A composite electrode, its preparation method, and a lithium-ion battery

Abstract

This invention provides a composite electrode, its preparation method, and a lithium-ion battery. The composite electrode includes a current collector and a composite material layer disposed on at least one side of the current collector. The composite material layer includes n alternating layers of active material and n-1 lithium replenishment layers, where n ≥ 3 and n is an integer. The side of the composite material layer closest to the current collector is the active material layer. Along the direction away from the current collector, the porosity gradient of the n-1 lithium replenishment layers increases. In the composite electrode of this invention, the lithium replenishment layer and the active material layer are in close contact, thereby shortening the diffusion path of lithium ions, accelerating the diffusion rate of lithium ions, and helping to improve the lithium replenishment rate and efficiency.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a composite electrode, its preparation method, and a lithium-ion battery. Background Technology

[0002] During the formation of lithium-ion batteries, the formation of the SEI film consumes the original lithium ions inside the battery, leading to problems such as initial capacity loss and reduced cycle life, thus limiting the improvement of lithium-ion battery energy density. To compensate for this lithium loss, lithium replenishment is usually performed.

[0003] Currently, the main methods for lithium replenishment in the negative electrode include: spraying ultrafine lithium metal powder onto the surface of the negative electrode sheet, spraying ultrafine lithium powder into a slurry onto the negative electrode surface, or combining ultrathin lithium strips with the negative electrode sheet through rolling. However, these methods result in poor uniformity of lithium replenishment and slow penetration of the lithium replenishing agent into the electrode sheet, which limits the rate and efficiency of lithium ion replenishment and thus reduces the effectiveness of lithium replenishment. The main method for lithium replenishment in the positive electrode is to add lithium-rich compounds such as Li2NiO2, Li5FeO4, Li3N, Li2O2, or Li2S to the positive electrode active material. However, uneven mixing can lead to uneven distribution of lithium elements in the battery, potentially resulting in excessive lithium replenishment in some areas and insufficient replenishment in others, thus affecting battery performance and lifespan. Furthermore, when the lithium replenishing agent is mixed with the positive electrode active material, side reactions may occur, leading to the generation of some undesirable chemical substances. These byproducts may negatively impact the electrochemical performance of the battery.

[0004] Therefore, there is an urgent need to provide a lithium replenishment method that can improve the replenishment speed and efficiency of lithium replenishment agents, improve the uniformity of lithium replenishment, and avoid side reactions caused by mixing lithium replenishment agents with electrode active materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite electrode, its preparation method, and a lithium-ion battery. The composite electrode of the present invention, by alternately stacking n active material layers and n-1 lithium replenishment layers, and defining the active material layer as the side of the composite material layer closest to the current collector, results in multiple lithium replenishment layers spaced apart within the composite material layer. This closer contact between the lithium replenishment layers and the active material layers shortens the lithium ion diffusion path, accelerates the lithium ion diffusion rate, improves the lithium replenishment rate and efficiency, enhances lithium replenishment uniformity, and avoids side reactions caused by direct mixing of the lithium replenishment material and the active material.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite electrode, the composite electrode comprising a current collector and a composite material layer disposed on at least one surface (e.g., one surface or both surfaces) of the current collector, the composite material layer comprising n layers of active material and n-1 layers of lithium replenishment layer alternately stacked, where n≥3 and n is an integer (e.g., it can be 3, 4, 5, 6, 8, 10, 12 or 15, etc.).

[0008] The layer of the composite material closest to the current collector is an active material layer;

[0009] Along the direction away from the current collector, the porosity gradient of the n-1 lithium replenishment layer increases.

[0010] It should be noted that the composite electrode can be a positive composite electrode or a negative composite electrode.

[0011] This invention provides a composite electrode that alternately stacks n active material layers and n-1 lithium replenishment layers, with the active material layer defined on the side of the composite material layer closest to the current collector. This arrangement results in multiple lithium replenishment layers within the composite material layer, leading to closer contact between the lithium replenishment layers and the active material layers. This shortens the lithium ion diffusion path, accelerating the lithium ion diffusion rate. This improves the rate and efficiency of lithium replenishment, enhances its uniformity, and prevents side reactions caused by direct mixing of the lithium replenishment material and the active material. Furthermore, by defining the porosity of the n-1 lithium replenishment layers as a gradient increasing away from the current collector, lithium ions can be better inserted into or extracted from the electrode surface. Therefore, using this composite electrode can reduce initial capacity loss and improve cycle performance, thereby increasing energy density.

[0012] Preferably, the porosity of the active material layer is 35-45%, for example, it can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 45%, etc.

[0013] Preferably, the porosity gradient of the n active material layers increases along the direction away from the current collector.

[0014] In this invention, when the porosity of the n-layer active material layer increases in a gradient away from the current collector, ion transport and diffusion can be improved, the utilization rate of the active material can be increased, and the internal resistance of the battery can be reduced.

[0015] This invention optimizes the ion diffusion path and speed by designing different layers and pore structures for the active material layer and the lithium replenishment layer, thereby improving the battery's charge / discharge rate and cycle life.

[0016] Preferably, the active material layer includes an active material and a conductive agent.

[0017] Preferably, the active material includes a positive electrode active material or a negative electrode active material.

[0018] This invention does not specifically limit the type of positive electrode active material, including but not limited to lithium iron phosphate, lithium nickel cobalt manganese oxide (NMC) or manganese oxide lithium salts.

