patterned and distributed on the current collector;

[0014] The negative electrode plate includes two or more carbon nanotube arrays spaced apart from each other, with an average distance M between the carbon nanotube arrays satisfying: d<M≤500 μm, preferably d<M≤50 μm.

[0015] In some embodiments, the negative electrode plate satisfies at least one of the following conditions:

[0016] (I) When viewed perpendicular to the plane of the current collector, the projected area enclosed by the top surface of the carbon nanotube array is S1, and the projected area enclosed by the bottom surface is S2, satisfying the following: 90% ≤ S1 / S2 ≤ 110%;

[0017] The projected area S1 enclosed by the top surface of the carbon nanotube array refers to the area obtained by horizontally extending the surface enclosed by the top of the carbon nanotube array (i.e., the upper top surface) to a horizontal plane in a direction perpendicular to the plane where the current collector is located; the projected area S2 enclosed by the lower bottom surface refers to the area obtained by horizontally extending the surface enclosed by the bottom of the carbon nanotube array (i.e., the lower bottom surface) to the same horizontal plane in a direction perpendicular to the plane where the current collector is located.

[0018] (II) On a longitudinal section perpendicular to the current collector surface, select any region of the carbon nanotube array for EDS analysis, where the mass content of silicon in the selected region is w, and satisfies the following conditions: 60% ≤ w ≤ 95%; and for any two selected regions, the difference in mass content of silicon is Δw, and satisfies the following conditions: Δw ≤ 20%;

[0019] The longitudinal cross-section refers to the one obtained by performing cross-section processing on the film layer provided on one side of the current collector in a direction perpendicular to the surface of the current collector. The processing method can be ion polishing to obtain the cross-section. The film layer includes the carbon nanotube array; the region generally refers to the region containing at least one carbon nanotube; the two arbitrarily selected regions refer to the two regions containing at least one different carbon nanotube.

[0020] (III) Select any region where the carbon nanotube array is located and observe along a direction perpendicular to the plane where the current collector is located. The ratio S of the projected area enclosed by the carbon nanotube array to the projected area of the current collector in the selected region satisfies the following: 50%≤S≤100%.

[0021] The projected area enclosed by the carbon nanotube array refers to the area obtained by horizontally extending the surface enclosed by the carbon nanotube array to a horizontal plane, which is the projected area enclosed by the carbon nanotube array; wherein, the surface formed by the encirclement may refer to the surface formed at any position of the carbon nanotube array, and the carbon nanotube array is in contact with the current collector; the current collector area of the selected area refers to the area on the current collector corresponding to the selected area.

[0022] In some embodiments, the negative electrode plate satisfies at least one of the following conditions:

[0023] (i) When viewed perpendicular to the plane of the current collector, the projected area of the top surface of the carbon nanotube array is S1, and the projected area of the bottom surface is S2, satisfying the following: 95% ≤ S1 / S2 ≤ 105%;

[0024] (ii) On a longitudinal section perpendicular to the current collector surface, select any region of the carbon nanotube array for EDS analysis, where the mass content of silicon in the selected region is w, and satisfies the following conditions: 80% ≤ w ≤ 95%; and for any two regions, the difference in mass content of silicon is Δw, and satisfies the following conditions: Δw ≤ 10%;

[0025] (iii) Select any region where the carbon nanotube array is located and observe it in a direction perpendicular to the plane where the current collector is located. The ratio S of the projected area enclosed by the carbon nanotube array to the projected area of the current collector in the selected region satisfies the following: 70%≤S≤100%.

[0026] At this time, on the one hand, it can further improve the electrolyte infiltration, accelerate ion conduction, and reduce concentration polarization; on the other hand, it can further buffer the volume expansion and ensure the integrity of the electrode shape, without wrinkles, active material shedding and other problems during the charging and discharging process.

[0027] In some embodiments, the negative electrode plate satisfies the following requirements: (A) the average particle size of the negative electrode active material is D, which satisfies: 5nm≤D≤2μm; (B) the spacing between adjacent carbon nanotubes is d, which satisfies: 20nm≤d≤5μm; (C) the diameter of the carbon nanotube is p, which satisfies: 5nm≤p≤100nm; (D) the length of the carbon nanotube is H, which satisfies: 5μm≤H≤80μm.

[0028] Adjacent carbon nanotubes may be adjacent in the length direction of the current collector or in the width direction of the current collector; for example, in the length direction of the current collector, the spacing d between adjacent carbon nanotubes refers to the spacing between two carbon nanotubes arranged horizontally along the length direction of the current collector; in the width direction of the current collector, the spacing d between adjacent carbon nanotubes refers to the spacing between two carbon nanotubes arranged longitudinally along the width direction of the current collector, and the spacing between two carbon nanotubes generally refers to the average spacing between the two carbon nanotubes.

[0029] The length direction of the carbon nanotube is perpendicular to the surface of the current collector. The length direction of the carbon nanotube refers to the extension direction from the bottom end of the carbon nanotube toward the top end of the carbon nanotube. It should be noted that the angle between the extension line of the carbon nanotube in the length direction and the surface of the current collector is in the range of 60° to 90°, which can be regarded as perpendicular to the surface as described in this application.

[0030] In some embodiments, the negative electrode plate satisfies at least one of the following conditions:

[0031] (a) The average particle size of the negative electrode active material is D, which satisfies the following conditions: 5 nm ≤ D ≤ 500 nm;

[0032] (b) the spacing between adjacent carbon nanotubes is d, satisfying the following: 20 nm ≤ d ≤ 1 μm;

[0033] (c) The length of the carbon nanotube is H, which satisfies the following conditions: 5 μm ≤ H ≤ 40 μm

[0034] (d) a ratio of the spacing d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material satisfies the following: 2<d / D<10;

[0035] (e) The ratio of the distance d between adjacent carbon nanotubes to the diameter p of the carbon nanotube satisfies the following: 0.2 nm ≤ d / p ≤ 500 nm.

[0036] By adjusting the average particle size of the negative electrode active material, the spacing between adjacent carbon nanotubes, and the length and diameter of the carbon tubes, on the one hand, the lithium replenishment performance of the silicon-containing material can be improved, thereby improving the initial efficiency; on the other hand, the cycle performance can be improved.