[0019] This invention does not specifically limit the type of negative electrode active material, including but not limited to graphite, silicon-oxygen-carbon materials, or lithium titanate.

[0020] Preferably, the mass content of the active substance is 96-98% based on the total mass of the active substance layer as 100%, for example, it can be 96%, 97% or 98%.

[0021] Preferably, the active material content gradient of the n active material layers increases along the direction away from the current collector.

[0022] In this invention, when the content of active material in the n-layer active material layer increases in a gradient away from the current collector, the electrode reaction rate can be improved, the material can be utilized more effectively, and the cost can be reduced.

[0023] Preferably, the particle size D50 of the active material is 0.4-20 μm, for example, it can be 0.4 μm, 0.8 μm, 1.2 μm, 1.6 μm, 2 μm, 5 μm, 8 μm, 11 μm, 14 μm, 17 μm or 20 μm, etc.; the particle size range of the conductive agent is 0.01-0.1 μm.

[0024] Preferably, the particle size D50 gradient of the active material in the n-layer active material layer increases along the direction away from the current collector.

[0025] In this invention, when the particle size D50 of the active material in the n-layer active material layer increases in a gradient away from the current collector, the electrode reaction rate and energy density can be improved.

[0026] Preferably, the thickness of the active material layer is 3-30 μm, for example, it can be 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm or 30 μm.

[0027] Preferably, the thickness gradient of the n active material layers increases along the direction away from the current collector.

[0028] In this invention, when the thickness of the n-layer active material layer increases in a gradient away from the current collector, the energy density of the battery can be improved and the internal resistance of the battery can be reduced.

[0029] This invention can precisely control the composition and structure of the active material layer and the lithium replenishment layer according to specific battery requirements and performance requirements. By adjusting the material combination, thickness, porosity and content of different layers, the electrochemical performance such as capacity and cycle life of the electrode can be customized.

[0030] Preferably, the porosity of the lithium replenishment layer is 5-20%, for example, it can be 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18% or 20%, etc.

[0031] In this invention, the lithium replenishment material filled in the lithium replenishment layer is relatively dense.

[0032] Preferably, the lithium replenishing material in the lithium replenishing layer includes metallic lithium or lithium-containing compounds.

[0033] In this invention, when the active material is a positive electrode active material, the lithium-containing compound is a lithium supplement material; when the active material is a negative electrode active material, the metallic lithium is a lithium supplement material.

[0034] Optionally, the lithium-containing compound includes at least one of Li2NiO2, Li5FeO4, Li3N, Li2O2, and Li2S.

[0035] Preferably, the particle size D50 of the lithium replenishing material in the lithium replenishing layer is 0.01-15μm, for example, it can be 0.01μm, 0.02μm, 0.05μm, 0.08μm, 0.1μm, 0.12μm, 0.15μm, 0.2μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm, etc.

[0036] Preferably, the particle size gradient of the lithium replenishment material in the n-1 lithium replenishment layer increases along the direction away from the current collector.

[0037] In this invention, when the particle size of the lithium replenishing material in the n-1 layer increases in a gradient away from the current collector, the battery cycle life and stability can be improved, and the battery capacity decay can be reduced.

[0038] Preferably, the thickness of the lithium replenishment layer is 0.02-1 μm, for example, it can be 0.02 μm, 0.03 μm, 0.05 μm, 0.07 μm, 0.1 μm, 0.12 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, etc.

[0039] In this invention, if the thickness of each lithium replenishment layer is too thin, it will lead to battery capacity loss, reduced battery cycle life, and unstable battery performance; if the thickness of each lithium replenishment layer is too thick, it will reduce battery energy density, increase battery weight, and increase battery cost.

[0040] Preferably, the thickness gradient of the n-1 lithium replenishment layer increases along the direction away from the current collector.

[0041] In this invention, when the thickness of the n-1 lithium replenishment layer increases in a gradient away from the current collector, the cycle life of the battery can be improved, the performance stability of the battery can be improved, and the degradation rate of the electrode material can be reduced.

[0042] In a second aspect, the present invention provides a method for preparing the composite electrode as described in the first aspect, the method comprising:

[0043] (1) The active material is vapor-deposited onto at least one surface of the current collector to form an active material layer;

[0044] (2) The lithium replenishing agent is vapor deposited onto the surface of the active material layer formed in step (1) to form a lithium replenishing layer;

[0045] (3) The active material is vapor-deposited onto the surface of the lithium replenishment layer formed in step (2) to form an active material layer;

[0046] (4) Repeat steps (2) and (3) at least once (e.g., once, twice, three times, four times, five times, eight times, ten times, twelve times or fifteen times, etc.) to obtain the composite electrode.

[0047] Traditional multilayer coating often uses multiple nozzles to simultaneously spray electrode materials of different components, mixing them together in a laminar flow to form a multilayer electrode structure. However, the resulting coating is relatively thick, and excessively thick coatings can easily lead to uneven coating, resulting in inconsistent electrode performance and potentially causing battery performance fluctuations and instability. It also increases the diffusion distance of ions or molecules within the electrode, leading to increased resistance to charge and mass transport. This can slow down the battery's response speed and reduce its power performance. Furthermore, it can cause poor interfaces between the electrode and electrolyte, limiting ion transport and charge conduction, which may affect the battery's cycle life and stability.

[0048] This invention utilizes vapor deposition to obtain a uniform active material layer and a lithium replenishment layer, resulting in a more even distribution of lithium ions and ensuring balanced migration of lithium ions during charge and discharge, thereby improving battery cycle life and performance stability. The vapor deposition process forms a multi-layered composite structure on the foil surface, enabling refined design at the electrode layer level. Furthermore, the vapor deposition method allows for controllable film thickness and is applicable to a wide range of electrode materials.

[0049] Before vapor deposition, the current collector needs to be pretreated to remove surface dirt, grease and impurities to ensure that the coating can be uniformly adhered to its surface.

[0050] Preferably, when depositing the active material by vapor deposition, the temperature of the evaporation source is 500-2500℃, for example, it can be 500℃, 600℃, 700℃, 900℃, 1000℃, 1200℃, 1500℃, 2000℃, 2200℃ or 2500℃, etc.

[0051] In this invention, during the vapor deposition of the active material, a lower evaporation rate at a lower evaporation source temperature generally contributes to the formation of larger particle sizes, while a higher evaporation rate at a higher evaporation source temperature generally results in the formation of smaller particle sizes. The thickness of the active material layer can be controlled by adjusting the vapor deposition time and the temperature of the evaporation source. Repeated vapor deposition can also be used to increase the thickness of the active material layer.

[0052] Preferably, when the active material is vapor-deposited, the distance between the substrate to be vapor-deposited and the evaporation source is 10-50cm, for example, it can be 10cm, 20cm, 30cm, 40cm or 50cm.

[0053] Preferably, when depositing the lithium replenishing agent by vapor deposition, the temperature of the evaporation source is 500-2500℃, for example, it can be 500℃, 600℃, 700℃, 900℃, 1000℃, 1200℃, 1500℃, 2000℃, 2200℃ or 2500℃, etc.

[0054] In this invention, during the deposition of the lithium replenishing agent, a lower evaporation rate at a lower evaporation source temperature generally contributes to the formation of larger particle sizes, while a higher evaporation rate at a higher evaporation source temperature generally results in the formation of smaller particle sizes. The thickness of the lithium replenishing layer can be controlled by adjusting the deposition time and the temperature of the evaporation source. Repeated deposition can also be used to increase the thickness of the lithium replenishing layer.

[0055] Preferably, when depositing the lithium replenishing agent, the distance between the substrate to be deposited and the evaporation source is 10-50cm, for example, it can be 10cm, 20cm, 30cm, 40cm or 50cm.

[0056] In this invention, when depositing active materials or lithium replenishing agents by vapor deposition, the distance between the substrate to be deposited and the evaporation source affects the particle accumulation and growth behavior. Adjusting the distance between the evaporation source and the substrate allows control over the particle deposition method and particle size. Furthermore, by controlling the temperature of the evaporation source and the distance between the substrate to be deposited and the evaporation source, the particle size of the material in the active material layer or lithium replenishing layer can be changed.

[0057] Preferably, after each vapor deposition, an inert gas (such as nitrogen) is introduced for cooling and curing.

[0058] Maintaining a certain inert gas flow rate within the vacuum chamber can accelerate the cooling process of the vapor-deposited substrate and the coating. This helps stabilize the coating and ensures its adhesion to the vapor-deposited substrate.

[0059] Thirdly, the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes the composite electrode described in the first aspect.

[0060] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0061] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0062] This invention provides a composite electrode that alternately stacks n active material layers and n-1 lithium replenishment layers, with the active material layer defined on the side of the composite material layer closest to the current collector. This arrangement results in multiple lithium replenishment layers within the composite material layer, leading to closer contact between the lithium replenishment layers and the active material layers. This shortens the lithium ion diffusion path, accelerating the lithium ion diffusion rate. This improves the rate and efficiency of lithium replenishment, enhances its uniformity, and prevents side reactions caused by direct mixing of the lithium replenishment material and the active material. Furthermore, by defining the porosity of the n-1 lithium replenishment layers as a gradient increasing away from the current collector, lithium ions can be better inserted into or extracted from the electrode surface. Therefore, using this composite electrode can reduce initial capacity loss and improve cycle performance, thereby increasing energy density. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the composite electrode sheet provided in Embodiment 1 of the present invention;

[0064] Wherein, 1-current collector; 2-first active material layer; 3-first lithium replenishment layer; 4-second active material layer; 5-second lithium replenishment layer; 6-third active material layer. Detailed Implementation

[0065] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0066] Example 1

[0067] This embodiment provides a composite electrode, which is a positive electrode, such as... Figure 1As shown, it includes a current collector 1 (i.e., aluminum foil) and a composite material layer disposed on both sides of the aluminum foil. The composite material layer includes three layers of active material and two layers of lithium replenishment layer that are alternately stacked. They are sequentially referred to as the first active material layer 2, the first lithium replenishment layer 3, the second active material layer 4, the second lithium replenishment layer 5 and the third active material layer 6 along the direction away from the current collector 1.