[0037] In some embodiments, the ratio of the spacing d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material satisfies: 2≤d / D≤5. In this case, the lithium replenishment performance of the silicon material can be improved, and the initial efficiency and cycle performance can be enhanced.

[0038] In some embodiments, the ratio of the spacing d between adjacent carbon nanotubes to the diameter p of the carbon nanotubes satisfies the following: 1nm≤d / p≤250nm, thereby further improving the lithium replenishment performance of the silicon material and enhancing the initial efficiency and cycle electrical performance.

[0039] In a second aspect, the present application provides an electronic device comprising any of the electrochemical devices described above.

[0040] The beneficial effects brought about by the technical solution of this application include at least:

[0041] (1) The present application provides a carbon nanotube array on a current collector, wherein the outer wall surface of the carbon nanotubes in the carbon nanotube array contacts a silicon-containing material, thereby increasing the contact area between the current collector and the silicon-containing material, reducing electronic resistance, increasing conductivity, and ensuring an effective electronic path; and lithium elements are deposited inside the silicon-containing material to improve the first efficiency; and an appropriate conductive material is introduced to coat the surface of the silicon-containing material to improve the conductivity of the silicon-containing material;

[0042] (2) The uniformly arranged carbon nanotube structure in the present application can, on the one hand, play a role in uniform heat conduction, effectively reducing the temperature rise of lithium replenishment, and on the other hand, can ensure rapid and uniform infiltration of the electrolyte; after the lithium ions on the positive electrode side pass through the diaphragm, the high-concentration lithium ions can be quickly transferred to the inside of the negative electrode along the uniform gap, accelerating the uniform and rapid conduction of ions during the electrochemical reaction, avoiding the phenomenon of uneven local lithium ion concentration, which leads to lithium plating problems, and thus improving the battery's initial efficiency, rate performance and cycle performance;

[0043] (3) In the present application, the silicon-containing material is bound between the carbon nanotube arrays. The carbon nanotube arrays have high mechanical strength, which can limit the deformation of the pole piece and even the battery caused by the volume expansion of the silicon-containing material during the cycle, effectively preventing poor interface contact. It can also avoid problems such as the active material falling off the current collector, poor contact between active material particles, and SEI thickening caused by particle rupture, thereby ensuring effective electron and ion conduction during the cycle, avoiding the aggravation of side reactions, and improving cycle performance.

[0044] (4) The carbon nanotubes in the carbon nanotube array of the present application can quickly dissipate the heat inside the battery, which helps to reduce the temperature rise and avoid the accumulation of heat inside the battery, thereby improving the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] 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.

[0046] Figure 1 This is a partial enlarged view of the fully covered carbon nanotube array in the embodiment of the present application;

[0047] Figure 2 A partially enlarged view of a patterned carbon nanotube array in an embodiment of the present application;

[0048] Figure 3 FIG. 1 is a top view of a patterned carbon nanotube array in an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0050] Silicon-based negative electrode materials have a gram capacity of up to 1500 to 4200 mAh / g, and are considered to be the most promising next-generation lithium-ion negative electrode materials for achieving high-energy-density lithium batteries. However, the low electrical conductivity of silicon (>108Ω.cm) and its excessive volume expansion during charging and discharging (with a volume expansion of about 300%) have hindered its further application to a certain extent. In addition, during the initial charging process, the formation of SEI requires the consumption of lithium, and the first efficiency of the material is low. At present, the first efficiency of silicon-based materials is mainly improved by lithium replenishment technology. Lithium strip lithium replenishment is the most common and low-cost lithium replenishment technology, but lithium strip lithium replenishment has the problems of low lithium replenishment efficiency and high lithium replenishment heat, and there are safety hazards. There are mainly the following means to improve the expansion of silicon-based materials and enhance the cycle performance and rate performance of silicon-based materials: designing porous silicon-based materials, reducing the size of silicon materials, using oxide / polymer coating, using plastic adhesives, etc. Among them, designing porous silicon-based materials and reducing the size of silicon materials can improve the rate performance to a certain extent, but as the cycle proceeds, side reactions The occurrence of stress and the uncontrollable growth of SEI film further limit the cycle stability of silicon materials; the use of oxide and polymer coating can avoid the coating of electrolyte and electrode materials, but due to their poor conductivity (>105Ω.cm), the electrochemical impedance will increase, and the coating layer is easily destroyed during the lithium insertion and deinsertion process, thereby reducing its cycle life; although the use of plastic adhesives can limit the problem of silicon volume expansion to a certain extent, there is also the problem of part of the adhesive breaking during the expansion process and poor contact of the active material particles, which affects the subsequent cycle performance.

[0051] In order to solve the above technical problems, the present application proposes an electrochemical device and an electronic device.

[0052] An electrochemical device

[0053] The electrochemical device includes a negative electrode plate, which includes a current collector and a carbon nanotube array arranged on at least one side of the current collector, wherein a first negative electrode active material is provided in the carbon nanotube array; the carbon nanotube array includes carbon nanotubes, the first negative electrode active material is located between the carbon nanotubes, and the outer tube wall of the carbon nanotube is in contact with the first negative electrode active material.

[0054] See Figure 1 and Figure 2 In this application, a carbon nanotube array is arranged on one side of the current collector. The carbon nanotube array has at least two arrangement modes, for example Figure 1 The fully covered carbon nanotube array shown is that at least one side of the current collector is covered with carbon nanotubes having an array structure; it can also be, for example Figure 2 or Figure 3The patterned arrangement of the carbon nanotube arrays shown in FIG. 1 is that a plurality of carbon nanotube arrays are provided on at least one side of the current collector, and the plurality of carbon nanotube arrays are patterned and arranged at a certain distance from each other; further, the average distance between different carbon nanotube arrays is M (e.g. Figure 3 As shown), M satisfies: d<M≤500μm, preferably d<M≤50μm, where d is the distance between adjacent carbon nanotubes. Figure 1 or Figure 2 It can be clearly seen that the outer tube wall surface of the carbon nanotubes with an array arrangement structure is in contact with the first negative electrode active material, that is, the first negative electrode active material is in contact with the surface of the outer tube wall of the carbon nanotubes; by arranging the carbon nanotubes with an array structure on the current collector, the carbon nanotubes have high conductivity, and there are uniform gaps between the carbon nanotubes in the array structure, which can ensure rapid and uniform infiltration of the electrolyte. After the lithium ions on the positive electrode side pass through the diaphragm, the high-concentration lithium ions can be quickly transferred to the inside of the negative electrode sheet along the uniform gap, accelerating the uniform and rapid conduction of ions in the electrochemical reaction process, avoiding the local lithium ion concentration unevenness phenomenon, and causing lithium plating problems; at the same time, by loading the first negative electrode active material on the surface of the outer tube wall of the carbon nanotubes with an array structure, it is beneficial to increase the contact area between the current collector and the negative electrode active material, reduce the electronic resistance, and increase the conductivity.