[0068] Each active material layer consists of lithium iron phosphate cathode active material and carbon black conductive agent. The active material mass contents of the first active material layer 2, the second active material layer 4, and the third active material layer 6 are 96%, 97%, and 98%, respectively. The particle sizes D50 of the active materials in the first active material layer 2, the second active material layer 4, and the third active material layer 6 are 0.6 μm, 1 μm, and 1.4 μm, respectively. The particle size range of the carbon black conductive agent in the three active material layers is 0.01-0.1 μm. The porosities of the first active material layer 2, the second active material layer 4, and the third active material layer 6 are 35%, 40%, and 45%, respectively. The thicknesses of the first active material layer 2, the second active material layer 4, and the third active material layer 6 are 5 μm, 10 μm, and 15 μm, respectively.

[0069] Each lithium replenishment layer is composed of lithium-rich nickel oxide (Li2NiO2); the particle sizes D50 of the lithium replenishment material in the first lithium replenishment layer 3 and the second lithium replenishment layer 5 are 1.3 μm and 1.5 μm, respectively; the porosities of the first lithium replenishment layer 3 and the second lithium replenishment layer 5 are 6% and 12%, respectively; and the thicknesses of the first lithium replenishment layer 3 and the second lithium replenishment layer 5 are 0.05 μm and 0.1 μm, respectively.

[0070] This embodiment also provides a method for preparing the above-mentioned composite electrode, the method comprising the following steps:

[0071] (1) Mix lithium iron phosphate and carbon black powder at a mass ratio of 96:4 and place them in an evaporation source; evacuate the chamber of the first vapor deposition equipment to a high vacuum state until 10 -4 ~10 -7 kPa prevents material oxidation and degeneration at high temperatures; at the same time, vacuum evaporation can provide a uniform atmosphere, allowing the coating to be deposited on the foil with a relatively uniform density and structure; and ensures that the gas pressure in the chamber is controlled and monitored to achieve the required evaporation environment.

[0072] (2) The foil to be vaporized is conveyed to the top of the evaporation source by the unwinding device and the winding device, and the distance between the foil and the evaporation source is 25cm. The evaporation source heating device is used to heat the foil to its sublimation temperature of 1000℃, so that the material sublimates and forms vapor. The sublimated material vapor is deposited on the surface of the foil in a vacuum environment for 0.15h. Then nitrogen is introduced for cooling and solidification, and the resulting active material layer is the first active material layer 2.

[0073] (3) Transfer the foil with the first active material layer 2 already deposited (i.e., the substrate to be deposited) to the second evaporation equipment, and place the lithium-rich nickel oxide (Li2NiO2) powder in the evaporation source; re-evacuate the chamber in the evaporation equipment to a high vacuum state, up to 10 -4 ~10 -7 kPa prevents the lithium replenishing agent from reacting and degenerating with oxygen at high temperatures; at the same time, vacuum evaporation can provide a uniform atmosphere, allowing the coating to be deposited on the substrate with a relatively uniform density and structure.

[0074] (4) The substrate to be vaporized is conveyed to the top of the evaporation source by the unwinding device and the winding device, and the distance between the substrate and the evaporation source is 25cm. The lithium replenishing agent is heated to its sublimation temperature of 500℃ by the evaporation source heating device, so that the lithium replenishing agent sublimates and forms vapor. The sublimated lithium replenishing agent vapor is deposited on the surface of the substrate to be vaporized in a vacuum environment for 0.15h. Then nitrogen is introduced for cooling and solidification. The resulting lithium replenishing layer is the first lithium replenishing layer 3.

[0075] (5) Repeat steps (1) and (2), and adjust the mass ratio of active material and conductive agent to 97:3, adjust the distance between the substrate to be vaporized and the evaporation source to 20cm, adjust the temperature of the evaporation source to 1100℃, and adjust the deposition time to 0.1h, so as to obtain the second active material layer 4.

[0076] (6) Repeat steps (3) and (4), and adjust the deposition time to 0.15h, the distance between the substrate to be vaporized and the evaporation source to 15cm, the temperature of the evaporation source to 600℃, and the deposition time to 0.1h, thereby obtaining the second lithium replenishment layer 5.

[0077] (7) Repeat steps (1) and (2), and adjust the mass ratio of active material to conductive agent to 98:2, adjust the distance between the substrate to be vaporized and the evaporation source to 15cm, adjust the temperature of the evaporation source to 1200℃, and adjust the deposition time to 0.05h, thereby obtaining the third active material layer 6.

[0078] Example 2

[0079] This embodiment provides a composite electrode, which is a positive electrode, comprising a current collector (i.e., aluminum foil) and a composite material layer disposed on one side surface of the aluminum foil. The composite material layer comprises five layers of active material and four layers of lithium replenishment layer stacked alternately, and are sequentially referred to as the first active material layer, the first lithium replenishment layer, the second active material layer, the second lithium replenishment layer, the third active material layer, the third lithium replenishment layer, the fourth active material layer, the fourth lithium replenishment layer, and the fifth active material layer along the direction away from the current collector.

[0080] Each active material layer consists of lithium iron phosphate cathode active material and carbon black conductive agent. The mass content of active material in the first, second, third, fourth, and fifth active material layers is 96%, 96.5%, 97%, 97.5%, and 98%, respectively. The particle sizes (D50) of the active material in the first, second, third, fourth, and fifth active material layers are 0.6 μm, 0.8 μm, 1 μm, and 1.2 μm, respectively. The particle size range of the carbon black conductive agent in the 5 active material layers is 0.01-0.1 μm and 1.4 μm; the porosities of the first, second, third, fourth, and fifth active material layers are 35%, 37.5%, 40%, 42.5%, and 45%, respectively; the thicknesses of the first, second, third, fourth, and fifth active material layers are 2 μm, 4 μm, 6 μm, 8 μm, and 10 μm, respectively.

[0081] Each lithium replenishment layer is composed of lithium-rich nickel oxide (Li2NiO2); the particle sizes D50 of the lithium replenishment materials in the first, second, third, and fourth lithium replenishment layers are 1.3 μm, 1.4 μm, 1.5 μm, and 1.6 μm, respectively; the porosities of the first, second, third, and fourth lithium replenishment layers are 6%, 8%, 10%, and 12%, respectively; and the thicknesses of the first, second, third, and fourth lithium replenishment layers are 0.015 μm, 0.03 μm, 0.045 μm, and 0.06 μm, respectively.

[0082] This embodiment also provides a method for preparing the above-mentioned composite electrode, the method comprising the following steps:

[0083] (1) Mix lithium iron phosphate and carbon black powder at a mass ratio of 96:4 and place them in an evaporation source; evacuate the chamber of the first vapor deposition equipment to a high vacuum state until 10 -4 ~10 -7 kPa prevents material oxidation and degeneration at high temperatures; at the same time, vacuum evaporation can provide a uniform atmosphere, allowing the coating to be deposited on the foil with a relatively uniform density and structure; and ensures that the gas pressure in the chamber is controlled and monitored to achieve the required evaporation environment.

[0084] (2) The foil to be vaporized is conveyed to the top of the evaporation source by the unwinding device and the winding device, and the distance between the foil and the evaporation source is 40cm. The evaporation source heating device is used to heat the foil to its sublimation temperature of 1000℃, so that the material sublimates and forms vapor. The sublimated material vapor is deposited on the surface of the foil in a vacuum environment for 0.2h. Then nitrogen is introduced for cooling and solidification. The resulting active material layer is the first active material layer.

[0085] (3) Transfer the foil with the first active material layer already deposited (i.e., the substrate to be deposited) to the second evaporation equipment, and place the lithium-rich nickel oxide (Li2NiO2) powder in the evaporation source; re-evacuate the chamber in the evaporation equipment to a high vacuum state, up to 10 -4 ~10 -7 kPa prevents the lithium replenishing agent from reacting and degenerating with oxygen at high temperatures; at the same time, vacuum evaporation can provide a uniform atmosphere, allowing the coating to be deposited on the substrate with a relatively uniform density and structure.

[0086] (4) The substrate to be vaporized is conveyed to the top of the evaporation source by the unwinding device and the winding device, and the distance between the substrate and the evaporation source is 40cm. The lithium replenishing agent is heated to its sublimation temperature of 1000℃ by the evaporation source heating device, so that the lithium replenishing agent sublimates and forms vapor. The sublimated lithium replenishing agent vapor is deposited on the surface of the substrate to be vaporized for 0.1h in a vacuum environment. Then nitrogen is introduced for cooling and solidification. The resulting lithium replenishing layer is the first lithium replenishing layer.

[0087] (5) Repeat steps (1) and (2), and adjust the mass ratio of active material to conductive agent to 96.5:3.5, adjust the distance between the substrate to be vaporized and the evaporation source to 35cm, adjust the temperature of the evaporation source to 1100℃, and adjust the deposition time to 0.17h, thereby obtaining the second active material layer.

[0088] (6) Repeat steps (3) and (4), and adjust the deposition time to 0.17h, the distance between the substrate to be vaporized and the evaporation source to 35cm, the temperature of the evaporation source to 1100℃, and the deposition time to 0.17h, thereby obtaining the second lithium replenishment layer;

[0089] (7) Repeat steps (1) and (2), and adjust the mass ratio of active material to conductive agent to 97:3, adjust the distance between the substrate to be vaporized and the evaporation source to 30cm, adjust the temperature of the evaporation source to 1200℃, and adjust the deposition time to 0.14h, thereby obtaining the third active material layer.

[0090] (8) Repeat steps (3) and (4), and adjust the deposition time to 0.14h, the distance between the substrate to be vaporized and the evaporation source to 30cm, the temperature of the evaporation source to 1200℃, and the deposition time to 0.14h, thereby obtaining the third lithium replenishment layer;

[0091] (9) Repeat steps (1) and (2), and adjust the mass ratio of active material to conductive agent to 97.5:2.5, adjust the distance between the substrate to be vaporized and the evaporation source to 25cm, adjust the temperature of the evaporation source to 1300℃, and adjust the deposition time to 0.11h, thereby obtaining the fourth active material layer.

[0092] (10) Repeat steps (3) and (4), and adjust the deposition time to 0.11h, the distance between the substrate to be vaporized and the evaporation source to 25cm, the temperature of the evaporation source to 1300℃, and the deposition time to 0.11h, thereby obtaining the fourth lithium replenishment layer;

[0093] (11) Repeat steps (1) and (2), and adjust the mass ratio of active material to conductive agent to 98:2, adjust the distance between the substrate to be vaporized and the evaporation source to 20cm, adjust the temperature of the evaporation source to 1400℃, and adjust the deposition time to 0.08h, thereby obtaining the fifth active material layer.

[0094] Example 3

[0095] This embodiment provides a composite electrode, which is a negative electrode, including a current collector (i.e., copper foil) and a composite material layer disposed on one side of the copper foil. The composite material layer includes three layers of active material and two layers of lithium replenishment layer that are alternately stacked. They are sequentially referred to as the first active material layer, the first lithium replenishment layer, the second active material layer, the second lithium replenishment layer and the third active material layer along the direction away from the current collector.