[0055] In some embodiments, the first negative electrode active material is a silicon-containing material; the silicon-containing material includes at least one of a silicon-carbon material, a silicon-oxygen material, or a pure silicon material. Attaching the silicon-containing material to the outer wall of the carbon nanotube facilitates sufficient contact between silicon particles (including silicon-carbon particles, silicon-oxygen particles, or pure silicon particles) in the silicon-containing material and the carbon nanotube, thereby ensuring an effective electron pathway.

[0056] In some embodiments, the silicon-containing material also contains lithium elements; the lithium elements are formed by depositing the lithium-supplementing material after contact with uniformly distributed carbon nanotubes; specifically, after the lithium-supplementing material contacts the uniformly distributed carbon nanotubes, it can be uniformly and quickly absorbed and deposited into the interior of the silicon-containing material. During the lithium replenishment process, uniformly distributed carbon nanotubes are arranged on one side of the current collector, and the surface of the carbon nanotubes is loaded with silicon-containing materials; when replenishing lithium, first, the lithium-supplementing material contacts the uniformly distributed carbon nanotubes, and at this time, the safety hazards caused by local overheating caused by uneven deposition can be avoided. Secondly, the lithium-supplementing material is uniformly absorbed and deposited into the interior of the silicon-containing material. At this time, the lithium precipitation problem caused by uneven lithium replenishment can be avoided. At the same time, the carbon nanotubes with an array structure can play a role in uniform heat conduction, which can greatly reduce the temperature rise of lithium replenishment. It can be seen that after combining lithium replenishment with a carbon nanotube array structure containing a first negative electrode active material, the problems of low lithium replenishment efficiency, high heat generation, and safety hazards can be improved, thereby improving the first effect.

[0057] In some embodiments, the mass ratio of lithium to silicon is 5% to 30%. On the one hand, controlling the mass ratio of lithium to silicon within an appropriate range can compensate for lithium loss caused by SEI film formation at the negative electrode, thereby improving initial efficiency and cycle performance. On the other hand, selecting an appropriate amount of lithium replenishment can achieve a balance between lithium replenishment cost, lithium replenishment efficiency / temperature rise, and electrical performance, facilitating large-scale production.

[0058] Illustratively, the mass ratio of the lithium element to the silicon element is 5%, 8%, 10%, 14%, 16%, 18%, 20%, 24%, 26%, 28%, 30% or a range consisting of any two of the above values.

[0059] Combine Figure 1 or Figure 2 As shown, a conductive material is provided on at least a portion of the surface of the silicon-containing material; the conductive material surrounds, coats, or dopes at least a portion of, or even the entire surface of, the silicon-containing material, and the conductive material includes at least one of a carbon material, a metal material, or other conductive material. The surface of the silicon-containing material is coated with a suitable conductive material to further enhance its conductivity.

[0060] In some embodiments, the negative electrode plate satisfies at least one of the following conditions:

[0061] (I) When viewed perpendicular to the plane of the current collector, the projected area enclosed by the top surface of the carbon nanotube array is S1, and the projected area enclosed by the bottom surface is S2, satisfying the following: 90% ≤ S1 / S2 ≤ 110%;

[0062] The projected area S1 enclosed by the top surface of the carbon nanotube array refers to the area obtained by horizontally extending the surface enclosed by the top of the carbon nanotube array (i.e., the upper top surface) to a horizontal plane in a direction perpendicular to the plane where the current collector is located; the projected area S2 enclosed by the lower bottom surface refers to the area obtained by horizontally extending the surface enclosed by the bottom of the carbon nanotube array (i.e., the lower bottom surface) to the same horizontal plane in a direction perpendicular to the plane where the current collector is located.

[0063] (II) On a longitudinal section perpendicular to the current collector surface, select any region of the carbon nanotube array for EDS analysis, where the mass content of silicon in the selected region is w, and satisfies the following conditions: 60% ≤ w ≤ 95%; and for any two selected regions, the difference in mass content of silicon is Δw, and satisfies the following conditions: Δw ≤ 20%;

[0064] The longitudinal cross-section is obtained by performing cross-section processing on the film layer provided on one side of the current collector in a direction perpendicular to the surface of the current collector, and the processing method can be ion polishing to obtain the cross-section; the region generally refers to a region containing at least one carbon nanotube; the two arbitrarily selected regions refer to the two regions containing at least one different carbon nanotube.

[0065] (III) Select any region where the carbon nanotube array is located and observe along a direction perpendicular to the plane where the current collector is located. The ratio S of the projected area enclosed by the carbon nanotube array to the projected area of the current collector in the selected region satisfies the following: 50%≤S≤100%.

[0066] The projected area enclosed by the carbon nanotube array refers to the area obtained by horizontally extending the surface enclosed by the carbon nanotube array to a horizontal plane, which is the projected area enclosed by the carbon nanotube array; wherein, the surface formed by the encirclement may refer to the surface formed at any position of the carbon nanotube array, and the carbon nanotube array is in contact with the current collector; the current collector area of the selected area refers to the area on the current collector corresponding to the selected area.

[0067] Illustratively, the ratio S1 / S2 of the projected area S1 enclosed by the top of the carbon nanotube array to the projected area S2 enclosed by the bottom thereof is 90%, 92%, 95%, 98%, 100%, 105%, 108%, 110% or a range consisting of any two of the above values.

[0068] Illustratively, the mass content w of silicon element in the selected region is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range consisting of any two of the above values.

[0069] Illustratively, the difference Δw between the mass contents of silicon elements in the plurality of regions is 0%, 1%, 5%, 8%, 10%, 15%, 20%, or a range consisting of any two of the above values.

[0070] Illustratively, the ratio S of the projected area enclosed by the carbon nanotube array to the current collector area of the selected region is 50%, 60%, 70%, 80%, 90%, 100% or a range consisting of any two of the above values.