[0096] Each active material layer consists of graphite anode active material and carbon black conductive agent. The active material mass contents of the first, second, and third active material layers are 96%, 97%, and 98%, respectively. The particle sizes (D50) of the active materials in the first, second, and third active material layers are 15 μm, 16 μm, and 17 μm, respectively. The particle size range of the carbon black conductive agent in the three active material layers is 0.01-0.1 μm. The porosities of the first, second, and third active material layers are 35%, 40%, and 45%, respectively. The thicknesses of the first, second, and third active material layers are 5 μm, 10 μm, and 15 μm, respectively.

[0097] Each lithium replenishment layer is composed of metallic lithium; the particle sizes D50 of the lithium replenishment material in the first and second lithium replenishment layers are 0.04 μm and 0.06 μm, respectively; the porosities of the first and second lithium replenishment layers are 6% and 12%, respectively; and the thicknesses of the first and second lithium replenishment layers are 0.05 μm and 0.1 μm, respectively.

[0098] This embodiment also provides a method for preparing the above-mentioned composite electrode, the method comprising the following steps:

[0099] (1) Mix graphite and carbon black powders at a mass ratio of 96:4 and place them in an evaporation source; evacuate the chamber of the first vapor deposition equipment to a high vacuum state until 10 -4 ~10 -7kPa prevents material oxidation and degeneration at high temperatures; at the same time, vacuum evaporation can provide a uniform atmosphere, allowing the coating to be deposited on the foil with a relatively uniform density and structure; and ensures that the gas pressure in the chamber is controlled and monitored to achieve the required evaporation environment.

[0100] (2) The foil to be vaporized is conveyed to the top of the evaporation source by the unwinding device and the winding device, and the distance between the foil and the evaporation source is 25cm. The evaporation source heating device is used to heat the foil to its sublimation temperature of 800℃, so that the material sublimates and forms vapor. The sublimated material vapor is deposited on the surface of the foil in a vacuum environment for 0.15h. Then nitrogen is introduced for cooling and solidification, and the resulting active material layer is the first active material layer.

[0101] (3) Transfer the foil with the first active material layer already deposited (i.e., the substrate to be deposited) to the second evaporation equipment, place the lithium replenishing agent powder (lithium metal) in the evaporation source; re-evacuate the chamber in the evaporation equipment to a high vacuum state until 10 -4 ~10 -7 kPa prevents the lithium replenishing agent from reacting and degenerating with oxygen at high temperatures; at the same time, vacuum evaporation can provide a uniform atmosphere, allowing the coating to be deposited on the substrate with a relatively uniform density and structure.

[0102] (4) The substrate to be vaporized is conveyed to the top of the evaporation source by the unwinding device and the winding device, and the distance between the substrate and the evaporation source is 25cm. The lithium replenishing agent is heated to its sublimation temperature of 1800℃ by the evaporation source heating device, so that the lithium replenishing agent sublimates and forms vapor. The sublimated lithium replenishing agent vapor is deposited on the surface of the substrate to be vaporized in a vacuum environment for 0.15h. Then nitrogen is introduced for cooling and solidification. The resulting lithium replenishing layer is the first lithium replenishing layer.

[0103] (5) Repeat steps (1) and (2), and adjust the mass ratio of active material and conductive agent to 97:3, adjust the distance between the substrate to be vaporized and the evaporation source to 20cm, adjust the temperature of the evaporation source to 900℃, and adjust the deposition time to 0.1h, so as to obtain the second active material layer.

[0104] (6) Repeat steps (3) and (4), and adjust the deposition time to 0.1h, the distance between the substrate to be vaporized and the evaporation source to 20cm, the temperature of the evaporation source to 2000℃, and the deposition time to 0.1h, thereby obtaining the second lithium replenishment layer;

[0105] (7) Repeat steps (1) and (2), and adjust the mass ratio of active material to conductive agent to 98:2, adjust the distance between the substrate to be vaporized and the evaporation source to 15cm, adjust the temperature of the evaporation source to 1000℃, and adjust the deposition time to 0.05h, thereby obtaining the third active material layer.

[0106] Example 4

[0107] The difference between this embodiment and Embodiment 1 is that the thickness of the first lithium replenishment layer is adjusted to 0.5 μm, and the thickness of the second lithium replenishment layer is adjusted to 1 μm. Everything else is exactly the same as in Embodiment 1.

[0108] Example 5

[0109] The difference between this embodiment and Embodiment 1 is that the thickness of the first lithium replenishment layer is adjusted to 0.02 μm, and the thickness of the second lithium replenishment layer is adjusted to 0.04 μm. Everything else is exactly the same as in Embodiment 1.

[0110] Example 6

[0111] The difference between this embodiment and Embodiment 1 is that the thickness of the first lithium replenishment layer and the second lithium replenishment layer is the same, both being 0.1 μm. Everything else is exactly the same as in Embodiment 1.

[0112] Example 7

[0113] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the lithium replenishing material in the first and second lithium replenishing layers is the same, both being 1.3 μm. Everything else is identical to Embodiment 1.

[0114] Example 8

[0115] The difference between this embodiment and Embodiment 1 is that the active substance content of the first active substance layer, the second active substance layer, and the third active substance layer is the same, all being 96%. Everything else is identical to Embodiment 1.