[0071] In some embodiments, the negative electrode plate satisfies at least one of the following conditions:

[0072] (i) When viewed perpendicular to the plane of the current collector, the projected area of the top surface of the carbon nanotube array is S1, and the projected area of the bottom surface is S2, satisfying the following: 95% ≤ S1 / S2 ≤ 105%;

[0073] (ii) On a longitudinal section perpendicular to the current collector surface, select any region of the carbon nanotube array for EDS analysis, where the mass content of silicon in the selected region is w, and satisfies the following conditions: 80% ≤ w ≤ 95%; and for any two regions, the difference in mass content of silicon is Δw, and satisfies the following conditions: Δw ≤ 10%;

[0074] (iii) Select any region where the carbon nanotube array is located and observe it in a direction perpendicular to the plane where the current collector is located. The ratio S of the projected area enclosed by the carbon nanotube array to the projected area of the current collector in the selected region satisfies the following: 70%≤S≤100%.

[0075] At this time, on the one hand, it can further improve the electrolyte infiltration, accelerate ion conduction, and reduce concentration polarization; on the other hand, it can further buffer the volume expansion and ensure the integrity of the electrode shape, without wrinkles, active material shedding and other problems during the charging and discharging process.

[0076] Illustratively, the ratio S1 / S2 of the projected area S1 enclosed by the top of the carbon nanotube array to the projected area S2 enclosed by the bottom thereof is 95%, 97%, 98%, 100%, 102%, 104%, 105% or a range consisting of any two of the above values.

[0077] Illustratively, the mass content w of silicon element in the selected region is 80%, 83%, 85%, 88%, 90%, 93%, 95% or a range consisting of any two of the above values.

[0078] Illustratively, the difference Δw between the mass contents of silicon elements in the plurality of regions is 0%, 1%, 3%, 5%, 7%, 9%, 10%, or a range consisting of any two of the above values.

[0079] Illustratively, the ratio S of the projected area enclosed by the carbon nanotube array to the current collector area of the selected region is 70%, 75%, 80%, 85%, 90%, 95%, 100% or a range consisting of any two of the above values.

[0080] In some embodiments, the negative electrode plate satisfies the following conditions: (A) the average particle size of the negative electrode active material is D, which satisfies: 5nm≤D≤2μm; (B) the spacing between adjacent carbon nanotubes is d, which satisfies: 20nm≤d≤5μm; (C) the diameter of the carbon nanotube is p, which satisfies: 5nm≤p≤100nm; (D) the length of the carbon nanotube is H, which satisfies: 5μm≤H≤80μm.

[0081] The adjacent carbon nanotubes may be adjacent in the length direction of the current collector or in the width direction of the current collector; for example, in the length direction of the current collector, the spacing d between adjacent carbon nanotubes refers to the spacing between two carbon nanotubes arranged transversely along the length direction of the current collector (e.g. Figure 3 In the width direction of the current collector, the spacing d between adjacent carbon nanotubes refers to the spacing between two carbon nanotubes arranged longitudinally along the width direction of the current collector. The spacing between two carbon nanotubes generally refers to the spacing between the corresponding positions in the middle of the two carbon nanotubes. The length H of the carbon nanotube refers to the distance between the bottom end of the carbon nanotube and the top end thereof (e.g. Figure 1 shown).

[0082] The length direction of the carbon nanotube is perpendicular to the surface of the current collector. The length direction of the carbon nanotube refers to the extension direction from the bottom end of the carbon nanotube toward the top end of the carbon nanotube. It should be noted that the angle between the extension line of the carbon nanotube in the length direction and the surface of the current collector is in the range of 60° to 90°, which can be regarded as perpendicular to the surface as described in this application.

[0083] Illustratively, the average particle size D of the negative electrode active material is 5 nm, 50 nm, 100 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, or a range consisting of any two of the foregoing values.

[0084] Illustratively, the spacing d between adjacent carbon nanotubes is 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm, 3000 nm, 3500 nm, 4000 nm, 4500 nm, 5000 nm, or a range consisting of any two of the above values.

[0085] Illustratively, the diameter p of the carbon nanotube is 5 nm, 10 nm, 15 nm, 20 nm, 35 nm, 50 nm, 70 nm, 85 nm, 90 nm, 100 nm, or a range consisting of any two of the above values.

[0086] Illustratively, the length H of the carbon nanotube is 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 80 μm, or a range consisting of any two of the above values.

[0087] In some embodiments, the negative electrode plate satisfies at least one of the following conditions:

[0088] (a) The average particle size of the negative electrode active material is D, which satisfies the following conditions: 5 nm ≤ D ≤ 500 nm;

[0089] (b) the spacing between adjacent carbon nanotubes is d, satisfying the following: 20 nm ≤ d ≤ 1 μm;

[0090] (c) The length of the carbon nanotube is H, which satisfies the following conditions: 5 μm ≤ H ≤ 40 μm

[0091] (d) a ratio of the spacing d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material satisfies the following: 2<d / D<10;

[0092] (e) The ratio of the distance d between adjacent carbon nanotubes to the diameter p of the carbon nanotube satisfies the following: 0.2 nm ≤ d / p ≤ 500 nm.

[0093] By adjusting the average particle size of the negative electrode active material, the spacing between adjacent carbon nanotubes, and the length and diameter of the carbon tubes, on the one hand, the lithium replenishment performance of the silicon-containing material can be improved, thereby improving the initial efficiency; on the other hand, the cycle performance can be improved.

[0094] Illustratively, the average particle size D of the negative electrode active material is 5 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range consisting of any two of the foregoing values.

[0095] Illustratively, the spacing d between adjacent carbon nanotubes is 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or a range consisting of any two of the foregoing values.

[0096] Illustratively, the length H of the carbon nanotube is 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or a range consisting of any two of the above values.

[0097] Illustratively, the ratio d / D of the spacing d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material is 2.1, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 9.9 or a range consisting of any two of the above values.

[0098] Exemplarily, the ratio d / p of the spacing d between adjacent carbon nanotubes to the tube diameter p of the carbon nanotube is 0.2nm, 1nm, 5nm, 10nm, 20nm, 40nm, 80nm, 100nm, 160nm, 180nm, 200nm, 250nm, 300nm, 400nm, 500nm or a range consisting of any two of the above values.

[0099] In some embodiments, the ratio of the spacing d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material satisfies: 2≤d / D≤5. This is used to improve the lithium replenishment performance of silicon materials and enhance the initial efficiency and cycle performance.

[0100] Illustratively, a ratio d / D of the distance d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material is 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two of the above values.

[0101] In some embodiments, the ratio of the spacing d between adjacent carbon nanotubes to the diameter p of the carbon nanotubes satisfies: 1nm≤d / p≤250nm, further improving the lithium replenishment performance of the silicon material and enhancing the initial efficiency and cycle electrical performance.

[0102] Illustratively, the ratio d / p of the spacing d between adjacent carbon nanotubes to the diameter p of the carbon nanotube is 1 nm, 5 nm, 10 nm, 30 nm, 60 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, or a range consisting of any two of the above values.

[0103] The present application also provides an electronic device comprising any of the above electrochemical devices. The electronic device of the present application can be used for, but is not limited to, a laptop computer, a pen-type 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 television, 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, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0104] The present application will be further described in detail below with reference to specific embodiments.

[0105] The two-dimensional planar conductive substrate (i.e., current collector) includes aluminum foil, copper foil, stainless steel foil, nickel film, iron film, gold film, silver film, platinum film, titanium film, zinc film, manganese film, carbon film, other composite metal films, conductive polymer films or composite polymer-metal films.

[0106] The positive electrode active material includes at least one of NCM811, NCM622, NCM523, NCM111, NCA, lithium iron phosphate, lithium cobaltate, lithium manganese oxide, lithium manganese iron phosphate or lithium titanate.

[0107] The negative electrode active material includes at least one of graphite, pure silicon, silicon carbon or silicon oxide, tin, tin compound, lithium metal and other high expansion negative electrode materials, preferably pure silicon material.

[0108] The electrolyte of the lithium-ion battery is not particularly limited, and any electrolyte known in the art can be used, which can be any of gel, solid and liquid. For example, the liquid electrolyte includes a lithium salt and a non-aqueous solvent.

[0109] The lithium salt is not particularly limited and any lithium salt known in the art can be used as long as the purpose of the present application can be achieved. For example, the lithium salt can include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or LiPO2F2. For example, LiPF6 can be used as the lithium salt.

[0110] The non-aqueous solvent is not particularly limited as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, or other organic solvents.

[0111] For example, the carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.

[0112] [Comparative Example 1]

[0113] Pure silicon pole piece without carbon nanotube array

[0114] Preparation of positive electrode

[0115] The positive electrode active material, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to create a slurry with a solids content of 0.75%, and the mixture was stirred evenly. The slurry was evenly coated on the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode sheet. After coating, the sheet was cut into 980mm × 58mm squares for later use.

[0116] After the above steps are completed, the single-sided coating of the positive electrode sheet is completed. Afterwards, these steps are also completed on the back of the sheet using the same method to obtain a double-sided coated positive electrode sheet.

[0117] Preparation of negative electrode sheet

[0118] The negative electrode active material, silicon, conductive carbon black (Super P), and binder are mixed in a weight ratio of 90:5:5. Deionized water (H2O) is added as a solvent to create a slurry with a solids content of 0.7%. The mixture is then stirred evenly. The slurry is evenly coated on the negative electrode current collector copper foil and dried at 110°C to obtain the negative electrode sheet. After coating, the sheet is cut into 1000mm × 60mm squares for later use.

[0119] After completing the above steps, the negative electrode sheet is coated on one side. Then, using the same method, repeat these steps on the back side of the sheet to obtain a double-sided negative electrode sheet. The film thickness is 10μm. Lithium tape is used to replenish lithium in the negative electrode sheet. Specific parameters are shown in Tables 1-3.

[0120] Preparation of electrolyte

[0121] In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0122] Preparation of isolation membrane

[0123] The isolation membrane substrate is 8 μm thick polyethylene (PE), and a 2 μm alumina ceramic layer is coated on both sides of the isolation membrane substrate. Finally, 2.5 mg of adhesive polyvinylidene fluoride (PVDF) is coated on both sides of the ceramic layer and dried.

[0124] Preparation of electrode assembly

[0125] The positive and negative electrode tabs are laser welded to the positive Al transfer tab and the negative Ni transfer tab, respectively, with the positive and negative tabs oriented in the same direction. A separator is placed between the positive and negative electrode sheets, and then wound together to form a wound electrode assembly.

[0126] Battery preparation

[0127] The wound electrode assembly can be packaged, injected with liquid, and then formed.

[0128] [Comparative Example 2]

[0129] Preparation of positive electrode

[0130] The positive electrode active material, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to create a slurry with a solids content of 0.75%, and the mixture was stirred evenly. The slurry was evenly coated on the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode sheet. After coating, the sheet was cut into 980mm × 58mm squares for later use.

[0131] After the above steps are completed, the single-sided coating of the positive electrode sheet is completed. Afterwards, these steps are also completed on the back of the sheet using the same method to obtain a double-sided coated positive electrode sheet.

[0132] Preparation of negative electrode sheet

[0133] On the surface of the current collector, carbon nanotube clusters (S1 / S2 = 30%) with a conical array structure are grown by chemical vapor deposition on the copper foil current collector. A silicon-containing material is then deposited onto the conical carbon nanotube clusters by vapor deposition. A layer of conductive material is then vapor-deposited around the silicon-containing material, completing the electrode fabrication. After completion, the electrode sheet is cut into 1000mm x 60mm sections for future use. The membrane thickness is 10μm. Specific parameters are shown in Tables 1-3.

[0134] After the above steps are completed, the negative electrode sheet is coated on one side. Then, the same steps are completed on the back side of the sheet in the same way to obtain a negative electrode sheet coated on both sides.

[0135] Preparation of electrolyte

[0136] In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0137] Preparation of isolation membrane

[0138] The isolation membrane substrate is 8 μm thick polyethylene (PE), and a 2 μm alumina ceramic layer is coated on both sides of the isolation membrane substrate. Finally, 2.5 mg of adhesive polyvinylidene fluoride (PVDF) is coated on both sides of the ceramic layer and dried.

[0139] Preparation of electrode assembly

[0140] The positive and negative electrode tabs are laser welded to the positive Al transfer tab and the negative Ni transfer tab, respectively, with the positive and negative tabs oriented in the same direction. A separator is placed between the positive and negative electrode sheets, and then wound together to form a wound electrode assembly.