[0116] Example 9

[0117] The difference between this embodiment and Embodiment 1 is that the thicknesses of the first active material layer, the second active material layer, and the third active material layer are all the same, at 10 μm. Everything else is identical to Embodiment 1.

[0118] Example 10

[0119] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the materials in the first active material layer, the second active material layer, and the third active material layer is the same, all being 1 μm. Everything else is identical to Embodiment 1.

[0120] Example 11

[0121] The difference between this embodiment and Embodiment 1 is that the porosity of the first active material layer, the second active material layer, and the third active material layer is the same, all being 35%. Everything else is identical to Embodiment 1.

[0122] Comparative Example 1

[0123] The difference between this comparative example and Example 1 is that the porosity of the first and second lithium replenishment layers is the same, both being 12%. Everything else is identical to Example 1.

[0124] Comparative Example 2

[0125] The difference between this comparative example and Example 1 is that the composite material layer includes two alternating layers of active material and one lithium replenishment layer. The two active material layers are a first active material layer and a second active material layer, and the one lithium replenishment layer is a first lithium replenishment layer. Everything else is exactly the same as in Example 1.

[0126] Comparative Example 3

[0127] This comparative example provides a positive electrode sheet, which includes an aluminum foil and an active material layer disposed on one side of the aluminum foil. The active material layer includes LiFePO4, carbon black, Li2NiO2 and polyvinylidene fluoride (PVDF) in a mass ratio of 7:1:1:1.

[0128] Comparative Example 4

[0129] This comparative example provides a negative electrode sheet, which includes a copper foil and an active material layer disposed on one side of the copper foil. The active material layer includes graphite and carbon black in a mass ratio of 97:3. Lithium is added by combining an ultrathin lithium strip with the active material layer in a calendered composite form.

[0130] Performance testing

[0131] The positive electrode sheets provided in Examples 1-2, 4-11 and Comparative Examples 1-3 were assembled into lithium-ion batteries, wherein the negative electrode was a graphite electrode sheet, the electrolyte was LiPF6 electrolyte, and the separator was polyethylene.

[0132] The negative electrode sheets provided in Example 3 and Comparative Example 4 were assembled into a lithium-ion battery, wherein the positive electrode was a lithium iron phosphate electrode, the electrolyte was a LiPF6 electrolyte, and the separator was polyethylene.

[0133] The assembled lithium-ion battery was tested as follows:

[0134] (1) Initial charge and discharge efficiency test

[0135] The prepared test batteries were placed in a constant temperature chamber, with the temperature controlled at 23℃±2℃, and allowed to stand for 2h~12h. The battery electrochemical performance was then tested using a lithium-ion battery electrochemical performance tester, with the following charge-discharge regime:

[0136] a) Charging limit voltage: At a rate of 0.1C, constant current charging to 3.65V, then constant voltage charging, with a constant voltage charging cutoff current of 0.05C;

[0137] b) Discharge termination voltage: at a rate of 0.1C, constant current discharge to 2.0V;

[0138] The constant current charge / discharge current at tC rate can be calculated using the following formula:

[0139] I c =m×C0×t;

[0140] Among them, I t The constant current charge / discharge current is in mA; m is the mass of the active material in the battery (such as lithium iron phosphate or graphite) in g; C0 is the theoretical specific capacity of the active material in mA·h / g; t is the rate at which charging or discharging is completed within 1 / t time in h, which in this article refers to 0.1 / h.

[0141] c) Data Recording:

[0142] After one charge-discharge cycle of the test battery, the charging and discharging capacities were recorded, and the initial charge-discharge efficiency of the battery was calculated. The initial charge-discharge efficiency of lithium iron phosphate was calculated using the following formula:

[0143]

[0144] Among them, Q ID and Q IC The battery is in I t The initial discharge capacity and initial charge capacity under current charge-discharge test.

[0145] (2) Cyclic life test

[0146] After capacity testing, the test batteries were subjected to cycle testing using a lithium-ion battery electrochemical performance tester, with the following charge / discharge voltage limits:

[0147] a) Charging limit voltage: constant current and constant voltage charging to 3.65V, constant voltage charging cutoff current is 0.05C;

[0148] b) Discharge termination voltage: 2.5V;

[0149] c) Charge and discharge cycle: In accordance with the provisions of GB / T18287, charge and discharge cycles shall be performed at 1C / 1C at an ambient temperature of (23±2)℃.

[0150] d) Data Recording: Record the charge and discharge capacity of the test battery at different cycle numbers during the cycle process. The discharge capacity at the termination voltage in the first cycle is recorded as Q1, and the discharge capacity at the termination voltage in the nth cycle is recorded as Q. n Calculate the capacity retention rate η over 1500 cycles using the following formula: η = (Q 1500 / Q1)×100%.

[0151] The test results are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] analyze:

[0156] As can be seen from the data of Examples 1-3 and Comparative Examples 3-4, by alternately stacking active material layers and lithium replenishment layers, and by setting various gradient parameters, the first charge-discharge efficiency of composite electrode assembled batteries can be improved, thereby reducing initial capacity loss, improving battery capacity retention, and enhancing cycle performance.