[0141] Battery preparation

[0142] The wound electrode assembly can be packaged, injected with liquid, and then formed.

[0143] [Comparative Example 3]

[0144] Conical CNT cluster + pure silicon pole piece

[0145] Preparation of positive electrode

[0146] The positive electrode active material, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to create a slurry with a solids content of 0.75%, and the mixture was stirred evenly. The slurry was evenly coated on the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode sheet. After coating, the sheet was cut into 980mm × 58mm squares for later use.

[0147] After the above steps are completed, the single-sided coating of the positive electrode sheet is completed. Afterwards, these steps are also completed on the back of the sheet using the same method to obtain a double-sided coated positive electrode sheet.

[0148] Preparation of negative electrode sheet

[0149] On the surface of the current collector, carbon tubes with an array structure are grown on the surface of the copper foil current collector by chemical vapor deposition, and then bombarded with inert atoms to form array-shaped conical carbon nanotube clusters. Then, a silicon-containing material is attached to the surface of the conical carbon nanotubes by vapor deposition, and then a layer of conductive material is wrapped around the outside of the silicon material by vapor deposition to complete the electrode preparation. After completion, the pole piece is cut into specifications (1000mm×60mm) for use, and the above pole piece is replenished with lithium. The membrane thickness is 10μm, and the specific parameters are shown in Tables 1 to 3.

[0150] After the above steps are completed, the negative electrode sheet is coated on one side. Then, the same steps are completed on the back side of the sheet in the same way to obtain a negative electrode sheet coated on both sides.

[0151] Preparation of electrolyte

[0152] In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0153] Preparation of isolation membrane

[0154] The isolation membrane substrate is 8 μm thick polyethylene (PE), and a 2 μm alumina ceramic layer is coated on both sides of the isolation membrane substrate. Finally, 2.5 mg of adhesive polyvinylidene fluoride (PVDF) is coated on both sides of the ceramic layer and dried.

[0155] Preparation of electrode assembly

[0156] The positive and negative electrode tabs are laser welded to the positive Al transfer tab and the negative Ni transfer tab, respectively, with the positive and negative tabs oriented in the same direction. A separator is placed between the positive and negative electrode sheets, and then wound into a wound electrode assembly.

[0157] Battery preparation

[0158] The wound battery can be packaged, injected with liquid and formed.

[0159] [Example 1]

[0160] Preparation of positive electrode

[0161] The positive electrode active material, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to create a slurry with a solids content of 0.75%, and the mixture was stirred evenly. The slurry was evenly coated on the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode sheet. After coating, the sheet was cut into 980mm × 58mm squares for later use.

[0162] After the above steps are completed, the single-sided coating of the positive electrode sheet is completed. Afterwards, these steps are also completed on the back of the sheet using the same method to obtain a double-sided coated positive electrode sheet.

[0163] Preparation of negative electrode sheet

[0164] On the surface of the current collector, a carbon nanotube array is grown via chemical vapor deposition (CVD) on a copper foil current collector. A silicon-containing material is then deposited onto the evenly distributed carbon nanotubes via vapor deposition. A layer of conductive material is then vapor-deposited onto the silicon material, completing the electrode fabrication. After completion, the electrode sheet is cut into 1000mm x 60mm sections for later use. Lithium is then added to the electrode sheet. The membrane thickness is 10μm. The relevant parameters are shown in Tables 1-3.

[0165] After the above steps are completed, the negative electrode sheet is coated on one side. Then, the same steps are completed on the back side of the sheet in the same way to obtain a negative electrode sheet coated on both sides.

[0166] Preparation of electrolyte

[0167] In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0168] Preparation of isolation membrane

[0169] The isolation membrane substrate is 8 μm thick polyethylene (PE), and a 2 μm alumina ceramic layer is coated on both sides of the isolation membrane substrate. Finally, 2.5 mg of adhesive polyvinylidene fluoride (PVDF) is coated on both sides of the ceramic layer and dried.

[0170] Preparation of electrode assembly

[0171] The positive and negative electrode tabs are laser welded to the positive Al transfer tab and the negative Ni transfer tab, respectively, with the positive and negative tabs oriented in the same direction. A separator is placed between the positive and negative electrode sheets, and then wound into a wound electrode assembly structure.

[0172] Battery preparation

[0173] The wound electrode assembly can be packaged, injected with liquid, and then formed.

[0174] [Example 2] to [Example 27]

[0175] Examples 2 to 27 include most of the operating steps in Example 1. The difference from Example 1 is that various parameters in the negative electrode sheet preparation process are regulated to vary within a certain range. For details, see Tables 1 to 3.

[0176] Test section

[0177] (1) Test of the mass ratio of lithium to silicon in silicon-containing materials

[0178] a. Sampling: After discharging the battery to 3.0V, disassemble it and remove the electrode. Rinse the electrode surface with DMC to clean the electrolyte on the electrode surface and dry it. Punch the electrode into regular small discs with a total mass of more than 0.5g.

[0179] b. Sample pretreatment - acid digestion: Take an appropriate amount of sample into a digestion tank, add digestion reagent (3ml pure water + 3ml nitric acid + 5ml HF), shake the digestion tank, place the digestion tank in an acid removal instrument, heat and evaporate to an appropriate volume (180℃ for 120min), take out the digestion tank and rinse the edges with ultrapure water;

[0180] c. Test: ① Preheat the instrument: Turn on the voltage regulator, adjust the argon gas to 0.6 MPa, turn on the instrument, and open the software; ② Establish the method: Use the calibration curve method to test, and select Li and silicon as the test elements; ③ Ignition; ④ Test: a) Use a 1 mg / L Mn single standard to align the torch and clean the injection system; b) Initialize the optics with an initialization value of <50 steps; c) Use the configured standard solutions to draw the working curve in sequence; d) Check whether the linearity of the curve is R2>0.999; e) Test the quality control sample to confirm the accuracy of the curve; f) Enter the sample information and test the sample; ⑤ Shut down the instrument; ⑥ Process the data; ⑦ Clean the container.

[0181] (2) Lithium supplementation temperature rise and lithium absorption rate test

[0182] Place the lithium strip on the electrode surface, press it and let it stand for 12 hours. Use a temperature sensor to record the temperature change during the entire standing process. The lithium supplementation temperature rise = maximum temperature - room temperature. Record the weight gain per unit area before and after 12 hours, which is the amount of lithium supplementation. The lithium absorption rate = lithium supplementation amount / time, unit mg / (cm 2 h).

[0183] (3) Initial effectiveness test

[0184] The electrochemical device was charged from 3.0 to 4.45 V at a charge rate of 0.2 C at 25°C, and the capacity was recorded as the first charge capacity. Then the device was discharged to 3.0 V at a discharge rate of 0.2 C, and the capacity was recorded as the first discharge capacity. The first efficiency = (first discharge capacity / first charge capacity) × 100%.

[0185] (4) Cyclic performance test

[0186] The electrochemical device was charged from 3.0 to 4.45 V at a charge rate of 0.5 C at 25°C, and then discharged to 3.0 V at a discharge rate of 0.2 C. The discharge capacity at this time was determined as the initial discharge capacity. The above charge and discharge cycle was repeated 200 times, and the discharge capacity at the 200th discharge was measured. The capacity retention rate after 200 cycles = 200th discharge capacity / initial discharge capacity = 100%.

[0187] (5) Rate performance test

[0188] At 25°C, the electrochemical device was charged from 3.0V to 4.45V at a charge rate of 0.1C, then discharged to 3.0V at a discharge rate of 0.1C, repeating this step twice. Next, the device was charged from 3.0V to 4.45V at a charge rate of 0.2C, then discharged to 3.0V at a discharge rate of 0.2C, recording the discharge capacity at this point as Q1. The device was charged from 3.0V to 4.45V at a charge rate of 0.2C, then discharged to 3.0V at a discharge rate of 2C, recording the discharge capacity at this point as Q2. The discharge capacity retention rate (2C / 0.2C) is then Q2 / Q1 × 100%.

[0189] (6) Membrane adhesion test after cycling

[0190] After the battery is cycled 200 times according to the test method in (3), it is fully discharged, that is, discharged to 3.0V at 0.2C, and then the battery is disassembled and the electrode is removed. Use a blade to cut a sample of 30mm wide and 100mm long from the electrode to be tested. Apply a special double-sided tape to the steel plate with a width of 20mm and a length of 90mm. Apply the electrode sample to the double-sided tape with the test surface facing down. Insert a paper tape with a width equal to the electrode and a length 80-200mm longer than the sample length under the electrode and fix it with wrinkle glue. Fix the end of the steel plate without the electrode with the lower clamp of the tensile machine. Fold the paper tape upwards and fix it with the upper clamp of the tensile machine. Use the "up" and "down" buttons on the manual controller attached to the tensile machine to adjust the position of the upper clamp. Start the tensile machine test program and test.

[0191] The test results of Comparative Examples 1 to 3 and Examples 1 to 27 are shown in Tables 1 to 3.

[0192] Table 1

[0193]

[0194]

[0195] Compared with Comparative Example 1, Examples 1 to 7 can improve the utilization rate of lithium and thus improve the first efficiency by combining lithium replenishment with a carbon nanotube array structure; and the carbon nanotube array structure can accelerate the absorption of lithium and increase the lithium absorption rate through the capillary force between carbon nanotubes. At the same time, due to the high thermal conductivity of carbon nanotubes, the heat generated during the lithium replenishment process can be quickly discharged to the external environment, thereby greatly reducing the temperature rise of lithium replenishment. Compared with Comparative Example 2, Examples 1 to 7 can compensate for the lithium loss caused by the formation of SEI film on the negative electrode by replenishing lithium, thereby improving the first efficiency and cycle performance. Examples 1 to 4 achieve a balance between lithium replenishment cost, lithium replenishment efficiency / temperature rise, and electrical performance by optimizing different lithium replenishment amounts. Example 5 can further reduce the lithium replenishment temperature rise and absorption rate by changing the lithium replenishment material, but the cost of lithium slurry is slightly higher. Example 6 proves that, with respect to different negative electrode active materials, similar technical effects can be achieved by combining carbon nanotube arrays and lithium replenishment. Example 7 demonstrates the feasibility of coating with different conductive layers. As can be seen from Table 1, it has similar technical effects, but the metal conductive layer has the risk of internal self-discharge caused by metal particles, resulting in a slight decrease in cycle performance.

[0196] Table 2

[0197]

[0198]

[0199] Compared with Comparative Example 1, Examples 8-17 demonstrate improved lithium utilization and initial efficiency, demonstrating that the carbon nanotube array structure can enhance lithium absorption rates and reduce the temperature rise associated with lithium replenishment. Without the carbon nanotube array, silicon alloys with lithium during cycling, leading to volume expansion and weakening the adhesion between the active material and the membrane. However, the high mechanical strength of carbon nanotubes restrains silicon's volume expansion during this process, improving membrane adhesion after cycling and preventing powder loss. This ensures a reliable electronic and ionic conductive network structure, resulting in superior cycling performance.

[0200] Compared with Comparative Example 3, Examples 8 to 17 have uniformly distributed carbon nanotube structures, while Comparative Example 3 is a conical carbon nanotube cluster structure. Since the CNT appears in the form of a conical carbon cluster, silicon is attached to the periphery of the conical carbon cluster by physical deposition, which reduces the conductive effect of the carbon tube. The silicon deposited on the outermost side of the conical carbon cluster has a long conductive path and poor conductivity. In addition, the active loading amount of this method is lower than that of the embodiments of the present application, resulting in low capacity per unit area. At the same time, since the carbon cluster is conical, the process of the electrolyte entering the carbon tube first passes through a narrow path. To a certain extent, the rapid transmission of the electrolyte per unit area makes it difficult for the active material particles near the lower end of the current collector to quickly obtain ions, affecting the dynamics. Compared with the conical carbon nanotube cluster structure, the uniform carbon nanotube distribution of the present application (90% ≤ S1 / S2 ≤ 110%) facilitates the uniform absorption of lithium replenishment substances, as well as uniform heat generation and thermal conductivity, thereby greatly reducing the temperature rise of lithium replenishment. In addition, since silicon is coated between the carbon tubes, compared with the gaps in the conical carbon nanotube cluster, each silicon can fully contact the carbon nanotube to ensure a conductive network. At the same time, silicon can be bound in small amounts / individually between the carbon tubes, rather than a large amount of silicon being deposited in the conical carbon nanotube cluster array, which can alleviate volume expansion and improve the adhesion of the membrane.