[0157] As can be seen from the data of Examples 1 and 4-5, if the thickness of each lithium replenishment layer is too thick, the battery capacity retention rate will be slightly lower and the cycle performance will be slightly worse; if the thickness of each lithium replenishment layer is too thin, the battery's first charge and discharge efficiency will be slightly lower, the initial capacity will be lost, the capacity retention rate will be slightly lower, and the cycle performance will be slightly worse.

[0158] Data from Examples 1 and 6-7 show that if the thickness of the first lithium replenishment layer and the second lithium replenishment layer are the same and no gradient is formed, the first charge-discharge efficiency and cycle performance of the composite electrode assembled battery will be reduced; if the particle size of the lithium replenishment material in the first lithium replenishment layer and the second lithium replenishment layer is the same and no gradient is formed, the cycle life of the battery will be reduced.

[0159] As can be seen from the data of Examples 1 and Examples 8-11, if the active material mass content, thickness and porosity of the first active material layer, the second active material layer and the third active material layer are made the same on their own, without forming a gradient, the cycle performance of the battery will be reduced.

[0160] As can be seen from the data of Example 1 and Comparative Example 1, if the porosity of the first lithium replenishment layer and the second lithium replenishment layer is the same and no gradient is formed, it will affect the insertion or extraction of lithium ions from the electrode surface into the electrode interior, thereby reducing the first charge and discharge efficiency of the composite electrode assembled battery.

[0161] As can be seen from the data of Example 1 and Comparative Example 2, if the composite material layer only includes two layers of active material and one layer of lithium replenishment layer that are stacked alternately, the battery cycle performance will be reduced.

[0162] As can be seen from the data of Example 1 and Comparative Example 3, for the positive electrode sheet, using conventional mixing methods for lithium replenishment will lead to a decrease in the cycle performance of the battery.

[0163] As can be seen from the data of Example 1 and Comparative Example 4, for the negative electrode sheet, using the conventional rolling composite method for lithium replenishment will reduce the first charge and discharge efficiency of the composite electrode assembled battery.

[0164] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite pole piece characterized by, The composite electrode includes a current collector and a composite material layer disposed on at least one side surface of the current collector. The composite material layer includes n layers of active material and n-1 layers of lithium replenishment layer alternately stacked, where n≥3 and n is an integer. The side of the composite material layer closest to the current collector is the active material layer; Along the direction away from the current collector, the porosity gradient of the n-1 lithium replenishment layer increases, and the thickness gradient of the n-1 lithium replenishment layer also increases. Along the direction away from the current collector, the porosity gradient of the n-layer active material layer increases, and the particle size D50 gradient of the active material in the n-layer active material layer also increases.

2. The composite electrode according to claim 1, characterized in that, The porosity of the active material layer is 35-45%.

3. The composite electrode according to claim 1, characterized in that, The active material layer includes active material and conductive agent.

4. The composite electrode according to claim 3, characterized in that, With the total mass of the active substance layer being 100%, the mass content of the active substance is 96-98%.

5. The composite electrode according to claim 3, characterized in that, Along the direction away from the current collector, the active material content gradient of the n active material layers increases.

6. The composite electrode according to claim 3, characterized in that, The particle size D50 of the active material is 0.4-20 μm; the particle size of the conductive agent is 0.01-0.1 μm.

7. The composite electrode according to claim 1, characterized in that, The thickness of the active material layer is 3-30 μm.

8. The composite electrode according to claim 1, characterized in that, Along the direction away from the current collector, the thickness gradient of the n-layer active material increases.

9. The composite electrode according to claim 1, characterized in that, The porosity of the lithium replenishment layer is 5-20%.

10. The composite electrode according to claim 1, characterized in that, The lithium replenishing material in the lithium replenishing layer includes metallic lithium or lithium-containing compounds.

11. The composite electrode according to claim 1, characterized in that, The particle size D50 of the lithium replenishing material in the lithium replenishing layer is 0.01-15 μm.

12. The composite electrode according to claim 1, characterized in that, Along the direction away from the current collector, the particle size gradient of the lithium replenishment material in the n-1 lithium replenishment layer increases.

13. The composite electrode according to claim 1, characterized in that, The thickness of the lithium replenishment layer is 0.02-1 μm.

14. A method for preparing a composite electrode according to any one of claims 1-13, characterized in that, The preparation method includes: (1) The active material is vapor-deposited onto at least one surface of the current collector to form an active material layer; (2) The lithium replenishing agent is vapor-deposited onto the surface of the active material layer formed in step (1) to form a lithium replenishing layer; (3) The active material is vapor-deposited onto the surface of the lithium replenishment layer formed in step (2) to form an active material layer; (4) Repeat steps (2) and (3) at least once to obtain the composite electrode.

15. The preparation method according to claim 14, characterized in that, When the active material is vapor-deposited, the temperature of the evaporation source is 500-2500℃.

16. The preparation method according to claim 14, characterized in that, When vapor-depositing the active material, the distance between the substrate to be vapor-deposited and the evaporation source is 10-50 cm.

17. The preparation method according to claim 14, characterized in that, When the lithium replenishing agent is vapor-deposited, the temperature of the evaporation source is 500-2500℃.

18. The preparation method according to claim 14, characterized in that, When depositing the lithium replenishing agent by vapor deposition, the distance between the substrate to be deposited and the evaporation source is 10-50 cm.

19. A lithium-ion battery, characterized in that, The lithium-ion battery includes the composite electrode as described in any one of claims 1-13.

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