[0201] In Examples 8-10, adjusting S1 / S2 demonstrates the positive effect of uniformly arranging carbon nanotubes. In Examples 11-13, adjusting w, a low w value has better performance than a high w value, but the ED is lower, and a balance between electrical performance and ED is required, with a preferred w value. In Examples 14-15, adjusting Δw, uniform deposition of silicon contributes to improved overall performance. In Examples 16-17, adjusting the distribution of carbon nanotubes, i.e., distributing them in a patterned structure, helps further improve electrical performance and reduce temperature rise, but there will be a certain degree of loss in ED.

[0202] Table 3

[0203]

[0204]

[0205] Compared to Comparative Example 1, Examples 18-27 optimize the negative electrode active material by adjusting various parameters: particle size D, spacing d between adjacent carbon nanotubes, diameter p, and length H. This improves the lithium replenishment performance of the silicon-containing material, enhancing both initial efficiency and cycle performance. Compared to Comparative Example 3, the uniform distribution of the carbon nanotubes further enhances cycle performance, particularly by increasing the carbon nanotubes' ability to restrain silicon expansion and, consequently, improve membrane adhesion.

[0206] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. An electrochemical device, characterized in that The negative electrode comprises a negative electrode plate; the negative electrode plate comprises a carbon nanotube array; the carbon nanotube array is provided with a first negative electrode active material; The negative electrode plate also includes a current collector; The carbon nanotube array is located on the current collector; The carbon nanotube array includes carbon nanotubes; The first negative electrode active material is located between the carbon nanotubes; The carbon nanotube array is patterned and distributed on the current collector; The negative electrode plate includes two or more spaced carbon nanotube arrays, the average distance between the carbon nanotube arrays is M; in one carbon nanotube array, the spacing between adjacent carbon nanotubes is d, satisfying: d<M≤500μm; Select any area where the carbon nanotube array is located and observe it in a direction perpendicular to the plane where the current collector is located. The ratio S of the projected area enclosed by the carbon nanotube array to the projected area of the current collector in the selected area satisfies: 50%≤S≤80%.

2. The electrochemical device according to claim 1, wherein d<M≤50μm.

3. The electrochemical device according to claim 1, wherein The first negative electrode active material is a silicon-containing material.

4. The electrochemical device according to claim 3, characterized in that The silicon-containing material includes at least one of a silicon-carbon material, a silicon-oxygen material or a pure silicon material.

5. The electrochemical device according to claim 3, characterized in that The silicon-containing material also includes lithium element; The mass ratio of the lithium element to the silicon element is 5% to 30%.

6. The electrochemical device according to claim 3, characterized in that At least a portion of the surface of the silicon-containing material is provided with a conductive material; the conductive material includes at least one of a carbon material, a metal material or other conductive materials.

7. The electrochemical device according to any one of claims 1 to 6, characterized in that At least one of the following conditions is met: (I) When viewed in a direction perpendicular to the plane of the current collector, the projected area enclosed by the top surface of the carbon nanotube array is S1, and the projected area enclosed by the bottom surface is S2, satisfying the following: 90% ≤ S1 / S2 ≤ 110%; (II) On a longitudinal section perpendicular to the current collector surface, a region of the carbon nanotube array is selected for EDS energy spectrum analysis, where the mass content of silicon in the selected region is w, satisfying the following: 60% ≤ w ≤ 95%; and for any two selected regions, the difference in the mass content of silicon is △w, satisfying the following: △w ≤ 20%.

8. The electrochemical device according to claim 7, characterized in that At least one of the following conditions is met: (i) When viewed in a direction perpendicular to the plane of the current collector, the projected area enclosed by the top surface of the carbon nanotube array is S1, and the projected area enclosed by the bottom surface is S2, satisfying the following: 95% ≤ S1 / S2 ≤ 105%; (ii) On a longitudinal section perpendicular to the current collector surface, select any region of the carbon nanotube array for EDS analysis. The mass content of silicon in the selected region is w, and it satisfies the following conditions: 80% ≤ w ≤ 95%; and for any two regions, the difference in the mass content of silicon is △w, and it satisfies the following conditions: △w ≤ 10%; (iii) Select any region where the carbon nanotube array is located and observe it in a direction perpendicular to the plane where the current collector is located. The ratio S of the projected area enclosed by the carbon nanotube array to the projected area of the current collector in the selected region satisfies the following conditions: 70%≤S≤100%.

9. The electrochemical device according to claim 1, wherein satisfy: (A) The average particle size of the negative electrode active material is D, which satisfies the following conditions: 5 nm ≤ D ≤ 2 μm; (B) The spacing between adjacent carbon nanotubes is d, which satisfies: 20 nm ≤ d ≤ 5 μm; (C) The diameter of the carbon nanotube is p, which satisfies the following conditions: 5 nm ≤ p ≤ 100 nm; (D) The length of the carbon nanotube is H, which satisfies: 5 μm ≤ H ≤ 80 μm.

10. The electrochemical device according to claim 9, characterized in that At least one of the following conditions is met: (a) The average particle size of the negative electrode active material is D, which satisfies the following conditions: 5 nm ≤ D ≤ 500 nm; (b) The spacing between adjacent carbon nanotubes is d, which satisfies the following conditions: 20 nm ≤ d ≤ 1 μm; (c) The length of the carbon nanotube is H, which satisfies: 5 μm ≤ H ≤ 40 μm (d) the ratio of the distance d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material satisfies the following: 2<d / D<10; (e) The ratio of the distance d between adjacent carbon nanotubes to the diameter p of the carbon nanotube satisfies the following: 0.2 nm ≤ d / p ≤ 500 nm.

11. The electrochemical device according to claim 10, characterized in that The ratio of the distance d between adjacent carbon nanotubes to the average particle size D of the negative electrode active material satisfies: 2≤d / D≤5.

12. The electrochemical device according to claim 10, wherein The ratio of the distance d between adjacent carbon nanotubes to the diameter p of the carbon nanotube satisfies: 1 nm ≤ d / p ≤ 250 nm.

13. An electronic device comprising the electrochemical device according to any one of claims 1 to 12.

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